Conformational studies on peptides as enzyme inhibitors: Chymotripsin inhibitors using Bowman-Birk type as models

A complete structural characterization in solution, by NMR spectroscopy, and in vacuo, by molecular dynamic simulations, of two synthetic peptide fragments from SBBI (Soybean Bowman–Birk Inhibitor) is reported. Peptide 197, corresponding to the SBBI(41–49) chymotrypsin recognition site, has free N- and C-terminal groups, while peptide 212, corresponding to the Leu 16-SBBI(14–22) has uncharged and fully protected terminal ends. Peptide 212 shows significant anti-chymotryptic activity while peptide 197 is inactive. Neither of the two peptides shows anti-tryptic activity. The structural information obtained in the present paper suggests a quantitative structure–activity relationship which may help both in understanding the mechanism of action of protease inhibitors, and in providing new directions for the rational design of more specific and potent inhibitors.