Biochemical characterization of a novel halo/organic-solvents/final-products tolerant GH39 xylosidase from saline soil and its synergic action with xylanase.

Xylosidases with tolerance to high concentration of salts, organic solvents, and enzyme hydrolytic products are preferential for industrial application but were rarely reported. In this study, a novel xylosidase XYL21 belong to glycoside hydrolase 39 was characterized with optimal temperature of 45 °C and optimal pH of 5.50. Different to other GH39 xylosidases, XYL21 had excellent tolerance to salts, the activity of which is not inhibited but slightly increased in 0.50-1.50 M NaCl. It is also tolerant to organic solvents, especially retaining 105.18% relative activity even in the presence of 15.00% (v/v) ethanol. Moreover, XYL21 was insensitive to the final lignocellulose hydrolysis products including glucose, xylose, arabinose, mannose and galactose, which retains 111.36% and 53.49% relative activity in 0.30 and 0.90 M xylose, respectively. Further structural modeling analysis indicated that its excellent tolerance may be attributed to its high structural flexibility caused by the high proportion of random coils. Furthermore, XYL21 had a wide substrate specificity to catalyze xylan and xylo-oligosaccharides, and it significantly cooperated with xylanase to improve the hydrolysis efficiency with 1.52-fold. Considering these unique properties, XYL21 is a good candidate for both basic research and various potential industrial applications such as seafood processing and bioethanol production.