1ex1

From Proteopedia

Revision as of 14:06, 5 November 2007

BETA-D-GLUCAN EXOHYDROLASE FROM BARLEY

Overview

BACKGROUND: Cell walls of the starchy endosperm and young vegetative, tissues of barley (Hordeum vulgare) contain high levels of, (1-->3,1-->4)-beta-D-glucans. The (1-->3,1-->4)-beta-D-glucans are, hydrolysed during wall degradation in germinated grain and during wall, loosening in elongating coleoptiles. These key processes of plant, development are mediated by several polysaccharide endohydrolases and, exohydrolases. RESULTS:. The three-dimensional structure of barley, beta-D-glucan exohydrolase isoenzyme ExoI has been determined by X-ray, crystallography. This is the first reported structure of a family 3, glycosyl hydrolase. The enzyme is a two-domain, globular protein of 605, amino acid residues and is N-glycosylated at three sites. The first 357, residues constitute an (alpha/beta)8 TIM-barrel domain. The second domain, consists of residues 374-559 arranged in a six-stranded beta sandwich, which contains a beta sheet of five parallel beta strands and one, antiparallel beta strand, with three alpha helices on either side of the, sheet. A glucose moiety is observed in a pocket at the interface of the, two domains, where Asp285 and Glu491 are believed to be involved in, catalysis. CONCLUSIONS: The pocket at the interface of the two domains is, probably the active site of the enzyme. Because amino acid residues that, line this active-site pocket arise from both domains, activity could be, regulated through the spatial disposition of the domains. Furthermore, there are sites on the second domain that may bind carbohydrate, as, suggested by previously published kinetic data indicating that, in, addition to the catalytic site, the enzyme has a second binding site, specific for (1-->3, 1-->4)-beta-D-glucans.

About this Structure

1EX1 is a Single protein structure of sequence from Hordeum vulgare with NAG and GLC as ligands. Active as Glucan 1,3-beta-glucosidase, with EC number 3.2.1.58 Structure known Active Site: GBS. Full crystallographic information is available from OCA.

Reference

Three-dimensional structure of a barley beta-D-glucan exohydrolase, a family 3 glycosyl hydrolase., Varghese JN, Hrmova M, Fincher GB, Structure. 1999 Feb 15;7(2):179-90. PMID:10368285

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