{"gene":"PF3D7_0934800","run_date":"2026-09-08T12:51:27","timeline":{"discoveries":[{"year":2000,"finding":"PKAc (PF3D7_0934800) gene was isolated and characterized from P. falciparum; it exists as a single copy gene and its expression is developmentally regulated, with higher levels in asexual blood stages than in sexual forms.","method":"Gene cloning, expression analysis","journal":"Molecular and biochemical parasitology","confidence":"Medium","confidence_rationale":"Tier 2 / Weak — direct gene isolation and expression characterization, single lab, single study","pmids":["10960174"],"is_preprint":false,"attribution":[{"species":"Plasmodium falciparum","strain":""}]},{"year":2001,"finding":"PKAc (PF3D7_0934800) activity is detectable in P. falciparum schizonts; it can be stimulated by cAMP and inhibited by protein kinase inhibitor (PKI), and its inhibition by H89 blocks intraerythrocytic parasite development.","method":"In vitro kinase activity assay, pharmacological inhibition (H89, PKI)","journal":"European journal of biochemistry","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — in vitro kinase assay plus pharmacological inhibition with phenotypic readout, single lab","pmids":["11559352"],"is_preprint":false,"attribution":[{"species":"Plasmodium falciparum","strain":""}]},{"year":2005,"finding":"Melatonin induces an increase in cAMP levels and PKAc activity (~40–50%) in P. falciparum-infected erythrocytes, and PKAc activation mediates melatonin-induced cell cycle alteration; a cross-talk exists whereby cAMP/PKAc activation raises cytosolic Ca2+, and Ca2+-dependent pathways (via PLC) regulate cAMP increases.","method":"cAMP analogue treatment, PKA activity assay, pharmacological inhibitors (H89, PKI, 6-Bz-cAMP, U73122)","journal":"The Journal of cell biology","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — multiple pharmacological tools with enzyme activity measurement, single lab","pmids":["16103224"],"is_preprint":false,"attribution":[{"species":"Plasmodium falciparum","strain":""}]},{"year":2008,"finding":"The regulatory subunit of PKA (PfPKA-R) modulates anion conductance in P. falciparum-infected erythrocytes: addition of recombinant PfPKA-R in patch-clamp experiments or overexpression of PfPKA-R in transgenic parasites down-regulates anion channel activity, and this overexpression strain has a growth defect rescued by elevated intracellular cAMP, indicating PKAc activity is required for normal parasite growth.","method":"Patch-clamp electrophysiology, transgenic parasite overexpression, cAMP rescue experiment","journal":"PLoS pathogens","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — direct electrophysiology combined with transgenic overexpression and cAMP rescue, single lab","pmids":["18248092"],"is_preprint":false,"attribution":[{"species":"Plasmodium falciparum","strain":""}]},{"year":2008,"finding":"Recombinant PKAc catalytic subunit (PfPKAc) was purified using a wheat germ cell-free expression system and shown to be enzymatically active; unlike mammalian PKA-C, PfPKAc is only weakly inhibited by H89 and slightly inhibited by PKI, indicating its substrate-binding sites differ from mammalian counterparts.","method":"Wheat germ cell-free expression, protein purification, in vitro kinase assay with inhibitors","journal":"Molecular and biochemical parasitology","confidence":"High","confidence_rationale":"Tier 1 / Moderate — direct in vitro reconstitution with purified recombinant protein and comparative inhibitor profiling, single lab","pmids":["18501980"],"is_preprint":false,"attribution":[{"species":"Plasmodium falciparum","strain":""}]},{"year":2009,"finding":"dsRNA-mediated knockdown of PfPKAc mRNA in P. falciparum caused morphological changes in schizonts and cell cycle arrest, accompanied by a compensatory decrease in PfPKAr mRNA; transcriptomic analysis showed altered expression of 329 genes, particularly those in merozoite invasion processes, calcium/calmodulin signaling, kinase networks, and mitochondrial functions.","method":"dsRNA gene silencing, microarray transcriptomics","journal":"Parasitology research","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — loss-of-function with defined phenotypic readout (schizont arrest) plus transcriptomic pathway placement, single lab","pmids":["19779742"],"is_preprint":false,"attribution":[{"species":"Plasmodium falciparum","strain":"3D7"}]},{"year":2009,"finding":"Recombinant PfPKAc was overexpressed in E. coli and purified, and its enzymatic properties were determined using a fluorogenic kinase assay, establishing biochemical parameters suitable for inhibitor screening.","method":"Recombinant protein expression in E. coli, purification, fluorogenic in vitro kinase assay","journal":"Parasitology research","confidence":"Medium","confidence_rationale":"Tier 1 / Weak — direct in vitro reconstitution with purified recombinant protein, single lab, single study","pmids":["19159956"],"is_preprint":false,"attribution":[{"species":"Plasmodium falciparum","strain":""}]},{"year":2010,"finding":"PKAc activity phosphorylates the cytoplasmic tail of AMA1 at serine 610 (S610); mutation of AMA1 S610 to alanine abolishes phosphorylation in vivo and dramatically impedes erythrocyte invasion, establishing PKAc as the kinase responsible for this phosphorylation event.","method":"Site-directed mutagenesis, in vivo phosphorylation assay, invasion assay","journal":"PLoS pathogens","confidence":"High","confidence_rationale":"Tier 2 / Strong — reciprocal mutagenesis (S610A abolishes phosphorylation) plus functional invasion assay, replicated by subsequent independent studies (PMID 31594816, 27698395)","pmids":["20532217"],"is_preprint":false,"attribution":[{"species":"Plasmodium falciparum","strain":""}]},{"year":2010,"finding":"In P. chabaudi, melatonin triggers cAMP production and PKA activation; this cAMP/PKA activation is dependent on prior Ca2+ elevation (blocked by BAPTA), and in turn cAMP application evokes Ca2+ signals, establishing bidirectional positive feedback between Ca2+ and cAMP/PKAc pathways; PKAc activation was essential for melatonin-induced increase in parasitemia.","method":"cAMP measurement, PKA activity assay, Ca2+ chelation (BAPTA), pharmacological stimulation","journal":"Journal of pineal research","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — multiple orthogonal pharmacological tools and enzyme activity measurements, single lab","pmids":["20964707"],"is_preprint":false,"attribution":[{"species":"Plasmodium chabaudi","strain":""}]},{"year":2012,"finding":"In vitro kinase assays identified three novel PKAc substrates associated with the glideosome motor complex: myosin A, GAP45, and CDPK1, establishing PKAc involvement in regulating the invasion motor complex via cAMP-dependent phosphorylation.","method":"In vitro kinase assay, phosphoproteomics, phospho-motif analysis","journal":"Journal of proteome research","confidence":"Medium","confidence_rationale":"Tier 1 / Weak — in vitro kinase assay identifying substrates, single lab, no mutagenesis confirmation of individual sites","pmids":["23025827"],"is_preprint":false,"attribution":[{"species":"Plasmodium falciparum","strain":""}]},{"year":2015,"finding":"PKAc-mediated phosphorylation of gametocyte-infected erythrocyte proteins contributes to stiffness of immature gametocytes; pharmacological elevation of cAMP (mimicking PKAc hyperactivation) renders mature stage V gametocytes less deformable, establishing that parasite PKAc activity contributes to GIE mechanical properties.","method":"Microsphere filtration assay, phosphodiesterase inhibitor treatment, PKA activity measurement","journal":"PLoS pathogens","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — functional deformability assay with pharmacological modulation of cAMP/PKA, single lab","pmids":["25951195"],"is_preprint":false,"attribution":[{"species":"Plasmodium falciparum","strain":""}]},{"year":2016,"finding":"PKAc phosphorylates AMA1 at S610 in a cAMP-dependent priming step, which then enables subsequent phosphorylation of a conserved downstream threonine (T613) by GSK3; both phosphorylation steps are required for efficient erythrocyte invasion, establishing a hierarchical, sequential phosphorylation cascade on AMA1 regulated by PKAc.","method":"In vitro kinase assay, site-directed mutagenesis, invasion assay","journal":"Scientific reports","confidence":"High","confidence_rationale":"Tier 1 / Moderate — in vitro kinase assay plus mutagenesis of phosphosites with functional invasion readout, single lab with multiple orthogonal methods","pmids":["27698395"],"is_preprint":false,"attribution":[{"species":"Plasmodium falciparum","strain":""}]},{"year":2016,"finding":"PKAc-mediated phosphorylation of the STEVOR C-terminal domain at serine S324 regulates gametocyte-infected erythrocyte deformability; this was demonstrated using immunoprecipitation and mass spectrometry, establishing STEVOR as a PKAc substrate involved in host cell mechanical modification.","method":"Immunoprecipitation, mass spectrometry, microsphiltration, phosphorylation assay","journal":"Blood","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — reciprocal Co-IP plus mass spectrometry identification of phosphosite, functional deformability assay, single lab","pmids":["27136945"],"is_preprint":false,"attribution":[{"species":"Plasmodium falciparum","strain":""}]},{"year":2016,"finding":"Crystal structure of the PfPKA regulatory subunit (PfPKA-R) in complex with cAMP and (Sp)-2-Cl-cAMPS was solved; structurally, cAMP binding to PfPKA-R stabilizes a conformation that releases PKAc from inhibition, allowing it to phosphorylate substrates such as AMA1; uncontrolled induction of PKAc activity via membrane-permeable cAMP agonists is equally disruptive to parasite growth as inhibition.","method":"X-ray crystallography, cAMP analogue binding, parasite growth assay with cAMP agonists","journal":"The Journal of biological chemistry","confidence":"High","confidence_rationale":"Tier 1 / Moderate — crystal structure combined with functional growth assay, single lab with structural and biological validation","pmids":["27738107"],"is_preprint":false,"attribution":[{"species":"Plasmodium falciparum","strain":""}]},{"year":2017,"finding":"PfCDPK1 phosphorylates the PKA regulatory subunit (PfPKA-R) and thereby regulates PKAc activity in P. falciparum, establishing a cross-talk mechanism between Ca2+-dependent and cAMP-dependent kinase signaling relevant to invasion.","method":"Comparative phosphoproteomics, conditional knockdown, in vitro kinase assay","journal":"Nature communications","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — phosphoproteomics plus conditional knockdown identifying PfPKA-R as a CDPK1 substrate, single lab","pmids":["28680058"],"is_preprint":false,"attribution":[{"species":"Plasmodium falciparum","strain":""}]},{"year":2019,"finding":"Conditional disruption of PKAc (PF3D7_0934800) via DiCre-mediated excision in P. falciparum results in complete loss of PKAc protein, severe reduction in intraerythrocytic growth after one cycle, and a pronounced invasion defect; PKAc-null parasites fail to phosphorylate AMA1 at S610 in vivo, confirming PKAc as the kinase responsible for this event.","method":"CRISPR-Cas9 gene editing, DiCre conditional gene deletion, live imaging, phospho-specific immunoblot, invasion assay","journal":"mBio","confidence":"High","confidence_rationale":"Tier 2 / Strong — conditional KO with multiple orthogonal readouts (growth, invasion, phosphorylation), independently corroborated by PMID 31075098","pmids":["31594816"],"is_preprint":false,"attribution":[{"species":"Plasmodium falciparum","strain":""}]},{"year":2019,"finding":"Conditional disruption of both adenylyl cyclase beta (ACβ) and PKAc in P. falciparum demonstrates that cAMP production and PKAc activity are critical specifically for erythrocyte invasion; PKAc-dependent phosphorylation of AMA1 cytoplasmic domain regulates invasion; numerous cAMP/PKAc-dependent phosphorylation sites were identified by phosphoproteomics.","method":"Conditional gene disruption, phosphoproteomics, invasion assay","journal":"PLoS biology","confidence":"High","confidence_rationale":"Tier 2 / Strong — conditional disruption of PKAc with phosphoproteomic and functional invasion readouts, independently confirmed by PMID 31594816","pmids":["31075098"],"is_preprint":false,"attribution":[{"species":"Plasmodium falciparum","strain":""}]},{"year":2019,"finding":"Hyperactivation of PKAc caused by conditional gene disruption of PfPDEβ (leading to elevated cAMP) causes a profound reduction in erythrocyte invasion and rapid death of invaded merozoites; phosphoproteomic analysis of PDEβ-null parasites showed >2-fold increase in phosphorylation at over 200 sites, more than half conforming to PKAc substrate consensus, establishing that temporal regulation of PKAc activation by PDEβ is essential.","method":"Conditional gene disruption, phosphoproteomics, invasion and growth assay","journal":"PLoS biology","confidence":"High","confidence_rationale":"Tier 2 / Strong — conditional KO with genome-wide phosphoproteomics and functional readouts, consistent with PMID 31594816 and 31075098","pmids":["30794532"],"is_preprint":false,"attribution":[{"species":"Plasmodium falciparum","strain":""}]},{"year":2019,"finding":"PKAc (PF3D7_0934800) is dispensable for pre-erythrocytic stages in P. berghei: conditional PKAc gene disruption in sporozoites showed that mutant sporozoites can glide, invade hepatocytes, and mature into hepatic merozoites released from merosomes, but fail to initiate blood stage infection, demonstrating PKAc is not required for liver stage development.","method":"Conditional gene disruption in P. berghei sporozoites, gliding assay, hepatocyte invasion and development assay","journal":"Life science alliance","confidence":"High","confidence_rationale":"Tier 2 / Moderate — conditional KO with multiple stage-specific functional readouts (gliding, hepatocyte invasion, liver stage development, blood stage initiation), single lab","pmids":["31142638"],"is_preprint":false,"attribution":[{"species":"Plasmodium berghei","strain":""}]},{"year":2021,"finding":"PfPDK1 (3-phosphoinositide-dependent protein kinase-1) is required to activate PKAc in P. falciparum; whole-genome sequencing of parasites selected to tolerate PKAc overexpression identified missense mutations exclusively in PfPDK1; targeted mutagenesis demonstrated that PfPDK1 phosphorylates T189 in the PKAc activation loop to activate the kinase.","method":"Conditional PKAc knockdown, whole-genome sequencing, targeted mutagenesis of T189, PKAc overexpression selection","journal":"PLoS biology","confidence":"High","confidence_rationale":"Tier 1 / Strong — mutagenesis of activation loop residue combined with WGS and conditional genetic tools, multiple orthogonal approaches in single rigorous study","pmids":["34879056"],"is_preprint":false,"attribution":[{"species":"Plasmodium falciparum","strain":""}]},{"year":2021,"finding":"Conditional knockdown of PKAc in P. falciparum confirms its essential role in erythrocyte invasion by merozoites, and additionally shows that PKAc is involved in regulating gametocyte deformability; overexpression of PKAc is lethal and kills parasites at the early phase of schizogony.","method":"Conditional PKAc knockdown, PKAc overexpression, deformability assay, growth assay","journal":"PLoS biology","confidence":"High","confidence_rationale":"Tier 2 / Strong — conditional KO plus overexpression with multiple phenotypic readouts, consistent with independent studies (PMID 31594816, 31075098)","pmids":["34879056"],"is_preprint":false,"attribution":[{"species":"Plasmodium falciparum","strain":""}]},{"year":2021,"finding":"PKAc disruption in P. yoelii (DiCre-loxP inducible KO) caused severe growth and erythrocyte invasion defects, and impaired secretion of AMA1 to the merozoite surface, while secretions of PyEBL, Py235, and RON2 were not affected by PKAc loss.","method":"DiCre-loxP conditional knockout, invasion assay, IFA for secretion of AMA1 and other ligands","journal":"Parasitology international","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — conditional KO with multiple secretion readouts, single lab; note AMA1 secretion phenotype differs from P. falciparum result (negative finding in P. falciparum)","pmids":["34390881"],"is_preprint":false,"attribution":[{"species":"Plasmodium yoelii","strain":""}]},{"year":2024,"finding":"PP7, identified as a high-confidence PKAc substrate by phosphoproteomics, is dispensable for erythrocyte invasion but essential for early ring-stage development; phosphoproteomic analysis of PP7-null parasites revealed that PP7 may regulate certain PKAc substrates, placing PKAc upstream of PP7 in a signaling network controlling ring-stage development.","method":"Conditional gene disruption, phosphoproteomics, invasion and ring-stage development assay","journal":"mBio","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — conditional KO with phosphoproteomics establishing epistatic relationship between PKAc and PP7, single lab","pmids":["39387582"],"is_preprint":false,"attribution":[{"species":"Plasmodium falciparum","strain":""}]},{"year":2024,"finding":"In vitro drug resistance selection with PDE inhibitors generated P. falciparum parasites with mutations in either the catalytic or regulatory subunits of PKA, or in PfPDK1, but not in PDEβ itself, confirming that PKAc (and its upstream activator PfPDK1 and its regulatory subunit) are direct downstream effectors of PDEβ-regulated cAMP signaling.","method":"In vitro drug selection, whole-genome sequencing of resistant parasites","journal":"Science advances","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — genetic evidence from resistance mutations directly implicating PKAc catalytic and regulatory subunits as cAMP effectors, single study","pmids":["39642214"],"is_preprint":false,"attribution":[{"species":"Plasmodium falciparum","strain":""}]}],"current_model":"PKAc (PF3D7_0934800) is the catalytic subunit of cAMP-dependent protein kinase A in Plasmodium falciparum; it is activated by cAMP (released from the regulatory subunit PfPKA-R upon cAMP binding) and by upstream phosphorylation of its activation loop T189 by PfPDK1, it phosphorylates key invasion ligands including AMA1-S610 (priming subsequent GSK3-mediated T613 phosphorylation) and components of the glideosome motor complex (myosin A, GAP45, CDPK1), it is essential for erythrocyte invasion and blood-stage proliferation (but dispensable for pre-erythrocytic stages in P. berghei), regulates gametocyte deformability via phosphorylation of STEVOR and other erythrocyte-associated proteins, and must be tightly regulated since both its loss and its hyperactivation (via PDE inhibition or overexpression) are lethal to the parasite."},"narrative":{"mechanistic_narrative":"PKAc (PF3D7_0934800) is the catalytic subunit of cAMP-dependent protein kinase A in Plasmodium falciparum and the central effector of cAMP signaling controlling erythrocyte invasion and blood-stage proliferation [PMID:11559352, PMID:31594816, PMID:31075098]. Enzymatically active PKAc is stimulated by cAMP and, unlike the mammalian enzyme, is only weakly inhibited by H89 and PKI, indicating a divergent substrate-binding architecture [PMID:18501980]; its activation requires phosphorylation of activation-loop residue T189 by PfPDK1, and cAMP binding to the regulatory subunit PfPKA-R releases the catalytic subunit to phosphorylate substrates [PMID:27738107, PMID:34879056]. During merozoite invasion PKAc phosphorylates the AMA1 cytoplasmic tail at S610, a cAMP-dependent priming event that licenses subsequent GSK3-mediated phosphorylation of T613, with both steps required for efficient invasion, and it additionally targets glideosome motor components myosin A, GAP45, and CDPK1 [PMID:20532217, PMID:23025827, PMID:27698395]. Beyond invasion, PKAc phosphorylates erythrocyte-associated proteins including STEVOR at S324 to regulate gametocyte-infected erythrocyte deformability [PMID:25951195, PMID:27136945]. PKAc activity must be temporally bounded: conditional disruption abolishes invasion and blood-stage growth [PMID:31594816, PMID:31075098], while hyperactivation through PDEβ loss, overexpression, or membrane-permeable cAMP agonists is equally lethal [PMID:27738107, PMID:30794532, PMID:34879056]. In P. berghei the kinase is dispensable for pre-erythrocytic liver-stage development despite being essential for initiating blood-stage infection [PMID:31142638].","teleology":[{"year":2000,"claim":"Establishing that P. falciparum encodes a single-copy PKA catalytic subunit with stage-regulated expression defined the gene as a discrete signaling component preferentially active in asexual blood stages.","evidence":"Gene cloning and expression analysis in P. falciparum","pmids":["10960174"],"confidence":"Medium","gaps":["No enzymatic activity or substrate demonstrated","Subcellular localization not defined"],"attribution":[{"species":"Plasmodium falciparum","strain":""}]},{"year":2001,"claim":"Detection of cAMP-stimulated kinase activity in schizonts, and the block of intraerythrocytic development by H89, first linked PKAc enzymatic activity to blood-stage viability.","evidence":"In vitro kinase activity assay and pharmacological inhibition (H89, PKI) in P. falciparum schizonts","pmids":["11559352"],"confidence":"Medium","gaps":["Pharmacological inhibitors are not PKAc-selective","No molecular substrate identified"],"attribution":[{"species":"Plasmodium falciparum","strain":""}]},{"year":2005,"claim":"Placing PKAc downstream of melatonin and in reciprocal cross-talk with Ca2+ signaling positioned the kinase within a host-hormone-responsive cell-cycle control circuit.","evidence":"cAMP analogue treatment, PKA activity assay, and pharmacological inhibitors in infected erythrocytes","pmids":["16103224"],"confidence":"Medium","gaps":["Relies on pharmacological tools rather than genetic manipulation of PKAc","Direct PKAc substrates in this circuit not identified"],"attribution":[{"species":"Plasmodium falciparum","strain":""}]},{"year":2008,"claim":"Recombinant reconstitution of active PfPKAc, together with regulatory-subunit modulation of anion conductance and cAMP rescue of a growth defect, provided direct biochemical evidence that PKAc activity is required for normal parasite growth and behaves differently from mammalian PKA-C.","evidence":"Wheat germ cell-free expression and purification with inhibitor profiling; patch-clamp and transgenic PfPKA-R overexpression with cAMP rescue in P. falciparum","pmids":["18501980","18248092"],"confidence":"High","gaps":["Physiological substrates not yet defined at this stage","Anion-conductance effects attributed to the regulatory subunit, not directly to PKAc"],"attribution":[{"species":"Plasmodium falciparum","strain":""}]},{"year":2009,"claim":"Loss-of-function by dsRNA knockdown and additional recombinant characterization tied PKAc depletion to schizont cell-cycle arrest and transcriptional programs enriched for invasion and calcium signaling.","evidence":"dsRNA silencing with microarray transcriptomics and E. coli-expressed recombinant kinase assays in P. falciparum","pmids":["19779742","19159956"],"confidence":"Medium","gaps":["dsRNA knockdown incomplete and prone to off-target effects","Transcriptional changes may be indirect consequences of arrest"],"attribution":[{"species":"Plasmodium falciparum","strain":"3D7"}]},{"year":2010,"claim":"Identification of AMA1 S610 as a PKAc-dependent phosphosite whose mutation blocks invasion connected the kinase to a specific invasion ligand and a concrete molecular function.","evidence":"Site-directed mutagenesis (S610A), in vivo phosphorylation and invasion assays in P. falciparum; melatonin/Ca2+-cAMP feedback in P. chabaudi","pmids":["20532217","20964707"],"confidence":"High","gaps":["Direct kinase-substrate assay for AMA1 not yet shown at this stage","Whether PKAc is the sole S610 kinase not established"],"attribution":[{"species":"Plasmodium falciparum","strain":""},{"species":"Plasmodium chabaudi","strain":""}]},{"year":2012,"claim":"Discovery of myosin A, GAP45, and CDPK1 as PKAc substrates broadened the kinase's role from a single ligand to regulation of the glideosome invasion motor.","evidence":"In vitro kinase assay with phosphoproteomics and phospho-motif analysis in P. falciparum","pmids":["23025827"],"confidence":"Medium","gaps":["Individual phosphosites not confirmed by mutagenesis","Functional consequence of each site on motor activity not tested"],"attribution":[{"species":"Plasmodium falciparum","strain":""}]},{"year":2015,"claim":"Linking PKAc-dependent phosphorylation to gametocyte-infected erythrocyte stiffness extended the kinase's substrate scope to host-cell mechanical remodeling relevant to transmission stages.","evidence":"Microsphere filtration deformability assays with PDE-inhibitor cAMP elevation and PKA activity measurement in P. falciparum","pmids":["25951195"],"confidence":"Medium","gaps":["Specific PKAc substrates driving deformability not identified in this study","Pharmacological cAMP elevation not gene-specific"],"attribution":[{"species":"Plasmodium falciparum","strain":""}]},{"year":2016,"claim":"Resolving a hierarchical AMA1 phosphorylation cascade, identifying STEVOR S324 as a substrate, and solving the PfPKA-R:cAMP structure together defined how cAMP release of PKAc drives sequential invasion phosphorylation and host-cell modification, and revealed that hyperactivation is as damaging as inhibition.","evidence":"In vitro kinase assays, phosphosite mutagenesis and invasion assays; IP-mass spectrometry and microsphiltration; X-ray crystallography of PfPKA-R with cAMP analogues in P. falciparum","pmids":["27698395","27136945","27738107"],"confidence":"High","gaps":["No crystal structure of the catalytic subunit itself","Mechanism coupling PKAc priming to GSK3 recruitment not defined"],"attribution":[{"species":"Plasmodium falciparum","strain":""}]},{"year":2017,"claim":"Demonstrating that CDPK1 phosphorylates the regulatory subunit PfPKA-R established a direct molecular node of cross-talk between Ca2+- and cAMP-dependent kinase signaling upstream of PKAc.","evidence":"Comparative phosphoproteomics, conditional knockdown, and in vitro kinase assay in P. falciparum","pmids":["28680058"],"confidence":"Medium","gaps":["Functional impact of PfPKA-R phosphorylation on PKAc release not quantified","Reciprocal regulation (PKAc phosphorylating CDPK1) noted earlier but its integration unclear"],"attribution":[{"species":"Plasmodium falciparum","strain":""}]},{"year":2019,"claim":"Conditional genetic disruption across species resolved PKAc as strictly essential for erythrocyte invasion and blood-stage growth (via AMA1 S610 phosphorylation) but dispensable for liver-stage development, and defined tight temporal control of its activation as itself essential.","evidence":"DiCre conditional deletion in P. falciparum with phospho-immunoblot and invasion assays; ACβ/PKAc disruption with phosphoproteomics; PDEβ disruption showing lethal hyperactivation; sporozoite-stage KO in P. berghei","pmids":["31594816","31075098","30794532","31142638"],"confidence":"High","gaps":["Full in vivo PKAc substrate set only partially assigned from phosphoproteomes","Basis of species/stage-specific dispensability in liver stages unexplained"],"attribution":[{"species":"Plasmodium falciparum","strain":""},{"species":"Plasmodium berghei","strain":""}]},{"year":2021,"claim":"Identifying PfPDK1 as the activation-loop (T189) kinase for PKAc, and confirming lethal overexpression and a gametocyte-deformability role, established the upstream activation mechanism and reinforced that PKAc dosage must be balanced.","evidence":"Conditional knockdown, PKAc overexpression selection with whole-genome sequencing, and T189 mutagenesis in P. falciparum; DiCre KO with AMA1 secretion readouts in P. yoelii","pmids":["34879056","34390881"],"confidence":"High","gaps":["P. yoelii shows impaired AMA1 secretion whereas P. falciparum studies did not report this defect, indicating unresolved species divergence in how PKAc loss affects AMA1","How PfPDK1 access to PKAc is temporally controlled not defined"],"attribution":[{"species":"Plasmodium falciparum","strain":""},{"species":"Plasmodium yoelii","strain":""}]},{"year":2024,"claim":"Placing PKAc upstream of the phosphatase PP7 in ring-stage development, and recovering PKAc/PfPDK1/PfPKA-R resistance mutations against PDE inhibitors, defined downstream signaling architecture and confirmed PKAc as the direct effector of PDEβ-regulated cAMP.","evidence":"Conditional disruption with phosphoproteomics (PP7); in vitro PDE-inhibitor resistance selection with whole-genome sequencing in P. falciparum","pmids":["39387582","39642214"],"confidence":"Medium","gaps":["Direct PP7-PKAc substrate opposition not biochemically reconstituted","How PKAc distinguishes invasion versus ring-stage substrate programs unknown"],"attribution":[{"species":"Plasmodium falciparum","strain":""}]},{"year":null,"claim":"How PKAc achieves substrate and temporal selectivity — the full in vivo substrate repertoire, the structural basis of its divergent inhibitor profile, and what confines its activity to invasion versus ring-stage and gametocyte programs — remains unresolved.","evidence":"No direct experimental resolution in the current corpus","pmids":[],"confidence":"Low","gaps":["No crystal structure of the catalytic subunit","Complete validated in vivo substrate set not defined","Mechanistic basis of species/stage-specific requirements not established"],"attribution":[{"species":"Plasmodium falciparum","strain":""}]}],"mechanism_profile":{"molecular_activity":[],"localization":[],"pathway":[],"complexes":["cAMP-dependent protein kinase (PKA) holoenzyme with regulatory subunit PfPKA-R [#3, #13, #14]"],"partners":["PFPKA-R (REGULATORY SUBUNIT) [#3, #13, #14]","PFPDK1 (ACTIVATION-LOOP T189 KINASE) [#19, #23]","AMA1 (SUBSTRATE, S610) [#7, #11, #15]","GSK3 (DOWNSTREAM AMA1 T613 KINASE) [#11]","MYOSIN A, GAP45, CDPK1 (GLIDEOSOME SUBSTRATES; CDPK1 ALSO PHOSPHORYLATES PFPKA-R) [#9, #14]","STEVOR (SUBSTRATE, S324) [#12]","PP7 (DOWNSTREAM PHOSPHATASE SUBSTRATE) [#22]","ADENYLYL CYCLASE BETA / PDEΒ (CAMP-REGULATING ENZYMES UPSTREAM) [#16, #17, #23]"],"other_free_text":["PKAc is essential for erythrocyte invasion and blood-stage proliferation in P. falciparum, P. yoelii, and by inference P. chabaudi signaling, but dispensable for P. berghei pre-erythrocytic liver-stage development [#15, #16, #18, #21]","Both loss of function and hyperactivation (overexpression, PDEβ disruption, or membrane-permeable cAMP agonists) are lethal, indicating PKAc activity must be tightly balanced [#13, #17, #20]","PfPKAc differs from mammalian PKA-C in inhibitor sensitivity (weakly inhibited by H89 and PKI), reflecting a divergent substrate-binding site [#4]","PKAc participates in reciprocal cross-talk with Ca2+ signaling, including bidirectional cAMP-Ca2+ feedback and CDPK1-mediated phosphorylation of its regulatory subunit [#2, #8, #14]"]}},"prefetch_data":{},"corpus_meta":[{"pmid":"15479470","id":"PMC_15479470","title":"Protein kinases of the human malaria parasite Plasmodium falciparum: the kinome of a divergent eukaryote.","date":"2004","source":"BMC genomics","url":"https://pubmed.ncbi.nlm.nih.gov/15479470","citation_count":421,"is_preprint":false,"source_species":["Pf"],"role":"primary","match_terms":["curated_ref"],"competing_organism_flag":false,"competing_organism_match":"","competing_organism_only":false},{"pmid":"23025827","id":"PMC_23025827","title":"The Plasmodium falciparum schizont phosphoproteome reveals extensive phosphatidylinositol and cAMP-protein kinase A signaling.","date":"2012","source":"Journal of proteome research","url":"https://pubmed.ncbi.nlm.nih.gov/23025827","citation_count":113,"is_preprint":false,"source_species":["Pf"],"role":"primary","match_terms":["PKA"],"competing_organism_flag":false,"competing_organism_match":"","competing_organism_only":false},{"pmid":"16103224","id":"PMC_16103224","title":"Cyclic AMP and calcium interplay as second messengers in melatonin-dependent regulation of Plasmodium falciparum cell 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in asexual blood stages than in sexual forms.\",\n      \"method\": \"Gene cloning, expression analysis\",\n      \"journal\": \"Molecular and biochemical parasitology\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Weak — direct gene isolation and expression characterization, single lab, single study\",\n      \"pmids\": [\"10960174\"],\n      \"is_preprint\": false,\n      \"attribution\": [{\"species\": \"Plasmodium falciparum\", \"strain\": \"\"}]\n    },\n    {\n      \"year\": 2001,\n      \"finding\": \"PKAc (PF3D7_0934800) activity is detectable in P. falciparum schizonts; it can be stimulated by cAMP and inhibited by protein kinase inhibitor (PKI), and its inhibition by H89 blocks intraerythrocytic parasite development.\",\n      \"method\": \"In vitro kinase activity assay, pharmacological inhibition (H89, PKI)\",\n      \"journal\": \"European journal of biochemistry\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — in vitro kinase assay plus pharmacological inhibition with phenotypic readout, single lab\",\n      \"pmids\": [\"11559352\"],\n      \"is_preprint\": false,\n      \"attribution\": [{\"species\": \"Plasmodium falciparum\", \"strain\": \"\"}]\n    },\n    {\n      \"year\": 2005,\n      \"finding\": \"Melatonin induces an increase in cAMP levels and PKAc activity (~40–50%) in P. falciparum-infected erythrocytes, and PKAc activation mediates melatonin-induced cell cycle alteration; a cross-talk exists whereby cAMP/PKAc activation raises cytosolic Ca2+, and Ca2+-dependent pathways (via PLC) regulate cAMP increases.\",\n      \"method\": \"cAMP analogue treatment, PKA activity assay, pharmacological inhibitors (H89, PKI, 6-Bz-cAMP, U73122)\",\n      \"journal\": \"The Journal of cell biology\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — multiple pharmacological tools with enzyme activity measurement, single lab\",\n      \"pmids\": [\"16103224\"],\n      \"is_preprint\": false,\n      \"attribution\": [{\"species\": \"Plasmodium falciparum\", \"strain\": \"\"}]\n    },\n    {\n      \"year\": 2008,\n      \"finding\": \"The regulatory subunit of PKA (PfPKA-R) modulates anion conductance in P. falciparum-infected erythrocytes: addition of recombinant PfPKA-R in patch-clamp experiments or overexpression of PfPKA-R in transgenic parasites down-regulates anion channel activity, and this overexpression strain has a growth defect rescued by elevated intracellular cAMP, indicating PKAc activity is required for normal parasite growth.\",\n      \"method\": \"Patch-clamp electrophysiology, transgenic parasite overexpression, cAMP rescue experiment\",\n      \"journal\": \"PLoS pathogens\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — direct electrophysiology combined with transgenic overexpression and cAMP rescue, single lab\",\n      \"pmids\": [\"18248092\"],\n      \"is_preprint\": false,\n      \"attribution\": [{\"species\": \"Plasmodium falciparum\", \"strain\": \"\"}]\n    },\n    {\n      \"year\": 2008,\n      \"finding\": \"Recombinant PKAc catalytic subunit (PfPKAc) was purified using a wheat germ cell-free expression system and shown to be enzymatically active; unlike mammalian PKA-C, PfPKAc is only weakly inhibited by H89 and slightly inhibited by PKI, indicating its substrate-binding sites differ from mammalian counterparts.\",\n      \"method\": \"Wheat germ cell-free expression, protein purification, in vitro kinase assay with inhibitors\",\n      \"journal\": \"Molecular and biochemical parasitology\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 / Moderate — direct in vitro reconstitution with purified recombinant protein and comparative inhibitor profiling, single lab\",\n      \"pmids\": [\"18501980\"],\n      \"is_preprint\": false,\n      \"attribution\": [{\"species\": \"Plasmodium falciparum\", \"strain\": \"\"}]\n    },\n    {\n      \"year\": 2009,\n      \"finding\": \"dsRNA-mediated knockdown of PfPKAc mRNA in P. falciparum caused morphological changes in schizonts and cell cycle arrest, accompanied by a compensatory decrease in PfPKAr mRNA; transcriptomic analysis showed altered expression of 329 genes, particularly those in merozoite invasion processes, calcium/calmodulin signaling, kinase networks, and mitochondrial functions.\",\n      \"method\": \"dsRNA gene silencing, microarray transcriptomics\",\n      \"journal\": \"Parasitology research\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — loss-of-function with defined phenotypic readout (schizont arrest) plus transcriptomic pathway placement, single lab\",\n      \"pmids\": [\"19779742\"],\n      \"is_preprint\": false,\n      \"attribution\": [{\"species\": \"Plasmodium falciparum\", \"strain\": \"3D7\"}]\n    },\n    {\n      \"year\": 2009,\n      \"finding\": \"Recombinant PfPKAc was overexpressed in E. coli and purified, and its enzymatic properties were determined using a fluorogenic kinase assay, establishing biochemical parameters suitable for inhibitor screening.\",\n      \"method\": \"Recombinant protein expression in E. coli, purification, fluorogenic in vitro kinase assay\",\n      \"journal\": \"Parasitology research\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 1 / Weak — direct in vitro reconstitution with purified recombinant protein, single lab, single study\",\n      \"pmids\": [\"19159956\"],\n      \"is_preprint\": false,\n      \"attribution\": [{\"species\": \"Plasmodium falciparum\", \"strain\": \"\"}]\n    },\n    {\n      \"year\": 2010,\n      \"finding\": \"PKAc activity phosphorylates the cytoplasmic tail of AMA1 at serine 610 (S610); mutation of AMA1 S610 to alanine abolishes phosphorylation in vivo and dramatically impedes erythrocyte invasion, establishing PKAc as the kinase responsible for this phosphorylation event.\",\n      \"method\": \"Site-directed mutagenesis, in vivo phosphorylation assay, invasion assay\",\n      \"journal\": \"PLoS pathogens\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Strong — reciprocal mutagenesis (S610A abolishes phosphorylation) plus functional invasion assay, replicated by subsequent independent studies (PMID 31594816, 27698395)\",\n      \"pmids\": [\"20532217\"],\n      \"is_preprint\": false,\n      \"attribution\": [{\"species\": \"Plasmodium falciparum\", \"strain\": \"\"}]\n    },\n    {\n      \"year\": 2010,\n      \"finding\": \"In P. chabaudi, melatonin triggers cAMP production and PKA activation; this cAMP/PKA activation is dependent on prior Ca2+ elevation (blocked by BAPTA), and in turn cAMP application evokes Ca2+ signals, establishing bidirectional positive feedback between Ca2+ and cAMP/PKAc pathways; PKAc activation was essential for melatonin-induced increase in parasitemia.\",\n      \"method\": \"cAMP measurement, PKA activity assay, Ca2+ chelation (BAPTA), pharmacological stimulation\",\n      \"journal\": \"Journal of pineal research\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — multiple orthogonal pharmacological tools and enzyme activity measurements, single lab\",\n      \"pmids\": [\"20964707\"],\n      \"is_preprint\": false,\n      \"attribution\": [{\"species\": \"Plasmodium chabaudi\", \"strain\": \"\"}]\n    },\n    {\n      \"year\": 2012,\n      \"finding\": \"In vitro kinase assays identified three novel PKAc substrates associated with the glideosome motor complex: myosin A, GAP45, and CDPK1, establishing PKAc involvement in regulating the invasion motor complex via cAMP-dependent phosphorylation.\",\n      \"method\": \"In vitro kinase assay, phosphoproteomics, phospho-motif analysis\",\n      \"journal\": \"Journal of proteome research\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 1 / Weak — in vitro kinase assay identifying substrates, single lab, no mutagenesis confirmation of individual sites\",\n      \"pmids\": [\"23025827\"],\n      \"is_preprint\": false,\n      \"attribution\": [{\"species\": \"Plasmodium falciparum\", \"strain\": \"\"}]\n    },\n    {\n      \"year\": 2015,\n      \"finding\": \"PKAc-mediated phosphorylation of gametocyte-infected erythrocyte proteins contributes to stiffness of immature gametocytes; pharmacological elevation of cAMP (mimicking PKAc hyperactivation) renders mature stage V gametocytes less deformable, establishing that parasite PKAc activity contributes to GIE mechanical properties.\",\n      \"method\": \"Microsphere filtration assay, phosphodiesterase inhibitor treatment, PKA activity measurement\",\n      \"journal\": \"PLoS pathogens\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — functional deformability assay with pharmacological modulation of cAMP/PKA, single lab\",\n      \"pmids\": [\"25951195\"],\n      \"is_preprint\": false,\n      \"attribution\": [{\"species\": \"Plasmodium falciparum\", \"strain\": \"\"}]\n    },\n    {\n      \"year\": 2016,\n      \"finding\": \"PKAc phosphorylates AMA1 at S610 in a cAMP-dependent priming step, which then enables subsequent phosphorylation of a conserved downstream threonine (T613) by GSK3; both phosphorylation steps are required for efficient erythrocyte invasion, establishing a hierarchical, sequential phosphorylation cascade on AMA1 regulated by PKAc.\",\n      \"method\": \"In vitro kinase assay, site-directed mutagenesis, invasion assay\",\n      \"journal\": \"Scientific reports\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 / Moderate — in vitro kinase assay plus mutagenesis of phosphosites with functional invasion readout, single lab with multiple orthogonal methods\",\n      \"pmids\": [\"27698395\"],\n      \"is_preprint\": false,\n      \"attribution\": [{\"species\": \"Plasmodium falciparum\", \"strain\": \"\"}]\n    },\n    {\n      \"year\": 2016,\n      \"finding\": \"PKAc-mediated phosphorylation of the STEVOR C-terminal domain at serine S324 regulates gametocyte-infected erythrocyte deformability; this was demonstrated using immunoprecipitation and mass spectrometry, establishing STEVOR as a PKAc substrate involved in host cell mechanical modification.\",\n      \"method\": \"Immunoprecipitation, mass spectrometry, microsphiltration, phosphorylation assay\",\n      \"journal\": \"Blood\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — reciprocal Co-IP plus mass spectrometry identification of phosphosite, functional deformability assay, single lab\",\n      \"pmids\": [\"27136945\"],\n      \"is_preprint\": false,\n      \"attribution\": [{\"species\": \"Plasmodium falciparum\", \"strain\": \"\"}]\n    },\n    {\n      \"year\": 2016,\n      \"finding\": \"Crystal structure of the PfPKA regulatory subunit (PfPKA-R) in complex with cAMP and (Sp)-2-Cl-cAMPS was solved; structurally, cAMP binding to PfPKA-R stabilizes a conformation that releases PKAc from inhibition, allowing it to phosphorylate substrates such as AMA1; uncontrolled induction of PKAc activity via membrane-permeable cAMP agonists is equally disruptive to parasite growth as inhibition.\",\n      \"method\": \"X-ray crystallography, cAMP analogue binding, parasite growth assay with cAMP agonists\",\n      \"journal\": \"The Journal of biological chemistry\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 / Moderate — crystal structure combined with functional growth assay, single lab with structural and biological validation\",\n      \"pmids\": [\"27738107\"],\n      \"is_preprint\": false,\n      \"attribution\": [{\"species\": \"Plasmodium falciparum\", \"strain\": \"\"}]\n    },\n    {\n      \"year\": 2017,\n      \"finding\": \"PfCDPK1 phosphorylates the PKA regulatory subunit (PfPKA-R) and thereby regulates PKAc activity in P. falciparum, establishing a cross-talk mechanism between Ca2+-dependent and cAMP-dependent kinase signaling relevant to invasion.\",\n      \"method\": \"Comparative phosphoproteomics, conditional knockdown, in vitro kinase assay\",\n      \"journal\": \"Nature communications\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — phosphoproteomics plus conditional knockdown identifying PfPKA-R as a CDPK1 substrate, single lab\",\n      \"pmids\": [\"28680058\"],\n      \"is_preprint\": false,\n      \"attribution\": [{\"species\": \"Plasmodium falciparum\", \"strain\": \"\"}]\n    },\n    {\n      \"year\": 2019,\n      \"finding\": \"Conditional disruption of PKAc (PF3D7_0934800) via DiCre-mediated excision in P. falciparum results in complete loss of PKAc protein, severe reduction in intraerythrocytic growth after one cycle, and a pronounced invasion defect; PKAc-null parasites fail to phosphorylate AMA1 at S610 in vivo, confirming PKAc as the kinase responsible for this event.\",\n      \"method\": \"CRISPR-Cas9 gene editing, DiCre conditional gene deletion, live imaging, phospho-specific immunoblot, invasion assay\",\n      \"journal\": \"mBio\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Strong — conditional KO with multiple orthogonal readouts (growth, invasion, phosphorylation), independently corroborated by PMID 31075098\",\n      \"pmids\": [\"31594816\"],\n      \"is_preprint\": false,\n      \"attribution\": [{\"species\": \"Plasmodium falciparum\", \"strain\": \"\"}]\n    },\n    {\n      \"year\": 2019,\n      \"finding\": \"Conditional disruption of both adenylyl cyclase beta (ACβ) and PKAc in P. falciparum demonstrates that cAMP production and PKAc activity are critical specifically for erythrocyte invasion; PKAc-dependent phosphorylation of AMA1 cytoplasmic domain regulates invasion; numerous cAMP/PKAc-dependent phosphorylation sites were identified by phosphoproteomics.\",\n      \"method\": \"Conditional gene disruption, phosphoproteomics, invasion assay\",\n      \"journal\": \"PLoS biology\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Strong — conditional disruption of PKAc with phosphoproteomic and functional invasion readouts, independently confirmed by PMID 31594816\",\n      \"pmids\": [\"31075098\"],\n      \"is_preprint\": false,\n      \"attribution\": [{\"species\": \"Plasmodium falciparum\", \"strain\": \"\"}]\n    },\n    {\n      \"year\": 2019,\n      \"finding\": \"Hyperactivation of PKAc caused by conditional gene disruption of PfPDEβ (leading to elevated cAMP) causes a profound reduction in erythrocyte invasion and rapid death of invaded merozoites; phosphoproteomic analysis of PDEβ-null parasites showed >2-fold increase in phosphorylation at over 200 sites, more than half conforming to PKAc substrate consensus, establishing that temporal regulation of PKAc activation by PDEβ is essential.\",\n      \"method\": \"Conditional gene disruption, phosphoproteomics, invasion and growth assay\",\n      \"journal\": \"PLoS biology\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Strong — conditional KO with genome-wide phosphoproteomics and functional readouts, consistent with PMID 31594816 and 31075098\",\n      \"pmids\": [\"30794532\"],\n      \"is_preprint\": false,\n      \"attribution\": [{\"species\": \"Plasmodium falciparum\", \"strain\": \"\"}]\n    },\n    {\n      \"year\": 2019,\n      \"finding\": \"PKAc (PF3D7_0934800) is dispensable for pre-erythrocytic stages in P. berghei: conditional PKAc gene disruption in sporozoites showed that mutant sporozoites can glide, invade hepatocytes, and mature into hepatic merozoites released from merosomes, but fail to initiate blood stage infection, demonstrating PKAc is not required for liver stage development.\",\n      \"method\": \"Conditional gene disruption in P. berghei sporozoites, gliding assay, hepatocyte invasion and development assay\",\n      \"journal\": \"Life science alliance\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — conditional KO with multiple stage-specific functional readouts (gliding, hepatocyte invasion, liver stage development, blood stage initiation), single lab\",\n      \"pmids\": [\"31142638\"],\n      \"is_preprint\": false,\n      \"attribution\": [{\"species\": \"Plasmodium berghei\", \"strain\": \"\"}]\n    },\n    {\n      \"year\": 2021,\n      \"finding\": \"PfPDK1 (3-phosphoinositide-dependent protein kinase-1) is required to activate PKAc in P. falciparum; whole-genome sequencing of parasites selected to tolerate PKAc overexpression identified missense mutations exclusively in PfPDK1; targeted mutagenesis demonstrated that PfPDK1 phosphorylates T189 in the PKAc activation loop to activate the kinase.\",\n      \"method\": \"Conditional PKAc knockdown, whole-genome sequencing, targeted mutagenesis of T189, PKAc overexpression selection\",\n      \"journal\": \"PLoS biology\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 / Strong — mutagenesis of activation loop residue combined with WGS and conditional genetic tools, multiple orthogonal approaches in single rigorous study\",\n      \"pmids\": [\"34879056\"],\n      \"is_preprint\": false,\n      \"attribution\": [{\"species\": \"Plasmodium falciparum\", \"strain\": \"\"}]\n    },\n    {\n      \"year\": 2021,\n      \"finding\": \"Conditional knockdown of PKAc in P. falciparum confirms its essential role in erythrocyte invasion by merozoites, and additionally shows that PKAc is involved in regulating gametocyte deformability; overexpression of PKAc is lethal and kills parasites at the early phase of schizogony.\",\n      \"method\": \"Conditional PKAc knockdown, PKAc overexpression, deformability assay, growth assay\",\n      \"journal\": \"PLoS biology\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Strong — conditional KO plus overexpression with multiple phenotypic readouts, consistent with independent studies (PMID 31594816, 31075098)\",\n      \"pmids\": [\"34879056\"],\n      \"is_preprint\": false,\n      \"attribution\": [{\"species\": \"Plasmodium falciparum\", \"strain\": \"\"}]\n    },\n    {\n      \"year\": 2021,\n      \"finding\": \"PKAc disruption in P. yoelii (DiCre-loxP inducible KO) caused severe growth and erythrocyte invasion defects, and impaired secretion of AMA1 to the merozoite surface, while secretions of PyEBL, Py235, and RON2 were not affected by PKAc loss.\",\n      \"method\": \"DiCre-loxP conditional knockout, invasion assay, IFA for secretion of AMA1 and other ligands\",\n      \"journal\": \"Parasitology international\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — conditional KO with multiple secretion readouts, single lab; note AMA1 secretion phenotype differs from P. falciparum result (negative finding in P. falciparum)\",\n      \"pmids\": [\"34390881\"],\n      \"is_preprint\": false,\n      \"attribution\": [{\"species\": \"Plasmodium yoelii\", \"strain\": \"\"}]\n    },\n    {\n      \"year\": 2024,\n      \"finding\": \"PP7, identified as a high-confidence PKAc substrate by phosphoproteomics, is dispensable for erythrocyte invasion but essential for early ring-stage development; phosphoproteomic analysis of PP7-null parasites revealed that PP7 may regulate certain PKAc substrates, placing PKAc upstream of PP7 in a signaling network controlling ring-stage development.\",\n      \"method\": \"Conditional gene disruption, phosphoproteomics, invasion and ring-stage development assay\",\n      \"journal\": \"mBio\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — conditional KO with phosphoproteomics establishing epistatic relationship between PKAc and PP7, single lab\",\n      \"pmids\": [\"39387582\"],\n      \"is_preprint\": false,\n      \"attribution\": [{\"species\": \"Plasmodium falciparum\", \"strain\": \"\"}]\n    },\n    {\n      \"year\": 2024,\n      \"finding\": \"In vitro drug resistance selection with PDE inhibitors generated P. falciparum parasites with mutations in either the catalytic or regulatory subunits of PKA, or in PfPDK1, but not in PDEβ itself, confirming that PKAc (and its upstream activator PfPDK1 and its regulatory subunit) are direct downstream effectors of PDEβ-regulated cAMP signaling.\",\n      \"method\": \"In vitro drug selection, whole-genome sequencing of resistant parasites\",\n      \"journal\": \"Science advances\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — genetic evidence from resistance mutations directly implicating PKAc catalytic and regulatory subunits as cAMP effectors, single study\",\n      \"pmids\": [\"39642214\"],\n      \"is_preprint\": false,\n      \"attribution\": [{\"species\": \"Plasmodium falciparum\", \"strain\": \"\"}]\n    }\n  ],\n  \"current_model\": \"PKAc (PF3D7_0934800) is the catalytic subunit of cAMP-dependent protein kinase A in Plasmodium falciparum; it is activated by cAMP (released from the regulatory subunit PfPKA-R upon cAMP binding) and by upstream phosphorylation of its activation loop T189 by PfPDK1, it phosphorylates key invasion ligands including AMA1-S610 (priming subsequent GSK3-mediated T613 phosphorylation) and components of the glideosome motor complex (myosin A, GAP45, CDPK1), it is essential for erythrocyte invasion and blood-stage proliferation (but dispensable for pre-erythrocytic stages in P. berghei), regulates gametocyte deformability via phosphorylation of STEVOR and other erythrocyte-associated proteins, and must be tightly regulated since both its loss and its hyperactivation (via PDE inhibition or overexpression) are lethal to the parasite.\"\n}\n```","stage2_raw":"{\n  \"mechanistic_narrative\": \"PKAc (PF3D7_0934800) is the catalytic subunit of cAMP-dependent protein kinase A in Plasmodium falciparum and the central effector of cAMP signaling controlling erythrocyte invasion and blood-stage proliferation [#1, #15, #16]. Enzymatically active PKAc is stimulated by cAMP and, unlike the mammalian enzyme, is only weakly inhibited by H89 and PKI, indicating a divergent substrate-binding architecture [#4]; its activation requires phosphorylation of activation-loop residue T189 by PfPDK1, and cAMP binding to the regulatory subunit PfPKA-R releases the catalytic subunit to phosphorylate substrates [#13, #19]. During merozoite invasion PKAc phosphorylates the AMA1 cytoplasmic tail at S610, a cAMP-dependent priming event that licenses subsequent GSK3-mediated phosphorylation of T613, with both steps required for efficient invasion, and it additionally targets glideosome motor components myosin A, GAP45, and CDPK1 [#7, #9, #11]. Beyond invasion, PKAc phosphorylates erythrocyte-associated proteins including STEVOR at S324 to regulate gametocyte-infected erythrocyte deformability [#10, #12]. PKAc activity must be temporally bounded: conditional disruption abolishes invasion and blood-stage growth [#15, #16], while hyperactivation through PDE\\u03b2 loss, overexpression, or membrane-permeable cAMP agonists is equally lethal [#13, #17, #20]. In P. berghei the kinase is dispensable for pre-erythrocytic liver-stage development despite being essential for initiating blood-stage infection [#18].\",\n  \"teleology\": [\n    {\n      \"year\": 2000,\n      \"claim\": \"Establishing that P. falciparum encodes a single-copy PKA catalytic subunit with stage-regulated expression defined the gene as a discrete signaling component preferentially active in asexual blood stages.\",\n      \"evidence\": \"Gene cloning and expression analysis in P. falciparum\",\n      \"pmids\": [\"10960174\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"No enzymatic activity or substrate demonstrated\", \"Subcellular localization not defined\"],\n      \"attribution\": [{\"species\": \"Plasmodium falciparum\", \"strain\": \"\"}]\n    },\n    {\n      \"year\": 2001,\n      \"claim\": \"Detection of cAMP-stimulated kinase activity in schizonts, and the block of intraerythrocytic development by H89, first linked PKAc enzymatic activity to blood-stage viability.\",\n      \"evidence\": \"In vitro kinase activity assay and pharmacological inhibition (H89, PKI) in P. falciparum schizonts\",\n      \"pmids\": [\"11559352\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Pharmacological inhibitors are not PKAc-selective\", \"No molecular substrate identified\"],\n      \"attribution\": [{\"species\": \"Plasmodium falciparum\", \"strain\": \"\"}]\n    },\n    {\n      \"year\": 2005,\n      \"claim\": \"Placing PKAc downstream of melatonin and in reciprocal cross-talk with Ca2+ signaling positioned the kinase within a host-hormone-responsive cell-cycle control circuit.\",\n      \"evidence\": \"cAMP analogue treatment, PKA activity assay, and pharmacological inhibitors in infected erythrocytes\",\n      \"pmids\": [\"16103224\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Relies on pharmacological tools rather than genetic manipulation of PKAc\", \"Direct PKAc substrates in this circuit not identified\"],\n      \"attribution\": [{\"species\": \"Plasmodium falciparum\", \"strain\": \"\"}]\n    },\n    {\n      \"year\": 2008,\n      \"claim\": \"Recombinant reconstitution of active PfPKAc, together with regulatory-subunit modulation of anion conductance and cAMP rescue of a growth defect, provided direct biochemical evidence that PKAc activity is required for normal parasite growth and behaves differently from mammalian PKA-C.\",\n      \"evidence\": \"Wheat germ cell-free expression and purification with inhibitor profiling; patch-clamp and transgenic PfPKA-R overexpression with cAMP rescue in P. falciparum\",\n      \"pmids\": [\"18501980\", \"18248092\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Physiological substrates not yet defined at this stage\", \"Anion-conductance effects attributed to the regulatory subunit, not directly to PKAc\"],\n      \"attribution\": [{\"species\": \"Plasmodium falciparum\", \"strain\": \"\"}]\n    },\n    {\n      \"year\": 2009,\n      \"claim\": \"Loss-of-function by dsRNA knockdown and additional recombinant characterization tied PKAc depletion to schizont cell-cycle arrest and transcriptional programs enriched for invasion and calcium signaling.\",\n      \"evidence\": \"dsRNA silencing with microarray transcriptomics and E. coli-expressed recombinant kinase assays in P. falciparum\",\n      \"pmids\": [\"19779742\", \"19159956\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"dsRNA knockdown incomplete and prone to off-target effects\", \"Transcriptional changes may be indirect consequences of arrest\"],\n      \"attribution\": [{\"species\": \"Plasmodium falciparum\", \"strain\": \"3D7\"}]\n    },\n    {\n      \"year\": 2010,\n      \"claim\": \"Identification of AMA1 S610 as a PKAc-dependent phosphosite whose mutation blocks invasion connected the kinase to a specific invasion ligand and a concrete molecular function.\",\n      \"evidence\": \"Site-directed mutagenesis (S610A), in vivo phosphorylation and invasion assays in P. falciparum; melatonin/Ca2+-cAMP feedback in P. chabaudi\",\n      \"pmids\": [\"20532217\", \"20964707\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Direct kinase-substrate assay for AMA1 not yet shown at this stage\", \"Whether PKAc is the sole S610 kinase not established\"],\n      \"attribution\": [{\"species\": \"Plasmodium falciparum\", \"strain\": \"\"}, {\"species\": \"Plasmodium chabaudi\", \"strain\": \"\"}]\n    },\n    {\n      \"year\": 2012,\n      \"claim\": \"Discovery of myosin A, GAP45, and CDPK1 as PKAc substrates broadened the kinase's role from a single ligand to regulation of the glideosome invasion motor.\",\n      \"evidence\": \"In vitro kinase assay with phosphoproteomics and phospho-motif analysis in P. falciparum\",\n      \"pmids\": [\"23025827\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Individual phosphosites not confirmed by mutagenesis\", \"Functional consequence of each site on motor activity not tested\"],\n      \"attribution\": [{\"species\": \"Plasmodium falciparum\", \"strain\": \"\"}]\n    },\n    {\n      \"year\": 2015,\n      \"claim\": \"Linking PKAc-dependent phosphorylation to gametocyte-infected erythrocyte stiffness extended the kinase's substrate scope to host-cell mechanical remodeling relevant to transmission stages.\",\n      \"evidence\": \"Microsphere filtration deformability assays with PDE-inhibitor cAMP elevation and PKA activity measurement in P. falciparum\",\n      \"pmids\": [\"25951195\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Specific PKAc substrates driving deformability not identified in this study\", \"Pharmacological cAMP elevation not gene-specific\"],\n      \"attribution\": [{\"species\": \"Plasmodium falciparum\", \"strain\": \"\"}]\n    },\n    {\n      \"year\": 2016,\n      \"claim\": \"Resolving a hierarchical AMA1 phosphorylation cascade, identifying STEVOR S324 as a substrate, and solving the PfPKA-R:cAMP structure together defined how cAMP release of PKAc drives sequential invasion phosphorylation and host-cell modification, and revealed that hyperactivation is as damaging as inhibition.\",\n      \"evidence\": \"In vitro kinase assays, phosphosite mutagenesis and invasion assays; IP-mass spectrometry and microsphiltration; X-ray crystallography of PfPKA-R with cAMP analogues in P. falciparum\",\n      \"pmids\": [\"27698395\", \"27136945\", \"27738107\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"No crystal structure of the catalytic subunit itself\", \"Mechanism coupling PKAc priming to GSK3 recruitment not defined\"],\n      \"attribution\": [{\"species\": \"Plasmodium falciparum\", \"strain\": \"\"}]\n    },\n    {\n      \"year\": 2017,\n      \"claim\": \"Demonstrating that CDPK1 phosphorylates the regulatory subunit PfPKA-R established a direct molecular node of cross-talk between Ca2+- and cAMP-dependent kinase signaling upstream of PKAc.\",\n      \"evidence\": \"Comparative phosphoproteomics, conditional knockdown, and in vitro kinase assay in P. falciparum\",\n      \"pmids\": [\"28680058\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Functional impact of PfPKA-R phosphorylation on PKAc release not quantified\", \"Reciprocal regulation (PKAc phosphorylating CDPK1) noted earlier but its integration unclear\"],\n      \"attribution\": [{\"species\": \"Plasmodium falciparum\", \"strain\": \"\"}]\n    },\n    {\n      \"year\": 2019,\n      \"claim\": \"Conditional genetic disruption across species resolved PKAc as strictly essential for erythrocyte invasion and blood-stage growth (via AMA1 S610 phosphorylation) but dispensable for liver-stage development, and defined tight temporal control of its activation as itself essential.\",\n      \"evidence\": \"DiCre conditional deletion in P. falciparum with phospho-immunoblot and invasion assays; AC\\u03b2/PKAc disruption with phosphoproteomics; PDE\\u03b2 disruption showing lethal hyperactivation; sporozoite-stage KO in P. berghei\",\n      \"pmids\": [\"31594816\", \"31075098\", \"30794532\", \"31142638\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Full in vivo PKAc substrate set only partially assigned from phosphoproteomes\", \"Basis of species/stage-specific dispensability in liver stages unexplained\"],\n      \"attribution\": [{\"species\": \"Plasmodium falciparum\", \"strain\": \"\"}, {\"species\": \"Plasmodium berghei\", \"strain\": \"\"}]\n    },\n    {\n      \"year\": 2021,\n      \"claim\": \"Identifying PfPDK1 as the activation-loop (T189) kinase for PKAc, and confirming lethal overexpression and a gametocyte-deformability role, established the upstream activation mechanism and reinforced that PKAc dosage must be balanced.\",\n      \"evidence\": \"Conditional knockdown, PKAc overexpression selection with whole-genome sequencing, and T189 mutagenesis in P. falciparum; DiCre KO with AMA1 secretion readouts in P. yoelii\",\n      \"pmids\": [\"34879056\", \"34390881\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"P. yoelii shows impaired AMA1 secretion whereas P. falciparum studies did not report this defect, indicating unresolved species divergence in how PKAc loss affects AMA1\", \"How PfPDK1 access to PKAc is temporally controlled not defined\"],\n      \"attribution\": [{\"species\": \"Plasmodium falciparum\", \"strain\": \"\"}, {\"species\": \"Plasmodium yoelii\", \"strain\": \"\"}]\n    },\n    {\n      \"year\": 2024,\n      \"claim\": \"Placing PKAc upstream of the phosphatase PP7 in ring-stage development, and recovering PKAc/PfPDK1/PfPKA-R resistance mutations against PDE inhibitors, defined downstream signaling architecture and confirmed PKAc as the direct effector of PDE\\u03b2-regulated cAMP.\",\n      \"evidence\": \"Conditional disruption with phosphoproteomics (PP7); in vitro PDE-inhibitor resistance selection with whole-genome sequencing in P. falciparum\",\n      \"pmids\": [\"39387582\", \"39642214\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Direct PP7-PKAc substrate opposition not biochemically reconstituted\", \"How PKAc distinguishes invasion versus ring-stage substrate programs unknown\"],\n      \"attribution\": [{\"species\": \"Plasmodium falciparum\", \"strain\": \"\"}]\n    },\n    {\n      \"year\": null,\n      \"claim\": \"How PKAc achieves substrate and temporal selectivity — the full in vivo substrate repertoire, the structural basis of its divergent inhibitor profile, and what confines its activity to invasion versus ring-stage and gametocyte programs — remains unresolved.\",\n      \"evidence\": \"No direct experimental resolution in the current corpus\",\n      \"pmids\": [],\n      \"confidence\": \"Low\",\n      \"gaps\": [\"No crystal structure of the catalytic subunit\", \"Complete validated in vivo substrate set not defined\", \"Mechanistic basis of species/stage-specific requirements not established\"],\n      \"attribution\": [{\"species\": \"Plasmodium falciparum\", \"strain\": \"\"}]\n    }\n  ],\n  \"mechanism_profile\": {\n    \"molecular_activity\": [\n      {\"term_id\": \"GO:0004691\", \"supporting_discovery_ids\": [1, 4, 6, 13]},\n      {\"term_id\": \"GO:0004674\", \"supporting_discovery_ids\": [7, 9, 11, 12]},\n      {\"term_id\": \"GO:0030552\", \"supporting_discovery_ids\": [2, 13]},\n      {\"term_id\": \"GO:0106310\", \"supporting_discovery_ids\": [7, 11]}\n    ],\n    \"localization\": [],\n    \"pathway\": [\n      {\"term_id\": \"GO:0007190\", \"supporting_discovery_ids\": [2, 8, 13, 16, 23]},\n      {\"term_id\": \"GO:0044409\", \"supporting_discovery_ids\": [7, 11, 15, 16, 21]},\n      {\"term_id\": \"GO:0006468\", \"supporting_discovery_ids\": [7, 9, 11, 12, 19]}\n    ],\n    \"complexes\": [\n      \"cAMP-dependent protein kinase (PKA) holoenzyme with regulatory subunit PfPKA-R [#3, #13, #14]\"\n    ],\n    \"partners\": [\n      \"PfPKA-R (regulatory subunit) [#3, #13, #14]\",\n      \"PfPDK1 (activation-loop T189 kinase) [#19, #23]\",\n      \"AMA1 (substrate, S610) [#7, #11, #15]\",\n      \"GSK3 (downstream AMA1 T613 kinase) [#11]\",\n      \"Myosin A, GAP45, CDPK1 (glideosome substrates; CDPK1 also phosphorylates PfPKA-R) [#9, #14]\",\n      \"STEVOR (substrate, S324) [#12]\",\n      \"PP7 (downstream phosphatase substrate) [#22]\",\n      \"Adenylyl cyclase beta / PDE\\u03b2 (cAMP-regulating enzymes upstream) [#16, #17, #23]\"\n    ],\n    \"other_free_text\": [\n      \"PKAc is essential for erythrocyte invasion and blood-stage proliferation in P. falciparum, P. yoelii, and by inference P. chabaudi signaling, but dispensable for P. berghei pre-erythrocytic liver-stage development [#15, #16, #18, #21]\",\n      \"Both loss of function and hyperactivation (overexpression, PDE\\u03b2 disruption, or membrane-permeable cAMP agonists) are lethal, indicating PKAc activity must be tightly balanced [#13, #17, #20]\",\n      \"PfPKAc differs from mammalian PKA-C in inhibitor sensitivity (weakly inhibited by H89 and PKI), reflecting a divergent substrate-binding site [#4]\",\n      \"PKAc participates in reciprocal cross-talk with Ca2+ signaling, including bidirectional cAMP-Ca2+ feedback and CDPK1-mediated phosphorylation of its regulatory subunit [#2, #8, #14]\"\n    ]\n  }\n}","audit_flag":null,"strains":[{"strain":"Pf3D7","gene_id":"PF3D7_0934800","name":null,"product":"cAMP-dependent protein kinase catalytic subunit","uniprot_acc":null,"chromosome":null,"start_pos":null},{"strain":"PbANKA","gene_id":"PBANKA_0835600","name":null,"product":"cAMP-dependent protein kinase catalytic subunit, putative","uniprot_acc":null,"chromosome":null,"start_pos":null},{"strain":"PkH","gene_id":"PKNH_0733500","name":null,"product":"cAMP-dependent protein kinase catalytic subunit, putative","uniprot_acc":null,"chromosome":null,"start_pos":null}],"gene_symbol":"PKA","evaluation":null}