Biosynthesis of two quercetin O-diglycosides in Escherichia coli

Economical one-pot synthesis of isoquercetin and D-allulose from quercetin and sucrose using whole-cell biocatalyst

Isoquercetin and D-allulose have diverse applications and significant value in antioxidant, antibacterial, antiviral, and lipid metabolism. Isoquercetin can be synthesized from quercetin, while D-allulose is converted from D-fructose. However, their production scale and overall quality are relatively low, leading to high production costs. In this study, we have devised a cost-effective one-pot method for biosynthesizing isoquercetin and D-allulose using a whole-cell biocatalyst derived from quercetin and sucrose. To achieve this, the optimized isoquercetin synthase and D-allulose-3-epimerase were initially identified through isofunctional gene screening. In order to reduce the cost of uridine diphosphate glucose (UDPG) during isoquercetin synthesis and ensure a continuous supply of UDPG, sucrose synthase is introduced to enable the self-circulation of UDPG. At the same time, the inclusion of sucrose permease was utilized to successfully facilitate the catalytic production of D-allulose in whole cells. Finally, the recombinant strain BL21/UGT-SUS+DAE-SUP, which overexpresses MiF3GTMUT, GmSUS, EcSUP, and DAEase, was obtained. This strain co-produced 41±2.4 mg/L of isoquercetin and 5.7±0.8 g/L of D-allulose using 120 mg/L of quercetin and 20 g/L of sucrose as substrates for 5 h after optimization. This is the first green synthesis method that can simultaneously produce flavonoid compounds and rare sugars. These findings provide valuable insights and potential for future industrial production, as well as practical applications in factories.

Metabolic Engineering of Escherichia coli for Hyperoside Biosynthesis

Hyperoside (quercetin 3-O-galactoside) exhibits many biological functions, along with higher bioactivities than quercetin. In this study, three UDP-dependent glycosyltransferases (UGTs) were screened for efficient hyperoside synthesis from quercetin. The highest hyperoside production of 58.5 mg·L⁻¹ was obtained in a recombinant Escherichia coli co-expressing UGT from Petunia hybrida (PhUGT) and UDP-glucose epimerase (GalE, a key enzyme catalyzing the conversion of UDP-glucose to UDP-galactose) from E. coli. When additional enzymes (phosphoglucomutase (Pgm) and UDP-glucose pyrophosphorylase (GalU)) were introduced into the recombinant E. coli, the increased flux toward UDP-glucose synthesis led to enhanced UDP-galactose-derived hyperoside synthesis. The efficiency of the recombinant strain was further improved by increasing the copy number of the PhUGT, which is a limiting step in the bioconversion. Through the optimization of the fermentation conditions, the production of hyperoside increased from 245.6 to 411.2 mg·L⁻¹. The production was also conducted using a substrate-fed batch fermentation, and the maximal hyperoside production was 831.6 mg·L⁻¹, with a molar conversion ratio of 90.2% and a specific productivity of 27.7 mg·L⁻¹·h⁻¹ after 30 h of fermentation. The efficient hyperoside synthesis pathway described here can be used widely for the glycosylation of other flavonoids and bioactive substances.

Synthetic spatial patterning in bacteria: advances based on novel diffusible signals

Engineering multicellular patterning may help in the understanding of some fundamental laws of pattern formation and thus may contribute to the field of developmental biology. Furthermore, advanced spatial control over gene expression may revolutionize fields such as medicine, through organoid or tissue engineering. To date, foundational advances in spatial synthetic biology have often been made in prokaryotes, using artificial gene circuits. In this review, engineered patterns are classified into four levels of increasing complexity, ranging from spatial systems with no diffusible signals to systems with complex multi‐diffusor interactions. This classification highlights how the field was held back by a lack of diffusible components. Consequently, we provide a summary of both previously characterized and some new potential candidate small‐molecule signals that can regulate gene expression in Escherichia coli. These diffusive signals will help synthetic biologists to successfully engineer increasingly intricate, robust and tuneable spatial structures.

Genome-wide analyses reveals a glucosyltransferase involved in rutin and emodin glucoside biosynthesis in tartary buckwheat

With people's increasing needs for health concern, rutin and emodin in tartary buckwheat have attracted much attention for their antioxidant, anti-diabetic and reducing weight function. However, the biosynthesis of rutin and emodin in tartary buckwheat is still unclear; especially their later glycosylation contributing to make them more stable and soluble is uncovered. Based on tartary buckwheat' genome, the gene structures of 106 UGTs were analyzed; 21 candidate FtUGTs were selected to enzymatic test by comparing their transcript patterns. Among them, FtUGT73BE5 and other 4 FtUGTs were identified to glucosylate flavonol or emodin in vitro; especially rFtUGT73BE5 could catalyze the glucosylation of all tested flavonoids and emodin. Furthermore, the identical in vivo functions of FtUGT73BE5 were demonstrated in tartary buckwheat hairy roots. The transcript profile of FtUGT73BE5 was consistent with the accumulation trend of rutin in plant; this gene may relate to anti-adversity for its transcripts were up-regulated by MeJA, and repressed by ABA.

A Review on Structure, Modifications and Structure-Activity Relation of Quercetin and Its Derivatives

Quercetin and its derivatives are important metabolites that belong to the flavonol class of flavonoids. Quercetin and some of the conjugates have been approved by the FDA for human use. They are widely distributed among plants and have various biological activities, such as being anticancer, antiviral, and antioxidant. Hence, the biosynthesis of novel derivatives is an important field of research. Glycosylation and methylation are two important modification strategies that have long been used and have resulted in many novel metabolites that are not present in natural sources. A strategy for modifying quercetin in E. coli by means of glycosylation, for example, involves overexpressing respective glycosyltransferases (GTs) in the host and metabolic engineering for increasing nucleoside diphosphate sugar (NDP sugar). Still others have used microorganisms other than E. coli, such as Streptomyces sp., for the biotransformation process. The overall study of the structural activity relationship has revealed that modification of some residues in quercetin decreased one activity but increased others. This review summarizes all of the information mentioned above.

Production of isoorientin and isovitexin from luteolin and apigenin using coupled catalysis of glycosyltransferase and sucrose synthase

Isoorientin and isovitexin, kinds of flavone C-glycosides, exhibit a number of biological properties. In this work, The C-glucosyltransferase (Gt6CGT) gene from Gentiana triflora was cloned and expressed in Escherichia coli BL21(DE3). The optimal activity of Gt6CGT was at pH 7.5 and 50° C. The enzyme was stable over pH range of 6.5-9.0, and had a 1-h half-life at 50° C. The V_max for luteolin and apigenin was 21.1 nmol/min/mg and 31.7 nmol/min/mg, while the K_m was 0.21 mM and 0.22 mM, respectively. Then, we developed an environmentally safe and efficient method for isoorientin and isovitexin production using the coupled catalysis of Gt6CGT and Glycine max sucrose synthase (GmSUS). By optimizing coupled reaction conditions, the titer of isoorientin and isovitexin reached 3820 mg/L with a corresponding molar conversion of 94.7% and 3772 mg/L with a corresponding molar conversion of 97.1%, respectively. The maximum number of UDP-glucose regeneration cycles (RC_max) reached 28.4 for isoorientin and 29.1 for isovitexin. The coupled catalysis reported herein represents a promising method to meet industrial requirements for large-scale isoorientin and isovitexin production in the future. Graphical Abstract.

Metabolic engineering of glycosylated polyketide biosynthesis

Microbial cell factories are extensively used for the biosynthesis of value-added chemicals, biopharmaceuticals, and biofuels. Microbial biosynthesis is also realistic for the production of heterologous molecules including complex natural products of plant and microbial origin. Glycosylation is a well-known post-modification method to engineer sugar-functionalized natural products. It is of particular interest to chemical biologists to increase chemical diversity of molecules. Employing the state-of-the-art systems and synthetic biology tools, a range of small to complex glycosylated natural products have been produced from microbes using a simple and sustainable fermentation approach. In this context, this review covers recent notable metabolic engineering approaches used for the biosynthesis of glycosylated plant and microbial polyketides in different microorganisms. This review article is broadly divided into two major parts. The first part is focused on the biosynthesis of glycosylated plant polyketides in prokaryotes and yeast cells, while the second part is focused on the generation of glycosylated microbial polyketides in actinomycetes.

One-Pot Synthesis of Hyperoside by a Three-Enzyme Cascade Using a UDP-Galactose Regeneration System

Hyperoside exhibits many biological properties and is more soluble in water than quercetin. A uridine 5'-diphosphate (UDP) galactose regeneration system and one-pot synthesis of hyperoside was described herein. Glycine max sucrose synthase (GmSUS) was coupled with Escherichia coli UDP-galactose 4-epimerase (GalE) to regenerate UDP-galactose from sucrose and UDP. Petunia hybrida glycosyltransferase (PhUGT) with high activity toward quercetin was used to synthesize hyperoside via the UDP-galactose regeneration system. The important factors for optimal synergistic catalysis were determined. Through the use of a fed-batch operation, the final titer of hyperoside increased to 2134 mg/L, with a corresponding molar conversion of 92% and maximum number of UDP-galactose regeneration cycles (RC_max) of 18.4 under optimal conditions. Therefore, the method described herein for the regeneration of UDP-galactose from UDP and sucrose can be widely used for the glycosylation of flavonoids and other bioactive substances.

Inhibitory Activities of Stauntonia hexaphylla Leaf Constituents on Rat Lens Aldose Reductase and Formation of Advanced Glycation End Products and Antioxidant

Stauntonia hexaphylla (Thunb.) Decne. (Lardizabalaceae) leaves (SHL) have been used traditionally as analgesics, sedatives, diuretics, and so on, in China. To date, no data have been reported on the inhibitory effect of SHL and its constituents on rat lens aldose reductase (RLAR) and advanced glycation end products (AGEs). Therefore, the inhibitory effect of compounds isolated from SHL extract on RLAR and AGEs was investigated to evaluate potential treatments of diabetic complications. The ethyl acetate (EtOAC) fraction of SHL extract showed strong inhibitory activity on RLAR and AGEs; therefore, EtOAc fraction (3.0 g) was subjected to Sephadex LH-20 column chromatography, for further fractionation, with 100% MeOH solvent system to investigate its effect on RLAR and AGEs. Phytochemical investigation of SHL led to the isolation of seven compounds. Among the isolated compounds, chlorogenic acid, calceolarioside B, luteolin-3'-O-β-D-glucopyranoside, quercetin-3-O-β-D-glucopyranoside, and luteolin-7-O-β-D-glucopyranoside exhibited significant inhibitory activity against RLAR with IC₅₀ in the range of 7.34-23.99 μM. In addition, 3-(3,4-dihydroxyphenyl) propionic acid, neochlorogenic acid, and luteolin-3'-O-β-D-glucopyranoside exhibited the most potent inhibitory activity against formation of AGEs, with an IC₅₀ value of 115.07-184.06 μM, compared to the positive control aminoguanidine (820.44 μM). Based on these findings, SHL dietary supplements could be considered for the prevention and/or treatment of diabetes complication.

Biosynthesis of three N-acetylaminosugar-conjugated flavonoids using engineered Escherichia coli

Background

Nucleotide sugars serve as sugar donors for the synthesis of various glycones. The biological and chemical properties of glycones can be altered depending which sugar is attached. Bacteria synthesize unusual nucleotide sugars. A novel nucleotide sugar can be synthesized in Escherichia coli by introducing nucleotide biosynthetic genes from other microorganisms into E. coli. The engineered E. coli strains can be used as a platform for the synthesis of novel glycones.

Results

Four genes, Pdeg (UDP-N-acetylglucosamine C4,6-dehydratase), Preq (UDP-4-reductase), UDP-GlcNAc 6-DH (UDP-N-acetylglucosamine 6-dehydrogenase), and UXNAcS (UDP-N-acetylxylosamine synthase), were employed to synthesize UDP-quinovosamine, UDP-N-acetylglucosaminuronic acid, and UDP-N-acetylxylosamine in E. coli. We engineered an E. coli nucleotide sugar biosynthetic pathway to increase the pool of substrate for the target nucleotide sugars. Uridine diphosphate dependent glycosyltransferase (UGT) was also selected and introduced into E. coli. Using engineered E. coli, high levels of three novel flavonoid glycosides were obtained; 158.3 mg/L quercetin 3-O-(N-acetyl)quinovosamine, 172.5 mg/L luteolin 7-O-(N-acetyl)glucosaminuronic acid, and 160.8 mg/L quercetin 3-O-(N-acetyl)xylosamine.

Conclusions

We reconstructed an E. coli nucleotide pathway for the synthesis of UDP-quinovosamine, UDP-N-acetylglucosaminuronic acid and UDP-N-acetylxylosamine in an E. coli galU (UDP-glucose 1-phosphate uridylyltransferase) or pgm (phosphoglucomutase) deletion mutant. Using engineered E. coli strains harboring a specific UGT, three novel flavonoids glycones were synthesized. The E. coli strains used in this study can be used for the synthesis of diverse glycones.

Electronic supplementary material

The online version of this article (doi:10.1186/s12934-016-0582-8) contains supplementary material, which is available to authorized users.