A novel beta-xylosidase from Anoxybacillus sp. 3M towards an improved agro-industrial residues saccharification

An intracellular ?-xylosidase (AbXyl), from the thermoalkaline Anoxybacillus sp. 3M, was purified and characterized. The homodimeric enzyme (140 kDa) was optimally active at 65°C and pH 5.5, exhibited half life of 10 h at 60°C, 78 and 88% residual activity after 24 h, at pH 4.5 and 8.0, respectively. Fe2+, Cu2+, Al3+, Ag+ and Hg2+ inhibited the enzyme; the activity was moderately stimulated by SDS and not influenced by ?-mercaptoethanol. In the presence of pnitrophenyl- ?-D-xylopyranoside, AbXyl exhibited Km of 0.19 mM, Kcat of 453.29 s -1, Kcat Km-1 of 2322 s-1 mM and was moderately influenced by xylose (Ki 21.25 mM). The enzyme hydrolyzed xylo -oligomers into xylose and catalyzed transxylosilation reactions also in presence of alcohols as acceptors, producing xylo -oligosaccharides and alkylxylosides. Finally AbXyl was applied towards a statistically optimized process of brewery's spent grain bioconversion, highlighting the important role of this biocatalyst in reaching high yields of fermentable sugars.