Affinage · Plasmodium

PPKL

PF3D7_1466100 · protein phosphatase containing kelch-like domains

Annotated
2026-09-08
5 papers in source corpus 4 papers cited in narrative 7 extracted findings

Mechanistic narrative

Synthesis pass · prose summary of the discoveries below

PPKL (PF3D7_1466100) is an enzymatically active protein serine/threonine phosphatase that governs the differentiation, cytoskeletal organization, and motility of the transmission-stage ookinete (PMID:23028336). In P. falciparum, the gene encodes a phosphatase with a large N-terminal extension carrying tandem kelch-like repeats predicted to form beta-propeller structures that mediate protein–protein interactions, and a catalytic domain of the PP1-related PPP class bearing five unique inserts (PMID:12034355, PMID:9803420). In P. berghei, the ortholog is preferentially expressed in female gametocytes and ookinetes, is produced in schizonts and maternally inherited, and localizes focally to the ookinete apical tip (PMID:23028336, PMID:22957089). Genetic deletion of ppkl in P. berghei produces abnormal ookinete development, dissociates apical microtubules from the inner-membrane complex, mislocalizes tubulin, actin, and the micronemal protein CTRP, and yields immotile parasites unable to invade the mosquito midgut epithelium; active-site mutagenesis establishes that catalytic phosphatase activity is required for this role (PMID:23028336, PMID:22957089). Loss of PPKL alters global phosphorylation during early zygote development and elevates dozi mRNA, while microneme cargo secretion itself is not abolished despite loss of the pronounced apical microneme distribution (PMID:23028336, PMID:22957089). The direct substrates and interaction partners of the kelch beta-propeller have not been experimentally identified in the available corpus.

Mechanistic history

Synthesis pass · year-by-year structured walk · 4 steps
  1. 1998 Low

    The initial question was what class of enzyme this locus encodes; sequence analysis established it as a putative serine/threonine phosphatase with an atypical architecture distinguishing it from canonical PP1 enzymes.

    Evidence Genomic sequence and domain analysis in P. falciparum

    PMID:9803420

    Open questions at the time
    • Sequence-only; no in vitro or cellular activity demonstrated
    • Function of the five catalytic inserts unknown
    • No expression or localization data
  2. 2002 Low

    Whether the large N-terminal extension had a defined structure was open; phylogenetic and domain analysis predicted tandem kelch repeats forming a beta-propeller for protein interactions and placed the catalytic domain in the PP1 group.

    Evidence Bioinformatic/phylogenetic domain prediction in P. falciparum

    PMID:12034355

    Open questions at the time
    • Beta-propeller structure not experimentally validated
    • No interaction partners identified for the kelch domain
    • Catalytic classification is computational
  3. 2012 High

    The physiological stage and requirement of PPKL were unknown; knockout and expression analysis in P. berghei showed it is an active phosphatase enriched in female gametocytes and ookinetes and essential for ookinete development, motility, and midgut invasion.

    Evidence GFP fusion, gene knockout, cytoskeletal/CTRP immunofluorescence, motility and invasion assays in P. berghei

    PMID:23028336

    Open questions at the time
    • Direct phosphatase substrates not identified
    • Molecular link between phosphatase activity and microtubule–IMC coupling unresolved
    • Cause of dozi mRNA elevation unclear
  4. 2012 High

    Whether catalytic activity per se drives the phenotype and where the protein acts were open; active-site mutagenesis and localization showed catalytic activity is required and that PPKL acts focally at the ookinete apical tip, is maternally inherited, and shapes apical complex deployment without abolishing microneme secretion.

    Evidence Gene disruption, active-site mutants, fluorescence/electron microscopy, microneme secretion assay in P. berghei

    PMID:22957089

    Open questions at the time
    • Dephosphorylation targets at the apical tip not defined
    • Mechanism coupling PPKL to microtubule–IMC assembly unknown
    • Role of the kelch beta-propeller in recruitment untested

Open questions

Synthesis pass · forward-looking unresolved questions
  • The direct substrates dephosphorylated by PPKL and the interaction partners engaged by its kelch beta-propeller remain unidentified, leaving the molecular mechanism linking its phosphatase activity to apical microtubule–IMC organization unresolved.
  • No substrate identified
  • No experimentally validated kelch-domain interactor
  • No structural model of the phosphatase–cytoskeleton interface

Mechanism profile

Synthesis pass · controlled-vocabulary classification
No controlled-vocabulary terms were assigned to this entry.

Evidence

Reading pass · 7 per-paper findings extracted from the source corpus
Year Finding Method Journal Conf PMIDs
2012 PPKL (PF3D7_1466100 ortholog in P. berghei) is an enzymatically active protein phosphatase preferentially expressed in female gametocytes and ookinetes; C-terminal GFP fusion confirmed active phosphatase activity in these stages. C-terminal GFP fusion, reverse genetics, stage-specific expression analysis PLoS pathogens Medium 23028336
2012 Deletion of ppkl in P. berghei caused abnormal ookinete development and differentiation, dissociated apical microtubules from the inner-membrane complex, generated an immotile phenotype, and prevented invasion of the mosquito midgut epithelium, demonstrating a stage-specific essential role for PPKL in parasite motility and transmission. Gene knockout (ppkl deletion), indirect immunofluorescence for tubulin, actin, and CTRP localization, ookinete motility and invasion assays PLoS pathogens High 23028336
2012 Loss of PPKL in P. berghei ookinetes altered the localization of cytoskeletal tubulin, actin, and the micronemal protein CTRP, and increased mRNA expression of dozi (a RNA helicase vital to zygote development), with global phosphorylation changes detected in the first hours of zygote development. Indirect immunofluorescence, qRT-PCR, global phosphoproteomics of ookinete differentiation (1.5–24 h post-fertilisation) PLoS pathogens Medium 23028336
2012 PPKL (PBANKA_132950) is produced in schizonts and female gametocytes and is maternally inherited; it localizes focally at the ookinete apical tip, linking its phosphatase activity to correct deployment of the apical complex and microtubule cytoskeleton. Gene disruption, active-site mutagenesis, fluorescence localization, ookinete morphology and invasion assays PloS one High 22957089
2012 Active-site mutants of PPKL confirmed that enzymatic phosphatase activity is required for normal ookinete development; ppkl(-) ookinetes display an extended apical protrusion and lack a pronounced apical distribution of micronemes, yet microneme cargo secretion is not abolished. Active-site mutagenesis, gene disruption, electron/fluorescence microscopy, microneme secretion assay PloS one Medium 22957089
2002 The N-terminal domain of PPKL (PfPPalpha in P. falciparum) contains tandem kelch-like repeats predicted to form beta-propeller structures capable of mediating protein-protein interactions; the catalytic domain is more closely related to the PP1 group than to other PPP phosphatases. Bioinformatics/phylogenetic analysis, domain architecture prediction Cellular signalling Low 12034355
1998 The P. falciparum PPKL gene encodes a putative protein serine/threonine phosphatase with a large N-terminal extension and five unique inserts in the catalytic domain relative to canonical PP1-family phosphatases. Genomic sequence analysis, domain identification Molecular and biochemical parasitology Low 9803420

Source papers

Stage 0 corpus · 5 papers · ranked by NIH iCite citations
Year Title Journal Citations PMID
2012 A unique protein phosphatase with kelch-like domains (PPKL) in Plasmodium modulates ookinete differentiation, motility and invasion. PLoS pathogens 76 23028336
2008 The protein-phosphatome of the human malaria parasite Plasmodium falciparum. BMC genomics 57 18793411
1998 A putative protein serine/threonine phosphatase from Plasmodium falciparum contains a large N-terminal extension and five unique inserts in the catalytic domain. Molecular and biochemical parasitology 34 9803420
2012 A unique Kelch domain phosphatase in Plasmodium regulates ookinete morphology, motility and invasion. PloS one 25 22957089
2002 Protein Ser/Thr phosphatases with kelch-like repeat domains. Cellular signalling 25 12034355