Isolation and Proteomic Analysis of Rhoptry-Enriched Fractions from Cryptosporidium parvum

Rhoptries are unique secretory/excretory organelles that are found exclusively in the Apicomplexa, and their contents are discharged at the time of invasion and are critical in the establishment of productive infection. Several rhoptry proteins have been identified in Toxoplasma gondii, Plasmodium falciparum and Neospora caninum and have been linked not only with the parasites’ adhesion and invasion processes but also with their intracellular pathways. To date, only one Cryptosporidium parvum rhoptry protein candidate related to TgRON1 of T. gondii and PfASP of P. falciparum has been reported. Subcellular fractionation of sporozoites was performed to obtain highly purified organelles. One-dimensional sodium dodecyl sulfate–polyacrylamide gel electrophoresis followed by liquid chromatography coupled with mass spectrometry was applied for fraction analysis, and 22 potential novel rhoptry proteins were detected by protein domain analysis using online softwares. Twenty-two potential novel rhoptry proteins were detected. A protein with T. gondii and N. caninum rhoptry protein homologs and some proteins with domains similar to that of T. gondii rhoptry proteins were identified. These novel candidate proteins may be considered targets for researching the invasion pathway of C. parvum and the pathogenic mechanisms of rhoptry proteins. The present work provides a starting point towards the elucidation of the repertoire and function of C. parvum rhoptry proteins.