May play a role in host cell invasion. Initially localizes to rhoptries, specialized secretory organelles of apicomplexan parasites important for host cell invasion. Upon host invasion by tachyzoites, the protein is injected into the host cell, where it spans the host cell membrane (By similarity). Readily detected in oocysts (at protein level). Specifically up-regulated in sporozoites, but not in tachyzoites and bradyzoites. Belongs to the apicomplexan parasites RON2 family.