Systematic optimization of the yeast cell factory for sustainable and high efficiency production of bioactive ginsenoside compound K

Engineering UDP-Glycosyltransferase UGTPg29 for the Efficient Synthesis of Ginsenoside Rg3 from Protopanaxadiol

Rare ginsenosides Rg3 and Rh2, which exhibit diverse pharmacological effects, are derivatives of protopanaxadiol (PPD). UDP-glycosyltransferases, such as the M315F variant of Bs-YjiC (Bs-YjiCm) from Bacillus subtilis and UGTPg29 from Panax ginseng, can efficiently convert PPD into Rh2 and Rh2 into Rg3, respectively. In the present study, the N178I mutation of Bs-YjiCm was introduced, resulting in an increase in Rh2 production. UDP-glycosyltransferase UGTPg29 was then engineered to improve its robustness through semi-rational design. The variant R91M/D184M/A287V/A342L, which indicated desirable stability and activity, was utilized in coupling with the N178I variant of Bs-YjiCm and sucrose synthase AtSuSy from Arabidopsis thaliana to set up a "one-pot" three-enzyme reaction for the biosynthesis of Rg3. The influential factors, including the ratio and concentration of UDP-glycosyltransferases, pH, and the concentrations of UDP, sucrose, and DMSO, were optimized. On this basis, a fed-batch strategy was adopted to achieve a Rg3 yield as high as 12.38 mM (9.72 g/L) with a final yield of 68.78% within 24 h. This work may provide promising UDP-glycosyltransferase candidates for ginsenoside biosynthesis.

Planning biosynthetic pathways of target molecules based on metabolic reaction prediction and AND-OR tree search

Bioretrosynthesis problem is to predict synthetic routes using substrates for given natural products (NPs). However, the huge number of metabolic reactions leads to a combinatorial explosion of searching space, which is high time-consuming and costly. Here, we propose a framework called BioRetro to predict bioretrosynthesis pathways using a one-step bioretrosynthesis network, termed HybridMLP combined with AND-OR tree heuristic search. The HybridMLP predicts precursors that will produce the target NPs, while the AND-OR tree generates the iterative multi-step biosynthetic pathways. The one-step bioretrosynthesis prediction experiments are conducted on MetaNetX dataset by using HybridMLP, which achieves 46.5%, 74.6%, 81.6% in terms of the top-1, top-5, top-10 accuracies. The great performance demonstrates the effectiveness of HybridMLP in one-step bioretrosynthesis. Besides, the evaluation of two benchmark datasets reveals that BioRetro can significantly improve the speed and success rate in predicting biosynthesis pathways. In addition, the BioRetro is further shown to find the synthetic pathway of compounds, such as ginsenoside F1 with the same substrates as reported but different enzymes, which may be the novel potential enzyme to have better catalytic performance.

Efficient Conversion of Stevioside to Rebaudioside M in Saccharomyces cerevisiae by a Engineering Hydrolase System and Prolonging the Growth Cycle

Rebaudioside (Reb) M is an important sweetener with high sweetness, but its low content in Stevia rebaudiana and low catalytic capacity of the glycosyltransferases in heterologous microorganisms limit its production. In order to improve the catalytic efficiency of the conversion of stevioside to Reb M by Saccharomyces cerevisiae, several key issues must be resolved including knocking out endogenous hydrolases, enhancing glycosylation, and extending the enzyme catalytic process. Herein, endogenous glycosyl hydrolase SCW2 was knocked out in S. cerevisiae. The glycosylation process was enhanced by screening glycosyltransferases, and UGT91D2 from S. rebaudiana was identified as the optimum glycosyltransferase. The UDP-glucose supply was enhanced by overexpressing UGP1, and co-expressing UGT91D2 and UGT76G1 achieved efficient conversion of stevioside to Reb M. In order to extend the catalytic process, the silencing information regulator 2 (SIR2) which can prolong the growth cycle of S. cerevisiae was introduced. Finally, combining these modifications produced 12.5 g/L Reb M and the yield reached 77.9% in a 5 L bioreactor with 10.0 g/L stevioside, the highest titer from steviol glycosides to Reb M reported to date. The engineered strain could facilitate the industrial production of Reb M, and the strategies provide references for the production of steviol glycosides.

Proteomic analysis reveals that the co-ordination of cytosolic and mitochondrial pathways is beneficial for sabinene biosynthesis in engineered Saccharomyces cerevisiae

Reconstruction and optimization of biosynthetic pathways can help to overproduce target chemicals in microbial cell factories based on genetic engineering. However, the perturbation of biosynthetic pathways on cellular metabolism is not well investigated and profiling the engineered microbes remains challenging. The rapid development of omics tools has the potential to characterize the engineered microbial cell factory. Here, we performed label-free quantitative proteomic analysis and metabolomic analysis of engineered sabinene overproducing Saccharomyces cerevisiae strains. Combined metabolic analysis andproteomic analysis of targeted mevalonate (MVA) pathway showed that co-ordination of cytosolic and mitochondrial pathways had balanced metabolism, and genome integration of biosynthetic genes had higher sabinene production with less MVA enzymes. Furthermore, comparative proteomic analysis showed that compartmentalized mitochondria pathway had perturbation on central cellular metabolism. This study provided an omics analysis example for characterizing engineered cell factory, which can guide future regulation of the cellular metabolism and maintaining optimal protein expression levels for the synthesis of target products.

Sustainable production of natural products using synthetic biology: Ginsenosides

Synthetic biology approaches offer potential for large-scale and sustainable production of natural products with bioactive potency, including ginsenosides, providing a means to produce novel compounds with enhanced therapeutic properties. Ginseng, known for its non-toxic and potent qualities in traditional medicine, has been used for various medical needs. Ginseng has shown promise for its antioxidant and neuroprotective properties, and it has been used as a potential agent to boost immunity against various infections when used together with other drugs and vaccines. Given the increasing demand for ginsenosides and the challenges associated with traditional extraction methods, synthetic biology holds promise in the development of therapeutics. In this review, we discuss recent developments in microorganism producer engineering and ginsenoside production in microorganisms using synthetic biology approaches.

Pharmacological effects of biologically synthesized ginsenoside CK-rich preparation (AceCK40) on the colitis symptoms in DSS-induced Caco-2 cells and C57BL mice

BACKGROUND

Despite the notable pharmacological potential of natural ginsenosides, their industrial application is hindered by low oral bioavailability. Recent research centers on the production of less-glycosylated minor ginsenosides.

PURPOSE

This study aimed to explore the effect of a biologically synthesized ginsenoside CK-rich minor ginsenoside complex (AceCK40), on ameliorating colitis using DSS-induced colitis models in vitro and in vivo.

METHODS

The ginsenoside composition of AceCK40 was determined by HPLC-ELSD and UHPLC-MS/MS analyses. In vitro colitis model was established using dextran sodium sulfate (DSS)-induced Caco-2 intestinal epithelial model. For in vivo experiments, DSS-induced severe colitis mouse model was established.

RESULTS

In DSS-stimulated Caco-2 cells, AceCK40 downregulated mitogen-activated protein kinase (MAPK) activation (p < 0.05), inhibited monocyte chemoattractant protein-1 (MCP-1) production (p < 0.05), and enhanced MUC2 expression (p < 0.05), mediated via signaling pathway regulation. Daily AceCK40 administration at doses of 10 and 30 mg/kg/day was well tolerated by DSS-induced severe colitis mice. These doses led to significant alleviation of disease activity index score (> 36.0% decrease, p < 0.05), increased luminal immunoglobulin (Ig)G (> 37.6% increase, p < 0.001) and IgA (> 33.8% increase, p < 0.001), lowered interleukin (IL)-6 (> 65.7% decrease, p < 0.01) and MCP-1 (> 116.2% decrease, p < 0.05), as well as elevated serum IgA (> 51.4% increase, p < 0.001) and lowered serum IL-6 (112.3% decrease at 30 mg/kg, p < 0.001). Hematoxylin and eosin (H&E) and periodic acid-Schiff (PAS) staining revealed that DSS-mediated thickening of the muscular externa, extensive submucosal edema, crypt distortion, and decreased mucin droplets were significantly alleviated by AceCK40 administration. Additionally, daily administration of AceCK40 led to significant recovery of colonic tight junctions damaged by DSS through the elevation in the expression of adhesion molecules, including occludin, E-cadherin, and N-cadherin.

CONCLUSION

This study presents the initial evidence elucidating the anti-colitis effects of AceCK40 and its underlying mechanism of action through sequential in vitro and in vivo systems employing DSS stimulation. Our findings provide valuable fundamental data for the utilization of AceCK40 in the development of novel anti-colitis candidates.

Engineering and transcriptome study of Saccharomyces cerevisiae to produce ginsenoside compound K by glycerol

Synthetic biology-based engineering of Saccharomyces cerevisiae to produce terpenoid natural products is an effective strategy for their industrial application. Previously, we observed that glycerol addition was beneficial for ginsenoside compound K (CK) production in a S. cerevisiae when it was fermented using the YPD medium. Here, we reconstructed the CK synthesis and glycerol catabolic pathway in a high-yield protopanaxadiol (PPD) S. cerevisiae strain. Remarkably, our engineered strain exhibited the ability to utilize glycerol as the sole carbon source, resulting in a significantly enhanced production of 433.1 ± 8.3 mg L-1 of CK, which was 2.4 times higher compared to that obtained in glucose medium. Transcriptomic analysis revealed that the transcript levels of several key genes involved in the mevalonate (MVA) pathway and the uridine diphosphate glucose (UDPG) synthesis pathway were up-regulated in response to glycerol. The addition of glycerol enhanced CK titers by augmenting the flux of the terpene synthesis pathway and facilitating the production of glycosyl donors. These results suggest that glycerol is a promising carbon source in S. cerevisiae, especially for the production of triterpenoid saponins.

Recent advances in triterpenoid pathway elucidation and engineering

Triterpenoids are among the most assorted class of specialized metabolites found in all the taxa of living organisms. Triterpenoids are the leading active ingredients sourced from plant species and are utilized in pharmaceutical and cosmetic industries. The triterpenoid precursor 2,3-oxidosqualene, which is biosynthesized via the mevalonate (MVA) pathway is structurally diversified by the oxidosqualene cyclases (OSCs) and other scaffold-decorating enzymes such as cytochrome P450 monooxygenases (P450s), UDP-glycosyltransferases (UGTs) and acyltransferases (ATs). A majority of the bioactive triterpenoids are harvested from the native hosts using the traditional methods of extraction and occasionally semi-synthesized. These methods of supply are time-consuming and do not often align with sustainability goals. Recent advancements in metabolic engineering and synthetic biology have shown prospects for the green routes of triterpenoid pathway reconstruction in heterologous hosts such as Escherichia coli, Saccharomyces cerevisiae and Nicotiana benthamiana, which appear to be quite promising and might lead to the development of alternative source of triterpenoids. The present review describes the biotechnological strategies used to elucidate complex biosynthetic pathways and to understand their regulation and also discusses how the advances in triterpenoid pathway engineering might aid in the scale-up of triterpenoid production in engineered hosts.

Manipulation of fungal cell wall integrity to improve production of fungal natural products

Fungi, as an important industrial microorganism, play an essential role in the production of natural products (NPs) due to their advantages of utilizing cheap raw materials as substrates and strong protein secretion ability. Although many metabolic engineering strategies have been adopted to enhance the biosynthetic pathway of NPs in fungi, the fungal cell wall as a natural barrier tissue is the final and key step that affects the efficiency of NPs synthesis. To date, many important progresses have been achieved in improving the synthesis of NPs by regulating the cell wall structure of fungi. In this review, we systematically summarize and discuss various strategies for modifying the cell wall structure of fungi to improve the synthesis of NPs. At first, the cell wall structure of different types of fungi is systematically described. Then, strategies to disrupt cell wall integrity (CWI) by regulating the synthesis of cell wall polysaccharides and binding proteins are summarized, which have been applied to improve the synthesis of NPs. In addition, we also summarize the studies on the regulation of CWI-related signaling pathway and the addition of exogenous components for regulating CWI to improve the synthesis of NPs. Finally, we propose the current challenges and essential strategies to usher in an era of more extensive manipulation of fungal CWI to improve the production of fungal NPs.

Biosynthesis and biotechnological production of the anti-obesity agent celastrol

Obesity is a major health risk still lacking effective pharmacological treatment. A potent anti-obesity agent, celastrol, has been identified in the roots of Tripterygium wilfordii. However, an efficient synthetic method is required to better explore its biological utility. Here we elucidate the 11 missing steps for the celastrol biosynthetic route to enable its de novo biosynthesis in yeast. First, we reveal the cytochrome P450 enzymes that catalyse the four oxidation steps that produce the key intermediate celastrogenic acid. Subsequently, we show that non-enzymatic decarboxylation-triggered activation of celastrogenic acid leads to a cascade of tandem catechol oxidation-driven double-bond extension events that generate the characteristic quinone methide moiety of celastrol. Using this acquired knowledge, we have developed a method for producing celastrol starting from table sugar. This work highlights the effectiveness of combining plant biochemistry with metabolic engineering and chemistry for the scalable synthesis of complex specialized metabolites.

Natural products of pentacyclic triterpenoids: from discovery to heterologous biosynthesis

Covering: up to 2022Pentacyclic triterpenoids are important natural bioactive substances that are widely present in plants and fungi. They have significant medicinal efficacy, play an important role in reducing blood glucose and protecting the liver, and have anti-inflammatory, anti-oxidation, anti-fatigue, anti-viral, and anti-cancer activities. Pentacyclic triterpenoids are derived from the isoprenoid biosynthetic pathway, which generates common precursors of triterpenes and steroids, followed by cyclization with oxidosqualene cyclases (OSCs) and decoration via cytochrome P450 monooxygenases (CYP450s) and glycosyltransferases (GTs). Many biosynthetic pathways of triterpenoid saponins have been elucidated by studying their metabolic regulation network through the use of multiomics and identifying their functional genes. Unfortunately, natural resources of pentacyclic triterpenoids are limited due to their low content in plant tissues and the long growth cycle of plants. Based on the understanding of their biosynthetic pathway and transcriptional regulation, plant bioreactors and microbial cell factories are emerging as alternative means for the synthesis of desired triterpenoid saponins. The rapid development of synthetic biology, metabolic engineering, and fermentation technology has broadened channels for the accumulation of pentacyclic triterpenoid saponins. In this review, we summarize the classification, distribution, structural characteristics, and bioactivity of pentacyclic triterpenoids. We further discuss the biosynthetic pathways of pentacyclic triterpenoids and involved transcriptional regulation. Moreover, the recent progress and characteristics of heterologous biosynthesis in plants and microbial cell factories are discussed comparatively. Finally, we propose potential strategies to improve the accumulation of triterpenoid saponins, thereby providing a guide for their future biomanufacturing.

Compound K Production: Achievements and Perspectives

Compound K (CK) is one of the major metabolites found in mammalian blood and organs following oral administration of Panax plants. CK, also known as minor ginsenoside, can be absorbed in the systemic circulation. It has garnered significant attention in healthcare and medical products due to its pharmacological activities, such as antioxidation, anticancer, antiproliferation, antidiabetics, neuroprotection, and anti-atherogenic activities. However, CK is not found in natural ginseng plants but in traditional chemical synthesis, which uses toxic solvents and leads to environmental pollution during the harvest process. Moreover, enzymatic reactions are impractical for industrial CK production due to low yield and high costs. Although CK could be generated from major ginsenosides, most ginsenosides, including protopanaxatriol-oleanane and ocotillol-type, are not converted into CK by catalyzing β-glucosidase. Therefore, microbial cell systems have been used as a promising solution, providing a safe and efficient approach to CK production. This review provides a summary of various approaches for the production of CK, including chemical and enzymatic reactions, biotransformation by the human intestinal bacteria and endophytes as well as engineered microbes. Moreover, the approaches for CK production have been discussed to improve the productivity of target compounds.

Advances in the biosynthesis and metabolic engineering of rare ginsenosides

Rare ginsenosides are the deglycosylated secondary metabolic derivatives of major ginsenosides, and they are more readily absorbed into the bloodstream and function as active substances. The traditional preparation methods hindered the potential application of these effective components. The continuous elucidation of ginsenoside biosynthesis pathways has rendered the production of rare ginsenosides using synthetic biology techniques effective for their large-scale production. Previously, only the progress in the biosynthesis and biotechnological production of major ginsenosides was highlighted. In this review, we summarized the recent advances in the identification of key enzymes involved in the biosynthetic pathways of rare ginsenosides, especially the glycosyltransferases (GTs). Then the construction of microbial chassis for the production of rare ginsenosides, mainly in Saccharomyces cerevisiae, was presented. In the future, discovery of more GTs and improving their catalytic efficiencies are essential for the metabolic engineering of rare ginsenosides. This review will give more clues and be helpful for the characterization of the biosynthesis and metabolic engineering of rare ginsenosides. KEY POINTS: • The key enzymes involved in the biosynthetic pathways of rare ginsenosides are summarized. • The recent progress in metabolic engineering of rare ginsenosides is presented. • The discovery of glycosyltransferases is essential for the microbial production of rare ginsenosides in the future.

Biotransformation of High Concentrations of Ginsenoside Substrate into Compound K by β-glycosidase from Sulfolobus solfataricus

The rare ginsenoside Compound K (CK) is an attractive ingredient in traditional medicines, cosmetics, and the food industry because of its various biological activities. However, it does not exist in nature. The commonly used method for the production of CK is enzymatic conversion. In order to further improve the catalytic efficiency and increase the CK content, a thermostable β-glycosidase from Sulfolobus solfataricus was successfully expressed in Pichia pastoris and secreted into fermentation broth. The recombinant SS-bgly in the supernatant showed enzyme activity of 93.96 U/mg at 120 h when using pNPG as substrate. The biotransformation conditions were optimized at pH 6.0 and 80 °C, and its activity was significantly enhanced in the presence of 3 mM Li⁺. When the substrate concentration was 10 mg/mL, the recombinant SS-bgly completely converted the ginsenoside substrate to CK with a productivity of 507.06 μM/h. Moreover, the recombinant SS-bgly exhibited extraordinary tolerance against high substrate concentrations. When the ginsenoside substrate concentration was increased to 30 mg/mL, the conversion could still reach 82.5% with a productivity of 314.07 μM/h. Thus, the high temperature tolerance, resistance to a variety of metals, and strong substrate tolerance make the recombinant SS-bgly expressed in P. pastoris a potential candidate for the industrial production of the rare ginsenoside CK.

Production of a Novel Protopanaxatriol-Type Ginsenoside by Yeast Cell Factories

Ginsenosides, the main active compounds in Panax species, are glycosides of protopanaxadiol (PPD) or protopanaxatriol (PPT). PPT-type ginsenosides have unique pharmacological activities on the central nervous system and cardiovascular system. As an unnatural ginsenoside, 3,12-Di-O-β-D-glucopyranosyl-dammar-24-ene-3β,6α,12β,20S-tetraol (3β,12β-Di-O-Glc-PPT) can be synthesized through enzymatic reactions but is limited by the expensive substrates and low catalytic efficiency. In the present study, we successfully produced 3β,12β-Di-O-Glc-PPT in Saccharomyces cerevisiae with a titer of 7.0 mg/L by expressing protopanaxatriol synthase (PPTS) from Panax ginseng and UGT109A1 from Bacillus subtilis in PPD-producing yeast. Then, we modified this engineered strain by replacing UGT109A1 with its mutant UGT109A1-K73A, overexpressing the cytochrome P450 reductase ATR2 from Arabidopsis thaliana and the key enzymes of UDP-glucose biosynthesis to increase the production of 3β,12β-Di-O-Glc-PPT, although these strategies did not show any positive effect on the yield of 3β,12β-Di-O-Glc-PPT. However, the unnatural ginsenoside 3β,12β-Di-O-Glc-PPT was produced in this study by constructing its biosynthetic pathway in yeast. To the best of our knowledge, this is the first report of producing 3β,12β-Di-O-Glc-PPT through yeast cell factories. Our work provides a viable route for the production of 3β,12β-Di-O-Glc-PPT, which lays a foundation for drug research and development.

Combinatorial Enzymatic Catalysis for Bioproduction of Ginsenoside Compound K

Ginsenoside compound K (CK) is an emerging functional food or pharmaceutical product. To date, there are still challenges to exploring effective catalytic enzymes for enzyme-catalyzed manufacturing processes and establishing enzyme-catalyzed processes. Herein, we identified three ginsenoside hydrolases BG07 (glucoamylase), BG19 (β-glucosidase), and BG23 (β-glucosidase) from Aspergillus tubingensis JE0609 by transcriptome analysis and peptide mass fingerprinting. Among them, BG23 was expressed in Komagataella phaffii with a high volumetric activity of 235.73 U mL-1 (pNPG). Enzymatic property studies have shown that BG23 is an acidic (pH adaptation range of 4.5-7.0) and mesophilic (thermostable < 50 °C) enzyme. Moreover, a one-pot combinatorial enzyme-catalyzed strategy based on BG23 and BGA35 (β-galactosidase from Aspergillus oryzae) was established, with a high CK yield of 396.7 mg L-1 h-1. This study explored the ginsenoside hydrolases derived from A. tubingensis at the molecular level and provided a reference for the efficient production of CK.

Recent Advances in Yeast Recombinant Biosynthesis of the Triterpenoid Protopanaxadiol and Glycosylated Derivatives Thereof

Plant natural products are a seemingly endless resource for novel chemical structures. However, their extraction often results in high prices, fluctuation in both quantity and quality, and negative environmental impact. The latter might result from the extraction procedure but more often from the high amount of plant biomass required. With the advent of synthetic biology, producing natural plant products in large quantities using yeasts as hosts has become possible. Here, we focus on the recent advances in metabolic engineering of the yeasts species Saccharomyces cerevisiae and Yarrowia lipolytica for the synthesis of ginsenoside triterpenoids, namely, dammarenediol-II, protopanaxadiol, protopanaxatriol, compound K, ginsenoside Rh1, ginsenoside Rh2, ginsenoside Rg3, and ginsenoside F1. A discussion is provided on advanced synthetic biology, bioprocess strategies, and current challenges for the biosynthesis of ginsenoside triterpenoids. Finally, future directions in metabolic and process engineering are summarized and may help reify sustainable ginsenoside production.

Production of ginsenoside compound K by microbial cell factory using synthetic biology-based strategy: a review

Ginsenoside compound K (CK) is a major intestinal bacterial metabolite of the protopanaxadiol-type ginsenoside family that can be absorbed in the systemic circulation. CK possesses diverse and important pharmacological properties. The low production and high cost of traditional manufacturing methods based on the extraction and biotransformation of total ginsenosides from ginseng have limited their medical application. However, considerable progress has been made in the area of de novo CK production via microbial cell factories using synthetic biology-based strategies. By introducing key enzymes responsible for CK biosynthesis into microbial cells, CK was produced via a series of in vivo enzymatic reactions that utilize the inherent precursors in microbial cells. After systematic optimization using various metabolic engineering strategies, the yield of CK increased significantly and exceeded the traditional plant extraction-biotransformation method, implying the commercial feasibility of this approach. This review summarizes recent novel advancements in the production of CK using microbial cell factories.

Engineering Critical Amino Acid Residues of Lanosterol Synthase to Improve the Production of Triterpenoids in Saccharomyces cerevisiae

Triterpenoids are a subgroup of terpenoids and have wide applications in the food, cosmetics, and pharmaceutical industries. The heterologous production of various triterpenoids in Saccharomyces cerevisiae, as well as other microbes, has been successfully implemented as these production hosts not only produce the precursor of triterpenoids 2,3-oxidosqualene by the mevalonate pathway but also allow simple expression of plant membrane-anchored enzymes. Nevertheless, 2,3-oxidosqualene is natively converted to lanosterol catalyzed by the endogenous lanosterol synthase (Erg7p), causing low production of recombinant triterpenoids. While simple deletion of ERG7 was not effective, in this study, the critical amino acid residues of Erg7p were engineered to lower this critical enzyme activity. The engineered S. cerevisiae indeed accumulated 2,3-oxidosqualene up to 180 mg/L. Engineering triterpenoid synthesis into the ERG7-modified strain resulted in 7.3- and 3-fold increases in the titers of dammarane-type and lupane-type triterpenoids, respectively. This study presents an efficient inducer-free strategy for lowering Erg7p activity, thereby providing 2,3-oxidosqualene for the enhanced production of various triterpenoids.

Pathway elucidation of bioactive rhamnosylated ginsenosides in Panax ginseng and their de novo high-level production by engineered Saccharomyces cerevisiae

Rg2 and Re are both rhamnose-containing ginsenosides isolated exclusively from Panax plants, which exhibit broad spectrum of pharmacological activities. However, limitations of current plant-relied manufacturing methods have largely hampered their medical applications. Here, we report elucidation of the complete biosynthetic pathway of these two ginsenosides by the identification of a rhamnosyltransferase PgURT94 from Panax ginseng. We then achieve de novo bio-production of Rg2 and Re from glucose by reconstituting their biosynthetic pathways in yeast. Through stepwise strain engineering and fed-batch fermentation, the maximum yield of Rg2 and Re reach 1.3 and 3.6 g/L, respectively. Our work completes the identification of the last missing enzyme for Rg2 and Re biosynthesis and achieves their high-level production by engineered yeasts. Once scaled, this microbial biosynthesis platform will enable a robust and stable supply of Rg2 and Re and facilitate their food and medical applications.

Glycosylation Modification Enhances (2S)-Naringenin Production in Saccharomyces cerevisiae

(2S)-Naringenin is an important flavonoid precursor, with multiple nutritional and pharmacological activities. Both (2S)-naringenin and other flavonoid production are hindered by poor water solubility and inhibited cell growth. To address this, we increased solubility and improved cell growth by partially glycosylating (2S)-naringenin to naringenin-7-O-glucoside, which facilitated increased extracellular secretion, by knocking out endogenous glycosyl hydrolase genes, EXG1 and SPR1, and expressing the glycosyltransferase gene (UGT733C6). Naringenin-7-O-glucoside synthesis was further improved by optimizing UDP-glucose and shikimate pathways. Then, hydrochloric acid was used to hydrolyze naringenin-7-O-glucoside to (2S)-naringenin outside the cell. Thus, our optimized Saccharomyces cerevisiae strain E32T19 produced 1184.1 mg/L (2S)-naringenin, a 7.9-fold increase on the starting strain. Therefore. we propose that glycosylation modification is a useful strategy for the efficient heterologous biosynthesis of (2S)-naringenin in S. cerevisiae.

Exploring the Strategy of Fusing Sucrose Synthase to Glycosyltransferase UGT76G1 in Enzymatic Biotransformation

Uridine diphosphate glycosyltransferases (UGTs) as fine catalysts of glycosylation are increasingly used in the synthesis of natural products. Sucrose synthase (SuSy) is recognized as a powerful tool for in situ regenerating sugar donors for the UGT-catalyzed reaction. It is crucial to select the appropriate SuSy for cooperation with UGT in a suitable way. In the present study, eukaryotic SuSy from Arabidopsisthaliana (AtSUS1) helped stevia glycosyltransferase UGT76G1 achieve the complete conversion of stevioside (30 g/L) into rebaudioside A (RebA). Position of the individual transcription units containing the genes encoding AtSUS1 and UGT76G1 in the expression plasmid has an effect, but less than that of the fusion order of these genes on RebA yield. Fusion of the C-terminal of AtSUS1 and the N-terminal of UGT76G1 with rigid linkers are conducive to maintaining enzyme activities. When the same fusion strategy was applied to a L637M-T640V double mutant of prokaryotic SuSy from Acidithiobacillus caldus (AcSuSym), 18.8 ± 0.6 g/L RebA (a yield of 78.2%) was accumulated in the reaction mixture catalyzed by the fusion protein Acm-R3-76G1 (the C-terminal of AcSuSym and the N-terminal of UGT76G1 were linked with (EAAAK)3). This work would hopefully reveal the potential of UGT-SuSy fusion in improving the cascade enzymatic glycosylation.

Metabolic engineering of yeasts for green and sustainable production of bioactive ginsenosides F2 and 3β,20S-Di-O-Glc-DM

Both natural ginsenoside F2 and unnatural ginsenoside 3β,20S-Di-O-Glc-DM were reported to exhibit anti-tumor activity. Traditional approaches for producing them rely on direct extraction from Panax ginseng, enzymatic catalysis or chemical synthesis, all of which result in low yield and high cost. Metabolic engineering of microbes has been recognized as a green and sustainable biotechnology to produce natural and unnatural products. Hence we engineered the complete biosynthetic pathways of F2 and 3β,20S-Di-O-Glc-DM in Saccharomyces cerevisiae via the CRISPR/Cas9 system. The titers of F2 and 3β,20S-Di-O-Glc-DM were increased from 1.2 to 21.0 mg/L and from 82.0 to 346.1 mg/L at shake flask level, respectively, by multistep metabolic engineering strategies. Additionally, pharmacological evaluation showed that both F2 and 3β,20S-Di-O-Glc-DM exhibited anti-pancreatic cancer activity and the activity of 3β,20S-Di-O-Glc-DM was even better. Furthermore, the titer of 3β,20S-Di-O-Glc-DM reached 2.6 g/L by fed-batch fermentation in a 3 L bioreactor. To our knowledge, this is the first report on demonstrating the anti-pancreatic cancer activity of F2 and 3β,20S-Di-O-Glc-DM, and achieving their de novo biosynthesis by the engineered yeasts. Our work presents an alternative approach to produce F2 and 3β,20S-Di-O-Glc-DM from renewable biomass, which lays a foundation for drug research and development.

Glycosyltransferases: Mining, engineering and applications in biosynthesis of glycosylated plant natural products

UDP-Glycosyltransferases (UGTs) catalyze the transfer of nucleotide-activated sugars to specific acceptors, among which the GT1 family enzymes are well-known for their function in biosynthesis of natural product glycosides. Elucidating GT function represents necessary step in metabolic engineering of aglycone glycosylation to produce drug leads, cosmetics, nutrients and sweeteners. In this review, we systematically summarize the phylogenetic distribution and catalytic diversity of plant GTs. We also discuss recent progress in the identification of novel GT candidates for synthesis of plant natural products (PNPs) using multi-omics technology and deep learning predicted models. We also highlight recent advances in rational design and directed evolution engineering strategies for new or improved GT functions. Finally, we cover recent breakthroughs in the application of GTs for microbial biosynthesis of some representative glycosylated PNPs, including flavonoid glycosides (fisetin 3-O-glycosides, astragalin, scutellarein 7-O-glucoside), terpenoid glycosides (rebaudioside A, ginsenosides) and polyketide glycosides (salidroside, polydatin).