Heterologous expression in Pichia pastoris and characterization of a novel GH11 xylanase from saline-alkali soil with excellent tolerance to high pH, high salt concentrations and ethanol

A GH11 xylanase gene (xyn11-1) cloned from saline-alkali soil was successfully expressed in Pichia pastoris GS115. The purified recombinant Xyn11-1 showed its maximal activity at pH 6.0, and retained more than 60.4% of activity at pH 10.0, with good pH stability. Its optimal temperature was 50 degrees C and it was stable after incubation for 1 h at 30 degrees C. Furthermore, Xyn11-1 was highly salt-tolerant, retaining more than 77.4% of activity in the presence of 0.25-4 M NaCl and displaying more than 47.2% relative activity after being incubated in the presence of 5 M NaCl at 37 degrees C for 10 min. In addition, 5 mM beta-Mercaptoethanol, Cu2+, Co2+, and Mn2+ increased the xylanase activity by 22.3%, 8.8%, 7.1%, and 4.4%, respectively. Significantly, 93.4% and 59.8% of the optimal activity was retained in the presence of 2% and 10% (v/v) ethanol, respectively. Under optimal conditions, the K-m, V-max, and K-cat value of Xyn11-1 for beechwood xylan were 3.7 mg ml(-1), 101.0 mu mol min(-1) mg(-1) and 42.1 s(-1), respectively. Xyn11-1 is a strict endo-beta-1,4-xylanase, its main enzymatic products being xylotetraose and xylopentaose. Xyn11-1 is the first reported GH11 xylanase isolated from saline-alkali soil, and has excellent tolerance of high pH, high salt concentrations and ethanol, which indicates its great potential for basic research and industrial applications. (C) 2017 Published by Elsevier Inc.