The use of electrochemistry for the synthesis of 17 alpha-hydroxyprogesterone by a fusion protein containing P450c17

[Methods for determining of cytochrome P450 isozymes functional activity]

The review is dedicated to modern methods and technologies for determining of cytochrome P450 isozymes functional activity, such as absorbance and fluorescent spectroscopy, electron paramagnetic resonance (EPR), nuclear magnetic resonance (NMR), Raman, Mossbauer, and X-ray spectroscopy, surface plasmon resonance (SPR), atomic force microscopy (AFM). Methods of molecular genetic analysis were reviewed from personalized medicine point of view. The use of chromate-mass-spectrometric methods for cytochrome P450-dependent catalytic reactions' products was discussed. The review covers modern electrochemical systems based on cytochrome P450 isozymes for their catalytic activity analysis, their use in practice and further development perspectives for experimental pharmacology, biotechnology and translational medicine.

Crystallographic insights into a cobalt (III) sepulchrate based alternative cofactor system of P450 BM3 monooxygenase

P450 BM3 is a multi-domain heme-containing soluble bacterial monooxygenase. P450 BM3 and variants are known to oxidize structurally diverse substrates. Crystal structures of individual domains of P450 BM3 are available. However, the spatial organization of the full-length protein is unknown. In this study, crystal structures of the P450 BM3 M7 heme domain variant with and without cobalt (III) sepulchrate are reported. Cobalt (III) sepulchrate acts as an electron shuttle in an alternative cofactor system employing zinc dust as the electron source. The crystal structure shows a binding site for the mediator cobalt (III) sepulchrate at the entrance of the substrate access channel. The mediator occupies an unusual position which is far from the active site and distinct from the binding of the natural redox partner (FAD/NADPH binding domain).

Electrochemistry of cytochrome P450 17α-hydroxylase/17,20-lyase (P450c17)

Within the superfamily of cytochrome P450 enzymes (P450s), there is a small class which is functionally employed for steroid biosynthesis. The enzymes in this class appear to have a small active site to accommodate the steroid substrates specifically and snuggly, prior to the redox transformation or hydroxylation to form a product. Cytochrome P450c17 is one of these and is also a multi-functional P450, with two activities, the first 17α-hydroxylation of pregnenolone is followed by a subsequent 17,20-lyase transformation to dehydroepiandrosterone (DHEA) as the dominant pathways to cortisol precursors or androgens in humans, respectively. How P450c17 regulates these two redox reactions is of special interest. There is a paucity of direct electrochemical studies on steroidogenic P450s, and in this mini-review we provide an overview of these studies with P450c17. Historical consideration as to the difficulties in obtaining reliable electrochemistry due to issues of handling proteins on an electrode, together with advances in the electrochemical techniques are addressed. Recent work using Fourier transformed alternating current voltammetry is highlighted as this technique can provide both catalytic information simultaneously with the underlying redox transfer with the P450 haem.

Laboratory evolution of P450 BM-3 for mediated electron transfer

Preparative synthesis with P450 monooxygenases is hampered in cell-free systems by the requirement for cofactors such as NAD(P)H as reduction equivalents. A validated medium-throughput screening system was designed for improving P450 monooxygenases by mediated electron transfer with zinc/cobalt(III)sepulchrate (Zn/Co(III)sep) as an alternative and cost-effective cofactor system. The monooxygenase P450 BM-3 F87A was used as a model system for developing the screening system in a 96-well format. A coefficient of variation of less than 10% was achieved under optimized screening conditions. The mediator evolution screen was validated by comparing the activity of P450 BM-3 to P450 BM-3 F87A and by screening a saturation mutagenesis library at amino acid position R47. For mediated electron transfer, two double mutants P450 BM-3(F87A R47F) and P450 BM-3 (F87A R47Y) were identified with a two-threefold increased catalytic efficiency (up to 32 microM(-1) min(-1) for P450 BM-3(F87A R47F) and 34 microM(-1) min(-1) for P450 BM-3 (F87A R47Y)) compared to P450 BM-3 F87A. The kinetic constants of the double mutants are, in contrast to those of P450 BM-3 F87A, dependent on Co(III)sep concentration in the presence of NADPH. kcat increases from 145 min(-1) (0.25 mM Co(III)sep) to 197 min(-1) (0.5 mM Co(III)sep), and Km decreases simultaneously from 7.0 microM to 3.7 microM, for P450 BM-3 (F87A R47F). For P450 BM-3 (F87A R47Y), kcat increases from 138 min(-1) (0.25 mM Co(III)sep) up to 187 min(-1) (0.5 mM Co(III)sep), and Km decreases from 8.2 microM to 4.2 microM. Due to lower Km values, the catalytic efficiencies were improved six times for P450 BM-3 (F87A R47F) and three times for P450 BM-3 (F87A R47Y), when comparing catalytic efficiencies of the mediated electron-transfer system to the natural reduction equivalent NADPH.

Enzyme Electrochemistry — Biocatalysis on an Electrode

Oxidoreductase enzymes catalyze single- or multi-electron reduction/oxidation reactions of small molecule inorganic or organic substrates, and they are integral to a wide variety of biological processes including respiration, energy production, biosynthesis, metabolism, and detoxification. All redox enzymes require a natural redox partner such as an electron-transfer protein (e.g. cytochrome, ferredoxin, flavoprotein) or a small molecule cosubstrate (e.g. NAD(P)H, dioxygen) to sustain catalysis, in effect to balance the substrate/product redox half-reaction. In principle, the natural electron-transfer partner may be replaced by an electrochemical working electrode. One of the great strengths of this approach is that the rate of catalysis (equivalent to the observed electrochemical current) may be probed as a function of applied potential through linear sweep and cyclic voltammetry, and insight to the overall catalytic mechanism may be gained by a systematic electrochemical study coupled with theoretical analysis. In this review, the various approaches to enzyme electrochemistry will be discussed, including direct and indirect (mediated) experiments, and a brief coverage of the theory relevant to these techniques will be presented. The importance of immobilizing enzymes on the electrode surface will be presented and the variety of ways that this may be done will be reviewed. The importance of chemical modification of the electrode surface in ensuring an environment conducive to a stable and active enzyme capable of functioning natively will be illustrated. Fundamental research into electrochemically driven enzyme catalysis has led to some remarkable practical applications. The glucose oxidase enzyme electrode is a spectacularly successful application of enzyme electrochemistry. Biosensors based on this technology are used worldwide by sufferers of diabetes to provide rapid and accurate analysis of blood glucose concentrations. Other applications of enzyme electrochemistry are in the sensing of macromolecular complexation events such as antigen–antibody binding and DNA hybridization. The review will include a selection of enzymes that have been successfully investigated by electrochemistry and, where appropriate, discuss their development towards practical biotechnological applications.

Electrochemical reduction of cytochrome P450 as an approach to the construction of biosensors and bioreactors

In the present review an attempt was made to present an up-to-date amount of the data on electrochemical reduction of the hemoprotein cytochrome P450. The concept and potentialities of enzyme electrodes--transducers--as the main element for construction of electrochemical biosensors were discussed. Different types of electrodes for bioelectrochemistry were analysed. New nanotechnological approaches to cytochrome P450 immobilisation were reported. It was shown that nanobiotechnology in electrochemistry has potential application in manufacturing biosensors and bioreactors for clinical medicine and pharmacology.

Formation and functioning of fused cholesterol side-chain cleavage enzymes

We studied the properties of various fused combinations of the components of the mitochondrial cholesterol side-chain cleavage system including cytochrome P450scc, adrenodoxin (Adx), and adrenodoxin reductase (AdR). When recombinant DNAs encoding these constructs were expressed in Escherichia coli, both cholesterol side-chain cleavage activity and sensitivity to intracellular proteolysis of the three-component fusions depended on the species of origin and the arrangement of the constituents. To understand the assembly of the catalytic domains in the fused molecules, we analyzed the catalytic properties of three two-component fusions: P450scc-Adx, Adx-P450scc, and AdR-Adx. We examined the ability of each fusion to carry out the side-chain cleavage reaction in the presence of the corresponding missing component of the whole system and examined the dependence of this reaction on the presence of exogenously added individual components of the double fusions. This analysis indicated that the active centers in the double fusions are either unable to interact or are misfolded; in some cases they were inaccessible to exogenous partners. Our data suggest that when fusion proteins containing P450scc, Adx, and AdR undergo protein folding, the corresponding catalytic domains are not formed independently of each other. Thus, the correct folding and catalytic activity of each domain is determined interactively and not independently.

Random mutagenesis of human cytochrome p450 2A6 and screening with indole oxidation products

Cytochrome P450 (P450) 2A6 mutants from randomized libraries generated in the substrate recognition sequence (SRS) regions were screened in Escherichia coli on the basis of indole metabolism. SRS 3 and 4 libraries yielded colonies that produced indigo at least as well as wild-type (WT) P450 2A6, and some colonies were consistently more blue upon replating. One mutant, F209T, showed indole 3-hydroxylation <WT but had a k(cat) for coumarin 7-hydroxylation 13-fold >WT. The double mutant L240C/N297Q consistently produced very blue colonies. Five mutants yielded mixtures of pigments from indole different than WT, as judged by visible spectra and HPLC of products. When bacteria expressing the mutants were grown in the presence of each of 26 substituted indoles, a variety of patterns of formation of different dyes was seen with several of the mutants. This approach has potential value in understanding P450 2A6 function and generating new dyestuffs and other products.

Engineering the CYP101 system for in vivo oxidation of unnatural substrates

The protein engineering of CYP enzymes for structure-activity studies and the oxidation of unnatural substrates for biotechnological applications will be greatly facilitated by the availability of functional, whole-cell systems for substrate oxidation. We report the construction of a tricistronic plasmid that expresses the CYP101 monooxygenase from Pseudomonas putida, and its physiological electron transfer co-factor proteins putidaredoxin reductase and putidaredoxin in Escherichia coli, giving a functional in vivo catalytic system. Wild-type CYP101 expressed in this system efficiently transforms camphor to 5-exo-hydroxycamphor without further oxidation to 5-oxo-camphor until >95% of camphor has been consumed. CYP101 mutants with increased activity for the oxidation of diphenylmethane (the Y96F-I395G mutant), styrene and ethylbenzene (the Y96F-V247L mutant) have been engineered. In particular, the Y96F-V247L mutant shows coupling efficiency of approximately 60% for styrene and ethylbenzene oxidation, with substrate oxidation rates of approximately 100/min. Escherichia coli cells transformed with tricistronic plasmids expressing these mutants readily gave 100-mg quantities of 4-hydroxydiphenylmethane and 1-phenylethanol in 24-72 h. This new in vivo system can be used for preparative scale reactions for product characterization, and will greatly facilitate directed evolution of the CYP101 enzyme for enhanced activity and selectivity of substrate oxidation.

Engineering of a functional human NADH-dependent cytochrome P450 system

A functional human NADH-dependent cytochrome P450 system has been developed by altering the cofactor preference of human NADPH cytochrome P450 reductase (CPR), the redox partner for P450s. This has been achieved by a single amino acid change of the conserved aromatic amino acid Trp-676, which covers the re-side of the FAD isoalloxazine ring in the nicotinamide-binding site. Of the mutations made, the substitution of Trp-676 with alanine (W676A) resulted in a functional NADH-dependent enzyme, which catalyzed the reduction of cytochrome c and ferricyanide as well as facilitated the metabolism of 7-ethoxyresorufin by CYP1A2. Kinetic analysis measuring cytochrome c activity revealed that the NADH-dependent k(cat) of W676A is equivalent (90%) to the NADPH-dependent k(cat) of the wild-type enzyme, with W676A having an approximately 1,000-fold higher specificity for NADH. The apparent K(M)(NADPH) and K(M)(NADH) values of W676A are 80- and 150-fold decreased, respectively. In accordance with structural data, which show a bipartite binding mode of NADPH, substitution of Trp-676 does not affect 2'-AMP binding as seen by the inhibition of both wild-type CPR and the W676A mutant. Furthermore, NADPH was a potent inhibitor of the W676A NADH-dependent cytochrome c reduction and CYP1A2 activity. Overall, the results show that Trp-676 of human CPR plays a major role in cofactor discrimination, and substitution of this conserved aromatic residue with alanine results in an efficient NADH-dependent cytochrome P450 system.

P450 in biotechnology: zinc driven omega-hydroxylation of p-nitrophenoxydodecanoic acid using P450 BM-3 F87A as a catalyst

Cytochrome P450 enzymes require the delivery of two electrons to the heme protein for their enzymatic function. NADPH or NADH are usually used as reduction equivalents. In the absence of a substrate, NADPH may inactivate P450 enzymes. Furthermore, it is expensive, making it unsuitable for the preparative synthesis of fine chemicals. Approaches for replacing NADPH with an electrochemically generated reduction by using platinum-electrodes and different mediators are known. In the present study, NADPH was substituted by the mediator cobalt(III)sepulchrate and zinc dust that serves as an electron source. The mutated fatty acid hydroxylase P450 BM-3 F87A from Bacillus megaterium was chosen as a catalyst, since it shows a three-fold higher sensitivity and a nearly five-fold higher activity for p-nitrophenoxydodecanoic acid (12-pNCA) than the wild-type enzyme. The formation of p-nitrophenolate can easily be monitored using a photometer at 410 nm. The turnover rate of the zinc/cobalt(III)sepulchrate system reaches 20% of the NADPH activity. Compared to the electrochemical approaches the activity is at least 77% higher (turnover 125 eq min-1). The presented alternative cofactor system can be used instead of NADPH or expensive electrochemical devices (platinum electrodes) for fine chemical synthesis.

Human cytochrome P450 enzymes expressed in bacteria: reagents to probe molecular interactions in toxicology

1. Phase I metabolism of drugs is accomplished by the concerted actions of a limited number of cytochrome P450 enzymes with wide but often overlapping substrate specificites. Although metabolism generally accelerates the clearance of drugs, reactive products may also be generated that cause toxic effects. 2. Because individuals vary in the range and levels of different P450 forms, it is useful to be able to determine the specific isoforms involved in a particular metabolic reaction, in order to estimate the extent of variation within a population in the pharmacokinetics of specific drugs. Such studies may also allow predictions to be made regarding the relative susceptibility of different individuals to possible adverse effects associated with drug treatment. 3. Human cytochrome P450 enzymes are now routinely expressed as recombinant proteins in many different systems, including mammalian cell culture, yeast, baculovirus and Escherichia coli. The latter system is particularly useful when large amounts of protein are required for biophysical studies, but can also be adapted to routine examination of pathways of drug metabolism and toxicology. 4. The present review provides an analysis of strategies used for enhancing cytochrome P450 expression in bacteria and for examining the activity of the recombinant proteins. The potential applications of recombinant P450 are discussed, with particular emphasis on investigation of the roles of cytochrome P450 forms in the metabolism and the toxicity of drugs.

Cytochrome P450 monooxygenases

The field of P450 research is progressing rapidly. The active sites of structurally characterized bacterial P450 enzymes have been rationally re-engineered to alter both substrate specificity and selectivity of substrate oxidation. Many human P450 enzymes have been functionally expressed and new methods of substrate turnover described. These developments, arising from our increased understanding of the chemistry and molecular biology of P450 enzymes, open up new and exciting research directions.