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Understanding How Noncatalytic Carbohydrate Binding Modules Can Display Specificity for Xyloglucan

DOI: 10.1074/jbc.M112.432781 DOI Help
PMID: 23229556 PMID Help

Authors: Ana S. Luis (CIISA, Universidade Técnica de Lisboa) , Immacolata Venditto (CIISA, Faculdade de Medicina Veterinaria, Universidade de Lisboa) , Max J. Temple (Newcastle University) , Artur Rogowski (Newcastle University) , Arnaud Basle (Newcastle University) , Jie Xue (University of Leeds) , J. Paul Knox (University of Leeds) , Jose A. M. Prates (CIISA, Universidade Técnica de Lisboa) , Luis M. A. Ferreira (CIISA, Universidade Técnica de Lisboa) , Carlos M. G. A. Fontes (CIISA, Universidade Técnica de Lisboa) , Shabir Najmudin (CIISA, Universidade Técnica de Lisboa) , Harry J. Gilbert (Newcastle University)
Co-authored by industrial partner: No

Type: Journal Paper
Journal: Journal Of Biological Chemistry , VOL 288 (7) , PAGES 4799 - 4809

State: Published (Approved)
Published: February 2013
Diamond Proposal Number(s): 1221

Abstract: Plant biomass is central to the carbon cycle and to environmentally sustainable industries exemplified by the biofuel sector. Plant cell wall degrading enzymes generally contain noncatalytic carbohydrate binding modules (CBMs) that fulfil a targeting function, which enhances catalysis. CBMs that bind β-glucan chains often display broad specificity recognizing β1,4-glucans (cellulose), β1,3-β1,4-mixed linked glucans and xyloglucan, a β1,4-glucan decorated with β1,6-xylose residues, by targeting structures common to the three polysaccharides. Thus, CBMs that recognize xyloglucan target the β1,4-glucan backbone and only accommodate the xylose decorations. Here we show that two closely related CBMs, CBM65A and CBM65B, derived from EcCel5A, a Eubacterium cellulosolvens endoglucanase, bind to a range of β-glucans but, uniquely, display significant preference for xyloglucan. The structures of the two CBMs reveal a β-sandwich fold. The ligand binding site comprises the β-sheet that forms the concave surface of the proteins. Binding to the backbone chains of β-glucans is mediated primarily by five aromatic residues that also make hydrophobic interactions with the xylose side chains of xyloglucan, conferring the distinctive specificity of the CBMs for the decorated polysaccharide. Significantly, and in contrast to other CBMs that recognize β-glucans, CBM65A utilizes different polar residues to bind cellulose and mixed linked glucans. Thus, Gln106 is central to cellulose recognition, but is not required for binding to mixed linked glucans. This report reveals the mechanism by which β-glucan-specific CBMs can distinguish between linear and mixed linked glucans, and show how these CBMs can exploit an extensive hydrophobic platform to target the side chains of decorated β-glucans.

Journal Keywords: Calorimetry; Carbohydrates; Catalysis; Cell; Cellulose; Crystallography; X-Ray; Escherichia; Glucans; Kinetics; Ligands; Mutagenesis; Site-Directed; Oligosaccharides; Polysaccharides; Protein; Thermodynamics; Xylans; beta-Glucans

Subject Areas: Chemistry, Biology and Bio-materials

Instruments: I02-Macromolecular Crystallography , I04-Macromolecular Crystallography

Other Facilities: SOLEIL

Added On: 28/03/2013 11:30

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