Metabolic engineering of Saccharomyces cerevisiae for production of ginsenosides

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.

Carnosic acid: an effective phenolic diterpenoid for prevention and management of cancers via targeting multiple signaling pathways

Cancer is a serious global public health issue, and a great deal of research has been made to treat cancer. Of these, discovery of promising compounds that effectively fight cancer always has been the main point of interest in pharmaceutical research. Carnosic acid (CA) is a phenolic diterpenoid compound widely present in Lamiaceae plants such as Rosemary (Rosmarinus officinalis L.). In recent years, there has been increasing evidence that CA has significant anti-cancer activity, such as leukaemia, colorectal cancer, breast cancer, lung cancer, liver cancer, pancreatic cancer, stomach cancer, lymphoma, prostate cancer, oral cancer, etc. The potential mechanisms involved by CA, including inhibiting cell proliferation, inhibiting metastasis, inducing cell apoptosis, stimulating autophagy, regulating the immune system, reducing inflammation, regulating the gut microbiota, and enhancing the effects of other anti-cancer drugs. This article reviews the biosynthesis, pharmacokinetics and metabolism, safety and toxicity, as well as the molecular mechanisms and signaling pathways of the anticancer activity of CA. This will contribute to the development of CA or CA-containing functional foods for the prevention and treatment of cancer, providing important advances in the advancement of cancer treatment strategies.

Metabolic engineering of Saccharomyces cerevisiae for high-level production of (+)-ambrein from glucose

(+)-Ambrein is the primary component of ambergris, a rare product found in sperm whales (Physeter microcephalus). Microbial production using sustainable resources is a promising way to replace animal extraction and chemical synthesis. We constructed an engineered yeast strain to produce (+)-ambrein de novo. Squalene is a substrate for the biosynthesis of (+)-ambrein. Firstly, strain LQ2, with a squalene yield of 384.4 mg/L was obtained by optimizing the mevalonate pathway. Then we engineered a method for the de novo production of (+)-ambrein using glucose as a carbon source by overexpressing codon-optimized tetraprenyl-β-curcumene cyclase (BmeTC) and its double mutant enzyme (BmeTCY167A/D373C), evaluating different promoters, knocking out GAL80, and fusing the protein with BmeTC and squalene synthase (AtSQS2). Nevertheless, the synthesis of (+)-ambrein is still limited, causing low catalytic activity in BmeTC. We carried out a protein surface amino acid modification of BmeTC. The dominant mutant BmeTCK6A/Q9E/N454A for the first step was obtained to improve its catalytic activity. The yield of (+)-ambrein increased from 35.2 to 59.0 mg/L in the shake flask and finally reached 457.4 mg/L in the 2 L fermenter, the highest titer currently available for yeast. Efficiently engineered strains and inexpensive fermentation conditions for the industrial production of (+)-ambrein. The metabolic engineering tools provide directions for optimizing the biosynthesis of other high-value triterpenes.

Sustainable biosynthesis of squalene from waste cooking oil by the yeast Yarrowia lipolytica

Squalene is a highly sought-after triterpene compound in growing demand, and its production offers a promising avenue for circular economy practices. In this study, we applied metabolic engineering principles to enhance squalene production in the nonconventional yeast Yarrowia lipolytica, using waste cooking oil as a substrate. By overexpressing key enzymes in the mevalonate pathway - specifically ERG9 encoding squalene synthase, ERG20 encoding farnesyl diphosphate synthase, and HMGR encoding hydroxy-methyl-glutaryl-CoA reductase - we achieved a yield of 779.9 mg/L of squalene. Further co-overexpression of DGA1, encoding diacylglycerol acyltransferase, and CAT2, encoding carnitine acetyltransferase, in combination with prior metabolic enhancements, boosted squalene production to 1381.4 mg/L in the engineered strain Po1g17. To enhance the supply of the precursor acetyl-CoA and inhibit downstream squalene conversion, we supplemented with 6 g/L pyruvic acid and 0.7 mg/L terbinafine, resulting in an overall squalene titer of 2594.1 mg/L. These advancements underscore the potential for sustainable, large-scale squalene production using Y. lipolytica cell factories, contributing to circular economy initiatives by valorizing waste materials.

Two-Phase Fermentation Systems for Microbial Production of Plant-Derived Terpenes

Microbial cell factories, renowned for their economic and environmental benefits, have emerged as a key trend in academic and industrial areas, particularly in the fermentation of natural compounds. Among these, plant-derived terpenes stand out as a significant class of bioactive natural products. The large-scale production of such terpenes, exemplified by artemisinic acid-a crucial precursor to artemisinin-is now feasible through microbial cell factories. In the fermentation of terpenes, two-phase fermentation technology has been widely applied due to its unique advantages. It facilitates in situ product extraction or adsorption, effectively mitigating the detrimental impact of product accumulation on microbial cells, thereby significantly bolstering the efficiency of microbial production of plant-derived terpenes. This paper reviews the latest developments in two-phase fermentation system applications, focusing on microbial fermentation of plant-derived terpenes. It also discusses the mechanisms influencing microbial biosynthesis of terpenes. Moreover, we introduce some new two-phase fermentation techniques, currently unexplored in terpene fermentation, with the aim of providing more thoughts and explorations on the future applications of two-phase fermentation technology. Lastly, we discuss several challenges in the industrial application of two-phase fermentation systems, especially in downstream processing.

Transcriptome-Wide Identification and Integrated Analysis of a UGT Gene Involved in Ginsenoside Ro Biosynthesis in Panax ginseng

Panax ginseng as a traditional medicinal plant with a long history of medicinal use. Ginsenoside Ro is the only oleanane-type ginsenoside in ginseng, and has various pharmacological activities, including anti-inflammatory, detoxification, and antithrombotic activities. UDP-dependent glycosyltransferase (UGT) plays a key role in the synthesis of ginsenoside, and the excavation of UGT genes involved in the biosynthesis of ginsenoside Ro has great significance in enriching ginsenoside genetic resources and further revealing the synthesis mechanism of ginsenoside. In this work, ginsenoside-Ro-synthesis-related genes were mined using the P. ginseng reference-free transcriptome database. Fourteen hub transcripts were identified by differential expression analysis and weighted gene co-expression network analysis. Phylogenetic and synteny block analyses of PgUGAT252645, a UGT transcript among the hub transcripts, showed that PgUGAT252645 belonged to the UGT73 subfamily and was relatively conserved in ginseng plants. Functional analysis showed that PgUGAT252645 encodes a glucuronosyltransferase that catalyzes the glucuronide modification of the C3 position of oleanolic acid using uridine diphosphate glucuronide as the substrate. Furthermore, the mutation at 622 bp of its open reading frame resulted in amino acid substitutions that may significantly affect the catalytic activity of the enzyme, and, as a consequence, affect the biosynthesis of ginsenoside Ro. Results of the in vitro enzyme activity assay of the heterologous expression product in E. coli of PgUGAT252645 verified the above analyses. The function of PgUGAT252645 was further verified by the result that its overexpression in ginseng adventitious roots significantly increased the content of ginsenoside Ro. The present work identified a new UGT gene involved in the biosynthesis of ginsenoside Ro, which not only enriches the functional genes in the ginsenoside synthesis pathway, but also provides the technical basis and theoretical basis for the in-depth excavation of ginsenoside-synthesis-related genes.

Novel cytochrome P450s for various hydroxylation of steroids from filamentous fungi

Hydroxylated steroids are value-added products with diverse biological activities mediated by cytochrome P450 enzymes, however, few has been thoroughly characterized in fungi. This study introduces a rapid identification strategy for filamentous fungi P450 enzymes through transcriptome and bioinformatics analysis. Five novel enzymes (CYP68J5, CYP68L10, CYP68J3, CYP68N1 and CYP68N3) were identified and characterized in Saccharomyces cerevisiae or Aspergillus oryzae. Molecular docking and dynamics simulations were employed to elucidate hydroxylation preferences of CYP68J5 (11α, 7α bihydroxylase) and CYP68N1 (11α hydroxylase). Additionally, redox partners (cytochrome P450 reductase and cytochrome b5) and ABC transporter were co-expressed with CYP68N1 to enhance 11α-OH-androstenedione (11α-OH-4AD) production. The engineered cell factory, co-expressing CPR1 and CYP68N1, achieved a significant increase of 11α-OH-4AD production, reaching 0.845 g·L-1, which increased by 14 times compared to the original strain. This study provides a comprehensive approach for identifying and implementing novel cytochrome P450 enzymes, paving the way for sustainable production of steroidal products.

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.

Engineering yeast for the production of plant terpenoids using synthetic biology approaches

Covering: 2011-2022The low amounts of terpenoids produced in plants and the difficulty in synthesizing these complex structures have stimulated the production of terpenoid compounds in microbial hosts by metabolic engineering and synthetic biology approaches. Advances in engineering yeast for terpenoid production will be covered in this review focusing on four directions: (1) manipulation of host metabolism, (2) rewiring and reconstructing metabolic pathways, (3) engineering the catalytic activity, substrate selectivity and product specificity of biosynthetic enzymes, and (4) localizing terpenoid production via enzymatic fusions and scaffolds, or subcellular compartmentalization.

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.

Reconstitution and Optimization of the Marmesin Biosynthetic Pathway in Yeast

Marmesin is essential in plant defense systems and exhibits various biological activities. In this study, we reconstituted the marmesin biosynthetic pathway in the Saccharomyces cerevisiae BY4741 chassis. We engineered the aromatic amino acid (AAA) biosynthetic pathways by introducing Escherichia coli-derived ppsA to improve the availability of the AAA precursor phosphoenolpyruvate, overexpressing the feedback inhibition resistance genes ARO4K229L and ARO7G141S to direct the metabolic flux toward the tyrosine branch, and deleting ARO10, PDC5, and PDC6 to reduce the byproducts from the Ehrlich pathway. The umbelliferone 6-dimethylallyltransferase (U6DT) and marmesin synthase (MS) involved in marmesin synthesis were optimized to increase marmesin production. Marmesin production was improved by truncating the transmembrane domains of PcU6DT, FcMS, and AtCPR1 and increasing the copy numbers of the genes encoding the truncated enzymes. Finally, a marmesin titer of 27.7 mg/L was obtained in shake flasks using the engineered yeast strain MU5. The constructed marmesin-producing strain provides the foundation for the green and large-scale production of pharmaceutically important furanocoumarins.

Human Serum Albumin Nanoparticles as a Carrier of 20(S)-Protopanaxadiol via Intramuscular Injection to Alleviate Cyclophosphamide-Induced Myelosuppression

Myelosuppression is a prevalent and potentially life-threatening side effect during chemotherapy. As the main active component of ginseng, 20(S)-protopanaxadiol (PPD) is capable of relieving myelosuppression by restoring hematopoiesis and immunity. In this study, PPD was encapsulated in human albumin nanoparticles (PPD-HSA NPs) by nanoparticle albumin-bound (Nab) technology for intramuscular injection to optimize its pharmacokinetic properties and promote recovery of myelosuppression. The prepared PPD-HSA NPs had a particle size of about 280 nm with a narrow size distribution. PPD dispersed as an amorphous state within the PPD-HSA NPs, and the NPs exhibited in vitro sustained release behavior. PPD-HSA NPs showed a favorable pharmacokinetic profile with high absolute bioavailability, probably due to the fact that NPs entered into the blood circulation via lymphatic circulation and were eliminated slowly. In vivo distribution experiments demonstrated that PPD-HSA NPs were mainly distributed in the liver and spleen, but a strong fluorescence signal was also found in the inguinal lymph node, indicating drug absorption via a lymph route. The myelosuppressive model was established using cyclophosphamide as the inducer. Pharmacodynamic studies confirmed that PPD-HSA NPs were effective in promoting the level of white blood cells. Moreover, the neutrophil and lymphocyte counts were significantly higher in the PPD-HSA NPs group compared with the control group. This preliminary investigation revealed that PPD-HSA NPs via intramuscular administration may be an effective intervention strategy to alleviate myelosuppression.

Mining and modification of Oryza sativa-derived squalene epoxidase for improved β-amyrin production in Saccharomyces cerevisiae

β-Amyrin is a pentacyclic triterpenoid and has anti-viral, anti-bacterial and anti-inflammatory activities. The synthetic pathway of β-amyrin has been analyzed and its heterogeneous synthesis has been achieved in Saccharomyces cerevisiae. Squalene epoxidase (SQE) catalyzes the oxygenation of squalene to form 2,3-oxidosqualene and is rate-limiting in the synthetic pathways of β-amyrin. The endogenous SQE in S. cerevisiae is insufficient for high production of β-amyrin. Herein, eight squalene epoxidases derived from different plants were selected and characterized in S. cerevisiae for improved biosynthesis of β-amyrin. Among them, the squalene epoxidase from Oryza sativa (OsSQE52) showed the best performance compared to other plant-derived sources. Through protein remodeling, the mutant OsSQE52L256R, obtained based on modeling analysis, increased the titer of β-amyrin by 2.43-fold compared to that in the control strain with ERG1 overexpressed under the same conditions. Moreover, the expression of OsSQE52L256R was optimized with the improvement of precursor supply to further increase the production of β-amyrin. Finally, the constructed strains produced 66.97 mg/L β-amyrin in the shake flask, which was 6.45-fold higher than the original strain. Our study provides alternative SQEs for efficient production of β-amyrin as well as other triterpenoids derived from 2,3-oxidosqualene.

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.

Promoting Photosynthetic Production of Dammarenediol-II in Chlamydomonas reinhardtii via Gene Loading and Culture Optimization

Ginsenosides are major bioactive compounds found in Panax ginseng that exhibit various pharmaceutical properties. Dammarenediol-II, the nucleus of dammarane-type ginsenosides, is a promising candidate for pharmacologically active triterpenes. Dammarenediol-II synthase (DDS) cyclizes 2,3-oxidosqualene to produce dammarenediol-II. Based on the native terpenoids synthetic pathway, a dammarane-type ginsenosides synthetic pathway was established in Chlamydomonas reinhardtii by introducing P. ginseng PgDDS, CYP450 enzyme (PgCYP716A47), or/and Arabidopsis thaliana NADPH-cytochrome P450 reductase gene (AtCPR), which is responsible for producing dammarane-type ginsenosides. To enhance productivity, strategies such as "gene loading" and "culture optimizing" were employed. Multiple copies of transgene expression cassettes were introduced into the genome to increase the expression of the key rate-limiting enzyme gene, PgDDS, significantly improving the titer of dammarenediol-II to approximately 0.2 mg/L. Following the culture optimization in an opt2 medium supplemented with 1.5 mM methyl jasmonate under a light:dark regimen, the titer of dammarenediol-II increased more than 13-fold to approximately 2.6 mg/L. The C. reinhardtii strains engineered in this study constitute a good platform for the further production of ginsenosides in microalgae.

Transcriptome Analysis and Identification of Sesquiterpene Synthases in Liverwort Jungermannia exsertifolia

The liverwort Jungermannia exsertifolia is one of the oldest terrestrial plants and rich in structurally specific sesquiterpenes. There are several sesquiterpene synthases (STSs) with non-classical conserved motifs that have been discovered in recent studies on liverworts; these motifs are rich in aspartate and bind with cofactors. However, more detailed sequence information is needed to clarify the biochemical diversity of these atypical STSs. This study mined J. exsertifolia sesquiterpene synthases (JeSTSs) through transcriptome analysis using BGISEQ-500 sequencing technology. A total of 257,133 unigenes was obtained, and the average length was 933 bp. Among them, a total of 36 unigenes participated in the biosynthesis of sesquiterpenes. In addition, the in vitro enzymatic characterization and heterologous expression in Saccharomyces cerevisiae showed that JeSTS1 and JeSTS2 produced nerolidol as the major product, while JeSTS4 could produce bicyclogermacrene and viridiflorol, suggesting a specificity of J. exsertifolia sesquiterpene profiles. Furthermore, the identified JeSTSs had a phylogenetic relationship with a new branch of plant terpene synthases, the microbial terpene synthase-like (MTPSL) STSs. This work contributes to the understanding of the metabolic mechanism for MTPSL-STSs in J. exsertifolia and could provide an efficient alternative to microbial synthesis of these bioactive sesquiterpenes.

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.

Current advances for omics-guided process optimization of microbial manufacturing

Currently, microbial manufacturing is widely used in various fields, such as food, medicine and energy, for its advantages of greenness and sustainable development. Process optimization is the committed step enabling the commercialization of microbial manufacturing products. However, the present optimization processes mainly rely on experience or trial-and-error method ignoring the intrinsic connection between cellular physiological requirement and production performance, so in many cases the productivity of microbial manufacturing could not been fully exploited at economically feasible cost. Recently, the rapid development of omics technologies facilitates the comprehensive analysis of microbial metabolism and fermentation performance from multi-levels of molecules, cells and microenvironment. The use of omics technologies makes the process optimization more explicit, boosting microbial manufacturing performance and bringing significant economic benefits and social value. In this paper, the traditional and omics technologies-guided process optimization of microbial manufacturing are systematically reviewed, and the future trend of process optimization is prospected.

Efficient biosynthesis of resveratrol via combining phenylalanine and tyrosine pathways in Saccharomyces cerevisiae

BACKGROUND

Resveratrol is a commercially available stilbenoid widely used as dietary supplements, functional food ingredients, and cosmetic ingredients due to its diverse physiological activities. The production of resveratrol in microorganisms provides an ideal source that reduces the cost of resveratrol, but the titer in Saccharomyces cerevisiae was still much lower than that in other hosts.

RESULTS

To achieve enhanced production of resveratrol in S. cerevisiae, we constructed a biosynthetic pathway via combining phenylalanine and tyrosine pathways by introducing a bi-functional phenylalanine/tyrosine ammonia lyase from Rhodotorula toruloides. The combination of phenylalanine pathway with tyrosine pathway led to a 462% improvement of resveratrol production in yeast extract peptone dextrose (YPD) medium with 4% glucose, suggesting an alternative strategy for producing p-coumaric acid-derived compounds. Then the strains were further modified by integrating multi-copy biosynthetic pathway genes, improving metabolic flux to aromatic amino acids and malonyl-CoA, and deleting by-pathway genes, which resulted in 1155.0 mg/L resveratrol in shake flasks when cultured in YPD medium. Finally, a non-auxotrophic strain was tailored for resveratrol production in minimal medium without exogenous amino acid addition, and the highest resveratrol titer (4.1 g/L) ever reported was achieved in S. cerevisiae to our knowledge.

CONCLUSIONS

This study demonstrates the advantage of employing a bi-functional phenylalanine/tyrosine ammonia lyase in the biosynthetic pathway of resveratrol, suggesting an effective alternative in the production of p-coumaric acid-derived compounds. Moreover, the enhanced production of resveratrol in S. cerevisiae lays a foundation for constructing cell factories for various stilbenoids.

Production of 11-Oxo-β-Amyrin in Saccharomyces cerevisiae at High Efficiency by Fine-Tuning the Expression Ratio of CYP450:CPR

The production of glycyrrhetinic acid (GA) and 11-oxo-β-amyrin, the major bioactive components in liquorice, was typically inhibited by P450 oxidation in Saccharomyces cerevisiae. This study focused on optimizing CYP88D6 oxidation by balancing its expression with cytochrome P450 oxidoreductase (CPR) for the efficient production of 11-oxo-β-amyrin in yeast. Results indicated that a high CPR:CYP88D6 expression ratio could decrease both 11-oxo-β-amyrin concentration and turnover ratio of β-amyrin to 11-oxo-β-amyrin, whereas a high CYP88D6:CPR expression ratio is beneficial for improving the catalytic activity of CYP88D6 and 11-oxo-β-amyrin production. Under such a scenario, 91.2% of β-amyrin was converted into 11-oxo-β-amyrin in the resulting S. cerevisiae Y321, and 11-oxo-β-amyrin production was further improved to 810.6 mg/L in fed-batch fermentation. Our study provides new insights into the expression of cytochrome P450 and CPR in maximizing the catalytic activity of P450s, which could guide the construction of cell factories in producing natural products.

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.

Microorganisms for Ginsenosides Biosynthesis: Recent Progress, Challenges, and Perspectives

Ginsenosides are major bioactive compounds present in the Panax species. Ginsenosides exhibit various pharmaceutical properties, including anticancer, anti-inflammatory, antimetastatic, hypertension, and neurodegenerative disorder activities. Although several commercial products have been presented on the market, most of the current chemical processes have an unfriendly environment and a high cost of downstream processing. Compared to plant extraction, microbial production exhibits high efficiency, high selectivity, and saves time for the manufacturing of industrial products. To reach the full potential of the pharmaceutical resource of ginsenoside, a suitable microorganism has been developed as a novel approach. In this review, cell biological mechanisms in anticancer activities and the present state of research on the production of ginsenosides are summarized. Microbial hosts, including native endophytes and engineered microbes, have been used as novel and promising approaches. Furthermore, the present challenges and perspectives of using microbial hosts to produce ginsenosides have been discussed.

Molecular Cloning and Functional Characterization of Oxidosqualene Cyclases from Panax vietnamensis

Panax vietnamensis is a valuable medicinal resource with promising preclinical applications. Ginsenosides, which are triterpenoids, are the primary active components in P. vietnamensis. Oxidosqualene cyclases (OSCs) catalyze the formation of the basic skeleton of triterpenes from 2,3-oxidosqualene, which is a crucial step in the biosynthesis of triterpenoids. The OSCs involved in triterpenoid biosynthesis in P. vietnamensis have not yet been characterized. Four OSC genes (PvOSC1-4) were cloned from P. vietnamensis and functionally characterized via heterologous expression in yeast. Transgenic yeast expressing PvOSC1, PvOSC3, and PvOSC4 produced the corresponding products β-amyrin, cycloartenol, and dammarenediol-II, respectively. PvOSC1, PvOSC3, and PvOSC4 are monofunctional OSCs. In this study, we characterized three PvOSC genes, providing a better understanding of the biosynthesis of triterpenoids in P. vietnamensis and the multiple choices of plant OSCs for metabolic engineering in yeast and other hosts.

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 the enzyme toolbox to tailor glycosylation in small molecule natural products and protein biologics

Many glycosylated small molecule natural products and glycoprotein biologics are important in a broad range of therapeutic and industrial applications. The sugar moieties that decorate these compounds often show a profound impact on their biological functions, thus biocatalytic methods for controlling their glycosylation are valuable. Enzymes from nature are useful tools to tailor bioproduct glycosylation but these sometimes have limitations in their catalytic efficiency, substrate specificity, regiospecificity, stereospecificity, or stability. Enzyme engineering strategies such as directed evolution or semi-rational and rational design have addressed some of the challenges presented by these limitations. In this review, we highlight some of the recent research on engineering enzymes to tailor the glycosylation of small molecule natural products (including alkaloids, terpenoids, polyketides, and peptides), as well as the glycosylation of protein biologics (including hormones, enzyme-replacement therapies, enzyme inhibitors, vaccines, and antibodies).

Non-invasive monitoring of microbial triterpenoid production using nonlinear microscopy techniques

Introduction: Bioproduction of plant-derived triterpenoids in recombinant microbes is receiving great attention to make these biologically active compounds industrially accessible as nutraceuticals, pharmaceutics, and cosmetic ingredients. So far, there is no direct method for detecting triterpenoids under physiological conditions on a cellular level, information yet highly relevant to rationalizing microbial engineering. Methods: Here, we show in a proof-of-concept study, that triterpenoids can be detected and monitored in living yeast cells by combining coherent anti-Stokes Raman scattering (CARS) and second-harmonic-generation (SHG) microscopy techniques. We applied CARS and SHG microscopy measurements, and for comparison classical Nile Red staining, on immobilized and growing triterpenoid-producing, and non-producing reference Saccharomyces cerevisiae strains. Results and Discussion: We found that the SHG signal in triterpenoid-producing strains is significantly higher than in a non-producing reference strain, correlating with lipophile content as determined by Nile red staining. In growing cultures, both CARS and SHG signals showed changes over time, enabling new insights into the dynamics of triterpenoid production and storage inside cells.

Protective effect of fermented aloe extract on glutamate-induced cytotoxicity in HT22 cells

Excessive glutamate can cause oxidative stress in neuronal cells and this can significantly contribute to the etiology of neurodegenerative disease. The present study mainly aims to investigate that aloe extract (AE) and fermented aloe extract (FAE) could protect against glutamate-induced cytotoxicity by modulating oxidative stress. In this study, both AE and FAE showed potent neuroprotective activity by inhibiting ROS and Ca²⁺ concentration, increasing mitochondria membrane potential, and activating glutathione-related enzymes against glutamate-insulted neurotoxicity in HT22 cells. In addition, the neuroprotective activity of FAE was more potent than that of AE. HPLC analysis reveals that the chemical composition of FAE is different from that of AE. Especially, the contents of aloin A, aloin B and aloenin were higher in FAE than in AE. In conclusion, this study indicates that both AE and FAE may have effective neuroprotective activity in glutamate-insulted pathological conditions such as Alzheimer's disease by managing oxidative stress.

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.

Heterologous Biosynthesis of Taraxerol by Engineered Saccharomyces cerevisiae

Taraxerol is an oleanane-type pentacyclic triterpenoid compound distributed in many plant species that has good effects on the treatment of inflammation and tumors. However, the taraxerol content in medicinal plants is low, and chemical extraction requires considerable energy and time, so taraxerol production is a problem. It is a promising strategy to produce taraxerol by applying recombinant microorganisms. In this study, a Saccharomyces cerevisiae strain WKde2 was constructed to produce taraxerol with a titer of 1.85 mg·L-1, and the taraxerol titer was further increased to 12.51 mg·L-1 through multiple metabolic engineering strategies. The endoplasmic reticulum (ER) size regulatory factor INO2, which was reported to increase squalene and cytochrome P450-mediated 2,3-oxidosqualene production, was overexpressed in this study, and the resultant strain WTK11 showed a taraxerol titer of 17.35 mg·L-1. Eventually, the highest reported titer of 59.55 mg·L-1 taraxerol was achieved in a 5 L bioreactor. These results will serve as a general strategy for the production of other triterpenoids in yeast.

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.

Developing Multi-Copy Chromosomal Integration Strategies for Heterologous Biosynthesis of Caffeic Acid in Saccharomyces cerevisiae

Caffeic acid, a plant-sourced phenolic compound, has a variety of biological activities, such as antioxidant and antimicrobial properties. The caffeic acid biosynthetic pathway was initially constructed in S. cerevisiae, using codon-optimized TAL (coTAL, encoding tyrosine ammonia lyase) from Rhodobacter capsulatus, coC3H (encoding p-coumaric acid 3-hydroxylase) and coCPR1 (encoding cytochrome P450 reductase 1) from Arabidopsis thaliana in 2 μ multi-copy plasmids to produce caffeic acid from glucose. Then, integrated expression of coTAL via delta integration with the POT1 gene (encoding triose phosphate isomerase) as selection marker and episomal expression of coC3H, coCPR1 using the episomal plasmid pLC-c3 were combined, and caffeic acid production was proved to be improved. Next, the delta and rDNA multi-copy integration methods were applied to integrate the genes coC3H and coCPR1 into the chromosome of high p-coumaric acid yielding strain QT3-20. The strain D9 constructed via delta integration outperformed the other strains, leading to 50-fold increased caffeic acid production in optimized rich media compared with the initial construct. The intercomparison between three alternative multi-copy strategies for de novo synthesis of caffeic acid in S. cerevisiae suggested that delta-integration was effective in improving caffeic acid productivity, providing a promising strategy for the production of valuable bio-based chemicals in recombinant S. cerevisiae.

De Novo Biosynthesis of Oleanane-Type Ginsenosides in Saccharomyces cerevisiae Using Two Types of Glycosyltransferases from Panax ginseng

Oleanane-type ginsenosides are highly biologically active substances in Panax ginseng, a popular Chinese dietary plant. Lack of key enzymes for glycosylation reactions has hindered de novo synthesis of these bioactive molecules. We mined candidate glycosyltransferases (GTs) of the ginseng database by combining key metabolites and transcriptome coexpression analyses and verified their function using in vitro enzymatic assays. The PgCSyGT1, a cellulose synthase-like GT rather than a UDP-dependent glucuronosyltransferase (UGT), was verified as the key enzyme for transferring a glucuronosyl moiety to the free C3-OH of oleanolic acid to synthesize calenduloside E. Two UGTs (PgUGT18 and PgUGT8) were first identified as, respectively, catalyzing the glycosylation reaction of the second sugar moiety of C3 and the C28 in the oleanane-type ginsenoside biosynthetic pathway. Then, we integrated these GTs in combinations into Saccharomyces cerevisiae genome and realized de novo biosynthesis of oleanane-type ginsenosides with a yield of 1.41 μg/L ginsenoside Ro in shake flasks. This report provides a basis for effective biosynthesis of diverse oleanane-type ginsenosides in microbial cell factories.

Engineering Saccharomyces cerevisiae for Hyperproduction of β-Amyrin by Mitigating the Inhibition Effect of Squalene on β-Amyrin Synthase

The study aims to enhance β-amyrin production in Saccharomyces cerevisiae by peroxisome compartmentalization. First, overaccumulated squalene was determined as a key limiting factor for the production of β-amyrin since it could inhibit the activity of β-amyrin synthase GgbAs1. Second, to mitigate the inhibition effect, the enhanced squalene synthesis pathway was compartmentalized into peroxisomes to insulate overaccumulated squalene from GgbAs1, and thus the specific titer of β-amyrin reached 57.8 mg/g dry cell weight (DCW), which was 2.6-fold higher than that of the cytosol engineering strain. Third, by combining peroxisome compartmentalization with the "push-pull-restrain" strategy (ERG1 and GgbAs1 overexpression and ERG7 weakening), the production of β-amyrin was further increased to 81.0 mg/g DCW (347.0 mg/L). Finally, through fed-batch fermentation in a 5 L fermenter, the titer of β-amyrin reached 2.6 g/L, which is the highest reported to date. The study provides a new perspective to engineering yeasts as a platform for triterpene production.

CRISPRi-Guided Metabolic Flux Engineering for Enhanced Protopanaxadiol Production in Saccharomyces cerevisiae

Protopanaxadiol (PPD), an aglycon found in several dammarene-type ginsenosides, has high potency as a pharmaceutical. Nevertheless, application of these ginsenosides has been limited because of the high production cost due to the rare content of PPD in Panax ginseng and a long cultivation time (4–6 years). For the biological mass production of the PPD, de novo biosynthetic pathways for PPD were introduced in Saccharomyces cerevisiae and the metabolic flux toward the target molecule was restructured to avoid competition for carbon sources between native metabolic pathways and de novo biosynthetic pathways producing PPD in S. cerevisiae. Here, we report a CRISPRi (clustered regularly interspaced short palindromic repeats interference)-based customized metabolic flux system which downregulates the lanosterol (a competing metabolite of dammarenediol-II (DD-II)) synthase in S. cerevisiae. With the CRISPRi-mediated suppression of lanosterol synthase and diversion of lanosterol to DD-II and PPD in S. cerevisiae, we increased PPD production 14.4-fold in shake-flask fermentation and 5.7-fold in a long-term batch-fed fermentation.

Metabolic compartmentalization in yeast mitochondria: Burden and solution for squalene overproduction

Harnessing mitochondria is considered as a promising method for biosynthesis of terpenes due to the adequate supply of acetyl-CoA and redox equivalents in mitochondria. However, mitochondrial engineering often causes serious metabolic burden indicated by poor cell growth. Here, we systematically analyzed the metabolic burden caused by the compartmentalization of the MVA pathway in yeast mitochondria for squalene synthesis. The phosphorylated intermediates of the MVA pathway, especially mevalonate-5-P and mevalonate-5-PP, conferred serious toxicity within mitochondria, which significantly compromised its possible advantages for squalene synthesis and was difficult to be significantly improved by routine pathway optimization. These phosphorylated intermediates were converted into ATP analogues, which strongly inhibited ATP-related cell function, such as mitochondrial oxidative respiration. Fortunately, the introduction of a partial MVA pathway from acetyl-CoA to mevalonate in mitochondria as well as the augmentation of the synthesis of mevalonate in cytosol could significantly promote the growth of yeasts. Accordingly, a combinatorial strategy of cytoplasmic and mitochondrial engineering was proposed to alleviate the metabolic burden caused by the compartmentalized MVA pathway in mitochondria and improve cell growth. The strategy also displayed the superimposed effect of cytoplasmic engineering and mitochondrial engineering on squalene production. Through a two-stage fermentation process, the squalene titer reached 21.1 g/L with a specific squalene titer of 437.1 mg/g dcw, which was the highest at present. This provides new insight into the production of squalene and other terpenes in yeasts based on the advantages of mitochondrial engineering.

Diverse triterpene skeletons are derived from the expansion and divergent evolution of 2,3-oxidosqualene cyclases in plants

Triterpenoids are one of the largest groups of secondary metabolites and exhibit diverse structures, which are derived from C30 skeletons that are biosynthesized via the isoprenoid pathway by cyclization of 2,3-oxidosqualene. Triterpenoids have a wide range of biological activities, and are used in functional foods, drugs, and as industrial materials. Due to the low content levels in their native plants and limited feasibility and efficiency of chemical synthesis, heterologous biosynthesis of triterpenoids is the most promising strategy. Herein, we classified 121 triterpene alcohols/ketones according to their conformation and ring numbers, among which 51 skeletons have been experimentally characterized as the products of oxidosqualene cyclases (OSCs). Interestingly, 24 skeletons that have not been reported from nature source were generated by OSCs in heterologous expression. Comprehensive evolutionary analysis of the identified 152 OSCs from 75 species in 25 plant orders show that several pentacyclic triterpene synthases repeatedly originated in multiple plant lineages. Comparative analysis of OSC catalytic reaction revealed that stabilization of intermediate cations, steric hindrance, and conformation of active center amino acid residues are primary factors affecting triterpene formation. Optimization of OSC could be achieved by changing of side-chain orientations of key residues. Recently, methods, such as rationally design of pathways, regulation of metabolic flow, compartmentalization engineering, etc., were introduced in improving chassis for the biosynthesis of triterpenoids. We expect that extensive study of natural variation of large number of OSCs and catalytical mechanism will provide basis for production of high level of triterpenoids by application of synthetic biology strategies.

De Novo Biosynthesis of the Oleanane-Type Triterpenoids of Tunicosaponins in Yeast

Tunicosaponins are natural products extracted from Psammosilene tunicoides, which is an important ingredient of Yunnan Baiyao Powder, an ancient and famous Asian herbal medicine. The representative aglycones of tunicosaponins are the oleanane-type triterpenoids of gypsogenin and quillaic acid, which were found to manipulate a broad range of virus-host fusion via wrapping the heptad repeat-2 (HR2) domain prevalent in viral envelopes. However, the unknown biosynthetic pathway and difficulty in chemical synthesis hinder the therapeutic use of tunicosaponins. Here, two novel cytochrome P450-dependent monooxygenases that take part in the biosynthesis of tunicosaponins, CYP716A262 (CYP091) and CYP72A567 (CYP099), were identified from P. tunicoides. In addition, the whole biosynthesis pathway of the tunicosaponin aglycones was reconstituted in yeast by transforming the platform strain BY-bAS with the CYP716A262 and CYP716A567 genes, the resulting strain could produce 146.84 and 314.01 mg/L of gypsogenin and quillaic acid, respectively. This synthetic biology platform for complicated metabolic pathways elucidation and microbial cell factories construction can provide alternative sources of important natural products, helping conserve natural plant resources.

Fine-tuning the expression of pathway gene in yeast using a regulatory library formed by fusing a synthetic minimal promoter with different Kozak variants

BACKGROUND

Tailoring gene expression to balance metabolic fluxes is critical for the overproduction of metabolites in yeast hosts, and its implementation requires coordinated regulation at both transcriptional and translational levels. Although synthetic minimal yeast promoters have shown many advantages compared to natural promoters, their transcriptional strength is still limited, which restricts their applications in pathway engineering.

RESULTS

In this work, we sought to expand the application scope of synthetic minimal yeast promoters by enhancing the corresponding translation levels using specific Kozak sequence variants. Firstly, we chose the reported UAS_F-E-C-Core1 minimal promoter as a library template and determined its Kozak motif (K₀). Next, we randomly mutated the K₀ to generate a chimeric promoter library, which was able to drive green fluorescent protein (GFP) expression with translational strengths spanning a 500-fold range. A total of 14 chimeric promoters showed at least two-fold differences in GFP expression strength compared to the K₀ control. The best one named K₅₂₈ even showed 8.5- and 3.3-fold increases in fluorescence intensity compared with UAS_F-E-C-Core1 and the strong native constitutive promoter P_TDH3, respectively. Subsequently, we chose three representative strong chimeric promoters (K₅₄₀, K₅₃₆, and K₅₂₈) from this library to regulate pathway gene expression. In conjunction with the tHMG1 gene for squalene production, the K₅₂₈ variant produced the best squalene titer of 32.1 mg/L in shake flasks, which represents a more than 10-fold increase compared to the parental K₀ control (3.1 mg/L).

CONCLUSIONS

All these results demonstrate that this chimeric promoter library developed in this study is an effective tool for pathway engineering in yeast.

Phytochemistry of ginsenosides: Recent advancements and emerging roles

Ginsenosides, a group of tetracyclic saponins, accounts for the nutraceutical and pharmaceutical relevance of the ginseng (Panax sp.) herb. Owing to the associated therapeutic potential of ginsenosides, their demand has been increased significantly in the last two decades. However, a slow growth cycle, low seed production, and long generation time of ginseng have created a gap between the demand and supply of ginsenosides. The biosynthesis of ginsenosides involves an intricate network of pathways with multiple oxidation and glycosylation reactions. However, the exact functions of some of the associated genes/proteins are still not completely deciphered. Moreover, ginsenoside estimation and extraction using analytical techniques are not feasible with high efficiency. The present review is a step forward in recapitulating the comprehensive aspects of ginsenosides including their distribution, structural diversity, biotransformation, and functional attributes in both plants and animals including humans. Moreover, ginsenoside biosynthesis in the potential plant sources and their metabolism in the human body along with major regulators and stimulators affecting ginsenoside biosynthesis have also been discussed. Furthermore, this review consolidates biotechnological interventions to enhance the biosynthesis of ginsenosides in their potential sources and advancements in the development of synthetic biosystems for efficient ginsenoside biosynthesis to meet their rising industrial demands.

Ginsenosides in Panax genus and their biosynthesis

Ginsenosides are a series of glycosylated triterpenoids which belong to protopanaxadiol (PPD)-, protopanaxatriol (PPT)-, ocotillol (OCT)- and oleanane (OA)-type saponins known as active compounds of Panax genus. They are accumulated in plant roots, stems, leaves, and flowers. The content and composition of ginsenosides are varied in different ginseng species, and in different parts of a certain plant. In this review, we summarized the representative saponins structures, their distributions and the contents in nearly 20 Panax species, and updated the biosynthetic pathways of ginsenosides focusing on enzymes responsible for structural diversified ginsenoside biosynthesis. We also emphasized the transcription factors in ginsenoside biosynthesis and non-coding RNAs in the growth of Panax genus plants, and highlighted the current three major biotechnological applications for ginsenosides production. This review covered advances in the past four decades, providing more clues for chemical discrimination and assessment on certain ginseng plants, new perspectives for rational evaluation and utilization of ginseng resource, and potential strategies for production of specific ginsenosides.

Advance in glycosyltransferases, the important bioparts for production of diversified ginsenosides

Ginsenosides are a series of glycosylated triterpenoids predominantly originated from Panax species with multiple pharmacological activities such as anti-aging, mediatory effect on the immune system and the nervous system. During the biosynthesis of ginsenosides, glycosyltransferases play essential roles by transferring various sugar moieties to the sapogenins in contributing to form structure and bioactivity diversified ginsenosides, which makes them important bioparts for synthetic biology-based production of these valuable ginsenosides. In this review, we summarized the functional elucidated glycosyltransferases responsible for ginsenoside biosynthesis, the advance in the protein engineering of UDP-glycosyltransferases (UGTs) and their application with the aim to provide in-depth understanding on ginsenoside-related UGTs for the production of rare ginsenosides applying synthetic biology-based microbial cell factories in the future.

Engineering yeast subcellular compartments for increased production of the lipophilic natural products ginsenosides

Eukaryotic yeasts have a variety of subcellular compartments and are ideal platform strains for the construction of complex heterologous natural product biosynthesis pathways. Improving the synthesis efficiency of microbial cell factories through the utilization and modification of subcellular compartments by synthetic biology has good application prospects. Here, we used the yeast PLN1 protein to target the normally endoplasmic reticulum (ER)-localized cytochrome P450 enzyme protopanaxadiol (PPD) synthase (PPDS) to lipid droplets (LDs), which are the storage organelles of the PPDS substrate dammarenediol-II (DD). The efficiency of converting DD to PPD was significantly increased by 394%, and the conversion rate of DD increased from 17.4% to 86.0%. Furthermore, increasing the volume of LDs can significantly enhance the production of DD and its derivatives, but the change in the ratio of the volume and surface area of LDs decreased the conversion efficiency of DD to PPD. Additionally, the biosynthetic pathways of the PPD-type saponin ginsenoside compound K (CK) was reconstituted in a PPD-producing chassis strain, and CK production reached 21.8 mg/L/OD, 4.4-fold higher compared to the native ER-expression strategy. Next, we enhanced the expression of the Pn3-29 gene module to further reduce the accumulation of PPD and increase the production of CK to 41.3 mg/L/OD. Finally, the CK titer of the resulting strain reached 5 g/L in 5 L fed-batch fermentations. This study provides a new strategy for engineering yeast to produce complex natural products.

Genetic engineering of yeast, filamentous fungi and bacteria for terpene production and applications in food industry

Terpenes are a major class of natural aromatic compounds in grapes and wines to offer the characteristic flavor and aroma, serving as important quality traits of wine products. Saccharomyces cerevisiae represents an excellent cell factory platform for large-scale bio-based terpene production. This review describes the biosynthetic pathways of terpenes in different organisms. The metabolic engineering of S. cerevisiae for promoting terpene biosynthesis and the alternative microbial engineering platforms including filamentous fungi and Escherichia coli are also elaborated. Additionally, the potential applications of the terpene products from engineered microorganisms in food and beverage industries are also discussed. This review provides comprehensive information for an innovative supply way of terpene via microbial cell factory, which could facilitate the development and application of this technique at the industrial scale.

Recent progress and new perspectives for diterpenoid biosynthesis in medicinal plants

Diterpenoids, including more than 18,000 compounds, represent an important class of metabolites that encompass both phytohormones and some industrially relevant compounds. These molecules with complex, diverse structures and physiological activities, have high value in the pharmaceutical industry. Most medicinal diterpenoids are extracted from plants. Major advances in understanding the biosynthetic pathways of these active compounds are providing unprecedented opportunities for the industrial production of diterpenoids by metabolic engineering and synthetic biology. Here, we summarize recent developments in the field of diterpenoid biosynthesis from medicinal herbs. An overview of the pathways and known biosynthetic enzymes is presented. In particular, we look at the main findings from the past decade and review recent progress in the biosynthesis of different groups of ringed compounds. We also discuss diterpenoid production using synthetic biology and metabolic engineering strategies, and draw on new technologies and discoveries to bring together many components into a useful framework for diterpenoid production.

Fermentation Strategies for Production of Pharmaceutical Terpenoids in Engineered Yeast

Terpenoids, also known as isoprenoids, are a broad and diverse class of plant natural products with significant industrial and pharmaceutical importance. Many of these natural products have antitumor, anti-inflammatory, antibacterial, antiviral, and antimalarial effects, support transdermal absorption, prevent and treat cardiovascular diseases, and have hypoglycemic activities. Production of these compounds are generally carried out through extraction from their natural sources or chemical synthesis. However, these processes are generally unsustainable, produce low yield, and result in wasting of substantial resources, most of them limited. Microbial production of terpenoids provides a sustainable and environment-friendly alternative. In recent years, the yeast Saccharomyces cerevisiae has become a suitable cell factory for industrial terpenoid biosynthesis due to developments in omics studies (genomics, transcriptomics, metabolomics, proteomics), and mathematical modeling. Besides that, fermentation development has a significant importance on achieving high titer, yield, and productivity (TYP) of these compounds. Up to now, there have been many studies and reviews reporting metabolic strategies for terpene biosynthesis. However, fermentation strategies have not been yet comprehensively discussed in the literature. This review summarizes recent studies of recombinant production of pharmaceutically important terpenoids by engineered yeast, S. cerevisiae, with special focus on fermentation strategies to increase TYP in order to meet industrial demands to feed the pharmaceutical market. Factors affecting recombinant terpenoids production are reviewed (strain design and fermentation parameters) and types of fermentation process (batch, fed-batch, and continuous) are discussed.

Antibacterial Prenylated p-Hydroxybenzoic Acid Derivatives from Oberonia myosurus and Identification of Putative Prenyltransferases

Twelve hitherto unknown tandem prenylated p-hydroxybenzoic acid derivatives, namely, oberoniamyosurusins A-L, together with five known derivatives, were isolated from an EtOH extract of the whole parts of the plant Oberonia myosurus. Compounds 10, 13, and 17 exhibited moderate inhibitory activity against Staphylococcus aureus subsp. aureus ATCC29213 with MIC₅₀ values ranging from 7.6 to 23 μg/mL. To determine the biosynthetic pathway of this class of tandem prenyl-substituted compounds, the full-length transcriptome of O. myosurus was sequenced, yielding 19.09 Gb of clean data and 10 949 nonredundant sequences. Two isoforms of p-hydroxybenzoic acid prenyltransferases were annotated and functionally characterized as the enzymes that might be involved in the biosynthesis of nervogenic acid (13) in Pichia pastoris.

Comparative transcriptome analysis of sesquiterpene biosynthesis and functional characterization of sesquiterpene synthases in Leonurus sibiricus L

Two sesquiterpene synthases were identified through comparative transcriptome analysis of Leonurus sibiricus. LsSqTPS2 could produce high titer of δ-cadinene in vivo which suggests the terpene specificity of L. sibiricus. Leonurus sibiricus L., a medicinal herb, is widely used in China due to its pharmacological activities. Cadinene type sesquiterpenes, one of major bioactive components mainly present in aerial parts of L. sibiricus, showed antibacterial, anti-inflammatory, antioxidant and antiproliferative properties. However, there is no report about the sesquiterpene biosynthesis in L. sibiricus. This study identified L. sibiricus sesquiterpene synthases (LsSqTPSs) through comparative transcriptome analysis of L. sibiricus leaf and root samples using the BGISEQ-500 sequencing technique. A total of 83,244 unigenes were obtained with an average length of 1025 bp. Among them, 50,356 unigenes (60.49%) acquired annotations according to the BLAST searching results. A total of 68 differentially expressed genes (DEGs) were potentially involved in the sesquiterpene biosynthesis. Furthermore, four candidate DEGs encoding LsSqTPSs were characterized. The enzymatic characterization in engineered yeast showed that LsSqTPS1 produced α-farnesene as the single product and LsSqTPS2 mainly produced 76.23 mg/L of δ-cadinene, which constituted the major component of L. sibiricus leaf essential oil. This work contributes to the investigation of sesquiterpene biosynthesis in L. sibiricus.

Synthesis of cembratriene-ol and cembratriene-diol in yeast via the MVA pathway

Background

Cembranoids are one kind of diterpenoids with multiple biological activities. The tobacco cembratriene-ol (CBT-ol) and cembratriene-diol (CBT-diol) have high anti-insect and anti-fungal activities, which is attracting great attentions for their potential usage in sustainable agriculture. Cembranoids were supposed to be formed through the 2-C-methyl-d-erythritol-4-phosphate (MEP) pathway, yet the involvement of mevalonate (MVA) pathway in their synthesis remains unclear. Exploring the roles of MVA pathway in cembranoid synthesis could contribute not only to the technical approach but also to the molecular mechanism for cembranoid biosynthesis.

Results

We constructed vectors to express cembratriene-ol synthase (CBTS1) and its fusion protein (AD-CBTS1) containing an N-terminal GAL4 AD domain as a translation leader in yeast. Eventually, the modified enzyme AD-CBTS1 was successfully expressed, which further resulted in the production of CBT-ol in the yeast strain BY-T20 with enhanced MVA pathway for geranylgeranyl diphosphate (GGPP) production but not in other yeast strains with low GGPP supply. Subsequently, CBT-diol was also synthesized by co-expression of the modified enzyme AD-CBTS1 and BD-CYP450 in the yeast strain BY-T20.

Conclusions

We demonstrated that yeast is insensitive to the tobacco anti-fungal compound CBT-ol or CBT-diol and could be applied to their biosynthesis. This study further established a feasibility for cembranoid production via the MVA pathway and provided an alternative bio-approach for cembranoid biosynthesis in microbes.

Unlocking Nature's Biosynthetic Power-Metabolic Engineering for the Fermentative Production of Chemicals

Fermentation as a production method for chemicals is especially attractive, as it is based on cheap renewable raw materials and often exhibits advantages in terms of costs and sustainability. The tremendous development of technology in bioscience has resulted in an exponentially increasing knowledge about biological systems and has become the main driver for innovations in the field of metabolic engineering. Progress in recombinant DNA technology, genomics, and computational methods open new, cheaper, and faster ways to metabolically engineer microorganisms. Existing biosynthetic pathways for natural products, such as vitamins, organic acids, amino acids, or secondary metabolites, can be discovered and optimized efficiently, thereby enabling competitive commercial production processes. Novel biosynthetic routes can now be designed by the rearrangement of nature's unlimited number of enzymes and metabolic pathways in microbial strains. This expands the range of chemicals accessible by biotechnology and has yielded the first commercial products, while new fermentation technologies targeting novel active ingredients, commodity chemicals, and CO₂ -fixation methods are on the horizon.