Author:

Keywords:

arabinoxylan arabinofuranohydrolase, bacillus subtilis, crystallography, enzyme-substrate complex, family 43 glycoside hydrolase, substrate-binding mechanism, alpha-l-arabinofuranosidase, crystal-structure, ligand-binding, bacillus-subtilis, diffraction data, module, specificities, bioconversion, refinement, sites, Science & Technology, Life Sciences & Biomedicine, Biochemistry & Molecular Biology, Bacillus subtilis, CRYSTAL-STRUCTURE, LIGAND-BINDING, MODULE, SITES, Biocatalysis, Catalytic Domain, Crystallography, X-Ray, Glycoside Hydrolases, Isoenzymes, Models, Molecular, Protein Binding, Protein Structure, Quaternary, Protein Structure, Tertiary, Substrate Specificity, Xylose, 03 Chemical Sciences, 06 Biological Sciences, 11 Medical and Health Sciences, 3101 Biochemistry and cell biology

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.