Role of Rabenosyn-5 and Rab5b in host cell cytosol uptake reveals conservation of endosomal transport in malaria parasites

PLoS Biol. 2024 May 31;22(5):e3002639. doi: 10.1371/journal.pbio.3002639. eCollection 2024 May.

Abstract

Vesicular trafficking, including secretion and endocytosis, plays fundamental roles in the unique biology of Plasmodium falciparum blood-stage parasites. Endocytosis of host cell cytosol (HCC) provides nutrients and room for parasite growth and is critical for the action of antimalarial drugs and parasite drug resistance. Previous work showed that PfVPS45 functions in endosomal transport of HCC to the parasite's food vacuole, raising the possibility that malaria parasites possess a canonical endolysosomal system. However, the seeming absence of VPS45-typical functional interactors such as rabenosyn 5 (Rbsn5) and the repurposing of Rab5 isoforms and other endolysosomal proteins for secretion in apicomplexans question this idea. Here, we identified a parasite Rbsn5-like protein and show that it functions with VPS45 in the endosomal transport of HCC. We also show that PfRab5b but not PfRab5a is involved in the same process. Inactivation of PfRbsn5L resulted in PI3P and PfRab5b decorated HCC-filled vesicles, typical for endosomal compartments. Overall, this indicates that despite the low sequence conservation of PfRbsn5L and the unusual N-terminal modification of PfRab5b, principles of endosomal transport in malaria parasite are similar to that of model organisms. Using a conditional double protein inactivation system, we further provide evidence that the PfKelch13 compartment, an unusual apicomplexa-specific endocytosis structure at the parasite plasma membrane, is connected upstream of the Rbsn5L/VPS45/Rab5b-dependent endosomal route. Altogether, this work indicates that HCC uptake consists of a highly parasite-specific part that feeds endocytosed material into an endosomal system containing more canonical elements, leading to the delivery of HCC to the food vacuole.

MeSH terms

  • Animals
  • Cytosol* / metabolism
  • Endocytosis
  • Endosomes* / metabolism
  • Erythrocytes / metabolism
  • Erythrocytes / parasitology
  • Host-Parasite Interactions
  • Humans
  • Malaria, Falciparum / metabolism
  • Malaria, Falciparum / parasitology
  • Plasmodium falciparum* / genetics
  • Plasmodium falciparum* / metabolism
  • Protein Transport
  • Protozoan Proteins* / genetics
  • Protozoan Proteins* / metabolism
  • Vacuoles / metabolism
  • Vesicular Transport Proteins / genetics
  • Vesicular Transport Proteins / metabolism
  • rab5 GTP-Binding Proteins* / metabolism

Substances

  • rab5 GTP-Binding Proteins
  • Protozoan Proteins
  • Vesicular Transport Proteins

Grants and funding

This work was funded by the European Research Council (ERC, grant 101021493 to TS) and the DFG funded research training group GRK2771 (to TS). MS thanks for funding from the Jürgen Manchot Stiftung and AGS thanks for funding from EMBO (Postdoctoral Fellowship EMBO ALTF Number 166-2022). The funders had no role in study design, data collection and analysis, decision to publish, or preparation of the manuscript.