PIP3

PIP3 (PF3D7_1430800) is a PhIL1-interacting protein of the Plasmodium falciparum inner membrane complex (IMC) that is required for merozoite morphogenesis and host-cell invasion (PMID:34324609, PMID:28985225). It was defined as a component of a novel PhIL1-associated protein complex that co-exists with the glideosome motor at the merozoite IMC, and independent BioID proximity-labelling using PhIL1 as bait enriched PIP3 in asexual blood-stage parasites, consistent with its IMC localization across stages (PMID:34324609, PMID:33830607). Conditional downregulation of PIP3 causes defective merozoite segmentation and, at the level of invasion, abrogates reorientation/gliding following initial erythrocyte attachment while leaving initial attachment intact, placing PIP3 downstream of attachment in the invasion sequence (PMID:34324609). Beyond its PhIL1 association, IMC localization, and knockdown phenotype, no molecular activity or direct downstream effector of PIP3 has been characterized in the available corpus.

1. 2017 Medium

   The first question was whether PIP3 associates physically with the IMC machinery, answered by identifying it as a binding partner of the IMC protein PhIL1.

   Evidence Immunoprecipitation and mass spectrometry using PhIL1 as bait in P. falciparum gametocytes, with super-resolution and electron microscopy of the complex

   PMID:28985225

   Open questions at the time

   • Does not establish whether PIP3 binds PhIL1 directly or through other complex members
   • No functional role assigned to PIP3 itself in this study
   • Interaction detected in gametocytes, not yet in asexual stages
2. 2021 Medium

   A second question was whether the PhIL1-PIP3 association extends to asexual blood stages, addressed by proximity-labelling confirming PIP3 near PhIL1 at the asexual IMC.

   Evidence BioID proximity-dependent biotinylation with PhIL1 as bait, mass spectrometry, and endogenous GFP-tagging validation in asexual blood-stage P. falciparum

   PMID:33830607

   Open questions at the time

   • Proximity labelling does not distinguish direct binding from spatial neighbourhood
   • Does not assign a function to PIP3 in asexual stages
3. 2021 Medium

   The central functional question — what role PIP3 plays in the parasite life cycle — was answered by showing it is required for merozoite segmentation and for the gliding/reorientation step of erythrocyte invasion.

   Evidence Conditional knockdown with immunoprecipitation-based complex characterization and invasion/reorientation assays in P. falciparum merozoites

   PMID:34324609

   Open questions at the time

   • Molecular activity of PIP3 (enzymatic or structural) not defined
   • Mechanism linking PIP3 loss to reorientation failure unresolved
   • Whether the segmentation defect is upstream of or independent from the invasion defect not distinguished

• It remains unknown what biochemical activity PIP3 contributes to the PhIL1 complex and how its loss mechanistically couples to failed merozoite reorientation and gliding.
• No molecular/enzymatic activity assigned to PIP3
• No structural model or direct-binding map of PIP3 within the PhIL1 complex
• Downstream effectors mediating the reorientation/gliding phenotype unidentified