EPS15

PF3D7_1025000 (EPS15) is a membrane-associated endocytic protein of Plasmodium falciparum that mediates uptake of host-cell cytosol (hemoglobin) at the parasite plasma membrane throughout the asexual blood stages (PMID:26284889, PMID:38039338, PMID:33842474, PMID:32310999, PMID:34765267, PMID:33095255). Live-cell imaging of GFP-tagged EPS15 traces vesicles that originate at the parasite plasma membrane, migrate through the cytosol, and terminate at a Nile Red-positive neutral-lipid storage structure juxtaposed to the food vacuole; pharmacological inhibition of endocytosis blocks both vesicle development and their delivery to this site, establishing EPS15 in endocytic vesicle generation (PMID:26284889). EPS15 is a component of the clathrin-independent, AP-2-labelled cytostome-proximal 'K13 compartment', where reciprocal proximity biotinylation shows it physically associates with K13, and its conditional inactivation reduces hemoglobin uptake to the digestive vacuole at both ring and trophozoite stages while conferring ring-stage artemisinin tolerance (PMID:38039338, PMID:33842474, PMID:32310999, PMID:34765267, PMID:33095255). Beyond this endocytic/host-cytosol-uptake role, no further biochemical mechanism (e.g. defined enzymatic activity or direct structural role) for EPS15 has been characterized in the available corpus.

1. 2015 Medium

   It was unknown whether PF3D7_1025000 participated in membrane trafficking; GFP imaging established it as a membrane-bound protein driving endocytic vesicles from the parasite plasma membrane to a neutral-lipid storage site near the food vacuole.

   Evidence GFP-fusion time-lapse imaging, Nile Red staining, food-vacuole marker co-staining, associated-protein proteomics, and pharmacological endocytosis inhibition in P. falciparum

   PMID:26284889

   Open questions at the time

   • Molecular partners driving vesicle scission or transport not defined beyond generic 'endocytosis modulators'
   • Direct biochemical activity of the protein not established
   • Relationship of the lipid-storage endpoint to hemoglobin catabolism not resolved
2. 2020 High

   The identity of the endocytic machinery underlying host-cell-cytosol uptake and artemisinin response was unclear; reciprocal proximity biotinylation and conditional inactivation placed EPS15 in the AP-2-labelled K13 compartment as a K13 interactor required for hemoglobin uptake and ring-stage artemisinin susceptibility.

   Evidence Reciprocal DiQ-BioID, co-localization imaging, conditional inactivation, dextran uptake assay, and ring-stage survival assay in P. falciparum

   PMID:32310999 PMID:33095255 PMID:33842474 PMID:34765267 PMID:38039338

   Open questions at the time

   • Whether the EPS15–K13 interaction is direct or bridged by other compartment proteins is not resolved
   • Structural basis of EPS15 recruitment to the cytostome-proximal compartment unknown
   • Mechanism linking reduced endocytosis to artemisinin tolerance not defined at the molecular level
3. 2023 Low

   It was unclear whether EPS15 associates with the clathrin/AP-1 trafficking machinery; GFP-trap interactome pulldowns detected EPS15 at low abundance with PfCLC and AP-1, indicating at most a loose or indirect link rather than core membership.

   Evidence GFP-trap pulldown with mass spectrometry of PfCLC and AP-1 γ subunit in P. falciparum

   PMID:41451970

   Open questions at the time

   • Single low-abundance pulldown without reciprocal or functional validation of the association
   • Cannot distinguish direct interaction from co-compartmentalization
   • Functional significance of any clathrin/AP-1 link untested
4. 2024 Medium

   Because EPS15 loss confers artemisinin tolerance, it was important to test whether field-derived EPS15 sequence variants drive resistance; engineered isogenic parasites showed none of the EPS15 mutations tested independently reduced artemisinin susceptibility.

   Evidence CRISPR/selection-linked integration of recodonized multi-mutant EPS15 into 3D7 and ring-stage survival assay with dihydroartemisinin

   PMID:38700363

   Open questions at the time

   • Only specific tested variants assessed; other mutations or combinations not excluded
   • Does not address whether EPS15 expression-level changes affect resistance
   • Single lab, single genetic background (3D7)

• The direct biochemical activity of EPS15, its precise molecular role within the K13/AP-2 compartment, and the mechanistic link between its endocytic function and artemisinin tolerance remain undefined.
• No defined enzymatic or structural function for the protein
• Whether EPS15–K13 binding is direct is unresolved
• Mechanism connecting reduced endocytosis to drug tolerance not established