1. Recognition of the helical structure of beta-1,4-galactan by a new family of carbohydrate-binding modules
- Author
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Henriette L. Pedersen, Melissa Cid, Satoshi Kaneko, William G.T. Willats, Bernard Henrissat, Pedro M. Coutinho, and Alisdair B. Boraston
- Subjects
Models, Molecular ,Protein Folding ,Glycoside Hydrolases ,Carbohydrates ,Oligosaccharides ,Glycobiology and Extracellular Matrices ,Plasma protein binding ,Crystallography, X-Ray ,Biochemistry ,Galactans ,Protein Structure, Secondary ,chemistry.chemical_compound ,Protein structure ,Bacterial Proteins ,Polysaccharides ,Hydrolase ,Thermotoga maritima ,Binding site ,Molecular Biology ,Binding Sites ,biology ,Galactose ,Cell Biology ,Galactan ,biology.organism_classification ,Microarray Analysis ,Protein Structure, Tertiary ,chemistry ,Microscopy, Fluorescence ,Protein folding ,Carbohydrate-binding module ,Protein Binding - Abstract
The microbial enzymes that depolymerize plant cell wall polysaccharides, ultimately promoting energy liberation and carbon recycling, are typically complex in their modularity and often contain carbohydrate-binding modules (CBMs). Here, through analysis of an unknown module from a Thermotoga maritima endo-β-1,4-galactanase, we identify a new family of CBMs that are most frequently found appended to proteins with β-1,4-galactanase activity. Polysaccharide microarray screening, immunofluorescence microscopy, and biochemical analysis of the isolated module demonstrate the specificity of the module, here called TmCBM61, for β-1,4-linked galactose-containing ligands, making it the founding member of family CBM61. The ultra-high resolution x-ray crystal structures of TmCBM61 (0.95 and 1.4 Å resolution) in complex with β-1,4-galactotriose reveal the molecular basis of the specificity of the CBM for β-1,4-galactan. Analysis of these structures provides insight into the recognition of an unexpected helical galactan conformation through a mode of binding that resembles the recognition of starch.
- Published
- 2010