Enzymatic Synthesis of Unnatural Ginsenosides Using a Promiscuous UDP-Glucosyltransferase from Bacillus subtilis.

Glycosylation, which is catalyzed by UDP-glycosyltransferases (UGTs), is an important biological modification for the structural and functional diversity of ginsenosides. In this study, the promiscuous UGT109A1 from Bacillus subtilis was used to synthesize unnatural ginsenosides from natural ginsenosides. UGT109A1 was heterologously expressed in Escherichia coli and then purified by Ni-NTA affinity chromatography. Ginsenosides Re, Rf, Rh1, and R1 were selected as the substrates to produce the corresponding derivatives by the recombinant UGT109A1. The results showed that UGT109A1 could transfer a glucosyl moiety to C3-OH of ginsenosides Re and R1, and C3-OH and C12-OH of ginsenosides Rf and Rh1, respectively, to produce unnatural ginsenosides 3,20-di-O-ß-d-glucopyranosyl-6-O-[α-l-rhamnopyrano-(1→2)-ß-d-glucopyranosyl]-dammar-24-ene-3ß,6α,12ß,20S-tetraol (1), 3,20-di-O-ß-d-glucopyranosyl-6-O-[ß-d-xylopyranosyl-(1→2)-ß-d-glucopyranosyl]-dammar-24-ene-3ß,6α,12ß,20S-tetraol (6), 3-O-ß-d-glucopyranosyl-6-O-[ß-d-glucopyranosyl-(1→2)-ß-d-glucopyranosyl]-dammar-24-ene-3ß,6α,12ß,20S-tetraol (3), 3,12-di-O-ß-d-glucopyranosyl-6-O-[ß-d-glucopyranosyl-(1→2)-ß-d-glucopyranosyl]-dammar-24-ene-3ß,6α,12ß,20S-tetraol (2), 3,6-di-O-ß-d-glucopyranosyl-dammar-24-ene-3ß,6α,12ß,20S-tetraol (5), and 3,6,12-tri-O-ß-d-glucopyranosyl-dammar-24-ene-3ß,6α,12ß,20S-tetraol (4). Among the above products, 1, 2, 3, and 6 are new compounds. The maximal activity of UGT109A1 was achieved at the temperature of 40 °C, in the pH range of 8.0⁻10.0. The activity of UGT109A1 was considerably enhanced by Mg2+, Mn2+, and Ca2+, but was obviously reduced by Cu2+, Co2+, and Zn2+. The study demonstrated that UGT109A1 was effective in producing a series of unnatural ginsenosides through enzymatic reactions, which could pave a way to generate promising leads for new drug discovery.

Progress on the Studies of the Key Enzymes of Ginsenoside Biosynthesis.

As the main bioactive constituents of Panax species, ginsenosides possess a wide range of notable medicinal effects such as anti-cancer, anti-oxidative, antiaging, anti-inflammatory, anti-apoptotic and neuroprotective activities. However, the increasing medical demand for ginsenosides cannot be met due to the limited resource of Panax species and the low contents of ginsenosides. In recent years, biotechnological approaches have been utilized to increase the production of ginsenosides by regulating the key enzymes of ginsenoside biosynthesis, while synthetic biology strategies have been adopted to produce ginsenosides by introducing these genes into yeast. This review summarizes the latest research progress on cloning and functional characterization of key genes dedicated to the production of ginsenosides, which not only lays the foundation for their application in plant engineering, but also provides the building blocks for the production of ginsenosides by synthetic biology.