2c4x

From Proteopedia

Revision as of 08:31, 3 February 2008

STRUCTURAL BASIS FOR THE PROMISCUOUS SPECIFICITY OF THE CARBOHYDRATE-BINDING MODULES FROM THE BETA-SANDWICH SUPER FAMILY

Overview

Enzyme systems that attack the plant cell wall contain noncatalytic, carbohydrate-binding modules (CBMs) that mediate attachment to this, composite structure and play a pivotal role in maximizing the hydrolytic, process. Although xyloglucan, which includes a backbone of beta-1,4-glucan, decorated primarily with xylose residues, is a key component of the plant, cell wall, CBMs that bind to this polymer have not been identified. Here, we showed that the C-terminal domain of the modular Clostridium, thermocellum enzyme CtCel9D-Cel44A (formerly known as CelJ) comprises a, novel CBM (designated CBM44) that binds with equal affinity to cellulose, and xyloglucan. We also showed that accommodation of xyloglucan side, chains is a general feature of CBMs that bind to single cellulose chains., The crystal structures of CBM44 and the other CBM (CBM30) in, CtCel9D-Cel44A display a beta-sandwich fold. The concave face of both CBMs, contains a hydrophobic platform comprising three tryptophan residues that, can accommodate up to five glucose residues. The orientation of these, aromatic residues is such that the bound ligand would adopt the twisted, conformation displayed by cello-oligosaccharides in solution. Mutagenesis, studies confirmed that the hydrophobic platform located on the concave, face of both CBMs mediates ligand recognition. In contrast to other CBMs, that bind to single polysaccharide chains, the polar residues in the, binding cleft of CBM44 play only a minor role in ligand recognition. The, mechanism by which these proteins are able to recognize linear and, decorated beta-1,4-glucans is discussed based on the structures of CBM44, and the other CBMs that bind single cellulose chains.

About this Structure

2C4X is a Single protein structure of sequence from Clostridium thermocellum with and as ligands. Known structural/functional Site: . Full crystallographic information is available from OCA.

Reference

Xyloglucan is recognized by carbohydrate-binding modules that interact with beta-glucan chains., Najmudin S, Guerreiro CI, Carvalho AL, Prates JA, Correia MA, Alves VD, Ferreira LM, Romao MJ, Gilbert HJ, Bolam DN, Fontes CM, J Biol Chem. 2006 Mar 31;281(13):8815-28. Epub 2005 Nov 28. PMID:16314409

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