Cytochrome P450 | |||||||||
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Identifiers | |||||||||
Symbol | p450 | ||||||||
Pfam | PF00067 | ||||||||
InterPro | IPR001128 | ||||||||
PROSITE | PDOC00081 | ||||||||
SCOP2 | 2cpp / SCOPe / SUPFAM | ||||||||
OPM superfamily | 39 | ||||||||
OPM protein | 2bdm | ||||||||
CDD | cd00302 | ||||||||
Membranome | 265 | ||||||||
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Cytochromes P450 (P450s or CYPs) are a superfamily of enzymes containing heme as a cofactor that mostly, but not exclusively, function as monooxygenases. [1] However, they are not omnipresent; for example, they have not been found in Escherichia coli . [2] In mammals, these enzymes oxidize steroids, fatty acids, xenobiotics, and participate in many biosyntheses. [1] By hydroxylation, CYP450 enzymes convert xenobiotics into hydrophilic derivatives, which are more readily excreted.
P450s are, in general, the terminal oxidase enzymes in electron transfer chains, broadly categorized as P450-containing systems. The term "P450" is derived from the spectrophotometric peak at the wavelength of the absorption maximum of the enzyme (450 nm) when it is in the reduced state and complexed with carbon monoxide. Most P450s require a protein partner to deliver one or more electrons to reduce the iron (and eventually molecular oxygen).
Genes encoding P450 enzymes, and the enzymes themselves, are designated with the root symbol CYP for the superfamily, followed by a number indicating the gene family, a capital letter indicating the subfamily, and another numeral for the individual gene. The convention is to italicise the name when referring to the gene. For example, CYP2E1 is the gene that encodes the enzyme CYP2E1—one of the enzymes involved in paracetamol (acetaminophen) metabolism. The CYP nomenclature is the official naming convention, although occasionally CYP450 or CYP450 is used synonymously. These names should never be used as according to the nomenclature convention (as they denote a P450 in family number 450). However, some gene or enzyme names for P450s are also referred to by historical names (e.g. P450BM3 for CYP102A1) or functional names, denoting the catalytic activity and the name of the compound used as substrate. Examples include CYP5A1, thromboxane A2 synthase, abbreviated to TBXAS1 (ThromBoXane A2Synthase 1), and CYP51A1, lanosterol 14-α-demethylase, sometimes unofficially abbreviated to LDM according to its substrate (Lanosterol) and activity (DeMethylation). [3]
The current nomenclature guidelines suggest that members of new CYP families share at least 40% amino-acid identity, while members of subfamilies must share at least 55% amino-acid identity. Nomenclature committees assign and track both base gene names (Cytochrome P450 Homepage Archived 2010-06-27 at the Wayback Machine ) and allele names (CYP Allele Nomenclature Committee). [4] [5]
Based on the nature of the electron transfer proteins, P450s can be classified into several groups: [6]
The most common reaction catalyzed by cytochromes P450 is a monooxygenase reaction, e.g., insertion of one atom of oxygen into the aliphatic position of an organic substrate (RH), while the other oxygen atom is reduced to water:
Many hydroxylation reactions (insertion of hydroxyl groups) use CYP enzymes, but many other hydroxylases exist. Alpha-ketoglutarate-dependent hydroxylases also rely on an Fe=O intermediate but lack hemes. Methane monooxygenase, which converts methane to methanol, are non-heme iron-and iron-copper-based enzymes. [7]
The active site of cytochrome P450 contains a heme-iron center. The iron is tethered to the protein via a cysteine thiolate ligand. This cysteine and several flanking residues are highly conserved in known P450s, and have the formal PROSITE signature consensus pattern [FW] - [SGNH] - x - [GD] - {F} - [RKHPT] - {P} - C - [LIVMFAP] - [GAD]. [8] In general, the P450 catalytic cycle proceeds as follows:
Mechanistic details, including the oxygen rebound mechanism, have been investigated with synthetic analogues, consisting of iron oxo heme complexes. [14]
Binding of substrate is reflected in the spectral properties of the enzyme, with an increase in absorbance at 390 nm and a decrease at 420 nm. This can be measured by difference spectroscopies and is referred to as the "type I" difference spectrum (see inset graph in figure). Some substrates cause an opposite change in spectral properties, a "reverse type I" spectrum, by processes that are as yet unclear. Inhibitors and certain substrates that bind directly to the heme iron give rise to the type II difference spectrum, with a maximum at 430 nm and a minimum at 390 nm (see inset graph in figure). If no reducing equivalents are available, this complex may remain stable, allowing the degree of binding to be determined from absorbance measurements in vitro [13] C: If carbon monoxide (CO) binds to reduced P450, the catalytic cycle is interrupted. This reaction yields the classic CO difference spectrum with a maximum at 450 nm. However, the interruptive and inhibitory effects of CO varies upon different CYPs such that the CYP3A family is relatively less affected. [15] [16]
Cytochrome P450 2E1 is a member of the cytochrome P450 mixed-function oxidase system, which is involved in the metabolism of xenobiotics in the body. This class of enzymes is divided up into a number of subcategories, including CYP1, CYP2, and CYP3, which as a group are largely responsible for the breakdown of foreign compounds in mammals.
Drug metabolism is the metabolic breakdown of drugs by living organisms, usually through specialized enzymatic systems. More generally, xenobiotic metabolism is the set of metabolic pathways that modify the chemical structure of xenobiotics, which are compounds foreign to an organism's normal biochemistry, such as any drug or poison. These pathways are a form of biotransformation present in all major groups of organisms and are considered to be of ancient origin. These reactions often act to detoxify poisonous compounds. The study of drug metabolism is called pharmacokinetics.
In biochemistry, flavin adenine dinucleotide (FAD) is a redox-active coenzyme associated with various proteins, which is involved with several enzymatic reactions in metabolism. A flavoprotein is a protein that contains a flavin group, which may be in the form of FAD or flavin mononucleotide (FMN). Many flavoproteins are known: components of the succinate dehydrogenase complex, α-ketoglutarate dehydrogenase, and a component of the pyruvate dehydrogenase complex.
Thromboxane A synthase 1 , also known as TBXAS1, is a cytochrome P450 enzyme that, in humans, is encoded by the TBXAS1 gene.
Any enzyme system that includes cytochrome P450 protein or domain can be called a P450-containing system.
Cytochrome P450 17A1 is an enzyme of the hydroxylase type that in humans is encoded by the CYP17A1 gene on chromosome 10. It is ubiquitously expressed in many tissues and cell types, including the zona reticularis and zona fasciculata of the adrenal cortex as well as gonadal tissues. It has both 17α-hydroxylase and 17,20-lyase activities, and is a key enzyme in the steroidogenic pathway that produces progestins, mineralocorticoids, glucocorticoids, androgens, and estrogens. More specifically, the enzyme acts upon pregnenolone and progesterone to add a hydroxyl (-OH) group at carbon 17 position (C17) of the steroid D ring, or acts upon 17α-hydroxyprogesterone and 17α-hydroxypregnenolone to split the side-chain off the steroid nucleus.
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 camphor 5-monooxygenase (EC 1.14.15.1) is an enzyme that catalyzes the chemical reaction
Cholesterol 24-hydroxylase, also commonly known as cholesterol 24S-hydroxylase, cholesterol 24-monooxygenase, CYP46, or CYP46A1, is an enzyme that catalyzes the conversion of cholesterol to 24S-hydroxycholesterol. It is responsible for the majority of cholesterol turnover in the human central nervous system. The systematic name of this enzyme class is cholesterol,NADPH:oxygen oxidoreductase (24-hydroxylating).
In enzymology, an unspecific monooxygenase (EC 1.14.14.1) is an enzyme that catalyzes the chemical reaction
Cytochrome P450 3A5 is a protein that in humans is encoded by the CYP3A5 gene.
Cytochrome P450 4F2 is a protein that in humans is encoded by the CYP4F2 gene. This protein is an enzyme, a type of protein that catalyzes chemical reactions inside cells. This specific enzyme is part of the superfamily of cytochrome P450 (CYP) enzymes, and the encoding gene is part of a cluster of cytochrome P450 genes located on chromosome 19.
CYP20A1 is a protein which in humans is encoded by the CYP20A1 gene.
(+)-Menthofuran synthase (EC 1.14.13.104, menthofuran synthase, (+)-pulegone 9-hydroxylase, (+)-MFS, cytochrome P450 menthofuran synthase) is an enzyme with systematic name (+)-pulegone,NADPH:oxygen oxidoreductase (9-hydroxylating). This enzyme catalyses the following chemical reaction
Tryptophan N-monooxygenase (EC 1.14.13.125, tryptophan N-hydroxylase, CYP79B1, CYP79B2, CYP79B3) is an enzyme with systematic name L-tryptophan,NADPH:oxygen oxidoreductase (N-hydroxylating). This enzyme catalyses the following chemical reaction
1,8-Cineole 2-endo-monooxygenase (EC 1.14.14.133, Formerly EC 1.14.13.156, P450cin, CYP176A, CYP176A1) is an enzyme with systematic name 1,8-cineole,NADPH:oxygen oxidoreductase (2-endo-hydroxylating). This enzyme catalyses the following chemical reaction
Cytochrome P450 omega hydroxylases, also termed cytochrome P450 ω-hydroxylases, CYP450 omega hydroxylases, CYP450 ω-hydroxylases, CYP omega hydroxylase, CYP ω-hydroxylases, fatty acid omega hydroxylases, cytochrome P450 monooxygenases, and fatty acid monooxygenases, are a set of cytochrome P450-containing enzymes that catalyze the addition of a hydroxyl residue to a fatty acid substrate. The CYP omega hydroxylases are often referred to as monoxygenases; however, the monooxygenases are CYP450 enzymes that add a hydroxyl group to a wide range of xenobiotic and naturally occurring endobiotic substrates, most of which are not fatty acids. The CYP450 omega hydroxylases are accordingly better viewed as a subset of monooxygenases that have the ability to hydroxylate fatty acids. While once regarded as functioning mainly in the catabolism of dietary fatty acids, the omega oxygenases are now considered critical in the production or break-down of fatty acid-derived mediators which are made by cells and act within their cells of origin as autocrine signaling agents or on nearby cells as paracrine signaling agents to regulate various functions such as blood pressure control and inflammation.
This article covers protein engineering of cytochrome (CYP) P450 enzymes. P450s are involved in a range of biochemical catabolic and anabolic process. Natural P450s can perform several different types of chemical reactions including hydroxylations, N,O,S-dealkylations, epoxidations, sulfoxidations, aryl-aryl couplings, ring contractions and expansions, oxidative cyclizations, alcohol/aldehyde oxidations, desaturations, nitrogen oxidations, decarboxylations, nitrations, as well as oxidative and reductive dehalogenations. Engineering efforts often strive for 1) improved stability 2) improved activity 3) improved substrate scope 4) enabled ability to catalyze unnatural reactions. P450 engineering is an emerging field in the areas of chemical biology and synthetic organic chemistry (chemoenzymatic).
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:
In biochemistry, cytochrome P450 enzymes have been identified in all kingdoms of life: animals, plants, fungi, protists, bacteria, and archaea, as well as in viruses. As of 2018, more than 300,000 distinct CYP proteins are known.