Isolation, cloning and molecular characterization of a thermotolerant xylanase from Streptomyces sp. THW31

Abstract

A xylan-degrading Streptomyces sp. THW31 was isolated from rubbish compost in Thailand. Analysis of a genomic library of nucleotide sequences from Streptomyces sp. THW31 revealed that the complete open reading frame (ORF) of xylanase (xlnW31) was 999 bp, and this gene encoded a member of the glycosyl hydrolase family 11. Sequence homology of the predicted amino acid sequence encoded by xlnW31 demonstrated that the enzyme consists of a signal peptide, catalytic and substrate-binding domains. The XlnW31 enzyme shared the highest identity (90%) to a xylanase family 11 member from Streptomyces lividans TK24. Cloning and expression of xlnW31 in Escherichia coli resulted in the production and purification of a 31.0 kDa enzyme. Purified XlnW31 show the highest activity at pH 6.0 and at a temperature 65 to 70°C. Enzyme stability tests indicated that XlnW31 retained its activity over a broad pH range (5.0 to 11.0) and at temperatures reaching 60°C for 2 h. Purified XlnW31 also exhibited endo-1,4--xylanase activity using xylan as a substrate and bound to insoluble xylan. Hydrolysis of xylan by the xylanase yielded xylobiose as the principal product.