title: Beta-xylosidase activity of a GH3 glucosidase/xylosidase from yak rumen metagenome promotes the enzymatic degradation of hemicellulosic xylans.
abstract: OBJECTIVE
  To characterize the duel activities of a glycosyl hydrolase family 3 β-glucosidase/xylosidase from rumen bacterial metagenome and to investigate the capabilities of its β-d-xylosidase activities for saccharification of hemicellulosic xylans.
  
  
  RESULTS
  A β-glucosidase/xylosidase gene RuBGX1 was cloned from yak (Bos grunniens) rumen using the metagenomic technology. Recombinant RuBGX1, expressed in Escherichia coli, demonstrated high hydrolytic activities on both p-nitrophenyl-β-d-glucopyranoside (pNP-Glc) and p-nitrophenyl-β-d-xylopyranoside (pNP-Xyl) substrates. Analysis of the kinetic properties indicated that RuBGX1 had a lower affinity for pNP-Glc substrate as the K(m) was 0·164 mmol l(-1) for pNP-Glc and 0·03 mmol l(-1) for pNP-Xyl at pH 6·0 and 50°C, respectively. The capabilities of RuBGX1 β-xylosidase for hydrolysis of xylooligosaccharide substrates were further investigated using an endoxylanase-coupled assay. Hydrolysis time courses illustrated that a significant increase (about 50%) in the reducing sugars, including xylobiose, xylotriose and xylotetraose, was achieved by supplementing endoxylanase with RuBGX1. Enzymatic product analysis using high-performance anion-exchange chromatography-pulsed amperometric detection showed that RuBGX1 could release xyloses from intermediate xylooligosaccharides produced by endoxylanase.
  
  
  CONCLUSIONS
  The RuBGX1 shows β-glucosidase activity in hydrolysis of cello-oligosaccharides; meanwhile, it has β-xylosidase activity and functions synergistically with endoxylanase to promote the degradation of hemicellulosic xylans.
  
  
  CONCLUSIONS
  This was the first to report the β-xylosidase activity of family 3 β-glucosidase/xylosidase functioned in the degradation of hemicellulosic xylans. The bifunctional β-glucosidase/xylosidase property of RuBGX1 can be used in simultaneous saccharification of cellulose and xylan into fermentable glucose and xylose.
authors.affiliation: State Key Laboratory Of Genetic Engineering, School Of Life Sciences, Fudan University, Shanghai, China.
authors.forename: J
authors.initials: J
authors.lastname: Zhou
authors.forename: L
authors.initials: L
authors.lastname: Bao
authors.forename: L
authors.initials: L
authors.lastname: Chang
authors.forename: Z
authors.initials: Z
authors.lastname: Liu
authors.forename: C
authors.initials: C
authors.lastname: You
authors.forename: H
authors.initials: H
authors.lastname: Lu
mesh_terms: D000595:Amino Acid Sequence; D000818:Animals; D001419:Bacteria / Q000201:enzymology* / Q000235:genetics; D002417:Cattle; D043364:Endo-1,4-beta Xylanases / Q000378:metabolism; D015964:Gene Expression Regulation, Bacterial; D006027:Glycosides; D007700:Kinetics; D054892:Metagenome; D008969:Molecular Sequence Data; D009844:Oligosaccharides / Q000378:metabolism; D011994:Recombinant Proteins / Q000235:genetics / Q000378:metabolism; D012417:Rumen / Q000382:microbiology*; D016415:Sequence Alignment; D013379:Substrate Specificity; D014990:Xylans / Q000235:genetics / Q000378:metabolism*; D014995:Xylosidases / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*; D001617:beta-Glucosidase / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*
chemical_list: D006027:Glycosides; D009844:Oligosaccharides; D011994:Recombinant Proteins; D014990:Xylans; C008646:4-nitrophenyl beta-D-xyloside; D014995:Xylosidases; D001617:beta-Glucosidase; C026579:exo-1,4-beta-D-xylosidase; D043364:Endo-1,4-beta Xylanases