Characterization of Sm13, a tegumental antigen of Schistosoma mansoni

Sm13, a 13-kDa Schistosoma mansoni tegumental antigen, is one of the princi pal polypeptides recognized by antibodies from mice protectively vaccinated with adult-worm tegumental membranes. To obtain the complete gene encoding Sm13 we subcloned and sequenced a cDNA and a fragment of a genomic clone. The collated sequence contains 1088 nucleotides and represents the full-len gth open reading frame of the gene, encoding a protein of 104 amino acids w ith a calculated molecular mass of 11,923 Da, compatible with the native pr otein identified in the tegumental membranes. The sequence derived from gen omic DNA contains a 45-nucleotide intron. The analysis of the predicted pro tein suggests the presence of both N- and C-terminal hydrophobic membrane-s panning segments, and the coding region contains no homology in the current ly available data bases. Additionally, the coding region is preceded by put ative CCAAT and TATA boxes that may be involved in the control of expressio n. Western-blot analysis and indirect immunofluorescence resulted in the id entification of a 13-kDa protein (Sm13) in the tegument of adult worms. The present study reveals that Sm13 behaves as an integral membrane protein up on partitioning in Triton X-114 and that it is present in worms of 3 weeks or older but not in schistosomula or miracidia. Moreover, it is also specif ically recognized by sera from some schistosomiasis patients in enzyme-link ed immunosorbent assay and Western-blot analysis, suggesting that it is imm unogenic in human schistosomiasis.