Secretory expression of a β-xylosidase gene fromThermomyces lanuginosusinEscherichia coliand characterization of its recombinant enzyme

AIMS: To characterize a β-xylosidase from the thermophilic fungus Thermomyces lanuginosus and to investigate its potential in saccharification of hemicellulosic xylans. METHODS AND RESULTS: A gene (designated TlXyl43) encoding β-xylosidase was cloned from T. lanuginosus CAU44 and expressed in Escherichia coli. The gene consists of a 1017-bp open reading frame without introns. It encodes a mature protein of 338 residues with no predicted signal peptide, belonging to glycoside hydrolase (GH) family 43. Over 60% of the recombinant β-xylosidase (TlXyl43) was secreted into the culture medium. TlXyl43 was purified 2·6-fold to homogeneity with an estimated mass of 51·6kDa by SDS-PAGE. The purified enzyme exhibited optimal activity at pH 6·5 and 55°C and was stable at 50°C. It was competitively inhibited by xylose with a Ki value of 63mmol l(-1). CONCLUSIONS: In this study, a GH family 43 β-xylosidase gene (TlXyl43) from T. lanuginosus CAU44 was cloned and functionally expressed in E. coli, and over 60% of recombinant protein was secreted into the culture. SIGNIFICANCE AND IMPACT OF THE STUDY: This is the first report of the cloning and functional expression of a β-xylosidase gene from Thermomyces species. TlXyl43 holds great potential for variety of industries.