Biochemical and kinetic characterization of GH43 β-D-xylosidase/α-L-arabinofuranosidase and GH30 α-L-arabinofuranosidase/β-D -xylosidase from rumen metagenome.

The present study focuses on characterization of two hemicellulases, RuXyn1 and RuXyn2, from rumen bacterial metagenome and their capabilities for degradation of xylans. Glycosyl hydrolase (GH) family 43 β-D -xylosidase/α-L -arabinofuranosidase RuXyn1 can hydrolyze p-nitrophenyl-β-D -xylopyranoside (pNPX), p-nitrophenyl-α-L -arabinofuranoside (pNPA), and xylo-oligosaccharide substrates, while GH30 1,5-α-L -arabinofuranosidase/β-D -xylosidase RuXyn2, the first α-L -arabinofuranosidase assigned to this GH family, shows activities towards 1,5-α-L -arabinobiose and pNPX substrates but no activity for pNPA. Kinetic analysis for aryl-glycosides revealed that RuXyn2 had higher catalytic efficiency than RuXyn1 toward pNPX substrate. RuXyn1 shows high synergism with endoxylanase, elevating by 73% the reducing sugars released from brichwood xylans, and converted most intermediate xylo-oligosaccharide hydrolysate into xylose. The high xylose conversion capability of RuXyn1 suggests it has potential applications in enzymatic production of xylose and improvement of hemicellulose saccharification for production of biofuels. RuXyn2 shows no obviously synergistic effect in the endoxylanase-coupled assay for enzymatic saccharification of xylan. Further cosmid DNA sequencing revealed a neighboring putative GH43 α-L -arabinofuranosidase RuAra1 and two putative GH3 β-xylosidase/arabinosidases, RuXyn3 and RuXyn5, downstream of RuXyn2, indicating that this hemicellulase gene cluster may be responsible for production of end-product, xylose and arabinose, from hemicellulose biomass.