Expression and characterization of a thermostable beta-xylosidase from the hyperthermophile, Thermotoga maritima

A thermostable beta-xylosidase from a hyperthermophilic bacterium, Thermotoga maritima, was over-expressed in Escherichia coli using the T7 polymerase expression system. The expressed beta-xylosidase was purified in two steps, heat treatment and immobilized metal affinity chromatography, and gave a single band on SDS-PAGE. The maximum activity on p-nitrophenyl beta-D-xylopyranoside was at 90 °C and pH 6.1. The purified enzyme had a half-life of over 22-min at 95 °C, and retained over 57% of its activity after holding a pH ranging from 5.4 to 8.5 for 1 h at 80 °C. Among all tested substrates, the purified enzyme had specific activities of 275, 50 and 29 U mg-1 on pNPX, pNPAF, and pNPG, respectively. The apparent Michaelis constant of the beta-xylosidase was 0.13 mM for pNPX with a Vmax of 280 U mg-1. When the purified beta-xylosidase was added to xylanase, corncob xylan was hydrolized completely to xylose.