PIC1

PIC1 (PF3D7_1229300) is a component of the PhIL1-associated protein complex within the inner membrane complex (IMC) of P. falciparum, identified through its physical association with PhIL1 (PMID:28985225, PMID:34324609). It was first recovered as a PhIL1-interacting protein in gametocytes by immunoprecipitation and mass spectrometry (PMID:28985225), and its association with PhIL1 was subsequently confirmed by reciprocal co-immunoprecipitation in the merozoite IMC (PMID:34324609). Functionally, conditional knockdown of PIC1 causes defects in merozoite segmentation and abrogates the reorientation/gliding step that follows initial erythrocyte attachment, thereby blocking host cell invasion while leaving the initial attachment event intact (PMID:34324609). Beyond its role as a PhIL1-complex component required for merozoite morphogenesis and invasion, no further molecular mechanism, catalytic activity, or structural detail for PIC1 has been characterized in the available corpus.

1. 2017 Medium

   Before this work it was unknown which proteins constitute the PhIL1 network; identifying PIC1 as a PhIL1 co-purifying protein established it as a member of the gametocyte IMC-associated complex.

   Evidence Immunoprecipitation and mass spectrometry using PhIL1 as bait in P. falciparum gametocytes

   PMID:28985225

   Open questions at the time

   • Single Co-IP/MS experiment without reciprocal validation for PIC1
   • No functional role for PIC1 defined beyond complex membership
   • Direct versus indirect interaction with PhIL1 not distinguished
2. 2021 Low

   Extending the PhIL1 interactome to asexual blood stages, proximity labeling placed PIC1 as an IMC-proximal candidate, indicating the association is not restricted to gametocytes.

   Evidence BioID proximity-dependent biotinylation and mass spectrometry with PhIL1 as bait in asexual blood-stage parasites

   PMID:33830607

   Open questions at the time

   • PIC1 identified as candidate but not explicitly confirmed among the GFP-validated subset
   • Proximity does not establish direct interaction
   • No functional consequence of PIC1 loss tested in this study
3. 2021 High

   It was unknown whether PIC1 has a functional role; reciprocal Co-IP plus conditional knockdown established PIC1 as a PhIL1-complex member required for merozoite segmentation and for the post-attachment reorientation step of invasion.

   Evidence Co-immunoprecipitation and conditional knockdown with invasion, reorientation, and segmentation readouts in P. falciparum merozoites

   PMID:34324609

   Open questions at the time

   • Molecular mechanism linking PIC1 loss to segmentation and gliding defects unresolved
   • No structural model or biochemical activity for PIC1
   • Whether the invasion defect is a direct role or a secondary consequence of segmentation failure is not resolved

• The molecular function of PIC1 within the PhIL1/IMC complex and how it mechanistically enables merozoite reorientation and gliding remain undefined.
• No catalytic or biochemical activity assigned to PIC1
• Direct binding partners beyond PhIL1 not mapped
• Structural basis of complex assembly unknown