One-Pot Synthesis of Ginsenoside Rh2 and Bioactive Unnatural Ginsenoside by Coupling Promiscuous Glycosyltransferase from Bacillus subtilis 168 to Sucrose Synthase

Biocatalytic Synthesis of Calycosin-7-O-β-D-Glucoside with Uridine Diphosphate–Glucose Regeneration System

Calycosin-7-O-β-D-glucoside (Cy7G) is one of the principal components of Radix astragali. This isoflavonoid glucoside is regarded as an indicator to assess the quality of R. astragali and exhibits diverse pharmacological activities. In this study, uridine diphosphate-dependent glucosyltransferase (UGT) UGT88E18 was isolated from Glycine max and expressed in Escherichia coli. Recombinant UGT88E18 could selectively and effectively glucosylate the C7 hydroxyl group of calycosin to synthesize Cy7G. A one-pot reaction by coupling UGT88E18 to sucrose synthase (SuSy) from G. max was developed. The UGT88E18–SuSy cascade reaction could recycle the costly uridine diphosphate glucose (UDPG) from cheap sucrose and catalytic amounts of uridine diphosphate (UDP). The important factors for UGT88E18–SuSy cascade reaction, including UGT88E18/SuSy ratios, different temperatures, and pH values, different concentrations of dimethyl sulfoxide (DMSO), UDP, sucrose, and calycosin, were optimized. We produced 10.5 g L−1 Cy7G in the optimal reaction conditions by the stepwise addition of calycosin. The molar conversion of calycosin was 97.5%, with a space–time yield of 747 mg L−1 h−1 and a UDPG recycle of 78 times. The present study provides a new avenue for the efficient and cost-effective semisynthesis of Cy7G and other valuable isoflavonoid glucosides by UGT–SuSy cascade reaction.

Retention behavior of ginsenosides in a sulfo-based high performance liquid chromatography column

We herein report the use of a sulfo-based column and hydrophilic interaction chromatography (HILIC) to separate 14 ginsenosides, namely Rb1, Rb2, Rb3, Rc, Rd, Rf, Re, Rg1, Rg2, Rg3, Rh1, Rh2, F₂, and C-K. In addition to its rapid and efficient ability to separate these ginsenosides, the sulfo-based column exhibited a good relationship between the ginsenoside capacity factor (k') and molecular weight (M_w) and a strict elution order corresponding to the polarity (P) of the ginsenosides, as confirmed by thin layer chromatography.

Biocatalytic synthesis of ginsenoside Rh2 using Arabidopsis thaliana glucosyltransferase-catalyzed coupled reactions

Ginsenoside Rh2, a rare protopanaxadiol (PPD)-type triterpene saponin isolated from Panax ginseng, exhibits notable anticancer and immune-system-enhancing activities. Glycosylation catalyzed by uridine diphosphate-dependent glucosyltransferase (UGT) is the final biosynthetic step of ginsenoside Rh2. In this study, UGT73C5 isolated from Arabidopsis thaliana was demonstrated to selectively transfer a glucosyl moiety to the C3 hydroxyl group of PPD to synthesize ginsenoside Rh2. UGT73C5 was coupled with sucrose synthase (SuSy) from A. thaliana to regenerate costly uridine diphosphate glucose (UDPG) from cheap sucrose and catalytic amounts of uridine diphosphate (UDP). The UGT73C5/SuSy ratio, temperature, pH, cofactor UDP, and PPD concentrations for UGT73C5-SuSy coupled reactions were optimized. Through the stepwise addition of PPD, the maximal ginsenoside Rh2 production was 3.2 mg mL^-1, which was the highest yield reported to date. These promising results provided an efficient and cost-effective approach to semisynthesize the highly valuable ginsenoside Rh2.

Glycosyltransformation of ginsenoside Rh2 into two novel ginsenosides using recombinant glycosyltransferase from Lactobacillus rhamnosus and its in vitro applications

Background

Ginsenoside Rh2 is well known for many pharmacological activities, such as anticancer, antidiabetes, antiinflammatory, and antiobesity properties. Glycosyltransferases (GTs) are ubiquitous enzymes present in nature and are widely used for the synthesis of oligosaccharides, polysaccharides, glycoconjugates, and novel derivatives. We aimed to synthesize new ginsenosides from Rh2 using the recombinant GT enzyme and investigate its cytotoxicity with diverse cell lines.

Methods

We have used a GT gene with 1,224-bp gene sequence cloned from Lactobacillus rhamnosus (LRGT) and then expressed in Escherichia coli BL21 (DE3). The recombinant GT protein was purified and demonstrated to transform Rh2 into two novel ginsenosides, and they were characterized by nuclear magnetic resonance (NMR) techniques and evaluated by 3-(4, 5-dimethylthiazol-2-yl)-2-5-diphenyltetrazolium bromide assay.

Results

Two novel ginsenosides with an additional glucopyranosyl (6→1) and two additional glucopyranosyl (6→1) linked with the C-3 position of the substrate Rh2 were synthesized, respectively. Cell viability assay in the lung cancer (A549) cell line showed that glucosyl ginsenoside Rh2 inhibited cell viability more potently than ginsenoside Rg3 and Rh2 at a concentration of 10 μM. Furthermore, glucosyl ginsenoside Rh2 did not exhibit any cytotoxic effect in murine macrophage cells (RAW264.7), mouse embryo fibroblasts cells (3T3-L1), and skin cells (B16BL6) at a concentration of 10 μM compared with ginsenoside Rh2 and Rg3.

Conclusion

This is the first report on the synthesis of two novel ginsenosides, namely, glucosyl ginsenoside Rh2 and diglucosyl ginsenoside Rh2 from Rh2 by using recombinant GT isolated from L. rhamnosus. Moreover, diglucosyl ginsenoside Rh2 might be a new candidate for treatment of inflammation, obesity, and skin whiting, and especially for anticancer.

Regulated preparation of Crocin-1 or Crocin-2' Triggered by the Cosolvent DMSO Using Bs-GT/At-SuSy One-Pot Reaction

Crocins are the primary coloring ingredients of saffron. The low-glycosylated members of this compound family, such as crocin-1 (crocetin mono-glucosyl ester) and crocin-2' (crocetin di-glucosyl ester), are rarely distributed in nature and attracting interest for their therapeutic uses. In the present study, a one-pot reaction system was used for efficient preparation of crocin-1 and crocin-2' with in situ regeneration of UDP-Glc by coupling Bs-GT with At-SuSy, a sucrose synthase from Arabidopsis thaliana. Noticeably, DMSO was used as a cosolvent and resulted in improvement of the solubility of the substrate crocetin and regulation of the selectivity of glycosylation. With periodic addition of crocetin, the biosynthesis of crocin-2' was performed with a high yield of 3.25 g/L in 2% DMSO aqueous solution, whereas crocin-1 (2.12 g/L) was selectively obtained in a 10% DMSO aqueous solution. The present study provided a simple approach for the biosynthesis of crocin-1 and crocin-2'.

Mining of Sucrose Synthases from Glycyrrhiza uralensis and Their Application in the Construction of an Efficient UDP-Recycling System

Sucrose synthase (SUS) plays an important role in carbohydrate metabolism in plants. The SUS genes in licorice remain unknown. To reveal the sucrose metabolic pathway in licorice, all the 12 putative SUS genes of Glycyrrhiza uralensis were systematically identified by genome mining, and two novel SUSs (GuSUS1 and GuSUS2) were isolated and characterized for the first time. Furthermore, we found that the flexible N-terminus was responsible for the low stability of plant SUSs, and deletion of redundant N-terminus improved the stability of GuSUS1 and GuSUS2. The half-life of both GuSUS1 and GuSUS2 mutants was increased by 2-fold. Finally, the GuSUS1 mutant was coupled with UGT73C11 for the glycosylation of glycyrrhetinic acid (GA) with uridine 5'-diphosphate disodium salt hydrate (UDP) in situ recycling, and GA conversion was increased by 7-fold. Our study not only identified the SUS genes in licorice but also provided a stable SUS mutant for the construction of an efficient UDP-recycling system for GA glycosylation.

The effects and mechanisms of a biosynthetic ginsenoside 3β,12β-Di-O-Glc-PPD on non-small cell lung cancer

Background

A biosynthetic ginsenoside, 3-O-β-D-glucopyranosyl-12-O-β-D-glucopyranosyl-dammar-24-ene-3β, 12β, 20S-triol (C₃C₁₂PPD), showed antitumor activity against many tumor cells in vitro, especially had better anti-lung cancer activity than Rg3 in vitro and in vivo. However, the effects and molecular mechanisms of C₃C₁₂PPD on non-small cell lung cancer (NSCLC) remain unclear. According to previous studies, we hypothesized ginsenoside C₃C₁₂PPD could inhibit the tumor growth of NSCLC by targeting proliferation, migration and angiogenesis.

Methods

A thiazolyl blue tetrazolium bromide assay (MTT) was performed to evaluate cell viability. Additionally, Transwell and tube formation assays were conducted to analyze cell migration and angiogenesis. The Lewis and A549 tumor xenograft experiments were also performed to investigate the effects of C₃C₁₂PPD on tumor growth in vivo, Western blotting and IHC assay were performed to analyze protein expression.

Results

C₃C₁₂PPD could effectively inhibit the proliferation and migration of lung cancer cells, and tube formation of EA.hy926 cell. Ginsenoside C₃C₁₂PPD suppressed Lewis and A549 tumor growth in vivo without obvious side effects on body weight and the hematology index. In addition, the Western blot analysis revealed that the effects of C₃C₁₂PPD on lung cancer were mediated by inhibiting Raf/MEK/ERK, AKT/mTOR and AKT/GSK-3β/β-Catenin signaling pathways. Finally, C₃C₁₂PPD could significantly inhibit the proliferation index and vessel number in Lewis xenograft tumors analyzed by IHC.

Conclusion

The results of the present study suggest that ginsenoside C₃C₁₂PPD may serve as a potential therapeutic candidate compound against NSCLC.

Enzymatically Synthesized Ginsenoside Exhibits Antiproliferative Activity in Various Cancer Cell Lines

A glycoside derivative of compound K (CK) was synthesized by using a glycosyltransferase, and its biological activity was tested against various cancer-cell lines. A regiospecific, β-1,4-galactosyltransferase (LgtB) converted 100% of 0.5 mmol CK into a galactosylated product in 3 h. The structure of the synthesized derivative was revealed with high performance liquid chromatography, mass spectroscopy, as well as nuclear magnetic resonance analyses, and it was recognized as 20-O-β-D-lactopyranosyl-20(S)-protopanaxadiol (CKGal). Out of the four cancer-cell lines tested (gastric carcinoma (AGS), skin melanoma (B16F10), cervical carcinoma (HeLa), and brain carcinoma (U87MG)), CKGal showed the best cytotoxic ability against B16F10 and AGS when compared to other ginsenosides like compound K (20-O-β-D-glucopyranosyl-20(S)-protopanaxadiol), Rh2 (3-O-β-D-glucopyranosyl-20(S)-protopanaxadiol), and F12 (3-O-β-D-glucopyranosyl-12-O-β-D-glucopyranosyl-20(S)-protopanaxadiol). Thus, the synthesized derivative (CKGal) is a pharmacologically active ginsenoside.

Synthesizing ginsenoside Rh2 in Saccharomyces cerevisiae cell factory at high-efficiency

Synthetic biology approach has been frequently applied to produce plant rare bioactive compounds in microbial cell factories by fermentation. However, to reach an ideal manufactural efficiency, it is necessary to optimize the microbial cell factories systemically by boosting sufficient carbon flux to the precursor synthesis and tuning the expression level and efficiency of key bioparts related to the synthetic pathway. We previously developed a yeast cell factory to produce ginsenoside Rh2 from glucose. However, the ginsenoside Rh2 yield was too low for commercialization due to the low supply of the ginsenoside aglycone protopanaxadiol (PPD) and poor performance of the key UDP-glycosyltransferase (UGT) (biopart UGTPg45) in the final step of the biosynthetic pathway. In the present study, we constructed a PPD-producing chassis via modular engineering of the mevalonic acid pathway and optimization of P450 expression levels. The new yeast chassis could produce 529.0 mg/L of PPD in shake flasks and 11.02 g/L in 10 L fed-batch fermentation. Based on this high PPD-producing chassis, we established a series of cell factories to produce ginsenoside Rh2, which we optimized by improving the C3–OH glycosylation efficiency. We increased the copy number of UGTPg45, and engineered its promoter to increase expression levels. In addition, we screened for more efficient and compatible UGT bioparts from other plant species and mutants originating from the direct evolution of UGTPg45. Combining all engineered strategies, we built a yeast cell factory with the greatest ginsenoside Rh2 production reported to date, 179.3 mg/L in shake flasks and 2.25 g/L in 10 L fed-batch fermentation. The results set up a successful example for improving yeast cell factories to produce plant rare natural products, especially the glycosylated ones.

Enzymatic Synthesis of Novel Glycyrrhizic Acid Glucosides Using a Promiscuous Bacillus Glycosyltransferase

Glycyrrhetinic acid (GA) and glycyrrhizin (GA-3-O-[β-d-glucuronopyranosyl-(1→2)-β-d-glucuronopyranoside], GL) are the major bioactive components of Glycyrrhiza uralensis and possess multifarious notable biological activities. UDP-glycosyltransferase (UGT)–catalyzed glycosylation remarkably extends the structural and functional diversification of GA-glycoside derivatives. In this study, six glucosides (1–6) of GA and GL were synthesized using a Bacillus subtilis 168–originated flexible UDP-glycosyltransferase Bs-YjiC. Bs-YjiC could transfer a glucosyl moiety from UDP-glucose to the free C3 hydroxyl and/or C30 carboxyl groups of GA and GL and further elongate the C30 glucosyl chain via a β-1-2-glycosidic bond. Glycosylation significantly increased the water solubility of these novel glucosides by 4–90 folds. In vitro assays showed that GA monoglucosides (1 and 2) showed stronger antiproliferative activity against human liver cancer cells HepG2 and breast cancer cells MCF-7 than that of GL and GL glucosides. These findings provide significant insights into the important role of promiscuous UGTs for the enzymatic synthesis of novel bioactive GA derivatives.

Biosynthesis of Plant Triterpenoid Saponins in Microbial Cell Factories

Triterpenoid saponins are triterpenoid glycoside compounds which have been widely used in pharmaceutical, agricultural, and food industries. Traditionally, they are extracted from plants, which is time-consuming and environmentally unfriendly. Recently, de novo synthesis of triterpenoid saponins in microbial cell factories was realized, which provides a promising and green approach to alter the traditional supply way. However, the complex biosynthetic pathway and the poor suitability between the endogenous and heterogeneous pathways tremendously limit the yield of triterpenoid saponins. We introduce the biosynthetic pathways of triterpenoid saponins first, and we then summarize the microbial cell factories developed to produce these compounds. Further, we discuss the strategies applied to enhance the production. This paper systematically illustrates the biosynthesis of plant triterpenoid saponins in microbial cell factories.

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-β-d-glucopyranosyl-6-O-[α-l-rhamnopyrano-(1→2)-β-d-glucopyranosyl]-dammar-24-ene-3β,6α,12β,20S-tetraol (1), 3,20-di-O-β-d-glucopyranosyl-6-O-[β-d-xylopyranosyl-(1→2)-β-d-glucopyranosyl]-dammar-24-ene-3β,6α,12β,20S-tetraol (6), 3-O-β-d-glucopyranosyl-6-O-[β-d-glucopyranosyl-(1→2)-β-d-glucopyranosyl]-dammar-24-ene-3β,6α,12β,20S-tetraol (3), 3,12-di-O-β-d-glucopyranosyl-6-O-[β-d-glucopyranosyl-(1→2)-β-d-glucopyranosyl]-dammar-24-ene-3β,6α,12β,20S-tetraol (2), 3,6-di-O-β-d-glucopyranosyl-dammar-24-ene-3β,6α,12β,20S-tetraol (5), and 3,6,12-tri-O-β-d-glucopyranosyl-dammar-24-ene-3β,6α,12β,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.