VPS33

PF3D7_0935200 (VPS33) is a conserved core subunit of the Vps-C tethering module shared by the HOPS and CORVET complexes in Plasmodium falciparum (PMID:24086721, PMID:40626728). Bioinformatic analysis across apicomplexan genomes first placed VPS33 among the four canonical Vps-C core subunits (VPS11, VPS16, VPS18, VPS33) retained from the ancestral eukaryotic tethering machinery (PMID:24086721, PMID:40198740), and immunoprecipitation-mass spectrometry using PfVps16 as bait experimentally confirmed VPS33 as a binding partner within this complex, alongside VPS11, VPS18, and the CORVET component VPS3 (PMID:40626728). At the process level the Vps-C core is required for endocytosis and host-cell cytosol uptake in trophozoites — its depletion causes developmental arrest and accumulation of endosomes that fail to fuse with the digestive vacuole — and for trafficking of rhoptry and microneme proteins to apical invasion organelles in schizonts (PMID:40198740). VPS33's individual molecular contribution has not been directly resolved in the available corpus: C-terminal tagging of VPS33 with GFP or HA was unsuccessful and appears detrimental to function, so the loss-of-function phenotypes are attributed to the complex as a whole rather than to VPS33 tested in isolation (PMID:40198740).

1. 2013 Low

   Whether P. falciparum retains the ancestral multi-subunit tethering machinery was unknown; identifying VPS33 as a conserved Vps-C core subunit established that the HOPS/CORVET complement persists in Apicomplexa.

   Evidence Comparative genomic/bioinformatic analysis across twelve apicomplexan genomes

   PMID:24086721

   Open questions at the time

   • Computational prediction only, with no experimental validation of VPS33 expression, interactions, or function
   • Does not distinguish VPS33's role in HOPS versus CORVET
   • No subcellular localization established
2. 2025 Medium

   To test whether the predicted VPS33 physically assembles into the Vps-C complex, PfVps16 was used as bait; recovery of VPS33 confirmed its membership in the canonical tethering complex in vivo.

   Evidence Immunoprecipitation followed by mass spectrometry with PfVps16 as bait

   PMID:40626728

   Open questions at the time

   • VPS33 was detected as a VPS16 interactor but was not independently validated as bait, leaving direct binding partners of VPS33 undefined
   • Does not resolve whether VPS33 participates in HOPS, CORVET, or both
   • Stoichiometry and architecture of the complex not determined
3. 2025 Medium

   The cellular requirement of the Vps-C core was addressed by conditional depletion, showing the complex is needed for endocytic fusion with the digestive vacuole and for apical organelle biogenesis, though VPS33's individual role could not be isolated because it could not be tagged.

   Evidence FKBP-based conditional knockdown of core HOPS/CORVET subunits with ultrastructure-expansion microscopy and organelle-marker co-localization; attempted C-terminal SLI tagging of VPS33 was unsuccessful

   PMID:40198740

   Open questions at the time

   • Phenotypes are attributed to the complex as a whole; VPS33 itself could not be tagged or depleted, so its specific contribution is inferred not measured
   • C-terminal tagging is detrimental, leaving no working genetic handle on endogenous VPS33
   • No mechanistic detail on how VPS33 contributes to tethering or SNARE-mediated fusion

• It remains unknown what VPS33 contributes to Vps-C function as an individual subunit, and how it can be genetically or biochemically interrogated without disrupting its function.
• No tagging or depletion strategy exists that preserves VPS33 function
• Direct binding partners and structural role of VPS33 within the complex are undefined
• No discrimination of VPS33's function between the HOPS and CORVET complexes