VPS16

PF3D7_1239900 (VPS16) is a core subunit of the P. falciparum Vps-C/HOPS/CORVET membrane-tethering machinery that operates in the parasite's endolysosomal system across the asexual erythrocytic cycle (PMID:40626728, PMID:40198740). It physically associates with the four canonical Vps-C members (Vps11, Vps16, Vps18, Vps33) and the CORVET-specific component Vps3 (PMID:40626728). Functionally, VPS16 acts at two developmental stages: in trophozoites it is required for fusion of endosomes to the digestive vacuole, supporting endocytic uptake of host-cell cytosol, while in schizonts it is required for correct trafficking of cargo to rhoptries and micronemes, such that its depletion causes developmental arrest with unfused endosomes on one hand and defective merozoite invasion with reduced rhoptry volume on the other (PMID:40198740). Beyond its role as a tethering-complex subunit, VPS16 also co-purifies with three Plasmodium-specific proteins of unknown function, two bearing folds predicted to resemble tethering-complex proteins, consistent with a parasite-specific extension of the canonical Vps-C complex (PMID:40626728).

1. 2013 Low

   Before any functional work, it was unknown whether P. falciparum retained a canonical vesicle-tethering apparatus; comparative genomics placed PF3D7_1239900 within the conserved Vps-C core, establishing it as a candidate HOPS/CORVET subunit in the apicomplexan endolysosomal system.

   Evidence Comparative genomic/bioinformatic analysis across twelve apicomplexan genomes

   PMID:24086721

   Open questions at the time

   • Computational prediction only, no direct experiment on this gene
   • Does not establish physical assembly into a complex
   • No cellular localization or function tested
2. 2025 Medium

   The predicted complex membership was tested directly, showing PF3D7_1239900 physically engages all four canonical Vps-C members and the CORVET-specific Vps3, confirming it as an assembled tethering-complex subunit rather than merely a sequence homolog.

   Evidence Reciprocal immunoprecipitation and mass spectrometry in P. falciparum

   PMID:40626728

   Open questions at the time

   • Single lab, single study without orthogonal validation of individual interactions
   • Does not resolve HOPS versus CORVET stoichiometry
   • Does not map interaction interfaces
3. 2025 Low

   To test whether the parasite complex is more than the canonical core, co-IP identified three Plasmodium-specific interactors of PF3D7_1239900, two with tethering-like predicted folds, raising the possibility of a parasite-specific extension of Vps-C.

   Evidence Immunoprecipitation, mass spectrometry, and structural fold prediction

   PMID:40626728

   Open questions at the time

   • Structural assignment is prediction-only; folds not experimentally verified
   • Functions of the three proteins are unknown
   • Stable incorporation into the complex not demonstrated
4. 2025 Low

   Expression and localization were assessed to place the complex spatially, indicating PF3D7_1239900 is present throughout the asexual cycle and potentially associates with the Golgi and rhoptries in schizonts.

   Evidence Immunofluorescence/co-localization imaging

   PMID:40626728

   Open questions at the time

   • Localization described as 'potential' with a single method
   • Endosomal/digestive-vacuole localization not directly shown
   • No dynamic tracking across stages
5. 2025 Medium

   The functional requirement was established by conditional depletion, revealing a stage-dependent dual role: endosome-to-digestive-vacuole fusion in trophozoites and rhoptry/microneme cargo delivery in schizonts, tying the tethering complex to both nutrient acquisition and merozoite invasion.

   Evidence Conditional knockdown of the HOPS/CORVET core with Giemsa smears, invasion assays, and ultrastructure-expansion microscopy

   PMID:40198740

   Open questions at the time

   • Depletion was of the HOPS/CORVET core, not isolating VPS16-specific contribution
   • Molecular basis of cargo mistargeting not defined
   • Direct tethering activity not reconstituted

• It remains unknown how PF3D7_1239900 switches between endocytic (digestive-vacuole fusion) and secretory (rhoptry/microneme) trafficking roles, and what the three Plasmodium-specific interactors contribute mechanistically.
• No mechanism for stage-specific target-membrane selection
• Roles of parasite-specific subunits uncharacterized
• No structural model of the assembled parasite complex