VPS45

VPS45 (PF3D7_0216400) is an essential endosomal trafficking factor in P. falciparum blood-stage parasites that mediates the delivery of host cell cytosol to the digestive (food) vacuole for hemoglobin degradation (PMID:30581113). Conditional inactivation of VPS45 blocks hemoglobin delivery and causes accumulation of host cell cytosol-filled vesicles, a proportion of which are decorated with phosphatidylinositol 3-phosphate (PI3P), marking them as endosomal intermediates, with a consequent arrest of parasite growth (PMID:30581113). VPS45 acts within a defined endosomal route together with a parasite Rabenosyn-5-like protein (PfRbsn5L) and PfRab5b — but not PfRab5a — and epistasis analysis places this Rbsn5L/VPS45/Rab5b-dependent step downstream of the PfKelch13 compartment (PMID:38820535). Beyond this host cell cytosol uptake pathway, VPS45 is additionally implicated in biogenesis of the inner membrane complex in coordination with the SNARE proteins Stx16 and Stx6 (PMID:33082261). No structural or biochemical characterization of the VPS45 protein itself, or of its direct molecular interactions, has been established in the available corpus.

1. 2018 High

   Establishing whether VPS45 has a required role in blood-stage parasite biology, this work showed it is essential for delivering host cell cytosol to the digestive vacuole for hemoglobin degradation.

   Evidence DiCre-based conditional inactivation in P. falciparum with fluorescence microscopy, vesicle accumulation phenotyping, and PI3P marker co-localization

   PMID:30581113

   Open questions at the time

   • Direct molecular partners of VPS45 mediating vesicle transport not identified
   • Biochemical/structural basis of VPS45 function not resolved
   • Whether VPS45 acts in vesicle formation, budding, or fusion not distinguished
2. 2020 Medium

   Extending VPS45 function beyond endocytic trafficking, this work implicated it in inner membrane complex (alveoli) biogenesis in coordination with SNARE proteins Stx16 and Stx6.

   Evidence Functional genetic analysis of SEC1/Munc18 and SNARE proteins in T. gondii and P. falciparum with vesicular trafficking assays

   PMID:33082261

   Open questions at the time

   • IMC biogenesis role inferred from SNARE partner perturbation rather than direct VPS45 loss-of-function in this context
   • Direct interaction of VPS45 with Stx16/Stx6 not biochemically demonstrated
   • Mechanism linking VPS45 to alveolar membrane formation unresolved
3. 2024 High

   Defining the pathway context of VPS45, this work placed it in a discrete endosomal route with PfRbsn5L and PfRab5b acting downstream of the PfKelch13 compartment.

   Evidence Single and conditional double protein inactivation in P. falciparum with PI3P/Rab5b co-localization and epistasis analysis

   PMID:38820535

   Open questions at the time

   • Direct physical interaction among VPS45, PfRbsn5L, and PfRab5b not shown biochemically
   • Specificity determinants selecting Rab5b over Rab5a unknown
   • Molecular link between the PfKelch13 compartment and the VPS45 step not defined

• The biochemical activity of VPS45, its direct binding partners, and its structural basis for coordinating endosomal transport remain undefined.
• No direct protein-protein interaction data for VPS45 in the corpus
• No structural model of VPS45 established
• Whether the endosomal and IMC roles are mechanistically related is unknown