1gbt

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spinqualitylabelsall models 1gbt, resolution 2.0Å Show:Asymmetric Unit Biological Assembly Drag the structure with the mouse to rotate   Export Animated Image

STRUCTURE OF AN ACYL-ENZYME INTERMEDIATE DURING CATALYSIS: (GUANIDINOBENZOYL) TRYPSIN

Overview

The crystal and molecular structure of trypsin at a transiently stable, intermediate step during catalysis has been determined by X-ray, diffraction methods. Bovine trypsin cleaved the substrate p-nitrophenyl, p-guanidinobenzoate during crystallization under conditions in which the, acyl-enzyme intermediate, (guanidinobenzoyl)trypsin, was stable., Orthorhombic crystals formed in space group P2(1)2(1)2(1), with a = 63.74, b = 63.54, and c = 68.93 A. This is a crystal form of bovine trypsin for, which a molecular structure has not been reported. Diffraction data were, measured with a FAST (Enraf Nonius) diffractometer. The structure was, refined to a crystallographic residual of R = 0.16 for data in the, resolution range 7.0-2.0 A. The refined model of (guanidinobenzoyl)trypsin, provides insight into the structural basis for its slow rate of, deacylation, which in solution at 25 degrees C and pH 7.4 exhibits a t1/2, of 12 h. In addition to the rotation of the Ser-195 hydroxyl away from, His-157, C beta of Ser-195 moves 0.7 A toward Asp-189 at the bottom of the, active site, with respect to the native structure. This allows formation, of energetically favorable H bonds and an ion pair between the carboxylate, of Asp-189 and the guanidino group of the substrate. This movement is, dictated by the rigidity of the aromatic ring in, guanidinobenzoate--model-building indicates that this should not occur, when arginine, with its more flexible aliphatic backbone, forms the ester, bond with Ser-195. As a consequence, highly ordered water molecules in the, active site are no longer close enough to the scissile ester bond to serve, as potential nucleophiles for hydrolysis.(ABSTRACT TRUNCATED AT 250 WORDS)

About this Structure

1GBT is a Single protein structure of sequence from Bos taurus with CA, SO4 and GBS as ligands. Active as Trypsin, with EC number 3.4.21.4 Full crystallographic information is available from OCA.

Reference

Structure of an acyl-enzyme intermediate during catalysis: (guanidinobenzoyl)trypsin., Mangel WF, Singer PT, Cyr DM, Umland TC, Toledo DL, Stroud RM, Pflugrath JW, Sweet RM, Biochemistry. 1990 Sep 11;29(36):8351-7. PMID:2252895

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