Restricting Promiscuity of Plant Flavonoid 3'-Hydroxylase and 4'-O-Methyltransferase Improves the Biosynthesis of (2S)-Hesperetin in E. coli

Constructing Protein-Scaffolded Multienzyme Assembly Enhances the Coupling Efficiency of the P450 System for Efficient Daidzein Biosynthesis from (2S)-Naringenin

Daidzein is a major isoflavone compound with an immense pharmaceutical value. This study applied a novel P450 CYP82D26 which can biosynthesize daidzein from (2S)-naringenin. However, the recombinant P450 systems often suffer from low coupling efficiency, leading to an electron transfer efficiency decrease and harmful reactive oxygen species release, thereby compromising their stability and catalytic efficiency. To address these challenges, the SH3-GBD-PDZ (SGP) protein scaffold was applied to assemble a multienzyme system comprising CYP82D26, P450 reductase, and NADP+-dependent aldehyde reductase in desired stoichiometric ratios. Results showed that the coupling efficiency of the P450 system was significantly increased, primarily attributed to the channeling effect of NADPH resulting from the proximity of tethered enzymes and the electrostatic interactions between NADPH and SGP. Assembling this SGP-scaffolded assembly system in Escherichia coli yielded a titer of 240.5 mg/L daidzein with an 86% (2S)-naringenin conversion rate, which showed a 9-fold increase over the free enzymes of the P450 system. These results underscore the potential application of the SGP-scaffolded multienzyme system in enhancing the coupling and catalytic efficiency of the P450 system.

High-Level De Novo Production of (2S)-Eriodictyol in Yarrowia Lipolytica by Metabolic Pathway and NADPH Regeneration Engineering

(2S)-Eriodictyol, a polyphenolic flavonoid, has found widespread applications in health supplements and food additives. However, the limited availability of plant-derived (2S)-eriodictyol cannot meet the market demand. Microbial production of (2S)-eriodictyol faces challenges, including the low catalytic efficiency of flavone 3'-hydroxylase/cytochrome P450 reductase (F3'H/CPR), insufficient precursor supplementation, and inadequate NADPH regeneration. This study systematically engineered Yarrowia lipolytica for high-level (2S)-eriodictyol production. In doing this, the expression of F3'H/CPR was balanced, and the supply of precursors was enhanced by relieving feedback inhibition of the shikimate pathway, promoting fatty acid β-oxidation, and increasing the copy number of synthetic pathway genes. These strategies, combined with NADPH regeneration, achieved an (2S)-eriodictyol titer of 423.6 mg/L. Finally, in fed-batch fermentation, a remarkable 6.8 g/L (2S)-eriodictyol was obtained, representing the highest de novo microbial titer reported to date and paving the way for industrial production.

Systems Metabolic Engineering of Saccharomyces cerevisiae for the High-Level Production of (2S)-Eriodictyol

(2S)-eriodictyol (ERD) is a flavonoid widely found in citrus fruits, vegetables, and important medicinal plants with neuroprotective, cardioprotective, antidiabetic, and anti-obesity effects. However, the microbial synthesis of ERD is limited by complex metabolic pathways and often results in a low production performance. Here, we engineered Saccharomyces cerevisiae by fine-tuning the metabolism of the ERD synthesis pathway. The results showed that the ERD titer was effectively increased, and the intermediate metabolites levels were reduced. First, we successfully reconstructed the de novo synthesis pathway of p-coumaric acid in S. cerevisiae and fine-tuned the metabolic pathway using promoter engineering and terminator engineering for the high-level production of (2S)-naringenin. Subsequently, the synthesis of ERD was achieved by introducing the ThF3'H gene from Tricyrtis hirta. Finally, by multiplying the copy number of the ThF3'H gene, the production of ERD was further increased, reaching 132.08 mg L-1. Our work emphasizes the importance of regulating the metabolic balance to produce natural products in microbial cell factories.

Engineering a Plant Polyketide Synthase for the Biosynthesis of Methylated Flavonoids

Homoeriodictyol and hesperetin are naturally occurring O-methylated flavonoids with many health-promoting properties. They are produced in plants in low abundance and as complex mixtures of similar compounds that are difficult to separate. Synthetic biology offers the opportunity to produce various flavonoids in a targeted, bottom-up approach in engineered microbes with high product titers. However, the production of O-methylated flavonoids is currently still highly inefficient. In this study, we investigated and engineered a combination of enzymes that had previously been shown to support homoeriodictyol and hesperetin production in Escherichia coli from fed O-methylated hydroxycinnamic acids. We determined the crystal structures of the enzyme catalyzing the first committed step of the pathway, chalcone synthase from Hordeum vulgare, in three ligand-bound states. Based on these structures and a multiple sequence alignment with other chalcone synthases, we constructed mutant variants and assessed their performance in E. coli toward producing methylated flavonoids. With our best mutant variant, HvCHS (Q232P, D234 V), we were able to produce homoeriodictyol and hesperetin at 2 times and 10 times higher titers than reported previously. Our findings will facilitate further engineering of this enzyme toward higher production of methylated flavonoids.

Expanding flavone and flavonol production capabilities in Escherichia coli

Flavones and flavonols are important classes of flavonoids with nutraceutical and pharmacological value, and their production by fermentation with recombinant microorganisms promises to be a scalable and economically favorable alternative to extraction from plant sources. Flavones and flavonols have been produced recombinantly in a number of microorganisms, with Saccharomyces cerevisiae typically being a preferred production host for these compounds due to higher yields and titers of precursor compounds, as well as generally improved ability to functionally express cytochrome P450 enzymes without requiring modification to improve their solubility. Recently, a rapid prototyping platform has been developed for high-value compounds in E. coli, and a number of gatekeeper (2S)-flavanones, from which flavones and flavonols can be derived, have been produced to high titers in E. coli using this platform. In this study, we extended these metabolic pathways using the previously reported platform to produce apigenin, chrysin, luteolin and kaempferol from the gatekeeper flavonoids naringenin, pinocembrin and eriodictyol by the expression of either type-I flavone synthases (FNS-I) or type-II flavone synthases (FNS-II) for flavone biosynthesis, and by the expression of flavanone 3-dioxygenases (F3H) and flavonol synthases (FLS) for the production of the flavonol kaempferol. In our best-performing strains, titers of apigenin and kaempferol reached 128 mg L-1 and 151 mg L-1 in 96-DeepWell plates in cultures supplemented with an additional 3 mM tyrosine, though titers for chrysin (6.8 mg L-1) from phenylalanine, and luteolin (5.0 mg L-1) from caffeic acid were considerably lower. In strains with upregulated tyrosine production, apigenin and kaempferol titers reached 80.2 mg L-1 and 42.4 mg L-1 respectively, without the further supplementation of tyrosine beyond the amount present in the rich medium. Notably, the highest apigenin, chrysin and luteolin titers were achieved with FNS-II enzymes, suggesting that cytochrome P450s can show competitive performance compared with non-cytochrome P450 enzymes in prokaryotes for the production of flavones.