1oh3
From Proteopedia
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E78R MUTANT OF A CARBOHYDRATE BINDING MODULE FAMILY 29
Overview
The structural and thermodynamic basis for carbohydrate-protein, recognition is of considerable importance. NCP-1, which is a component of, the Piromyces equi cellulase/hemicellulase complex, presents a provocative, model for analyzing how structural and mutational changes can influence, the ligand specificity of carbohydrate-binding proteins. NCP-1 contains, two "family 29" carbohydrate-binding modules designated CBM29-1 and, CBM29-2, respectively, that display unusually broad specificity; the, proteins interact weakly with xylan, exhibit moderate affinity for, cellulose and mannan, and bind tightly to the beta-1,4-linked, glucose-mannose heteropolymer glucomannan. The crystal structure of, CBM29-2 in complex with cellohexaose and mannohexaose identified key, residues involved in ligand recognition. By exploiting this structural, information and the broad specificity of CBM29-2, we have used this, protein as a template to explore the evolutionary mechanisms that can lead, to significant changes in ligand specificity. Here, we report the, properties of the E78R mutant of CBM29-2, which displays ligand, specificity that is different from that of wild-type CBM29-2; the protein, retains significant affinity for cellulose but does not bind to mannan or, glucomannan. Significantly, E78R exhibits a stoichiometry of 0.5 when, binding to cellohexaose, and both calorimetry and ultracentrifugation show, that the mutant protein displays ligand-mediated dimerization in solution., The three-dimensional structure of E78R in complex with cellohexaose, reveals the intriguing molecular basis for this "dimeric" binding mode, that involves the lamination of the oligosaccharide between two CBM, molecules. The 2-fold screw axis of the ligand is mirrored in the, orientation of the two protein domains with adjacent sugar rings stacking, against the equivalent aromatic residues in the binding site of each, protein molecule of the molecular sandwich. The sandwiching of an, oligosaccharide chain between two protein modules, leading to, ligand-induced formation of the binding site, represents a completely, novel mechanism for protein-carbohydrate recognition that may mimic that, displayed by naturally dimeric protein-carbohydrate interactions.
About this Structure
1OH3 is a Single protein structure of sequence from Piromyces equi with GLC as ligand. Structure known Active Site: AC1. Full crystallographic information is available from OCA.
Reference
Ligand-mediated dimerization of a carbohydrate-binding molecule reveals a novel mechanism for protein-carbohydrate recognition., Flint J, Nurizzo D, Harding SE, Longman E, Davies GJ, Gilbert HJ, Bolam DN, J Mol Biol. 2004 Mar 19;337(2):417-26. PMID:15003456
Page seeded by OCA on Mon Nov 5 16:54:28 2007
