RAB11A

Toxoplasma gondii Rab11A is a small GTPase that governs vesicular trafficking at multiple stages of the parasite life cycle by directing the delivery of membrane and secretory cargo to specific cellular destinations (PMID:19165333, PMID:32463830). During cytokinesis it supplies new plasma membrane to nascent daughter cells, and its loss produces daughters with incompletely formed Inner Membrane Complex and a block at a late stage of division; this membrane traffic is coupled to the glideosome motor through physical association with MTIP/MLC1, implicating an MTIP-Myosin motor in Rab11A-driven IMC maturation (PMID:19165333). Rab11A additionally drives cytoskeleton-dependent transport and constitutive secretion of dense granules, regulates transmembrane protein delivery to the plasma membrane during replication, and mediates apically polarized delivery that controls MIC2 secretion and early secretory events during host cell invasion (PMID:32463830). Its activity is regulated by phosphorylation by TgCDPK7, which is critical for intracellular development and protein trafficking, and by the ER-localized TBC-domain GAP TBC9, which physically interacts with Rab11A and functions in early vesicular transport and daughter IMC formation (PMID:33635921, PMID:38762629). On the host side, Toxoplasma sequesters host Rab11A-positive class I FIP vesicles into the parasitophorous vacuole intravacuolar network in a TgGRA2/GRA6-dependent manner, where they are lipolytically processed by the phospholipase TgLCAT, and host autophagy limits parasite access to these vesicles to restrict replication (PMID:29070609, PMID:35274991, PMID:36532461).

1. 2009 High

   Established the first cellular role for apicomplexan Rab11A by asking what drives membrane delivery during parasite cell division, showing it is required to build daughter cell surfaces.

   Evidence Dominant-negative/ablation of Rab11A with live imaging and phenotypic readout of IMC formation and cytokinesis, plus association with the MTIP/MLC1 glideosome component

   PMID:19165333

   Open questions at the time

   • Direct GTPase cycle/effector biochemistry not resolved
   • MTIP association shown by a single co-IP without reciprocal validation
   • Vesicle cargo composition not defined
2. 2017 High

   Extended Rab11A biology to the host-parasite interface by asking whether Toxoplasma exploits host Rab11A vesicles, demonstrating selective sequestration into the PV and their lipolytic processing.

   Evidence Correlative light/EM plus genetic deletion of gra2/gra6 and TgLCAT overexpression with quantitative microscopy of intra-PV GFP-Rab11A vesicles

   PMID:29070609

   Open questions at the time

   • Mechanism by which GRA2/GRA6 stabilize tubules for capture not resolved
   • TgLCAT-Rab11A degradation link rests on single overexpression experiment
   • Nutrient/cargo actually acquired not directly identified
3. 2020 High

   Defined the secretory scope of parasite Rab11A by asking which trafficking events it controls, revealing roles in dense granule transport/secretion, transmembrane protein delivery, and apically polarized MIC2 secretion during invasion.

   Evidence Loss-of-function of Rab11A with live imaging of dense granule and Rab11A-GFP dynamics plus secretion assays including MIC2

   PMID:32463830

   Open questions at the time

   • Effectors linking Rab11A to the cytoskeleton not identified
   • How apical polarization of Rab11A vesicles is established is unknown
   • Direct versus indirect effect on MIC2 secretion not dissected
4. 2021 Medium

   Addressed how parasite Rab11A activity is regulated by identifying it as a substrate of TgCDPK7, linking a kinase signal to trafficking and intracellular development.

   Evidence Quantitative phosphoproteomics of TgCDPK7 knockout with functional validation of phosphosite importance

   PMID:33635921

   Open questions at the time

   • Functional consequence of the specific phosphorylation on Rab11A GTPase activity not defined
   • Whether phosphorylation alters effector binding unknown
   • Single-study phosphoproteomic identification
5. 2022 Medium

   Refined the host vesicle recruitment mechanism by asking which host Rab11A vesicle subclass is captured, showing selectivity for class I FIP (FIP5) but not class II FIP (FIP3) vesicles, and demonstrating host autophagy restricts parasite access.

   Evidence Host Rab11A depletion with quantitative microscopy of intra-PV FIP vesicles and dominant-negative FIP3 mutants (MBoC); CRISPR knockout of host atg5/rab11a with replication assays and qRT-PCR (Front Microbiol)

   PMID:35274991 PMID:36532461

   Open questions at the time

   • Parasite receptor/factor that discriminates FIP subclasses not identified
   • Mechanistic link between autophagy and Rab11A vesicle availability unresolved
   • Studies focus on host Rab11A, not parasite Rab11A
6. 2024 Medium

   Identified a candidate regulatory GAP by asking what controls the parasite Rab11A GTPase cycle, showing the ER-localized TBC9 interacts with Rab11A and functions in early transport and daughter IMC formation.

   Evidence Pull-down assay of TBC9 with Rab11A/Rab11B/Rab2, fluorescence localization, and TBC9 loss-of-function phenotyping

   PMID:38762629

   Open questions at the time

   • GAP activity on Rab11A not biochemically demonstrated
   • Interaction shown by a single pull-down without reciprocal validation
   • TBC9 binds multiple Rabs, so Rab11A specificity of its function is unclear

• How Rab11A GTPase cycling, phosphorylation, and GAP regulation are integrated with its distinct effector complexes at each trafficking step remains unresolved.
• No structural or biochemical map of Rab11A GEF/GAP/effector cycle in the parasite
• Direct effectors linking Rab11A to cytoskeletal transport not identified
• Consequences of TgCDPK7 phosphorylation on nucleotide state and effector engagement unknown