Exploration of glycosylated flavonoids from metabolically engineered E. coli

Molecular cloning and in silico analysis of chalcone isomerase from Polygonum minus

BACKGROUND

Chalcone isomerase (CHI; EC 5.5.1.6) is one of the key enzymes in the flavonoid biosynthetic pathway that is responsible for the intramolecular cyclization of chalcones into specific 2S-flavanones.

METHODS AND RESULTS

In this study, the open reading frame (ORF) of CHI was successfully isolated from the cDNA of Polygonum minus at 711-bp long, encoding for 236 amino acid residues, with a predicted molecular weight of 25.4 kDa. Multiple sequence alignment and phylogenetic analysis revealed that the conserved residues (Thr50, Tyr108, Asn115, and Ser192) in the cleft of CHI enzyme group active site are present in PmCHI protein sequence and classified as type I. PmCHI comprises more hydrophobic residues without a signal peptide and transmembrane helices. The three-dimensional (3D) structure of PmCHI predicted through homology modeling was validated by Ramachandran plot and Verify3D, with values within the acceptable range of a good model. PmCHI was cloned into pET-28b(+) plasmid, expressed in Escherichia coli BL21(DE3) at 16 °C and partially purified.

CONCLUSION

These findings contribute to a deeper understanding of the PmCHI protein and its potential for further characterization of its functional properties in the flavonoid biosynthetic pathway.

Recent advancement of engineering microbial hosts for the biotechnological production of flavonoids

Flavonoids are polyphenols that are important organic chemicals in plants. The health benefits of flavonoids that result in high commercial values make them attractive targets for large-scale production through bioengineering. Strategies such as engineering a flavonoid biosynthetic pathway in microbial hosts provide an alternative way to produce these beneficial compounds. Escherichia coli, Saccharomyces cerevisiae and Streptomyces sp. are among the expression systems used to produce recombinant products, as well as for the production of flavonoid compounds through various bioengineering approaches including clustered regularly interspaced short palindromic repeats (CRISPR)-based genome engineering and genetically encoded biosensors to detect flavonoid biosynthesis. In this study, we review the recent advances in engineering model microbial hosts as being the factory to produce targeted flavonoid compounds.

Flavonol glycosides in Dyssodia tagetiflora and its temporal variation, chemoprotective and ameliorating activities

Dyssodia tagetiflora is known as 'Tzaracata' and 'flor de muerto'. Recently, D. tagetiflora has been reported to have antioxidant activities in its polar extracts as well as insecticidal activities. Hyperoside (1), avicularin (2) and avicularin acetate (3) have been isolated previously. However, the temporary variation in glycoside flavonoids biosynthesis, as well as antibacterial and chemoprotective activities, have not been reported. The amount of 1, 2 and 3 in the different collections was characterized by HPLC-MS. Two new C-glycosides were characterized, quercetin-4'-methyl ether 6-C glucoside (A1) and quercetin-4'-methyl ether 8-C glucoside (A2), as well as [2-(3,4-dihydroxyphenyl)-5,7-dihydroxy-4-oxochromen-3-yl]3,4,5-trihydroxyoxane-2,6-dicarboxylate (A3). This is the first report of the presence of C-C flavonoid glycosides compounds in the genus Dyssodia. Hyperoside was the majority compound at all collections. The methanolic extracts of August 2016 and October 2017 were active against Micrococcus luteus and Bacillus subtillis. The methanolic extract has chemoprotective effects because, when applied topically in SKH-1 mice, it decreases the severity of epidermal damage induced by acute exposure to ultraviolet radiation. In addition, cutaneous photocarcinogenesis was decreased in mice treated with the extract. The methanolic extract of D. tagetiflora has chemoprotective properties by decreasing the damage caused by acute and chronic exposure to UV in mice.

Recent developments in the enzymatic O-glycosylation of flavonoids

The glycosylation of bioactive compounds, such as flavonoids, is of particular relevance, as it modulates many of their pharmacokinetic parameters. This article reviews the literature between 2010 and the end of 2015 that deals with the enzymatic O-glycosylation of this class of compounds. Enzymes of glycosyltransferase family 1 remain the biocatalysts of choice for glycodiversification of flavonoids, in spite of relatively low yields. Transfers of 14 different sugars, in addition to glucose, were reported. Several Escherichia coli strains were metabolically engineered to enable a (more efficient) synthesis of the required donor during in vivo glycosylations. For the transfer of glucose, enzymes of glycoside hydrolase families 13 and 70 were successfully assayed with several flavonoids. The number of acceptor substrates and of regiospecificities characterized so far is smaller than for glycosyltransferases. However, their glycosyl donors are much cheaper and yields are considerably higher. A few success stories of enzyme engineering were reported. These improved the catalytic efficiency as well as donor, acceptor, or product ranges. Currently, the development of appropriate high-throughput screening systems appears to be the major bottleneck for this powerful technology.

Systems metabolic engineering of Escherichia coli to enhance the production of flavonoid glucuronides

Through modulating UDPGA biosynthetic pathway and introducting SbUGT, an engineered strain was constructed to enhance the production of flavonoid glucuronides.

Biotransformations and biological activities of hop flavonoids

Female hop cones are used extensively in the brewing industry, but there is now increasing interest in possible uses of hops for non-brewing purposes, especially in the pharmaceutical industry. Among pharmaceutically important compounds from hops are flavonoids, having proven anticarcinogenic, antioxidant, antimicrobial, anti-inflammatory and estrogenic effects. In this review we aim to present current knowledge on the biotransformation of flavonoids from hop cones with respect to products, catalysis and conversion. A list of microbial enzymatic reactions associated with gastrointestinal microbiota is presented. A comparative analysis of the biological activities of hop flavonoids and their biotransformation products is described, indicating where further research has potential for applications in the pharmaceutical industry.

Metabolic engineering of Escherichia coli for the biosynthesis of flavonoid-O-glucuronides and flavonoid-O-galactoside

Most flavonoids are glycosylated and the nature of the attached sugar can strongly affect their physiological properties. Although many flavonoid glycosides have been synthesized in Escherichia coli, most of them are glucosylated. In order to synthesize flavonoids attached to alternate sugars such as glucuronic acid and galactoside, E. coli was genetically modified to express a uridine diphosphate (UDP)-dependent glycosyltransferase (UGT) specific for UDP-glucuronic acid (AmUGT10 from Antirrhinum majus or VvUGT from Vitis vinifera) and UDP-galactoside (PhUGT from Petunia hybrid) along with the appropriate nucleotide biosynthetic genes to enable simultaneous production of their substrates, UDP-glucuronic acid and UDP-galactose. To engineer UDP-glucuronic acid biosynthesis, the araA gene encoding UDP-4-deoxy-4-formamido-L-arabinose formyltransferase/UDP-glucuronic acid C-4″ decarboxylase, which also used UDP-glucuronic acid as a substrate, was deleted in E. coli, and UDP-glucose dehydrogenase (ugd) gene was overexpressed to increase biosynthesis of UDP-glucuronic acid. Using these strategies, luteolin-7-O-glucuronide and quercetin-3-O-glucuronide were biosynthesized to levels of 300 and 687 mg/L, respectively. For the synthesis of quercetin 3-O-galactoside, UGE (encoding UDP-glucose epimerase from Oryza sativa) was overexpressed along with a glycosyltransferase specific for quercetin and UDP-galactose. Using this approach, quercetin 3-O-galactoside was successfully synthesized to a level of 280 mg/L.

WITHDRAWN: The paradox of natural flavonoid C-glycosides and health benefits: When more occurrence is less research

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