Cloning and expression in E. coli of a synthetic gene for the bacteriocidal protein caltrin/seminalplasmin.

A synthetic gene coding for the bacteriocidal protein caltrin/seminalplasmin was constructed and expressed in Escherichia coli as a fusion with beta-galactosidase. The gene was designed with a recognition site for the plasma protease, Factor Xa, coded for immediately prior to the N-terminus of caltrin. The beta-galactosidase-caltrin fusion protein was cleaved with Factor Xa to give caltrin, which was identified by its size on SDS-PAGE, its ability to react with an antiserum raised to the N-terminal nonapeptide of caltrin and its N-terminal amino acid sequence. After partial purification, synthetic caltrin was found to be active in an assay involving inhibition of growth of E.coli.