Isoflavone Aglycones Production from Isoflavone Glycosides by Display of Beta-glucosidase from Aspergillus Oryzae on Yeast Cell Surface

For efficient production of isoflavone aglycones from soybean isoflavones, we isolated three novel types of beta-glucosidase (BGL1, BGL3, and BGL5) from the filamentous fungi Aspergillus oryzae. Three enzymes were independently displayed on the cell surface of a yeast Saccharomyces cerevisiae as a fusion protein with alpha-agglutinin. Three beta-glucosidase-displaying yeast strains hydrolyzed isoflavone glycosides efficiently but exhibited different substrate specificities. Among these beta-glucosidases, BGL1 exhibited the highest activity and also broad substrate specificity to isoflavone glycosides. Although glucose released from isoflavone glycosides are generally known to inhibit beta-glucosidase, the residual ratio of isoflavone glycosides in the reaction mixture with BGL1-displaying yeast strain (Sc-BGL1) reached approximately 6.2%, and the glucose concentration in the reaction mixture was maintained at lower level. This result indicated that Sc-BGL1 assimilated the glucose before they inhibited the hydrolysis reaction, and efficient production of isoflavone aglycones was achieved by engineered yeast cells displaying beta-glucosidase.