Essential rhoptry neck protein that plays an important role in host cell invasion. Upon host invasion by tachyzoites, the protein is injected into the host cell where it functions as a receptor for apical membrane antigen 1 (AMA1) on the parasite. Part of the moving junction (MJ) complex, a ringlike structure formed between the plasma membranes of the apical tip of the parasite and the target host cell. During invasion, the MJ migrates from the anterior to the posterior of the parasite, leading to internalization of the parasite into a parasitophorous vacuole (PV). Component of the moving junction (MJ) complex, composed of AMA1, a transmembrane protein on the parasite surface, and a complex of the rhoptry neck proteins RON2, RON4, RON5 and RON8 localized to the cytoplasmic face of the host plasma membrane. Interacts (via C-terminus) with AMA1 (via ectodomain); RON2 serves as the receptor for AMA1 on the host plasma membrane. AMA1 and the RON proteins are initially in distinct compartments within the parasite, namely the micronemes and the rhoptries, and interaction happens only upon initiation of invasion when the micronemes and rhoptries discharge. Initially localizes to rhoptries, specialized secretory organelles of apicomplexan parasites important for host cell invasion (PubMed:16002398,PubMed:16244709). Upon host invasion by tachyzoites, the protein is injected into the host cell, where it spans the host cell membrane (PubMed:21347343). Belongs to the apicomplexan parasites RON2 family.