title: Crystal structure of the bifunctional soybean Bowman-Birk inhibitor at 0.28-nm resolution. Structural peculiarities in a folded protein conformation.
abstract: The Bowman-Birk inhibitor from soybean is a small protein that contains a binary arrangement of trypsin-reactive and chymotrypsin-reactive subdomains. In this report, the crystal structure of this anticarcinogenic protein has been determined to 0.28-nm resolution by molecular replacement from crystals grown at neutral pH. The crystal structure differs from a previously determined NMR structure [Werner, M. H. & Wemmer, D. E. (1992) Biochemistry 31, 999-1010] in the relative orientation of the two enzyme-insertion loops, in some details of the main chain trace, in the presence of favourable contacts in the trypsin-insertion loop, and in the orientation of several amino acid side chains. The proximity of Met27 and Gln48 in the X-ray structure contradicts the solution structure, in which these two side chains point away from each other. The significant effect of a Met27-->Ile replacement on the inhibitory activity of the chymotrypsin-reactive subdomain agrees with the X-ray structure. Exposed hydrophobic patches, the presence of charged amino acid residues, and the presence of water molecules in the protein interior are in contrast to standard proteins that comprise a hydrophobic core and exposed polar amino acids.
authors.affiliation: Max-Planck-Institut für Biophysik, Frankfurt am Main, Germany.
authors.forename: R H
authors.initials: RH
authors.lastname: Voss
authors.forename: U
authors.initials: U
authors.lastname: Ermler
authors.forename: L O
authors.initials: LO
authors.lastname: Essen
authors.forename: G
authors.initials: G
authors.lastname: Wenzl
authors.forename: Y M
authors.initials: YM
authors.lastname: Kim
authors.forename: P
authors.initials: P
authors.lastname: Flecker
mesh_terms: D000595:Amino Acid Sequence; D002918:Chymotrypsin / Q000037:antagonists & inhibitors; D018360:Crystallography, X-Ray; D007700:Kinetics; D009682:Magnetic Resonance Spectroscopy; D008958:Models, Molecular; D008969:Molecular Sequence Data; D011487:Protein Conformation; D017433:Protein Structure, Secondary; D014358:Trypsin Inhibitor, Bowman-Birk Soybean / Q000737:chemistry*; D014867:Water
chemical_list: D014358:Trypsin Inhibitor, Bowman-Birk Soybean; D014867:Water; D002918:Chymotrypsin