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

Combined metabolic and enzymatic engineering for de novo biosynthesis of δ-tocotrienol in Yarrowia lipolytica

δ-Tocotrienol, an isomer of vitamin E with anti-inflammatory, neuroprotective and anti-coronary arteriosclerosis properties, is widely used in health care, medicine and other fields. Microbial synthesis of δ-tocotrienol offers significant advantages over plant extraction and chemical synthesis methods, including increased efficiency, cost-effectiveness and environmental sustainability. However, limited precursor availability and low catalytic efficiency of key enzymes remain major bottlenecks in the biosynthesis of δ-tocotrienol. In this study, we assembled the complete δ-tocotrienol biosynthetic pathway in Yarrowia lipolytica and enhanced the precursor supply, resulting in a titre of 102.8 mg/L. The catalytic efficiency of the rate-limiting steps in the pathway was then enhanced through various strategies, including fusion expression of key enzymes homogentisate phytyltransferaseand and tocopherol cyclase, semi-rational design of SyHPT and multi-copy integration of pathway genes. The final a δ-tocotrienol titre in a 5 L bioreactor was 466.8 mg/L following fed-batchfermentation. This study represents the first successful de novo biosynthesis of δ-tocotrienol in Y. lipolytica, providing valuable insights into the synthesis of vitamin E-related compounds.

Introduction of human m6Am methyltransferase PCIF1 facilitates the biosynthesis of terpenoids in Saccharomyces cerevisiae

BACKGROUND

The application of synthetic biology techniques has been recognized as an efficient alternative for the biosynthesis of high-value natural products, and various metabolic engineering strategies have been employed to develop microbial cell factories. However, exploration of more efficient metabolic pathway optimization strategies is still required to further improve the producing potential of microbial cell factories to meet the industrial requirements.

RESULTS

In this study, we found that the introduction of human N6,2'-O-dimethyladenosine (m6Am) methyltransferase PCIF1 into Saccharomyces cerevisiae significantly promoted the biosynthesis of squalene, increased by 2.3-fold. Transcriptome analysis revealed that PCIF1 upregulated genes associated with glycolysis and acetyl-CoA biosynthesis pathways, and also activated the cell wall integrity mitogen-activated protein kinase (MAPK) pathway to improve the cell wall stress response. Importantly, PCIF1 expression notably enhanced squalene and sesquiterpenoid longifolene production in engineered yeast strains, with 2.3-fold and 1.4-fold higher increase, respectively.

CONCLUSION

This study presents a PCIF1-based metabolic engineering strategy that could serve as an effective approach for the optimization of terpene biosynthesis in yeast cell factories.

Overexpression of tRNA m7G modification methyltransferase complex promotes the biosynthesis of triterpene in yeast

Background

The sustainable production of valuable compounds using microbial cell factories is an effective approach, yet further metabolic engineering strategies are needed to enhance their biosynthetic potential. Recent studies suggest that RNA modifications can influence cellular metabolism, but their role in metabolic engineering remains largely unexplored.

Methods

The production of squalene and lupeol in different yeast strains was detected by gas chromatography-mass spectrometry (GC-MS) equipment. Transcriptomic analysis was performed to identify metabolic changes associated with the epigenetic modification. The transcriptional and translational expression of targeted genes were determined by real-time quantitative polymerase chain reaction and western blotting, respectively. The mRNA stability of targeted genes was measured by mRNA decay assay.

Results

In this study, the overexpression of Trm8 and Trm82 complex, mediating the tRNA 7-methylguanosine (m7G) modification in yeast, significantly increased the production of squalene in CEN.PK2-1C. Transcriptome analysis indicated that Trm8/Trm82 overexpression upregulated the expression levels of genes involved in amino acid synthesis, glycolysis, and tricarboxylic acid cycle, and the enhanced glycolysis, upstream of acetyl-CoA biosynthesis, might be responsible for the promoted biosynthesis of squalene. Further investigation demonstrated that Trm8/Trm82 complex could increase the production of squalene and lupeol in engineered yeast.

Conclusion

These findings indicate that tRNA m7G modification can regulate central metabolism and enhance terpenoid biosynthesis. This study provides new insights into RNA modifications as a potential metabolic engineering strategy for improving the production of high-value compounds.

Metabolic Engineering of Corynebacterium glutamicum for Producing Different Types of Triterpenoids

Triterpenoids widely exist in nature with diverse structures and possess various functional properties and biological effects. However, research on triterpenoids biosynthesis in Corynebacterium glutamicum is still limited to squalene, which restricts the development of C. glutamicum to produce high-value triterpenoids. In this study, C. glutamicum was developed as an efficient and flexible platform for the biosynthesis of different types of triterpenoids. Squalene was synthesized and the titer was improved to 400.1 mg/L in flask combining strategies of metabolic engineering and fermentation optimization. Particularly, intracellular squalene accounted for more than 97%, addressing the problem of leaking squalene in C. glutamicum, which may restrict the subsequent synthesis of other triterpenoids derived from squalene. Furthermore, 201.9 mg/L (3S)-2,3-oxidosqualene (SQO) and 264.9 mg/L (3S,22S)-2,3,22,23-dioxidosqualene (SDO) were successfully synthesized in strains harboring heterogeneous squalene epoxidase from Arabidopsis thaliana with different expression strengths. Therefore, a platform for de novo triterpenoids synthesis based on SQO or SDO was constructed in C. glutamicum. For instance, biosynthesis of α-amyrin and α-onocerin was achieved for the first time by introducing oxidosqualene cyclases in SQO- and SDO-producing C. glutamicum strains, respectively. After optimization, the titer of α-amyrin and α-onocerin was improved to 65.3 and 136.85 mg/L, respectively. Furthermore, ursolic acid, derived from α-amyrin, was synthesized after expressing cytochrome P450 enzyme and its compatible cytochrome P450 reductases with a titer of 486 μg/L. For the first time, reactions of epoxidation, cyclization, and oxidation from squalene were achieved in C. glutamicum, leading to the production of different types of triterpenoids. Our study provides a new platform for the production of triterpenoids, which will be helpful for the large-scale production of triterpenoids employing C. glutamicum as a chassis strain.

Exploration of In Situ Extraction for Enhanced Triterpenoid Production by Saccharomyces cerevisiae

Plant-derived triterpenoids are in high demand due to their valuable applications in cosmetic, nutraceutical, and pharmaceutical industries. To meet this demand, microbial production of triterpenoids is being developed for large-scale production. However, a prominent limitation of microbial synthesis is the intracellular accumulation, requiring cell disruption during downstream processing. Destroying the whole-cell catalyst drives up production costs and limits productivity and product yield per cell. Here, in situ product extraction of triterpenoids into a second organic phase was researched to address this limitation. An organic solvent screening identified water-immiscible isopropyl myristate as a suitable in situ extractant, enabling extraction of up to 90% of total triterpenoids from engineered Saccharomyces cerevisiae. Combining isopropyl myristate and β-cyclodextrins improved extraction efficiency. In a first configuration, repeated batch fermentation with sequential product extraction and cell recycling resulted in 1.8 times higher production than a reference fermentation without in situ product extraction. In the second configuration, yeast cells were in contact with the second organic phase throughout a fed-batch fermentation to continuously extract triterpenoids. This resulted in 90% product extraction and an extended production phase. Further improvement of triterpenoid production was not achieved due to microbial host limitations uncovered through omics analyses.

Efficient Plant Triterpenoids Synthesis in Saccharomyces cerevisiae: from Mechanisms to Engineering Strategies

Triterpenoids possess a range of biological activities and are extensively utilized in the pharmaceutical, food, cosmetic, and chemical industries. Traditionally, they are acquired through chemical synthesis and plant extraction. However, these methods have drawbacks, including high energy consumption, environmental pollution, and being time-consuming. Recently, the de novo synthesis of triterpenoids in microbial cell factories has been achieved. This represents a promising and environmentally friendly alternative to traditional supply methods. Saccharomyces cerevisiae, known for its robustness, safety, and ample precursor supply, stands out as an ideal candidate for triterpenoid biosynthesis. However, challenges persist in industrial production and economic feasibility of triterpenoid biosynthesis. Consequently, metabolic engineering approaches have been applied to improve the triterpenoid yield, leading to substantial progress. This review explores triterpenoids biosynthesis mechanisms in S. cerevisiae and strategies for efficient production. Finally, the review also discusses current challenges and proposes potential solutions, offering insights for future engineering.

Engineering amino acid residues of pentacyclic triterpene synthases for improving the activity

Pentacyclic triterpenoids exhibit a wide range of biological activities which have wide applications in the food, cosmetics, and pharmaceutical industries. High-performance chassis strains have been developed for the production of various pentacyclic triterpenoids, e.g., lupane-type and oleanane-type triterpenoids. The production of common pentacyclic triterpenes and their derivatives is limited by the poor activity of typical pentacyclic triterpene synthases (PTSs). However, a general strategy applicable to typical PTSs is still lacking. As typical pentacyclic triterpenes are derived from the baccharenyl cation, engineering the non-active-site residues in the MXXXXR motif might be beneficial for the catalytic efficiencies of typical PTSs by the stabilization of the baccharenyl cation. Here, we develop a general strategy for improving the activity of typical PTSs. As a proof of concept, the activity of three PTSs such as lupeol synthase, β-amyrin synthase, and α-amyrin synthases was significantly increased up to 7.3-fold by site-directed saturation mutagenesis. This strategy could be applied to improve the activity of various typical PTSs. KEY POINTS: • The strategy could be applied to typical PTSs for improving the activity. • The catalytic activity of typical PTSs was significantly increased.

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.

Transcription Factors ZjMYB39 and ZjMYB4 Regulate Farnesyl Diphosphate Synthase- and Squalene Synthase-Mediated Triterpenoid Biosynthesis in Jujube

Jujube (Ziziphus jujuba Mill.) is rich in valuable bioactive triterpenoids. However, the regulatory mechanism underlying triterpenoid biosynthesis in jujube remains poorly studied. Here, we characterized the triterpenoid content in wild jujube and cultivated jujube. The triterpenoid content was higher in wild jujube than in cultivated jujube, triterpenoids were most abundant in young leaves, buds, and later stages of development. The transcriptome analysis and correlation analysis showed that differentially expressed genes (DEGs) were enriched in the terpenoid synthesis pathways, and triterpenoids content was strongly correlated with farnesyl diphosphate synthase (ZjFPS), squalene synthase (ZjSQS), and transcription factors ZjMYB39 and ZjMYB4 expression. Gene overexpression and silencing analysis indicated that ZjFPS and ZjSQS were key genes in triterpenoid biosynthesis and transcription factors ZjMYB39 and ZjMYB4 regulated triterpenoid biosynthesis. Subcellular localization experiments showed that ZjFPS and ZjSQS were localized to the nucleus and endoplasmic reticulum and ZjMYB39 and ZjMYB4 were localized to the nucleus. Yeast one-hybrid, glucuronidase activity, and dual-luciferase activity assays suggested that ZjMYB39 and ZjMYB4 regulate triterpenoid biosynthesis by directly binding and activating the promoters of ZjFPS and ZjSQS. These findings provide insights into the underlying regulatory network of triterpenoids metabolism in jujube and lay theoretical and practical foundation for molecular breeding.

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.