P450-containing systems

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Any enzyme system that includes cytochrome P450 protein or domain can be called a P450-containing system. [1] [2] [3] [4]

Contents

P450 enzymes usually function as a terminal oxidase in multicomponent electron-transfer chains, called P450-containing monooxygenase systems, although self-sufficient, non-monooxygenase P450s have been also described. All known P450-containing monooxygenase systems share common structural and functional domain architecture. Apart from the cytochrome itself, these systems contain one or more fundamental redox domains: FAD-containing flavoprotein or domain, FMN domain, ferredoxin and cytochrome b5. These ubiquitous redox domains, in various combinations, are widely distributed in biological systems. FMN domain, ferredoxin or cytochrome b5 transfer electrons between the flavin reductase (protein or domain) and P450. While P450-containing systems are found throughout all kingdoms of life, some organisms lack one or more of these redox domains.

FR/Fd/P450 systems

Mitochondrial and some bacterial P450 systems employ soluble Fe2S2 ferredoxins (Fd) that act as single electron carriers between FAD-containing ferredoxin reductase (FR) and P450. In mitochondrial monooxygenase systems, adrenodoxin functions as a soluble electron carrier between NADPH:adrenodoxin reductase and several membrane-bound P450s (CYP11A, CYP11B, CYP27). In bacteria, putidaredoxin, terpredoxin, and rhodocoxin serve as electron carriers between corresponding NADH-dependent ferredoxin reductases and soluble P450s (CYP101, CYP108, CYP116).

NADH putidaredoxin reductase putidaredoxinCYP101O2
NADHterpredoxin reductaseterpredoxinCYP108O2
NADHrhodocoxin reductaserhodocoxinCYP116O2
NADPH adrenodoxin reductase adrenodoxin CYP11A1 O2

The general scheme of electron flow in the P450 systems containing adrenodoxin-type ferredoxins is:

NAD(P)HFADFe2S2P450O2

The sterol demethylase system from Mycobacterium tuberculosis contains flavoprotein reductase A (FprA), bacterial-type Fe3S4 ferredoxin and CYP51 hemoprotein. [5]

NAD(P)HFADFe3S4P450O2

CPR/P450 systems

Eukaryotic microsomal P450 enzymes and some bacterial P450s receive electrons from a FAD- and FMN-containing enzyme known as cytochrome P450 reductase (CPR; EC 1.6.2.4). Microsomal CPR is membrane-bound protein that interacts with different P450s. In Bacillus megaterium and Bacillus subtilis, CPR is a C-terminal domain of CYP102, a single polypeptide self-sufficient soluble P450 system (P450 is an N-terminal domain). The general scheme of electron flow in the CPR/P450 system is:

NADPHFADFMNP450O2

CBR/b5/P450 systems

The ubiquitous electron-transport protein cytochrome b5 can serve as an effector (activator or inhibitor) of P450s. It was hypothesized that cytochrome b5 is involved in the transfer of the second electron to P450, either from CPR or from NADH:cytochrome b5 reductase (CBR; EC 1.6.2.2):

NADPHCPRcyt b5P450O2
NADHCBRcyt b5P450O2

The ability of the CBR/cytochrome b5 system to support P450 catalysis has been demonstrated in vitro using purified CBR and cytochrome b5 from Saccharomyces cerevisiae and CYP51 enzyme from Candida albicans. In this system, both the first and second electrons are donated by CBR.

NAD(P)HFADb5P450O2

FMN/Fd/P450 systems

An unusual one-component P450 system was originally found in Rhodococcus sp. NCIMB 9784 (CYP116B2). In this system, the N-terminal P450 domain is fused to the reductase domain that shows sequence similarity to phthalate dioxygenase reductase and consists, in its turn, of FMN-binding domain and C-terminal plant-type ferredoxin domain. [6] Similar systems have been identified in the heavy-metal-tolerant bacterium Ralstonia metallidurans (CYP116A1) and in several species of Burkolderia. The general scheme of electron flow in this system appears to be:

NADHFMNFe2S2P450O2

P450-only systems

Nitric oxide reductase (P450nor) is a P450 enzyme involved in denitrification in several fungal species. The best-characterized P450nor is CYP55A1 from Fusarium oxysporum . This enzyme does not have monooxygenase activity but is able to reduce nitric oxide (NO·) to form nitrous oxide (N2O) directly using NAD(P)H as electron donor:

NAD(P)HP450NO·

Fatty acid β-hydroxylase P450BSβ from Bacillus subtilis (CYP152A1) and fatty acid α-hydroxylase P450SPα from Pseudomonas paucimobilis (CYP152B1) catalyse the hydroxylation reaction of long-chain fatty acids using hydrogen peroxide (H2O2) as an oxidant. These enzymes do not require any reduction system for catalysis.

Allene oxide synthase (CYP74A; EC 4.2.1.92), fatty acid hydroperoxide lyase (CYP74B), prostacyclin synthase (CYP8; EC 5.3.99.4) and thromboxane synthase (CYP5; EC 5.3.99.5) are examples of P450 enzymes that do not require a reductase or molecular oxygen for their catalytic activity. Substrates for all these enzymes are fatty acid derivatives containing partially reduced dioxygen (either hydroperoxy or epidioxy groups).

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<span class="mw-page-title-main">Cytochrome P450</span> Class of enzymes

Cytochromes P450 are a superfamily of enzymes containing heme as a cofactor that mostly, but not exclusively, function as monooxygenases. In mammals, these proteins oxidize steroids, fatty acids, and xenobiotics, and are important for the clearance of various compounds, as well as for hormone synthesis and breakdown. In 1963, Estabrook, Cooper, and Rosenthal described the role of CYP as a catalyst in steroid hormone synthesis and drug metabolism. In plants, these proteins are important for the biosynthesis of defensive compounds, fatty acids, and hormones.

<span class="mw-page-title-main">CYP2E1</span> Protein-coding gene in the species Homo sapiens

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<span class="mw-page-title-main">Nitric oxide synthase</span> Enzyme catalysing the formation of the gasotransmitter NO(nitric oxide)

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<span class="mw-page-title-main">Nicotinamide adenine dinucleotide phosphate</span> Chemical compound

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<span class="mw-page-title-main">Flavin adenine dinucleotide</span> Redox-active coenzyme

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<span class="mw-page-title-main">Rieske protein</span> Protein family with an iron–sulfur center transferring electrons

Rieske proteins are iron–sulfur protein (ISP) components of cytochrome bc1 complexes and cytochrome b6f complexes and are responsible for electron transfer in some biological systems. John S. Rieske and co-workers first discovered the protein and in 1964 isolated an acetylated form of the bovine mitochondrial protein. In 1979 Trumpower's lab isolated the "oxidation factor" from bovine mitochondria and showed it was a reconstitutively-active form of the Rieske iron-sulfur protein
It is a unique [2Fe-2S] cluster in that one of the two Fe atoms is coordinated by two histidine residues rather than two cysteine residues. They have since been found in plants, animals, and bacteria with widely ranging electron reduction potentials from -150 to +400 mV.

<span class="mw-page-title-main">Flavoprotein</span> Protein family

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Cytochrome b<sub>5</sub>

Cytochromes b5 are ubiquitous electron transport hemoproteins found in animals, plants, fungi and purple phototrophic bacteria. The microsomal and mitochondrial variants are membrane-bound, while bacterial and those from erythrocytes and other animal tissues are water-soluble. The family of cytochrome b5-like proteins includes hemoprotein domains covalently associated with other redox domains in flavocytochrome cytochrome b2, sulfite oxidase, plant and fungal nitrate reductases, and plant and fungal cytochrome b5/acyl lipid desaturase fusion proteins.

<span class="mw-page-title-main">Cholesterol side-chain cleavage enzyme</span> Mammalian protein found in Homo sapiens

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<span class="mw-page-title-main">Cytochrome P450 reductase</span> Mammalian protein found in Homo sapiens

Cytochrome P450 reductase is a membrane-bound enzyme required for electron transfer from NADPH to cytochrome P450 and other heme proteins including heme oxygenase in the endoplasmic reticulum of the eukaryotic cell.

In enzymology, a ferredoxin-NADP+ reductase (EC 1.18.1.2) abbreviated FNR, is an enzyme that catalyzes the chemical reaction

<span class="mw-page-title-main">CYB5R3</span> Protein-coding gene in the species Homo sapiens

NADH-cytochrome b5 reductase 3 is an enzyme that in humans is encoded by the CYB5R3 gene.

<span class="mw-page-title-main">Adrenal ferredoxin</span> Mammalian protein found in Homo sapiens

Adrenal ferredoxin is a protein that in humans is encoded by the FDX1 gene. In addition to the expressed gene at this chromosomal locus (11q22), there are pseudogenes located on chromosomes 20 and 21.

<span class="mw-page-title-main">Adrenodoxin reductase</span> Protein-coding gene in the species Homo sapiens

Adrenodoxin reductase, was first isolated from bovine adrenal cortex where it functions as the first enzyme in the mitochondrial P450 systems that catalyze essential steps in steroid hormone biosynthesis. Examination of complete genome sequences revealed that adrenodoxin reductase gene is present in most metazoans and prokaryotes.

Flavoprotein pyridine nucleotide cytochrome reductases catalyse the interchange of reducing equivalents between one-electron carriers and the two-electron-carrying nicotinamide dinucleotides. The enzymes include ferredoxin-NADP+ reductases, plant and fungal NAD(P)H:nitrate reductases, cytochrome b5 reductases, cytochrome P450 reductases, sulphite reductases, nitric oxide synthases, phthalate dioxygenase reductase, and various other flavoproteins.

Oxidoreductase NAD-binding domain is an evolutionary conserved protein domain present in a variety of proteins that include, bacterial flavohemoprotein, mammalian NADH-cytochrome b5 reductase, eukaryotic NADPH-cytochrome P450 reductase, nitrate reductase from plants, nitric-oxide synthase, bacterial vanillate demethylase and others.

<span class="mw-page-title-main">Cytochrome P450 aromatic O-demethylase</span>

Cytochrome P450 aromatic O-demethylase is a bacterial enzyme that catalyzes the demethylation of lignin and various lignols. The net reaction follows the following stoichiometry, illustrated with a generic methoxy arene:

References

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