Pathways of biotransformation of zingiberen newsaponin from Dioscorea zingiberensis C. H. Wright to diosgenin

A new steroidal saponin-β-glucosidase from Aspergillus flavus that specifically hydrolyzed the terminal β-d-glucosyl group at the C-3 position of zingiberen newsaponin, deltonin and trillin from Dioscorea zingiberensis C. H. Wright (DZW) was purified, and characterized. The optimal temperature and pH for the new steroidal saponin-β-glucosidase was 50 °C and pH 5.0. The steroidal saponin-β-glucosidase was stable at 30–60 °C, and retained more than 80% activity. Further, the purified protein was analyzed by ESI-Q-TOF proteomic analyzer. The results indicated that this enzyme is a β-glucosidase of the type glycosidase hydrolase 3 (GH3). Using a combination of the steroidal saponin-β-glucosidase and steroidal saponin-α-1,2-rhamnosidase from Curvularia lunata obtained previously in our lab, the saponins zingieren newsaponin and deltonin could be converted to diosgenin. The pathways of converting zingiberen newsaponin and deltonin into diosgenin by the two key enzymes were elucidated in this study.