The immunological selection of recombinant peptides from Cryptosporidium parvum reveals 14 proteins expressed at the sporozoite stage, 7 of which are conserved in other apicomplexa.

Cryptosporidium parvum is an apicomplexan parasite that infects various mammals, including humans, yet no specific treatment has been developed. C. parvum sporozoites are the initial invasive forms that infect the intestinal epithelial cells of the host. To identify novel proteins expressed at the sporozoite stage, we analyzed around 100 recombinant peptides from a C. parvum expression library with an anti-sporozoite serum. We selected 14 peptides recognized by the serum and identified the corresponding genes in the C. parvum genomic database. Twelve of the 14 genes had been previously annotated in the genome database, whereas 2 of them (the CpC2C and the CpMT1 genes) were newly identified. We established that 13 of the 14 genes are expressed in the sporozoites and that the only multi-exon gene (CpC2C) produces a detectable amount of unspliced mRNA. The search for conserved domains revealed various structural features of these proteins, including signal peptides, transmembrane domains, WD repeats, C2 domain, and Myosin tails. Interestingly, among the 14 proteins, we also identified a putative rhomboid (CpRom) which, similarly to those found in other apicomplexa, could be involved in the host-cell invasion process. The search for similar proteins, conducted on 13 proteins, showed that 4 of these proteins belong to widely conserved families, whereas 7 of them are of apicomplexan origin and only 2 are restricted to the Cryptosporidium genus.