Affinage · Plasmodium

PP1

PF3D7_1414400 · serine/threonine protein phosphatase PP1

Annotated
2026-09-08
22 papers in source corpus 18 papers cited in narrative 18 extracted findings

Mechanistic narrative

Synthesis pass · prose summary of the discoveries below

PF3D7_1414400 (PP1) is a conserved 304-residue serine/threonine protein phosphatase whose catalytic activity is essential throughout the P. falciparum intraerythrocytic and sexual life cycle (PMID:12057017). Its enzymatic mechanism was established by recombinant phosphatase assays, PP1-class inhibitor sensitivity (calyculin A), and active-site mutagenesis, and heterologous complementation of the yeast glc7 mutant confirmed its catalytic conservation; knockdown of PP1 blocks parasite DNA synthesis, establishing a requirement in intraerythrocytic replication (PMID:12057017, PMID:12062492). PP1 governs egress at multiple steps: it is exported to the Maurer's clefts where it dephosphorylates the amino-terminal domain of PfSBP1, and its inhibition blocks merozoite release (PMID:16548885); conditional and inducible depletion further shows PP1 is essential for egress, controlling rounding-up of the parasitophorous vacuole as the initiating step by acting upstream of the cGMP-PKG-Ca2+ cascade through modulation of guanylyl cyclase alpha (GCα) activity, with calcium ionophore bypassing the PP1-null defect (PMID:32669539, PMID:39808636). In gametocytes, PP1 dephosphorylates PKA substrates to maintain infected-erythrocyte deformability and stimulates cGMP/PKG signaling for gamete activation, functions required for transmission (PMID:40823845); in the P. berghei ortholog PP1 is also required for mitotic exit during male gametogenesis and zygote polarity in the mosquito midgut (PMID:34145386). Consistent with the PP1 holoenzyme paradigm, its activity and targeting are directed by a set of regulatory partners engaging conserved docking motifs (notably RVxF): the inhibitory PfLRR1/Sds22 and PfI2 (two-site RVxF plus FxxR/KxR/K binding), and the activating PfI3, GEXP15, PfRCC-PIP, PfeIF2β, and the pseudokinase PfpTKL (PMID:16629662, PMID:22128182, PMID:23837822, PMID:25132288, PMID:27303372, PMID:30429842, PMID:31148576, PMID:37628837).

Mechanistic history

Synthesis pass · year-by-year structured walk · 12 steps
  1. 2002 High

    Establishing that PF3D7_1414400 is a bona fide, catalytically active PP1-class phosphatase was the prerequisite for assigning it any cellular role; enzymatic reconstitution and knockdown showed it is required for parasite DNA synthesis.

    Evidence Recombinant phosphatase assay, inhibitor profiling, active-site mutagenesis, and siRNA knockdown with a DNA synthesis readout, plus yeast glc7 complementation

    PMID:12057017 PMID:12062492

    Open questions at the time
    • Direct physiological substrates for the replication role not identified
    • Mechanism linking PP1 activity to DNA synthesis unresolved
  2. 2006 High

    Localization of PP1 to exported Maurer's clefts and identification of PfSBP1 as a dephosphorylation target tied PP1 activity to a specific export-compartment substrate and to merozoite release.

    Evidence Immunolocalization/fractionation, reciprocal co-immunoprecipitation, and calyculin A inhibition with phosphorylation and egress readouts

    PMID:16548885

    Open questions at the time
    • Whether PfSBP1 dephosphorylation is directly causal for egress vs correlative not fully resolved
    • How PP1 is exported and retained at Maurer's clefts unknown
  3. 2006 High

    Identification of PfLRR1/Sds22 as an inhibitory PP1 partner active in cell-cycle control opened the question of how PP1 activity is regulated by binding proteins rather than being constitutive.

    Evidence GST pull-down, co-IP from parasite lysate, in vitro phosphatase assay, and Xenopus oocyte GVBD functional assay

    PMID:16629662

    Open questions at the time
    • Endogenous cell-cycle substrates of the PP1–LRR1 complex in parasite not defined
    • Xenopus GVBD is a heterologous proxy for parasite cell cycle
  4. 2011 High

    Discovery of PfI3 as a high-affinity partner that activates rather than inhibits PP1 revealed that Plasmodium PP1 regulators diverge functionally from their yeast/human homologs.

    Evidence NMR, in vitro binding and phosphatase assays, W45A mutagenesis, GFP localization, and reverse genetics

    PMID:22128182

    Open questions at the time
    • Physiological consequence of PfI3-driven activation on specific substrates unknown
    • Nuclear function of the PP1–I3 pairing uncharacterized
  5. 2014 High

    Mapping the two-site (RVxF plus FxxR/KxR/K) architecture of the PfI2–PP1 interaction defined druggable docking surfaces and demonstrated that competing peptides have antiplasmodial activity.

    Evidence NMR, dual-motif mutagenesis, Xenopus GVBD assay, and antiplasmodial penetrating-peptide assays with infected-erythrocyte accumulation

    PMID:23837822 PMID:25132288

    Open questions at the time
    • In-parasite substrates controlled by the PP1–I2 complex not enumerated
    • Peptide antiplasmodial mechanism assumed but not proven to act via PP1 in situ
  6. 2016 Medium

    Identification of PfeIF2β as a two-motif PP1 partner co-localizing in cytoplasm and nucleus extended PP1 regulation to translation-associated machinery across compartments.

    Evidence In vitro interaction with motif mutagenesis, Xenopus GVBD assay, subcellular fractionation, and reverse genetics

    PMID:27303372

    Open questions at the time
    • Functional consequence of PP1–eIF2β interaction on translation not tested
    • Localization by fractionation only, single lab
  7. 2019 Medium

    Characterization of PfRCC-PIP and the pseudokinase PfpTKL as RVxF-dependent PP1 regulators showed PP1 is embedded in scaffolds that can co-organize kinase and phosphatase activities.

    Evidence In vitro pull-down/motif mapping, co-IP from parasite, and Xenopus oocyte maturation/PP1 activity assays; reverse genetics

    PMID:30429842 PMID:31148576

    Open questions at the time
    • Direct parasite substrates of these scaffolded complexes unknown
    • Regulatory direction inferred largely from heterologous oocyte assays
  8. 2020 High

    Conditional knockdown with phosphoproteomics separated PP1's roles, showing it is absolutely essential for egress (vs merely required for efficient replication) and identifying GCα and a HECT E3 ligase as direct functional targets with phosphatidylcholine as an upstream lipid stimulus.

    Evidence Chemical-genetic conditional knockdown, phosphoproteomics, epistasis, and phosphatidylcholine stimulation assays

    PMID:32669539

    Open questions at the time
    • Direct dephosphorylation of GCα by PP1 vs indirect regulation not fully resolved
    • How PC sensing is transduced to PP1 unknown
  9. 2022 High

    Ortholog interactome mapping and genetic depletion in P. berghei confirmed the PP1–LRR1 inhibitory complex across asexual and sexual stages and placed I3 phosphorylation under its control, linking regulator hierarchy to oocyst development.

    Evidence Co-IP from parasite, phosphatase assay, PbLRR1 depletion with phosphoproteomics, and mCherry-affinity interactome MS

    PMID:35162991 PMID:35920043

    Open questions at the time
    • Species-generalization of P. berghei findings to PF3D7_1414400 not directly shown for all partners
    • Direct substrates among interactome hits (spliceosome/proteasome) not validated
  10. 2023 High

    Confirmation of the activating GEXP15–PP1 interaction in P. falciparum via the RVxF motif, with nuclear localization and ribosome association, generalized the P. berghei finding and connected PP1 to translational machinery.

    Evidence In vitro interaction with RVxF mutagenesis, phosphatase assay, live microscopy, co-IP/MS, and recombinant GYF-domain pull-down; P. berghei precedent by GEXP15

    PMID:31348803 PMID:37628837

    Open questions at the time
    • Functional consequence of GEXP15-directed PP1 activity on ribosome/RNA-binding substrates not defined
    • Stage-specific role of the complex unresolved
  11. 2025 High

    Inducible knockout resolved the initiating step of egress, showing PP1 controls parasitophorous vacuole rounding-up upstream of cGMP-PKG via GCα/cGMP homeostasis, with Ca2+ ionophore bypass placing rounding-up downstream of PP1-dependent Ca2+ signaling.

    Evidence Conditional PP1 iKO, fluorescent PV-morphology reporters, live egress imaging, and chemical rescue with egress inducers and A23187

    PMID:39808636

    Open questions at the time
    • Direct dephosphorylation target on GCα controlling basal activity not pinpointed
    • Molecular events driving PV rounding-up downstream of Ca2+ not defined
  12. 2025 High

    Conditional gametocyte depletion extended PP1 function to transmission biology, showing it maintains infected-erythrocyte deformability via PKA-substrate dephosphorylation and drives gamete activation via cGMP/PKG.

    Evidence Conditional depletion in gametocytes, deformability/permeability assays, phosphoproteomics of PKA substrates, cGMP/PKG assays, and mosquito transmission assays

    PMID:40823845

    Open questions at the time
    • Specific PKA substrates mediating mechanical properties not individually validated
    • How a single phosphatase coordinates opposing PKA and PKG signaling arms unclear

Open questions

Synthesis pass · forward-looking unresolved questions
  • How the many competing regulators (LRR1, I2, I3, GEXP15, RCC-PIP, eIF2β, pTKL) are hierarchically or temporally coordinated to direct PP1 to its stage-specific substrates in vivo remains unresolved.
  • No integrated model of regulator competition/succession across stages
  • Most direct parasite substrates beyond PfSBP1 and GCα remain unidentified
  • Structural basis of holoenzyme assembly with each regulator incomplete

Mechanism profile

Synthesis pass · controlled-vocabulary classification
Partners
GCΑ (GUANYLYL CYCLASE ALPHA)GEXP15HECT E3 UBIQUITIN LIGASEPFEIF2ΒPFI2PFI3PFLRR1/SDS22PFPTKLPFRCC-PIPPFSBP1
Complex memberships
PP1–GEXP15 (activating, RVxF; ribosome-associated)PP1–PfI2 (two-site RVxF + FxxR/KxR/K)PP1–PfI3 (activating)PP1–PfLRR1/Sds22 (inhibitory)PP1–PfRCC-PIPPP1–PfeIF2βPP1–PfpTKL (pseudokinase scaffold)

Evidence

Reading pass · 18 per-paper findings extracted from the source corpus
Year Finding Method Journal Conf PMIDs
2002 PF3D7_1414400 (PP1) encodes a 304-amino acid serine/threonine phosphatase with potent phosphatase activity in vitro; sensitivity to PP1-class inhibitors (e.g., calyculin A) and mutational analysis of catalytic residues confirmed its enzymatic mechanism; siRNA knockdown of PP1 inhibited parasite DNA synthesis, establishing an essential role in intraerythrocytic replication. Recombinant protein phosphatase assay, inhibitor sensitivity profiling, active-site mutagenesis, siRNA knockdown with DNA synthesis readout Malaria journal High 12057017
2002 PF3D7_1414400 (PP1) functionally complements the glc7 (PP1) mutant of Saccharomyces cerevisiae, rescuing the low-glycogen phenotype, demonstrating conserved catalytic function and interaction with yeast proteins of the glycogen metabolism pathway; calyculin A (but not okadaic acid) caused hyperphosphorylation of a 51 kDa parasite protein, indicating predominant PP1 (over PP2A) activity in intraerythrocytic parasites. Yeast complementation assay (glc7 mutant rescue), phosphatase inhibitor treatment with phosphoprotein detection International journal for parasitology High 12062492
2006 PF3D7_1414400 (PP1) is exported to the Maurer's clefts in the host erythrocyte cytoplasm, where it modulates the phosphorylation status of the amino-terminal domain of PfSBP1 (a trans-membrane Maurer's cleft protein); co-immunoprecipitation confirmed the PP1–PfSBP1 interaction; inhibition of PP1 with calyculin A caused hyperphosphorylation of PfSBP1 and blocked merozoite release, demonstrating that PP1 activity in the Maurer's clefts is required for parasite egress. Subcellular fractionation/immunolocalization, co-immunoprecipitation, calyculin A inhibition with phosphorylation and egress readouts Cellular microbiology High 16548885
2006 PF3D7_1414400 (PP1) interacts with PfLRR1 (the P. falciparum Sds22 orthologue) as shown by GST pull-down and co-immunoprecipitation from parasite extracts; PfLRR1 inhibits PP1 phosphatase activity; in Xenopus oocytes PfLRR1 overcame the G2/M checkpoint to promote germinal vesicle breakdown (GVBD), mirroring effects of anti-PP1 antibodies or okadaic acid, placing PP1 regulation by PfLRR1 in cell cycle control. GST pull-down, co-immunoprecipitation from parasite lysate, in vitro phosphatase activity assay, Xenopus oocyte GVBD functional assay Molecular microbiology High 16629662
2011 PF3D7_1414400 (PP1) binds PfI3 (a P. falciparum Inhibitor-3 homolog) with high affinity (apparent KD ~100 nM) via the conserved KVVRW motif (Trp45 critical); unlike yeast/human I3, PfI3 increases PP1 phosphatase activity in vitro; PfI3 localizes to the nucleus of all blood-stage parasites (GFP tagging) and is essential for blood-stage survival (no viable knockouts obtained). NMR (structural characterization of PfI3), in vitro binding assays (multiple methods), in vitro phosphatase activity assay, site-directed mutagenesis (W45A), GFP localization, reverse genetics The Journal of biological chemistry High 22128182
2013 PF3D7_1414400 (PP1) interacts with PfI2 (P. falciparum Inhibitor-2) via RVxF and HYNE motifs; both motifs are critical for binding and inhibition of PP1 phosphatase activity; PfI2 can overcome the G2/M checkpoint in Xenopus oocytes (GVBD), and peptides from PfI2 competing with RVxF binding sites in PP1 show antiplasmodial activity against blood-stage parasites in vitro. Biochemical interaction assays, in vitro phosphatase activity assay, site-directed mutagenesis of PfI2 motifs, Xenopus oocyte GVBD assay, antiplasmodial peptide assay BMC biology High 23837822
2014 PF3D7_1414400 (PP1) engages PfI2 through a two-site interaction: the canonical RVxF motif and a second FxxR/KxR/K motif (residues D94–T117); NMR spectroscopy identified the second site; mutation of either motif alone prevented PfI2-triggered GVBD in Xenopus oocytes, while only combined mutations abolished PP1 binding, showing that tight two-site association is necessary for PP1 regulation; a penetrating peptide derived from the FxxR/KxR/K motif accumulated specifically in infected erythrocytes and displayed antiplasmodial activity. NMR spectroscopy, site-directed mutagenesis of both binding motifs, Xenopus oocyte GVBD functional assay, antiplasmodial peptide assay with infected erythrocyte accumulation The FEBS journal High 25132288
2016 PF3D7_1414400 (PP1) directly interacts with PfeIF2β (eukaryotic translation initiation factor 2β) via two binding motifs (FGEKKK and KVAW); both motifs are required for PP1 binding and for inducing GVBD in Xenopus oocytes; PP1 and PfeIF2β co-localize in cytoplasm and nuclear fractions of P. falciparum, suggesting regulation of PP1 in both compartments; attempts to knock out PfeIF2β were unsuccessful, indicating its essential role. In vitro interaction assay, site-directed mutagenesis of PfeIF2β binding motifs, Xenopus oocyte GVBD assay, subcellular fractionation, reverse genetics Frontiers in microbiology Medium 27303372
2018 PF3D7_1414400 (PP1) directly interacts with PfRCC-PIP in vitro and forms a complex with it in the parasite; in Xenopus oocytes, RCC-PIP interacts with endogenous PP1 and acts in synergy with suboptimal progesterone to trigger oocyte maturation, suggesting a regulatory (activating) effect on PP1; RCC-PIP also interacts with the parasite kinase CDPK7 via its RCC1 motifs, indicating it is a dual kinase/phosphatase anchoring protein. In vitro pull-down, co-immunoprecipitation from parasite extracts, Xenopus oocyte maturation assay, reverse genetics Frontiers in microbiology Medium 30429842
2019 PF3D7_1414400 (PP1) interacts with the pseudokinase PfpTKL via its SAM/RVxF motif; PP1 catalytic activity in Xenopus oocytes is modulated in an RVxF-dependent manner by pTKL, suggesting a scaffolding/regulatory role for pTKL toward PP1. In vitro interaction assay (SAM and RVxF motif mapping), Xenopus oocyte PP1 activity assay, reverse genetics in P. berghei Scientific reports Medium 31148576
2019 In P. berghei, PP1 (orthologue of PF3D7_1414400) interacts with GEXP15 via the RVxF binding motif; GEXP15 increases PP1 phosphatase activity in vitro; mutation of the RVxF motif abolishes this regulatory effect; immunoprecipitation with mass spectrometry confirmed the PP1–GEXP15 complex in both schizont and gametocyte stages, with associated proteins linked to spliceosome and proteasome pathways. In vitro interaction assay (RVxF mutagenesis), in vitro phosphatase activity assay, co-immunoprecipitation with mass spectrometry, phenotypic analysis of GEXP15-deficient P. berghei PLoS pathogens High 31348803
2020 PF3D7_1414400 (PP1) is absolutely essential for egress of P. falciparum merozoites from host erythrocytes (but only required for efficient replication); phosphoproteomic and chemical-genetic analysis identified two direct functional targets of PP1 for egress: a HECT E3 ubiquitin ligase and GCα (a fusion guanylyl cyclase/phospholipid transporter); phosphatidylcholine stimulates PP1-dependent egress, implicating PP1 in lipid sensing via GCα. Conditional knockdown (chemical-genetic), phosphoproteomics, chemical-genetic epistasis analysis, phosphatidylcholine stimulation assay Nature communications High 32669539
2021 PP1 (P. berghei orthologue of PF3D7_1414400) is required for mitotic exit during rapid male gamete formation and potentially for establishing cell polarity during zygote development in the mosquito midgut; conditional knockdown combined with live-cell imaging, RNA-seq, and proteomics showed these roles in sexual/mosquito stages. Conditional gene knockdown, real-time live-cell imaging, ultrastructural imaging, RNA-seq, proteomics Communications biology High 34145386
2022 In P. berghei, PP1 (orthologue of PF3D7_1414400) forms a complex with PbLRR1 (Sds22 orthologue) in both asexual and sexual stages; PbLRR1 inhibits PP1 phosphatase activity; LRR1 depletion adversely affects oocyst development; phosphoproteomic analysis showed that Inhibitor-3 (I3) is drastically hypophosphorylated in LRR1-depleted parasites, suggesting that the phosphorylation status of I3 is controlled by the PP1–LRR1 complex. Co-immunoprecipitation from parasite extracts, in vitro phosphatase activity assay, genetic depletion of PbLRR1, interactome/phosphoproteomics Open biology High 35920043
2022 PF3D7_1414400 (PP1) interactome mapped by mCherry-affinity pulldown followed by mass spectrometry in P. berghei asexual and sexual stages; PP1c-associated proteins are enriched in cellular component assembly (both stages), biosynthetic processes/translation (schizonts), and protein transport (gametocytes); nuclear export mediator factor and peptidyl-prolyl cis-trans isomerase were identified as potential targets of the PP1c/I2 complex in both stages. mCherry affinity pulldown from transgenic P. berghei, mass spectrometry interactome mapping International journal of molecular sciences Medium 35162991
2023 PF3D7_1414400 (PP1) directly interacts with GEXP15 in P. falciparum via the RVxF binding motif; this interaction enhances PP1 phosphatase activity; GEXP15 localizes predominantly to the nucleus in late asexual stages (live microscopy of tagged line); immunoprecipitation/mass spectrometry identified GEXP15 interaction with ribosomal and RNA-binding proteins, and pull-down of GEXP15 domains confirmed binding to the ribosomal complex via the GYF domain. In vitro interaction assay (RVxF mutagenesis), in vitro phosphatase activity assay, live microscopy of GFP/mCherry-tagged line, co-immunoprecipitation with mass spectrometry, recombinant domain pull-down International journal of molecular sciences High 37628837
2025 PF3D7_1414400 (PP1) controls the initiation of egress by regulating rounding-up of the parasitophorous vacuole, a step that is almost completely abolished in PP1-null schizonts; PP1 acts upstream of the cGMP-PKG signaling pathway by modulating basal guanylyl cyclase alpha (GCα) activity, thus controlling cGMP homeostasis and PKG-dependent Ca2+ signaling; the calcium ionophore A23187 bypasses the PP1-null egress defect, demonstrating Ca2+-dependence of rounding-up downstream of PP1. Conditional PP1 inducible knockout (iKO), fluorescent reporters of parasitophorous vacuole morphology, live microscopy of egress kinetics, chemical rescue with egress inducers and Ca2+ ionophore PLoS pathogens High 39808636
2025 PF3D7_1414400 (PP1) regulates the mechanical properties (deformability and permeability) of mature gametocyte-infected erythrocytes through dephosphorylation of protein kinase A (PKA) substrates, which is required for gametocyte persistence in the bloodstream; PP1 also controls gametocyte activation into gametes via stimulation of the cGMP/PKG signaling pathway. Conditional depletion of PP1 in gametocytes, functional analysis of gametocyte deformability and permeability, phosphoproteomic identification of PKA substrates, cGMP/PKG pathway assay, mosquito transmission assays mBio High 40823845

Source papers

Stage 0 corpus · 22 papers · ranked by NIH iCite citations
Year Title Journal Citations PMID
2002 Characterisation and expression of a PP1 serine/threonine protein phosphatase (PfPP1) from the malaria parasite, Plasmodium falciparum: demonstration of its essential role using RNA interference. Malaria journal 58 12057017
2008 The protein-phosphatome of the human malaria parasite Plasmodium falciparum. BMC genomics 57 18793411
2005 Use of penetrating peptides interacting with PP1/PP2A proteins as a general approach for a drug phosphatase technology. Molecular pharmacology 45 16387795
2020 Co-option of Plasmodium falciparum PP1 for egress from host erythrocytes. Nature communications 40 32669539
2006 Protein phosphatase 1, a Plasmodium falciparum essential enzyme, is exported to the host cell and implicated in the release of infectious merozoites. Cellular microbiology 40 16548885
2006 Regulation of protein phosphatase type 1 and cell cycle progression by PfLRR1, a novel leucine-rich repeat protein of the human malaria parasite Plasmodium falciparum. Molecular microbiology 34 16629662
2002 Plasmodium falciparum protein phosphatase type 1 functionally complements a glc7 mutant in Saccharomyces cerevisiae. International journal for parasitology 30 12062492
2013 Plasmodium falciparum encodes a conserved active inhibitor-2 for Protein Phosphatase type 1: perspectives for novel anti-plasmodial therapy. BMC biology 27 23837822
2021 Protein phosphatase 1 regulates atypical mitotic and meiotic division in Plasmodium sexual stages. Communications biology 18 34145386
2011 Plasmodium falciparum inhibitor-3 homolog increases protein phosphatase type 1 activity and is essential for parasitic survival. The Journal of biological chemistry 18 22128182
2019 Essential role of GEXP15, a specific Protein Phosphatase type 1 partner, in Plasmodium berghei in asexual erythrocytic proliferation and transmission. PLoS pathogens 15 31348803
2014 Identification of a Plasmodium falciparum inhibitor-2 motif involved in the binding and regulation activity of protein phosphatase type 1. The FEBS journal 14 25132288
2016 Identification of Plasmodium falciparum Translation Initiation eIF2β Subunit: Direct Interaction with Protein Phosphatase Type 1. Frontiers in microbiology 12 27303372
2020 The Multifaceted Role of Protein Phosphatase 1 in Plasmodium. Trends in parasitology 11 33036936
2018 Characterization of a Protein Phosphatase Type-1 and a Kinase Anchoring Protein in Plasmodium falciparum. Frontiers in microbiology 11 30429842
2019 Plasmodium pseudo-Tyrosine Kinase-like binds PP1 and SERA5 and is exported to host erythrocytes. Scientific reports 9 31148576
2025 The malaria parasite PP1 phosphatase controls the initiation of the egress pathway of asexual blood-stages by regulating the rounding-up of the vacuole. PLoS pathogens 7 39808636
2022 Plasmodium berghei leucine-rich repeat protein 1 downregulates protein phosphatase 1 activity and is required for efficient oocyst development. Open biology 5 35920043
2016 Phosphatases are emerging as novel druggable targets in Plasmodium. Future microbiology 4 27159136
2022 Mapping PP1c and Its Inhibitor 2 Interactomes Reveals Conserved and Specific Networks in Asexual and Sexual Stages of Plasmodium. International journal of molecular sciences 3 35162991
2023 Characterization of GEXP15 as a Potential Regulator of Protein Phosphatase 1 in Plasmodium falciparum. International journal of molecular sciences 1 37628837
2025 Plasmodium falciparum PP1 phosphatase is a key regulator of malaria parasite transmission. mBio 0 40823845