Molecular characterisation of a Cryptosporidium parvum rhoptry protein candidate related to the rhoptry neck proteins TgRON1 of Toxoplasma gondii and PfASP of Plasmodium falciparum.

Given the lack of knowledge on the rhoptry proteins of Cryptosporidium parvum, we searched for putative members of this protein class in the CryptoDB database using as queries known Toxoplasma gondii rhoptry molecules. We cloned a C. parvum sporozoite cDNA of 4269bp encoding the sushi domain-containing protein cgd8_2530, which shared low amino acid sequence identity, yet a highly conserved domain architecture with the rhoptry neck proteins TgRON1 of T. gondii and PfASP of Plasmodium falciparum. On denaturing and native gels, cgd8_2530 migrated at approximately 150 and 1000 kDa, respectively, suggesting an involvement in a multi-subunit protein complex. Immunoflorescence localised cgd8_2530 to a single, elongated area anterior to sporozoite micronemes and showed protein relocation to the parasite-host cell interface in early epicellular stages. Our data strongly suggest a rhoptry localization for the newly characterised protein, which was therefore renamed C. parvum putative rhoptry pro