Cloning of a New Xylanase Gene from Streptomyces sp TN119 Using a Modified Thermal Asymmetric Interlaced-PCR Specific for GC-Rich Genes and Biochemical Characterization

A bacterial strain, Streptomyces sp. TN119, was isolated from the gut of Batocera horsfieldi larvae and showed xylanolytic activity. A degenerate primer set was designed based on the base usage of G and C in Actinobacteria xylanase-coding sequences belonging to the glycosyl hydrolases family 10 (GH 10), and used to clone the partial xylanase gene from Streptomyces sp. TN119. A modified thermal asymmetric interlaced (TAIL)-PCR specific for high-GC genes, named GC TAIL-PCR, was developed to obtain the full-length xylanase gene (xynA119; 1089 bp). Rich in GC content (67.8%), xynA119 encodes a new GH 10 xylanase (XynA119), which shares highest identity (48.8%) with an endo-1,4-beta-xylanase from Cellulosimicrobium sp. HY-12. Recombinant XynA119 was expressed in Escherichia coli BL21 (DE3) and purified to electrophoretic homogeneity. The enzyme showed maximal activity at pH 6.5 and 60 A degrees C, was stable at pH 4.0 to 10.0 and 50 A degrees C, was resistant to most chemicals (except for Cu2+, Mn2+, Ag+, Hg2+ and SDS) and trypsin, and produced simple products. The specific activity, K (m), V (max), and k (cat) using oat-spelt xylan as substrate were 57.9 U mg(-1), 1.0 mg ml(-1), 74.8 mu mol min(-1) mg(-1), and 49.2 s(-1), respectively.