Identification of the gene family encoding the 160-kilodalton Trypanosoma cruzi complement regulatory protein.

Trypanosoma cruzi trypomastigotes are exquisitely resistant to the lytic effects of vertebrate complement, and this characteristic contributes to the survival of the parasites in the host bloodstream. Trypomastigotes avoid complement-mediated lysis by the production of a surface glycoprotein that inhibits the formation of the alternative and classical C3 convertase, thus preventing activation and amplification of the complement cascade at the parasite surface. We have developed a monoclonal antibody to the 160-kDa T. cruzi complement regulatory protein (CRP) and describe a one-step immunoaffinity purification procedure. The CRP was purified to homogeneity and subjected to amino-terminal peptide sequence analysis. Based on the protein sequence obtained, the CRP was identified as a member of a large family of trypomastigote-specific genes, and a complete cDNA was isolated and sequenced. The complete coding sequence was cloned in Escherichia coli, and antibodies raised against the full-length recombinant protein reacted specifically with a 160-kDa protein in trypomastigote membrane protein preparations as well as with native, purified CRP. Indirect immunofluorescence revealed that the protein is uniformly expressed at the cell surfaces of trypomastigotes.