Improved conversion of ginsenoside Rb1 to compound K by semi-rational design of Sulfolobus solfataricus β-glycosidase

Ginsenoside compound K has been used as a key nutritional and cosmetic component because of its anti-fatigue and skin anti-aging effects. β-Glycosidase from Sulfolobus solfataricus (SS-BGL) is known as the most efficient enzyme for compound K production. The hydrolytic pathway from ginsenoside Rb1 to compound K via Rd and F2 is the most important because Rb1 is the most abundant component in ginseng extract. However, the enzymatic conversion of ginsenoside Rd to F2 is a limiting step in the hydrolytic pathway because of the relatively low activity for Rd. A V209 residue obtained from error-prone PCR was related to Rd-hydrolyzing activity, and a docking pose showing an interaction with Val209 was selected from numerous docking poses. W361F was obtained by rational design using the docking pose that exhibited 4.2-fold higher activity, 3.7-fold higher catalytic efficiency, and 3.1-fold lower binding energy for Rd than the wild-type enzyme, indicating that W361F compensated for the limiting step. W361F completely converted Rb1 to compound K with a productivity of 843 mg l-1 h-1 in 80 min, and showed also 7.4-fold higher activity for the flavanone, hesperidin, than the wild-type enzyme. Therefore, the W361F variant SS-BGL can be useful for hydrolysis of other glycosides as well as compound K production from Rb1, and semi-rational design is a useful tool for enhancing hydrolytic activity of β-glycosidase.