![]() Xylans, the most abundant hemicellulosic heteropolysaccharides in plant cell wall, have to be efficiently decomposed into constituent sugars before they can be utilized as a biofuel substrate and other feedstock commodities. ![]() In addition to the active site, nine other xylose-binding sites were consistently observed in each of the four monomers, providing a possible reason for the high tolerance of product inhibition. ![]() On the basis of the crystal structures and in agreement with previous kinetic data, we propose that XylC cleaves the glycosidic bond by the retaining mechanism using two acidic residues Asp 382 (nucleophile) and Glu 405 (general acid/base). The enzyme contains an open carbohydrate-binding cleft, allowing accommodation of longer xylo-oligosaccharides. The core domain is a right-handed parallel β-helix (residues 1–75 and 201–638) and the flanking region (residues 76–200) folds into a β-sandwich domain. ![]() XylC assembles into a tetramer, and each monomer comprises two distinct domains. In the present paper, we report three crystal structures of XylC in complex with Tris, xylobiose and xylose at 1.48–2.05 Å (1 Å=0.1 nm) resolution. Recently, XylC, a β-xylosidase from Thermoanaerobacterium saccharolyticum JW/SL-YS485, was found to be structurally different from corresponding glycosyl hydrolases in the CAZy database ( ), and was subsequently classified as the first member of a novel family of glycoside hydrolases (GH120). Xylan-1,4-β-xylosidase (β-xylosidase) hydrolyses xylo-oligomers at their non-reducing ends into individual xylose units.
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June 2023
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