Abstract
A gene encoding a -xylosidase (designated as Thxyl43A) was cloned from strain Thermobifida halotolerans YIM 90462(T). The open reading frame of this gene encodes 550 amino acid residues. The gene was over-expressed in Escherichia coli and the recombinant protein was purified. The monomeric Thxyl43A protein presented a molecular mass of 61.5kDa. When p-nitrophenyl--d-xylopyranoside was used as the substrate, recombinant Thxyl43A exhibited optimal activity at 55 degrees C and pH 4.0 to 7.0, being thermostable by maintaining 47% of its activity after 30h incubation at 55 degrees C. The recombinant enzyme retained more than 80% residual activity after incubation at pH range of 4.0 to 12.0 for 24h, respectively, which indicated notable thermostability and pH stability of Thxyl43A. Moreover, Thxyl43A displayed high catalytic activity (>60%) in presence of 5-35% NaCl (w/v) or 1-20% ionic liquid (w/v) or 1-50mM xylose. These properties suggest that Thxyl43A has potential for promoting hemicellulose degradation and other industrial applications.