Production of ortho-hydroxydaidzein derivatives by a recombinant strain of Pichia pastoris harboring a cytochrome P450 fusion gene

Protein Engineering for Enhancing Electron Transfer in P450-Mediated Catalysis

Cytochrome P450 enzymes (P450s) are versatile biocatalysts with applications spanning pharmaceutical development and natural product biosynthesis. A critical bottleneck in P450-mediated reactions is the electron transfer process, which often limits catalytic efficiency and promotes uncoupling events leading to reactive oxygen species (ROS) formation. This review comprehensively examines recent protein engineering strategies aimed at enhancing electron transfer efficiency in P450 systems. We explore the design and application of different fusion constructs, which improve proximity between the P450 enzyme and its redox partners (RPs), as well as scaffold-mediated protein assembly, enabling precise spatial organization of P450s and RPs. Furthermore, we discuss targeted modifications at the P450-RP interaction interface and optimization of electron transfer pathways through site-directed mutagenesis and directed evolution. These strategies enhance catalytic activity, improve coupling efficiency, and reduce ROS formation. Finally, we address the remaining challenges in understanding and engineering P450 electron transfer, and discuss the future directions, emphasizing the need for advanced computational modeling, structural characterization, and integration of synthetic and systems biology approaches.

Engineering Saccharomyces cerevisiae for De Novo Biosynthesis of 3'-Hydroxygenistein

The polyhydroxy isoflavone 3'-hydroxygenistein (3'-OHG) has a wide range of pharmaceutical and nutraceutical benefits. Therefore, it is important to develop an efficient and sustainable method for 3'-OHG production. Here, we engineered the metabolic pathways of Saccharomyces cerevisiae to achieve de novo biosynthesis of 3'-OHG. First, we screened 2-hydroxyisoflavanone synthase (IFS), cytochrome P450 reductase, and 2-hydroxyisoflavanone dehydratase from different sources and optimized the best combination via promoter engineering. Next, we demonstrated that amplification of the rate-limiting enzyme PlIFS from Pueraria lobata improved genistein production. Increasing the availability of the cofactor heme further increased genistein titer to 44.55 ± 1.82 mg/L. Subsequently, screening and multicopy integration of isoflavone-3'-hydroxylase achieved 13.23 ± 0.27 mg/L 3'-OHG from 100 mg/L naringenin. Finally, 1.40 ± 0.02 mg/L 3'-OHG could be achieved via the de novo biosynthesis pathway. The final strain generated in this study will facilitate the production of polyhydroxy isoflavones via the 3'-OHG biosynthetic pathway.

Development of a P450 Fusion Enzyme for Biaryl Coupling in Yeast

Despite the diverse and potent bioactivities displayed by axially chiral biaryl natural products, their application in drug discovery is limited by restricted access to these complex molecular scaffolds. In particular, fundamental challenges remain in controlling the site- and atroposelectivity in biaryl coupling reactions. In contrast, Nature has a wealth of biosynthetic enzymes that catalyze biaryl coupling reactions with catalyst-controlled selectivity. In particular, a growing subset of fungal P450s have been identified to catalyze site- and atroposelective biaryl couplings. Herein, we optimize a whole-cell biocatalytic platform in Pichia pastoris to synthesize biaryl molecules through the recombinant production of the fungal P450 KtnC. Moreover, engineering redox self-sufficient fusion enzymes further improves the efficiency of the system. Altogether, this work provides a platform for biaryl coupling reactions in yeast that can be applied to engineering a currently underexplored pool of fungal P450s into selective biocatalysts for the synthesis of complex biaryl compounds.

A Novel Soy Isoflavone Derivative, 3′-Hydroxyglycitin, with Potent Antioxidant and Anti-α-Glucosidase Activity

This study demonstrated the enzymatic hydroxylation of glycitin to 3′-hydroxyglycitin, confirming the structure by mass and nucleic magnetic resonance spectral analyses. The bioactivity assays further revealed that the new compound possessed over 100-fold higher 1,1-diphenyl-2-picrylhydrazine free-radical scavenging activity than the original glycitin, although its half-time of stability was 22.3 min. Furthermore, the original glycitin lacked anti-α-glucosidase activity, whereas the low-toxic 3′-hydroxyglycitin displayed a 10-fold higher anti-α-glucosidase activity than acarbose, a standard clinical antidiabetic drug. The inhibition mode of 3′-hydroxyglycitin was noncompetitive, with a K_i value of 0.34 mM. These findings highlight the potential use of the new soy isoflavone 3′-hydroxyglycitin in biotechnology industries in the future.

Metabolic Engineering of Microorganisms for the Production of Flavonoids

Flavonoids are a class of secondary metabolites found in plant and fungus. They have been widely used in food, pharmaceutical, and nutraceutical industries owing to their significant biological activities, such as antiaging, antioxidant, anti-inflammatory, and anticancer. However, the traditional approaches for the production of flavonoids including chemical synthesis and plant extraction involved hazardous materials and complicated processes and also suffered from low product titer and yield. Microbial synthesis of flavonoids from renewable biomass such as glucose and xylose has been considered as a sustainable and environmentally friendly method for large-scale production of flavonoids. Recently, construction of microbial cell factories for efficient biosynthesis of flavonoids has gained much attention. In this article, we summarize the recent advances in microbial synthesis of flavonoids including flavanones, flavones, isoflavones, flavonols, flavanols, and anthocyanins. We put emphasis on developing pathway construction and optimization strategies to biosynthesize flavonoids and to improve their titer and yield. Then, we discuss the current challenges and future perspectives on successful strain development for large-scale production of flavonoids in an industrial level.

Recent advances in the microbial hydroxylation and reduction of soy isoflavones

Soy isoflavones are naturally occurring phytochemicals, which are biotransformed into functional derivatives through oxidative and reductive metabolic pathways of diverse microorganisms. Such representative derivatives, ortho-dihydroxyisoflavones (ODIs) and equols, have attracted great attention for their versatile health benefits since they were found from soybean fermented foods and human intestinal fluids. Recently, scientists in food technology, nutrition and microbiology began to understand their correct biosynthetic pathways and nutraceutical values, and have attempted to produce the valuable bioactive compounds using microbial fermentation and whole-cell/enzyme-based biotransformation. Furthermore, artificial design of microbial catalysts and/or protein engineering of oxidoreductases were also conducted to enhance production efficiency and regioselectivity of products. This minireview summarizes and introduces the past year's studies and recent advances in notable production of ODIs and equols, and provides information on available microbial species and their catalytic performance with perspectives on industrial application.

Production of New Isoflavone Glucosides from Glycosylation of 8-Hydroxydaidzein by Glycosyltransferase from Bacillus subtilis ATCC 6633

8-Hydroxydaidzein (8-OHDe) has been proven to possess some important bioactivities; however, the low aqueous solubility and stability of 8-OHDe limit its pharmaceutical and cosmeceutical applications. The present study focuses on glycosylation of 8-OHDe to improve its drawbacks in solubility and stability. According to the results of phylogenetic analysis with several identified flavonoid-catalyzing glycosyltransferases (GTs), three glycosyltransferase genes (BsGT110, BsGT292 and BsGT296) from the genome of the Bacillus subtilis ATCC 6633 strain were cloned and expressed in Escherichia coli. The three BsGTs were then purified and the glycosylation activity determined toward 8-OHDe. The results showed that only BsGT110 possesses glycosylation activity. The glycosylated metabolites were then isolated with preparative high-performance liquid chromatography and identified as two new isoflavone glucosides, 8-OHDe-7-O-β-glucoside and8-OHDe-8-O-β-glucoside, whose identity was confirmed by mass spectrometry and nuclear magnetic resonance spectroscopy. The aqueous solubility of 8-OHDe-7-O-β-glucoside and 8-OHDe-8-O-β-glucoside is 9.0- and 4.9-fold, respectively, higher than that of 8-OHDe. Moreover, more than 90% of the initial concentration of the two 8-OHDe glucoside derivatives remained after 96 h of incubation in 50 mM of Tris buffer at pH 8.0. In contrast, the concentration of 8-OHDe decreased to 0.8% of the initial concentration after 96 h of incubation. The two new isoflavone glucosides might have potential in pharmaceutical and cosmeceutical applications.

Recombinant production of eukaryotic cytochrome P450s in microbial cell factories

Cytochrome P450s (P450s) comprise one of the largest known protein families. They occur in every kingdom of life and catalyze essential reactions, such as carbon source assimilation, synthesis of hormones and secondary metabolites, or degradation of xenobiotics. Due to their outstanding ability of specifically hydroxylating complex hydrocarbons, there is a great demand to use these enzymes for biocatalysis, including applications at an industrial scale. Thus, the recombinant production of these enzymes is intensively investigated. However, especially eukaryotic P450s are difficult to produce. Challenges are faced due to complex cofactor requirements and the availability of a redox-partner (cytochrome P450 reductase, CPR) can be a key element to get active P450s. Additionally, most eukaryotic P450s are membrane bound which complicates the recombinant production. This review describes current strategies for expression of P450s in the microbial cell factories Escherichia coli, Saccharomyces cerevisiae, and Pichia pastoris.

Improving Free Radical Scavenging Activity of Soy Isoflavone Glycosides Daidzin and Genistin by 3'-Hydroxylation Using Recombinant Escherichia coli

The present study describes the biotransformation of a commercially available crude extract of soy isoflavones, which contained significant amounts of the soy isoflavone glycosides daidzin and genistin, by recombinant Escherichia coli expressing tyrosinase from Bacillus megaterium. Two major products were isolated from the biotransformation and identified as 3'-hydroxydaidzin and 3'-hydroxygenistin, respectively, based on their mass and nuclear magnetic resonance spectral data. The two 3'-hydroxyisoflavone glycosides showed potent 2,2-diphenyl-1-picrylhydrazyl free radical scavenging activity with IC50 values of 7.4 and 9.8 μM for 3'-hydroxydaidzin and 3'-hydroxygenistin, respectively. The free radical scavenging activities of the two 3'-hydroxyisoflavone glycosides were, respectively, 120 and 72 times higher than the activity of their precursors, daidzin and genistin, and were also stronger than the activity of ascorbic acid, which showed an IC50 value of 15.1 μM. This is the first report of the bio-production and potential antioxidant applications of both 3'-hydroxydaidzin and 3'-hydroxygenistin.

Production of Two Novel Methoxy-Isoflavones from Biotransformation of 8-Hydroxydaidzein by Recombinant Escherichia coli Expressing O-Methyltransferase SpOMT2884 from Streptomyces peucetius

Biotransformation of 8-hydroxydaidzein by recombinant Escherichia coli expressing O-methyltransferase (OMT) SpOMT2884 from Streptomyces peucetius was investigated. Two metabolites were isolated and identified as 7,4′-dihydroxy-8-methoxy-isoflavone (1) and 8,4′-dihydroxy-7-methoxy-isoflavone (2), based on mass, 1H-nuclear magnetic resonance (NMR) and 13C-NMR spectrophotometric analysis. The maximum production yields of compound (1) and (2) in a 5-L fermenter were 9.3 mg/L and 6.0 mg/L, respectively. The two methoxy-isoflavones showed dose-dependent inhibitory effects on melanogenesis in cultured B16 melanoma cells under non-toxic conditions. Among the effects, compound (1) decreased melanogenesis to 63.5% of the control at 25 μM. This is the first report on the 8-O-methylation activity of OMT toward isoflavones. In addition, the present study also first identified compound (1) with potent melanogenesis inhibitory activity.

Isolation, bioactivity, and production of ortho-hydroxydaidzein and ortho-hydroxygenistein

Daidzein and genistein are two major components of soy isoflavones. They exist abundantly in plants and possess multiple bioactivities. In contrast, ortho-hydroxydaidzein (OHD) and ortho-hydroxygenistein (OHG), including 6-hydroxydaidzein (6-OHD), 8-hydroxydaidzein (8-OHD), 3'-hydroxydaidzein (3'-OHD), 6-hydroxygenistein (6-OHG), 8-hydroxygenistein (8-OHG), and 3'-hydroxygenistein (3'-OHG), are rarely found in plants. Instead, they are usually isolated from fermented soybean foods or microbial fermentation broth feeding with soybean meal. Accordingly, the bioactivity of OHD and OHG has been investigated less compared to that of soy isoflavones. Recently, OHD and OHG were produced by genetically engineering microorganisms through gene cloning of cytochrome P450 (CYP) enzyme systems. This success opens up bioactivity investigation and industrial applications of OHD and OHG in the future. This article reviews isolation of OHD and OHG from non-synthetic sources and production of the compounds by genetically modified microorganisms. Several bioactivities, such as anticancer and antimelanogenesis-related activities, of OHD and OHG, are also discussed.