Beta-xylosidase activity of a GH3 glucosidase/xylosidase from yak rumen metagenome promotes the enzymatic degradation of hemicellulosic xylans.

J Zhou, L Bao, L Chang, Z Liu, C You, H Lu

文献索引：Lett. Appl. Microbiol. 54(2) , 79-87, (2012)

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摘要

  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.  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.  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.  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.© 2011 The Authors. Letters in Applied Microbiology © 2011 The Society for Applied Microbiology.