A stage-specific calcium-binding protein expressed in eggs of Schistosoma mansoni.

A cDNA sequence encoding a Schistosoma mansoni egg antigen SmE16 was cloned in Escherichia coli. The 16-kDa polypeptide deduced from the nucleotide sequence is related to the calmodulin and troponin C gene families of calcium-binding proteins, and the most significant homology is displayed around the four calcium-binding sites. The antigen was expressed as a hybrid protein of the bacteriophage MS2 polymerase. The MS2-SmE16 fusion protein binds calcium, as demonstrated via ligand blotting with 45Calcium. The detection of antibodies to the purified recombinant egg antigen in sera of schistosomiasis patients opens up the possibility that it may be a useful candidate for the development of serodiagnostic assays. The function of the protein in the egg is presently unclear.