2exo

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spinqualitylabelsall models 2exo, resolution 1.8Å Show:Asymmetric Unit Biological Assembly Drag the structure with the mouse to rotate   Export Animated Image

CRYSTAL STRUCTURE OF THE CATALYTIC DOMAIN OF THE BETA-1,4-GLYCANASE CEX FROM CELLULOMONAS FIMI

Overview

beta-1,4-Glycanases, principally cellulases and xylanases, are responsible, for the hydrolysis of plant biomass. The bifunctional, beta-1,4-xylanase/glucanase Cex from the bacterium Cellulomonas fimi, one, of a large family of cellulases/xylanases, depolymerizes oligosaccharides, and releases a disaccharide unit from the substrate nonreducing end., Hydrolysis occurs with net retention of the anomeric configuration of the, sugar through a double-displacement mechanism involving a covalent, glycosyl-enzyme intermediate. The active site nucleophile, Glu233, has, been unambiguously identified by trapping of such an intermediate [Tull et, al. (1991) J. Biol. Chem. 266, 15621-15625] and the acid/base catalyst, Glu127, by detailed kinetic analysis of mutants [MacLeod et al. (1994), Biochemistry 33, 6371-6376]. However, little is known about the enzyme's, overall folding and its active site architecture. We report here the, high-resolution crystal structure of the catalytic domain of Cex. The, atomic structure refinement results in a model that includes 2400 protein, atoms and 45 water molecules, with an R-factor of 0.217 for data extending, to 1.8-A resolution. The protein forms an eight-parallel-stranded, alpha/beta-barrel, which is a novel folding pattern for a microbial, beta-glycanase. The active site, inferred from the location of Glu233, Glu127, and other conserved residues, is an open cleft on the, carboxy-terminal end of the alpha/beta-barrel. An extensive, hydrogen-bonding network stabilizes the ionization states of the key, residues; in particular, the Asp235-His205-Glu233 hydrogen-bonding network, may play a role in modulating the ionization state of Glu233 and in, controlling local charge balance during the reaction.

About this Structure

2EXO is a Single protein structure of sequence from Cellulomonas fimi. Active as Cellulose 1,4-beta-cellobiosidase, with EC number 3.2.1.91 Full crystallographic information is available from OCA.

Reference

Crystal structure of the catalytic domain of the beta-1,4-glycanase cex from Cellulomonas fimi., White A, Withers SG, Gilkes NR, Rose DR, Biochemistry. 1994 Oct 25;33(42):12546-52. PMID:7918478

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