Expression of a Trichoderma reesei β-xylanase gene in Escherichia coli and activity of the enzyme on fiber-bound substrates

A recombinant gene Xyn2 (570 bp) encoding the main Trichoderma reesei Rut C-30 endo-β-1,4-xylanase was successfully cloned and expressed in Escherichia coli BL21 under the control of strong bacteriophage T7 transcription and translation signals. The molecular weight of the recombinant protein was estimated by SDS–PAGE to be 24 kDa. The expressed protein was purified by Ni2+–NTA affinity chromatography and enzyme activity assay verified the protein as a xylanase. Like with the T. reesei Xyn2, the optimal activity of the recombinant Xyn2 was at 50 °C. However, the recombinant xylanase had an improved thermostability and more than 70% of its activity remained after 30 min incubation at 60 °C. In addition, the recombinant xylanase was active over the range of pH 3.5–7.5 with maximum activity at pH 5.0. The enzyme was highly specific towards xylans but exhibited very low activities towards cellulosic substrates. Using Birchwood xylan, the determined apparent Km and kcat values were 0.11 mg/ml and 106 s−1, respectively. These properties should make the enzyme an attractive candidate for various industrial applications.