CHC

CHC (PF3D7_1219100) is the clathrin heavy chain of Plasmodium falciparum and functions in coated-vesicle traffic at the parasite periphery, where it is required for cytostome-mediated endocytosis of host cytosol (PMID:41451970). It localizes predominantly at the parasite periphery and near the cis-Golgi, and ultrastructural APEX2-based electron microscopy places it at coated vesicle-like structures and at the collars of cytostomes (PMID:41451970). Distinct from the canonical clathrin function in receptor-mediated endocytosis in other eukaryotes, CHC associates predominantly with AP-1 and cytostome-formation proteins and does not interact with the AP-2 complex, as reciprocal clathrin-nanobody immunoprecipitation and interactome mass spectrometry both failed to recover AP-2 subunits (PMID:32098816, PMID:41451970). Conditional knockdown produces abnormally elongated cytostome tubes and impaired hemoglobin uptake, establishing CHC as functionally required for cytostome-mediated host-cytosol endocytosis (PMID:41451970). Beyond these findings, no further mechanistic detail—including structural characterization or the biochemical basis of its AP-1 selectivity—has been characterized in the available corpus.

1. 2020 Medium

   Whether P. falciparum clathrin uses the canonical AP-2 adaptor for endocytosis was unknown; reciprocal immunoprecipitation resolved which adaptor complexes CHC engages.

   Evidence Reverse immunoprecipitation with a clathrin nanobody followed by mass spectrometry

   PMID:32098816

   Open questions at the time

   • Does not identify which specific AP-1 subunits mediate the interaction
   • Does not establish the functional consequence of AP-2 absence
   • Absence of AP-2 in the pulldown does not exclude transient or context-specific contacts
2. 2025 Low

   Proximity labelling asked whether CHC participates in Golgi-to-microneme traffic by placing it near a PIP-binding protein.

   Evidence BioID-type proximity labelling mass spectrometry of PfPX2 (Pf3D7_0704400)

   PMID:41125830

   Open questions at the time

   • Single proximity-labelling experiment with no direct validation of the CHC–PfPX2 interaction
   • Does not establish that CHC functions in the Golgi-to-microneme pathway
   • Proximity does not distinguish direct binding from shared compartment residence
3. 2026 Medium

   The subcellular site of CHC action was unresolved; multi-modal imaging localized it to coated vesicles and cytostome collars, defining where it operates.

   Evidence Live-cell imaging, immunofluorescence colocalization, and APEX2-based electron microscopy in trophozoites

   PMID:41451970

   Open questions at the time

   • Does not resolve whether the peripheral and cis-Golgi pools represent distinct functional roles
   • Ultrastructural assignment does not establish the composition of the coats it forms
4. 2026 Medium

   Whether CHC is functionally required for host-cytosol uptake was unknown; conditional knockdown established a causal role in cytostome-mediated endocytosis.

   Evidence Conditional knockdown with cytostome-morphology and hemoglobin-uptake readouts, plus interactome mass spectrometry confirming AP-1 (not AP-2) association

   PMID:41451970

   Open questions at the time

   • Mechanism by which loss of CHC produces elongated cytostome tubes is not defined
   • Does not identify the molecular step (invagination, scission, coat assembly) that fails on knockdown
   • Single-lab loss-of-function without orthogonal genetic complementation

• How CHC selectively partners with AP-1 rather than AP-2 and how it drives cytostome scission remain undefined.
• No structural model of the CHC coat or its adaptor interface
• The biochemical basis of AP-1 selectivity is uncharacterized
• The CHC–PfPX2 link and any Golgi-to-microneme role remain unvalidated