Cloning and expression of a gene encoding Sm16, an anti-inflammatory protein from Schistosoma mansoni

The gene encoding Sm16, an anti-inflammatory, immunomodulatory protein present abundantly in secretions of the infective stages of Schistosoma mansoni was cloned and partially characterized. A data base analysis showed sequence homology to an earlier reported schistosomular stathmin-like gene sequences reported in dbEST and Genbank. The putative gene coding for Sm16 is of 500 bp with an open reading frame of 117 aa that included an N-terminal signal peptide sequence of 18 aa. There are three potential sites for phosphorylation (two serine and one tyrosine residue) but no glycosylation sites in the sequence. The coding region of Sm16 was amplified from cercarial cDNA, cloned and expressed in bacterial and insect expression systems. The purified recombinant protein showed strong immunoreactivity with a polyclonal rabbit anti-Sm16 antibody raised against the native anti-inflammatory protein Sm16. Contrary to earlier report, this gene appears to be not stage-specific. Metabolic labeling studies suggested that Sm16 is phosphorylated and is synthesized by both cercariae and schistosomula of S. mansoni. Sequence homology with human stathmin, a cell cycle regulatory phospho protein, was 30%. However, when probed with specific antibodies, no cross reactivity was observed between Sm16 and human stathmin.