Molecular cloning and characterization of a novel β-glucosidase with high hydrolyzing ability for soybean isoflavone glycosides and glucose-tolerance from soil metagenomic library

A novel β-glucosidase (Bgl1269) was identified from a metagenomic library of mangrove soil by activity-based functional screening. Sequence analysis revealed that Bgl1269 encodes a protein of 422 amino acids. After being overexpressed in Escherichia coli and purified, the enzymatic properties of Bgl1269 were investigated. The recombinant enzyme displayed a pH optimum of 6.0 and a temperature optimum of 40 °C, and the addition of most common metal ions (1 or 10 mM) increased the enzymatic activity evidently. In addition, the enzyme showed high hydrolyzing ability for soybean isoflavone glycosides, and 0.8 unit of enzyme could completely converted daidzin and genistin (0.5 mg/mL) to daidzein and genistein at 40 °C for 0.5 h. Interestingly, Bgl1269 also exhibited a very high glucose-tolerance, with the highest inhibition constant Ki (4.28 M) among β-glucosidases reported so far. These properties make it a good candidate in the production of soybean isoflavone aglycones after further study.