Tuesday, April 25, 2017

A novel dense granule protein, GRA41, regulates timing of egress and calcium sensitivity in Toxoplasma gondii

2017 Apr 24. doi: 10.1111/cmi.12749. [Epub ahead of print]

Toxoplasma gondii is an obligate intracellular apicomplexan parasite with high seroprevalence in humans. Repeated lytic cycles of invasion, replication and egress drive both the propagation and the virulence of this parasite. Key steps in this cycle, including invasion and egress, depend on tightly regulated calcium fluxes and, while many of the calcium-dependent effectors have been identified, the factors that detect and regulate the calcium fluxes are mostly unknown. To address this knowledge gap, we used a forward genetic approach to isolate mutants resistant to extracellular exposure to the calcium ionophore A23187. Through whole genome sequencing and complementation we have determined that a nonsense mutation in a previously uncharacterized protein is responsible for the ionophore resistance of one of the mutants. The complete loss of this protein recapitulates the resistance phenotype and importantly shows defects in calcium regulation and in the timing of egress. The affected protein, GRA41, localizes to the dense granules and is secreted into the parasitophorous vacuole where it associates with the tubulovesicular network (TVN). Our findings support a connection between the TVN and ion homeostasis within the parasite, and thus a novel role for the vacuole of this important pathogen.


GRA41; Toxoplasma gondii; calcium; dense granule; egress; tubulovesicular network

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