Cryptosporidium parvum glycoprotein gp40 localizes to the sporozoite surface by association with gp15

Cryptosporidium spp. are waterborne apicomplexan parasites responsible for outbreaks of diarrheal disease worldwide. Antigens involved in zoite invasion into host cells have been the focus of many investigations as these may prove to be good vaccine candidates. gp40/15 is a zoite antigen synthesized as a precursor protein and proteolytically cleaved into the mature glycoproteins, gp40 and gp15. gp15 is anchored in the sporozoite membrane by a glycosylphosphatidyl inositol moiety, while gp40 is predicted to be soluble. However, gp40 bears epitopes that recognize a host cell receptor. If this interaction is important for zoite invasion, then gp40 must have some mechanism of associating with the parasite membrane. In these studies we demonstrate that gp40 and gp15 co-localize to the surface membrane of sporozoites and merozoites, and co-immunoprecipitate, suggesting that these antigens associate after proteolytic cleavage to generate a protein complex capable of linking zoite and host cell surfaces.