Cloning, expression, and characterization of a novel alkali‐tolerant xylanase from alkaliphilic B acillus sp. SN 5

A xylanase gene ( xyn11A ) was cloned from the genomic library of alkalophilic Bacillus sp. SN5. It encoded a polypeptide of 366 amino acids, consisting of a family 11 glycoside hydrolase, a short linker region, and a family 36 carbohydrate‐binding module ( CBM ). The intact xylanase Xyn11A and the CBM ‐linker‐truncated Xyn11A‐LC were expressed in E scherichia coli BL21 (DE3). Both purified recombinant proteins exhibited the highest activity at 55 °C. The optimal pH for Xyn11A activity was 7.5, whereas Xyn11A‐LC showed a broad pH profile (>80% activity at pH 5.5–8.5) with optimal activity at pH 5.5 and 7.5–8.0. They had high alkali tolerance, retaining over 80% residual activity after preincubation at pH 8.5–11.0 at 37 °C for 1 H. Xyn11A‐LC showed better thermal stability, lower affinity, and lower catalytic activity to insoluble xylan than Xyn11A, whereas its specific activity for soluble beechwood xylan (4,511.9 U/mg) was greater than that of Xyn11A (3,136.4 U/mg). These results implied that the CBM of Xyn11A could change the enzymatic properties and play a role in degrading insoluble xylan. Xyn11A‐LC is a family 11 alkali‐tolerant cellulase‐free xylanase with high specific activity, which qualifies it as a potential candidate for industrial applications, especially in the paper industry.