Cloning, expression, and characterization of a new xylanase with broad temperature adaptability from Streptomyces sp S9

A new xylanase gene, xynAS9, was cloned from Streptomyces sp. S9, which was isolated from Turpan Basin, China. The full-length gene consists of 1,395 bp and encodes 465 amino acids including 38 residues of a putative signal peptide. The overall amino acid sequence shares the highest identity (50.8%) with a putative endo-1,4-beta-xylanase from Streptomyces avermitilis of the glycoside hydrolase family 10. The gene fragment encoding the mature xylanase was expressed in Escherichia coli BL21 (DE3). The recombinant protein was purified to electrophoretic homogeneity and subsequently characterized. The optimal pH and temperature for the recombinant enzyme were 6.5 and 60 degrees C, respectively. The enzyme showed broad temperature adaptability, retaining more than 65% of the maximum activity when assayed at 50-80 degrees C. The enzyme also had good thermal and pH stability. The K-m values for oat spelt xylan and birchwood xylan substrates were 2.85 and 2.43 mg ml(-1), with the V-max values of 772.20 and 490.87 mu mol min(-1) mg(-1), respectively. The hydrolysis products of xylan were mainly xylose and xylobiose. These favorable properties should make XynAS9 a good candidate in various industrial applications.