title: Biochemical Characterization of a GH43 β-Xylosidase from Bacteroides ovatus.
abstract: Divalent metal-activated glycoside hydrolase family 43 (GH43) β-xylosidases have been found to have high kcat/Kmfor xylooligosaccharides and may demonstrate high efficacy in industrial reactors digesting hemicellulose. By searching an amino acid database, we found a Bacteroides ovatus GH43 β-xylosidase termed BoXA that is 81% identical in overall amino acid sequence to a GH43, divalent metal-activated β-xylosidase with high kcat/Km, and also it has 19 of 20 residues in the active site conserved. However, unlike its metal-activated homolog, the B. ovatus enzyme does not lose activity after extensive EDTA treatment nor does it gain activity by addition of divalent metal ions. Thus, either it cannot be activated by divalent metal or it maintains a tightly bound, non-exchangeable metal ion. At 25 °C and pH 6.0, the kcatis 69 s-1for xylobiose and kcat/Kmis 210 s-1mM-1for xylotriose, with the latter being 0.7 that of the highest known value. The determined Kifor D-glucose is 4.9 M, which is the highest known for a β-xylosidase. The enzyme has potential utility operating in bioreactors digesting plant biomass.
authors.affiliation: USDA-ARS-National Center for Agricultural Utilization Research, Peoria, IL, 61604, USA. douglas.jordan@ars.usda.gov.
authors.forename: Douglas B
authors.initials: DB
authors.lastname: Jordan
authors.affiliation: USDA-ARS-National Center for Agricultural Utilization Research, Peoria, IL, 61604, USA.
authors.forename: J Rose
authors.initials: JR
authors.lastname: Stoller
authors.affiliation: USDA-ARS-Western Regional Research Center, 800 Buchanan Street, Albany, CA, 94710, USA.
authors.forename: Charles C
authors.initials: CC
authors.lastname: Lee
authors.affiliation: USDA-ARS-Western Regional Research Center, 800 Buchanan Street, Albany, CA, 94710, USA.
authors.forename: Victor J
authors.initials: VJ
authors.lastname: Chan
authors.affiliation: USDA-ARS-Western Regional Research Center, 800 Buchanan Street, Albany, CA, 94710, USA.
authors.forename: Kurt
authors.initials: K
authors.lastname: Wagschal
mesh_terms: D001426:Bacterial Proteins / Q000737:chemistry* / Q000235:genetics / Q000302:isolation & purification; D001439:Bacteroides / Q000737:chemistry* / Q000201:enzymology / Q000235:genetics; D001483:Base Sequence; D020134:Catalytic Domain; D002413:Cations, Divalent; D004187:Disaccharides / Q000737:chemistry; D004492:Edetic Acid / Q000737:chemistry; D004789:Enzyme Activation; D015870:Gene Expression; D005947:Glucose / Q000737:chemistry; D005965:Glucuronates / Q000737:chemistry*; D006863:Hydrogen-Ion Concentration; D007700:Kinetics; D009844:Oligosaccharides / Q000737:chemistry*; D011994:Recombinant Proteins / Q000737:chemistry / Q000235:genetics / Q000302:isolation & purification; D013379:Substrate Specificity; D013696:Temperature; D014312:Trisaccharides / Q000737:chemistry; D014995:Xylosidases / Q000737:chemistry* / Q000235:genetics / Q000302:isolation & purification
chemical_list: D001426:Bacterial Proteins; D002413:Cations, Divalent; D004187:Disaccharides; D005965:Glucuronates; D009844:Oligosaccharides; D011994:Recombinant Proteins; D014312:Trisaccharides; C570991:xylooligosaccharide; C515044:xylotriose; D004492:Edetic Acid; D014995:Xylosidases; C026579:exo-1,4-beta-D-xylosidase; C004173:xylobiose; D005947:Glucose
keywords: Divalent metal activation; Family 43; Glycoside hydrolase; Oligoxylosides; β-xylosidase