Cysteine-S-nitrosylation inhibits Rop5-mediated immune evasion in Toxoplasma gondii.

Reactive nitrogen species (RNS) are a mechanism to control microbial infections conserved across the host species of the obligate intracellular parasite Toxoplasma gondii. Cysteine S-nitrosylation (SNO) is a reversible post-translational modification that controls complex cell behaviors by regulating protein interactions and signal transduction events. Here we identified a cluster of T. gondii secreted effector proteins that are SNO-modified in a host inducible nitric oxide synthetase (iNOS)-dependent manner. Among these were the rhoptry protein 5 (ROP5) paralogs, which are the major virulence determinants in T. gondii and an immunodominant antigen in B6 mice. ROP5 was necessary for Type I and Type II parasites to evade IFN-γ-mediated immune clearance in iNOS-deficient macrophages. RNS led to the loss of ROP5 association with the parasitophorous vacuole membrane, which is necessary for the known functions of ROP5. Infection with ROP5 knockout parasites rescued the susceptibility of iNOS-deficient mice to infection with Type II T. gondii. Together, these data indicate that RNS can promote cell-autonomous parasite clearance by inhibiting the function of ROP5 paralogs at the parasitophorous vacuole membrane.