Optimizations to achieve high-level expression of cytochrome P450 proteins using Escherichia coli expression systems

Trial and error: New insights into recombinant expression of membrane-bound insect cytochromes P450 in Escherichia coli systems

Insect cytochromes P450 (CYP450s) are key enzymes responsible for a wide array of oxidative transformations of both endogenous and exogenous substrates. However, there is currently no a universal guideline established for heterologous expression of membrane-bound CYP450s, which hampers their downstream biochemical and structural studies. In this study, we conducted large-scale screening of protein overexpression in Escherichia coli using 71 insect CYP450 sequences and optimized the expression of a difficult-to-express CYP450 (CYP6HX3) using eight different optimizations, including selection of host strains and expression vectors, alternative of leader signal peptides, and N-terminal modifications. We confirmed that 1) Only insect CYP450s belonging to the CYP347 family could be expressed with N-terminal fusion of ompA2+ signal peptide in E. coli expression system. 2) E. coli Lemo 21 (DE3) effectively improved the expression of CYP6HX3 in the plasma membrane. 3) A brick-red appearance occurred frequently in the expressed thallus or membrane proteins, but this phenomenon could not necessarily indicate successful overexpression of target CYP450s. These findings provide new insights into the recombinant expression of insect CYP450s in E. coli systems and will facilitate the theoretical approaches for functional expression and production of eukaryotic CYP450s.

Overexpressing CYP81D11 enhances 2,4,6-trinitrotoluene tolerance and removal efficiency in Arabidopsis

Phytoremediation is a promising technology for removing the high-toxic explosive 2,4,6-trinitrotoluene (TNT) pollutant from the environment. Mining dominant genes is the key research direction of this technology. Most previous studies have focused on the detoxification of TNT rather than plants' TNT tolerance. Here, we conducted a transcriptomic analysis of wild type Arabidopsis plants under TNT stress and found that the Arabidopsis cytochrome P450 gene CYP81D11 was significantly induced in TNT-treated plants. Under TNT stress, the root length was approximately 1.4 times longer in CYP81D11-overexpressing transgenic plants than in wild type plants. The half-removal time for TNT was much shorter in CYP81D11-overexpressing transgenic plants (1.1 days) than in wild type plants (t1/2 = 2.2 day). In addition, metabolic analysis showed no difference in metabolites in transgenic plants compared to wild type plants. These results suggest that the high TNT uptake rates of CYP81D11-overexpressing transgenic plants were most likely due to increased tolerance and biomass rather than TNT degradation. However, CYP81D11-overexpressing plants were not more tolerant to osmotic stresses, such as salt or drought. Taken together, our results indicate that CYP81D11 is a promising target for producing bioengineered plants with high TNT removing capability.

Efficient stereoselective hydroxylation of deoxycholic acid by the robust whole-cell cytochrome P450 CYP107D1 biocatalyst

Deoxycholic acid (DCA) has been authorized by the Federal Drug Agency for cosmetic reduction of redundant submental fat. The hydroxylated product (6β-OH DCA) was developed to improve the solubility and pharmaceutic properties of DCA for further applications. Herein, a combinatorial catalytic strategy was applied to construct a powerful Cytochrome P450 biocatalyst (CYP107D1, OleP) to convert DCA to 6β-OH DCA. Firstly, the weak expression of OleP was significantly improved using pRSFDuet-1 plasmid in the E. coli C41 (DE3) strain. Next, the supply of heme was enhanced by the moderate overexpression of crucial genes in the heme biosynthetic pathway. In addition, a new biosensor was developed to select the appropriate redox partner. Furthermore, a cost-effective whole-cell catalytic system was constructed, resulting in the highest reported conversion rate of 6β-OH DCA (from 4.8% to 99.1%). The combinatorial catalytic strategies applied in this study provide an efficient method to synthesize high-value-added hydroxylated compounds by P450s.

Computational redesign of taxane-10β-hydroxylase for de novo biosynthesis of a key paclitaxel intermediate

Paclitaxel (Taxol®) is the most popular anticancer diterpenoid predominantly present in Taxus. The core skeleton of paclitaxel is highly modified, but researches on the cytochrome P450s involved in post-modification process remain exceedingly limited. Herein, the taxane-10β-hydroxylase (T10βH) from Taxus cuspidata, which is the third post-modification enzyme that catalyzes the conversion of taxadiene-5α-yl-acetate (T5OAc) to taxadiene-5α-yl-acetoxy-10β-ol (T10OH), was investigated in Escherichia coli by combining computation-assisted protein engineering and metabolic engineering. The variant of T10βH, M3 (I75F/L226K/S345V), exhibited a remarkable 9.5-fold increase in protein expression, accompanied by respective 1.3-fold and 2.1-fold improvements in turnover frequency (TOF) and total turnover number (TTN). Upon integration into the engineered strain, the variant M3 resulted in a substantial enhancement in T10OH production from 0.97 to 2.23 mg/L. Ultimately, the titer of T10OH reached 3.89 mg/L by fed-batch culture in a 5-L bioreactor, representing the highest level reported so far for the microbial de novo synthesis of this key paclitaxel intermediate. This study can serve as a valuable reference for further investigation of other P450s associated with the artificial biosynthesis of paclitaxel and other terpenoids. KEY POINTS: • The T10βH from T. cuspidata was expressed and engineered in E. coli unprecedentedly. • The expression and activity of T10βH were improved through protein engineering. • De novo biosynthesis of T10OH was achieved in E. coli with a titer of 3.89 mg/L.

Systematic engineering pinpoints a versatile strategy for the expression of functional cytochrome P450 enzymes in Escherichia coli cell factories

Production of plant secondary metabolites in engineered microorganisms provides a scalable and sustainable alternative to their sourcing from nature or through chemical synthesis. However, the biosynthesis of many valuable plant-derived products relies on cytochromes P450 - enzymes notoriously difficult to express in microbes. To improve their expression in Escherichia coli, an arsenal of engineering strategies was developed, often paired with an extensive screening of enzyme variants. Here, attempting to identify a broadly applicable strategy, we systematically evaluated six common cytochrome P450 N-terminal modifications and their effect on in vivo activity of enzymes from the CYP79 and CYP83 families. We found that transmembrane domain truncation was the only modification with a significantly positive effect for all seven tested enzymes, increasing their product titres by 2- to 170-fold. Furthermore, when comparing the changes in the protein titre and product generation, we show that higher protein expression does not directly translate to higher in vivo activity, thus making the protein titre an unreliable screening target in the context of cell factories. We propose the transmembrane domain truncation as a first-line approach that enables the expression of wide range of highly active P450 enzymes in E. coli and circumvents the time-consuming screening process. Our results challenge the notion that the engineering strategy must be tailored for each individual cytochrome P450 enzyme and have the potential to simplify and accelerate the future design of E. coli cell factories.

Concise synthesis of (R)-reticuline and (+)-salutaridine by combining early-stage organic synthesis and late-stage biocatalysis

Efficient access to the morphinan scaffold remains a major challenge in both synthetic chemistry and biotechnology. Here, a biomimetic chemo-enzymatic strategy to synthesize the natural promorphinan intermediate (+)-salutaridine is demonstrated. By combining early-stage organic synthesis with enzymatic asymmetric key step transformations, the prochiral natural intermediate 1,2-dehydroreticuline was prepared and subsequently stereoselectively reduced by the enzyme 1,2-dehydroreticuline reductase obtaining (R)-reticuline in high ee and yield (>99% ee, up to quant. conversion, 92% isol. yield). In the final step, membrane-bound salutaridine synthase was used to perform the selective ortho-para phenol coupling to give (+)-salutaridine. The synthetic route shows the potential of combining early-stage advanced organic chemistry to minimize protecting group techniques with late-stage multi-step biocatalysis to provide an unprecedented access to the medicinally important compound class of promorphinans.

β-Cryptoxanthin Production in Escherichia coli by Optimization of the Cytochrome P450 CYP97H1 Activity

Cytochromes P450, forming a superfamily of monooxygenases containing heme as a cofactor, show great versatility in substrate specificity. Metabolic engineering can take advantage of this feature to unlock novel metabolic pathways. However, the cytochromes P450 often show difficulty being expressed in a heterologous chassis. As a case study in the prokaryotic host Escherichia coli, the heterologous synthesis of β-cryptoxanthin was addressed. This carotenoid intermediate is difficult to produce, as its synthesis requires a monoterminal hydroxylation of β-carotene whereas most of the classic carotene hydroxylases are dihydroxylases. This study was focused on the optimization of the in vivo activity of CYP97H1, an original P450 β-carotene monohydroxylase. Engineering the N-terminal part of CYP97H1, identifying the matching redox partners, defining the optimal cellular background and adjusting the culture and induction conditions improved the production by 400 times compared to that of the initial strain, representing 2.7 mg/L β-cryptoxanthin and 20% of the total carotenoids produced.

Heterologous Expression of Recombinant Human Cytochrome P450 (CYP) in Escherichia coli: N-Terminal Modification, Expression, Isolation, Purification, and Reconstitution

Cytochrome P450 (CYP) enzymes play important roles in metabolising endogenous and xenobiotic substances. Characterisations of human CYP proteins have been advanced with the rapid development of molecular technology that allows heterologous expression of human CYPs. Among several hosts, bacteria systems such as Escherichia coli (E. coli) have been widely used thanks to their ease of use, high level of protein yields, and affordable maintenance costs. However, the levels of expression in E. coli reported in the literature sometimes differ significantly. This paper aims to review several contributing factors, including N-terminal modifications, co-expression with a chaperon, selections of vectors and E. coli strains, bacteria culture and protein expression conditions, bacteria membrane preparations, CYP protein solubilizations, CYP protein purifications, and reconstitution of CYP catalytic systems. The common factors that would most likely lead to high expression of CYPs were identified and summarised. Nevertheless, each factor may still require careful evaluation for individual CYP isoforms to achieve a maximal expression level and catalytic activity. Recombinant E. coli systems have been evidenced as a useful tool in obtaining the ideal level of human CYP proteins, which ultimately allows for subsequent characterisations of structures and functions.

Codon usage bias and genetic diversity in chloroplast genomes of Elaeagnus species (Myrtiflorae: Elaeagnaceae)

Codon usage bias (CUB) reveals the characteristics of species and can be utilized to understand their evolutionary relationship, increase the target genes' expression in the heterologous receptor plants, and further provide theoretic assistance for correlative study on molecular biology and genetic breeding. The chief aim of this work was to analyze the CUB in chloroplast (cp.) genes in nine Elaeagnus species to provide references for subsequent studies. The codons of Elaeagnus cp. genes preferred to end with A/T bases rather than with G/C bases. Most of the cp. genes were prone to mutation, while the rps7 genes were identical in sequences. Natural selection was inferred to have a powerful impact on the CUB in Elaeagnus cp. genomes, and their CUB was extremely strong. In addition, the optimal codons were identified in the nine cp. genomes based on the relative synonymous codon usage (RSCU) values, and the optimal codon numbers were between 15 and 19. The clustering analyses based on RSCU were contrasted with the maximum likelihood (ML)-based phylogenetic tree derived from coding sequences, suggesting that the t-distributed Stochastic Neighbor Embedding clustering method was more appropriate for evolutionary relationship analysis than the complete linkage method. Moreover, the ML-based phylogenetic tree based on the conservative matK genes and the whole cp. genomes had visible differences, indicating that the sequences of specific cp. genes were profoundly affected by their surroundings. Following the clustering analysis, Arabidopsis thaliana was considered the optimal heterologous expression receptor plant for the Elaeagnus cp. genes.

Supplementary Information

The online version contains supplementary material available at 10.1007/s12298-023-01289-6.

Dynamic feedback regulation for efficient membrane protein production using a small RNA-based genetic circuit in Escherichia coli

BACKGROUND

Membrane proteins (MPs) are an important class of molecules with a wide array of cellular functions and are part of many metabolic pathways. Despite their great potential-as therapeutic drug targets or in microbial cell factory optimization-many challenges remain for efficient and functional expression in a host such as Escherichia coli.

RESULTS

A dynamically regulated small RNA-based circuit was developed to counter membrane stress caused by overexpression of different MPs. The best performing small RNAs were able to enhance the maximum specific growth rate with 123%. On culture level, the total MP production was increased two-to three-fold compared to a system without dynamic control. This strategy not only improved cell growth and production of the studied MPs, it also suggested the potential use for countering metabolic burden in general.

CONCLUSIONS

A dynamically regulated feedback circuit was developed that can sense metabolic stress caused by, in casu, the overexpression of an MP and responds to it by balancing the metabolic state of the cell and more specifically by downregulating the expression of the MP of interest. This negative feedback mechanism was established by implementing and optimizing simple-to-use genetic control elements based on post-transcriptional regulation: small non-coding RNAs. In addition to membrane-related stress when the MP accumulated in the cytoplasm as aggregates, the sRNA-based feedback control system was still effective for improving cell growth but resulted in a decreased total protein production. This result suggests promiscuity of the MP sensor for more than solely membrane stress.

N-Dealkylation of Amines

N-dealkylation, the removal of an N-alkyl group from an amine, is an important chemical transformation which provides routes for the synthesis of a wide range of pharmaceuticals, agrochemicals, bulk and fine chemicals. N-dealkylation of amines is also an important in vivo metabolic pathway in the metabolism of xenobiotics. Identification and synthesis of drug metabolites such as N-dealkylated metabolites are necessary throughout all phases of drug development studies. In this review, different approaches for the N-dealkylation of amines including chemical, catalytic, electrochemical, photochemical and enzymatic methods will be discussed.

Systems Metabolic Engineering of Escherichia coli Coculture for De Novo Production of Genistein

Genistein is a plant-derived isoflavone possessing various bioactivities to prevent aging, carcinogenesis, and neurodegenerative and inflammation diseases. As a typical complex flavonoid, its microbial production from sugar remains to be completed. Here, we use systems metabolic engineering stategies to design and develop a three-strain commensalistic Escherichia coli coculture that for the first time realized the de novo production of genistein. First, we reconstituted the naringenin module by screening and incorporating chalcone isomerase-like protein, an auxiliary component to rectify the chalcone synthase promiscuity. Furthermore, we devised and constructed the genistein module by N-terminal modifications of plant P450 enzyme 2-hydroxyisoflavanone synthase and cytochrome P450 enzyme reductase. When naringenin-producing strain was cocultivated with p-coumaric acid-overproducing strain (a phenylalanine-auxotroph), two-strain coculture worked as commensalism through a unidirectional nutrient flow, which favored the efficient production of naringenin with a titer of 206.5 mg/L from glucose. A three-strain commensalistic coculture was subsequently engineered, which produced the highest titer to date of 60.8 mg/L genistein from a glucose and glycerol mixture. The commensalistic coculture is a flexible and versatile platform for the production of flavonoids, indicating a promising future for production of complex natural products in engineered E. coli.

Anthracycline derivatives inhibit cardiac CYP2J2

Anthracycline chemotherapeutics are highly effective, but their clinical usefulness is hampered by adverse side effects such as cardiotoxicity. Cytochrome P450 2J2 (CYP2J2) is a cytochrome P450 epoxygenase in human cardiomyocytes that converts arachidonic acid (AA) to cardioprotective epoxyeicosatrienoic acid (EET) regioisomers. Herein, we performed biochemical studies to understand the interaction of anthracycline derivatives (daunorubicin, doxorubicin, epirubicin, idarubicin, 5-iminodaunorubicin, zorubicin, valrubicin, and aclarubicin) with CYP2J2. We utilized fluorescence polarization (FP) to assess whether anthracyclines bind to CYP2J2. We found that aclarubicin bound the strongest to CYP2J2 despite it having large bulky groups. We determined that ebastine competitively inhibits anthracycline binding, suggesting that ebastine and anthracyclines may share the same binding site. Molecular dynamics and ensemble docking revealed electrostatic interactions between the anthracyclines and CYP2J2, contributing to binding stability. In particular, the glycosamine groups in anthracyclines are stabilized by binding to glutamate and aspartate residues in CYP2J2 forming salt bridge interactions. Furthermore, we used iterative ensemble docking schemes to gauge anthracycline influence on EET regioisomer production and anthracycline inhibition on AA metabolism. This was followed by experimental validation of CYP2J2-mediated metabolism of anthracycline derivatives using liquid chromatography tandem mass spectrometry fragmentation analysis and inhibition of CYP2J2-mediated AA metabolism by these derivatives. Taken together, we use both experimental and theoretical methodologies to unveil the interactions of anthracycline derivatives with CYP2J2. These studies will help identify alternative mechanisms of how anthracycline cardiotoxicity may be mediated through the inhibition of cardiac P450, which will aid in the design of new anthracycline derivatives with lower toxicity.

Alternative metabolic pathways and strategies to high-titre terpenoid production in Escherichia coli

Covering: up to 2021Terpenoids are a diverse group of chemicals used in a wide range of industries. Microbial terpenoid production has the potential to displace traditional manufacturing of these compounds with renewable processes, but further titre improvements are needed to reach cost competitiveness. This review discusses strategies to increase terpenoid titres in Escherichia coli with a focus on alternative metabolic pathways. Alternative pathways can lead to improved titres by providing higher orthogonality to native metabolism that redirects carbon flux, by avoiding toxic intermediates, by bypassing highly-regulated or bottleneck steps, or by being shorter and thus more efficient and easier to manipulate. The canonical 2-C-methyl-D-erythritol 4-phosphate (MEP) and mevalonate (MVA) pathways are engineered to increase titres, sometimes using homologs from different species to address bottlenecks. Further, alternative terpenoid pathways, including additional entry points into the MEP and MVA pathways, archaeal MVA pathways, and new artificial pathways provide new tools to increase titres. Prenyl diphosphate synthases elongate terpenoid chains, and alternative homologs create orthogonal pathways and increase product diversity. Alternative sources of terpenoid synthases and modifying enzymes can also be better suited for E. coli expression. Mining the growing number of bacterial genomes for new bacterial terpenoid synthases and modifying enzymes identifies enzymes that outperform eukaryotic ones and expand microbial terpenoid production diversity. Terpenoid removal from cells is also crucial in production, and so terpenoid recovery and approaches to handle end-product toxicity increase titres. Combined, these strategies are contributing to current efforts to increase microbial terpenoid production towards commercial feasibility.

Redox metabolism for improving whole-cell P450-catalysed terpenoid biosynthesis

The growing preference for producing cytochrome P450-mediated natural products in microbial systems stems from the challenging nature of the organic chemistry approaches. The P450 enzymes are redox-dependent proteins, through which they source electrons from reducing cofactors to drive their activities. Widely researched in biochemistry, most of the previous studies have extensively utilised expensive cell-free assays to reveal mechanistic insights into P450 functionalities in presence of commercial redox partners. However, in the context of microbial bioproduction, the synergic activity of P450- reductase proteins in microbial systems have not been largely investigated. This is mainly due to limited knowledge about their mutual interactions in the context of complex systems. Hence, manipulating the redox potential for natural product synthesis in microbial chassis has been limited. As the potential of redox state as crucial regulator of P450 biocatalysis has been greatly underestimated by the scientific community, in this review, we re-emphasize their pivotal role in modulating the in vivo P450 activity through affecting the product profile and yield. Particularly, we discuss the applications of widely used in vivo redox engineering methodologies for natural product synthesis to provide further suggestions for patterning on P450-based terpenoids production in microbial platforms.

Synthesis of (-)-deoxypodophyllotoxin and (-)-epipodophyllotoxin via a multi-enzyme cascade in E. coli

Background

The aryltetralin lignan (−)−podophyllotoxin is a potent antiviral and anti-neoplastic compound that is mainly found in Podophyllum plant species. Over the years, the commercial demand for this compound rose notably because of the high clinical importance of its semi-synthetic chemotherapeutic derivatives etoposide and teniposide. To satisfy this demand, (−)−podophyllotoxin is conventionally isolated from the roots and rhizomes of Sinopodophyllum hexandrum, which can only grow in few regions and is now endangered by overexploitation and environmental damage. For these reasons, targeting the biosynthesis of (−)−podophyllotoxin precursors or analogues is fundamental for the development of novel, more sustainable supply routes.

Results

We recently established a four-step multi-enzyme cascade to convert (+)−pinoresinol into (−)−matairesinol in E. coli. Herein, a five-step multi-enzyme biotransformation of (−)−matairesinol to (−)−deoxypodophyllotoxin was proven effective with 98 % yield at a concentration of 78 mg/L. Furthermore, the extension of this cascade to a sixth step leading to (−)−epipodophyllotoxin was evaluated. To this end, seven enzymes were combined in the reconstituted pathway involving inter alia three plant cytochrome P450 monooxygenases, with two of them being functionally expressed in E. coli for the first time.

Conclusions

Both, (−)−deoxypodophyllotoxin and (−)−epipodophyllotoxin, are direct precursors to etoposide and teniposide. Thus, the reconstitution of biosynthetic reactions of Sinopodophyllum hexandrum as an effective multi-enzyme cascade in E. coli represents a solid step forward towards a more sustainable production of these essential pharmaceuticals.

Supplementary Information

The online version contains supplementary material available at 10.1186/s12934-021-01673-5.

Case Study 1: Practical Considerations with Experimental Design and Interpretation

This chapter deals with practical considerations on key issues such as choosing an enzyme source, determining linear conditions, and choosing appropriate substrate and organic solvent concentrations. Practical solutions for working with limited resources and carrying out inhibition experiments are also addressed. Thus, after reading this chapter, the novice reader should have a better idea of how to design, develop, and interpret basic experiments using drug metabolism enzymes.

Characterization of a commercially available line of iPSC hepatocytes as models of hepatocyte function and toxicity for regulatory purposes

It has recently become possible to produce hepatocytes from human induced pluripotent stem cells (iPSC-heps), which may offer some advantages over primary human hepatocytes (Prim-heps) in the regulatory environment. The aim of this research was to assess similarities and differences between commercially available iPSC-heps and Prim-heps in preliminary assays of drug metabolism, hepatotoxicity, and drug transport. Hepatocytes were either cultured in collagen-coated 96-well plates (Prim-heps and 2d-iPSC-heps) or in ultra-low adhesion plates as spheroids (3d-iPSC-heps). 3d-iPSC-heps were used to enhance physiological cell-cell contacts, which is essential to maintain the phenotype of mature hepatocytes. Cytochrome P450 (CYP) 3A4, CYP1A2, and CYP2B6 activity levels were evaluated using fluorescent assays. Phase II metabolism was assessed by HPLC measurement of formation of glucuronides and sulfates of 4-methylumbelliferone, 1-naphthol, and estradiol. The toxicity of acetaminophen, amiodarone, aspirin, clozapine, tacrine, tamoxifen, and troglitazone was monitored using a luminescent cell viability assay. Canaliculi formation was monitored by following the fluorescence of 5,6-carboxy-2',7'-dichlorofluorescein diacetate. All culture models showed similar levels of basal CYP3A4, CYP1A2 and CYP2B6 activity. However, while Prim-heps showed a vigorous response to CYP inducing agents, 2d-iPSC-heps showed no response and 3d-iPSC-heps displayed an inconclusive response. 2d-iPSC-heps showed reduced, yet appreciable, glucuronide and sulfate formation compared to Prim-heps. All culture models showed similar activity in tests of hepatotoxicity, with Prim-heps generally being more sensitive. All models formed canaliculi capable of transporting carboxy-2',7'-dichlorofluorescein. The iPSC-heps appear to be useful for toxicity and transport studies, but metabolic activity is not optimum, and metabolism studies would benefit from a more mature model.

Progress in heterologous biosynthesis of forskolin

Forskolin, a class of labdane-type diterpenoid, has significant medicinal value in anticancer, antiasthmatic, antihypertensive, and heart-strengthening treatments. The main source of natural forskolin is its extraction from the cork tissue of the root of Coleus forskohlii. However, conventional modes of extraction pose several challenges. In recent years, the construction of microbial cell factories to produce medicinal natural products via synthetic biological methods has effectively solved the current problems and is a research hotspot in this field. This review summarizes the recent progress in the heterologous synthesis of forskolin via synthetic biological technology, analyzes the current challenges, and proposes corresponding strategies.

Heterologous expression of insect P450 enzymes that metabolize xenobiotics

Insect cytochrome P450-monooxygenases (P450s) are an enzyme superfamily involved in the oxidative transformation of endogenous and exogenous substrates, including insecticides. They were also shown to determine insecticide selectivity in beneficial arthropods such as bee pollinators, and to detoxify plant secondary metabolites. The recent explosion in numbers of P450s due to increased invertebrate genomes sequenced, allowed researchers to study their functional relevance for xenobiotic metabolism by recombinant expression using different expression systems. Troubleshooting strategies, including different systems and protein modifications typically adapted from mammalian P450s, have been applied to improve the functional expression, with partial success. The aim of this mini review is to critically summarize different strategies recently developed and used to produce recombinant insect P450s for xenobiotic metabolism studies.

Assembly of Plant Enzymes in E. coli for the Production of the Valuable (-)-Podophyllotoxin Precursor (-)-Pluviatolide

Lignans are plant secondary metabolites with a wide range of reported health-promoting bioactivities. Traditional routes toward these natural products involve, among others, the extraction from plant sources and chemical synthesis. However, the availability of the sources and the complex chemical structures of lignans often limit the feasibility of these approaches. In this work, we introduce a newly assembled biosynthetic route in E. coli for the efficient conversion of the common higher-lignan precursor (+)-pinoresinol to the noncommercially available (-)-pluviatolide via three intermediates. (-)-Pluviatolide is considered a crossroad compound in lignan biosynthesis, because the methylenedioxy bridge in its structure, resulting from the oxidation of (-)-matairesinol, channels the biosynthetic pathway toward the microtubule depolymerizer (-)-podophyllotoxin. This oxidation reaction is catalyzed with high regio- and enantioselectivity by a cytochrome P450 monooxygenase from Sinopodophyllum hexandrum (CYP719A23), which was expressed and optimized regarding redox partners in E. coli. Pinoresinol-lariciresinol reductase from Forsythia intermedia (FiPLR), secoisolariciresinol dehydrogenase from Podophyllum pleianthum (PpSDH), and CYP719A23 were coexpressed together with a suitable NADPH-dependent reductase to ensure P450 activity, allowing for four sequential biotransformations without intermediate isolation. By using an E. coli strain coexpressing the enzymes originating from four plants, (+)-pinoresinol was efficiently converted, allowing the isolation of enantiopure (-)-pluviatolide at a concentration of 137 mg/L (ee ≥99% with 76% isolated yield).

CYP2J2 Molecular Recognition: A New Axis for Therapeutic Design

Cytochrome P450 (CYP) epoxygenases are a special subset of heme-containing CYP enzymes capable of performing the epoxidation of polyunsaturated fatty acids (PUFA) and the metabolism of xenobiotics. This dual functionality positions epoxygenases along a metabolic crossroad. Therefore, structure-function studies are critical for understanding their role in bioactive oxy-lipid synthesis, drug-PUFA interactions, and for designing therapeutics that directly target the epoxygenases. To better exploit CYP epoxygenases as therapeutic targets, there is a need for improved understanding of epoxygenase structure-function. Of the characterized epoxygenases, human CYP2J2 stands out as a potential target because of its role in cardiovascular physiology. In this review, the early research on the discovery and activity of epoxygenases is contextualized to more recent advances in CYP epoxygenase enzymology with respect to PUFA and drug metabolism. Additionally, this review employs CYP2J2 epoxygenase as a model system to highlight both the seminal works and recent advances in epoxygenase enzymology. Herein we cover CYP2J2's interactions with PUFAs and xenobiotics, its tissue-specific physiological roles in diseased states, and its structural features that enable epoxygenase function. Additionally, the enumeration of research on CYP2J2 identifies the future needs for the molecular characterization of CYP2J2 to enable a new axis of therapeutic design.

Discovery and modification of cytochrome P450 for plant natural products biosynthesis

Cytochrome P450s are widespread in nature and play key roles in the diversification and functional modification of plant natural products. Over the last few years, there has been remarkable progress in plant P450s identification with the rapid development of sequencing technology, "omics" analysis and synthetic biology. However, challenges still persist in respect of crystal structure, heterologous expression and enzyme engineering. Here, we reviewed several research hotspots of P450 enzymes involved in the biosynthesis of plant natural products, including P450 databases, gene mining, heterologous expression and protein engineering.

Functional characterization of cytochrome P450 CYP81A subfamily to disclose the pattern of cross-resistance in Echinochloa phyllopogon

CYP81A P450s armor Echinochloa phyllopogon against diverse and several herbicide chemistries. CYP81A substrate preferences can be a basis for cross-resistance prediction and management in E. phyllopogon and other related species. Metabolism-based herbicide resistance is a major threat to agriculture, as it is unpredictable and could extend resistance to different chemical groups and modes of action, encompassing existing, novel and to-be-discovered herbicides. Limited information on the enzymes involved in herbicide metabolism has hindered the prediction of cross-resistance in weeds. Members of CYP81A subfamily in multiple herbicide resistant (MHR) Echinochloa phyllopogon were previously identified for conferring cross-resistance to six unrelated herbicide classes. This suggests a critical role of CYP81As in endowing unpredictable cross-resistances in E. phyllopogon, thus the functions of all its nine putative functional CYP81A genes to 33 herbicides from 24 chemical groups were characterized. Ectopic expression in Arabidopsis thaliana identified the CYP81As that can confer resistance to multiple and diverse herbicides. The CYP81As were further characterized for their enzymatic functions in Escherichia coli. CYP81A expression in E. coli was optimized via modification of the N-terminus, co-expression with HemA gene and culture at optimal temperature. CYP81As metabolized its herbicide substrates into hydroxylated, N-/O-demethylated or both products. The cross-resistance pattern conferred by CYP81As is geared towards all chemical groups of acetolactate synthase inhibitors and is expanded to herbicides inhibiting photosystem II, phytoene desaturase, protoporphyrinogen oxidase, 4-hydroxyphenylpyruvate dioxygenase, and 1-deoxy-D-xylulose 5-phosphate synthase. Cross-resistance to herbicides pyrimisulfan, propyrisulfuron, and mesotrione was predicted and confirmed in MHR E. phyllopogon. This study demonstrated that the functional characterization of the key enzymes for herbicide metabolism could disclose the cross-resistance pattern and identify appropriate chemical options to manage the existing and unexpected cross-resistances in E. phyllopogon.

Biochemical and structural insights into the cytochrome P450 reductase from Candida tropicalis

Cytochrome P450 reductases (CPRs) are diflavin oxidoreductases that supply electrons to type II cytochrome P450 monooxygenases (CYPs). In addition, it can also reduce other proteins and molecules, including cytochrome c, ferricyanide, and different drugs. Although various CPRs have been functionally and structurally characterized, the overall mechanism and its interaction with different redox acceptors remain elusive. One of the main problems regarding electron transfer between CPRs and CYPs is the so-called “uncoupling”, whereby NAD(P)H derived electrons are lost due to the reduced intermediates’ (FAD and FMN of CPR) interaction with molecular oxygen. Additionally, the decay of the iron-oxygen complex of the CYP can also contribute to loss of reducing equivalents during an unproductive reaction cycle. This phenomenon generates reactive oxygen species (ROS), leading to an inefficient reaction. Here, we present the study of the CPR from Candida tropicalis (CtCPR) lacking the hydrophobic N-terminal part (Δ2–22). The enzyme supports the reduction of cytochrome c and ferricyanide, with an estimated 30% uncoupling during the reactions with cytochrome c. The ROS produced was not influenced by different physicochemical conditions (ionic strength, pH, temperature). The X-ray structures of the enzyme were solved with and without its cofactor, NADPH. Both CtCPR structures exhibited the closed conformation. Comparison with the different solved structures revealed an intricate ionic network responsible for the regulation of the open/closed movement of CtCPR.

Biochemical and structural insights into the cytochrome P450 reductase from Candida tropicalis

Cytochrome P450 reductases (CPRs) are diflavin oxidoreductases that supply electrons to type II cytochrome P450 monooxygenases (CYPs). In addition, it can also reduce other proteins and molecules, including cytochrome c, ferricyanide, and different drugs. Although various CPRs have been functionally and structurally characterized, the overall mechanism and its interaction with different redox acceptors remain elusive. One of the main problems regarding electron transfer between CPRs and CYPs is the so-called "uncoupling", whereby NAD(P)H derived electrons are lost due to the reduced intermediates' (FAD and FMN of CPR) interaction with molecular oxygen. Additionally, the decay of the iron-oxygen complex of the CYP can also contribute to loss of reducing equivalents during an unproductive reaction cycle. This phenomenon generates reactive oxygen species (ROS), leading to an inefficient reaction. Here, we present the study of the CPR from Candida tropicalis (CtCPR) lacking the hydrophobic N-terminal part (Δ2-22). The enzyme supports the reduction of cytochrome c and ferricyanide, with an estimated 30% uncoupling during the reactions with cytochrome c. The ROS produced was not influenced by different physicochemical conditions (ionic strength, pH, temperature). The X-ray structures of the enzyme were solved with and without its cofactor, NADPH. Both CtCPR structures exhibited the closed conformation. Comparison with the different solved structures revealed an intricate ionic network responsible for the regulation of the open/closed movement of CtCPR.

Polymorphisms of CYP2C8 Alter First-Electron Transfer Kinetics and Increase Catalytic Uncoupling

Cytochrome P450 2C8 (CYP2C8) epoxygenase is responsible for the metabolism of over 60 clinically relevant drugs, notably the anticancer drug Taxol (paclitaxel, PAC). Specifically, there are naturally occurring polymorphisms, CYP2C8*2 and CYP2C8*3, that display altered PAC hydroxylation rates despite these mutations not being located in the active site. Herein, we demonstrate that these polymorphisms result in a greater uncoupling of PAC metabolism by increasing the amount of hydrogen peroxide formed per PAC turnover. Anaerobic stopped-flow measurements determined that these polymorphisms have altered first electron transfer kinetics, compared to CYP2C8*1 (wildtype), that suggest electron transfer from cytochrome P450 reductase (CPR) is disfavored. Therefore, these data demonstrate that these polymorphisms affect the catalytic cycle of CYP2C8 and suggest that redox interactions with CPR are disrupted.

Lipid composition and macromolecular crowding effects on CYP2J2-mediated drug metabolism in nanodiscs

Lipid composition and macromolecular crowding are key external effectors of protein activity and stability whose role varies between different proteins. Therefore, it is imperative to study their effects on individual protein function. CYP2J2 is a membrane-bound cytochrome P450 in the heart involved in the metabolism of fatty acids and xenobiotics. In order to facilitate this metabolism, cytochrome P450 reductase (CPR), transfers electrons to CYP2J2 from NADPH. Herein, we use nanodiscs to show that lipid composition of the membrane bilayer affects substrate metabolism of the CYP2J2-CPR nanodisc (ND) system. Differential effects on both NADPH oxidation and substrate metabolism by CYP2J2-CPR are dependent on the lipid composition. For instance, sphingomyelin containing nanodiscs produced more secondary substrate metabolites than discs of other lipid compositions, implying a possible conformational change leading to processive metabolism. Furthermore, we demonstrate that macromolecular crowding plays a role in the lipid-solubilized CYP2J2-CPR system by increasing the K_m and decreasing the V_max , and effect that is size-dependent. Crowding also affects the CYP2J2-CPR-ND system by decreasing both the K_m and V_max for Dextran-based macromolecular crowding agents, implying an increase in substrate affinity but a lack of metabolism. Finally, protein denaturation studies show that crowding agents destabilize CYP2J2, while the multidomain protein CPR is stabilized. Overall, these studies are the first report on the role of the surrounding lipid environment and macromolecular crowding in modulating enzymatic function of CYP2J2-CPR membrane protein system.

Bacterial Expression of Membrane-Associated Cytochrome P450s and Their Activity Assay in Nanodiscs

Eukaryotic membrane bound cytochrome P450s are expressed in bacterial systems to produce large yields of catalytically active protein for structure function studies. Recently, there have been several instances of expressing eukaryotic membrane bound CYPs in bacteria after making various modifications to both the N-terminus membrane binding domains of the protein and to noncontiguous F-G membrane binding loop that is also implicated in substrate binding. These modifications have been shown not to disturb the function of the protein of interest. The major factors that have been key to express the membrane bound cytochrome P450s in bacteria have been the following: (a) exon optimization (b) selection of the appropriate vector and host strain, and (c) growth and expression conditions with respect to temperature and speed of shaking the media flask. Herein, we describe methods to express and purify eukaryotic membrane bound cytochrome P450s. We also describe the measurement of the activity of the cytochrome P450 expressed by taking the example of cytochrome P450 2J2, the primary P450 expressed in the human heart and CYP725A4, the primary cytochrome P450 expressed in the first step of taxol synthesis. Additionally, we discuss the pros and cons of the different modifications done in order to express the membrane bound cytochrome P450s.

Cytochrome P450 Monooxygenases in Biotechnology and Synthetic Biology

Cytochromes P450 (P450 or CYP) are heme-containing enzymes that catalyze the introduction of one atom of molecular oxygen into nonactivated C-H bonds, often in a regio- and stereoselective manner. This ability, combined with a tremendous number of accepted substrates, makes P450s powerful biocatalysts. Sixty years after their discovery, P450 systems are recognized as essential bio-bricks in synthetic biology approaches to enable production of high-value complex molecules in recombinant hosts. Recent impressive results in protein engineering led to P450s with tailored properties that are even able to catalyze abiotic reactions. The introduction of P450s in artificial multi-enzymatic cascades reactions and chemo-enzymatic processes offers exciting future perspectives to access novel compounds that cannot be synthesized by nature or by chemical routes.

Endocannabinoid Virodhamine Is an Endogenous Inhibitor of Human Cardiovascular CYP2J2 Epoxygenase

The human body contains endogenous cannabinoids (endocannabinoids) that elicit effects similar to those of Δ9-tetrahydrocanabinol, the principal bioactive component of cannabis. The endocannabinoid virodhamine (O-AEA) is the constitutional isomer of the well-characterized cardioprotective and anti-inflammatory endocannabinoid anandamide (AEA). The chemical structures of O-AEA and AEA contain arachidonic acid (AA) and ethanolamine; however, AA in O-AEA is connected to ethanolamine via an ester linkage, whereas AA in AEA is connected through an amide linkage. O-AEA is involved in regulating blood pressure and cardiovascular function. We show that O-AEA is found at levels 9.6-fold higher than that of AEA in porcine left ventricle. On a separate note, the cytochrome P450 (CYP) epoxygenase CYP2J2 is the most abundant CYP in the heart where it catalyzes the metabolism of AA and AA-derived eCBs to bioactive epoxides that are involved in diverse cardiovascular functions. Herein, using competitive binding studies, kinetic metabolism measurements, molecular dynamics, and wound healing assays, we have shown that O-AEA is an endogenous inhibitor of CYP2J2 epoxygenase. As a result, the role of O-AEA as an endogenous eCB inhibitor of CYP2J2 may provide a new mode of regulation to control the activity of cardiovascular CYP2J2 in vivo and suggests a potential cross-talk between the cardiovascular endocannabinoids and the cytochrome P450 system.

Coexpression of 5-Aminolevulinic Acid Synthase Gene Facilitates Heterologous Production of Thermostable Cytochrome P450, CYP119, in Holo Form in Escherichia coli

Cytochrome P450 enzymes are heme-containing monooxygenases that exhibit potential as biocatalysts for practical applications. The Escherichia coli expression system is frequently used for biocatalyst production; however, heterologous production of hemeproteins in their holo form is difficult due to insufficient heme synthesis by the host. In this study, 5-aminolevulinic acid synthase (ALAS) from Rhodobacter capsulatus is used to accelerate intracellular heme biosynthesis in E. coli; this demonstrates that coexpression of the ALAS gene (ALAS) improves the heterologous production of cytochrome P450, CYP119, from Sulfolobus acidocaldarius. Coexpression of ALAS increased the amount of heterologous CYP119 isolated and the ratio of its holo form. The ratio of holo-CYP119 resulting from the coexpression of ALAS in E. coli was 99 %, whereas that from cells expressing CYP119 exclusively was 66 %. Coexpression of ALAS is a promising alternative for the efficient heterologous production of hemeproteins by using E. coli.

Characterization of Cytochrome P450 Enzymes and Their Applications in Synthetic Biology

The cytochrome P450 monooxygenase enzymes (P450s) catalyze a diverse array of chemical transformations, most originating from the insertion of an oxygen atom into a substrate that binds close to the P450 heme. The oxygen is delivered by a highly reactive heme iron-oxo species (compound I) and, according to the chemical nature of the substrate and its position in the active site, the P450 can catalyze a wide range of reactions including, e.g., hydroxylation, reduction, decarboxylation, sulfoxidation, N- and O-demethylation, epoxidation, deamination, CC bond formation and breakage, nitration, and dehalogenation. In this chapter, we describe the structural, biochemical, and catalytic properties of the P450s, along with spectroscopic and analytical methods used to characterize P450 enzymes and their redox partners. Important uses of P450 enzymes are highlighted, including how various P450s have been exploited for applications in synthetic biology.

Rational engineering of photosynthetic electron flux enhances light-powered cytochrome P450 activity

In this study, we exploited a modified photosynthetic electron transfer chain (PET) in the model cyanobacterium Synechococcus PCC 7002, where electrons derived from water-splitting are used to power reactions catalyzed by a heterologous cytochrome P450 (CYP1A1). A simple in vivo fluorescent assay for CYP1A1 activity was employed to determine the impact of rationally engineering of photosynthetic electron flow. This showed that knocking out a subunit of the type I NADH dehydrogenase complex (NDH-1), suggested to be involved in cyclic photosynthetic electron flow (ΔndhD2), can double the activity of CYP1A1, with a concomitant increase in the flux of electrons from photosynthesis. This also resulted in an increase in cellular adenosine triphosphate (ATP) and the ATP/nicotinamide adenine dinucleotide phosphate (NADPH) ratio, suggesting that expression of a heterologous electron sink in photosynthetic organisms can be used to modify the bioenergetic landscape of the cell. We therefore demonstrate that CYP1A1 is limited by electron supply and that photosynthesis can be re-engineered to increase heterologous P450 activity for the production of high-value bioproducts. The increase in cellular ATP achieved could be harnessed to support metabolically demanding heterologous processes. Furthermore, this experimental system could provide valuable insights into the mechanisms of photosynthesis.

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.

Reconstructing Biosynthetic Pathway of the Plant-Derived Cancer Chemopreventive-Precursor Glucoraphanin in Escherichia coli

Epidemiological data confirmed a strong correlation between regular consumption of cruciferous vegetables and lower cancer risk. This cancer preventive property is mainly attributed to the glucosinolate products, such as glucoraphanin found in broccoli that is derived from methionine. Here we report the first successful reconstruction of the complete biosynthetic pathway of glucoraphanin from methionine in Escherichia coli via gene selection, pathway design, and protein engineering. We used branched-chain amino transferase 3 to catalyze two transamination steps to ensure the purity of precursor molecules and used cysteine as a sulfur donor to simplify the synthesis pathway. Two chimeric cytochrome P450 enzymes were engineered and expressed in E. coli functionally. The original plant C-S lyase was replaced by the Neurospora crassa hercynylcysteine sulfoxide lyase. Other pathway enzymes were successfully mined from Arabidopsis thaliana, Brassica rapa, and Brassica oleracea. Biosynthesis of glucoraphanin upon coexpression of the optimized enzymes in vivo was confirmed by liquid chromatography-tandem mass spectrometry analysis. No other glucosinolate analogues (except for glucoiberin) were identified that could facilitate the downstream purification processes. Production of glucoraphanin in this study laid the foundation for microbial production of such health-beneficial glucosinolates in a large-scale.

Insights into the functional properties of the marneral oxidase CYP71A16 from Arabidopsis thaliana

The Arabidopsis thaliana gene encoding CYP71A16 is part of the gene cluster for the biosynthesis and modification of the triterpenoid marneral. Previous investigations of A. thaliana have revealed that CYP71A16 catalyzes marneral oxidation, while it also can accept marnerol as substrate. The aim of the present study was to investigate functional properties of CYP71A16 in vitro. For this purpose, heterologous expression of a N-terminally modified version of CYP71A16 was established in Escherichia coli, which yielded up to 50mgL^-1 recombinant enzyme. The enzyme was purified and activity was reconstituted in vitro with different redox partners. A heterologous bacterial redox partner system consisting of the flavodoxin YkuN from Bacillus subtilis and the flavodoxin reductase Fpr from E. coli clearly outperformed the cytochrome P450 reductase ATR2 from A. thaliana in supporting the CYP71A16-mediated hydroxylation of marnerol. Substrate binding experiments with CYP71A16 revealed a dissociation constant K_D of 225μM for marnerol. CYP71A16 catalyzed the hydroxylation of marnerol to 23-hydroxymarnerol with a K_M of 142μM and a k_cat of 3.9min^-1. Furthermore, GC/MS analysis revealed an as of yet unidentified overoxidation product of this in vitro reaction. This article is part of a Special Issue entitled: Cytochrome P450 biodiversity and biotechnology, edited by Erika Plettner, Gianfranco Gilardi, Luet Wong, Vlada Urlacher, Jared Goldstone.

Cell foundry with high product specificity and catalytic activity for 21-deoxycortisol biotransformation

Background

21-deoxycortisol (21-DF) is the key intermediate to manufacture pharmaceutical glucocorticoids. Recently, a Japan patent has realized 21-DF production via biotransformation of 17-hydroxyprogesterone (17-OHP) by purified steroid 11β-hydroxylase CYP11B1. Due to the less costs on enzyme isolation, purification and stabilization as well as cofactors supply, whole-cell should be preferentially employed as the biocatalyst over purified enzymes. No reports as so far have demonstrated a whole-cell system to produce 21-DF. Therefore, this study aimed to establish a whole-cell biocatalyst to achieve 21-DF transformation with high catalytic activity and product specificity.

Results

In this study, Escherichia coli MG1655(DE3), which exhibited the highest substrate transportation rate among other tested chassises, was employed as the host cell to construct our biocatalyst by co-expressing heterologous CYP11B1 together with bovine adrenodoxin and adrenodoxin reductase. Through screening CYP11B1s (with mutagenesis at N-terminus) from nine sources, Homo sapiens CYP11B1 mutant (G25R/G46R/L52 M) achieved the highest 21-DF transformation rate at 10.6 mg/L/h. Furthermore, an optimal substrate concentration of 2.4 g/L and a corresponding transformation rate of 16.2 mg/L/h were obtained by screening substrate concentrations. To be noted, based on structural analysis of the enzyme-substrate complex, two types of site-directed mutations were designed to adjust the relative position between the catalytic active site heme and the substrate. Accordingly, 1.96-fold enhancement on 21-DF transformation rate (to 47.9 mg/L/h) and 2.78-fold improvement on product/by-product ratio (from 0.36 to 1.36) were achieved by the combined mutagenesis of F381A/L382S/I488L. Eventually, after 38-h biotransformation in shake-flask, the production of 21-DF reached to 1.42 g/L with a yield of 52.7%, which is the highest 21-DF production as known.

Conclusions

Heterologous CYP11B1 was manipulated to construct E. coli biocatalyst converting 17-OHP to 21-DF. Through the strategies in terms of (1) screening enzymes (with N-terminal mutagenesis) sources, (2) optimizing substrate concentration, and most importantly (3) rational design novel mutants aided by structural analysis, the 21-DF transformation rate was stepwise improved by 19.5-fold along with 4.67-fold increase on the product/byproduct ratio. Eventually, the highest 21-DF reported production was achieved in shake-flask after 38-h biotransformation. This study highlighted above described methods to obtain a high efficient and specific biocatalyst for the desired biotransformation.

Electronic supplementary material

The online version of this article (doi:10.1186/s12934-017-0720-y) contains supplementary material, which is available to authorized users.

Ligand characterization of CYP4B1 isoforms modified for high-level expression in Escherichia coli and HepG2 cells

Human CYP4B1, a cytochrome P450 monooxygenase predominantly expressed in the lung, inefficiently metabolizes classical CYP4B1 substrates, such as the naturally occurring furan pro-toxin 4-ipomeanol (4-IPO). Highly active animal forms of the enzyme convert 4-IPO to reactive alkylating metabolite(s) that bind(s) to cellular macromolecules. By substitution of 13 amino acids, we restored the enzymatic activity of human CYP4B1 toward 4-IPO and this modified cDNA is potentially valuable as a suicide gene for adoptive T-cell therapies. In order to find novel pro-toxins, we tested numerous furan analogs in in vitro cell culture cytotoxicity assays by expressing the wild-type rabbit and variants of human CYP4B1 in human liver-derived HepG2 cells. To evaluate the CYP4B1 substrate specificities and furan analog catalysis, we optimized the N-terminal sequence of the CYP4B1 variants by modification/truncation and established their heterologous expression in Escherichia coli (yielding 70 and 800 nmol·l-1 of recombinant human and rabbit enzyme, respectively). Finally, spectral binding affinities and oxidative metabolism of the furan analogs by the purified recombinant CYP4B1 variants were analyzed: the naturally occurring perilla ketone was found to be the tightest binder to CYP4B1, but also the analog that was most extensively metabolized by oxidative processes to numerous non-reactive reaction products.

Heterologous expression and characterization of plant Taxadiene-5α-Hydroxylase (CYP725A4) in Escherichia coli

Taxadiene-5α-Hydroxylase (CYP725A4) is a membrane-bound plant cytochrome P450 that catalyzes the oxidation of taxadiene to taxadiene-5α-ol. This oxidation is a key step in the production of the valuable cancer therapeutic and natural plant product, taxol. In this work, we report the bacterial expression and purification of six different constructs of CYP725A4. All six of these constructs are N-terminally modified and three of them are fused to cytochrome P450 reductase to form a chimera construct. The construct with the highest yield of CYP725A4 protein was then selected for substrate binding and kinetic analysis. Taxadiene binding followed type-1 substrate patterns with an observed K_D of 2.1 ± 0.4 μM. CYP725A4 was further incorporated into nanoscale lipid bilayers (nanodiscs) and taxadiene metabolism was measured. Taxadiene metabolism followed Michaelis-Menten kinetics with an observed V_max of 30 ± 8 pmol/min/nmol_CYP725A4 and a K_M of 123 ± 52 μM. Additionally, molecular operating environment (MOE) modeling was performed in order to gain insight into the interactions of taxadiene with CYP725A4 active site. Taken together, we demonstrate the successful expression and purification of the functional membrane-bound plant CYP, CYP725A4, in E. coli.

Tapping the Unused Potential of Photosynthesis with a Heterologous Electron Sink

Increasing the efficiency of the conversion of light energy to products by photosynthesis represents a grand challenge in biotechnology. Photosynthesis is limited by the carbon-fixing enzyme Rubisco resulting in much of the absorbed energy being wasted as heat or fluorescence or lost as excess reductant via alternative electron dissipation pathways. To harness this wasted reductant, we engineered the model cyanobacterium Synechococcus PCC 7002 to express the mammalian cytochrome P450 CYP1A1 to serve as an artificial electron sink for excess electrons derived from light-catalyzed water-splitting. This improved photosynthetic efficiency by increasing the maximum rate of photosynthetic electron flow by 31.3%. A simple fluorescent assay for CYP1A1 activity demonstrated that the P450 was functional in the absence of its native reductase, that activity was light-dependent and scaled with irradiance. We show for the first time in live cells that photosynthetic reductant can be redirected to power a heterologous cytochrome P450. Furthermore, Synechococcus PCC 7002 expressing CYP1A1 degraded the herbicide atrazine, which is a widespread environmental pollutant.

Lactococcus lactis is an Efficient Expression System for Mammalian Membrane Proteins Involved in Liver Detoxification, CYP3A4, and MGST1

Despite the great importance of human membrane proteins involved in detoxification mechanisms, their wide use for biochemical approaches is still hampered by several technical difficulties considering eukaryotic protein expression in order to obtain the large amounts of protein required for functional and/or structural studies. Lactococcus lactis has emerged recently as an alternative heterologous expression system to Escherichia coli for proteins that are difficult to express. The aim of this work was to check its ability to express mammalian membrane proteins involved in liver detoxification, i.e., CYP3A4 and two isoforms of MGST1 (rat and human). Genes were cloned using two different strategies, i.e., classical or Gateway-compatible cloning, and we checked the possible influence of two affinity tags (6×-His-tag and Strep-tag II). Interestingly, all proteins could be successfully expressed in L. lactis at higher yields than those previously obtained for these proteins with classical expression systems (E. coli, Saccharomyces cerevisiae) or those of other eukaryotic membrane proteins expressed in L. lactis. In addition, rMGST1 was fairly active after expression in L. lactis. This study highlights L. lactis as an attractive system for efficient expression of mammalian detoxification membrane proteins at levels compatible with further functional and structural studies.

Asymmetric Binding and Metabolism of Polyunsaturated Fatty Acids (PUFAs) by CYP2J2 Epoxygenase

Cytochrome P450 (CYP) 2J2 is the primary epoxygenase in the heart and is responsible for the epoxidation of arachidonic acid (AA), an ω-6 polyunsaturated fatty acid (PUFA), into anti-inflammatory epoxide metabolites. It also epoxidizes other PUFAs such as docosahexaenoic acid (DHA), linoleic acid (LA), and eicosapentaenoic acid (EPA). Herein, we have performed detailed thermodynamic and kinetic analyses to determine how DHA, LA, and EPA modulate the metabolism of AA by CYP2J2. We use the Nanodisc system to stabilize CYP2J2 and its redox partner, CYP reductase (CPR). We observe that DHA strongly inhibits CYP2J2-mediated AA metabolism, LA only moderately inhibits AA metabolism, and EPA exhibits insignificant inhibition. We also characterized the binding of these molecules using ebastine competitive binding assays and show that DHA binds significantly tighter to CYP2J2 than AA, EPA, or LA. Furthermore, we utilize a combined approach of molecular dynamics (MD) simulations and docking to predict key residues mediating the tight binding of DHA. We show that although all the tested fatty acids form similar contacts to the active site residues, the affinity of DHA for CYP2J2 is tighter because of the interaction of DHA with residues Arg-321, Thr-318, and Ser-493. To demonstrate the importance of these residues in binding, we mutated these residues to make two mutant variants, CYP2J2-T318A and CYP2J2-T318V/S493A. Both mutant variants showed weaker binding than the wild type (WT) to DHA and AA; DHA inhibition of AA was also mitigated in the mutants compared to the WT. Therefore, using a combined experimental and MD simulation approach, we establish that CYP2J2 inhibition of AA metabolism by DHA, EPA, and LA is asymmetric because of tighter binding of DHA to select residues in the active site.

Versatile biocatalysis of fungal cytochrome P450 monooxygenases

Cytochrome P450 (CYP) monooxygenases, the nature’s most versatile biological catalysts have unique ability to catalyse regio-, chemo-, and stereospecific oxidation of a wide range of substrates under mild reaction conditions, thereby addressing a significant challenge in chemocatalysis. Though CYP enzymes are ubiquitous in all biological kingdoms, the divergence of CYPs in fungal kingdom is manifold. The CYP enzymes play pivotal roles in various fungal metabolisms starting from housekeeping biochemical reactions, detoxification of chemicals, and adaptation to hostile surroundings. Considering the versatile catalytic potentials, fungal CYPs has gained wide range of attraction among researchers and various remarkable strategies have been accomplished to enhance their biocatalytic properties. Numerous fungal CYPs with multispecialty features have been identified and the number of characterized fungal CYPs is constantly increasing. Literature reveals ample reviews on mammalian, plant and bacterial CYPs, however, modest reports on fungal CYPs urges a comprehensive review highlighting their novel catalytic potentials and functional significances. In this review, we focus on the diversification and functional diversity of fungal CYPs and recapitulate their unique and versatile biocatalytic properties. As such, this review emphasizes the crucial issues of fungal CYP systems, and the factors influencing efficient biocatalysis.

Orthogonal Assays Clarify the Oxidative Biochemistry of Taxol P450 CYP725A4

Natural product metabolic engineering potentially offers sustainable and affordable access to numerous valuable molecules. However, challenges in characterizing and assembling complex biosynthetic pathways have prevented more rapid progress in this field. The anticancer agent Taxol represents an excellent case study. Assembly of a biosynthetic pathway for Taxol has long been stalled at its first functionalization, putatively an oxygenation performed by the cytochrome P450 CYP725A4, due to confounding characterizations. Here, through combined in vivo (Escherichia coli), in vitro (lipid nanodisc), and metabolite stability assays, we verify the presence and likely cause of this enzyme's inherent promiscuity. Thereby, we remove the possibility that promiscuity simply existed as an artifact of previous metabolic engineering approaches. Further, spontaneous rearrangement and the stabilizing effect of a hydrophobic overlay suggest a potential role for nonenzymatic chemistry in Taxol's biosynthesis. Taken together, this work confirms taxadiene-5α-ol as a primary enzymatic product of CYP725A4 and provides direction for future Taxol metabolic and protein engineering efforts.

Heterologous expression of fungal cytochromes P450 (CYP5136A1 and CYP5136A3) from the white-rot basidiomycete Phanerochaete chrysosporium: Functionalization with cytochrome b5 in Escherichia coli

Cytochromes P450 from the white-rot basidiomycete Phanerochaete chrysosporium, CYP5136A1 and CYP5136A3, are capable of catalyzing oxygenation reactions of a wide variety of exogenous compounds, implying their significant roles in the metabolism of xenobiotics by the fungus. It is therefore interesting to explore their biochemistry to better understand fungal biology and to enable the use of fungal enzymes in the biotechnology sector. In the present study, we developed heterologous expression systems for CYP5136A1 and CYP5136A3 using the T7 RNA polymerase/promoter system in Escherichia coli. Expression levels of recombinant P450s were dramatically improved by modifications and optimization of their N-terminal amino acid sequences. A CYP5136A1 reaction system was reconstructed in E. coli whole cells by coexpression of CYP5136A1 and a redox partner, NADPH-dependent P450 reductase (CPR). The catalytic activity of CYP5136A1 was significantly increased when cytochrome b5 (Cyt-b5) was further coexpressed with CPR, indicating that Cyt-b5 supports electron transfer reactions from NAD(P)H to CYP5136A1. Notably, P450 reaction occurred in E. coli cells that harbored CYP5136A1 and Cyt-b5 but not CPR, implying that the reducing equivalents required for the P450 catalytic cycle were transferred via a CPR-independent pathway. Such an "alternative" electron transfer system in CYP5136A1 reaction was also demonstrated using purified enzymes in vitro. The fungal P450 reaction system may be associated with sophisticated electron transfer pathways.

Overcoming heterologous protein interdependency to optimize P450-mediated Taxol precursor synthesis in Escherichia coli

Recent advances in metabolic engineering have demonstrated the potential to exploit biological chemistry for the synthesis of complex molecules. Much of the progress to date has leveraged increasingly precise genetic tools to control the transcription and translation of enzymes for superior biosynthetic pathway performance. However, applying these approaches and principles to the synthesis of more complex natural products will require a new set of tools for enabling various classes of metabolic chemistries (i.e., cyclization, oxygenation, glycosylation, and halogenation) in vivo. Of these diverse chemistries, oxygenation is one of the most challenging and pivotal for the synthesis of complex natural products. Here, using Taxol as a model system, we use nature's favored oxygenase, the cytochrome P450, to perform high-level oxygenation chemistry in Escherichia coli. An unexpected coupling of P450 expression and the expression of upstream pathway enzymes was discovered and identified as a key obstacle for functional oxidative chemistry. By optimizing P450 expression, reductase partner interactions, and N-terminal modifications, we achieved the highest reported titer of oxygenated taxanes (∼570 ± 45 mg/L) in E. coli. Altogether, this study establishes E. coli as a tractable host for P450 chemistry, highlights the potential magnitude of protein interdependency in the context of synthetic biology and metabolic engineering, and points to a promising future for the microbial synthesis of complex chemical entities.