Molecular cloning and expression of a synthetic gene encoding a ?-glucosidase of Aspergillus niger in the methylotrophic yeast Pichia pastoris

A 2526 bp gene encoding Aspergillus niger ?-glucosidase was chemically synthesized for its heterologous expression in methylotrophic yeast Pichia pastoris, using methanol as inducer. The enzyme was purified from the induction medium to homogeneity by using ammonium sulfate precipitation, DEAE-cellulose chromatography and Sephadex G-100 gel filtration. The recombinant ?-glucosidase catalyses the hydrolysis of cellobiose and salicin. The specific activity (51.2 U/mg) for cellobiose hydrolysis was enriched 7.4 fold with a recovery of 13.6%. Optimum activity was observed in pH 5.0 at 50°C. The enzyme was a monomer with an apparent molecular mass of 90kDa as estimated by sodium dodecyl sulfate polyacrylamide gel electrophoresis.