Secretion of correctly processed and folded pancreatic secretory trypsin inhibitor by Bacillus subtilis.

We constructed a plasmid, designated pNPP126, containing a DNA sequence encoding a fusion protein composed of Bacillus amyloliquefaciens neutral protease prepeptide (signal peptide) and human pancreatic secretory trypsin inhibitor (hPSTI), where the mature hPSTI is accurately fused to the 3'-terminal of the prepeptide coding region. It was observed that the strain Bacillus subtilis MT600 harboring pNPP126 could secrete a trypsin inhibitory activity into the culture medium. The N-terminal amino acid sequence, the amino acid composition and the stoichiometry of the purified hPSTI produced by B. subtilis were the same as those of natural hPSTI, indicating that the transformant B. subtilis MT600 (pNPP126) could efficiently secrete the correctly processed and folded hPSTI into the culture medium.