1ovw

From Proteopedia

Revision as of 15:41, 18 December 2007

ENDOGLUCANASE I COMPLEXED WITH NON-HYDROLYSABLE SUBSTRATE ANALOGUE

Overview

Endoglucanase I (EG I) is a cellulase, from glycosyl hydrolase family 7, which cleaves the beta-1,4 linkages of cellulose with overall retention of, configuration. The structure of the EG I from Fusarium oxysproum, complexed to a nonhydrolyzable thiooligosaccharide substrate analogue, has, been determined by X-ray crystallography at a resolution of 2.7 A, utilizing the 4-fold noncrystallographic symmetry present in the, asymmetric unit. The electron density map clearly reveals the presence of, three glucosyl units of the inhibitor, consistent with the known number of, sugar-binding subsites, located at the active site of the enzyme in the, -2, -1, and +1 subsites, i.e., actually spanning the point of enzymatic, cleavage. The pyranose ring at the point of potential enzymatic cleavage, is clearly distorted from the standard 4C1 chair as was originally, suggested for beta-retaining enzymes by Phillips [Ford, L.O., Johnson, L.N., Machin, P. A., Phillips, D.C., & Tijan, T. (1974) J. Mol. Biol, 88, 349-371]. The distortion observed goes beyond the "sofa" conformation, observed in previous studies and results in a conformation whose salient, feature is the resulting quasi-axial orientation for the glycosidic bond, and leaving group, as predicted by stereoelectronic theory. An almost, identical conformation has recently been observed in a complex of, chitobiase with its unhydrolyzed substrate [Tews, I., Perrakis, A., Oppenheim, A., Dauter, Z., Wilson, K. S., & Vorgias, C. E. (1996) Nat., Struct. Biol. 3, 638-648]. The striking similarity between these two, complexes extends beyond the almost identical pyranose ring distortion., The overlap of the two respective sugars places the enzymatic nucleophile, of endoglucanase I in coincidence with the C2 acetamido oxygen of, N-acetylglucosamine in the catalytic site of the chitobiase, substantiating the involvement of this group in the catalytic mechanism of, chitobiase and related chitinolytic enzymes. The endoglucanase I complex, with the thiosaccharide substrate analogue clearly illustrates the, potential of nonhydrolyzable sulfur-linked oligosaccharides in the, elucidation of substrate binding and catalysis by glycosyl hydrolases.

About this Structure

1OVW is a Single protein structure of sequence from Fusarium oxysporum with NAG and DP5 as ligands. Active as Cellulase, with EC number 3.2.1.4 Known structural/functional Sites: , , and . Full crystallographic information is available from OCA.

Reference

Structure of the Fusarium oxysporum endoglucanase I with a nonhydrolyzable substrate analogue: substrate distortion gives rise to the preferred axial orientation for the leaving group., Sulzenbacher G, Driguez H, Henrissat B, Schulein M, Davies GJ, Biochemistry. 1996 Dec 3;35(48):15280-7. PMID:8952478

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