Toxoplasma gondii rhoptry discharge factor 3 is essential for invasion and microtubule-associated vesicle biogenesis.

Toxoplasma gondii rhoptry discharge factor 3 is essential for invasion and microtubule-associated vesicle biogenesis.

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Rhoptries are specialized secretory organelles conserved across the Apicomplexa phylum, essential for host cell invasion and critical for subverting KERA 3 MASK of host cellular and immune functions.They contain proteins and membranous materials injected directly into the host cells, participating in parasitophorous vacuole formation.Toxoplasma gondii tachyzoites harbor 8 to 12 rhoptries, 2 of which are docked to an apical vesicle (AV), a central element associated with a rhoptry secretory apparatus prior to injection into the host cell.This parasite is also equipped with 5 to 6 microtubule-associated vesicles, presumably serving as AV replenishment MOTHERWORT for iterative rhoptry discharge.

Here, we characterized a rhoptry protein, rhoptry discharge factor 3 (RDF3), crucial for rhoptry discharge and invasion.RDF3 enters the secretory pathway, localizing near the AV and associated with the rhoptry bulb.Upon invasion, RDF3 dynamically delocalizes, suggesting a critical role at the time of rhoptry discharge.Cryo-electron tomography analysis of RDF3-depleted parasites reveals irregularity in microtubule-associated vesicles morphology, presumably impacting on their preparedness to function as an AV.

Our findings suggest that RDF3 is priming the microtubule-associated vesicles for rhoptry discharge by a mechanism distinct from the rhoptry secretory apparatus contribution.