title: Structural analysis of a glycoside hydrolase family 43 arabinoxylan arabinofuranohydrolase in complex with xylotetraose reveals a different binding mechanism compared with other members of the same family.
abstract: AXHs (arabinoxylan arabinofuranohydrolases) are alpha-L-arabinofuranosidases that specifically hydrolyse the glycosidic bond between arabinofuranosyl substituents and xylopyranosyl backbone residues of arabinoxylan. Bacillus subtilis was recently shown to produce an AXH that cleaves arabinose units from O-2- or O-3-mono-substituted xylose residues: BsAXH-m2,3 (B. subtilis AXH-m2,3). Crystallographic analysis reveals a two-domain structure for this enzyme: a catalytic domain displaying a five-bladed beta-propeller fold characteristic of GH (glycoside hydrolase) family 43 and a CBM (carbohydrate-binding module) with a beta-sandwich fold belonging to CBM family 6. Binding of substrate to BsAXH-m2,3 is largely based on hydrophobic stacking interactions, which probably allow the positional flexibility needed to hydrolyse both arabinose substituents at the O-2 or O-3 position of the xylose unit. Superposition of the BsAXH-m2,3 structure with known structures of the GH family 43 exo-acting enzymes, beta-xylosidase and alpha-L-arabinanase, each in complex with their substrate, reveals a different orientation of the sugar backbone.
authors.affiliation: Laboratory for Biocrystallography, Department of Pharmaceutical Sciences, Katholieke Universiteit Leuven, Herestraat 49, O&N II, bus 822, 3000 Leuven, Belgium.
authors.forename: Elien
authors.initials: E
authors.lastname: Vandermarliere
authors.forename: Tine M
authors.initials: TM
authors.lastname: Bourgois
authors.forename: Martyn D
authors.initials: MD
authors.lastname: Winn
authors.forename: Steven
authors.initials: S
authors.lastname: van Campenhout
authors.forename: Guido
authors.initials: G
authors.lastname: Volckaert
authors.forename: Jan A
authors.initials: JA
authors.lastname: Delcour
authors.forename: Sergei V
authors.initials: SV
authors.lastname: Strelkov
authors.forename: Anja
authors.initials: A
authors.lastname: Rabijns
authors.forename: Christophe M
authors.initials: CM
authors.lastname: Courtin
mesh_terms: D001412:Bacillus subtilis / Q000201:enzymology / Q000235:genetics; D055162:Biocatalysis; D020134:Catalytic Domain; D018360:Crystallography, X-Ray; D006026:Glycoside Hydrolases / Q000737:chemistry* / Q000145:classification / Q000235:genetics / Q000378:metabolism*; D007527:Isoenzymes / Q000378:metabolism; D008958:Models, Molecular; D011485:Protein Binding; D020836:Protein Structure, Quaternary; D017434:Protein Structure, Tertiary; D013379:Substrate Specificity; D014994:Xylose / Q000737:chemistry* / Q000378:metabolism*
chemical_list: D007527:Isoenzymes; D014994:Xylose; D006026:Glycoside Hydrolases; C019713:alpha-N-arabinofuranosidase