title: A novel β-xylosidase structure from Geobacillus thermoglucosidasius: the first crystal structure of a glycoside hydrolase family GH52 enzyme reveals unpredicted similarity to other glycoside hydrolase folds.
abstract: Geobacillus thermoglucosidasius is a thermophilic bacterium that is able to ferment both C6 and C5 sugars to produce ethanol. During growth on hemicellulose biomass, an intracellular β-xylosidase catalyses the hydrolysis of xylo-oligosaccharides to the monosaccharide xylose, which can then enter the pathways of central metabolism. The gene encoding a G. thermoglucosidasius β-xylosidase belonging to CAZy glycoside hydrolase family GH52 has been cloned and expressed in Escherichia coli. The recombinant enzyme has been characterized and a high-resolution (1.7 Å) crystal structure has been determined, resulting in the first reported structure of a GH52 family member. A lower resolution (2.6 Å) structure of the enzyme-substrate complex shows the positioning of the xylobiose substrate to be consistent with the proposed retaining mechanism of the family; additionally, the deep cleft of the active-site pocket, plus the proximity of the neighbouring subunit, afford an explanation for the lack of catalytic activity towards the polymer xylan. Whilst the fold of the G. thermoglucosidasius β-xylosidase is completely different from xylosidases in other CAZy families, the enzyme surprisingly shares structural similarities with other glycoside hydrolases, despite having no more than 13% sequence identity.
authors.affiliation: Centre for Extremophile Research, Department of Biology and Biochemistry, University of Bath, Claverton Down, Bath BA2 7AY, England.
authors.forename: Giannina
authors.initials: G
authors.lastname: Espina
authors.affiliation: TMO Renewables Ltd, Alan Turing Road, Surrey Research Park, Guildford GU2 7YF, England.
authors.forename: Kirstin
authors.initials: K
authors.lastname: Eley
authors.affiliation: European Molecular Biology Laboratory (EMBL) Hamburg c/o DESY, Notkestrasse 85, 22603 Hamburg, Germany.
authors.forename: Guillaume
authors.initials: G
authors.lastname: Pompidor
authors.affiliation: European Molecular Biology Laboratory (EMBL) Hamburg c/o DESY, Notkestrasse 85, 22603 Hamburg, Germany.
authors.forename: Thomas R
authors.initials: TR
authors.lastname: Schneider
authors.affiliation: Centre for Extremophile Research, Department of Biology and Biochemistry, University of Bath, Claverton Down, Bath BA2 7AY, England.
authors.forename: Susan J
authors.initials: SJ
authors.lastname: Crennell
authors.affiliation: Centre for Extremophile Research, Department of Biology and Biochemistry, University of Bath, Claverton Down, Bath BA2 7AY, England.
authors.forename: Michael J
authors.initials: MJ
authors.lastname: Danson
mesh_terms: D020134:Catalytic Domain; D003001:Cloning, Molecular; D018360:Crystallography, X-Ray; D004187:Disaccharides / Q000737:chemistry / Q000378:metabolism; D004926:Escherichia coli / Q000235:genetics; D056506:Geobacillus / Q000201:enzymology*; D008958:Models, Molecular; D011487:Protein Conformation; D014995:Xylosidases / Q000737:chemistry* / Q000235:genetics / Q000378:metabolism*
chemical_list: D004187:Disaccharides; D014995:Xylosidases; C026579:exo-1,4-beta-D-xylosidase; C004173:xylobiose
keywords: GH family 52; Geobacillus thermoglucosidasius; fold conservation; retaining mechanism; thermophile; β-xylosidase