CYP119 plus a Sulfolobus tokodaii strain 7 ferredoxin and 2-oxoacid:ferredoxin oxidoreductase constitute a high-temperature cytochrome P450 catalytic system

Small angle X-ray scattering analysis of thermophilic cytochrome P450 CYP119 and the effects of the N-terminal histidine tag

Combining size exclusion chromatography-small angle X-ray scattering (SEC-SAXS) and molecular dynamics (MD) analysis is a promising approach to investigate protein behavior in solution, particularly for understanding conformational changes due to substrate binding in cytochrome P450s (CYPs). This study investigates conformational changes in CYP119, a thermophilic CYP from Sulfolobus acidocaldarius that exhibits structural flexibility similar to mammalian CYPs. Although the crystal structure of ligand-free (open state) and ligand-bound (closed state) forms of CYP119 is known, the overall structure of the enzyme in solution has not been explored until now. It was found that theoretical scattering profiles from the crystal structures of CYP119 did not align with the SAXS data, but conformers from MD simulations, particularly starting from the open state (46 % of all frames), agreed well. Interestingly, a small percentage of closed-state conformers also fit the data (9 %), suggesting ligand-free CYP119 samples ligand-bound conformations. Ab initio SAXS models for N-His tagged CYP119 revealed a tail-like unfolded structure impacting protein flexibility, which was confirmed by in silico modeling. SEC-SAXS analysis of N-His CYP119 indicated pentameric structures in addition to monomers in solution, affecting the stability and activity of the enzyme. This study adds insights into the conformational dynamics of CYP119 in solution.

Evolution of Cytochrome P450 Enzymes and Their Redox Partners in Archaea

Cytochrome P450 monooxygenases (CYPs/P450s) and their redox partners, ferredoxins, are ubiquitous in organisms. P450s have been studied in biology for over six decades owing to their distinct catalytic activities, including their role in drug metabolism. Ferredoxins are ancient proteins involved in oxidation-reduction reactions, such as transferring electrons to P450s. The evolution and diversification of P450s in various organisms have received little attention and no information is available for archaea. This study is aimed at addressing this research gap. Genome-wide analysis revealed 1204 P450s belonging to 34 P450 families and 112 P450 subfamilies, where some families and subfamilies are expanded in archaea. We also identified 353 ferredoxins belonging to the four types 2Fe-2S, 3Fe-4S, 7Fe-4S and 2[4Fe-4S] in 40 archaeal species. We found that bacteria and archaea shared the CYP109, CYP147 and CYP197 families, as well as several ferredoxin subtypes, and that these genes are co-present on archaeal plasmids and chromosomes, implying the plasmid-mediated lateral transfer of these genes from bacteria to archaea. The absence of ferredoxins and ferredoxin reductases in the P450 operons suggests that the lateral transfer of these genes is independent. We present different scenarios for the evolution and diversification of P450s and ferredoxins in archaea. Based on the phylogenetic analysis and high affinity to diverged P450s, we propose that archaeal P450s could have diverged from CYP109, CYP147 and CYP197. Based on this study's results, we propose that all archaeal P450s are bacterial in origin and that the original archaea had no P450s.

Rational design of thermophilic CYP119 for progesterone hydroxylation by in silico mutagenesis and docking screening

Steroid-based chemicals can affect the metabolism, immune functions, and development of sexual characteristics. Because of these effects, steroid derivatives are widely used in the pharmaceutical industry. Progesterone is a steroid-based hormone that mainly controls the ovulation period of women but is also a precursor molecule for the synthesis of important hormones like testosterone and cortisone. Cytochrome P450 (CYP) enzymes are important for the production of hydroxyprogesterones in the industry since they can catalyze regio- and enantioselective hydroxylation reactions. Although human CYP enzymes can catalyze hydroxyprogesterone synthesis with high selectivity, these enzymes are membrane bound, which limits their application for industrial production. CYP119 is a soluble and thermophilic enzyme from the archaea Sulfolobus acidocaldarius. Even though the native substrate of the enzyme is not known, CYP119 can catalyze styrene epoxidation, lauric acid hydroxylation, and Amplex®Red peroxidation. In this work, an in silico mutagenesis approach was used to design CYP119 mutants with high progesterone affinity. Energy scores of progesterone docking simulations were used for the design and elimination of single, double, and triple mutants of CYP119. Among designed 674 mutants, five of them match the criteria for progesterone hydroxylation. The most common mutation of these five mutants, L69G mutant was analyzed using independent molecular dynamics (MD) simulations in comparison with the wild-type (WT) enzyme. L69G CYP119, was expressed and isolated from Escherichia coli; it showed 800-fold higher affinity for progesterone compared to WT CYP119. L69G CYP119 also catalyzed progesterone hydroxylation. The novel designed enzyme L69G CYP119 is a potential versatile biocatalyst for progesterone hydroxylation that is expected to be stable under industrial production conditions.

Pseudomonas aeruginosa cytochrome P450 CYP168A1 is a fatty acid hydroxylase that metabolizes arachidonic acid to the vasodilator 19-HETE

Pseudomonas aeruginosa is a Gram-negative opportunistic human pathogen that is highly prevalent in individuals with cystic fibrosis (CF). A major problem in treating CF patients infected with P. aeruginosa is the development of antibiotic resistance. Therefore, the identification of novel P. aeruginosa antibiotic drug targets is of the utmost urgency. The genome of P. aeruginosa contains four putative cytochrome P450 enzymes (CYPs) of unknown function that have never before been characterized. Analogous to some of the CYPs from Mycobacterium tuberculosis, these P. aeruginosa CYPs may be important for growth and colonization of CF patients’ lungs. In this study, we cloned, expressed, and characterized CYP168A1 from P. aeruginosa and identified it as a subterminal fatty acid hydroxylase. Spectral binding data and computational modeling of substrates and inhibitors suggest that CYP168A1 has a large, expansive active site and preferentially binds long chain fatty acids and large hydrophobic inhibitors. Furthermore, metabolic experiments confirm that the enzyme is capable of hydroxylating arachidonic acid, an important inflammatory signaling molecule present in abundance in the CF lung, to 19-hydroxyeicosatetraenoic acid (19-HETE; K_m = 41 μM, V_max = 220 pmol/min/nmol P450), a potent vasodilator, which may play a role in the pathogen’s ability to colonize the lung. Additionally, we found that the in vitro metabolism of arachidonic acid is subject to substrate inhibition and is also inhibited by the presence of the antifungal agent ketoconazole. This study identifies a new metabolic pathway in this important human pathogen that may be of utility in treating P. aeruginosa infections.

Advanced Understanding of the Electron Transfer Pathway of Cytochrome P450s

Cytochrome P450s are heme-thiolate enzymes that participate in carbon source assimilation, natural compound biosynthesis and xenobiotic metabolism in all kingdoms of life. P450s can catalyze various reactions by using a wide range of organic compounds, thus exhibiting great potential in biotechnological applications. The catalytic reactions of P450s are driven by electron equivalents that are sourced from pyridine nucleotides and delivered by cognate or matching redox partners (RPs). The electron transfer (ET) route from RPs to P450s involves one or more redox center-containing domains. As the rate of ET is one of the main determinants of P450 efficacy, an in-depth understanding of the P450 ET pathway should increase our knowledge of these important enzymes and benefit their further applications. Here, the various P450 RP systems along with current understanding of their ET routes will be reviewed. Notably, state-of-the-art structural studies of the two main types of self-sufficient P450 will also be summarized.

Unrivalled diversity: the many roles and reactions of bacterial cytochromes P450 in secondary metabolism

Covering: 2000 up to 2018 The cytochromes P450 (P450s) are a superfamily of heme-containing monooxygenases that perform diverse catalytic roles in many species, including bacteria. The P450 superfamily is widely known for the hydroxylation of unactivated C-H bonds, but the diversity of reactions that P450s can perform vastly exceeds this undoubtedly impressive chemical transformation. Within bacteria, P450s play important roles in many biosynthetic and biodegradative processes that span a wide range of secondary metabolite pathways and present diverse chemical transformations. In this review, we aim to provide an overview of the range of chemical transformations that P450 enzymes can catalyse within bacterial secondary metabolism, with the intention to provide an important resource to aid in understanding of the potential roles of P450 enzymes within newly identified bacterial biosynthetic pathways.

Determinants of thermostability in the cytochrome P450 fold

Cytochromes P450 are found throughout the biosphere in a wide range of environments, serving a multitude of physiological functions. The ubiquity of the P450 fold suggests that it has been co-opted by evolution many times, and likely presents a useful compromise between structural stability and conformational flexibility. The diversity of substrates metabolized and reactions catalyzed by P450s makes them attractive starting materials for use as biocatalysts of commercially useful reactions. However, process conditions impose different requirements on enzymes to those in which they have evolved naturally. Most natural environments are relatively mild, and therefore most P450s have not been selected in Nature for the ability to withstand temperatures above ~40°C, yet industrial processes frequently require extended incubations at much higher temperatures. Thus, there has been considerable interest and effort invested in finding or engineering thermostable P450 systems. Numerous P450s have now been identified in thermophilic organisms and analysis of their structures provides information as to mechanisms by which the P450 fold can be stabilized. In addition, protein engineering, particularly by directed or artificial evolution, has revealed mutations that serve to stabilize particular mesophilic enzymes of interest. Here we review the current understanding of thermostability as it applies to the P450 fold, gleaned from the analysis of P450s characterized from thermophilic organisms and the parallel engineering of mesophilic forms for greater thermostability. We then present a perspective on how this information might be used to design stable P450 enzymes for industrial application. 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.

Unraveling the Transcriptional Basis of Temperature-Dependent Pinoxaden Resistance in Brachypodium hybridum

Climate change endangers food security and our ability to feed the ever-increasing human population. Weeds are the most important biotic stress, reducing crop-plant productivity worldwide. Chemical control, the main approach for weed management, can be strongly affected by temperature. Previously, we have shown that temperature-dependent non-target site (NTS) resistance of Brachypodium hybridum is due to enhanced detoxification of acetyl-CoA carboxylase inhibitors. Here, we explored the transcriptional basis of this phenomenon. Plants were characterized for the transcriptional response to herbicide application, high-temperature and their combination, in an attempt to uncover the genetic basis of temperature-dependent pinoxaden resistance. Even though most of the variance among treatments was due to pinoxaden application (61%), plants were able to survive pinoxaden application only when grown under high-temperatures. Biological pathways and expression patterns of members of specific gene families, previously shown to be involved in NTS metabolic resistance to different herbicides, were examined. Cytochrome P450, glucosyl transferase and glutathione-S-transferase genes were found to be up-regulated in response to pinoxaden application under both control and high-temperature conditions. However, biological pathways related to oxidation and glucose conjugation were found to be significantly enriched only under the combination of pinoxaden application and high-temperature. Analysis of reactive oxygen species (ROS) was conducted at several time points after treatment using a probe detecting H2O2/peroxides. Comparison of ROS accumulation among treatments revealed a significant reduction in ROS quantities 24 h after pinoxaden application only under high-temperature conditions. These results may indicate significant activity of enzymatic ROS scavengers that can be correlated with the activation of herbicide-resistance mechanisms. This study shows that up-regulation of genes related to metabolic resistance is not sufficient to explain temperature-dependent pinoxaden resistance. We suggest that elevated activity of enzymatic processes at high-temperature may induce rapid and efficient pinoxaden metabolism leading to temperature-dependent herbicide resistance.

Enhanced turnover rate and enantioselectivity in the asymmetric epoxidation of styrene by new T213G mutants of CYP 119

New CYP 119 T213G mutants were constructed and characterized. Introduction of T213G mutation into the wild-type CYP 119 enhances the turnover rate for the styrene epoxidation to 346.2 min⁻¹, and the double T213G/T214V mutant improves the ratio of the S- and R-enantiomers of the epoxide products to 5.8. The molecular docking results support our initial design and experimental data.

Structural biology of redox partner interactions in P450cam monooxygenase: a fresh look at an old system

The P450cam monooxygenase system consists of three separate proteins: the FAD-containing, NADH-dependent oxidoreductase (putidaredoxin reductase or Pdr), cytochrome P450cam and the 2Fe2S ferredoxin (putidaredoxin or Pdx), which transfers electrons from Pdr to P450cam. Over the past few years our lab has focused on the interaction between these redox components. It has been known for some time that Pdx can serve as an effector in addition to its electron shuttle role. The binding of Pdx to P450cam is thought to induce structural changes in the P450cam active site that couple electron transfer to substrate hydroxylation. The nature of these structural changes has remained unclear until a particular mutant of P450cam (Leu358Pro) was found to exhibit spectral perturbations similar to those observed in wild type P450cam bound to Pdx. The crystal structure of the L358P variant has provided some important insights on what might be happening when Pdx docks. In addition to these studies, many Pdx mutants have been analyzed to identify regions important for electron transfer. Somewhat surprisingly, we found that Pdx residues predicted to be at the P450cam-Pdx interface play different roles in the reduction of ferric P450cam and the ferrous P450-O(2) complex. More recently we have succeeded in obtaining the structure of a chemically cross-linked Pdr-Pdx complex. This fusion protein represents a valid model for the noncovalent Pdr-Pdx complex as it retains the redox activities of native Pdr and Pdx and supports monooxygenase reactions catalyzed by P450cam. The insights gained from these studies will be summarized in this review.

Using molecular dynamics to probe the structural basis for enhanced stability in thermal stable cytochromes P450

High-temperature molecular dynamics (MD) has been used to assess if MD can be employed as a useful tool for probing the structural basis for enhanced stability in thermal stable cytochromes P450. CYP119, the most thermal stable P450 known, unfolds more slowly during 500 K MD simulations than P450s that melt at lower temperatures, P450cam and P450cin. A comparison of the 500 K MD trajectories shows that the Cys ligand loop, a critically important structural feature just under the heme, in both P450cin and P450cam completely unfolds while this region is quite stable in CYP119. In CYP119, this region is stabilized by tight nonpolar interactions involving Tyr26 and Leu308. The corresponding residues in P450cam are Gly and Thr, respectively. The in silico generated Y26A/L308A CYP119 double mutant is substantially less stable than wild-type CYP119, and the Cys ligand loop unfolds in a manner similar to that of P450cam. The MD thus has identified a potential "hot spot" important for stability. As an experimental test of the MD results, the Y26A/L308A double mutant was prepared, and thermal melting curves show that the double mutant exhibits a melting temperature (T(m)) 16 degrees C lower than that of wild-type CYP119. Control mutations that were predicted by MD not to destabilize the protein were also generated, and the experimental melting temperature was not significantly different from that of the wild-type enzyme. Therefore, high-temperature MD is a useful tool in predicting the structural underpinnings of thermal stability in P450s.

Novel haem co-ordination variants of flavocytochrome P450 BM3

Bacillus megaterium flavocytochrome P450 BM3 is a catalytically self-sufficient fatty acid hydroxylase formed by fusion of soluble NADPH–cytochrome P450 reductase and P450 domains. Selected mutations at residue 264 in the haem (P450) domain of the enzyme lead to novel amino acid sixth (distal) co-ordination ligands to the haem iron. The catalytic, spectroscopic and thermodynamic properties of the A264M, A264Q and A264C variants were determined in both the intact flavocytochromes and haem domains of P450 BM3. Crystal structures of the mutant haem domains demonstrate axial ligation of P450 haem iron by methionine and glutamine ligands trans to the cysteine thiolate, creating novel haem iron ligand sets in the A264M/Q variants. In contrast, the crystal structure of the A264C variant reveals no direct interaction between the introduced cysteine side chain and the haem, although EPR data indicate Cys264 interactions with haem iron in solution. The A264M haem potential is elevated by comparison with wild-type haem domain, and substrate binding to the A264Q haem domain results in a ∼360 mV increase in potential. All mutant haem domains occupy the conformation adopted by the substrate-bound form of wild-type BM3, despite the absence of added substrate. The A264M mutant (which has higher dodecanoate affinity than wild-type BM3) co-purifies with a structurally resolved lipid. These data demonstrate that a single mutation at Ala264 is enough to perturb the conformational equilibrium between substrate-free and substrate-bound P450 BM3, and provide firm structural and spectroscopic data for novel haem iron ligand sets unprecedented in Nature.

Spectra and kinetic studies of the compound I derivative of cytochrome P450 119

The Compound I derivative of cytochrome P450 119 (CYP119) was produced by laser flash photolysis of the corresponding Compound II derivative, which was first prepared by reaction of the resting enzyme with peroxynitrite. The UV-vis spectrum of the Compound I species contained an asymmetric Soret band that could be resolved into overlapping transitions centered at approximately 367 and approximately 416 nm and a Q band with lambda(max) approximately 650 nm. Reactions of the Compound I derivative with organic substrates gave epoxidized (alkene oxidation) and hydroxylated (C-H oxidation) products, as demonstrated by product studies and oxygen-18 labeling studies. The kinetics of oxidations by CYP119 Compound I were measured directly; the reactions included hydroxylations of benzyl alcohol, ethylbenzene, Tris buffer, lauric acid, and methyl laurate and epoxidations of styrene and 10-undecenoic acid. Apparent second-order rate constants, equal to the product of the equilibrium binding constant (K(bind)) and the first-order oxidation rate constant (k(ox)), were obtained for all of the substrates. The oxidations of lauric acid and methyl laurate displayed saturation kinetic behavior, which permitted the determination of both K(bind) and k(ox) for these substrates. The unactivated C-H positions of lauric acid reacted with a rate constant of k(ox) = 0.8 s(-1) at room temperature. The CYP119 Compound I derivative is more reactive than model Compound I species [iron(IV)-oxo porphyrin radical cations] and similar in reactivity to the Compound I derivative of the heme-thiolate enzyme chloroperoxidase. Kinetic isotope effects (kH/kD) for oxidations of benzyl alcohol and ethylbenzene were small, reflecting the increased reactivity of the Compound I derivative in comparison to models. Nonetheless, CYP119 Compound I apparently is much less reactive than the oxidizing species formed in the P450 cam reaction cycle. Studies of competition kinetics employing CYP119 activated by hydrogen peroxide indicated that the same oxidizing transient is formed in the photochemical reaction and in the hydrogen peroxide shunt reaction.

Characterization of the peroxidase activity of CYP119, a thermostable P450 from Sulfolobus acidocaldarius

We report the cloning, expression, and purification of CYP119, a thermostable enzyme previously thought to derive from Sulfolobus solfataricus. Sequence analysis suggested that, in contrast to the conclusions of earlier studies, the enzyme stems from the closely related Sulfolobus acidocaldarius, and we were indeed able to clone the gene from the genomic DNA of this organism. For the first time, we report here on the peroxidase activity of this enzyme and the optimization of the associated reaction parameters. The optimized reaction conditions were then applied to the biocatalytic epoxidation of styrene. The values obtained for k(cat) (78.2+/-20.6 min(-1)) and K(M) (9.2+/-4.3 mM) indicated an approximately 100-fold increased catalytic activity over previously reported results.

Engineering and assaying of cytochrome P450 biocatalysts

Cytochrome P450s constitute a highly fascinating superfamily of enzymes which catalyze a broad range of reactions. They are essential for drug metabolism and promise industrial applications in biotechnology and biosensing. The constant search for cytochrome P450 enzymes with enhanced catalytic performances has generated a large body of research. This review will concentrate on two key aspects related to the identification and improvement of cytochrome P450 biocatalysts, namely the engineering and assaying of these enzymes. To this end, recent advances in cytochrome P450 development are reported and commonly used screening methods are surveyed.

Cytochrome P450 systems—biological variations of electron transport chains

Cytochromes P450 (P450) are hemoproteins encoded by a superfamily of genes nearly ubiquitously distributed in different organisms from all biological kingdoms. The reactions carried out by P450s are extremely diverse and contribute to the biotransformation of drugs, the bioconversion of xenobiotics, the bioactivation of chemical carcinogens, the biosynthesis of physiologically important compounds such as steroids, fatty acids, eicosanoids, fat-soluble vitamins and bile acids, the conversion of alkanes, terpenes and aromatic compounds as well as the degradation of herbicides and insecticides. Cytochromes P450 belong to the group of external monooxygenases and thus receive the necessary electrons for oxygen cleavage and substrate hydroxylation from different redox partners. The classical as well as the recently discovered P450 redox systems are compiled in this paper and classified according to their composition.

Protein dynamics and imidazole binding in cytochrome P450 enzymes

P450 (cytochrome P450) enzymes have major roles in the biosynthesis of endogenous factors such as steroids and eicosanoids, in the termination of the action of endogenous factors such as retinoic acid, in the metabolism of most drugs and xenobiotics and in the generation of toxic and carcinogenic products. Understanding the determinants of the substrate and inhibitor specificities of these enzymes is important for drug design. The crystallographic analysis of the deformability of two bacterial P450 active sites associated with the binding of azole (a class of inhibitors with an imidazole or triazole ring that co-ordinates to the haem iron) inhibitors described in the present study illustrates the importance of protein conformational malleability in the binding of imidazole derivatives.

Cytochrome P450--redox partner fusion enzymes

The cytochromes P450 (P450s) are a broad class of heme b-containing mono-oxygenase enzymes. The vast majority of P450s catalyse reductive scission of molecular oxygen using electrons usually derived from coenzymes (NADH and NADPH) and delivered from redox partner proteins. Evolutionary advantages may be gained by fusion of one or more redox partners to the P450 enzyme in terms of e.g. catalytic efficiency. This route was taken by the well characterized flavocytochrome P450(BM3) system (CYP102A1) from Bacillus megaterium, in which soluble P450 and cytochrome P450 reductase enzymes are covalently linked to produce a highly efficient electron transport system for oxygenation of fatty acids and related molecules. However, genome analysis and ongoing enzyme characterization has revealed that there are a number of other novel classes of P450-redox partner fusion enzymes distributed widely in prokaryotes and eukaryotes. This review examines our current state of knowledge of the diversity of these fusion proteins and explores their structural composition and evolutionary origins.

Protein film electrochemistry of microsomes genetically enriched in human cytochrome p450 monooxygenases

This communication demonstrates direct electron delivery from electrodes to cyt P450 reductases in stable films ( approximately 100 nm thick) of genetically enriched CYP1A2 and CYP3A4 microsomes made by layer-by-layer assembly with polyions. Reversible voltammetry of films containing genetically enriched cyt P450 monooxygenase microsomes was shown to involve cyt P450 reductase by comparison with the pure rabbit reductase and by lack of characteristic reactions of iron heme enzymes, such as reaction of the FeII form with CO and catalytic electrochemical reduction of oxygen and hydrogen peroxide. The microsome films were activated electrochemically to catalyze styrene epoxidation, consistent with the pathway utilized in the human liver, although further work is required to establish this definitively.

Reconstitution of β-carotene hydroxylase activity of thermostable CYP175A1 monooxygenase

CYP175A1 is a thermostable P450 Monooxygenase from Thermus thermophilus HB27, demonstrating in vivo activity towards beta-carotene. Activity of CYP175A1 was reconstituted in vitro using artificial electron transport proteins. First results were obtained in the mixture with a crude Escherichia coli cell extract at 37 degrees C. In this system, beta-carotene was hydroxylated to beta-cryptoxanthin. The result indicated the presence of electron transport enzymes among the E. coli proteins, which are suitable for CYP175A1. However, upon in vitro reconstitution of CYP175A1 activity with purified recombinant flavodoxin and flavodoxin reductase from E. coli, only very low beta-cryptoxanthin production was observed. Remarkably, with another artificial electron transport system, putidaredoxin and putidaredoxin reductase from Pseudomonas putida, purified CYP175A1 enzyme hydroxylated beta-carotene at 3- and also 3'-positions, resulting in beta-cryptoxanthin and zeaxanthin. Under the optimal reaction conditions, the turnover rate of the enzyme reached 0.23 nmol beta-cryptoxanthin produced per nmol P450 per min.

Creation of a P450 Array toward High-throughput Analysis

The rapid metabolism testing of many new chemical entities enables unsuitable candidates to be eliminated from consideration at an early stage of the drug discovery process. We have developed a P450 array toward high-throughput analysis of P450-mediated metabolic reaction. The microsomes containing expressed human P450 enzymes were immobilized on the microassay plate using sol-gel chemistry. A thin-film hydrogel containing microsomes was fabricated using aqueous silicate as a starting material. The TEM image clearly showed that the nanoclusters derived from the silicate formed branched chains, and microsomes were entrapped in the silica network. The different P450 isozymes were immobilized on the microassay plate, and the metabolites by each isozyme were visualized as fluorescent images, which creates opportunity for the inhibitor assays. This method offers several advantages over use of conventional enzyme preparations, including increased storage stability, ease of product isolation from the incubation mixture, and the ability to recover and reuse the enzyme. Because this methodology enabled the development of assay system using P450 that is unstable and involves other enzymes for its function, it can be applicable to various screening assays that require complicated reactions involving many biological components.

Thermophilic cytochrome P450 enzymes

Thermophilic cytochrome P450 enzymes are of potential interest from structural, mechanistic, and biotechnological points of view. The structures and properties of two such enzymes, CYP119 and CYP175A1, have been investigated and provide the foundation for future work on thermophilic P450 enzymes.

Cytochrome P450 biosensors—a review

Cytochrome P450 (CYP) is a large family of enzymes containing heme as the active site. Since their discovery and the elucidation of their structure, they have attracted the interest of scientist for many years, particularly due to their catalytic abilities. Since the late 1970s attempts have concentrated on the construction and development of electrochemical sensors. Although sensors based on mediated electron transfer have also been constructed, the direct electron transfer approach has attracted most of the interest. This has enabled the investigation of the electrochemical properties of the various isoforms of CYP. Furthermore, CYP utilized to construct biosensors for the determination of substrates important in environmental monitoring, pharmaceutical industry and clinical practice.

Cyclopropyl containing fatty acids as mechanistic probes for cytochromes P450

[reaction: see text] The mechanism of aliphatic hydroxylation by cytochromes P450 has been the subject of intense debate with several proposed mechanistic alternatives. Various cyclopropyl containing compounds (radical clocks), which can produce both unrearranged and ring opened products upon oxidation, have been key tools in these investigations. In this study, we introduce several cyclopropyl containing fatty acids 1a-4a with which to probe the mechanism of P450s capable of fatty acid hydroxylation. The probes are shown to be capable of distinguishing radical from cationic intermediates due to the rapid equilibration of isomeric cyclopropyl cations. Ring opening of a radical intermediate in an oxidative transformation is expected to yield a single rearranged alcohol, whereas a cation isomerizes prior to ring opening, leading to two isomeric homoallylic alcohols. Oxidation of these probes by P450(BM3) and P450(BioI) gives results consistent with a radical but not a cationic intermediate in fatty acid hydroxylation by these enzymes. Quantitation of the unrearranged and ring opened products gives remarkably homogeneous rates for oxygen rebound of (2-3) x 10(10) s(-1). The effects of introduction of a cyclopropane ring into a fatty acid upon the regiochemistry of hydroxylation are discussed.

The Sulfolobus solfataricus electron donor partners of thermophilic CYP119: an unusual non-NAD(P)H-dependent cytochrome P450 system

CYP119 from Sulfolobus solfataricus is the first well-characterized thermophilic cytochrome P450 enzyme. The endogenous substrate for this enzyme is not known but it hydroxylates lauric acid in a reaction supported by surrogate mesophilic electron donors. However, reconstitution of a high-temperature catalytic system requires identification of the normal thermophilic electron donor partners of CYP119. Here, we describe cloning, expression in Escherichia coli, and characterization of the requisite electron donor partners from S. solfataricus. One is a thermostable ferredoxin and the second a 2-oxoacid-ferredoxin oxidoreductase that utilizes pyruvic acid rather than NAD(P)H as the source of reducing equivalents. CYP119 is the only cytochrome P450 to date known to obtain electrons from a non-NAD(P)H-dependent protein. The two thermophilic partners have been used to reconstitute a catalytic system that hydroxylates lauric acid at 70 degrees C, and the optimal conditions for this system have been defined. This first high-temperature in vitro catalytic system represents an important step in the development of industrially relevant catalysts.

High-Temperature Electrocatalysis Using Thermophilic P450 CYP119: Dehalogenation of CCl4 to CH4

The use of a thermophilic cytochrome P450, CYP119, in electrocatalytic dehalogenations of C1 halocarbon solvents is studied. Temperature stable enzyme-modified electrodes were constructed using sol-gel and polymeric surfactant approaches. CYP119 deposited in a dimethyldidodecylammonium poly(p-styrene sulfonate) (DDAPSS) film has good retention of electrochemical activity up to 80 degrees C. At potentials approaching the FeII/I couple, the CYP119/DDAPSS films demonstrate high catalytic dehalogenations of the C1 chloromethanes CCl4, CHCl3, and CH2Cl2. Product analysis identified mixtures of sequentially dechlorinated products up to methane; no evidence for radical-coupled products was observed. The yield of methane from the CYP119-catalyzed reduction of CCl4 is increased 35-fold from 25 degrees C to 55 degrees C. In combination with the lack of C2 products, the facility of an overall eight-electron reductive dehalogenation suggests that the substrate is constrained within the protein during electrocatalytic turnover.