RAB5B

In Toxoplasma gondii, Rab5b regulates a cycle of plasma membrane endocytosis and exocytosis during intracellular replication, functioning together with MyoF to control formation of the plasma membrane reservoir (PMR) (PMID:41026795). Genetic perturbation of the Rab5b-dependent endo-exocytic balance disrupts PMR formation, producing increased number and size of PMRs and ultimately a complete loss of membrane organization (PMID:41026795). Despite this membrane-organizing role, Rab5b is dispensable for completion of the parasite's lytic cycle, in contrast to its ortholog in Plasmodium falciparum (PMID:41026795). Beyond these findings, no further biochemical mechanism, effector, or interaction detail for Rab5b has been characterized in the available corpus.

1. 2025 Medium

   Whether a Rab5-family GTPase governs plasma membrane turnover during Toxoplasma replication was unresolved; conditional perturbation established that Rab5b drives an endo-exocytic membrane cycle required for proper plasma membrane reservoir formation together with MyoF.

   Evidence Conditional depletion/genetic perturbation with live imaging of membrane dynamics and assessment of PMR number and size in Toxoplasma gondii

   PMID:41026795

   Open questions at the time

   • No orthogonal biochemical validation of the Rab5b-MyoF functional relationship reported
   • Direct effectors, GEFs/GAPs, or membrane-recruitment mechanism of Rab5b not identified
   • Molecular basis linking Rab5b activity to PMR size control not defined
2. 2025 Medium

   Whether Rab5b is essential for the parasite's replicative lytic cycle was untested; genetic depletion showed it is dispensable, distinguishing Toxoplasma Rab5b from the essential Plasmodium falciparum ortholog.

   Evidence Genetic depletion of Rab5b with assessment of lytic cycle completion in Toxoplasma gondii

   PMID:41026795

   Open questions at the time

   • Single method (depletion) reported without complementation/rescue
   • Basis for the divergence in essentiality between Toxoplasma and Plasmodium orthologs not addressed

• The molecular effectors, regulatory GTPase cycle, and membrane-trafficking pathway through which Rab5b controls PMR dynamics remain unknown.
• No Rab5b effectors or interaction partners identified beyond a functional link to MyoF
• Mechanism of Rab5b recruitment to the plasma membrane not characterized
• No structural or biochemical characterization of Rab5b GTPase activity