Heterologous expression of human cytochromes P450 2D6 and CYP3A4 in Escherichia coli and their functional characterization

Computer-aided design and implementation of efficient biosynthetic pathways to produce high added-value products derived from tyrosine in Escherichia coli

Developing efficient bioprocesses requires selecting the best biosynthetic pathways, which can be challenging and time-consuming due to the vast amount of data available in databases and literature. The extension of the shikimate pathway for the biosynthesis of commercially attractive molecules often involves promiscuous enzymes or lacks well-established routes. To address these challenges, we developed a computational workflow integrating enumeration/retrosynthesis algorithms, a toolbox for pathway analysis, enzyme selection tools, and a gene discovery pipeline, supported by manual curation and literature review. Our focus has been on implementing biosynthetic pathways for tyrosine-derived compounds, specifically L-3,4-dihydroxyphenylalanine (L-DOPA) and dopamine, with significant applications in health and nutrition. We selected one pathway to produce L-DOPA and two different pathways for dopamine-one already described in the literature and a novel pathway. Our goal was either to identify the most suitable gene candidates for expression in Escherichia coli for the known pathways or to discover innovative pathways. Although not all implemented pathways resulted in the accumulation of target compounds, in our shake-flask experiments we achieved a maximum L-DOPA titer of 0.71 g/L and dopamine titers of 0.29 and 0.21 g/L for known and novel pathways, respectively. In the case of L-DOPA, we utilized, for the first time, a mutant version of tyrosinase from Ralstonia solanacearum. Production of dopamine via the known biosynthesis route was accomplished by coupling the L-DOPA pathway with the expression of DOPA decarboxylase from Pseudomonas putida, resulting in a unique biosynthetic pathway never reported in literature before. In the context of the novel pathway, dopamine was produced using tyramine as the intermediate compound. To achieve this, tyrosine was initially converted into tyramine by expressing TDC from Levilactobacillus brevis, which, in turn, was converted into dopamine through the action of the enzyme encoded by ppoMP from Mucuna pruriens. This marks the first time that an alternative biosynthetic pathway for dopamine has been validated in microbes. These findings underscore the effectiveness of our computational workflow in facilitating pathway enumeration and selection, offering the potential to uncover novel biosynthetic routes, thus paving the way for other target compounds of biotechnological interest.

Synthesis of mono Cytochrome P450 in a modified CHO-CPR cell-free protein production platform

Cytochromes P450 (CYPs) are a group of monooxygenases that can be found in almost all kinds of organisms. For CYPs to receive electrons from co-substrate NADPH, the activity of NADPH-Cytochrome-P450-oxidoreductase (CPR) is required as well. In humans, CYPs are an integral part of liver-based phase-1 biotransformation, which is essential for the metabolization of multiple xenobiotics and drugs. Consequently, CYPs are important players during drug development and therefore these enzymes are implemented in diverse screening applications. For these applications it is usually advantageous to use mono CYP microsomes containing only the CYP of interest. The generation of mono-CYP containing mammalian cells and vesicles is difficult since endogenous CYPs are present in many cell types that contain the necessary co-factors. By obtaining translationally active lysates from a modified CHO-CPR cell line, it is now possible to generate mono CYPs in a cell-free protein synthesis process in a straightforward manner. As a proof of principle, the synthesis of active human CYPs from three different CYP450 gene families (CYP1A2, CYP2B6 and CYP3A4), which are of outstanding interest in industry and academia was demonstrated. Luciferase based activity assays confirm the activity of the produced CYPs and enable the individual adaptation of the synthesis process for efficient cell-free enzyme production. Furthermore, they allow for substrate and inhibitor screenings not only for wild-type CYPs but also for mutants and further CYP isoforms and variants. As an example, the turnover of selected CYP substrates by cell-free synthesized CYPs was demonstrated via an indirect luciferase assay-based screening setup.

Generation of human steroidogenic cytochrome P450 enzymes for structural and functional characterization

Six cytochrome P450 enzymes are involved in human steroidogenesis, converting cholesterol to sex steroids, mineralocorticoids, and glucocorticoids. While early work was accomplished with steroidogenic P450 orthologs from more accessible sources, knowledge of basic biochemistry through successful drug design have been greatly facilitated by recombinantly-expressed, highly purified human versions of these membrane proteins. Many membrane proteins are difficult to express and purify and are unstable. Membrane P450 expression in E. coli has been facilitated by modification and/or truncation of the membrane-interacting N-terminus, while metal-affinity resins and histidine-tagging greatly facilitates purification. However, substantial optimization is still frequently required to maintain protein stability. Over time, a generalized three-column purification scheme has been developed and tweaked to generate substantial quantities of fully active, highly purified human cytochrome P450 enzymes that have made possible the application of many structural, biochemical, and biophysical techniques to elucidate the mysteries of these critical human enzymes.

Efficient heterologous expression of cytochrome P450 enzymes in microorganisms for the biosynthesis of natural products

Natural products, a chemically and structurally diverse class of molecules, possess a wide spectrum of biological activities, have been used therapeutically for millennia, and have provided many lead compounds for the development of synthetic drugs. Cytochrome P450 enzymes (P450s, CYP) are widespread in nature and are involved in the biosynthesis of many natural products. P450s are heme-containing enzymes that use molecular oxygen and the hydride donor NAD(P)H (coupled via enzymic redox partners) to catalyze the insertion of oxygen into C-H bonds in a regio- and stereo-selective manner, effecting hydroxylation and several other reactions. With the rapid development of systems biology, numerous novel P450s have been identified for the biosynthesis of natural products, but there are still several challenges to the efficient heterologous expression of active P450s. This review covers recent developments in P450 research and development, including the properties and functions of P450s, discovery and mining of novel P450s, modification and screening of P450 mutants, improved heterologous expression of P450s in microbial hosts, efficient whole-cell transformation with P450s, and current applications of P450s for the biosynthesis of natural products. This resource provides a solid foundation for the application of highly active and stable P450s in microbial cell factories to biosynthesize natural products.

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.

Current state and future perspectives of cytochrome P450 enzymes for C–H and C=C oxygenation

Cytochrome P450 enzymes (CYPs) catalyze a series of C–H and C=C oxygenation reactions, including hydroxylation, epoxidation, and ketonization. They are attractive biocatalysts because of their ability to selectively introduce oxygen into inert molecules under mild conditions. This review provides a comprehensive overview of the C–H and C=C oxygenation reactions catalyzed by CYPs and the various strategies for achieving higher selectivity and enzymatic activity. Furthermore, we discuss the application of C–H and C=C oxygenation catalyzed by CYPs to obtain the desired chemicals or pharmaceutical intermediates in practical production. The rapid development of protein engineering for CYPs provides excellent biocatalysts for selective C–H and C=C oxygenation reactions, thereby promoting the development of environmentally friendly and sustainable production processes.

In vitro inhibitory effects of glucosamine, chondroitin and diacerein on human hepatic CYP2D6

OBJECTIVES

Glucosamine, chondroitin and diacerein are natural compounds commonly used in treating osteoarthritis. Their concomitant intake may trigger drug-natural product interactions. Cytochrome P450 (CYP) has been implicated in such interactions. Cytochrome P450 2D6 (CYP2D6) is a major hepatic CYP involved in metabolism of 25% of the clinical drugs. This study aimed to investigate the inhibitory effect of these antiarthritic compounds on CYP2D6.

METHODS

CYP2D6 was heterologously expressed in Escherichia coli. CYP2D6-antiarthritic compound interactions were studied using in vitro enzyme kinetics assay and molecular docking.

RESULTS

The high-performance liquid chromatography (HPLC)-based dextromethorphan O-demethylase assay was established as CYP2D6 marker. All glucosamines and chondroitins weakly inhibited CYP2D6 (IC₅₀ values >300 µM). Diacerein exhibited moderate inhibition with IC₅₀ and K _i values of 34.99 and 38.27 µM, respectively. Its major metabolite, rhein displayed stronger inhibition potencies (IC₅₀=26.22 μM and K _i =32.27 μM). Both compounds exhibited mixed-mode of inhibition. In silico molecular dockings further supported data from the in vitro study. From in vitro-in vivo extrapolation, rhein presented an area under the plasma concentration-time curve (AUC) ratio of 1.5, indicating low potential to cause in vivo inhibition.

CONCLUSIONS

Glucosamine, chondroitin and diacerein unlikely cause clinical interaction with the drug substrates of CYP2D6. Rhein, exhibits only low potential to cause in vivo inhibition.

In vitro inhibitory effects of glucosamine, chondroitin and diacerein on human hepatic CYP2D6

OBJECTIVES

Glucosamine, chondroitin and diacerein are natural compounds commonly used in treating osteoarthritis. Their concomitant intake may trigger drug-natural product interactions. Cytochrome P450 (CYP) has been implicated in such interactions. Cytochrome P450 2D6 (CYP2D6) is a major hepatic CYP involved in metabolism of 25% of the clinical drugs. This study aimed to investigate the inhibitory effect of these antiarthritic compounds on CYP2D6.

METHODS

CYP2D6 was heterologously expressed in Escherichia coli. CYP2D6-antiarthritic compound interactions were studied using in vitro enzyme kinetics assay and molecular docking.

RESULTS

The high-performance liquid chromatography (HPLC)-based dextromethorphan O-demethylase assay was established as CYP2D6 marker. All glucosamines and chondroitins weakly inhibited CYP2D6 (IC50 values >300 µM). Diacerein exhibited moderate inhibition with IC50 and K i values of 34.99 and 38.27 µM, respectively. Its major metabolite, rhein displayed stronger inhibition potencies (IC50=26.22 μM and K i =32.27 μM). Both compounds exhibited mixed-mode of inhibition. In silico molecular dockings further supported data from the in vitro study. From in vitro-in vivo extrapolation, rhein presented an area under the plasma concentration-time curve (AUC) ratio of 1.5, indicating low potential to cause in vivo inhibition.

CONCLUSIONS

Glucosamine, chondroitin and diacerein unlikely cause clinical interaction with the drug substrates of CYP2D6. Rhein, exhibits only low potential to cause in vivo inhibition.

Effect of a functional recombinant cytochrome P450 enzyme of Helicoverpa armigera on gossypol metabolism co-expressed with NADPH-cytochrome P450 reductase in Pichia pastoris

Gossypol is a polyphonic toxic compound that is present in cotton plants. The P450 cytochromes CYP6AE14 and CYP9A12 of Helicoverpa armigera are highly induced by gossypol and have been reported to be possibly involved in gossypol degradation. To determine whether the candidate H. armigera CYP6AE14 and CYP9A12 enzymes could metabolize gossypol in vitro, functional recombinant H. armigera CYP6AE14 and CPR (CYP9A12 and CPR) enzymes were successfully expressed in Pichia pastoris (P. pastoris). UPLC-QTOF/MS demonstrated the following results: (1) Free gossypol was spontaneously degraded to the gossypol metabolites G1 (m/z 265) and G2 (m/z 293) without the addition of any enzyme. (2) Free gossypol was observed following the addition of the endogenous or recombinant H. armigera P450 cytochrome CYP6AE14/CYP9A12 enzyme: in the first pathway, free gossypol was dehydroxylated and decarboxylated to G3 (m/z 453), and in the second pathway, the aldehyde group of gossypol and its metabolite were covalently bound with the amine products to form G4 (m/z 437) and G5 (m/z 783). (3) In addition to the gossypol binding pathways, the recombinant H. armigera CPR and CYP9A12 enzymes was found that could further decarboxylate the gossypol intermediate demethylated reduction of gossypolonic acid (m/z 294) and demethylated gossic acid (m/z 265) to G0 (m/z 209) and G0' (m/z 249) respectively.

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.

Comparison of human cytochrome P450 1A1-catalysed oxidation of benzo[a]pyrene in prokaryotic and eukaryotic expression systems

ABSTRACT

Cytochrome P450 (CYP) 1A1 is the most important enzyme activating and detoxifying the human carcinogen benzo[a]pyrene (BaP). In the previous studies, we had shown that not only the canonic NADPH:CYP oxidoreductase (POR) can act as electron donor but also cytochrome b5 and its reductase, NADH:cytochrome b5 reductase. Here, we studied the role of the expression system used on the metabolites generated and the levels of DNA adducts formed by activated BaP. We used an eukaryotic and a prokaryotic cellular system (Supersomes, microsomes isolated from insect cells, and Bactosomes, a membrane fraction of Escherichia coli, each transfected with cDNA of human CYP1A1 and POR). These were reconstituted with cytochrome b5 with and without NADH:cytochrome b5 reductase. We evaluated the effectiveness of each cofactor, NADPH and NADH, to mediate BaP metabolism. We found that both systems differ in catalysing the reactions activating and detoxifying BaP. Two BaP-derived DNA adducts were generated by the CYP1A1-Supersomes, both in the presence of NADPH and NADH, whereas NADPH but not NADH was able to support this reaction in the CYP1A1-Bactosomes. Seven BaP metabolites were found in Supersomes with NADPH or NADH, whereas NADPH but not NADH was able to generate five BaP metabolites in Bactosomes. Our study demonstrates different catalytic efficiencies of CYP1A1 expressed in prokaryotic and eukaryotic cells in BaP bioactivation indicating some limitations in the use of E. coli cells for such studies.

GRAPHICAL ABSTRACT

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.

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.

In Vitro Functional Characterisation of Cytochrome P450 (CYP) 2C19 Allelic Variants CYP2C19*23 and CYP2C19*24

Cytochrome P450 (CYP) 2C19 is essential for the metabolism of clinically used drugs including omeprazole, proguanil, and S-mephenytoin. This hepatic enzyme exhibits genetic polymorphism with inter-individual variability in catalytic activity. This study aimed to characterise the functional consequences of CYP2C19*23 (271 G>C, 991 A>G) and CYP2C19*24 (991 A>G, 1004 G>A) in vitro. Mutations in CYP2C19 cDNA were introduced by site-directed mutagenesis, and the CYP2C19 wild type (WT) as well as variants proteins were subsequently expressed using Escherichia coli cells. Catalytic activities of CYP2C19 WT and those of variants were determined by high performance liquid chromatography-based essay employing S-mephenytoin and omeprazole as probe substrates. Results showed that the level of S-mephenytoin 4'-hydroxylation activity of CYP2C19*23 (V _max 111.5 ± 16.0 pmol/min/mg, K _m 158.3 ± 88.0 μM) protein relative to CYP2C19 WT (V _max 101.6 + 12.4 pmol/min/mg, K _m 123.0 ± 19.2 μM) protein had no significant difference. In contrast, the K _m of CYP2C19*24 (270.1 ± 57.2 μM) increased significantly as compared to CYP2C19 WT (123.0 ± 19.2 μM) and V _max of CYP2C19*24 (23.6 ± 2.6 pmol/min/mg) protein was significantly lower than that of the WT protein (101.6 ± 12.4 pmol/min/mg). In vitro intrinsic clearance (CL_int = V _max/K _m) for CYP2C19*23 protein was 85.4 % of that of CYP2C19 WT protein. The corresponding CL_int value for CYP2C19*24 protein reduced to 11.0 % of that of WT protein. These findings suggested that catalytic activity of CYP2C19 was not affected by the corresponding amino acid substitutions in CYP2C19*23 protein; and the reverse was true for CYP2C19*24 protein. When omeprazole was employed as the substrate, K _m of CYP2C19*23 (1911 ± 244.73 μM) was at least 100 times higher than that of CYP2C19 WT (18.37 ± 1.64 μM) and V _max of CYP2C19*23 (3.87 ± 0.74 pmol/min/mg) dropped to 13.4 % of the CYP2C19 WT (28.84 ± 0.61 pmol/min/mg) level. Derived from V _max/K _m, the CL_int value of CYP2C19 WT was 785 folds of CYP2C19*23. K _m and V _max values could not be determined for CYP2C19*24 due to its low catalytic activity towards omeprazole 5'-hydroxylation. Therefore, both CYP2C19*23 and CYP2C19*24 showed marked reduced activities of metabolising omeprazole to 5-hydroxyomeprazole. Hence, carriers of CYP2C19*23 and CYP2C19*24 allele are potentially poor metabolisers of CYP2C19-mediated substrates.

Cloning, expression and purification of isoflavone-2'-hydroxylase from Astragalus membranaceus Bge. Var. mongolicus (Bge.) Hsiao

Plant cytochrome P450 enzymes play vital roles in the biosynthesis of plant secondary metabolites, including phenylpropanoids and phytoalexins. Isoflavone-2'-hydroxylase (AmI2'H) from Astragalus membranaceus Bge. Var. mongolicus (Bge.) Hsiao is a membrane protein and an eukaryotic cytochrome P450 enzyme involved in isoflavonoid biosynthesis. We cloned the AmI2'H gene by employing RACE methods and modified the gene sequence to facilitate protein expression and increase protein solubility. Two vectors, pET-28a(+) and pCW ori(+), were used to express AmI2'H in Escherichia coli. The expression efficiency and purity of target protein were analyzed and demonstrated that pET-28a(+) vector containing the AmI2'H gene could produce larger amounts of target proteins with higher purity than pCWori(+). The purified proteins were identified as AmI2'H by LC-ESI-MS/MS analysis and their proper folding was assessed by CO difference spectrum.

Effect of eurycomanone on cytochrome P450 isoforms CYP1A2, CYP2A6, CYP2C8, CYP2C9, CYP2C19, CYP2E1 and CYP3A4 in vitro

Eurycomanone, an active constituent isolated from Eurycoma longifolia Jack, was examined for modulatory effects on cytochrome P450 (CYP) isoforms CYP1A2, CYP2A6, CYP2C8, CYP2C9, CYP2C19, CYP2E1 and CYP3A4 using in vitro assays. The IC50 value was determined to assess the potencies of modulation for each CYP isoform. Our results indicated that eurycomanone did not potently inhibit any of the CYP isoforms investigated, with IC50 values greater than 250 μg/ml. Hence there appears to be little likelihood of drug-herb interaction between eurycomanone or herbal products with high content of this compound and CYP drug substrates via CYP inhibition.

Double site saturation mutagenesis of the human cytochrome P450 2D6 results in regioselective steroid hydroxylation

The human cytochrome P450 2D6 (CYP2D6) is one of the major human drug metabolizing enzymes and acts preferably on substrates containing a basic nitrogen atom. Testosterone - just as other steroids - is an atypical substrate and only poorly metabolized by CYP2D6. The present study intended to investigate the influence of the two active site residues 216 and 483 on the capability of CYP2D6 to hydroxylate steroids such as for example testosterone. All 400 possible combinatorial mutations at these two positions have been generated and expressed individually in Pichia pastoris. Employing whole-cell biotransformations coupled with HPLC-MS analysis the testosterone hydroxylase activity and regioselectivity of every single CYP2D6 variant was determined. Covering the whole sequence space, CYP2D6 variants with improved activity and so far unknown regio-preference in testosterone hydroxylation were identified. Most intriguingly and in contrast to previous literature reports about mutein F483I, the mutation F483G led to preferred hydroxylation at the 2β-position, while the slow formation of 6β-hydroxytestosterone, the main product of wild-type CYP2D6, was further reduced. Two point mutations have already been sufficient to convert CYP2D6 into a steroid hydroxylase with the highest ever reported testosterone hydroxylation rate for this enzyme, which is of the same order of magnitude as for the conversion of the standard substrate bufuralol by wild-type CYP2D6. Furthermore, this study is also an example for efficient human CYP engineering in P. pastoris for biocatalytic applications and to study so far unknown pharmacokinetic effects of individual and combined mutations in these key enzymes of the human drug metabolism.

Heterologous expression of human cytochrome P450 (CYP) 2C19 in Escherichia coli and establishment of RP-HPLC method to serve as activity marker

In this study, a simple and reliable reverse-phase high-performance liquid chromatography (RP-HPLC) method was established and validated to analyze S-mephenytoin 4-hydroxylase activity of a recombinant CYP2C19 system. This system was obtained by co-expressing CYP2C19 and NADPH-CYP oxidoreductase (OxR) proteins in Escherichia coli (E. coli) cells. In addition to RP-HPLC, the expressed proteins were evaluated by immunoblotting and reduced CO difference spectral scanning. The RP-HPLC assay showed good linearity (r(2) = 1.00) with 4-hydroxymephenytoin concentration from 0.100 to 50.0 μm and the limit of detection was 5.00 × 10(-2) μm. Intraday and interday precisions determined were from 1.90 to 8.19% and from 2.20 to 14.9%, respectively. Recovery and accuracy of the assay were from 83.5 to 85.8% and from 95.0 to 105%. Enzyme kinetic parameters (Km , Vmax and Ki ) were comparable to reported values. The presence of CYP2C19 in bacterial membranes was confirmed by immunoblotting and the characteristic absorbance peak at 450 nm was determined in the reduced CO difference spectral assay. Moreover, the activity level of co-expressed OxR was found to be comparable to that of the literature. As a conclusion, the procedures described here have generated catalytically active CYP2C19 and the RP-HPLC assay developed is able to serve as CYP2C19 activity marker for pharmacokinetic drug interaction study in vitro.