A novel multi-domain mucin-like glycoprotein of Cryptosporidium parvum mediates invasion.

Cryptosporidium parvum is a protozoan parasite which produces self-limited disease in immunocompetent hosts and devastating, persistent diarrhea in immunocompromised individuals. There is no effective treatment for cryptosporidiosis and little is known about the basic biology of the organism. Cloning and sequence analysis of the gene encoding GP900, a previously identified > 900 kDa glycoprotein, predicts a mucin-like glycoprotein composed of distal cysteine-rich domains separated by polythreonine domains and a large membrane proximal N-glycosylated core region. A trinucleotide repeat composed predominantly of the triplet ACA encodes the threonine domains. GP900 is stored in micronemes prior to appearance on the surface of invasive forms. The concentration of native GP900 which inhibits 50% (IC50) of invasion in vitro is low picomolar; the IC50 for a recombinant cysteine rich-domain is low nanomolar. These observations indicate that GP900 is a parasite ligand for a host receptor involved in attachment/invasion and suggest that immunotherapy or chemotherapy directed against GP900 may be feasible.