Structure of the complex formed by bovine trypsin and bovine pancreatic trypsin inhibitor. Crystal structure determination and stereochemistry of the contact region

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作者：

A Rühlmann，D Kukla，P Schwager，K Bartels，R Huber

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摘要：

The structure of the complex of bovine trypsin and bovine pancreatic trypsin inhibitor has been determined by crystal structure analysis at 2.8 Å resolution. The structure is closely similar to the model predicted from the structures of the components. The complex is a tetrahedral adduct with a covalent bond between the carbonyl carbon of Lys-15I of the inhibitor and the γ-oxygen of Ser-195 of the enzyme. The imidazole of His-57 is hydrogen-bonded to Asp-102 and the bound seryl γ-oxygen in accord with the histidine being charged. The negatively charged carbonyl oxygen of Lys-15I forms two hydrogen bonds with the amide nitrogens of Gly-193 and Ser-195. Protonation of the leaving group N-H of Ala-16I to form an acyl-complex requires a conformational change of the imidazole of His-57. The tetrahedral adduct is further stabilized by hydrogen bonds between groups at the leaving group side and inhibitor and enzyme, which would be weakened in the acyl-enzyme. The kinetic data of inhibitor-enzyme interaction are reconciled with the structural model, and relations between enzyme-inhibitor interaction and productive enzyme-substrate interaction are proposed.

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关键词：

Animals Cattle Pancreas Aspartic Acid Lysine Serine Glycine Trypsin Trypsin Inhibitors X-Ray Diffraction