Proteolytic processing and host nuclear targeting of the novel effector GRA84 in Toxoplasma gondii

Toxoplasma gondii and its relative Neospora caninum are apicomplexan pathogens that secrete an array of dense granule proteins into the parasitophorous vacuole and host cell, where they play roles in acquiring nutrients and modulating host cell functions. Here, we characterize the novel GRA protein GRA84 in T. gondii and N. caninum, which is secreted into the PV and exported into the host cell nucleus. Disruption of Toxoplasma GRA84 does not affect in vitro parasite replication or establishment or maintenance of the chronic infection in vivo. We show that this effector uses the MYR translocon to traverse the vacuolar membrane and is dependent on the aspartyl protease ASP5 for its export to the host nucleus. We demonstrate that GRA84 undergoes processing that removes over 90 amino acids from its N-terminus, an event that is independent of ASP5. We also use mutagenesis to disrupt processing and show that maturation is critical for transit across the vacuolar membrane. Taken together, this work identifies GRA84 in both T. gondii and N. caninum and reveals an unusual processing event that is necessary for maturation of the protein and export of the effector into the host cell.