1v0a

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spinqualitylabelsall models 1v0a, resolution 1.98Å Show:Asymmetric Unit Biological Assembly Drag the structure with the mouse to rotate   Export Animated Image

FAMILY 11 CARBOHYDRATE-BINDING MODULE OF CELLULOSOMAL CELLULASE LIC26A-CEL5E OF CLOSTRIDIUM THERMOCELLUM

Overview

Modular glycoside hydrolases that attack recalcitrant polymers generally, contain noncatalytic carbohydrate-binding modules (CBMs), which play a, critical role in the action of these enzymes by localizing the appended, catalytic domains onto the surface of insoluble polysaccharide substrates., Type B CBMs, which recognize single polysaccharide chains, display ligand, specificities that are consistent with the substrates hydrolyzed by the, associated catalytic domains. In enzymes that contain multiple catalytic, domains with distinct substrate specificities, it is unclear how these, different activities influence the evolution of the ligand recognition, profile of the appended CBM. To address this issue, we have characterized, the properties of a family 11 CBM (CtCBM11) in Clostridium thermocellum, Lic26A-Cel5E, an enzyme that contains GH5 and GH26 catalytic domains that, display beta-1,4- and beta-1,3-1,4-mixed linked endoglucanase activity, respectively. Here we show that CtCBM11 binds to both beta-1,4- and, beta-1,3-1,4-mixed linked glucans, displaying K(a) values of 1.9 x 10(5), 4.4 x 10(4), and 2 x 10(3) m(-1) for, Glc-beta1,4-Glc-beta1,4-Glc-beta1,3-Glc, Glc-beta1,4-Glc-beta1,4-Glc-beta1,4-Glc, and, Glc-beta1,3-Glc-beta1,4-Glc-beta1,3-Glc, respectively, demonstrating that, CBMs can display a preference for mixed linked glucans. To determine, whether these ligands are accommodated in the same or diverse sites in, CtCBM11, the crystal structure of the protein was solved to a resolution, of 1.98 A. The protein displays a beta-sandwich with a concave side that, forms a potential binding cleft. Site-directed mutagenesis revealed that, Tyr(22), Tyr(53), and Tyr(129), located in the putative binding cleft, play a central role in the recognition of all the ligands recognized by, the protein. We propose, therefore, that CtCBM11 contains a single, ligand-binding site that displays affinity for both beta-1,4- and, beta-1,3-1,4-mixed linked glucans.

About this Structure

1V0A is a Single protein structure of sequence from Clostridium thermocellum with CA and SO4 as ligands. Active as Cellulase, with EC number 3.2.1.4 Structure known Active Site: AC1. Full crystallographic information is available from OCA.

Reference

The family 11 carbohydrate-binding module of Clostridium thermocellum Lic26A-Cel5E accommodates beta-1,4- and beta-1,3-1,4-mixed linked glucans at a single binding site., Carvalho AL, Goyal A, Prates JA, Bolam DN, Gilbert HJ, Pires VM, Ferreira LM, Planas A, Romao MJ, Fontes CM, J Biol Chem. 2004 Aug 13;279(33):34785-93. Epub 2004 Jun 10. PMID:15192099

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