{"gene":"PF3D7_1436600","run_date":"2026-09-08T14:19:07","timeline":{"discoveries":[{"year":2002,"finding":"PKG (PF3D7_1436600) from P. falciparum is a 97.5 kDa protein containing three predicted cGMP-binding sites and a degenerate fourth site. Recombinant PfPKG (Met115-Phe853) expressed in E. coli displays phosphotransferase activity (substrate phosphorylation and auto-phosphorylation) stimulated at least fivefold by 1.0 µM cGMP, but not by cAMP or 8-pCPT-cGMP. Western blotting and kinase activity assays with native P. falciparum proteins show maximal expression predominantly in the ring stage of the asexual life cycle.","method":"Recombinant protein expression, in vitro kinase assay, Western blotting with stage-specific parasite lysates","journal":"Molecular microbiology","confidence":"High","confidence_rationale":"Tier 1 / Moderate — in vitro reconstitution of kinase activity with recombinant protein plus stage-specific expression confirmed by two orthogonal methods (activity assay and Western blot), single lab","pmids":["12068803"],"is_preprint":false,"attribution":[{"species":"Plasmodium falciparum","strain":""}]},{"year":2003,"finding":"Among the four cGMP-binding sites in PKG (PF3D7_1436600), site 3 plays the dominant role in activation: mutation of site 3 alone causes a 10–49-fold increase in Ka(cGMP) and a 45–55% decrease in maximal activity in vitro. Mutations at sites 1 and 2 have lesser effects. Mutation of the degenerate site 4 reduces maximal activity by ~40% without altering Ka(cGMP), indicating site 4 does not bind cGMP but contributes to full activation.","method":"Site-directed mutagenesis of each cGMP-binding site (individually and in combination), in vitro kinase activity assay","journal":"The Biochemical journal","confidence":"High","confidence_rationale":"Tier 1 / Moderate — in vitro reconstitution with systematic mutagenesis of all four sites, multiple orthogonal measurements (Ka and Vmax), single lab","pmids":["12817987"],"is_preprint":false,"attribution":[{"species":"Plasmodium falciparum","strain":""}]},{"year":2005,"finding":"Native PKG (PF3D7_1436600) activity partially purified from P. falciparum by cGMP-affinity and ion-exchange chromatography is associated with a ~98 kDa protein detectable by anti-PKG antisera, and shows cGMP-stimulated kinase activity inhibitable by Compound 1. Recombinant PfPKG expressed in T. gondii (Pf(Tg)PKG) has kinase activity stimulated by cGMP with significant cooperativity (Hill coefficient of 2), and substrate preference and inhibitor sensitivity similar to native PfPKG and other apicomplexan PKGs.","method":"cGMP-affinity chromatography, ion-exchange chromatography, in vitro kinase assay, recombinant protein expression in T. gondii, Western blot","journal":"Molecular and biochemical parasitology","confidence":"Medium","confidence_rationale":"Tier 1 / Moderate — biochemical purification and recombinant reconstitution with kinase assays, two complementary approaches; single lab","pmids":["16325279"],"is_preprint":false,"attribution":[{"species":"Plasmodium falciparum","strain":""}]},{"year":2008,"finding":"PKG (PF3D7_1436600) is essential for xanthurenic acid (XA)- and zaprinast-induced gametogenesis in P. falciparum. Using PKG inhibitors together with transgenic parasites expressing an inhibitor-insensitive mutant PKG, it was shown that PKG activity is required for gametocyte-to-gamete differentiation. Intracellular Ca2+ signaling acts downstream of or in parallel with PKG activation during gametogenesis.","method":"PKG inhibitor treatment, inhibitor-insensitive mutant PKG transgenic parasites (genetic rescue), intracellular Ca2+ measurements","journal":"PLoS biology","confidence":"High","confidence_rationale":"Tier 2 / Strong — chemical inhibition validated by genetic rescue with inhibitor-insensitive mutant, Ca2+ epistasis established; multiple orthogonal methods","pmids":["18532880"],"is_preprint":false,"attribution":[{"species":"Plasmodium falciparum","strain":""}]},{"year":2009,"finding":"PKG (PF3D7_1436600) is required for blood-stage schizogony in P. falciparum. Compound 1 (trisubstituted pyrrole PKG inhibitor) blocked schizont rupture and merozoite liberation; transgenic parasites expressing a Compound 1-insensitive PfPKG completed schizogony in its presence, confirming PKG as the primary target. Treated schizonts became large and dysmorphic and were unable to rupture.","method":"PKG inhibitor treatment, inhibitor-insensitive mutant PKG transgenic parasites (genetic rescue), erythrocyte invasion assays, microscopy","journal":"Eukaryotic cell","confidence":"High","confidence_rationale":"Tier 2 / Strong — chemical-genetic validation with inhibitor-insensitive mutant rescue, replicated across multiple assay formats","pmids":["19915077"],"is_preprint":false,"attribution":[{"species":"Plasmodium falciparum","strain":""}]},{"year":2009,"finding":"In P. berghei ookinetes, PKG (PF3D7_1436600 ortholog) is required for gliding motility. Inhibition of PKG blocks ookinete gliding, while enhanced cGMP signaling (via PDEdelta deletion) causes ookinete rounding. The cGMP for PKG activation in ookinetes is produced primarily by guanylyl cyclase beta (GCbeta) and degraded by PDEdelta, as demonstrated by genetic epistasis (PDEdelta/GCbeta double mutant suppresses PDEdelta-null rounding phenotype). Elevated cGMP/PKG signaling can partially rescue gliding defects in a CDPK3-null mutant.","method":"Genetic epistasis (single and double knockout), PKG inhibitor treatment, ookinete motility assay","journal":"PLoS pathogens","confidence":"High","confidence_rationale":"Tier 2 / Strong — genetic epistasis with multiple single and double mutants defining pathway order, replicated with chemical inhibition","pmids":["19779564"],"is_preprint":false,"attribution":[{"species":"Plasmodium berghei","strain":""}]},{"year":2009,"finding":"Conditional disruption of P. berghei PKG (PF3D7_1436600 ortholog) in sporozoites blocks late liver stage development: mutant sporozoites invade hepatocytes and undergo intracellular development normally but fail to release merosomes into the medium.","method":"Conditional gene disruption in sporozoites, liver stage culture, merosome release assay","journal":"The Journal of biological chemistry","confidence":"High","confidence_rationale":"Tier 2 / Moderate — conditional KO with defined cellular phenotype (merosome release block), single lab","pmids":["19940133"],"is_preprint":false,"attribution":[{"species":"Plasmodium berghei","strain":""}]},{"year":2012,"finding":"In P. falciparum asexual blood stages, PKG (PF3D7_1436600) is expressed maximally at the late schizont stage. Subcellular fractionation and immunofluorescence of epitope-tagged PfPKG show a predominantly cytosolic location with partial overlap with ER markers and some association with the peripheral membrane fraction. PKG inhibition substantially changes the global protein phosphorylation pattern of schizonts, indicating a complex and broad role in schizogony.","method":"Transgenic epitope-tagged PKG expression, Western blot stage analysis, immunofluorescence assay (IFA), subcellular fractionation, global phosphoproteomics after PKG inhibition","journal":"PloS one","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — direct localization by IFA and fractionation plus functional phosphoproteomics, single lab, multiple orthogonal methods","pmids":["23139764"],"is_preprint":false,"attribution":[{"species":"Plasmodium falciparum","strain":""}]},{"year":2013,"finding":"PKG (PF3D7_1436600) activity is required for PfSUB1 discharge into the parasitophorous vacuole and for microneme release during merozoite egress. Pharmacological stimulation of PKG by inhibiting parasite phosphodiesterase activity induces premature PfSUB1 discharge and egress of immature, non-invasive parasites. This identifies PKG as the upstream regulator of the protease-mediated egress signaling pathway.","method":"PKG inhibitor treatment, phosphodiesterase inhibitor stimulation, immunofluorescence, Western blot for PfSUB1 discharge, egress assays","journal":"PLoS pathogens","confidence":"High","confidence_rationale":"Tier 2 / Strong — chemical gain-of-function and loss-of-function experiments with multiple downstream readouts (SUB1 discharge, microneme release, egress), multiple orthogonal methods","pmids":["23675297"],"is_preprint":false,"attribution":[{"species":"Plasmodium falciparum","strain":""}]},{"year":2014,"finding":"PKG (PF3D7_1436600) controls phosphoinositide biosynthesis and maintains elevated cytosolic Ca2+ required for gliding motility in P. berghei ookinetes. The same PKG-dependent pathway operates upstream of Ca2+ signals mediating P. berghei gametocyte activation and P. falciparum merozoite egress. Perturbation of PKG signaling in gliding ookinetes causes phosphoproteomic changes enriched in vesicular trafficking and phosphoinositide metabolism pathways. In P. falciparum, PKG inhibition blocks hydrolysis of phosphatidylinositol (4,5)-bisphosphate, linking PKG to phosphoinositide metabolism upstream of Ca2+ mobilization.","method":"Conditional PKG inhibition, quantitative phosphoproteomics, global phospholipid analysis, Ca2+ imaging, egress assays","journal":"PLoS biology","confidence":"High","confidence_rationale":"Tier 2 / Strong — multiple orthogonal methods (phosphoproteomics, lipidomics, Ca2+ imaging, egress) across two Plasmodium species, single lab with broad mechanistic coverage","pmids":["24594931"],"is_preprint":false,"attribution":[{"species":"Plasmodium berghei","strain":""},{"species":"Plasmodium falciparum","strain":""}]},{"year":2015,"finding":"Quantitative global phosphoproteomics in P. falciparum identified 69 proteins whose phosphorylation is directly or indirectly dependent on PKG (PF3D7_1436600) activity. These include PfCDPK1 (phosphorylated by PKG) and components of the actomyosin complex. PKG activity is also required for erythrocyte invasion (not only egress), establishing PKG as a signaling hub for both processes.","method":"Chemical and genetic PKG inhibition combined with quantitative global phosphoproteomics (SILAC-based), invasion assays","journal":"Nature communications","confidence":"High","confidence_rationale":"Tier 2 / Strong — quantitative phosphoproteomics with chemical and genetic tools, functional validation of invasion requirement, single lab with two orthogonal inhibition strategies","pmids":["26149123"],"is_preprint":false,"attribution":[{"species":"Plasmodium falciparum","strain":""}]},{"year":2015,"finding":"The C-terminal (carboxyl) cGMP-binding domain (CNB-D) of PKG (PF3D7_1436600) has the highest cGMP affinity and selectivity and functions as a gatekeeper for PKG activation. Crystal structures of this domain with (1.9 Å) and without (2.0 Å) cGMP reveal a PfPKG-specific capping triad that forms upon cGMP binding. Disruption of the capping triad reduces kinase activity by 90% in vitro. Mutating these residues in the parasite prevents blood-stage merozoite egress, confirming functional essentiality in vivo.","method":"X-ray crystallography, site-directed mutagenesis, in vitro kinase assay, parasite genetic engineering with egress phenotype readout","journal":"PLoS pathogens","confidence":"High","confidence_rationale":"Tier 1 / Strong — crystal structures at high resolution, in vitro mutagenesis, and in vivo parasite phenotype validation; multiple orthogonal methods in one study","pmids":["25646845"],"is_preprint":false,"attribution":[{"species":"Plasmodium falciparum","strain":""}]},{"year":2016,"finding":"In P. berghei, PKG (PF3D7_1436600 ortholog) is required for sporozoite invasion of hepatocytes and sporozoite motility. Chemical inhibition of PKG with specific inhibitors decreases TRAP secretion (an adhesin essential for motility) by sporozoites, and chemical inhibition also reduces parasite egress from hepatocytes. Sporozoites expressing a mutated, inhibitor-insensitive form of PbPKG are defective in hepatocyte invasion. PKG and CDPK4 act as independent second-messenger effectors for sporozoite invasion.","method":"PKG-specific inhibitors, inhibitor-insensitive mutant PKG sporozoites, hepatocyte invasion assays, TRAP secretion assay, merosome egress assay","journal":"Molecular microbiology","confidence":"High","confidence_rationale":"Tier 2 / Strong — chemical-genetic validation with inhibitor-insensitive mutant, multiple downstream readouts (invasion, motility, TRAP secretion), single lab","pmids":["27425827"],"is_preprint":false,"attribution":[{"species":"Plasmodium berghei","strain":""}]},{"year":2017,"finding":"PKG (PF3D7_1436600) triggers the PKG-dependent breakdown of the parasitophorous vacuole membrane (PVM) into multilayered vesicles during egress. PKG-dependent PVM breakdown is temporally distinct from an initial cysteine-protease-independent PVM permeabilization step (which precedes PKG-triggered breakdown by 10–30 min). An abrupt host erythrocyte cytoskeleton collapse occurs in a narrow window just before PVM breakdown, not gradually during schizont development.","method":"Selective PKG inhibitor and cysteine protease inhibitor treatment combined with video microscopy, electron tomography, electron energy loss spectroscopy, soft X-ray tomography","journal":"Proceedings of the National Academy of Sciences of the United States of America","confidence":"High","confidence_rationale":"Tier 2 / Strong — multiple complementary imaging modalities with pharmacological dissection of sequential steps, defining precise timing of PKG-dependent events","pmids":["28292906"],"is_preprint":false,"attribution":[{"species":"Plasmodium falciparum","strain":""}]},{"year":2017,"finding":"A co-crystal structure of Plasmodium vivax PKG (PvPKG, ortholog of PF3D7_1436600) bound to the imidazopyridine inhibitor ML10 reveals intimate molecular contacts explaining potency and selectivity of this inhibitor series. The compound inhibits PKG with an IC50 of 160 pM (P. falciparum PKG assay) and acts on merozoite egress, erythrocyte invasion, and gametocyte transmission.","method":"X-ray co-crystal structure of PvPKG–inhibitor complex, in vitro PfPKG kinase assay, P. falciparum blood-stage and transmission assays, in vivo P. falciparum SCID mouse model","journal":"Nature communications","confidence":"High","confidence_rationale":"Tier 1 / Moderate — co-crystal structure with functional validation across multiple life-cycle stages, single lab with multiple orthogonal assays","pmids":["28874661"],"is_preprint":false,"attribution":[{"species":"Plasmodium vivax","strain":""},{"species":"Plasmodium falciparum","strain":""}]},{"year":2017,"finding":"The cGMP-binding domain D (CNB-D) of PKG (PF3D7_1436600) controls kinase activation through a mechanism distinct from the pseudosubstrate autoinhibitory sequence used by human PKG. A construct containing only CNB-D and the catalytic domain is inactive without cGMP and efficiently activated by cGMP. cGMP binding to CNB-D induces a conformational change at the αC-helix; the inactive state involves an interaction between Asp597 (catalytic domain) and Arg528 (αC-helix of CNB-D), while the active state involves Arg528 stabilizing cGMP via Tyr480 of the phosphate binding cassette.","method":"Truncation constructs, in vitro kinase assays, structural analysis based on existing crystal data","journal":"ACS infectious diseases","confidence":"Medium","confidence_rationale":"Tier 1 / Moderate — biochemical reconstitution with truncation constructs and structural mechanistic model, single lab; structural evidence from prior crystal data rather than new structure","pmids":["29251493"],"is_preprint":false,"attribution":[{"species":"Plasmodium falciparum","strain":""}]},{"year":2018,"finding":"PKG (PF3D7_1436600) cooperates with PfCDPK5 to fully activate the protease cascade critical for parasite egress. Hyperactivation of PKG (by phosphodiesterase inhibitor treatment) overcomes the egress block caused by PfCDPK5 knockdown and restores microneme release, placing PKG upstream of or in parallel with PfCDPK5 in the egress signaling pathway.","method":"PfCDPK5 knockdown, PKG hyperactivation (phosphodiesterase inhibitor), microneme release assay, egress assay","journal":"mBio","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — genetic knockdown combined with chemical PKG activation as epistasis, single lab, two orthogonal approaches","pmids":["29487234"],"is_preprint":false,"attribution":[{"species":"Plasmodium falciparum","strain":""}]},{"year":2018,"finding":"In P. berghei, a hypomorphic allele of PKG (PF3D7_1436600 ortholog) combined with CDPK4 deletion causes a synthetic negative interaction for erythrocyte invasion, conserved also in P. falciparum. When PKG-dependent Ca2+ signals are attenuated, CDPK4 becomes critical for phosphorylating proteins important for inner membrane complex stability, which anchors the acto-myosin motor required for motility and invasion.","method":"Genetic interaction screen (294 kinase combinations), hypomorphic PKG allele, CDPK4 deletion, P. falciparum genetic validation, invasion assays, phosphoproteomics","journal":"Nature communications","confidence":"High","confidence_rationale":"Tier 2 / Strong — systematic genetic epistasis screen with biochemical follow-up, validated in two Plasmodium species, multiple methods","pmids":["30315162"],"is_preprint":false,"attribution":[{"species":"Plasmodium berghei","strain":""},{"species":"Plasmodium falciparum","strain":""}]},{"year":2018,"finding":"PKG (PF3D7_1436600) directly interacts with and phosphorylates RPT1, a subunit of the 19S regulatory particle of the P. falciparum proteasome. PfPKG and RPT1 interact in vitro (yeast two-hybrid and in vitro binding confirmed). A peptide from the RPT1 interacting region contains a PfPKG consensus phosphorylation site and is efficiently phosphorylated by PfPKG, and competes with full-length RPT1 fragment for binding to PfPKG. Phosphoproteomic mining using the consensus motif identified additional likely direct PKG substrates.","method":"Yeast two-hybrid library screen, in vitro binding/competition assay, in vitro kinase assay with peptide substrates, consensus phosphorylation site analysis","journal":"Infection and immunity","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — yeast two-hybrid plus in vitro kinase assay with defined substrate and competition, single lab","pmids":["30323024"],"is_preprint":false,"attribution":[{"species":"Plasmodium falciparum","strain":""}]},{"year":2019,"finding":"Crystal structures of full-length PKG (PF3D7_1436600) from P. falciparum and P. vivax in the cGMP-free (inactive) state reveal an overall pentagonal arrangement of the four CNBs and kinase domain, with an N-terminal autoinhibitory segment (AIS) docked in the substrate site of the kinase domain in a swapped-domain dimer. The AIS is necessary to maintain the inactive state. A helix serves the dual role of N-terminal helix of the kinase domain and capping helix of the neighboring CNB. Cooperative cGMP binding, beginning at the CNB closest to the kinase domain, transmits conformational changes around the pentagonal molecule via a structural relay mechanism to activate PKG.","method":"X-ray crystallography of full-length PfPKG and PvPKG (cGMP-free), structural analysis, analytical ultracentrifugation (monomer/dimer determination)","journal":"Proceedings of the National Academy of Sciences of the United States of America","confidence":"High","confidence_rationale":"Tier 1 / Strong — first full-length crystal structures of malarial PKG solved for two species, structural relay mechanism defined, multiple structural and biophysical methods","pmids":["31239348"],"is_preprint":false,"attribution":[{"species":"Plasmodium falciparum","strain":""},{"species":"Plasmodium vivax","strain":""}]},{"year":2020,"finding":"8-NBD-cGMP is an effective allosteric antagonist of PKG (PF3D7_1436600) that inhibits PfPKG not by a simple two-state active/inactive switch, but by stabilizing a distinct inactive 'mixed' intermediate state sharing features of both apo and cGMP-bound forms. This was demonstrated by NMR chemical shift analysis, molecular dynamics simulations, and site-directed mutagenesis of the key regulatory CNB-D domain.","method":"NMR chemical shift perturbation analysis, molecular dynamics simulations, site-directed mutagenesis, surface plasmon resonance","journal":"The Journal of biological chemistry","confidence":"High","confidence_rationale":"Tier 1 / Moderate — NMR, MD simulations, mutagenesis, and SPR together define a novel allosteric mechanism; single lab with multiple orthogonal biophysical methods","pmids":["32317283"],"is_preprint":false,"attribution":[{"species":"Plasmodium falciparum","strain":""}]},{"year":2020,"finding":"PKG (PF3D7_1436600) activity is required for P. falciparum asexual blood stage egress, hepatocyte invasion by sporozoites, and male gamete exflagellation. Metabolomic, phosphoproteomic, and chemoproteomic studies combined with conditional knockdown parasites, molecular docking, and recombinant kinase assays identified PKG as the primary cellular target of MMV030084. Resistance selection and gene editing identified tyrosine kinase-like protein 3 as a low-level resistance mediator for PKG inhibitors, while PKG itself never mutated under selection pressure.","method":"Metabolomics, phosphoproteomics, chemoproteomics, conditional knockdown, molecular docking, recombinant kinase assay, resistance selection, gene editing","journal":"Cell chemical biology","confidence":"High","confidence_rationale":"Tier 2 / Strong — target validation by multiple orthogonal omics approaches plus genetic knockdown, resistance genetics, and biochemical assay; multi-method single study","pmids":["32359426"],"is_preprint":false,"attribution":[{"species":"Plasmodium falciparum","strain":""}]},{"year":2020,"finding":"Using the DiCre system with multiple lox sites, simultaneous conditional disruption and allelic replacement of PKG (PF3D7_1436600) demonstrated that PfPKG has no scaffolding or adaptor role in intraerythrocytic development, acting solely at merozoite egress. A phosphorylation-deficient PfPKG (with key phosphorylation sites mutated) is functionally incompetent, showing that phosphorylation of PKG itself is required for its in vivo function.","method":"DiCre conditional disruption, multiple simultaneous allelic replacement, egress assays, phosphorylation-deficient mutant","journal":"Life science alliance","confidence":"High","confidence_rationale":"Tier 2 / Strong — genetic structure-function analysis with multiple simultaneous allelic replacements plus complementation controls, conclusively demonstrating both catalytic necessity and lack of scaffolding role","pmids":["32179592"],"is_preprint":false,"attribution":[{"species":"Plasmodium falciparum","strain":""}]},{"year":2021,"finding":"A multipass membrane protein ICM1 is tightly associated with PKG (PF3D7_1436600) in both asexual blood stages and transmission stages of Plasmodium. Multiple ICM1 phosphorylation events are dependent on PKG activity (shown by phosphoproteomics). Conditional depletion of P. berghei ICM1 prevents gametogenesis due to a block in intracellular calcium mobilization; conditional loss of P. falciparum ICM1 results in severely reduced calcium mobilization, defective egress, and lack of invasion. ICM1 is proposed as the missing link transducing PKG-dependent signals to intracellular Ca2+ release.","method":"Co-immunoprecipitation (PKG–ICM1 interaction), phosphoproteomics (PKG-dependent ICM1 phosphorylation), conditional stage-specific depletion (P. berghei and P. falciparum), Ca2+ imaging, egress and invasion assays","journal":"Science advances","confidence":"High","confidence_rationale":"Tier 2 / Strong — reciprocal Co-IP establishing direct PKG–ICM1 association, PKG-dependent phosphoproteomics, genetic KO with Ca2+ and phenotypic readouts across two species","pmids":["33762339"],"is_preprint":false,"attribution":[{"species":"Plasmodium berghei","strain":""},{"species":"Plasmodium falciparum","strain":""}]},{"year":2021,"finding":"GCα is the sole enzyme responsible for cGMP production in P. falciparum asexual blood stages and is required for PKG (PF3D7_1436600)-driven Ca2+ mobilization and merozoite egress. GCα-null parasites cannot synthesize cGMP or mobilize calcium; chemical complementation with a cGMP analogue rescues egress. Point mutagenesis of a conserved residue in the P4-ATPase domain of GCα abolishes cGMP synthesis, showing P4-ATPase activity is upstream of and linked to cGMP synthesis and hence PKG activation.","method":"Conditional KO of GCα, cGMP measurement, Ca2+ mobilization assay, egress assay, chemical complementation with cGMP analogue, site-directed mutagenesis of P4-ATPase domain","journal":"mBio","confidence":"High","confidence_rationale":"Tier 2 / Strong — genetic KO with multiple biochemical readouts, chemical complementation, and mutagenesis defining pathway order upstream of PKG; multiple orthogonal methods","pmids":["33500341"],"is_preprint":false,"attribution":[{"species":"Plasmodium falciparum","strain":""}]},{"year":2021,"finding":"SEA1 (PF3D7_1021800) undergoes phosphorylation dependent on PKG (PF3D7_1436600) activity, placing SEA1 as a PKG substrate during schizont development. However, SEA1 does not play a direct mechanistic role in egress per se; instead it functions upstream of egress as a regulator of correct nuclear segregation into daughter merozoites.","method":"PKG-dependent phosphoproteomics, conditional SEA1 disruption, egress and nuclear segregation phenotyping","journal":"mBio","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — PKG-dependent phosphoproteomics with genetic validation of SEA1 function, single lab; PKG's role is as an upstream kinase identified by phosphoproteomics","pmids":["33688001"],"is_preprint":false,"attribution":[{"species":"Plasmodium falciparum","strain":""}]},{"year":2024,"finding":"PKG (PF3D7_1436600) is regulated by two distinct mechanisms in P. falciparum asexual blood stages: (1) cGMP occupancy of cyclic nucleotide binding domain B (CNB-B) — reduced cGMP binding to CNB-B does not affect in vitro kinase activity but abolishes parasite egress in vivo; (2) phosphorylation of Thr695 in the activation loop — T695 phosphorylation is dispensable for in vitro kinase activity but essential for in vivo PKG function, with loss of T695 phosphorylation causing aberrant proteome-wide phosphorylation events and altered substrate specificity.","method":"Genetic engineering of CNB-B cGMP-binding mutants and T695A activation-loop mutants, in vitro kinase assay, quantitative phosphoproteomics, egress assay","journal":"PLoS pathogens","confidence":"High","confidence_rationale":"Tier 2 / Strong — genetic structure-function approach with multiple mutants validated by in vitro kinase assays and in vivo phosphoproteomics; multiple orthogonal methods in single study","pmids":["38935780"],"is_preprint":false,"attribution":[{"species":"Plasmodium falciparum","strain":""}]},{"year":2024,"finding":"The crystal structure of PfPKG (PF3D7_1436600) bound to a pyrrole-series inhibitor was solved, revealing the structural basis for inhibitor binding at the ATP-binding site and enabling structure-activity relationship analysis for the pyrrole series.","method":"X-ray crystallography of PfPKG–inhibitor co-crystal, structure-based modeling, in vitro recombinant PfPKG kinase assay, gatekeeper mutant transgenic parasite selectivity assay","journal":"Journal of medicinal chemistry","confidence":"Medium","confidence_rationale":"Tier 1 / Moderate — co-crystal structure with functional validation using gatekeeper mutant parasites, single lab","pmids":["38372781"],"is_preprint":false,"attribution":[{"species":"Plasmodium falciparum","strain":""}]},{"year":2025,"finding":"PP1 phosphatase controls the homeostasis of cGMP in P. falciparum by modulating the basal activity of guanylyl cyclase alpha (GCα), thereby acting upstream of PKG (PF3D7_1436600) and PKG-dependent downstream Ca2+ signaling. PP1 also regulates the rounding-up of the parasitophorous vacuole, the first step in the egress cascade, a process reliant on Ca2+ and occurring upstream of PKG-driven membrane breakdown.","method":"Conditional PfPP1 knockout (iKO), fluorescent reporters of PV morphology, live-microscopy, cGMP measurement, egress kinetics with PKG pathway inducers/inhibitors, Ca2+ ionophore rescue","journal":"PLoS pathogens","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — conditional KO with live imaging and chemical epistasis experiments placing PP1 upstream of PKG, single lab with multiple readouts","pmids":["39808636"],"is_preprint":false,"attribution":[{"species":"Plasmodium falciparum","strain":""}]},{"year":2025,"finding":"In P. falciparum gametocytes, PfPP1 controls crucial steps of gametocyte activation through stimulation of the cGMP/PKG (PF3D7_1436600) pathway, placing PfPP1 upstream of PKG activation during sexual stage transmission.","method":"Conditional PfPP1 depletion, cGMP measurement, gametocyte activation assays, mosquito transmission experiments","journal":"mBio","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — conditional depletion with cGMP measurement and functional transmission assays, single lab","pmids":["40823845"],"is_preprint":false,"attribution":[{"species":"Plasmodium falciparum","strain":""}]},{"year":2022,"finding":"PKG (PF3D7_1436600) resistance mutations in P. falciparum mapped to the gatekeeper residue T618I upon in vitro selection with PKG-targeting compounds TCMDC-141334 and TCDMC-140674, consistent with direct interaction of these compounds with the PKG active site. CRISPR editing of T618I in naive parasites confirmed the resistance phenotype and thus validated PKG as the target.","method":"In vitro evolution of resistance, whole-genome sequencing, CRISPR editing, in vitro activity assays with recombinant proteins, molecular docking","journal":"mBio","confidence":"High","confidence_rationale":"Tier 2 / Strong — resistance genetics with CRISPR validation and biochemical confirmation, multiple orthogonal methods","pmids":["41277867"],"is_preprint":false,"attribution":[{"species":"Plasmodium falciparum","strain":""}]}],"current_model":"PKG (PF3D7_1436600) is the sole cGMP sensor and master signaling kinase in Plasmodium, activated by cooperative cGMP binding to a unique four-CNB regulatory module (with CNB-D serving as the primary activation gate and CNB-B binding required for in vivo function) that releases an autoinhibitory segment from the kinase domain via a pentagonal structural relay; it is further regulated by activation-loop phosphorylation at T695; upstream, GCα (the sole cGMP synthase in blood stages) and PP1 phosphatase control cGMP levels, while downstream PKG phosphorylates ICM1 (a membrane channel required for Ca2+ mobilization from intracellular stores), PfCDPK1, actomyosin complex components, proteasome subunit RPT1, and at least 69 other targets to orchestrate PfSUB1/microneme discharge, PV membrane breakdown, host-cell egress, and invasion across asexual blood stages, gametogenesis, ookinete gliding, sporozoite motility, and liver-stage merosome release."},"narrative":{"mechanistic_narrative":"PKG (PF3D7_1436600) is the sole cGMP-activated protein kinase and master signaling hub of Plasmodium, orchestrating the transitions of the parasite life cycle through cGMP-triggered phosphorylation of downstream effectors [PMID:12068803, PMID:26149123]. Recombinant PfPKG is a cGMP-selective phosphotransferase whose activity is stimulated at least fivefold by cGMP but not by cAMP, and whose regulatory module contains four cyclic-nucleotide-binding sites, of which one dominant site (later assigned to the C-terminal CNB-D) governs activation while the degenerate fourth site contributes to full activity without binding cGMP [PMID:12068803, PMID:12817987, PMID:25646845]. Structurally, full-length PfPKG adopts a pentagonal arrangement of the four CNBs around the kinase domain in which an N-terminal autoinhibitory segment docks into the substrate site; cooperative cGMP binding, initiated at the CNB nearest the catalytic domain, propagates conformational change through a structural relay to release autoinhibition and activate the kinase [PMID:31239348, PMID:29251493]. In vivo, full function additionally requires cGMP occupancy of CNB-B and activation-loop phosphorylation at Thr695, both of which are dispensable for in vitro catalysis but essential in the parasite [PMID:38935780, PMID:32179592]. Upstream, GCα is the sole cGMP synthase in asexual blood stages and PP1 phosphatase sets cGMP homeostasis by tuning GCα, positioning both as controllers of PKG activation [PMID:33500341, PMID:39808636]. Once active, PKG drives phosphoinositide hydrolysis and intracellular Ca2+ mobilization—transduced in part through its tightly associated multipass membrane partner ICM1—to trigger PfSUB1 discharge, microneme release, parasitophorous vacuole membrane breakdown, host-cell egress, and erythrocyte invasion, and it phosphorylates a broad substrate set including PfCDPK1, actomyosin components, and the proteasome subunit RPT1 [PMID:23675297, PMID:24594931, PMID:33762339, PMID:26149123, PMID:28292906, PMID:30323024]. This PKG-centered pathway operates across the life cycle, being required for asexual schizogony and egress, gametogenesis, ookinete and sporozoite motility, and liver-stage merosome release [PMID:19915077, PMID:18532880, PMID:19779564, PMID:19940133, PMID:27425827]. PKG is a validated antimalarial drug target: potent selective inhibitors act across multiple stages, and resistance selection maps to gatekeeper mutations rather than loss of PKG itself [PMID:28874661, PMID:41277867, PMID:32359426].","teleology":[{"year":2002,"claim":"Establishing that PF3D7_1436600 encodes a genuine cGMP-selective kinase was the founding question, defining it as a distinct second-messenger effector expressed in a stage-specific manner.","evidence":"Recombinant PfPKG expressed in E. coli assayed for cGMP-stimulated phosphotransferase activity, with stage expression by Western blot","pmids":["12068803"],"confidence":"High","gaps":["Physiological substrates unknown","Cellular function untested","Structural basis of cGMP selectivity undefined"],"attribution":[{"species":"Plasmodium falciparum","strain":""}]},{"year":2003,"claim":"Which of the four nucleotide-binding sites drives activation was resolved, showing a hierarchical contribution and that the degenerate fourth site aids activation without binding cGMP.","evidence":"Systematic site-directed mutagenesis of each cGMP-binding site with in vitro Ka and Vmax measurements","pmids":["12817987"],"confidence":"High","gaps":["No structural view of the activation mechanism","Relationship between sites in the intact protein unresolved"],"attribution":[{"species":"Plasmodium falciparum","strain":""}]},{"year":2005,"claim":"Native PfPKG activity was purified and shown to match recombinant enzyme in cooperativity, substrate preference, and inhibitor sensitivity, validating the recombinant tools and Compound 1 as a probe.","evidence":"cGMP-affinity and ion-exchange purification of native activity, plus recombinant expression in T. gondii with kinase assays","pmids":["16325279"],"confidence":"Medium","gaps":["Endogenous substrates still unidentified","Cellular role not yet tested"],"attribution":[{"species":"Plasmodium falciparum","strain":""}]},{"year":2009,"claim":"Chemical-genetic experiments established PKG as essential for asexual schizont rupture and gametogenesis, moving it from a biochemical entity to a functional gatekeeper of key life-cycle transitions.","evidence":"Compound 1 inhibition rescued by inhibitor-insensitive mutant PKG in P. falciparum blood stages and gametocytes, with Ca2+ epistasis","pmids":["19915077","18532880"],"confidence":"High","gaps":["Direct substrates driving egress/gametogenesis unknown","Mechanistic link to Ca2+ undefined"],"attribution":[{"species":"Plasmodium falciparum","strain":""}]},{"year":2009,"claim":"Work in P. berghei extended PKG's role to ookinete gliding and late liver-stage merosome release, and placed GCbeta/PDEdelta as the cGMP source/sink in ookinetes.","evidence":"Genetic epistasis with single/double cyclase and phosphodiesterase knockouts, PKG inhibition, motility assays, and conditional sporozoite disruption","pmids":["19779564","19940133"],"confidence":"High","gaps":["Downstream motility substrates unidentified","How merosome release is controlled unresolved"],"attribution":[{"species":"Plasmodium berghei","strain":""}]},{"year":2013,"claim":"PKG was placed at the apex of the protease-mediated egress pathway by showing it controls PfSUB1 discharge and microneme release, and that its hyperactivation triggers premature egress.","evidence":"PKG inhibition and phosphodiesterase-mediated hyperactivation with SUB1 discharge, microneme, and egress readouts in P. falciparum","pmids":["23675297"],"confidence":"High","gaps":["Direct PKG substrates in the discharge pathway unknown","Signal transduction to Ca2+ not yet mechanistic"],"attribution":[{"species":"Plasmodium falciparum","strain":""}]},{"year":2014,"claim":"The intermediate signaling logic was clarified: PKG controls phosphoinositide metabolism and PIP2 hydrolysis upstream of the Ca2+ signal required for gliding, gametocyte activation, and egress.","evidence":"Conditional PKG inhibition with quantitative phosphoproteomics, lipidomics, and Ca2+ imaging across P. berghei and P. falciparum","pmids":["24594931"],"confidence":"High","gaps":["Enzyme(s) linking PKG to phosphoinositide hydrolysis unresolved","Identity of the Ca2+ channel unknown at this stage"],"attribution":[{"species":"Plasmodium berghei","strain":""},{"species":"Plasmodium falciparum","strain":""}]},{"year":2015,"claim":"The substrate landscape was mapped and PKG was shown to be required for invasion as well as egress, establishing it as a shared signaling hub.","evidence":"SILAC phosphoproteomics under chemical and genetic PKG inhibition identifying 69 dependent proteins including PfCDPK1 and actomyosin components, plus invasion assays in P. falciparum","pmids":["26149123"],"confidence":"High","gaps":["Direct versus indirect substrates not fully distinguished","Functional consequence of most phosphosites untested"],"attribution":[{"species":"Plasmodium falciparum","strain":""}]},{"year":2015,"claim":"The structural gate for activation was defined: CNB-D is the high-affinity gatekeeper whose cGMP-induced capping triad is required for both in vitro activity and in vivo egress.","evidence":"Crystal structures of CNB-D with and without cGMP, mutagenesis of the capping triad, in vitro kinase assays, and parasite egress phenotyping in P. falciparum","pmids":["25646845"],"confidence":"High","gaps":["Full-length activation mechanism not yet visualized","How CNB-D change reaches the catalytic domain unresolved"],"attribution":[{"species":"Plasmodium falciparum","strain":""}]},{"year":2017,"claim":"The mechanistic and cellular consequences of PKG activation were refined: CNB-D activates via an alphaC-helix relay distinct from human PKG, and PKG triggers a temporally defined PVM breakdown step during egress.","evidence":"Truncation constructs with kinase assays and structural modeling; and selective inhibitor dissection with multimodal imaging of egress steps in P. falciparum","pmids":["29251493","28292906"],"confidence":"Medium","gaps":["Effectors executing PVM breakdown unknown","Structural relay inferred rather than seen in full-length enzyme"],"attribution":[{"species":"Plasmodium falciparum","strain":""}]},{"year":2016,"claim":"PKG's motility role in sporozoites was defined and separated from CDPK4, showing it acts as an independent second-messenger effector controlling TRAP secretion, invasion, and egress.","evidence":"PKG-specific inhibitors, inhibitor-insensitive mutant sporozoites, invasion/motility and TRAP secretion assays in P. berghei","pmids":["27425827"],"confidence":"High","gaps":["Direct substrates driving TRAP secretion unknown","Molecular link between PKG and adhesin release unresolved"],"attribution":[{"species":"Plasmodium berghei","strain":""}]},{"year":2018,"claim":"PKG's cooperative relationships with other kinases were mapped, placing it upstream of/parallel to PfCDPK5 in egress and revealing synthetic interaction with CDPK4 in invasion.","evidence":"PfCDPK5 knockdown with PKG hyperactivation epistasis; systematic kinase genetic interaction screen with hypomorphic PKG and CDPK4 deletion validated in both species","pmids":["29487234","30315162"],"confidence":"High","gaps":["Shared versus distinct substrates of PKG and CDPKs unresolved","Nature of the parallel Ca2+ inputs undefined"],"attribution":[{"species":"Plasmodium falciparum","strain":""},{"species":"Plasmodium berghei","strain":""}]},{"year":2018,"claim":"A specific direct substrate/partner was identified, linking PKG to proteasome regulation through phosphorylation of the 19S subunit RPT1.","evidence":"Yeast two-hybrid, in vitro binding/competition, and in vitro peptide kinase assays with consensus-motif mining in P. falciparum","pmids":["30323024"],"confidence":"Medium","gaps":["Functional consequence of RPT1 phosphorylation in vivo untested","Single-lab interaction without reciprocal in-parasite validation"],"attribution":[{"species":"Plasmodium falciparum","strain":""}]},{"year":2019,"claim":"The full-length inactive structure revealed the pentagonal architecture and autoinhibitory segment, defining the cooperative structural relay by which cGMP activates PKG.","evidence":"X-ray structures of full-length cGMP-free PfPKG and PvPKG with analytical ultracentrifugation","pmids":["31239348"],"confidence":"High","gaps":["Active-state full-length structure not solved","Dynamics of the relay not directly observed"],"attribution":[{"species":"Plasmodium falciparum","strain":""},{"species":"Plasmodium vivax","strain":""}]},{"year":2020,"claim":"Regulatory subtlety was added by showing an allosteric antagonist stabilizes a distinct mixed intermediate rather than a simple off-state, refining the activation model.","evidence":"NMR chemical shift analysis, molecular dynamics, SPR, and CNB-D mutagenesis with 8-NBD-cGMP on P. falciparum PKG","pmids":["32317283"],"confidence":"High","gaps":["Relevance of the intermediate state to cellular regulation unknown"],"attribution":[{"species":"Plasmodium falciparum","strain":""}]},{"year":2020,"claim":"Genetic dissection established that PKG acts purely catalytically at egress with no scaffolding role, and that phosphorylation of PKG itself is required for its in vivo function.","evidence":"DiCre conditional disruption with simultaneous allelic replacement, phosphorylation-deficient mutant, and egress assays; plus multi-omic target validation of MMV030084 in P. falciparum","pmids":["32179592","32359426"],"confidence":"High","gaps":["Kinase(s) phosphorylating PKG not identified","Role in stages other than egress not addressed by these knockouts"],"attribution":[{"species":"Plasmodium falciparum","strain":""}]},{"year":2021,"claim":"The long-missing link from PKG to Ca2+ was identified as the membrane protein ICM1, a PKG-associated, PKG-phosphorylated channel required for calcium mobilization.","evidence":"Co-immunoprecipitation, PKG-dependent phosphoproteomics, and conditional ICM1 depletion with Ca2+ imaging and egress/invasion assays in P. berghei and P. falciparum","pmids":["33762339"],"confidence":"High","gaps":["Direct proof that ICM1 conducts Ca2+ not established","How ICM1 phosphorylation gates channel activity unknown"],"attribution":[{"species":"Plasmodium berghei","strain":""},{"species":"Plasmodium falciparum","strain":""}]},{"year":2021,"claim":"The upstream cGMP source and additional substrates were pinned down: GCα is the sole cGMP synthase feeding PKG in blood stages, and SEA1 is a PKG substrate acting in nuclear segregation upstream of egress.","evidence":"Conditional GCα KO with cGMP/Ca2+/egress readouts and cGMP chemical complementation; PKG-dependent phosphoproteomics with conditional SEA1 disruption in P. falciparum","pmids":["33500341","33688001"],"confidence":"High","gaps":["How GCα activity is triggered at egress unresolved","Direct versus indirect SEA1 phosphorylation not distinguished"],"attribution":[{"species":"Plasmodium falciparum","strain":""}]},{"year":2024,"claim":"Dual in vivo regulatory requirements were defined: cGMP binding to CNB-B and activation-loop phosphorylation at Thr695 are each dispensable in vitro but essential in the parasite and shape substrate specificity.","evidence":"Genetic CNB-B and T695A mutants with in vitro kinase assays, quantitative phosphoproteomics, and egress assays in P. falciparum","pmids":["38935780"],"confidence":"High","gaps":["Mechanism by which CNB-B and T695 tune specificity unknown","In vitro/in vivo discrepancy in requirement unexplained"],"attribution":[{"species":"Plasmodium falciparum","strain":""}]},{"year":2025,"claim":"The upstream homeostatic control of cGMP was extended by showing PP1 phosphatase modulates GCα basal activity and PV rounding, positioning PP1 above PKG in both asexual and sexual stages.","evidence":"Conditional PfPP1 knockout with cGMP measurement, PV morphology imaging, chemical epistasis, and transmission assays in P. falciparum blood and gametocyte stages","pmids":["39808636","40823845"],"confidence":"Medium","gaps":["Whether PP1 acts directly on GCα or intermediaries unresolved","PP1 targets controlling cGMP homeostasis unidentified"],"attribution":[{"species":"Plasmodium falciparum","strain":""}]},{"year":2017,"claim":"PKG was advanced as an antimalarial target with defined inhibitor pharmacology, culminating in co-crystal structures and picomolar-potency compounds active across life-cycle stages.","evidence":"Co-crystal structures of PvPKG–ML10 and PfPKG–pyrrole inhibitors with in vitro kinase, multi-stage parasite, and in vivo mouse assays","pmids":["28874661","38372781"],"confidence":"High","gaps":["Long-term resistance liability incompletely defined at this stage"],"attribution":[{"species":"Plasmodium vivax","strain":""},{"species":"Plasmodium falciparum","strain":""}]},{"year":2022,"claim":"Resistance genetics confirmed PKG as a bona fide drug target, with mutations mapping to gatekeeper residues rather than loss of PKG function.","evidence":"In vitro evolution, whole-genome sequencing, CRISPR editing of gatekeeper mutations, and biochemical assays in P. falciparum","pmids":["41277867","32359426"],"confidence":"High","gaps":["Full spectrum of clinically relevant resistance mechanisms unknown"],"attribution":[{"species":"Plasmodium falciparum","strain":""}]},{"year":null,"claim":"How PKG achieves precise substrate selection and stage-specific outputs from a single cGMP input—including the direct effectors executing PVM breakdown and the biophysical proof of ICM1 as the Ca2+ conduit—remains open.","evidence":"","pmids":[],"confidence":"Medium","gaps":["Direct substrates driving each cellular event not fully resolved","ICM1 channel activity not directly demonstrated","Active-state full-length structure and in-parasite dynamics undefined"],"attribution":[{"species":"Plasmodium falciparum","strain":""}]}],"mechanism_profile":{"molecular_activity":[],"localization":[],"pathway":[],"complexes":["PKG (PF3D7_1436600)–ICM1 membrane-associated complex [#23]"],"partners":["ICM1 (MULTIPASS MEMBRANE CHANNEL, PKG-ASSOCIATED AND PKG-PHOSPHORYLATED) [#23]","RPT1 (19S PROTEASOME REGULATORY SUBUNIT; DIRECT BINDING AND SUBSTRATE) [#18]","PFCDPK1 (PKG-DEPENDENT PHOSPHORYLATION) [#10]","GCΑ (GUANYLYL CYCLASE; SOLE BLOOD-STAGE CGMP SOURCE UPSTREAM OF PKG) [#24]","PP1 PHOSPHATASE (UPSTREAM REGULATOR OF CGMP HOMEOSTASIS VIA GCΑ) [#28, #29]","PFCDPK5 (COOPERATES IN EGRESS PATHWAY) [#16]","CDPK4 (SYNTHETIC GENETIC INTERACTION IN INVASION) [#17]","SEA1 (PKG-DEPENDENT PHOSPHORYLATION, NUCLEAR SEGREGATION) [#25]"],"other_free_text":["Activated by cooperative cGMP binding to a four-CNB regulatory module; CNB-D is the high-affinity activation gatekeeper and site 3 dominates activation in vitro [#1, #11].","Full-length inactive enzyme adopts a pentagonal CNB/kinase arrangement with an N-terminal autoinhibitory segment; cGMP activation propagates via a structural relay [#19].","In vivo function additionally requires cGMP occupancy of CNB-B and activation-loop phosphorylation at Thr695, both dispensable for in vitro catalysis [#26].","PKG acts purely catalytically at egress with no scaffolding/adaptor role [#22].","Validated antimalarial drug target inhibited by Compound 1, ML10, pyrrole and imidazopyridine series; resistance maps to gatekeeper residues (T618I) rather than loss of PKG [#4, #14, #27, #30].","Required across the life cycle: asexual schizogony/egress and invasion, gametogenesis, ookinete gliding, sporozoite motility/invasion, and liver-stage merosome release [#3, #4, #5, #6, #12, #10]."]}},"prefetch_data":{},"corpus_meta":[{"pmid":"23675297","id":"PMC_23675297","title":"Malaria parasite cGMP-dependent protein kinase regulates blood stage merozoite secretory organelle discharge and egress.","date":"2013","source":"PLoS 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Recombinant PfPKG (Met115-Phe853) expressed in E. coli displays phosphotransferase activity (substrate phosphorylation and auto-phosphorylation) stimulated at least fivefold by 1.0 µM cGMP, but not by cAMP or 8-pCPT-cGMP. Western blotting and kinase activity assays with native P. falciparum proteins show maximal expression predominantly in the ring stage of the asexual life cycle.\",\n      \"method\": \"Recombinant protein expression, in vitro kinase assay, Western blotting with stage-specific parasite lysates\",\n      \"journal\": \"Molecular microbiology\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 / Moderate — in vitro reconstitution of kinase activity with recombinant protein plus stage-specific expression confirmed by two orthogonal methods (activity assay and Western blot), single lab\",\n      \"pmids\": [\"12068803\"],\n      \"is_preprint\": false,\n      \"attribution\": [{\"species\": \"Plasmodium falciparum\", \"strain\": \"\"}]\n    },\n    {\n      \"year\": 2003,\n      \"finding\": \"Among the four cGMP-binding sites in PKG (PF3D7_1436600), site 3 plays the dominant role in activation: mutation of site 3 alone causes a 10–49-fold increase in Ka(cGMP) and a 45–55% decrease in maximal activity in vitro. Mutations at sites 1 and 2 have lesser effects. Mutation of the degenerate site 4 reduces maximal activity by ~40% without altering Ka(cGMP), indicating site 4 does not bind cGMP but contributes to full activation.\",\n      \"method\": \"Site-directed mutagenesis of each cGMP-binding site (individually and in combination), in vitro kinase activity assay\",\n      \"journal\": \"The Biochemical journal\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 / Moderate — in vitro reconstitution with systematic mutagenesis of all four sites, multiple orthogonal measurements (Ka and Vmax), single lab\",\n      \"pmids\": [\"12817987\"],\n      \"is_preprint\": false,\n      \"attribution\": [{\"species\": \"Plasmodium falciparum\", \"strain\": \"\"}]\n    },\n    {\n      \"year\": 2005,\n      \"finding\": \"Native PKG (PF3D7_1436600) activity partially purified from P. falciparum by cGMP-affinity and ion-exchange chromatography is associated with a ~98 kDa protein detectable by anti-PKG antisera, and shows cGMP-stimulated kinase activity inhibitable by Compound 1. Recombinant PfPKG expressed in T. gondii (Pf(Tg)PKG) has kinase activity stimulated by cGMP with significant cooperativity (Hill coefficient of 2), and substrate preference and inhibitor sensitivity similar to native PfPKG and other apicomplexan PKGs.\",\n      \"method\": \"cGMP-affinity chromatography, ion-exchange chromatography, in vitro kinase assay, recombinant protein expression in T. gondii, Western blot\",\n      \"journal\": \"Molecular and biochemical parasitology\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 1 / Moderate — biochemical purification and recombinant reconstitution with kinase assays, two complementary approaches; single lab\",\n      \"pmids\": [\"16325279\"],\n      \"is_preprint\": false,\n      \"attribution\": [{\"species\": \"Plasmodium falciparum\", \"strain\": \"\"}]\n    },\n    {\n      \"year\": 2008,\n      \"finding\": \"PKG (PF3D7_1436600) is essential for xanthurenic acid (XA)- and zaprinast-induced gametogenesis in P. falciparum. Using PKG inhibitors together with transgenic parasites expressing an inhibitor-insensitive mutant PKG, it was shown that PKG activity is required for gametocyte-to-gamete differentiation. Intracellular Ca2+ signaling acts downstream of or in parallel with PKG activation during gametogenesis.\",\n      \"method\": \"PKG inhibitor treatment, inhibitor-insensitive mutant PKG transgenic parasites (genetic rescue), intracellular Ca2+ measurements\",\n      \"journal\": \"PLoS biology\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Strong — chemical inhibition validated by genetic rescue with inhibitor-insensitive mutant, Ca2+ epistasis established; multiple orthogonal methods\",\n      \"pmids\": [\"18532880\"],\n      \"is_preprint\": false,\n      \"attribution\": [{\"species\": \"Plasmodium falciparum\", \"strain\": \"\"}]\n    },\n    {\n      \"year\": 2009,\n      \"finding\": \"PKG (PF3D7_1436600) is required for blood-stage schizogony in P. falciparum. Compound 1 (trisubstituted pyrrole PKG inhibitor) blocked schizont rupture and merozoite liberation; transgenic parasites expressing a Compound 1-insensitive PfPKG completed schizogony in its presence, confirming PKG as the primary target. Treated schizonts became large and dysmorphic and were unable to rupture.\",\n      \"method\": \"PKG inhibitor treatment, inhibitor-insensitive mutant PKG transgenic parasites (genetic rescue), erythrocyte invasion assays, microscopy\",\n      \"journal\": \"Eukaryotic cell\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Strong — chemical-genetic validation with inhibitor-insensitive mutant rescue, replicated across multiple assay formats\",\n      \"pmids\": [\"19915077\"],\n      \"is_preprint\": false,\n      \"attribution\": [{\"species\": \"Plasmodium falciparum\", \"strain\": \"\"}]\n    },\n    {\n      \"year\": 2009,\n      \"finding\": \"In P. berghei ookinetes, PKG (PF3D7_1436600 ortholog) is required for gliding motility. Inhibition of PKG blocks ookinete gliding, while enhanced cGMP signaling (via PDEdelta deletion) causes ookinete rounding. The cGMP for PKG activation in ookinetes is produced primarily by guanylyl cyclase beta (GCbeta) and degraded by PDEdelta, as demonstrated by genetic epistasis (PDEdelta/GCbeta double mutant suppresses PDEdelta-null rounding phenotype). Elevated cGMP/PKG signaling can partially rescue gliding defects in a CDPK3-null mutant.\",\n      \"method\": \"Genetic epistasis (single and double knockout), PKG inhibitor treatment, ookinete motility assay\",\n      \"journal\": \"PLoS pathogens\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Strong — genetic epistasis with multiple single and double mutants defining pathway order, replicated with chemical inhibition\",\n      \"pmids\": [\"19779564\"],\n      \"is_preprint\": false,\n      \"attribution\": [{\"species\": \"Plasmodium berghei\", \"strain\": \"\"}]\n    },\n    {\n      \"year\": 2009,\n      \"finding\": \"Conditional disruption of P. berghei PKG (PF3D7_1436600 ortholog) in sporozoites blocks late liver stage development: mutant sporozoites invade hepatocytes and undergo intracellular development normally but fail to release merosomes into the medium.\",\n      \"method\": \"Conditional gene disruption in sporozoites, liver stage culture, merosome release assay\",\n      \"journal\": \"The Journal of biological chemistry\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — conditional KO with defined cellular phenotype (merosome release block), single lab\",\n      \"pmids\": [\"19940133\"],\n      \"is_preprint\": false,\n      \"attribution\": [{\"species\": \"Plasmodium berghei\", \"strain\": \"\"}]\n    },\n    {\n      \"year\": 2012,\n      \"finding\": \"In P. falciparum asexual blood stages, PKG (PF3D7_1436600) is expressed maximally at the late schizont stage. Subcellular fractionation and immunofluorescence of epitope-tagged PfPKG show a predominantly cytosolic location with partial overlap with ER markers and some association with the peripheral membrane fraction. PKG inhibition substantially changes the global protein phosphorylation pattern of schizonts, indicating a complex and broad role in schizogony.\",\n      \"method\": \"Transgenic epitope-tagged PKG expression, Western blot stage analysis, immunofluorescence assay (IFA), subcellular fractionation, global phosphoproteomics after PKG inhibition\",\n      \"journal\": \"PloS one\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — direct localization by IFA and fractionation plus functional phosphoproteomics, single lab, multiple orthogonal methods\",\n      \"pmids\": [\"23139764\"],\n      \"is_preprint\": false,\n      \"attribution\": [{\"species\": \"Plasmodium falciparum\", \"strain\": \"\"}]\n    },\n    {\n      \"year\": 2013,\n      \"finding\": \"PKG (PF3D7_1436600) activity is required for PfSUB1 discharge into the parasitophorous vacuole and for microneme release during merozoite egress. Pharmacological stimulation of PKG by inhibiting parasite phosphodiesterase activity induces premature PfSUB1 discharge and egress of immature, non-invasive parasites. This identifies PKG as the upstream regulator of the protease-mediated egress signaling pathway.\",\n      \"method\": \"PKG inhibitor treatment, phosphodiesterase inhibitor stimulation, immunofluorescence, Western blot for PfSUB1 discharge, egress assays\",\n      \"journal\": \"PLoS pathogens\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Strong — chemical gain-of-function and loss-of-function experiments with multiple downstream readouts (SUB1 discharge, microneme release, egress), multiple orthogonal methods\",\n      \"pmids\": [\"23675297\"],\n      \"is_preprint\": false,\n      \"attribution\": [{\"species\": \"Plasmodium falciparum\", \"strain\": \"\"}]\n    },\n    {\n      \"year\": 2014,\n      \"finding\": \"PKG (PF3D7_1436600) controls phosphoinositide biosynthesis and maintains elevated cytosolic Ca2+ required for gliding motility in P. berghei ookinetes. The same PKG-dependent pathway operates upstream of Ca2+ signals mediating P. berghei gametocyte activation and P. falciparum merozoite egress. Perturbation of PKG signaling in gliding ookinetes causes phosphoproteomic changes enriched in vesicular trafficking and phosphoinositide metabolism pathways. In P. falciparum, PKG inhibition blocks hydrolysis of phosphatidylinositol (4,5)-bisphosphate, linking PKG to phosphoinositide metabolism upstream of Ca2+ mobilization.\",\n      \"method\": \"Conditional PKG inhibition, quantitative phosphoproteomics, global phospholipid analysis, Ca2+ imaging, egress assays\",\n      \"journal\": \"PLoS biology\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Strong — multiple orthogonal methods (phosphoproteomics, lipidomics, Ca2+ imaging, egress) across two Plasmodium species, single lab with broad mechanistic coverage\",\n      \"pmids\": [\"24594931\"],\n      \"is_preprint\": false,\n      \"attribution\": [\n        {\"species\": \"Plasmodium berghei\", \"strain\": \"\"},\n        {\"species\": \"Plasmodium falciparum\", \"strain\": \"\"}\n      ]\n    },\n    {\n      \"year\": 2015,\n      \"finding\": \"Quantitative global phosphoproteomics in P. falciparum identified 69 proteins whose phosphorylation is directly or indirectly dependent on PKG (PF3D7_1436600) activity. These include PfCDPK1 (phosphorylated by PKG) and components of the actomyosin complex. PKG activity is also required for erythrocyte invasion (not only egress), establishing PKG as a signaling hub for both processes.\",\n      \"method\": \"Chemical and genetic PKG inhibition combined with quantitative global phosphoproteomics (SILAC-based), invasion assays\",\n      \"journal\": \"Nature communications\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Strong — quantitative phosphoproteomics with chemical and genetic tools, functional validation of invasion requirement, single lab with two orthogonal inhibition strategies\",\n      \"pmids\": [\"26149123\"],\n      \"is_preprint\": false,\n      \"attribution\": [{\"species\": \"Plasmodium falciparum\", \"strain\": \"\"}]\n    },\n    {\n      \"year\": 2015,\n      \"finding\": \"The C-terminal (carboxyl) cGMP-binding domain (CNB-D) of PKG (PF3D7_1436600) has the highest cGMP affinity and selectivity and functions as a gatekeeper for PKG activation. Crystal structures of this domain with (1.9 Å) and without (2.0 Å) cGMP reveal a PfPKG-specific capping triad that forms upon cGMP binding. Disruption of the capping triad reduces kinase activity by 90% in vitro. Mutating these residues in the parasite prevents blood-stage merozoite egress, confirming functional essentiality in vivo.\",\n      \"method\": \"X-ray crystallography, site-directed mutagenesis, in vitro kinase assay, parasite genetic engineering with egress phenotype readout\",\n      \"journal\": \"PLoS pathogens\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 / Strong — crystal structures at high resolution, in vitro mutagenesis, and in vivo parasite phenotype validation; multiple orthogonal methods in one study\",\n      \"pmids\": [\"25646845\"],\n      \"is_preprint\": false,\n      \"attribution\": [{\"species\": \"Plasmodium falciparum\", \"strain\": \"\"}]\n    },\n    {\n      \"year\": 2016,\n      \"finding\": \"In P. berghei, PKG (PF3D7_1436600 ortholog) is required for sporozoite invasion of hepatocytes and sporozoite motility. Chemical inhibition of PKG with specific inhibitors decreases TRAP secretion (an adhesin essential for motility) by sporozoites, and chemical inhibition also reduces parasite egress from hepatocytes. Sporozoites expressing a mutated, inhibitor-insensitive form of PbPKG are defective in hepatocyte invasion. PKG and CDPK4 act as independent second-messenger effectors for sporozoite invasion.\",\n      \"method\": \"PKG-specific inhibitors, inhibitor-insensitive mutant PKG sporozoites, hepatocyte invasion assays, TRAP secretion assay, merosome egress assay\",\n      \"journal\": \"Molecular microbiology\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Strong — chemical-genetic validation with inhibitor-insensitive mutant, multiple downstream readouts (invasion, motility, TRAP secretion), single lab\",\n      \"pmids\": [\"27425827\"],\n      \"is_preprint\": false,\n      \"attribution\": [{\"species\": \"Plasmodium berghei\", \"strain\": \"\"}]\n    },\n    {\n      \"year\": 2017,\n      \"finding\": \"PKG (PF3D7_1436600) triggers the PKG-dependent breakdown of the parasitophorous vacuole membrane (PVM) into multilayered vesicles during egress. PKG-dependent PVM breakdown is temporally distinct from an initial cysteine-protease-independent PVM permeabilization step (which precedes PKG-triggered breakdown by 10–30 min). An abrupt host erythrocyte cytoskeleton collapse occurs in a narrow window just before PVM breakdown, not gradually during schizont development.\",\n      \"method\": \"Selective PKG inhibitor and cysteine protease inhibitor treatment combined with video microscopy, electron tomography, electron energy loss spectroscopy, soft X-ray tomography\",\n      \"journal\": \"Proceedings of the National Academy of Sciences of the United States of America\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Strong — multiple complementary imaging modalities with pharmacological dissection of sequential steps, defining precise timing of PKG-dependent events\",\n      \"pmids\": [\"28292906\"],\n      \"is_preprint\": false,\n      \"attribution\": [{\"species\": \"Plasmodium falciparum\", \"strain\": \"\"}]\n    },\n    {\n      \"year\": 2017,\n      \"finding\": \"A co-crystal structure of Plasmodium vivax PKG (PvPKG, ortholog of PF3D7_1436600) bound to the imidazopyridine inhibitor ML10 reveals intimate molecular contacts explaining potency and selectivity of this inhibitor series. The compound inhibits PKG with an IC50 of 160 pM (P. falciparum PKG assay) and acts on merozoite egress, erythrocyte invasion, and gametocyte transmission.\",\n      \"method\": \"X-ray co-crystal structure of PvPKG–inhibitor complex, in vitro PfPKG kinase assay, P. falciparum blood-stage and transmission assays, in vivo P. falciparum SCID mouse model\",\n      \"journal\": \"Nature communications\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 / Moderate — co-crystal structure with functional validation across multiple life-cycle stages, single lab with multiple orthogonal assays\",\n      \"pmids\": [\"28874661\"],\n      \"is_preprint\": false,\n      \"attribution\": [\n        {\"species\": \"Plasmodium vivax\", \"strain\": \"\"},\n        {\"species\": \"Plasmodium falciparum\", \"strain\": \"\"}\n      ]\n    },\n    {\n      \"year\": 2017,\n      \"finding\": \"The cGMP-binding domain D (CNB-D) of PKG (PF3D7_1436600) controls kinase activation through a mechanism distinct from the pseudosubstrate autoinhibitory sequence used by human PKG. A construct containing only CNB-D and the catalytic domain is inactive without cGMP and efficiently activated by cGMP. cGMP binding to CNB-D induces a conformational change at the αC-helix; the inactive state involves an interaction between Asp597 (catalytic domain) and Arg528 (αC-helix of CNB-D), while the active state involves Arg528 stabilizing cGMP via Tyr480 of the phosphate binding cassette.\",\n      \"method\": \"Truncation constructs, in vitro kinase assays, structural analysis based on existing crystal data\",\n      \"journal\": \"ACS infectious diseases\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 1 / Moderate — biochemical reconstitution with truncation constructs and structural mechanistic model, single lab; structural evidence from prior crystal data rather than new structure\",\n      \"pmids\": [\"29251493\"],\n      \"is_preprint\": false,\n      \"attribution\": [{\"species\": \"Plasmodium falciparum\", \"strain\": \"\"}]\n    },\n    {\n      \"year\": 2018,\n      \"finding\": \"PKG (PF3D7_1436600) cooperates with PfCDPK5 to fully activate the protease cascade critical for parasite egress. Hyperactivation of PKG (by phosphodiesterase inhibitor treatment) overcomes the egress block caused by PfCDPK5 knockdown and restores microneme release, placing PKG upstream of or in parallel with PfCDPK5 in the egress signaling pathway.\",\n      \"method\": \"PfCDPK5 knockdown, PKG hyperactivation (phosphodiesterase inhibitor), microneme release assay, egress assay\",\n      \"journal\": \"mBio\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — genetic knockdown combined with chemical PKG activation as epistasis, single lab, two orthogonal approaches\",\n      \"pmids\": [\"29487234\"],\n      \"is_preprint\": false,\n      \"attribution\": [{\"species\": \"Plasmodium falciparum\", \"strain\": \"\"}]\n    },\n    {\n      \"year\": 2018,\n      \"finding\": \"In P. berghei, a hypomorphic allele of PKG (PF3D7_1436600 ortholog) combined with CDPK4 deletion causes a synthetic negative interaction for erythrocyte invasion, conserved also in P. falciparum. When PKG-dependent Ca2+ signals are attenuated, CDPK4 becomes critical for phosphorylating proteins important for inner membrane complex stability, which anchors the acto-myosin motor required for motility and invasion.\",\n      \"method\": \"Genetic interaction screen (294 kinase combinations), hypomorphic PKG allele, CDPK4 deletion, P. falciparum genetic validation, invasion assays, phosphoproteomics\",\n      \"journal\": \"Nature communications\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Strong — systematic genetic epistasis screen with biochemical follow-up, validated in two Plasmodium species, multiple methods\",\n      \"pmids\": [\"30315162\"],\n      \"is_preprint\": false,\n      \"attribution\": [\n        {\"species\": \"Plasmodium berghei\", \"strain\": \"\"},\n        {\"species\": \"Plasmodium falciparum\", \"strain\": \"\"}\n      ]\n    },\n    {\n      \"year\": 2018,\n      \"finding\": \"PKG (PF3D7_1436600) directly interacts with and phosphorylates RPT1, a subunit of the 19S regulatory particle of the P. falciparum proteasome. PfPKG and RPT1 interact in vitro (yeast two-hybrid and in vitro binding confirmed). A peptide from the RPT1 interacting region contains a PfPKG consensus phosphorylation site and is efficiently phosphorylated by PfPKG, and competes with full-length RPT1 fragment for binding to PfPKG. Phosphoproteomic mining using the consensus motif identified additional likely direct PKG substrates.\",\n      \"method\": \"Yeast two-hybrid library screen, in vitro binding/competition assay, in vitro kinase assay with peptide substrates, consensus phosphorylation site analysis\",\n      \"journal\": \"Infection and immunity\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — yeast two-hybrid plus in vitro kinase assay with defined substrate and competition, single lab\",\n      \"pmids\": [\"30323024\"],\n      \"is_preprint\": false,\n      \"attribution\": [{\"species\": \"Plasmodium falciparum\", \"strain\": \"\"}]\n    },\n    {\n      \"year\": 2019,\n      \"finding\": \"Crystal structures of full-length PKG (PF3D7_1436600) from P. falciparum and P. vivax in the cGMP-free (inactive) state reveal an overall pentagonal arrangement of the four CNBs and kinase domain, with an N-terminal autoinhibitory segment (AIS) docked in the substrate site of the kinase domain in a swapped-domain dimer. The AIS is necessary to maintain the inactive state. A helix serves the dual role of N-terminal helix of the kinase domain and capping helix of the neighboring CNB. Cooperative cGMP binding, beginning at the CNB closest to the kinase domain, transmits conformational changes around the pentagonal molecule via a structural relay mechanism to activate PKG.\",\n      \"method\": \"X-ray crystallography of full-length PfPKG and PvPKG (cGMP-free), structural analysis, analytical ultracentrifugation (monomer/dimer determination)\",\n      \"journal\": \"Proceedings of the National Academy of Sciences of the United States of America\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 / Strong — first full-length crystal structures of malarial PKG solved for two species, structural relay mechanism defined, multiple structural and biophysical methods\",\n      \"pmids\": [\"31239348\"],\n      \"is_preprint\": false,\n      \"attribution\": [\n        {\"species\": \"Plasmodium falciparum\", \"strain\": \"\"},\n        {\"species\": \"Plasmodium vivax\", \"strain\": \"\"}\n      ]\n    },\n    {\n      \"year\": 2020,\n      \"finding\": \"8-NBD-cGMP is an effective allosteric antagonist of PKG (PF3D7_1436600) that inhibits PfPKG not by a simple two-state active/inactive switch, but by stabilizing a distinct inactive 'mixed' intermediate state sharing features of both apo and cGMP-bound forms. This was demonstrated by NMR chemical shift analysis, molecular dynamics simulations, and site-directed mutagenesis of the key regulatory CNB-D domain.\",\n      \"method\": \"NMR chemical shift perturbation analysis, molecular dynamics simulations, site-directed mutagenesis, surface plasmon resonance\",\n      \"journal\": \"The Journal of biological chemistry\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 / Moderate — NMR, MD simulations, mutagenesis, and SPR together define a novel allosteric mechanism; single lab with multiple orthogonal biophysical methods\",\n      \"pmids\": [\"32317283\"],\n      \"is_preprint\": false,\n      \"attribution\": [{\"species\": \"Plasmodium falciparum\", \"strain\": \"\"}]\n    },\n    {\n      \"year\": 2020,\n      \"finding\": \"PKG (PF3D7_1436600) activity is required for P. falciparum asexual blood stage egress, hepatocyte invasion by sporozoites, and male gamete exflagellation. Metabolomic, phosphoproteomic, and chemoproteomic studies combined with conditional knockdown parasites, molecular docking, and recombinant kinase assays identified PKG as the primary cellular target of MMV030084. Resistance selection and gene editing identified tyrosine kinase-like protein 3 as a low-level resistance mediator for PKG inhibitors, while PKG itself never mutated under selection pressure.\",\n      \"method\": \"Metabolomics, phosphoproteomics, chemoproteomics, conditional knockdown, molecular docking, recombinant kinase assay, resistance selection, gene editing\",\n      \"journal\": \"Cell chemical biology\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Strong — target validation by multiple orthogonal omics approaches plus genetic knockdown, resistance genetics, and biochemical assay; multi-method single study\",\n      \"pmids\": [\"32359426\"],\n      \"is_preprint\": false,\n      \"attribution\": [{\"species\": \"Plasmodium falciparum\", \"strain\": \"\"}]\n    },\n    {\n      \"year\": 2020,\n      \"finding\": \"Using the DiCre system with multiple lox sites, simultaneous conditional disruption and allelic replacement of PKG (PF3D7_1436600) demonstrated that PfPKG has no scaffolding or adaptor role in intraerythrocytic development, acting solely at merozoite egress. A phosphorylation-deficient PfPKG (with key phosphorylation sites mutated) is functionally incompetent, showing that phosphorylation of PKG itself is required for its in vivo function.\",\n      \"method\": \"DiCre conditional disruption, multiple simultaneous allelic replacement, egress assays, phosphorylation-deficient mutant\",\n      \"journal\": \"Life science alliance\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Strong — genetic structure-function analysis with multiple simultaneous allelic replacements plus complementation controls, conclusively demonstrating both catalytic necessity and lack of scaffolding role\",\n      \"pmids\": [\"32179592\"],\n      \"is_preprint\": false,\n      \"attribution\": [{\"species\": \"Plasmodium falciparum\", \"strain\": \"\"}]\n    },\n    {\n      \"year\": 2021,\n      \"finding\": \"A multipass membrane protein ICM1 is tightly associated with PKG (PF3D7_1436600) in both asexual blood stages and transmission stages of Plasmodium. Multiple ICM1 phosphorylation events are dependent on PKG activity (shown by phosphoproteomics). Conditional depletion of P. berghei ICM1 prevents gametogenesis due to a block in intracellular calcium mobilization; conditional loss of P. falciparum ICM1 results in severely reduced calcium mobilization, defective egress, and lack of invasion. ICM1 is proposed as the missing link transducing PKG-dependent signals to intracellular Ca2+ release.\",\n      \"method\": \"Co-immunoprecipitation (PKG–ICM1 interaction), phosphoproteomics (PKG-dependent ICM1 phosphorylation), conditional stage-specific depletion (P. berghei and P. falciparum), Ca2+ imaging, egress and invasion assays\",\n      \"journal\": \"Science advances\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Strong — reciprocal Co-IP establishing direct PKG–ICM1 association, PKG-dependent phosphoproteomics, genetic KO with Ca2+ and phenotypic readouts across two species\",\n      \"pmids\": [\"33762339\"],\n      \"is_preprint\": false,\n      \"attribution\": [\n        {\"species\": \"Plasmodium berghei\", \"strain\": \"\"},\n        {\"species\": \"Plasmodium falciparum\", \"strain\": \"\"}\n      ]\n    },\n    {\n      \"year\": 2021,\n      \"finding\": \"GCα is the sole enzyme responsible for cGMP production in P. falciparum asexual blood stages and is required for PKG (PF3D7_1436600)-driven Ca2+ mobilization and merozoite egress. GCα-null parasites cannot synthesize cGMP or mobilize calcium; chemical complementation with a cGMP analogue rescues egress. Point mutagenesis of a conserved residue in the P4-ATPase domain of GCα abolishes cGMP synthesis, showing P4-ATPase activity is upstream of and linked to cGMP synthesis and hence PKG activation.\",\n      \"method\": \"Conditional KO of GCα, cGMP measurement, Ca2+ mobilization assay, egress assay, chemical complementation with cGMP analogue, site-directed mutagenesis of P4-ATPase domain\",\n      \"journal\": \"mBio\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Strong — genetic KO with multiple biochemical readouts, chemical complementation, and mutagenesis defining pathway order upstream of PKG; multiple orthogonal methods\",\n      \"pmids\": [\"33500341\"],\n      \"is_preprint\": false,\n      \"attribution\": [{\"species\": \"Plasmodium falciparum\", \"strain\": \"\"}]\n    },\n    {\n      \"year\": 2021,\n      \"finding\": \"SEA1 (PF3D7_1021800) undergoes phosphorylation dependent on PKG (PF3D7_1436600) activity, placing SEA1 as a PKG substrate during schizont development. However, SEA1 does not play a direct mechanistic role in egress per se; instead it functions upstream of egress as a regulator of correct nuclear segregation into daughter merozoites.\",\n      \"method\": \"PKG-dependent phosphoproteomics, conditional SEA1 disruption, egress and nuclear segregation phenotyping\",\n      \"journal\": \"mBio\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — PKG-dependent phosphoproteomics with genetic validation of SEA1 function, single lab; PKG's role is as an upstream kinase identified by phosphoproteomics\",\n      \"pmids\": [\"33688001\"],\n      \"is_preprint\": false,\n      \"attribution\": [{\"species\": \"Plasmodium falciparum\", \"strain\": \"\"}]\n    },\n    {\n      \"year\": 2024,\n      \"finding\": \"PKG (PF3D7_1436600) is regulated by two distinct mechanisms in P. falciparum asexual blood stages: (1) cGMP occupancy of cyclic nucleotide binding domain B (CNB-B) — reduced cGMP binding to CNB-B does not affect in vitro kinase activity but abolishes parasite egress in vivo; (2) phosphorylation of Thr695 in the activation loop — T695 phosphorylation is dispensable for in vitro kinase activity but essential for in vivo PKG function, with loss of T695 phosphorylation causing aberrant proteome-wide phosphorylation events and altered substrate specificity.\",\n      \"method\": \"Genetic engineering of CNB-B cGMP-binding mutants and T695A activation-loop mutants, in vitro kinase assay, quantitative phosphoproteomics, egress assay\",\n      \"journal\": \"PLoS pathogens\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Strong — genetic structure-function approach with multiple mutants validated by in vitro kinase assays and in vivo phosphoproteomics; multiple orthogonal methods in single study\",\n      \"pmids\": [\"38935780\"],\n      \"is_preprint\": false,\n      \"attribution\": [{\"species\": \"Plasmodium falciparum\", \"strain\": \"\"}]\n    },\n    {\n      \"year\": 2024,\n      \"finding\": \"The crystal structure of PfPKG (PF3D7_1436600) bound to a pyrrole-series inhibitor was solved, revealing the structural basis for inhibitor binding at the ATP-binding site and enabling structure-activity relationship analysis for the pyrrole series.\",\n      \"method\": \"X-ray crystallography of PfPKG–inhibitor co-crystal, structure-based modeling, in vitro recombinant PfPKG kinase assay, gatekeeper mutant transgenic parasite selectivity assay\",\n      \"journal\": \"Journal of medicinal chemistry\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 1 / Moderate — co-crystal structure with functional validation using gatekeeper mutant parasites, single lab\",\n      \"pmids\": [\"38372781\"],\n      \"is_preprint\": false,\n      \"attribution\": [{\"species\": \"Plasmodium falciparum\", \"strain\": \"\"}]\n    },\n    {\n      \"year\": 2025,\n      \"finding\": \"PP1 phosphatase controls the homeostasis of cGMP in P. falciparum by modulating the basal activity of guanylyl cyclase alpha (GCα), thereby acting upstream of PKG (PF3D7_1436600) and PKG-dependent downstream Ca2+ signaling. PP1 also regulates the rounding-up of the parasitophorous vacuole, the first step in the egress cascade, a process reliant on Ca2+ and occurring upstream of PKG-driven membrane breakdown.\",\n      \"method\": \"Conditional PfPP1 knockout (iKO), fluorescent reporters of PV morphology, live-microscopy, cGMP measurement, egress kinetics with PKG pathway inducers/inhibitors, Ca2+ ionophore rescue\",\n      \"journal\": \"PLoS pathogens\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — conditional KO with live imaging and chemical epistasis experiments placing PP1 upstream of PKG, single lab with multiple readouts\",\n      \"pmids\": [\"39808636\"],\n      \"is_preprint\": false,\n      \"attribution\": [{\"species\": \"Plasmodium falciparum\", \"strain\": \"\"}]\n    },\n    {\n      \"year\": 2025,\n      \"finding\": \"In P. falciparum gametocytes, PfPP1 controls crucial steps of gametocyte activation through stimulation of the cGMP/PKG (PF3D7_1436600) pathway, placing PfPP1 upstream of PKG activation during sexual stage transmission.\",\n      \"method\": \"Conditional PfPP1 depletion, cGMP measurement, gametocyte activation assays, mosquito transmission experiments\",\n      \"journal\": \"mBio\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — conditional depletion with cGMP measurement and functional transmission assays, single lab\",\n      \"pmids\": [\"40823845\"],\n      \"is_preprint\": false,\n      \"attribution\": [{\"species\": \"Plasmodium falciparum\", \"strain\": \"\"}]\n    },\n    {\n      \"year\": 2022,\n      \"finding\": \"PKG (PF3D7_1436600) resistance mutations in P. falciparum mapped to the gatekeeper residue T618I upon in vitro selection with PKG-targeting compounds TCMDC-141334 and TCDMC-140674, consistent with direct interaction of these compounds with the PKG active site. CRISPR editing of T618I in naive parasites confirmed the resistance phenotype and thus validated PKG as the target.\",\n      \"method\": \"In vitro evolution of resistance, whole-genome sequencing, CRISPR editing, in vitro activity assays with recombinant proteins, molecular docking\",\n      \"journal\": \"mBio\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Strong — resistance genetics with CRISPR validation and biochemical confirmation, multiple orthogonal methods\",\n      \"pmids\": [\"41277867\"],\n      \"is_preprint\": false,\n      \"attribution\": [{\"species\": \"Plasmodium falciparum\", \"strain\": \"\"}]\n    }\n  ],\n  \"current_model\": \"PKG (PF3D7_1436600) is the sole cGMP sensor and master signaling kinase in Plasmodium, activated by cooperative cGMP binding to a unique four-CNB regulatory module (with CNB-D serving as the primary activation gate and CNB-B binding required for in vivo function) that releases an autoinhibitory segment from the kinase domain via a pentagonal structural relay; it is further regulated by activation-loop phosphorylation at T695; upstream, GCα (the sole cGMP synthase in blood stages) and PP1 phosphatase control cGMP levels, while downstream PKG phosphorylates ICM1 (a membrane channel required for Ca2+ mobilization from intracellular stores), PfCDPK1, actomyosin complex components, proteasome subunit RPT1, and at least 69 other targets to orchestrate PfSUB1/microneme discharge, PV membrane breakdown, host-cell egress, and invasion across asexual blood stages, gametogenesis, ookinete gliding, sporozoite motility, and liver-stage merosome release.\"\n}\n```","stage2_raw":"{\n  \"mechanistic_narrative\": \"PKG (PF3D7_1436600) is the sole cGMP-activated protein kinase and master signaling hub of Plasmodium, orchestrating the transitions of the parasite life cycle through cGMP-triggered phosphorylation of downstream effectors [#0, #10]. Recombinant PfPKG is a cGMP-selective phosphotransferase whose activity is stimulated at least fivefold by cGMP but not by cAMP, and whose regulatory module contains four cyclic-nucleotide-binding sites, of which one dominant site (later assigned to the C-terminal CNB-D) governs activation while the degenerate fourth site contributes to full activity without binding cGMP [#0, #1, #11]. Structurally, full-length PfPKG adopts a pentagonal arrangement of the four CNBs around the kinase domain in which an N-terminal autoinhibitory segment docks into the substrate site; cooperative cGMP binding, initiated at the CNB nearest the catalytic domain, propagates conformational change through a structural relay to release autoinhibition and activate the kinase [#19, #15]. In vivo, full function additionally requires cGMP occupancy of CNB-B and activation-loop phosphorylation at Thr695, both of which are dispensable for in vitro catalysis but essential in the parasite [#26, #22]. Upstream, GC\\u03b1 is the sole cGMP synthase in asexual blood stages and PP1 phosphatase sets cGMP homeostasis by tuning GC\\u03b1, positioning both as controllers of PKG activation [#24, #28]. Once active, PKG drives phosphoinositide hydrolysis and intracellular Ca2+ mobilization\\u2014transduced in part through its tightly associated multipass membrane partner ICM1\\u2014to trigger PfSUB1 discharge, microneme release, parasitophorous vacuole membrane breakdown, host-cell egress, and erythrocyte invasion, and it phosphorylates a broad substrate set including PfCDPK1, actomyosin components, and the proteasome subunit RPT1 [#8, #9, #23, #10, #13, #18]. This PKG-centered pathway operates across the life cycle, being required for asexual schizogony and egress, gametogenesis, ookinete and sporozoite motility, and liver-stage merosome release [#4, #3, #5, #6, #12]. PKG is a validated antimalarial drug target: potent selective inhibitors act across multiple stages, and resistance selection maps to gatekeeper mutations rather than loss of PKG itself [#14, #30, #21].\"\n  ,\n  \"teleology\": [\n    {\n      \"year\": 2002,\n      \"claim\": \"Establishing that PF3D7_1436600 encodes a genuine cGMP-selective kinase was the founding question, defining it as a distinct second-messenger effector expressed in a stage-specific manner.\",\n      \"evidence\": \"Recombinant PfPKG expressed in E. coli assayed for cGMP-stimulated phosphotransferase activity, with stage expression by Western blot\",\n      \"pmids\": [\"12068803\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Physiological substrates unknown\", \"Cellular function untested\", \"Structural basis of cGMP selectivity undefined\"],\n      \"attribution\": [{\"species\": \"Plasmodium falciparum\", \"strain\": \"\"}]\n    },\n    {\n      \"year\": 2003,\n      \"claim\": \"Which of the four nucleotide-binding sites drives activation was resolved, showing a hierarchical contribution and that the degenerate fourth site aids activation without binding cGMP.\",\n      \"evidence\": \"Systematic site-directed mutagenesis of each cGMP-binding site with in vitro Ka and Vmax measurements\",\n      \"pmids\": [\"12817987\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"No structural view of the activation mechanism\", \"Relationship between sites in the intact protein unresolved\"],\n      \"attribution\": [{\"species\": \"Plasmodium falciparum\", \"strain\": \"\"}]\n    },\n    {\n      \"year\": 2005,\n      \"claim\": \"Native PfPKG activity was purified and shown to match recombinant enzyme in cooperativity, substrate preference, and inhibitor sensitivity, validating the recombinant tools and Compound 1 as a probe.\",\n      \"evidence\": \"cGMP-affinity and ion-exchange purification of native activity, plus recombinant expression in T. gondii with kinase assays\",\n      \"pmids\": [\"16325279\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Endogenous substrates still unidentified\", \"Cellular role not yet tested\"],\n      \"attribution\": [{\"species\": \"Plasmodium falciparum\", \"strain\": \"\"}]\n    },\n    {\n      \"year\": 2009,\n      \"claim\": \"Chemical-genetic experiments established PKG as essential for asexual schizont rupture and gametogenesis, moving it from a biochemical entity to a functional gatekeeper of key life-cycle transitions.\",\n      \"evidence\": \"Compound 1 inhibition rescued by inhibitor-insensitive mutant PKG in P. falciparum blood stages and gametocytes, with Ca2+ epistasis\",\n      \"pmids\": [\"19915077\", \"18532880\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Direct substrates driving egress/gametogenesis unknown\", \"Mechanistic link to Ca2+ undefined\"],\n      \"attribution\": [{\"species\": \"Plasmodium falciparum\", \"strain\": \"\"}]\n    },\n    {\n      \"year\": 2009,\n      \"claim\": \"Work in P. berghei extended PKG's role to ookinete gliding and late liver-stage merosome release, and placed GCbeta/PDEdelta as the cGMP source/sink in ookinetes.\",\n      \"evidence\": \"Genetic epistasis with single/double cyclase and phosphodiesterase knockouts, PKG inhibition, motility assays, and conditional sporozoite disruption\",\n      \"pmids\": [\"19779564\", \"19940133\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Downstream motility substrates unidentified\", \"How merosome release is controlled unresolved\"],\n      \"attribution\": [{\"species\": \"Plasmodium berghei\", \"strain\": \"\"}]\n    },\n    {\n      \"year\": 2013,\n      \"claim\": \"PKG was placed at the apex of the protease-mediated egress pathway by showing it controls PfSUB1 discharge and microneme release, and that its hyperactivation triggers premature egress.\",\n      \"evidence\": \"PKG inhibition and phosphodiesterase-mediated hyperactivation with SUB1 discharge, microneme, and egress readouts in P. falciparum\",\n      \"pmids\": [\"23675297\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Direct PKG substrates in the discharge pathway unknown\", \"Signal transduction to Ca2+ not yet mechanistic\"],\n      \"attribution\": [{\"species\": \"Plasmodium falciparum\", \"strain\": \"\"}]\n    },\n    {\n      \"year\": 2014,\n      \"claim\": \"The intermediate signaling logic was clarified: PKG controls phosphoinositide metabolism and PIP2 hydrolysis upstream of the Ca2+ signal required for gliding, gametocyte activation, and egress.\",\n      \"evidence\": \"Conditional PKG inhibition with quantitative phosphoproteomics, lipidomics, and Ca2+ imaging across P. berghei and P. falciparum\",\n      \"pmids\": [\"24594931\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Enzyme(s) linking PKG to phosphoinositide hydrolysis unresolved\", \"Identity of the Ca2+ channel unknown at this stage\"],\n      \"attribution\": [{\"species\": \"Plasmodium berghei\", \"strain\": \"\"}, {\"species\": \"Plasmodium falciparum\", \"strain\": \"\"}]\n    },\n    {\n      \"year\": 2015,\n      \"claim\": \"The substrate landscape was mapped and PKG was shown to be required for invasion as well as egress, establishing it as a shared signaling hub.\",\n      \"evidence\": \"SILAC phosphoproteomics under chemical and genetic PKG inhibition identifying 69 dependent proteins including PfCDPK1 and actomyosin components, plus invasion assays in P. falciparum\",\n      \"pmids\": [\"26149123\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Direct versus indirect substrates not fully distinguished\", \"Functional consequence of most phosphosites untested\"],\n      \"attribution\": [{\"species\": \"Plasmodium falciparum\", \"strain\": \"\"}]\n    },\n    {\n      \"year\": 2015,\n      \"claim\": \"The structural gate for activation was defined: CNB-D is the high-affinity gatekeeper whose cGMP-induced capping triad is required for both in vitro activity and in vivo egress.\",\n      \"evidence\": \"Crystal structures of CNB-D with and without cGMP, mutagenesis of the capping triad, in vitro kinase assays, and parasite egress phenotyping in P. falciparum\",\n      \"pmids\": [\"25646845\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Full-length activation mechanism not yet visualized\", \"How CNB-D change reaches the catalytic domain unresolved\"],\n      \"attribution\": [{\"species\": \"Plasmodium falciparum\", \"strain\": \"\"}]\n    },\n    {\n      \"year\": 2017,\n      \"claim\": \"The mechanistic and cellular consequences of PKG activation were refined: CNB-D activates via an alphaC-helix relay distinct from human PKG, and PKG triggers a temporally defined PVM breakdown step during egress.\",\n      \"evidence\": \"Truncation constructs with kinase assays and structural modeling; and selective inhibitor dissection with multimodal imaging of egress steps in P. falciparum\",\n      \"pmids\": [\"29251493\", \"28292906\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Effectors executing PVM breakdown unknown\", \"Structural relay inferred rather than seen in full-length enzyme\"],\n      \"attribution\": [{\"species\": \"Plasmodium falciparum\", \"strain\": \"\"}]\n    },\n    {\n      \"year\": 2016,\n      \"claim\": \"PKG's motility role in sporozoites was defined and separated from CDPK4, showing it acts as an independent second-messenger effector controlling TRAP secretion, invasion, and egress.\",\n      \"evidence\": \"PKG-specific inhibitors, inhibitor-insensitive mutant sporozoites, invasion/motility and TRAP secretion assays in P. berghei\",\n      \"pmids\": [\"27425827\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Direct substrates driving TRAP secretion unknown\", \"Molecular link between PKG and adhesin release unresolved\"],\n      \"attribution\": [{\"species\": \"Plasmodium berghei\", \"strain\": \"\"}]\n    },\n    {\n      \"year\": 2018,\n      \"claim\": \"PKG's cooperative relationships with other kinases were mapped, placing it upstream of/parallel to PfCDPK5 in egress and revealing synthetic interaction with CDPK4 in invasion.\",\n      \"evidence\": \"PfCDPK5 knockdown with PKG hyperactivation epistasis; systematic kinase genetic interaction screen with hypomorphic PKG and CDPK4 deletion validated in both species\",\n      \"pmids\": [\"29487234\", \"30315162\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Shared versus distinct substrates of PKG and CDPKs unresolved\", \"Nature of the parallel Ca2+ inputs undefined\"],\n      \"attribution\": [{\"species\": \"Plasmodium falciparum\", \"strain\": \"\"}, {\"species\": \"Plasmodium berghei\", \"strain\": \"\"}]\n    },\n    {\n      \"year\": 2018,\n      \"claim\": \"A specific direct substrate/partner was identified, linking PKG to proteasome regulation through phosphorylation of the 19S subunit RPT1.\",\n      \"evidence\": \"Yeast two-hybrid, in vitro binding/competition, and in vitro peptide kinase assays with consensus-motif mining in P. falciparum\",\n      \"pmids\": [\"30323024\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Functional consequence of RPT1 phosphorylation in vivo untested\", \"Single-lab interaction without reciprocal in-parasite validation\"],\n      \"attribution\": [{\"species\": \"Plasmodium falciparum\", \"strain\": \"\"}]\n    },\n    {\n      \"year\": 2019,\n      \"claim\": \"The full-length inactive structure revealed the pentagonal architecture and autoinhibitory segment, defining the cooperative structural relay by which cGMP activates PKG.\",\n      \"evidence\": \"X-ray structures of full-length cGMP-free PfPKG and PvPKG with analytical ultracentrifugation\",\n      \"pmids\": [\"31239348\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Active-state full-length structure not solved\", \"Dynamics of the relay not directly observed\"],\n      \"attribution\": [{\"species\": \"Plasmodium falciparum\", \"strain\": \"\"}, {\"species\": \"Plasmodium vivax\", \"strain\": \"\"}]\n    },\n    {\n      \"year\": 2020,\n      \"claim\": \"Regulatory subtlety was added by showing an allosteric antagonist stabilizes a distinct mixed intermediate rather than a simple off-state, refining the activation model.\",\n      \"evidence\": \"NMR chemical shift analysis, molecular dynamics, SPR, and CNB-D mutagenesis with 8-NBD-cGMP on P. falciparum PKG\",\n      \"pmids\": [\"32317283\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Relevance of the intermediate state to cellular regulation unknown\"],\n      \"attribution\": [{\"species\": \"Plasmodium falciparum\", \"strain\": \"\"}]\n    },\n    {\n      \"year\": 2020,\n      \"claim\": \"Genetic dissection established that PKG acts purely catalytically at egress with no scaffolding role, and that phosphorylation of PKG itself is required for its in vivo function.\",\n      \"evidence\": \"DiCre conditional disruption with simultaneous allelic replacement, phosphorylation-deficient mutant, and egress assays; plus multi-omic target validation of MMV030084 in P. falciparum\",\n      \"pmids\": [\"32179592\", \"32359426\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Kinase(s) phosphorylating PKG not identified\", \"Role in stages other than egress not addressed by these knockouts\"],\n      \"attribution\": [{\"species\": \"Plasmodium falciparum\", \"strain\": \"\"}]\n    },\n    {\n      \"year\": 2021,\n      \"claim\": \"The long-missing link from PKG to Ca2+ was identified as the membrane protein ICM1, a PKG-associated, PKG-phosphorylated channel required for calcium mobilization.\",\n      \"evidence\": \"Co-immunoprecipitation, PKG-dependent phosphoproteomics, and conditional ICM1 depletion with Ca2+ imaging and egress/invasion assays in P. berghei and P. falciparum\",\n      \"pmids\": [\"33762339\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Direct proof that ICM1 conducts Ca2+ not established\", \"How ICM1 phosphorylation gates channel activity unknown\"],\n      \"attribution\": [{\"species\": \"Plasmodium berghei\", \"strain\": \"\"}, {\"species\": \"Plasmodium falciparum\", \"strain\": \"\"}]\n    },\n    {\n      \"year\": 2021,\n      \"claim\": \"The upstream cGMP source and additional substrates were pinned down: GC\\u03b1 is the sole cGMP synthase feeding PKG in blood stages, and SEA1 is a PKG substrate acting in nuclear segregation upstream of egress.\",\n      \"evidence\": \"Conditional GC\\u03b1 KO with cGMP/Ca2+/egress readouts and cGMP chemical complementation; PKG-dependent phosphoproteomics with conditional SEA1 disruption in P. falciparum\",\n      \"pmids\": [\"33500341\", \"33688001\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"How GC\\u03b1 activity is triggered at egress unresolved\", \"Direct versus indirect SEA1 phosphorylation not distinguished\"],\n      \"attribution\": [{\"species\": \"Plasmodium falciparum\", \"strain\": \"\"}]\n    },\n    {\n      \"year\": 2024,\n      \"claim\": \"Dual in vivo regulatory requirements were defined: cGMP binding to CNB-B and activation-loop phosphorylation at Thr695 are each dispensable in vitro but essential in the parasite and shape substrate specificity.\",\n      \"evidence\": \"Genetic CNB-B and T695A mutants with in vitro kinase assays, quantitative phosphoproteomics, and egress assays in P. falciparum\",\n      \"pmids\": [\"38935780\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Mechanism by which CNB-B and T695 tune specificity unknown\", \"In vitro/in vivo discrepancy in requirement unexplained\"],\n      \"attribution\": [{\"species\": \"Plasmodium falciparum\", \"strain\": \"\"}]\n    },\n    {\n      \"year\": 2025,\n      \"claim\": \"The upstream homeostatic control of cGMP was extended by showing PP1 phosphatase modulates GC\\u03b1 basal activity and PV rounding, positioning PP1 above PKG in both asexual and sexual stages.\",\n      \"evidence\": \"Conditional PfPP1 knockout with cGMP measurement, PV morphology imaging, chemical epistasis, and transmission assays in P. falciparum blood and gametocyte stages\",\n      \"pmids\": [\"39808636\", \"40823845\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Whether PP1 acts directly on GC\\u03b1 or intermediaries unresolved\", \"PP1 targets controlling cGMP homeostasis unidentified\"],\n      \"attribution\": [{\"species\": \"Plasmodium falciparum\", \"strain\": \"\"}]\n    },\n    {\n      \"year\": 2017,\n      \"claim\": \"PKG was advanced as an antimalarial target with defined inhibitor pharmacology, culminating in co-crystal structures and picomolar-potency compounds active across life-cycle stages.\",\n      \"evidence\": \"Co-crystal structures of PvPKG\\u2013ML10 and PfPKG\\u2013pyrrole inhibitors with in vitro kinase, multi-stage parasite, and in vivo mouse assays\",\n      \"pmids\": [\"28874661\", \"38372781\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Long-term resistance liability incompletely defined at this stage\"],\n      \"attribution\": [{\"species\": \"Plasmodium vivax\", \"strain\": \"\"}, {\"species\": \"Plasmodium falciparum\", \"strain\": \"\"}]\n    },\n    {\n      \"year\": 2022,\n      \"claim\": \"Resistance genetics confirmed PKG as a bona fide drug target, with mutations mapping to gatekeeper residues rather than loss of PKG function.\",\n      \"evidence\": \"In vitro evolution, whole-genome sequencing, CRISPR editing of gatekeeper mutations, and biochemical assays in P. falciparum\",\n      \"pmids\": [\"41277867\", \"32359426\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Full spectrum of clinically relevant resistance mechanisms unknown\"],\n      \"attribution\": [{\"species\": \"Plasmodium falciparum\", \"strain\": \"\"}]\n    },\n    {\n      \"year\": null,\n      \"claim\": \"How PKG achieves precise substrate selection and stage-specific outputs from a single cGMP input\\u2014including the direct effectors executing PVM breakdown and the biophysical proof of ICM1 as the Ca2+ conduit\\u2014remains open.\",\n      \"evidence\": \"\",\n      \"pmids\": [],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Direct substrates driving each cellular event not fully resolved\", \"ICM1 channel activity not directly demonstrated\", \"Active-state full-length structure and in-parasite dynamics undefined\"],\n      \"attribution\": [{\"species\": \"Plasmodium falciparum\", \"strain\": \"\"}]\n    }\n  ],\n  \"mechanism_profile\": {\n    \"molecular_activity\": [\n      {\"term_id\": \"GO:0004692\", \"supporting_discovery_ids\": [0, 2, 15, 26]},\n      {\"term_id\": \"GO:0030553\", \"supporting_discovery_ids\": [0, 1, 11, 19]},\n      {\"term_id\": \"GO:0004674\", \"supporting_discovery_ids\": [10, 18, 23, 25]},\n      {\"term_id\": \"GO:0046872\", \"supporting_discovery_ids\": [1]}\n    ],\n    \"localization\": [\n      {\"term_id\": \"GO:0005829\", \"supporting_discovery_ids\": [7]},\n      {\"term_id\": \"GO:0005783\", \"supporting_discovery_ids\": [7]},\n      {\"term_id\": \"GO:0005886\", \"supporting_discovery_ids\": [7, 23]}\n    ],\n    \"pathway\": [\n      {\"term_id\": \"GO:0035556\", \"supporting_discovery_ids\": [8, 9, 23, 24]},\n      {\"term_id\": \"GO:0051209\", \"supporting_discovery_ids\": [9, 23, 24]},\n      {\"term_id\": \"GO:0006935\", \"supporting_discovery_ids\": [5, 12, 9]},\n      {\"term_id\": \"GO:0044409\", \"supporting_discovery_ids\": [8, 13, 10, 4]}\n    ],\n    \"complexes\": [\n      \"PKG (PF3D7_1436600)\\u2013ICM1 membrane-associated complex [#23]\"\n    ],\n    \"partners\": [\n      \"ICM1 (multipass membrane channel, PKG-associated and PKG-phosphorylated) [#23]\",\n      \"RPT1 (19S proteasome regulatory subunit; direct binding and substrate) [#18]\",\n      \"PfCDPK1 (PKG-dependent phosphorylation) [#10]\",\n      \"GC\\u03b1 (guanylyl cyclase; sole blood-stage cGMP source upstream of PKG) [#24]\",\n      \"PP1 phosphatase (upstream regulator of cGMP homeostasis via GC\\u03b1) [#28, #29]\",\n      \"PfCDPK5 (cooperates in egress pathway) [#16]\",\n      \"CDPK4 (synthetic genetic interaction in invasion) [#17]\",\n      \"SEA1 (PKG-dependent phosphorylation, nuclear segregation) [#25]\"\n    ],\n    \"other_free_text\": [\n      \"Activated by cooperative cGMP binding to a four-CNB regulatory module; CNB-D is the high-affinity activation gatekeeper and site 3 dominates activation in vitro [#1, #11].\",\n      \"Full-length inactive enzyme adopts a pentagonal CNB/kinase arrangement with an N-terminal autoinhibitory segment; cGMP activation propagates via a structural relay [#19].\",\n      \"In vivo function additionally requires cGMP occupancy of CNB-B and activation-loop phosphorylation at Thr695, both dispensable for in vitro catalysis [#26].\",\n      \"PKG acts purely catalytically at egress with no scaffolding/adaptor role [#22].\",\n      \"Validated antimalarial drug target inhibited by Compound 1, ML10, pyrrole and imidazopyridine series; resistance maps to gatekeeper residues (T618I) rather than loss of PKG [#4, #14, #27, #30].\",\n      \"Required across the life cycle: asexual schizogony/egress and invasion, gametogenesis, ookinete gliding, sporozoite motility/invasion, and liver-stage merosome release [#3, #4, #5, #6, #12, #10].\"\n    ]\n  }\n}","audit_flag":null,"strains":[{"strain":"Pf3D7","gene_id":"PF3D7_1436600","name":null,"product":"cGMP-dependent protein kinase","uniprot_acc":null,"chromosome":null,"start_pos":null},{"strain":"PbANKA","gene_id":"PBANKA_1008200","name":null,"product":"cGMP-dependent protein kinase","uniprot_acc":null,"chromosome":null,"start_pos":null},{"strain":"PkH","gene_id":"PKNH_0423200","name":null,"product":"cGMP-dependent protein kinase, putative","uniprot_acc":null,"chromosome":null,"start_pos":null}],"gene_symbol":"PKG","evaluation":null}