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

Cytochrome P450 monooxygenases in whole-cell format: Application notes from a biotechnological perspective

Cytochrome P450 monooxygenases (CYPs) are versatile heme-containing enzymes found across a diverse range of organisms. They play essential roles in hydrocarbon degradation, fatty acid metabolism, hormone biosynthesis, and xenobiotic detoxification. Their remarkable catalytic potential makes them attractive for biotechnological applications, particularly in the production of fine chemicals, pharmaceuticals, and bioactive compounds. However, scaling up the use of purified CYPs presents significant challenges due to their reliance on specific electron transfer partners (e.g., ferredoxin reductase and ferredoxin), cosubstrates such as NAD(P)H, and the tendency of these enzymes to lose activity outside of their native cellular environment. These factors result in costly and inefficient processes when purified enzymes are used in isolation. Whole-cell biotransformation offers a promising alternative, where CYPs are produced and function within living microbial hosts, providing a natural source of electron transfer partners and cosubstrates. This approach simplifies the reaction setup, enhances enzyme stability, and circumvents the need for costly purified components, thus facilitating industrial-scale applications. Moreover, whole-cell systems can leverage genetic engineering to optimize gene expression, improve substrate specificity, and increase yields. By exploring CYPs in a whole-cell format, this chapter highlights the potential of these enzymes to become a sustainable, cost-effective solution for the synthesis of high-value compounds, paving the way for environmentally friendly biocatalytic processes in the chemical and pharmaceutical industries.

Cytochrome P450 monooxygenase systems: Diversity and plasticity for adaptive stress response

Superfamily of cytochromes P450 (CYPs) is composed of heme-thiolate-containing monooxygenase enzymes, which play crucial roles in the biosynthesis, bioactivation, and detoxification of a variety of organic compounds, both endogenic and exogenic. Majority of CYP monooxygenase systems are multi-component and contain various redox partners, cofactors and auxiliary proteins, which contribute to their diversity in both prokaryotes and eukaryotes. Recent progress in bioinformatics and computational biology approaches make it possible to undertake whole-genome and phylogenetic analyses of CYPomes of a variety of organisms. Considerable variations in sequences within and between CYP families and high similarity in secondary and tertiary structures between all CYPs along with dramatic conformational changes in secondary structure elements of a substrate binding site during catalysis have been reported. This provides structural plasticity and substrate promiscuity, which underlie functional diversity of CYPs. Gene duplication and mutation events underlie CYP evolutionary diversity and emergence of novel selectable functions, which provide the involvement of CYPs in high adaptability to changing environmental conditions and dietary restrictions. In our review, we discuss the recent advancements and challenges in the elucidating the evolutionary origin and mechanisms underlying the CYP monooxygenase system diversity and plasticity. Our review is in the view of hypothesis that diversity of CYP monooxygenase systems is translated into the broad metabolic profiles, and this has been acquired during the long evolutionary time to provide structural plasticity leading to high adaptative capabilities to environmental stress conditions.

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.

Characterization of a thermophilic cytochrome P450 of the CYP203A subfamily from Binh Chau hot spring in Vietnam

Cytochromes P450 (CYPs or P450s) comprise a superfamily of heme-containing monooxygenases that are involved in a variety of biological processes. CYPs have broad utilities in industry, but most exhibit low thermostability, limiting their use on an industrial scale. Highly thermostable enzymes can be obtained from thermophiles in geothermal areas, including hot springs, offshore oil-producing wells and volcanoes. Here, we report the identification of a gene encoding for a thermophilic CYP from the Binh Chau hot spring metagenomic database, which was designated as P450-T2. The deduced amino acid sequence showed the highest identity of 73.15% with CYP203A1 of Rhodopseudomonas palustris, supporting that P450-T2 is a member of the CYP203A subfamily. Recombinant protein expression yielded 541 nm. The optimal temperature and pH of P450-T2 were 50 °C and 8.0, respectively. The half-life of P450-T2 was 50.2 min at 50 °C, and its melting temperature was 56.80 ± 0.08 °C. It was found to accept electrons from all tested redox partners systems, with BmCPR-Fdx2 being the most effective partner. Screening for putative substrates revealed binding of phenolic compounds, such as l-mimosine and emodin, suggesting a potential application of this new thermophilic P450 in the production of the corresponding hydroxylated products.

Cytochromes P450 (P450s): A review of the class system with a focus on prokaryotic P450s

Cytochromes P450 (P450s) are a large superfamily of heme-containing monooxygenases. P450s are found in all Kingdoms of life and exhibit incredible diversity, both at sequence level and also on a biochemical basis. In the majority of cases, P450s can be assigned into one of ten classes based on their associated redox partners, domain architecture and cellular localization. Prokaryotic P450s now represent a large diverse collection of annotated/known enzymes, of which many have great potential biocatalytic potential. The self-sufficient P450 classes (Class VII/VIII) have been explored significantly over the past decade, with many annotated and biochemically characterized members. It is clear that the prokaryotic P450 world is expanding rapidly, as the number of published genomes and metagenome studies increases, and more P450 families are identified and annotated (CYP families).

Coupling efficiency in light-driven hybrid P450BM3 and CYP119 enzymes

The light-driven hybrid P450 enzyme approach utilizing the photochemical properties of a covalently attached Ru(II)-diimine photosensitizer was extended to the archaeal Sulfolobus acidocaldarius CYP119 enzyme leading to high photocatalytic activity in the hydroxylation of the chromogenic substrate, 11-nitrophenoxyundecanoic acid. The determined k_cat was greater than those reported with various natural redox partners. In addition, the sacrificial electron donor, diethyldithiocarbamate, used in the photocatalytic reaction is shown to play a dual role. It acts as an efficient quencher of the Ru(II) excited state leading to a highly reducing species necessary to inject electrons into the heme. It is also known for its antioxidant properties and is shown herein to be a useful probe to determine coupling efficiency in the light-driven hybrid enzymes.

Enhanced Activity and Substrate Specificity by Site-Directed Mutagenesis for the P450 119 Peroxygenase Catalyzed Sulfoxidation of Thioanisole

P450 119 peroxygenase was found to catalyze the sulfoxidation of thioanisole and the sulfonation of sulfoxide in the presence of tert-butyl hydroperoxide (TBHP) for the first time with turnover rates of 1549 min^-1 and 196 min^-1 respectively. Several mutants were designed to improve the peroxygenation activity and thioanisole specificity by site-directed mutagenesis. The F153G/T213G mutant gave an increase of sulfoxide yield and a decrease of sulfone yield. Moreover the S148P/I161T/K199E/T214V mutant and the K199E mutant with acidic Glu residue contributed to improving the product ratio of sulfoxide to sulfone. Addition of short-alkyl-chain organic acids to the P450 119 peroxygenase-catalyzed sulfur oxidation of thioanisole was investigated. Octanoic acid was found to induce a preferred sulfoxidation of thioanisole catalyzed by the F153G/T213G mutant to give approximately 2.4-fold increase in turnover rate with a k _cat value of 3687 min^-1 relative to that of the wild-type, and by the F153G mutant to give the R-sulfoxide up to 30 % ee. The experimental control and the proposed mechanism for the P450 119 peroxygenase-catalyzed sulfoxidation of thioanisole in the presence of octanoic acid suggested that octanoic acid could partially occupy the substrate pocket; meanwhile the F153G mutation could enhance the substrate specificity, which could lead to efficiently regulate the spatial orientation of thioanisole and facilitate the formation of Compound I. This is the most effective catalytic system for the P450 119 peroxygenase-catalyzed sulfoxidation of thioanisole.

Mechanistic Studies of Fatty Acid Activation by CYP152 Peroxygenases Reveal Unexpected Desaturase Activity

The majority of cytochrome P450 enzymes (CYPs) predominantly operate as monooxygenases, but recently a class of P450 enzymes was discovered, that can act as peroxygenases (CYP152). These enzymes convert fatty acids through oxidative decarboxylation, yielding terminal alkenes, and through α- and β-hydroxylation to yield hydroxy-fatty acids. Bioderived olefins may serve as biofuels, and hence understanding the mechanism and substrate scope of this class of enzymes is important. In this work, we report on the substrate scope and catalytic promiscuity of CYP OleT_JE and two of its orthologues from the CYP152 family, utilizing α-monosubstituted branched carboxylic acids. We identify α,β-desaturation as an unexpected dominant pathway for CYP OleT_JE with 2-methylbutyric acid. To rationalize product distributions arising from α/β-hydroxylation, oxidative decarboxylation, and desaturation depending on the substrate’s structure and binding pattern, a computational study was performed based on an active site complex of CYP OleT_JE containing the heme cofactor in the substrate binding pocket and 2-methylbutyric acid as substrate. It is shown that substrate positioning determines the accessibility of the oxidizing species (Compound I) to the substrate and hence the regio- and chemoselectivity of the reaction. Furthermore, the results show that, for 2-methylbutyric acid, α,β-desaturation is favorable because of a rate-determining α-hydrogen atom abstraction, which cannot proceed to decarboxylation. Moreover, substrate hydroxylation is energetically impeded due to the tight shape and size of the substrate binding pocket.

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.

Novel insights into gene regulation of the rudivirus SIRV2 infecting Sulfolobus cells

Microarray analysis of infection by a lytic Sulfolobus rudivirus, SIRV2, revealed both the temporal expression of viral genes and the differential regulation of host genes. A highly susceptible strain derived from Sulfolobus solfataricus P2 with a large genomic deletion spanning CRISPR clusters A to D was infected with SIRV2, and subjected to a microarray analysis. Transcripts from a few viral genes were detected at 15 min post-infection and all except one were expressed within 2 h. The earliest expressed genes were located mainly at the termini of the linear viral genome while later expressed genes were concentrated in the central region. Timing of the expression correlated with the known or predicted functions of the viral gene products and, thus, should facilitate functional characterization of many hypothetical viral genes. Evaluation of the microarray data with quantitative reverse-transcription PCR analyses of a few selected viral genes revealed a good correlation between the two methods. Expression of about 3,000 host genes was examined. Seventy-two were downregulated>2-fold that were mainly associated with stress response and vesicle formation, as well as chromosome structure maintenance, which appears to contribute to host chromosome degradation and cellular collapse. A further 76 host genes were upregulated>2-fold and they were dominated by genes associated with metabolism and membrane transport, including phosphate transport and DNA precursor synthesis. The altered transcriptional patterns suggest that the virus reprograms the host cellular machinery to facilitate its own DNA replication and to inhibit cellular processes required for defense against viruses.

Microbial cytochromes P450: biodiversity and biotechnology. Where do cytochromes P450 come from, what do they do and what can they do for us?

The first eukaryote genome revealed three yeast cytochromes P450 (CYPs), hence the subsequent realization that some microbial fungal genomes encode these proteins in 1 per cent or more of all genes (greater than 100) has been surprising. They are unique biocatalysts undertaking a wide array of stereo- and regio-specific reactions and so hold promise in many applications. Based on ancestral activities that included 14α-demethylation during sterol biosynthesis, it is now seen that CYPs are part of the genes and metabolism of most eukaryotes. In contrast, Archaea and Eubacteria often do not contain CYPs, while those that do are frequently interesting as producers of natural products undertaking their oxidative tailoring. Apart from roles in primary and secondary metabolism, microbial CYPs are actual/potential targets of drugs/agrochemicals and CYP51 in sterol biosynthesis is exhibiting evolution to resistance in the clinic and the field. Other CYP applications include the first industrial biotransformation for corticosteroid production in the 1950s, the diversion into penicillin synthesis in early mutations in fungal strain improvement and bioremediation using bacteria and fungi. The vast untapped resource of orphan CYPs in numerous genomes is being probed and new methods for discovering function and for discovering desired activities are being investigated.

Characterization of cytochrome P450 monooxygenase CYP154H1 from the thermophilic soil bacterium Thermobifida fusca

Cytochrome P450 monooxygenases are valuable biocatalysts due to their ability to hydroxylate unactivated carbon atoms using molecular oxygen. We have cloned the gene for a new cytochrome P450 monooxygenase, named CYP154H1, from the moderately thermophilic soil bacterium Thermobifida fusca. The enzyme was overexpressed in Escherichia coli at up to 14% of total soluble protein and purified to homogeneity in three steps. CYP154H1 activity was reconstituted using putidaredoxin reductase and putidaredoxin from Pseudomonas putida DSM 50198 as surrogate electron transfer partners. In biocatalytic reactions with different aliphatic and aromatic substrates of varying size, the enzyme converted small aromatic and arylaliphatic compounds like ethylbenzene, styrene, and indole. Furthermore, CYP154H1 also accepted different arylaliphatic sulfides as substrates chemoselectively forming the corresponding sulfoxides and sulfones. The enzyme is moderately thermostable with an apparent melting temperature of 67°C and exhibited still 90% of initial activity after incubation at 50°C.

Structural diversity of cytochrome P450 enzyme system

Cytochrome P450 enzyme system consists of P450 and its NAD(P)H-linked reductase or reducing system, and catalyses monooxygenation reactions. The most prevalent type in eukaryotic organisms is 'microsomes type', which consists of membrane-bound P450 and NADPH-P450 reductase. The second type is 'mitochondria type', in which P450 is bound to the inner membrane while the reducing system consisting of an NADPH-linked flavoprotein and a ferredoxin-type iron-sulphur protein is soluble in the matrix space. The third type is 'bacteria type', in which both P450 and the reducing system are soluble in the cytoplasm. In addition to these three types, several forms of P450-reductase fusion proteins have been found in prokaryotic organisms. On the other hand, some P450s catalyse the re-arrangement of the oxygen atoms in the substrate molecules that does not require the supply of reducing equivalents for the reaction. A peculiar P450, P450nor, receives electrons directly from NADH for the reduction of nitric oxide.

Kinetics and activation parameters for oxidations of styrene by Compounds I from the cytochrome P450(BM-3) (CYP102A1) heme domain and from CYP119

Cytochrome P450 (CYP or P450) enzymes are ubiquitous in nature where they catalyze a vast array of oxidation reactions. The active oxidants in P450s have long been assumed to be iron(IV)-oxo porphyrin radical cations termed Compounds I, but P450 Compounds I have proven to be difficult to prepare. The recent development of an entry to these transients by photo-oxidation of the corresponding iron(IV)-oxo neutral porphyrin species (Compounds II) permits spectroscopic and kinetic studies. We report here application of the photo-oxidation method for production of Compound I from the heme domain of CYP102A1 (cytochrome P450(BM-3)), and product and kinetic studies of reactions of styrene with this Compound I transient and also Compound I from CYP119. The studies were performed at low temperatures in 1:1 (v:v) mixtures of glycerol and phosphate buffer. Single-turnover reactions at 0 degrees C gave styrene oxide in good yields. In kinetic studies conducted between -10 and -50 degrees C, both Compounds I displayed saturation kinetics permitting determinations of binding constants and first-order oxidation rate constants. Temperature-dependent functions for the binding constants and rate constants were determined for both Compounds I. In the temperature range studied, the Compound I transient from the CYP102A1 heme domain bound styrene more strongly than Compound I from CYP119, but the rate constants for oxidations of styrene by the latter were somewhat larger than those for the former. The temperature-dependent functions for the first-order oxidation reactions are as follows: log k = 13.2-15.2/2.303RT and log k = 13.3-14.6/2.303RT (kilocalories per mole) for Compounds I from the CYP102A1 heme domain and CYP119, respectively.

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.

Electron transfer between cytochrome P450cin and its FMN-containing redox partner, cindoxin

Cytochrome P450 reductase, which delivers electrons from NADPH to microsomal P450s, consists of a single polypeptide that contains both FAD and FMN. The bacterial P450cin utilizes a similar electron transport system except the FAD/FMN reductase consists of two separate polypeptides where the FMN protein, cindoxin, shuttles electrons between the FAD-containing cindoxin reductase and P450cin. Here we characterize the kinetics and specificity of electron transfer between cindoxin and P450cin as well as discuss the influence of possible binding surface interactions using homology models.

Electron Transport Pathway for a Streptomyces Cytochrome P450

Streptomyces and other bacterial actinomycete species produce many important natural products, including the majority of known antibiotics, and cytochrome P450 (P450) enzymes catalyze important biosynthetic steps. Relatively few electron transport pathways to P450s have been characterized in bacteria, particularly streptomycete species. One of the 18 P450s in Streptomyces coelicolor A3(2), P450 105D5, was found to bind fatty acids tightly and form hydroxylated products when electrons were delivered from heterologous systems. The six ferredoxin (Fdx) and four flavoprotein Fdx reductase (FDR) proteins coded by genes in S. coelicolor were expressed in Escherichia coli, purified, and used to characterize the electron transfer pathway. Of the many possibilities, the primary pathway was NADH --> FDR1 --> Fdx4 --> P450 105D5. The genes coding for FDR1, Fdx4, and P450 105D5 are located close together in the S. coelicolor genome. Several fatty acids examined were substrates, including those found in S. coelicolor extracts, and all yielded several products. Mass spectra of the products of lauric acid imply the 8-, 9-, 10-, and 11-hydroxy derivatives. Hydroxylated fatty acids were also detected in vivo in S. coelicolor. Rates of electron transfer between the proteins were measured; all steps were faster than overall hydroxylation and consistent with rates of NADH oxidation. Substrate binding, product release, and oxygen binding were relatively fast in the catalytic cycle; high kinetic deuterium isotope effects for all four lauric acid hydroxylations indicated that the rate of C-H bond breaking is rate-limiting in every case. Thus, an electron transfer pathway to a functional Streptomyces P450 has been established.

Untargeted analysis of mass spectrometry data for elucidation of metabolites and function of enzymes

A Matlab-based computer program termed Discovery of General Endo- and Xenobiotics (DoGEX) was developed, which uses wavelets and morphological analysis to process liquid chromatography-mass spectrometry (LC-MS) data. The output of the program is a list of integration areas as a function of retention time and molecular mass. A feature of the computer program is spectral filtering to facilitate the detection of chromatographic peaks with a particular isotopic ratio. The program DoGEX was used to automatically select oxidation products formed from felodipine (i.e., two chlorine atoms) and bromocriptine (one bromine atom) with cytochrome P450 3A4. The recognized isotope ratio can be changed to permit a natural or artificial mixture of isotopes to be monitored for selections. This computer program can be used to analyze LC-MS data for untargeted metabolic profiling experiments, e.g., to assign endogenous functions to newly characterized cytochrome P450 enzymes. In a representative example, an incubation of testosterone, NADPH, and a 1:1 16O2/18O2 mixture yielded products with M and M+2 ions resembling bromine doublets. Another use of the program is the subtraction of one set of tR, m/z data from another, e.g., in comparisons of changes in patterns during enzyme reactions.

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 monooxygenases: perspectives for synthetic application

Cytochrome P450 monooxygenases are versatile biocatalysts that introduce oxygen into a vast range of molecules. These enzymes catalyze diverse reactions in a regio- and stereoselective manner, and their properties have been used for drug development, bioremediation and the synthesis of fine chemicals and other useful compounds. However, the potential of P450 monooxygenases has not been fully exploited; there are some drawbacks limiting the broader implementation of these catalysts for commercial needs. Protein engineering has produced P450 enzymes with widely altered substrate specificities, substantially increased activity and higher stability. Furthermore, electrochemical and enzymatic approaches for the replacement or regeneration of NAD(P)H have been developed, enabling the more cost-effective use of P450 enzymes. In this review, we focus on the aspects relevant to the synthetic applications of P450 enzymes and their optimization for commercial needs.

Cytochrome p450 compound I

Cytochrome P450 enzymes (P450s) comprise a large class of enzymes that effect numerous oxidations in nature. The active oxidants in P450s are thought to be iron(IV)-oxo porphyrin radical cations termed Compounds I, and these intermediates have been sought since the discovery of P450s 40 years ago. We report formation of the Compound I derivative of a P450 enzyme by laser flash photolysis oxidation of the corresponding Compound II species, an iron(IV)-oxo neutral porphyrin intermediate. The Compound II derivative in turn was produced by oxidation of the P450 with peroxynitrite, which effected a net one-electron, oxo-transfer reaction to the iron(III) atom of the resting enzyme. For the P450 studied in this work, CYP119 from the thermophile Sulfolobus solfactaricus, the P450 Compound II derivative was stable for seconds at ambient temperature, and the Compound I transient decayed with a lifetime of ca. 200 ms.

Non-Redox Assisted Oxygen-Oxygen Bond Homolysis in Titanocene Alkylperoxide Complexes: [Cp(2)Ti(eta-OOBu)L], L = Cl, OTf, Br, OEt(2), Et(3)P

The titanium(IV) alkylperoxide complex Cp(2)Ti(OO(t)Bu)Cl (1) is formed on treatment of Cp(2)TiCl(2) with NaOO(t)Bu in THF at -20 degrees C. Treatment of 1 with AgOTf at -20 degrees C gives the triflate complex Cp(2)Ti(OO(t)Bu)OTf (2), which is rapidly converted to the bromide Cp(2)Ti(OO(t)Bu)Br (3) on addition of (n)Bu(4)NBr. The X-ray crystal structures of 1 and 3 both show eta(1)-OO(t)Bu ligands. Complex 2 is stable only below -20 degrees C; (1)H, (13)C, and (19)F NMR spectra suggest that it also contains an eta(1)-OO(t)Bu ligand. Removal of the chloride from 1 with [Ag(Et(2)O)(2)]BAr'(4) (Ar' = 3,5-(CF(3))(2)C(6)H(3))) yields the etherate complex [Cp(2)Ti(OO(t)Bu)(OEt(2))]BAr'(4) (4). Again, coordination of a fourth ligand to the Ti center indicates an eta(1)-OO(t)Bu ligand in 4. These peroxide complexes do not directly oxidize olefins or phosphines. For instance, the cationic etherate complex 4 reacts with excess Et(3)P simply by displacement of the ether to form [Cp(2)Ti(eta(1)-OO(t)Bu)(Et(3)P)]BAr'(4) (5). Compounds 1-5 all decompose by O-O bond homolysis, based on trapping and computational studies. The lack of direct oxygen atom transfer reactivity is likely due to the eta(1) coordination of the peroxide and the inability to adopt more reactive eta(2) geometry. DFT calculations indicate that the steric bulk of the (t)Bu group inhibits formation of the hypothetical [Cp(2)Ti(eta(2)-OO(t)Bu)](+) species.

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.

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.