Purification and Characterization of a Glycoside Hydrolase Family 43 β-xylosidase from Geobacillus thermoleovorans IT-08.

Kurt Wagschal; Chamroeun Heng; Charles Lee; George Robertson; William Orts; Dominic Wong

Abstract  The gene encoding a glycoside hydrolase family 43 β-xylosidase (GbtXyl43A) from the thermophilic bacterium Geobacillus thermoleovorans strain IT-08 was synthesized and cloned with a C-terminal His-tag into a pET29b expression vector. The recombinant gene product termed GbtXyl43A was expressed in Escherichia coli and purified to apparent homogeneity. Michaelis–Menten kinetic parameters were obtained for the artificial substrates p-nitrophenyl-β-d-xylopyranose (4NPX) and p-nitrophenyl-α-l-arabinofuranose (4NPA), and it was found that the ratio k cat/K m 4NPA/k cat/K m 4NPX was ∼7, indicting greater catalytic efficiency for 4NP hydrolysis from the arabinofuranose aglycon moiety. Substrate inhibition was observed for the substrates 4-methylumbelliferyl xylopyranoside (muX) and the arabinofuranoside cogener (muA), and the ratio k cat/K m muA/k cat/K m muX was ∼5. The enzyme was competitively inhibited by monosaccharides, with an arabinose K i of 6.8 ± 0.62 mM and xylose K i of 76 ± 8.5 mM. The pH maxima was 5.0, and the enzyme was not thermally stable above 54 °C, with a t 1/2 of 35 min at 57.5 °C. GbtXyl43A showed a broad substrate specificity for hydrolysis of xylooligosaccharides up to the highest degree of polymerization tested (xylopentaose), and also released xylose from birch and beechwood arabinoxylan.

GLYCOSIDASES; GENETIC code; ESCHERICHIA coli; MOLECULAR cloning; GENE expression; MONOSACCHARIDES; POLYMERIZATION; THERMOPHILIC bacteria

Applied Biochemistry & Biotechnology, 2009, Vol 155, Issue 1-3, p1

0273-2289

Academic Journal

10.1007/s12010-008-8362-5