A novel, noncatalytic carbohydrate-binding module displays specificity for galactose-containing polysaccharides through calcium-mediated oligomerization

Montanier, C. Y., Correia, M. A. S., Flint, J. E. , Zhu, Y., Basl���©, A., McKee, L. S., Prates, J. A. M., Polizzi, S., Coutinho, P. M., Lewis, R. J., Henrissat, B., Fontes, C. M. G. A. and Gilbert, H. J. (2011) A novel, noncatalytic carbohydrate-binding module displays specificity for galactose-containing polysaccharides through calcium-mediated oligomerization. Journal of Biological Chemistry, 286 (25). pp. 22499-22509. ISSN 0021-9258

Full content URL: http://dx.doi.org/10.1074/jbc.M110.217372

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The enzymic degradation of plant cell walls plays a central role in the carbon cycle and is of increasing environmental and industrial significance. The catalytic modules of enzymes that catalyze this process are generally appended to noncatalytic carbohydrate-binding modules (CBMs). CBMs potentiate the rate of catalysis by bringing their cognate enzymes into intimate contact with the target substrate.Apowerful plant cell wall-degrading system is the Clostridium thermocellum multienzyme complex, termed the "cellulosome." Here, we identify a novel CBM (CtCBM62) within the large C. thermocellum cellulosomal protein Cthe-2193 (defined as CtXyl5A), which establishes a new CBM family. Phylogenetic analysis of CBM62 members indicates that a circular permutation occurred within the family. CtCBM62 binds to D-galactose and L-arabinopyranose in either anomeric configuration. The crystal structures of CtCBM62, in complex with oligosaccharides containing α- and β-galactose residues, show that the ligand-binding site in the β-sandwich protein is located in the loops that connect the two β-sheets. Specificity is conferred through numerous interactions with the axial O4 of the target sugars, a feature that distinguishes galactose and arabinose from the other major sugars located in plant cell walls. CtCBM62 displays tighter affinity for multivalent ligands compared with molecules containing single galactose residues, which is associated with precipitation of these complex carbohydrates. These avidity effects, which confer the targeting of polysaccharides, are mediated by calcium-dependent oligomerization of the CBM. © 2011 by The American Society for Biochemistry and Molecular Biology, Inc.

Keywords:Anomeric configuration, Carbohydrate-binding modules, Carbon cycles, Catalytic modules, Cellulosomes, Circular permutation, Clostridium thermocellum, Complex carbohydrates, D-galactose, Enzymic degradation, Galactose residues, Ligand-binding sites, Multienzyme complexes, Multivalent ligands, Non-catalytic, Phylogenetic analysis, Plant cell wall, Plant cells, Catalysts, Enzymes, Ligands, Oligomerization, Oligomers, Organic compounds, Polysaccharides, Sugars, Plant cell culture, arabinose, calcium, carbohydrate binding protein, cellulosome, galactose, polysaccharide, protein CtCBM62, protein CtXyl5A, unclassified drug, article, binding affinity, binding site, catalysis, cell wall, controlled study, enzyme specificity, ligand binding, molecular phylogeny, nonhuman, nucleotide sequence, plant cell, priority journal, protein family, protein localization, protein protein interaction, protein structure, Bacterial Proteins, Crystallography, X-Ray, Models, Molecular, Protein Multimerization, Protein Structure, Quaternary, Protein Structure, Secondary, Receptors, Cell Surface, Substrate Specificity, Clostridium thermocellum
Subjects:C Biological Sciences > C720 Biological Chemistry
Divisions:College of Science > School of Life Sciences
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ID Code:12455
Deposited On:21 Dec 2013 22:45

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