Enhancing Glycosylation of Flavonoids by Engineering the Uridine Diphosphate Glucose Supply in Escherichia coli

Reshaping UDP-binding pocket of bacterial sucrose synthase to improve efficiency of UDP-glucose production

UDP-glucose (UDPG), a nucleoside diphosphate sugar, is an important sugar donor for the biosynthesis of various glycoside compounds. Sucrose synthase (SuSy) can catalyze the synthesis of high-value UDPG from the cost-effective sucrose. By redesigning the substrate-binding pocket of SuSy in Denitrovibrio acetiphilus DSM 12809, a variant with 8.1-fold increased activity was generated in this study. Structural analysis revealed that the synergistic effect of the newly introduced hydrogen bonds and salt bridges was crucial for the enhanced activity. The yield of UDPG reached 127.6 g/L/h using this variant for catalysis. Moreover, when cascaded with glycosyltransferase for salidroside production, the yield of salidroside increased 2.7-fold, and a UDP recycling number of 3.2 was achieved. These results provide technical support for the industrial application of SuSy in the biosynthesis of nucleotide sugars and glycosides.

Efficient production of hydroxysalidroside in Escherichia coli via enhanced glycosylation and semi-rational design of UGT85A1

Hydroxysalidroside is an important natural phenylethanoid glycoside with broad application prospects in the food and pharmaceutical fields. However, its low concentration in plants and complex extraction hinder its production. Despite being a promising way to synthesize hydroxysalidroside in Escherichia coli, glycosylation remains the limiting factor for its production. A de novo biosynthetic pathway for hydroxysalidroside was successfully constructed in E. coli via the screening of glycosyltransferase, overexpressing phosphoglucomutase (pgm) and UDP-glucose pyrophosphorylase (galU) to ensure a sufficient supply of UDP-glucose (UDPG). Additionally, a semi-rational design of UGT85A1 was conducted to expand the acceptor-binding pocket to eliminate steric hindrance interfering with the binding of hydroxytyrosol. The endogenous genes ushA and otsA were knocked out to further reduce the consumption of UDPG. Finally, a titer of 5837.2 mg/L was achieved in a 5 L fermenter by optimizing the feeding times of carbon sources. This laid the foundation for the subsequent biosynthesis of phenylethanoid glycosides.

Characterization and Engineering of Multifunctional Glycosyltransferase HtUGT73EW3 for the Highly Efficient Synthesis of Flavonoid Mono/di-O-glycosides

Glycosylation modification is an effective way to improve the solubility, stability, and bioavailability of flavonoids. In this study, a multifunctional flavonoid glycosyltransferase HtUGT73EW3 was identified from Helleborus thibetanus. HtUGT73EW3 exhibited multisite selectivity for 3-, 6-, 7-, 2'-, 3'-, and 4'-OH of flavonoids and showed potent 3/3'-, 3/4'-, and 7/4'-di-O-glycosylation activity. HtUGT73EW3 was able to glycosylate structurally diverse flavonoid aglycones and monoglycosides, and showed efficient glycosylation capacity toward flavonoid structures modified with functional groups at the C-3, C-7, C-8, and C-4' positions. Notably, the mutation of Gln85 to Leu greatly enhanced its catalytic activity, enabling not only the conversion of steroids and terpenoids, but also the improved utilization of UDP-sugars. Furthermore, the Q85L and I94A variants were found to catalyze specific 7,4'- and 3,4'-di-O-glycosylation, respectively. A cost-effective one-pot synthetic reaction was established by coupling AtSuSy and HtUGT73EW3, and the gram-scale synthesis of flavonoid 4'-O-glucoside and 3,4'-/7,4'-di-O-glucoside was achieved by a fed-batch strategy.

Rhamnosyltransferases: Biochemical activities, potential biotechnology for production of natural products and their applications

Rhamnosyltransferase is an enzyme that catalyzes the transfer of rhamnose moieties from an activated donor molecule, typically nucleotide diphosphate-rhamnose (NDP-rhamnose), to a wide range of acceptor molecules, including proteins, lipids, saccharides, glycoproteins, glycans, and glycolipids. This enzymatic process, known as rhamnosylation, plays a fundamental role in the biosynthesis of critical biomolecules, such as components of the cell wall, plasma membrane channels, receptors, antigens, signaling molecules, antibiotics, and other secondary metabolites. Due to its essential involvement in both primary and secondary metabolic pathways, rhamnosyltransferase is indispensable for various biological processes and exhibits significant potential for applications in human health and industrial biotechnology. In recent years, this enzyme has garnered substantial attention from the scientific community, owing to its unique biochemical properties and its utility in diverse sectors, including medicine, food technology, and cosmetics. This review aims to synthesize recent advancements in the study of rhamnosyltransferase, with a focus on its catalytic mechanisms, biological significance, and emerging applications in biotechnological innovation.

Optimization of vanillin biosynthesis in Escherichia coli K12 MG1655 through metabolic engineering

Vanillin is an important flavouring agent applied in food, spices, pharmaceutical industries and other fields. Microbial biosynthesis of vanillin is considered a sustainable and economically feasible alternative to traditional chemical synthesis. In this study, Escherichia coli K12 MG1655 was used for the de novo synthesis of VAN by screening highly active carboxylic acid reductases and catechol O-methyltransferases, optimising the protocatechuic acid pathway, and regulating competitive metabolic pathways. Additionally, major alcohol by-products were identified and decreased by deleting three endogenous aldo-keto reductases and three alcohol dehydrogenases. Finally, a highest VAN titer was achieved to 481.2 mg/L in a 5 L fermenter from glucose. This work provides a valuable example of pathway engineering and screens several enzyme variants for the first time in E. coli.

Efficient and green production of flavone-5-O-glycosides by glycosyltransferases in Escherichia coli

O-Glycosylflavonoids exhibit diverse biological activities but their low content in plants is difficult to extract and isolate, and chemical synthesis steps are cumbersome, which are harmful to the environment. Therefore, the biosynthesis of O-glycosylflavonoids represents a green and sustainable alternative strategy, with glycosyltransferases playing a crucial role in this process. However, there are few studies on flavone 5-O-glycosyltransferases, which limits the synthesis of rare flavone 5-O glycosides by microorganisms. In this study, we characterized a highly regioselectivity flavone 5-O glycosyltransferase from Panicum hallii. Site-directed mutagenesis at residue P141 switches glucosylation to xylosylation. Using a combinatorial strategy of metabolic engineering, we generated a series of Escherichia coli recombinant strains to biocatalyze glycosylation of the typical flavone apigenin. Ultimately, further optimization of transformation conditions, apigenin-5-O-glucoside and apigenin-5-O-xyloside were biosynthesized for the first time so far, and the yields were 1490 mg/L and 1210 mg/L, respectively. This study provides a biotechnological component for the biosynthesis of flavone-5-O-glycosides, and established a green and sustainable approach for the industrial production of high-value O-glycosylflavones by engineering, which lays a foundation for their further development and application in food and pharmaceutical fields.

Cloning and Direct Evolution of a Novel 7-O-Glycosyltransferase from Cucurbita moschata and Its Application in the Efficient Biocatalytic Synthesis of Luteolin-7-O-glucoside

Luteolin-7-O-glucoside(L7G), a glycosylation product of luteolin, is present in a variety of foods, vegetables, and medicinal herbs and is commonly used in dietary supplements due to its health benefits. Meanwhile, luteolin-7-O-glucoside is an indicator component for the quality control of honeysuckle in the pharmacopoeia. However, its low content in plants has hindered its use in animal pharmacological studies and clinical practice. In this study, a novel 7-O-glycosyltransferase CmGT from Cucurbita moschata was cloned, which could efficiently convert luteolin into luteolin-7-O-glucoside under optimal conditions (40 °C and pH 8.5). To further improve the catalytic efficiency of CmGT, a 3D structure of CmGT was constructed, and directed evolution was performed. The mutant CmGT-S16A-T80W was obtained by using alanine scanning and iterative saturation mutagenesis. This mutant exhibited a kcat/Km value of 772 s-1·M-1, which was 3.16-fold of the wild-type enzyme CmGT. Finally, by introducing a soluble tag and UDPG synthesis pathway, the strain BXC was able to convert 1.25 g/L of luteolin into 1.91 g/L of luteolin-7-O-glucoside under optimal conditions, achieving a molar conversion rate of 96% and a space-time yield of 27.08 mg/L/h. This study provides an efficient method for the biosynthesis of luteolin-7-O-glucoside, which holds broad application prospects in the food and pharmaceutical industry.

Metabolic Engineering of Corynebacterium glutamicum for the Production of Flavonoids and Stilbenoids

Flavonoids and stilbenoids, crucial secondary metabolites abundant in plants and fungi, display diverse biological and pharmaceutical activities, including potent antioxidant, anti-inflammatory, and antimicrobial effects. However, conventional production methods, such as chemical synthesis and plant extraction, face challenges in sustainability and yield. Hence, there is a notable shift towards biological production using microorganisms like Escherichia coli and yeast. Yet, the drawbacks of using E. coli and yeast as hosts for these compounds persist. For instance, yeast's complex glycosylation profile can lead to intricate protein production scenarios, including hyperglycosylation issues. Consequently, Corynebacterium glutamicum emerges as a promising alternative, given its adaptability and recent advances in metabolic engineering. Although extensively used in biotechnological applications, the potential production of flavonoid and stilbenoid in engineered C. glutamicum remains largely untapped compared to E. coli. This review explores the potential of metabolic engineering in C. glutamicum for biosynthesis, highlighting its versatility as a cell factory and assessing optimization strategies for these pathways. Additionally, various metabolic engineering methods, including genomic editing and biosensors, and cofactor regeneration are evaluated, with a focus on C. glutamicum. Through comprehensive discussion, the review offers insights into future perspectives in production, aiding researchers and industry professionals in the field.

Engineering Redox Cofactor Balance for Improved 5-Methyltetrahydrofolate Production in Escherichia coli

5-Methyltetrahydrofolate (5-MTHF) is the sole active form of folate functioning in the human body and is widely used as a nutraceutical. Unlike the pollution from chemical synthesis, microbial synthesis enables green production of 5-MTHF. In this study, Escherichia coli BL21 (DE3) was selected as the host. Initially, by deleting 6-phosphofructokinase 1 and overexpressing glucose-6-phosphate 1-dehydrogenase and 6-phosphogluconate dehydrogenase, the glycolysis pathway flux decreased, while the pentose phosphate pathway flux enhanced. The ratios of NADH/NAD+ and NADPH/NADP+ increased, indicating elevated NAD(P)H supply. This led to more folate being reduced and the successful accumulation of 5-MTHF to 44.57 μg/L. Subsequently, formate dehydrogenases from Candida boidinii and Candida dubliniensis were expressed, which were capable of catalyzing the reaction of sodium formate oxidation for NAD(P)H regeneration. This further increased the NAD(P)H supply, leading to a rise in 5-MTHF production to 247.36 μg/L. Moreover, to maintain the balance between NADH and NADPH, pntAB and sthA, encoding transhydrogenase, were overexpressed. Finally, by overexpressing six key enzymes in the folate to 5-MTHF pathway and employing fed-batch cultivation in a 3 L fermenter, strain Z13 attained a peak 5-MTHF titer of 3009.03 μg/L, the highest level reported in E. coli so far. This research is a significant step toward industrial-scale microbial 5-MTHF production.