In tachyzoites, required for the cellular trafficking of guanylate cyclase GC to the cell membrane and for GC guanylate cyclase activity. Interacts with guanylate cyclase GC; the interaction regulates guanylate cyclase GC trafficking and catalytic activity. In intracellular tachyzoites, localizes to the apical cap, to the cytoplasm in disperse foci and to the residual body. Conditional knockout in tachyzoites severely impairs lytic parasite growth in host cells (PubMed:30742070). Guanylate cyclase GC is unstable and remains trapped along the secretory pathway (PubMed:30742070). Tachyzoite natural and induced egress, motility and invasion are impaired (PubMed:30742070). Loss of microneme secretion in response to phosphatidic acid or a decrease in vacuolar pH (PubMed:30742070).