Characterisation of a recombinant β-xylosidase (xylA) from Aspergillus oryzae expressed in Pichia pastoris

β-xylosidases catalyse the hydrolysis of short chain xylooligosaccharides from their non-reducing ends into xylose. In this study we report the heterologous expression of Aspergillus oryzae β-xylosidase (XylA) in Pichia pastoris under the control of the glyceraldehyde-3-phosphate dehydrogenase promoter. The recombinant enzyme was optimally active at 55°C and pH 4.5 with K(m) and V(max) values of 1.0 mM and 250 μmol min(−1) mg(−1) respectively against 4-nitrophenyl β-xylopyranoside. Xylose was a competitive inhibitor with a K(i) of 2.72 mM, whereas fructose was an uncompetitive inhibitor reducing substrate binding affinity (K(m)) and conversion efficiency (V(max)). The enzyme was characterised to be an exo-cutting enzyme releasing xylose from the non-reducing ends of β-1,4 linked xylooligosaccharides (X(2), X(3) and X(4)). Catalytic conversion of X(2), X(3) and X(4) decreased (V(max) and k(cat)) with increasing chain length.