Differences in binding modes of enantiomers of 1-acetamido boronic acid based protease inhibitors: Crystal structures of gamma-chymotrypsin and subtilisin Carlsberg complexes

摘要

In order to probe the structural basis of stereoselectivity in the serine protease family, a series of enantiomeric boronic acids RCH2CH(NHCOCH3)B(OH)(2) has been synthesized and kinetically characterized as transition-state analog inhibitors using alpha-chymotrypsin and subtilisin Carlsberg as model systems. When the R-substituent in this series was changed from a p-chlorophenyl to a l-naphthyl group, alpha-chymotrypsin, but not subtilisin, reversed its usual preference for L-enantiomers and bound more tightly to the D-enantiomer [Martichonok, V., & Jones, J. B. (1996)J. Aln. Chem. Sec. 118, 950-958]. The structural factors responsible for the differences in stereoselectivity between the two enzymes have been explored by X-ray crystallographic examination of subtilisin Carlsberg and gamma-chymotrypsin complexes of the L-and D-enantiomers of p-chlorophenyl and l-naphthyl boronic acid derivatives. In both enzymes, the L-isomers of the inhibitors, which are more closely related to the natural L-amino acid substrates, form tetrahedral adducts, covalently linking the central boron atom and O-gamma of the catalytic serine. The D-isomers, however, differ in the way they interact with subtilisin or gamma-chymotrypsin. With subtilisin, both the D-p-chlorophenyl and D-l-naphthyl inhibitor complexes form covalent Ser O-gamma-to-boron bonds, but with gamma-chymotrypsin, the same inhibitors lead to novel tetrahedral adducts covalently linking both Ser195 O-gamma and His57 N-epsilon 2 covalently via the boron atom. [References: 42]