Purification, characterization, gene cloning and sequencing of a new β-glucosidase from Aspergillus niger BE-2

The cDNA gene (BgL1), encoding GH3 family β-glucosidase (EC 3.2.1.21) from Aspergillus niger BE-2 (abbreviated to BgL1), was amplified and inserted into the yeast expression pPIC9K vector at the site of Bln I (Avr II) and NotI. The recombinant expression vector, designated as pPIC9K-BgL1, was transformed into Pichia pastoris GS115. The transformants were screened on minimal dextrose plates, which inoculated on geneticin G418-containing yeast extract-peptone-dextrose plates. The transformants expressed the high β-glucosidase activity of 22.6 U/mL. SDS-PAGE demonstrated that the BgL1 was extracellularly expressed with an apparent molecular weight of 90.0 kDa. The purified BgL1 displayed the maximum activity at pH 6.0 and 60°C. It was highly stable at a broad pH range of 4.0–7.5 and temperature of 60°C. The BgL1 displayed high similarity to the β-glucosidases of A. niger FN430671 and A. niger DQ655704, the members of the GH3 family. Its three-dimensional structure was predicted using http://swiss-model.expasy.org/ on-line programs based on the crystal structure of Aspergillus aculeatus β-glucosidase.