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

Abstract

An intracellular β-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 β-mercaptoethanol. In the presence of p-nitrophenyl-β-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 alkyl-xylosides. 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.

Keywords: Anoxybacillus sp. 3M; Biotransformation; Thermo-alkali stable; Transxylosilation; β-Xylosidase.