title: Differences in binding modes of enantiomers of 1-acetamido boronic acid based protease inhibitors: crystal structures of gamma-chymotrypsin and subtilisin Carlsberg complexes.
abstract: 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 1-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. Am. Chem. Soc. 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 1-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 Ogamma 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-1-naphthyl inhibitor complexes form covalent Ser Ogamma-to-boron bonds, but with gamma-chymotrypsin, the same inhibitors lead to novel tetrahedral adducts covalently linking both Ser195 Ogamma and His57 Nepsilon2 covalently via the boron atom.
authors.affiliation: Department of Biochemistry, University of Toronto, 1 King's College Circle, Toronto, Ontario M5S 1A8, Canada.
authors.forename: V S
authors.initials: VS
authors.lastname: Stoll
authors.forename: B T
authors.initials: BT
authors.lastname: Eger
authors.forename: R C
authors.initials: RC
authors.lastname: Hynes
authors.forename: V
authors.initials: V
authors.lastname: Martichonok
authors.forename: J B
authors.initials: JB
authors.lastname: Jones
authors.forename: E F
authors.initials: EF
authors.lastname: Pai
mesh_terms: D001665:Binding Sites; D001897:Boronic Acids / Q000737:chemistry*; D002918:Chymotrypsin / Q000037:antagonists & inhibitors / Q000737:chemistry*; D018360:Crystallography, X-Ray; D006639:Histidine / Q000737:chemistry; D008958:Models, Molecular; D008968:Molecular Conformation; D008969:Molecular Sequence Data; D011487:Protein Conformation; D012694:Serine / Q000737:chemistry; D015842:Serine Proteinase Inhibitors / Q000737:chemistry*; D013237:Stereoisomerism; D013381:Subtilisins / Q000037:antagonists & inhibitors / Q000737:chemistry*
chemical_list: C110175:(1-acetamido-2-(1-naphthyl)ethyl)boronic acid; C110174:(1-acetamido-2-(4-chlorophenyl)ethyl)boronic acid; D001897:Boronic Acids; D015842:Serine Proteinase Inhibitors; D012694:Serine; D006639:Histidine; D013381:Subtilisins; D002918:Chymotrypsin