Immobilization of snailase on glutamate modified MIL-88B(Fe) to efficiently convert the rare ginsenoside CK with high enzyme recyclability and stability

Abstract

The carboxyl groups on MIL-88B(Fe) are crucial for the covalent immobilization of snailase, and the enzyme can convert common ginsenoside Rb1 into the rare ginsenoside compound K (CK) with higher bioavailability. The present study proposed glutamate-modified MIL-88B(Fe) for the immobilization of snailase to improve enzymatic activity and loading capacity. The surface topography characterized by SEM and CLSM indicated snailase was successfully encapsulated and uniformly distributed in the Sna@MIL-88B(Fe). The maximum immobilized capacities of snailase by MIL-88B(Fe)-Glu and MIL-88B(Fe) were 185 mg/g and 140 mg/g, respectively. Moreover, covalently immobilized snailase on MIL-88B(Fe)-Glu showed better pH, thermal, solvent, and storage stabilities than those immobilized on MIL-88B(Fe) and resolvase. Meanwhile, the reaction kinetics exhibited that the Km value of Sna@MIL-88B(Fe)-Glu (1.6 mM) was significantly lower than that of free snailase (2.1 mM), indicating a higher substrate affinity. Besides, more ginsenoside CK with higher conversion (60.71 %) was generated by Sna@MIL-88B(Fe)-Glu, even after five cycles. The glutamate modified covalent grafting method provides a highly efficient strategy for biocatalysis and a reference for the immobilized snailase-catalyzed transformation of rare ginsenosides CK.