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Pelletier RD, Rettie AE, Kowalski JP. Improved methods for the detection of heme and protoporphyrin IX adducts and quantification of heme B from cytochrome P450 containing systems. J Chromatogr B Analyt Technol Biomed Life Sci 2023; 1231:123921. [PMID: 37956555 PMCID: PMC10842765 DOI: 10.1016/j.jchromb.2023.123921] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/19/2023] [Revised: 11/01/2023] [Accepted: 11/02/2023] [Indexed: 11/15/2023]
Abstract
Heme B is a critical prosthetic group for the function of numerous proteins including the cytochrome P450 (CYP) family of enzymes. CYP enzymes are involved in the metabolism of endogenous and xenobiotic molecules that are of central interest in drug development. Formation of reactive metabolites by CYPs can lead to heme modification and destruction of the enzyme. The structure of the adducted heme can provide key information on the mechanism of inactivation, which is of great interest during preclinical drug discovery. Historically, techniques to extract the modified heme or protoporphyrin IX species involved harsh extraction conditions and esterification of propionate groups to aid chromatography. We have developed a simplified extraction method and LC/MS chromatography system that does not require derivatization to quantify heme B and identify modified heme B species from multiple CYP-containing matrices. The method uses mass defect filter triggered data dependent MS2 scans to rapidly identify heme and protoporphyrin IX adducts. These methods may also be useful for the analysis of other heme variants and hemoproteins.
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Affiliation(s)
- Robert D Pelletier
- Department of Medicinal Chemistry, School of Pharmacy, University of Washington, Seattle, WA 98105, USA.
| | - Allan E Rettie
- Department of Medicinal Chemistry, School of Pharmacy, University of Washington, Seattle, WA 98105, USA
| | - John P Kowalski
- Department of Medicinal Chemistry, School of Pharmacy, University of Washington, Seattle, WA 98105, USA
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2
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Rivett ED, Addis HG, Dietz JV, Carroll-Deaton JA, Gupta S, Foreman KL, Dang MA, Fox JL, Khalimonchuk O, Hegg EL. Evidence that the catalytic mechanism of heme a synthase involves the formation of a carbocation stabilized by a conserved glutamate. Arch Biochem Biophys 2023; 744:109665. [PMID: 37348627 PMCID: PMC10529832 DOI: 10.1016/j.abb.2023.109665] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/05/2023] [Accepted: 06/07/2023] [Indexed: 06/24/2023]
Abstract
In eukaryotes and many aerobic prokaryotes, the final step of aerobic respiration is catalyzed by an aa3-type cytochrome c oxidase, which requires a modified heme cofactor, heme a. The conversion of heme b, the prototypical cellular heme, to heme o and ultimately to heme a requires two modifications, the latter of which is conversion of a methyl group to an aldehyde, catalyzed by heme a synthase (HAS). The N- and C-terminal halves of HAS share homology, and each half contains a heme-binding site. Previous reports indicate that the C-terminal site is occupied by a heme b cofactor. The N-terminal site may function as the substrate (heme o) binding site, although this has not been confirmed experimentally. Here, we assess the role of conserved residues from the N- and C-terminal heme-binding sites in HAS from prokaryotic (Shewanella oneidensis) and eukaryotic (Saccharomyces cerevisiae) species - SoHAS/CtaA and ScHAS/Cox15, respectively. A glutamate within the N-terminal site is found to be critical for activity in both types of HAS, consistent with the hypothesis that a carbocation forms transiently during catalysis. In contrast, the residue occupying the analogous C-terminal position is dispensable for enzyme activity. In SoHAS, the C-terminal heme ligands are critical for stability, while in ScHAS, substitutions in either heme-binding site have little effect on global structure. In both species, in vivo accumulation of heme o requires the presence of an inactive HAS variant, highlighting a potential regulatory role for HAS in heme o biosynthesis.
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Affiliation(s)
- Elise D Rivett
- Department of Biochemistry & Molecular Biology, Michigan State University, East Lansing, MI, 48824, USA
| | - Hannah G Addis
- Department of Chemistry and Biochemistry, College of Charleston, Charleston, SC, 29424, USA
| | - Jonathan V Dietz
- Department of Biochemistry, University of Nebraska, Lincoln, NE, 68588, USA
| | - Jayda A Carroll-Deaton
- Department of Chemistry and Biochemistry, College of Charleston, Charleston, SC, 29424, USA
| | - Shipra Gupta
- Department of Biochemistry & Molecular Biology, Michigan State University, East Lansing, MI, 48824, USA
| | - Koji L Foreman
- Department of Biochemistry & Molecular Biology, Michigan State University, East Lansing, MI, 48824, USA
| | - Minh Anh Dang
- Department of Biochemistry & Molecular Biology, Michigan State University, East Lansing, MI, 48824, USA
| | - Jennifer L Fox
- Department of Chemistry and Biochemistry, College of Charleston, Charleston, SC, 29424, USA.
| | - Oleh Khalimonchuk
- Department of Biochemistry, University of Nebraska, Lincoln, NE, 68588, USA; Nebraska Redox Biology Center, University of Nebraska, Lincoln, NE, 68588, USA; Fred & Pamela Buffett Cancer Center, Omaha, NE, 68198, USA.
| | - Eric L Hegg
- Department of Biochemistry & Molecular Biology, Michigan State University, East Lansing, MI, 48824, USA.
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Zhou J, Wang Z, Bian H, Jiang Y, Zhang R, Wang X. Structure of the Green Heme Isolated from Allylbenzene-Modified Chloroperoxidase: A Novel Heme Architecture Implicating the Mechanisms of CPO Inactivation and Epoxidation. Comput Struct Biotechnol J 2023; 21:2365-2372. [PMID: 37066123 PMCID: PMC10090953 DOI: 10.1016/j.csbj.2023.03.042] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/01/2022] [Revised: 03/21/2023] [Accepted: 03/24/2023] [Indexed: 03/29/2023] Open
Abstract
The chemical identification of the modified heme (the green heme) during chloroperoxidase catalyzed epoxidation of allylbenzene remains unestablished due to its high instability within the protein matrix, the absence of paramagnetically shifted signals, and the difficulty in obtaining crystals of the modified enzyme. We have established the unambiguous structure of the modified prosthetic heme group, which was extracted from the protein matrix using 2D NMR spectroscopy and LC-MS spectrometry. The modified heme was isolated as a µ-oxo dimer that can be quantitatively converted to the corresponding monomer. The depolymerized green heme displayed characteristic NMR signatures of iron porphyrin complexes, but no Nuclear Overhauser Effect was observable to assist in signal assignment. An alternative strategy was applied by removing the iron center of the green heme, resulting in a stable demetallated green porphyrin species. Complete assignment of all the NMR resonances in the demetallated green heme allowed us to establish the molecular architecture of the modified species as a novel N-alkylated heme. Decisive space correlations between the propyl protons of allylbenzene and the γ meso proton coupled with clear dipolar connectivities between the propyl-2H of the substrate and the β proton in the side chain of the propionic acid at carbon-6 of the porphyrin ring, clearly indicate that allylbenzene was covalently attached to the nitrogen atom of the pyrrole ring III of the prosthetic heme. In this study, the mechanism of green CPO formation and its relation to CPO catalyzed chiral transformations are also discussed. It is concluded that the double-phenyl clamp formed by two phenylalanine residues at the distal heme pocket plays a critical role in fine-tuning substrate orientation that determines the outcome of CPO catalyzed epoxidation of substituted styrenes.
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Affiliation(s)
- Jieying Zhou
- Department of Chemistry and Biochemistry, Florida International University, Miami, FL 33199, United States of America
| | - Zhonghua Wang
- Department of Chemistry and Biochemistry, Florida International University, Miami, FL 33199, United States of America
| | - Hedong Bian
- Key Laboratory of Chemistry and Engineering of Forest Products (State Ethnic Affairs Commission), Guangxi Collaborative Innovation Center for Chemistry and Engineering of Forest Products, School of Chemistry and Chemical Engineering, Guangxi University for Nationalities, Nanning, Guangxi 530006, PR China
| | - Yucheng Jiang
- School of Chemistry and Materials Science, Shaanxi Normal University, Xi’an 710062, PR China
| | - Rui Zhang
- Department of Chemistry and Biochemistry, Florida International University, Miami, FL 33199, United States of America
| | - Xiaotang Wang
- Department of Chemistry and Biochemistry, Florida International University, Miami, FL 33199, United States of America
- Corresponding author.
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4
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Spotlight on CYP4B1. Int J Mol Sci 2023; 24:ijms24032038. [PMID: 36768362 PMCID: PMC9916508 DOI: 10.3390/ijms24032038] [Citation(s) in RCA: 4] [Impact Index Per Article: 4.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/29/2022] [Revised: 01/16/2023] [Accepted: 01/17/2023] [Indexed: 01/22/2023] Open
Abstract
The mammalian cytochrome P450 monooxygenase CYP4B1 can bioactivate a wide range of xenobiotics, such as its defining/hallmark substrate 4-ipomeanol leading to tissue-specific toxicities. Similar to other members of the CYP4 family, CYP4B1 has the ability to hydroxylate fatty acids and fatty alcohols. Structural insights into the enigmatic role of CYP4B1 with functions in both, xenobiotic and endobiotic metabolism, as well as its unusual heme-binding characteristics are now possible by the recently solved crystal structures of native rabbit CYP4B1 and the p.E310A variant. Importantly, CYP4B1 does not play a major role in hepatic P450-catalyzed phase I drug metabolism due to its predominant extra-hepatic expression, mainly in the lung. In addition, no catalytic activity of human CYP4B1 has been observed owing to a unique substitution of an evolutionary strongly conserved proline 427 to serine. Nevertheless, association of CYP4B1 expression patterns with various cancers and potential roles in cancer development have been reported for the human enzyme. This review will summarize the current status of CYP4B1 research with a spotlight on its roles in the metabolism of endogenous and exogenous compounds, structural properties, and cancer association, as well as its potential application in suicide gene approaches for targeted cancer therapy.
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Liu J, Machalz D, Wolber G, Sorensen EJ, Bureik M. New Proluciferin Substrates for Human CYP4 Family Enzymes. Appl Biochem Biotechnol 2020; 193:218-237. [PMID: 32869209 DOI: 10.1007/s12010-020-03388-6] [Citation(s) in RCA: 5] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Key Words] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/03/2020] [Accepted: 07/16/2020] [Indexed: 02/08/2023]
Abstract
We report the synthesis of seven new proluciferins for convenient activity determination of enzymes belonging to the cytochrome P450 (CYP) 4 family. Biotransformation of these probe substrates was monitored using each of the twelve human CYP4 family members, and eight were found to act at least on one of them. For all substrates, activity of CYP4Z1 was always highest, while that of CYP4F8 was always second highest. Site of metabolism (SOM) predictions involving SMARTCyp and docking experiments helped to rationalize the observed activity trends linked to substrate accessibility and reactivity. We further report the first homology model of CYP4F8 including suggested substrate recognition residues in a catalytically competent conformation accessed by replica exchange solute tempering (REST) simulations.
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Affiliation(s)
- Jingyao Liu
- School of Pharmaceutical Science and Technology, Health Sciences Platform, Tianjin University, Tianjin, 300072, China
| | - David Machalz
- Pharmaceutical and Medicinal Chemistry (Computer-Aided Drug Design), Institute of Pharmacy, Freie Universität Berlin, 14195, Berlin, Germany
| | - Gerhard Wolber
- Pharmaceutical and Medicinal Chemistry (Computer-Aided Drug Design), Institute of Pharmacy, Freie Universität Berlin, 14195, Berlin, Germany
| | - Erik J Sorensen
- School of Pharmaceutical Science and Technology, Health Sciences Platform, Tianjin University, Tianjin, 300072, China. .,Department of Chemistry, Princeton University, Princeton, NJ, 08544, USA.
| | - Matthias Bureik
- School of Pharmaceutical Science and Technology, Health Sciences Platform, Tianjin University, Tianjin, 300072, China.
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6
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Du W, Machalz D, Yan Q, Sorensen EJ, Wolber G, Bureik M. Importance of asparagine-381 and arginine-487 for substrate recognition in CYP4Z1. Biochem Pharmacol 2020; 174:113850. [PMID: 32044355 DOI: 10.1016/j.bcp.2020.113850] [Citation(s) in RCA: 17] [Impact Index Per Article: 4.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/11/2019] [Accepted: 02/06/2020] [Indexed: 12/14/2022]
Abstract
The human cytochrome P450 enzyme CYP4Z1 remains an understudied enzyme despite its association with poor prognosis and overexpression in breast cancer. Hence, CYP4Z1 has previously been suggested as an anti-breast cancer target. In the present study we employed extended mutation analysis to increase our understanding of the substrate binding mode of this enzyme. In a combined in vitro and in silico approach we show for the first time that residue Arg487 plays an important role in substrate recognition and binding of CYP4Z1. Using a large array of recombinant CYP4Z1 mutants we show that, apart from Asn381, all other postulated binding residues only play an auxiliary role in substrate recognition and binding. Different substrate interaction motifs were identified via dynamic pharmacophores (dynophores) and their impact on catalytically competent substrate binding was classified. These new insights on the substrate recognition and binding mode represent an important step towards the rational design of CYP4Z1 prodrugs and guide further investigations into the so far poorly understood physiological role of CYP4Z1.
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Affiliation(s)
- Wei Du
- School of Pharmaceutical Science and Technology, Health Sciences Platform, Tianjin University, Tianjin 30072, China
| | - David Machalz
- Pharmaceutical and Medicinal Chemistry (Computer-Aided Drug Design), Institute of Pharmacy, Freie Universität Berlin, Germany
| | - Qi Yan
- School of Pharmaceutical Science and Technology, Health Sciences Platform, Tianjin University, Tianjin 30072, China
| | - Erik J Sorensen
- School of Pharmaceutical Science and Technology, Health Sciences Platform, Tianjin University, Tianjin 30072, China; Department of Chemistry, Princeton University, Princeton, NJ 08544, USA
| | - Gerhard Wolber
- Pharmaceutical and Medicinal Chemistry (Computer-Aided Drug Design), Institute of Pharmacy, Freie Universität Berlin, Germany.
| | - Matthias Bureik
- School of Pharmaceutical Science and Technology, Health Sciences Platform, Tianjin University, Tianjin 30072, China.
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7
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Albertolle ME, Song HD, Wilkey CJ, Segrest JP, Guengerich FP. Glutamine-451 Confers Sensitivity to Oxidative Inhibition and Heme-Thiolate Sulfenylation of Cytochrome P450 4B1. Chem Res Toxicol 2019; 32:484-492. [PMID: 30701961 PMCID: PMC7279892 DOI: 10.1021/acs.chemrestox.8b00353] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/20/2022]
Abstract
Human cytochrome P450 (P450) family 4 enzymes are involved in the metabolism of fatty acids and the bioactivation of carcinogenic arylamines and toxic natural products, e.g., 4-ipomeanol. These and other drug-metabolizing P450s are redox sensitive, showing a loss of activity resulting from preincubation with H2O2 and recovery with mild reducing agents [Albertolle, M. W., et al. (2017) J. Biol. Chem. 292, 11230-11242]. The inhibition is due to sulfenylation of the heme-thiolate ligand, as determined by chemopreoteomics and spectroscopy. This phenomenon may have implications for chemical toxicity and observed disease-drug interactions, in which the decreased metabolism of P450 substrates occurs in patients with inflammatory diseases (e.g., influenza and autoimmunity). Human P450 1A2 was determined to be redox insensitive. To determine the mechanism underlying the differential redox sensitivity, molecular dynamics (MD) simulations were employed using the crystal structure of rabbit P450 4B1 (Protein Data Bank entry 5T6Q ). In simulating either the thiolate (Cys-S-) or the sulfenic acid (Cys-SOH) at the heme ligation site, MD revealed Gln-451 in either an "open" or "closed" conformation, respectively, between the cytosol and heme-thiolate cysteine. Mutation to either an isosteric leucine (Q451L) or glutamate (Q451E) abrogated the redox sensitivity, suggesting that this "open" conformation allows for reduction of the sulfenic acid and religation of the thiolate to the heme iron. In summary, MD simulations suggest that Gln-451 in P450 4B1 adopts conformations that may stabilize and protect the heme-thiolate sulfenic acid; mutating this residue destabilizes the interaction, producing a redox insensitive enzyme.
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Affiliation(s)
- Matthew E. Albertolle
- Department of Biochemistry, Vanderbilt University School of Medicine, Nashville, Tennessee 37232-0146, United States
| | - Hyun D. Song
- Department of Medicine, Division of Cardiovascular Medicine, Vanderbilt University Medical Center, Nashville, Tennessee 37232-6300, United States
| | - Clayton J. Wilkey
- Department of Biochemistry, Vanderbilt University School of Medicine, Nashville, Tennessee 37232-0146, United States
| | - Jere P. Segrest
- Department of Medicine, Division of Cardiovascular Medicine, Vanderbilt University Medical Center, Nashville, Tennessee 37232-6300, United States
| | - F. Peter Guengerich
- Department of Biochemistry, Vanderbilt University School of Medicine, Nashville, Tennessee 37232-0146, United States
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8
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McDonald MG, Ray S, Amorosi CJ, Sitko KA, Kowalski JP, Paco L, Nath A, Gallis B, Totah RA, Dunham MJ, Fowler DM, Rettie AE. Expression and Functional Characterization of Breast Cancer-Associated Cytochrome P450 4Z1 in Saccharomyces cerevisiae. Drug Metab Dispos 2017; 45:1364-1371. [PMID: 29018033 PMCID: PMC5697098 DOI: 10.1124/dmd.117.078188] [Citation(s) in RCA: 33] [Impact Index Per Article: 4.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/19/2017] [Accepted: 10/04/2017] [Indexed: 12/22/2022] Open
Abstract
CYP4Z1 is an "orphan" cytochrome P450 (P450) enzyme that has provoked interest because of its hypothesized role in breast cancer through formation of the signaling molecule 20-hydroxyeicosatetraenoic acid (20-HETE). We expressed human CYP4Z1 in Saccharomyces cerevisiae and evaluated its catalytic capabilities toward arachidonic and lauric acids (AA and LA). Specific and sensitive mass spectrometry assays enabled discrimination of the regioselectivity of hydroxylation of these two fatty acids. CYP4Z1 generated 7-, 8-, 9-, 10-, and 11-hydroxy LA, whereas the 12-hydroxy metabolite was not detected. HET0016, the prototypic CYP4 inhibitor, only weakly inhibited laurate metabolite formation (IC50 ∼15 μM). CYP4Z1 preferentially oxidized AA to the 14(S),15(R)-epoxide with high regioselectivity and stereoselectivity, a reaction that was also insensitive to HET0016, but neither 20-HETE nor 20-carboxy-AA were detectable metabolites. Docking of LA and AA into a CYP4Z1 homology model was consistent with this preference for internal fatty acid oxidation. Thus, human CYP4Z1 has an inhibitor profile and product regioselectivity distinct from most other CYP4 enzymes, consistent with CYP4Z1's lack of a covalently linked heme. These data suggest that, if CYP4Z1 modulates breast cancer progression, it does so by a mechanism other than direct production of 20-HETE.
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Affiliation(s)
- Matthew G McDonald
- Departments of Medicinal Chemistry (M.G.M., S.R., J.P.K., L.P., A.N., B.G., R.A.T., A.E.R.), Genome Sciences (K.A.S., C.J.A., M.J.D., D.M.F.), and Bioengineering (D.M.F.), University of Washington, Seattle, Washington
| | - Sutapa Ray
- Departments of Medicinal Chemistry (M.G.M., S.R., J.P.K., L.P., A.N., B.G., R.A.T., A.E.R.), Genome Sciences (K.A.S., C.J.A., M.J.D., D.M.F.), and Bioengineering (D.M.F.), University of Washington, Seattle, Washington
| | - Clara J Amorosi
- Departments of Medicinal Chemistry (M.G.M., S.R., J.P.K., L.P., A.N., B.G., R.A.T., A.E.R.), Genome Sciences (K.A.S., C.J.A., M.J.D., D.M.F.), and Bioengineering (D.M.F.), University of Washington, Seattle, Washington
| | - Katherine A Sitko
- Departments of Medicinal Chemistry (M.G.M., S.R., J.P.K., L.P., A.N., B.G., R.A.T., A.E.R.), Genome Sciences (K.A.S., C.J.A., M.J.D., D.M.F.), and Bioengineering (D.M.F.), University of Washington, Seattle, Washington
| | - John P Kowalski
- Departments of Medicinal Chemistry (M.G.M., S.R., J.P.K., L.P., A.N., B.G., R.A.T., A.E.R.), Genome Sciences (K.A.S., C.J.A., M.J.D., D.M.F.), and Bioengineering (D.M.F.), University of Washington, Seattle, Washington
| | - Lorela Paco
- Departments of Medicinal Chemistry (M.G.M., S.R., J.P.K., L.P., A.N., B.G., R.A.T., A.E.R.), Genome Sciences (K.A.S., C.J.A., M.J.D., D.M.F.), and Bioengineering (D.M.F.), University of Washington, Seattle, Washington
| | - Abhinav Nath
- Departments of Medicinal Chemistry (M.G.M., S.R., J.P.K., L.P., A.N., B.G., R.A.T., A.E.R.), Genome Sciences (K.A.S., C.J.A., M.J.D., D.M.F.), and Bioengineering (D.M.F.), University of Washington, Seattle, Washington
| | - Byron Gallis
- Departments of Medicinal Chemistry (M.G.M., S.R., J.P.K., L.P., A.N., B.G., R.A.T., A.E.R.), Genome Sciences (K.A.S., C.J.A., M.J.D., D.M.F.), and Bioengineering (D.M.F.), University of Washington, Seattle, Washington
| | - Rheem A Totah
- Departments of Medicinal Chemistry (M.G.M., S.R., J.P.K., L.P., A.N., B.G., R.A.T., A.E.R.), Genome Sciences (K.A.S., C.J.A., M.J.D., D.M.F.), and Bioengineering (D.M.F.), University of Washington, Seattle, Washington
| | - Maitreya J Dunham
- Departments of Medicinal Chemistry (M.G.M., S.R., J.P.K., L.P., A.N., B.G., R.A.T., A.E.R.), Genome Sciences (K.A.S., C.J.A., M.J.D., D.M.F.), and Bioengineering (D.M.F.), University of Washington, Seattle, Washington
| | - Douglas M Fowler
- Departments of Medicinal Chemistry (M.G.M., S.R., J.P.K., L.P., A.N., B.G., R.A.T., A.E.R.), Genome Sciences (K.A.S., C.J.A., M.J.D., D.M.F.), and Bioengineering (D.M.F.), University of Washington, Seattle, Washington
| | - Allan E Rettie
- Departments of Medicinal Chemistry (M.G.M., S.R., J.P.K., L.P., A.N., B.G., R.A.T., A.E.R.), Genome Sciences (K.A.S., C.J.A., M.J.D., D.M.F.), and Bioengineering (D.M.F.), University of Washington, Seattle, Washington
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9
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Hsu MH, Baer BR, Rettie AE, Johnson EF. The Crystal Structure of Cytochrome P450 4B1 (CYP4B1) Monooxygenase Complexed with Octane Discloses Several Structural Adaptations for ω-Hydroxylation. J Biol Chem 2017; 292:5610-5621. [PMID: 28167536 DOI: 10.1074/jbc.m117.775494] [Citation(s) in RCA: 28] [Impact Index Per Article: 4.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/06/2017] [Revised: 02/02/2017] [Indexed: 11/06/2022] Open
Abstract
P450 family 4 fatty acid ω-hydroxylases preferentially oxygenate primary C-H bonds over adjacent, energetically favored secondary C-H bonds, but the mechanism explaining this intriguing preference is unclear. To this end, the structure of rabbit P450 4B1 complexed with its substrate octane was determined by X-ray crystallography to define features of the active site that contribute to a preference for ω-hydroxylation. The structure indicated that octane is bound in a narrow active-site cavity that limits access of the secondary C-H bond to the reactive intermediate. A highly conserved sequence motif on helix I contributes to positioning the terminal carbon of octane for ω-hydroxylation. Glu-310 of this motif auto-catalytically forms an ester bond with the heme 5-methyl, and the immobilized Glu-310 contributes to substrate positioning. The preference for ω-hydroxylation was decreased in an E310A mutant having a shorter side chain, but the overall rates of metabolism were retained. E310D and E310Q substitutions having longer side chains exhibit lower overall rates, likely due to higher conformational entropy for these residues, but they retained high preferences for octane ω-hydroxylation. Sequence comparisons indicated that active-site residues constraining octane for ω-hydroxylation are conserved in family 4 P450s. Moreover, the heme 7-propionate is positioned in the active site and provides additional restraints on substrate binding. In conclusion, P450 4B1 exhibits structural adaptations for ω-hydroxylation that include changes in the conformation of the heme and changes in a highly conserved helix I motif that is associated with selective oxygenation of unactivated primary C-H bonds.
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Affiliation(s)
- Mei-Hui Hsu
- From the Department of Molecular Medicine, The Scripps Research Institute, La Jolla, California 92037 and
| | - Brian R Baer
- the Department of Medicinal Chemistry, University of Washington, Seattle, Washington 98195
| | - Allan E Rettie
- the Department of Medicinal Chemistry, University of Washington, Seattle, Washington 98195
| | - Eric F Johnson
- From the Department of Molecular Medicine, The Scripps Research Institute, La Jolla, California 92037 and
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10
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Lin YW. The broad diversity of heme-protein cross-links: An overview. BIOCHIMICA ET BIOPHYSICA ACTA-PROTEINS AND PROTEOMICS 2015; 1854:844-59. [DOI: 10.1016/j.bbapap.2015.04.019] [Citation(s) in RCA: 20] [Impact Index Per Article: 2.2] [Reference Citation Analysis] [Track Full Text] [Subscribe] [Scholar Register] [Received: 02/12/2015] [Revised: 03/26/2015] [Accepted: 04/17/2015] [Indexed: 12/30/2022]
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11
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Yan DJ, Li W, Xiang Y, Wen GB, Lin YW, Tan X. A Novel Tyrosine-Heme CO Covalent Linkage in F43Y Myoglobin: A New Post-translational Modification of Heme Proteins. Chembiochem 2014; 16:47-50. [DOI: 10.1002/cbic.201402504] [Citation(s) in RCA: 31] [Impact Index Per Article: 3.1] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/04/2014] [Indexed: 12/18/2022]
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12
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Yoshigae Y, Kent UM, Hollenberg PF. Role of the highly conserved threonine in cytochrome P450 2E1: prevention of H2O2-induced inactivation during electron transfer. Biochemistry 2013; 52:4636-47. [PMID: 23750736 DOI: 10.1021/bi4004843] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Abstract
A highly conserved threonine in the I-helix of cytochrome P450s has been suggested to play an important role in dioxygen activation, a critical step for catalytic turnover. However, subsequent studies with some P450s in which this highly conserved threonine was replaced by another residue such as alanine showed that significant catalytic activities were still retained when the variants were compared with the wild type enzymes. These results make the role of this residue unclear. We provide data here that suggest a novel role for this highly conserved threonine (Thr303) in the function of P450 2E1. We found that the P450 2E1 T303A mutant undergoes rapid autoinactivation in the reconstituted system during catalytic turnover when the electrons are provided by NADPH. This inactivation was much faster than that of the wild type P450 2E1 and was prevented by catalase. Both the P450 2E1 wild type and T303A mutants produce hydrogen peroxide during the incubations. The inactivation was accompanied by heme destruction with part of the heme becoming covalently attached to protein. The heme destruction was prevented by catalase or by the presence of substrate. Interestingly, this inactivation occurred much more rapidly in the presence of both an electron transfer system and hydrogen peroxide externally added to the enzyme. This accelerated inactivation during catalytic turnover was also found with a 2B4 T302A mutant, which corresponds to 2E1 T303A. Our results suggest that the conserved threonine in these P450s prevents rapid autoinactivation during the catalytic cycle and that this residue may be highly conserved in P450s since it allows them to remain catalytically active for longer periods of time.
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Affiliation(s)
- Yasushi Yoshigae
- Department of Pharmacology, The University of Michigan Medical School , 2301 MSRB III, 1150 West Medical Center Drive, Ann Arbor, Michigan 48109-5632, United States
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13
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Aicart-Ramos C, Valhondo Falcón M, Ortiz de Montellano PR, Rodriguez-Crespo I. Covalent attachment of heme to the protein moiety in an insect E75 nitric oxide sensor. Biochemistry 2012; 51:7403-16. [PMID: 22946928 DOI: 10.1021/bi300848x] [Citation(s) in RCA: 13] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/31/2022]
Abstract
We have recombinantly expressed and purified the ligand binding domains (LBDs) of four insect nuclear receptors of the E75 family. The Drosophila melanogaster and Bombyx mori nuclear receptors were purified as ferric hemoproteins with Soret maxima at 424 nm, whereas their ferrous forms had a Soret maximum at 425 nm that responds to (•)NO and CO binding. In contrast, the purified LBD of Oncopeltus fasciatus displayed a Soret maximum at 415 nm for the ferric protein that shifted to 425 nm in its ferrous state. Binding of (•)NO to the heme moiety of the D. melanogaster and B. mori E75 LBD resulted in the appearance of a peak at 385 nm, whereas this peak appeared at 416 nm in the case of the O. fasciatus hemoprotein, resembling the behavior displayed by its human homologue, Rev-erbβ. High-performance liquid chromatography analysis revealed that, unlike the D. melanogaster and B. mori counterparts, the heme group of O. fasciatus is covalently attached to the protein through the side chains of two amino acids. The high degree of sequence homology with O. fasciatus E75 led us to clone and express the LBD of Blattella germanica, which established that its spectral properties closely resemble those of O. fasciatus and that it also has the heme group covalently bound to the protein. Hence, (•)NO/CO regulation of the transcriptional activity of these nuclear receptors might be differently controlled among various insect species. In addition, covalent heme binding provides strong evidence that at least some of these nuclear receptors function as diatomic gas sensors rather than heme sensors. Finally, our findings expand the classes of hemoproteins in which the heme group is normally covalently attached to the polypeptide chain.
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Affiliation(s)
- Clara Aicart-Ramos
- Departamento de Bioquímica y Biología Molecular I, Universidad Complutense, 28040 Madrid, Spain
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14
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Bryson D, Lim PL, Lawson A, Manjunath S, Raner GM. Isotopic labeling of the heme cofactor in cytochrome P450 and other heme proteins. Biotechnol Lett 2011; 33:2019-26. [PMID: 21660572 DOI: 10.1007/s10529-011-0661-1] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/04/2011] [Accepted: 05/26/2011] [Indexed: 11/26/2022]
Abstract
A recombinant bacterial expression system that generates (13)C-labeled heme or (15)N-labeled heme in functional cytochrome P450 enzymes and other heme-containing systems is reported here using a mutant strain of Escherichia coli (HU227) in which the HemA gene is inactive. By synthesizing several isotopomers of aminolevulinic acid with (13)C or (15)N at different locations, isotopes have been incorporated with high abundance into the heme cofactor of five different cytochrome P450 isoforms, along with one peroxidase. Confirmed both (13)C- and (15)N-incorporation; spectral and catalytic assays show the labeled enzymes produced in this system are functional.
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Affiliation(s)
- David Bryson
- The Department of Chemistry and Biochemistry, The University of North Carolina at Greensboro, 416 Sullivan Science Building, Greensboro, NC 27402, USA
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15
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Johnston JB, Ouellet H, Podust LM, Ortiz de Montellano PR. Structural control of cytochrome P450-catalyzed ω-hydroxylation. Arch Biochem Biophys 2010; 507:86-94. [PMID: 20727847 DOI: 10.1016/j.abb.2010.08.011] [Citation(s) in RCA: 51] [Impact Index Per Article: 3.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/02/2010] [Revised: 08/11/2010] [Accepted: 08/13/2010] [Indexed: 11/25/2022]
Abstract
The regiospecific or preferential ω-hydroxylation of hydrocarbon chains is thermodynamically disfavored because the ease of C-H bond hydroxylation depends on the bond strength, and the primary C-H bond of a terminal methyl group is stronger than the secondary or tertiary C-H bond adjacent to it. The hydroxylation reaction will therefore occur primarily at the adjacent secondary or tertiary C-H bond unless the protein structure specifically enforces primary C-H bond oxidation. Here we review the classes of enzymes that catalyze ω-hydroxylation and our current understanding of the structural features that promote the ω-hydroxylation of unbranched and methyl-branched hydrocarbon chains. The evidence indicates that steric constraints are used to favor reaction at the ω-site rather than at the more reactive (ω-1)-site.
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Affiliation(s)
- Jonathan B Johnston
- Department of Pharmaceutical Chemistry, University of California-San Francisco, CA 94158-2517, United States
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16
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Pipirou Z, Guallar V, Basran J, Metcalfe CL, Murphy EJ, Bottrill AR, Mistry SC, Raven EL. Peroxide-Dependent Formation of a Covalent Link between Trp51 and the Heme in Cytochrome c Peroxidase. Biochemistry 2009; 48:3593-9. [DOI: 10.1021/bi802210g] [Citation(s) in RCA: 12] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
Affiliation(s)
- Zoi Pipirou
- Department of Chemistry, Henry Wellcome Building, University of Leicester, University Road, Leicester LE1 7RH, England, ICREA, Life Science Department, Barcelona Supercomputing Center, Jordi Girona 29, 08034 Barcelona, Spain, Department of Biochemistry, Henry Wellcome Building, University of Leicester, Lancaster Road, Leicester LE1 9HN, England, and Protein and Nucleic Acid Chemistry Laboratory, Hodgkin Building, University of Leicester, Lancaster Road, Leicester LE1 9HN, England
| | - Victor Guallar
- Department of Chemistry, Henry Wellcome Building, University of Leicester, University Road, Leicester LE1 7RH, England, ICREA, Life Science Department, Barcelona Supercomputing Center, Jordi Girona 29, 08034 Barcelona, Spain, Department of Biochemistry, Henry Wellcome Building, University of Leicester, Lancaster Road, Leicester LE1 9HN, England, and Protein and Nucleic Acid Chemistry Laboratory, Hodgkin Building, University of Leicester, Lancaster Road, Leicester LE1 9HN, England
| | - Jaswir Basran
- Department of Chemistry, Henry Wellcome Building, University of Leicester, University Road, Leicester LE1 7RH, England, ICREA, Life Science Department, Barcelona Supercomputing Center, Jordi Girona 29, 08034 Barcelona, Spain, Department of Biochemistry, Henry Wellcome Building, University of Leicester, Lancaster Road, Leicester LE1 9HN, England, and Protein and Nucleic Acid Chemistry Laboratory, Hodgkin Building, University of Leicester, Lancaster Road, Leicester LE1 9HN, England
| | - Clive L. Metcalfe
- Department of Chemistry, Henry Wellcome Building, University of Leicester, University Road, Leicester LE1 7RH, England, ICREA, Life Science Department, Barcelona Supercomputing Center, Jordi Girona 29, 08034 Barcelona, Spain, Department of Biochemistry, Henry Wellcome Building, University of Leicester, Lancaster Road, Leicester LE1 9HN, England, and Protein and Nucleic Acid Chemistry Laboratory, Hodgkin Building, University of Leicester, Lancaster Road, Leicester LE1 9HN, England
| | - Emma J. Murphy
- Department of Chemistry, Henry Wellcome Building, University of Leicester, University Road, Leicester LE1 7RH, England, ICREA, Life Science Department, Barcelona Supercomputing Center, Jordi Girona 29, 08034 Barcelona, Spain, Department of Biochemistry, Henry Wellcome Building, University of Leicester, Lancaster Road, Leicester LE1 9HN, England, and Protein and Nucleic Acid Chemistry Laboratory, Hodgkin Building, University of Leicester, Lancaster Road, Leicester LE1 9HN, England
| | - Andrew R. Bottrill
- Department of Chemistry, Henry Wellcome Building, University of Leicester, University Road, Leicester LE1 7RH, England, ICREA, Life Science Department, Barcelona Supercomputing Center, Jordi Girona 29, 08034 Barcelona, Spain, Department of Biochemistry, Henry Wellcome Building, University of Leicester, Lancaster Road, Leicester LE1 9HN, England, and Protein and Nucleic Acid Chemistry Laboratory, Hodgkin Building, University of Leicester, Lancaster Road, Leicester LE1 9HN, England
| | - Sharad C. Mistry
- Department of Chemistry, Henry Wellcome Building, University of Leicester, University Road, Leicester LE1 7RH, England, ICREA, Life Science Department, Barcelona Supercomputing Center, Jordi Girona 29, 08034 Barcelona, Spain, Department of Biochemistry, Henry Wellcome Building, University of Leicester, Lancaster Road, Leicester LE1 9HN, England, and Protein and Nucleic Acid Chemistry Laboratory, Hodgkin Building, University of Leicester, Lancaster Road, Leicester LE1 9HN, England
| | - Emma Lloyd Raven
- Department of Chemistry, Henry Wellcome Building, University of Leicester, University Road, Leicester LE1 7RH, England, ICREA, Life Science Department, Barcelona Supercomputing Center, Jordi Girona 29, 08034 Barcelona, Spain, Department of Biochemistry, Henry Wellcome Building, University of Leicester, Lancaster Road, Leicester LE1 9HN, England, and Protein and Nucleic Acid Chemistry Laboratory, Hodgkin Building, University of Leicester, Lancaster Road, Leicester LE1 9HN, England
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17
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Abstract
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.
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18
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Ortiz de Montellano PR. Mechanism and Role of Covalent Heme Binding in the CYP4 Family of P450 Enzymes and the Mammalian Peroxidases. Drug Metab Rev 2008; 40:405-26. [DOI: 10.1080/03602530802186439] [Citation(s) in RCA: 37] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/21/2022]
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19
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Fer M, Corcos L, Dréano Y, Plée-Gautier E, Salaün JP, Berthou F, Amet Y. Cytochromes P450 from family 4 are the main omega hydroxylating enzymes in humans: CYP4F3B is the prominent player in PUFA metabolism. J Lipid Res 2008; 49:2379-89. [PMID: 18577768 DOI: 10.1194/jlr.m800199-jlr200] [Citation(s) in RCA: 70] [Impact Index Per Article: 4.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/06/2023] Open
Abstract
Human CYP450 omega-hydroxylases of the CYP4 family are known to convert arachidonic acid (AA) to its metabolite 20-hydroxyeicosatetraenoic acid (20-HETE). This study deals with hydroxylations of four PUFAs, eicosatrienoic acid (ETA), AA, eicosapentaenoic acid (EPA), and docosahexaenoic acid (DHA) by either human recombinant CYP4s enzymes or human liver microsomal preparations. CYP4F3A and CYP4F3B were the most efficient omega-hydroxylases of these PUFAs. Moreover, the differences in the number of unsaturations of ETA, AA, and EPA allowed us to demonstrate a rise in the metabolic rate of hydroxylation when the double bond in 14-15 or 17-18 was missing. With the CYP4F enzymes, the main pathway was always the omega-hydroxylation of PUFAs, whereas it was the (omega-1)-hydroxylation with CYP1A1, CYP2C19, and CYP2E1. Finally, we demonstrated that the omega9 and omega3 PUFAs (ETA, EPA, and DHA) could all be used as alternative substrates in AA metabolism by human CYP4F2 and -4F3B. Thus, they decreased the ability of these enzymes to convert AA to 20-HETE. However, although ETA was the most hydroxylated substrate, EPA and DHA were the most potent inhibitors of the conversion of AA to 20-HETE. These findings suggest that some physiological effects of omega3 FAs could partly result from a shift in the generation of active hydroxylated metabolites of AA through a CYP-mediated catalysis.
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Affiliation(s)
- Maude Fer
- Laboratoire de Biochimie EA 948, Faculté de Médecine, Université de Bretagne Occidentale, Brest, France
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20
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Metcalfe C, Daltrop O, Ferguson S, Raven E. Tuning the formation of a covalent haem-protein link by selection of reductive or oxidative conditions as exemplified by ascorbate peroxidase. Biochem J 2008; 408:355-61. [PMID: 17714075 PMCID: PMC2267360 DOI: 10.1042/bj20071041] [Citation(s) in RCA: 14] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/31/2022]
Abstract
Previous work [Metcalfe, Ott, Patel, Singh, Mistry, Goff and Raven (2004) J. Am. Chem. Soc. 126, 16242-16248] has shown that the introduction of a methionine residue (S160M variant) close to the 2-vinyl group of the haem in ascorbate peroxidase leads to the formation of a covalent haem-methionine linkage under oxidative conditions (i.e. on reaction with H2O2). In the present study, spectroscopic, HPLC and mass spectrometric evidence is presented to show that covalent attachment of the haem to an engineered cysteine residue can also occur in the S160C variant, but, in this case, under reducing conditions analogous to those used in the formation of covalent links in cytochrome c. The data add an extra dimension to our understanding of haem to protein covalent bond formation because they show that different types of covalent attachment (one requiring an oxidative mechanism, the other a reductive pathway) are both accessible within same protein architecture.
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Affiliation(s)
- Clive L. Metcalfe
- *Department of Chemistry, University of Leicester, University Road, Leicester LE1 7RH, U.K
| | - Oliver Daltrop
- †Department of Biochemistry, University of Oxford, South Parks Road, Oxford OX1 3QU, U.K
| | - Stuart J. Ferguson
- †Department of Biochemistry, University of Oxford, South Parks Road, Oxford OX1 3QU, U.K
- Correspondence may be addressed to either of these authors (email or )
| | - Emma Lloyd Raven
- *Department of Chemistry, University of Leicester, University Road, Leicester LE1 7RH, U.K
- Correspondence may be addressed to either of these authors (email or )
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21
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Baer BR, Kunze KL, Rettie AE. Mechanism of formation of the ester linkage between heme and Glu310 of CYP4B1: 18O protein labeling studies. Biochemistry 2007; 46:11598-605. [PMID: 17880109 PMCID: PMC3423087 DOI: 10.1021/bi701064b] [Citation(s) in RCA: 10] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/26/2022]
Abstract
Cytochrome P450s in the CYP4 family covalently bind their heme prosthetic group to a conserved acidic I-helix residue via an autocatalytic oxidation. This study was designed to evaluate the source of oxygen atoms in the covalent ester link in CYP4B1 enzymes labeled with [18O]glutamate and [18O]aspartate. The fate of the heavy isotope was then traced into wild-type CYP4B1 or the E310D mutant-derived 5-hydroxyhemes. Glutamate-containing tryptic peptides of wild-type CYP4B1 were found labeled to a level of 11-13% 18O. Base hydrolysis of labeled protein released 5-hydroxyheme which contained 12.8 +/- 1.9% 18O. Aspartate-containing peptides of the E310D mutant were labeled with 6.0-6.5% 18O, but as expected, no label was transmitted to recovered 5-hydroxyheme. These data demonstrate that the oxygen atom in 5-hydroxyheme derived from wild-type CYP4B1 originates in Glu310. Stoichiometric incorporation of the heavy isotope from the wild-type enzyme supports a perferryl-initiated carbocation mechanism for covalent heme formation in CYP4B1.
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Affiliation(s)
| | | | - Allan E. Rettie
- To whom correspondence should be addressed. Telephone: (206) 685-0615. Fax (206) 685-3252.
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22
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Zederbauer M, Furtmüller PG, Brogioni S, Jakopitsch C, Smulevich G, Obinger C. Heme to protein linkages in mammalian peroxidases: impact on spectroscopic, redox and catalytic properties. Nat Prod Rep 2007; 24:571-84. [PMID: 17534531 DOI: 10.1039/b604178g] [Citation(s) in RCA: 79] [Impact Index Per Article: 4.6] [Reference Citation Analysis] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/17/2023]
Affiliation(s)
- Martina Zederbauer
- BOKU-University of Natural Resources and Applied Life Sciences, Department of Chemistry, Division of Biochemistry, Muthgasse 18, A-1190 Vienna, Austria
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23
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Kalsotra A, Strobel HW. Cytochrome P450 4F subfamily: at the crossroads of eicosanoid and drug metabolism. Pharmacol Ther 2006; 112:589-611. [PMID: 16926051 DOI: 10.1016/j.pharmthera.2006.03.008] [Citation(s) in RCA: 99] [Impact Index Per Article: 5.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/22/2006] [Accepted: 03/22/2006] [Indexed: 12/13/2022]
Abstract
The cytochrome P450 4F (CYP4F) subfamily has over the last few years come to be recognized for its dual role in modulating the concentrations of eicosanoids during inflammation as well as in the metabolism of clinically significant drugs. The first CYP4F was identified because it catalyzed the hydroxylation of leukotriene B(4) (LTB(4)) and since then many additional members of this subfamily have been documented for their distinct catalytic roles and functional significance. Recent evidence emerging in relation to the temporal change of CYP4F expression in response to injury and infection supports an important function for these isozymes in curtailing inflammation. Their tissue-dependent expression, isoform-based catalytic competence and unique response to the external stimuli imply a critical role for them to regulate organ-specific functions. From this standpoint variations in relative CYP4F levels in humans may have direct influence on the metabolic outcome through their ability to generate and/or degrade bioactive eicosanoids or therapeutic agents. This review covers the enzymatic characteristics and regulatory properties of human and rodent CYP4F isoforms and their physiological relevance to major pathways in eicosanoid and drug metabolism.
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Affiliation(s)
- Auinash Kalsotra
- Department of Biochemistry and Molecular Biology, The University of Texas-Houston Medical School, P.O. Box 20708, 6431 Fannin Street Houston, TX 77225, USA
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24
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Ngo SNT, McKinnon RA, Stupans I. Cloning and expression of koala (Phascolarctos cinereus) liver cytochrome P450 CYP4A15. Gene 2006; 376:123-32. [PMID: 16677781 DOI: 10.1016/j.gene.2006.02.020] [Citation(s) in RCA: 14] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/20/2005] [Revised: 02/14/2006] [Accepted: 02/21/2006] [Indexed: 10/24/2022]
Abstract
In the present study, the cloning, expression and characterization of hepatic cytochrome P450 (CYP) CYP4A from koala (Phascolarctos cinereus), an obligate eucalyptus feeder, is described. It has been previously reported that microsomal lauric acid hydroxylase activity (a CYP4A marker) and CYP content were higher in koala liver in comparison to that in human, rat or wallaby, species that do not ingest eucalyptus leaves as food [Ngo, S., Kong, S., Kirlich, A., Mckinnon, R.A., Stupans, I., 2000. Cytochrome P450 4A, peroxisomal enzymes and nicotinamide cofactors in koala liver. Comp. Biochem. Physiol., C 127, 327-334]. A 1544 bp koala liver CYP4A cDNA, designated CYP4A15, was cloned by reverse transcription-polymerase chain reaction and rapid amplification of cDNA ends. The koala CYP4A15 cDNA encodes a protein of 500 amino acids and shares 69% nucleotide and 65% amino acid sequence identity to human CYP4A11. Transfection of the koala CYP4A15 cDNA into Cos-7 cells resulted in the expression of a protein with lauric acid hydroxylase activity. The koala CYP4A15 cDNA-expressed enzyme catalysed lauric acid hydroxylation at the rates of 0.45+/-0.18 nmol/min/mg protein and 4.79+/-1.91 nmol/min/nmol CYP (mean+/-SD, n=3), which were comparable to that of rat CYP4A subfamilies. Total CYP content for koala CYP4A15-expressed protein in Cos-7 cells was 0.094+/-0.001 nmol/mg protein (mean+/-SD, n=3) with negligible CYP content in untransfected Cos-7 cells lysate. Immunoblot analysis, using a sheep anti-rat CYP4A polyclonal antibody, detected multiple CYP4A immunoreactive bands in the liver from all species studied. The koala bands were found to be fainter and less confined but appeared much broader as compared to rat, human and wallaby. Northern blot analysis, utilising the koala CYP4A15 cDNA 417 bp probe, detected a mRNA species of approximately 2.6 kb in the koala liver and a mRNA species of approximately 2.4 kb in other species studied. Relative to the intensity of the beta-actin mRNA species, much stronger CYP4A mRNA signal was detected for koala liver relative to rat and human. In Southern blot analysis of EcoR 1-digested genomic DNAs, using the same koala CYP4A15 cDNA probe, the size of CYP4A gene fragments observed for the koala and other species were different, suggested a different CYP4A gene organization across species. Collectively, this study provides primary molecular data regarding koala CYP4A15 gene. The possibility that there may be higher CYP4A15 expression in the koala liver could not be excluded.
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Affiliation(s)
- Suong Ngoc Thi Ngo
- Sansom Institute, School of Pharmacy and Medical Sciences, City East Campus, University of South Australia, North Terrace, Adelaide, SA 5000, Australia.
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Huang L, Ortiz de Montellano PR. Heme-protein covalent bonds in peroxidases and resistance to heme modification during halide oxidation. Arch Biochem Biophys 2006; 446:77-83. [PMID: 16375846 DOI: 10.1016/j.abb.2005.11.011] [Citation(s) in RCA: 21] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/17/2005] [Revised: 11/14/2005] [Accepted: 11/15/2005] [Indexed: 10/25/2022]
Abstract
Plant peroxidases, as typified by horseradish peroxidase (HRP), primarily catalyze the one-electron oxidation of phenols and other low oxidation potential substrates. In contrast, the mammalian homologues such as lactoperoxidase (LPO) and myeloperoxidase primarily oxidize halides and pseudohalides to the corresponding hypohalides (e.g., Br(-) to HOBr, Cl(-) to HOCl). A further feature that distinguishes the mammalian from the plant and fungal enzymes is the presence of two or more covalent bonds between the heme and the protein only in the mammalian enzymes. The functional roles of these covalent links in mammalian peroxidases remain uncertain. We have previously reported that HRP can oxidize chloride and bromide ions, but during oxidation of these ions undergoes autocatalytic modification of its heme vinyl groups that virtually inactivates the enzyme. We report here that autocatalytic heme modification during halide oxidation is not unique to HRP but is a general feature of the oxidation of halide ions by fungal and plant peroxidases, as illustrated by studies with Arthromyces ramosus and soybean peroxidases. In contrast, LPO, a prototypical mammalian peroxidase, is protected from heme modification and its heme remains intact during the oxidation of halide ions. These results support the hypothesis that the covalent heme-protein links in the mammalian peroxidases protect the heme from modification during the oxidation of halide ions.
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Affiliation(s)
- Liusheng Huang
- Department of Pharmaceutical Chemistry, University of California, 600 16th Street, San Francisco, CA 94143-2280, USA
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26
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Stark K, Wongsud B, Burman R, Oliw EH. Oxygenation of polyunsaturated long chain fatty acids by recombinant CYP4F8 and CYP4F12 and catalytic importance of Tyr-125 and Gly-328 of CYP4F8. Arch Biochem Biophys 2005; 441:174-81. [PMID: 16112640 DOI: 10.1016/j.abb.2005.07.003] [Citation(s) in RCA: 31] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/14/2005] [Accepted: 07/12/2005] [Indexed: 10/25/2022]
Abstract
Recombinant CYP4F8 and CYP4F12 metabolize prostaglandin H2 (PGH2) analogs by omega2- and omega3-hydroxylation and arachidonic acid (20:4n-6) by omega3-hydroxylation. CYP4F8 was found to catalyze epoxidation of docosahexaenoic acid (22:6n-3) and docosapentaenoic acid (22:5n-3) and omega3-hydroxylation of 22:5n-6. CYP4F12 oxidized 22:6n-3 and 22:5n-3 in the same way, but 22:5n-6 was a poor substrate. The products were identified by liquid chromatography-mass spectrometry. The missense mutation 374A>T of CYP4F8 (Tyr125Phe in substrate recognition site-1 (SRS-1)) occurs in low frequency. This variant oxidized two PGH2 analogs, U-51605 and U-44069, in analogy with CYP4F8, but 20:4n-6 and 22:5n-6 were not oxidized. CYP4F enzymes with omega-hydroxylase activity contain a heme-binding Glu residue, whereas CYP4F8 (and CYP4F12) with omega2- and omega 3-hydroxylase activities has a Gly residue in this position of SRS-4. The mutant CYP4F8 Gly328Glu oxidized U-51605 and U-44069 as recombinant CYP4F8, but the hydroxylation of arachidonic acid was shifted from C-18 to C-19. Single amino acid substitutions in SRS-1 and SRS-4 of CYP4F8 may thus influence oxygenation of certain substrates. We conclude that CYP4F8 and CYP4F12 catalyze epoxidation of 22:6n-3 and 22:5n-3, and CYP4F8 omega3-hydroxylation of 22:5n-6.
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Affiliation(s)
- Katarina Stark
- Department of Pharmaceutical Biosciences, Division of Biochemical Pharmacology, Uppsala University, SE-751 24 Uppsala, Sweden
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27
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Huang L, Colas C, Ortiz de Montellano PR. Oxidation of carboxylic acids by horseradish peroxidase results in prosthetic heme modification and inactivation. J Am Chem Soc 2005; 126:12865-73. [PMID: 15469283 DOI: 10.1021/ja046455w] [Citation(s) in RCA: 22] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/12/2023]
Abstract
Hemoproteins are powerful oxidative catalysts. However, despite the diversity of functions known to be susceptible to oxidation by these catalysts, it is not known whether they can oxidize carboxylic acids to carboxylic radicals. We report here that incubation of horseradish peroxidase (HRP) at acidic pH with H(2)O(2) in acetate buffer results in rapid modification of the heme group and loss of catalytic activity. Mass spectrometry and NMR indicate that an acetoxy group is covalently bound to the delta-meso-carbon in the modified heme. A heme with a hydroxyl group on the 8-methyl is also formed as a minor product. These reactions do not occur if protein-free heme and H(2)O(2) are co-incubated in acetate buffer, if the HRP reaction is carried out at pH 7, in the absence of H(2)O(2), or if citrate rather than acetate buffer is used. A similar heme modification is observed in incubations with n-caproic and phenylacetic acids. A mechanism involving oxidation of the carboxyl group to a carboxylic radical followed by addition to the delta-meso-position is proposed. This demonstration of the oxidation of a carboxylic acid solidifies the proposal that a carboxylic radical mediates the normal covalent attachment of the heme to the protein in the mammalian peroxidases and CYP4 family of P450 enzymes. The hemoprotein-mediated oxidation of carboxylic acids, ubiquitous natural constituents, may play other roles in biology.
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Affiliation(s)
- Liusheng Huang
- Contribution from the Department of Pharmaceutical Chemistry, University of California, 600 16th Street, San Francisco, CA 94143-2280, USA
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Kroetz DL, Xu F. Regulation and inhibition of arachidonic acid omega-hydroxylases and 20-HETE formation. Annu Rev Pharmacol Toxicol 2005; 45:413-38. [PMID: 15822183 DOI: 10.1146/annurev.pharmtox.45.120403.100045] [Citation(s) in RCA: 114] [Impact Index Per Article: 6.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/09/2022]
Abstract
Cytochrome P450-catalyzed metabolism of arachidonic acid is an important pathway for the formation of paracrine and autocrine mediators of numerous biological effects. The omega-hydroxylation of arachidonic acid generates significant levels of 20-hydroxyeicosatetraenoic acid (20-HETE) in numerous tissues, particularly the vasculature and kidney tubules. Members of the cytochrome P450 4A and 4F families are the major omega-hydroxylases, and the substrate selectivity and regulation of these enzymes has been the subject of numerous studies. Altered expression and function of arachidonic acid omega-hydroxylases in models of hypertension, diabetes, inflammation, and pregnancy suggest that 20-HETE may be involved in the pathogenesis of these diseases. Our understanding of the biological significance of 20-HETE has been greatly aided by the development and characterization of selective and potent inhibitors of the arachidonic acid omega-hydroxylases. This review discusses the substrate selectivity and expression of arachidonic acid omega-hydroxylases, regulation of these enzymes during disease, and the application of enzyme inhibitors to study 20-HETE function.
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Affiliation(s)
- Deanna L Kroetz
- Department of Biopharmaceutical Sciences, University of California, San Francisco, California 94143-2911, USA.
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Vatsis KP, Peng HM, Coon MJ. Abolition of oxygenase function, retention of NADPH oxidase activity, and emergence of peroxidase activity upon replacement of the axial cysteine-436 ligand by histidine in cytochrome P450 2B4. Arch Biochem Biophys 2005; 434:128-38. [PMID: 15629116 DOI: 10.1016/j.abb.2004.10.015] [Citation(s) in RCA: 17] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/08/2004] [Revised: 10/14/2004] [Indexed: 11/22/2022]
Abstract
A fundamental aspect of cytochrome P450 function is the role of the strictly conserved axial cysteine ligand, replacement of which by histidine has invariably resulted in mammalian and bacterial preparations devoid of heme. Isolation of the His-436 variant of NH2-truncated P450 2B4 partly as the holoenzyme was achieved in the present study by mutagenesis of the I-helix Ala-298 residue to Glu and subsequent conversion of the axial Cys-436 to His. The expressed A298E/C436H double mutant, cloned with a hexahistidine tag, had a molecular mass equivalent to that of the primary structure of His-tagged truncated 2B4 and the sum of the two mutated residues, and contained a heme group which, when released on HPLC, showed a retention time and spectrum identical to those of iron protoporphyrin IX. The absolute spectra of A298E/C436H indicate a change in heme coordination structure from low- to high-spin, and, as expected for a His-ligated hemeprotein, the Soret maximum of the ferrous CO complex is at 422 nm. The double mutant has no oxygenase activity with representative substrates known to undergo transformation by the oxene [(FeO)3+] or peroxo activated oxygen species, but catalyzes significant H2O2 formation that is NADPH- and time-dependent, and directly proportional to the concentration of A298E/C436H in the presence of saturating reductase. Moreover, the catalytic efficiency of A298E/C436H in the H2O2-supported peroxidation of pyrogallol is more than two orders of magnitude greater than that of wild-type 2B4 or the A298E variant. The results unambiguously demonstrate that the proximal thiolate ligand is essential for substrate oxygenation by P450.
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Affiliation(s)
- Kostas P Vatsis
- Department of Biological Chemistry, Medical School, The University of Michigan, Ann Arbor, MI 48109-0606, USA.
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Abstract
Cytochromes P450 are a ubiquitous group of hemoproteins that perform vital cellular reactions in all lifeforms. Until recently, it was thought that P450s contained non-covalently bound heme. However, it was established that covalent linkage of the heme macrocycle occurs naturally in one major group of the P450 superfamily. The reaction involves heme linkage to a conserved amino acid and is autocatalytic, occurring as a consequence of P450 turnover. This finding presents opportunities to engineer biotechnologically important P450s to covalently link the heme, in order to stabilize cofactor binding and to enhance operational stability of these P450s. This opportunity has been taken in studies on two important bacterial P450s and has produced variants with intriguingly different properties. In this article we survey the developments in the field, the relationships with heme macrocycle ligations in other proteins and the important impact that recent studies of heme ligation have had on our general appreciation of P450 structure and mechanism.
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Affiliation(s)
- Harriet E Seward
- Department of Biochemistry, University of Leicester, Henry Wellcome Building, Lancaster Road, Leicester, UK LE1 9HN.
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31
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Metcalfe CL, Ott M, Patel N, Singh K, Mistry SC, Goff HM, Raven EL. Autocatalytic formation of green heme: evidence for H2O2-dependent formation of a covalent methionine-heme linkage in ascorbate peroxidase. J Am Chem Soc 2004; 126:16242-8. [PMID: 15584761 DOI: 10.1021/ja048242c] [Citation(s) in RCA: 35] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
Abstract
The mammalian heme peroxidases are distinguished from their plant and fungal counterparts by the fact that the heme group is covalently bound to the protein through ester links from glutamate and aspartate residues to the heme 1- and 5-methyl groups and, in the case of myeloperoxidase, through an additional sulfonium link from the Cbeta of the 2-vinyl group to a methionine residue. To duplicate the sulfonium link in myeloperoxidase and to obtain information on its mechanism of formation, we have engineered a methionine residue close to the 2-vinyl group in recombinant pea cytosolic ascorbate peroxidase (rpAPX) by replacement of Ser160 by Met (S160M variant). The S160M variant is isolated from Escherichia coli as apo-protein. Reconstitution of apo-S160M with exogenous heme gives a red protein (S160M(R)) which has UV-visible (lambda(max)/nm = 407, 511, 633) and steady-state kinetic (kcat = 156 +/- 7 s(-1), KM = 102 +/- 15 microM) properties that are analogous to those of rpAPX. The reaction of S160M(R) with H2O2 gives a green protein (S160M(G)). Electronic spectroscopy, mass spectrometry, and HPLC analyses are consistent with the formation of a covalent linkage between the methionine residue and the heme vinyl group in S160M(G). Single-wavelength and photodiode array stopped-flow kinetic analyses identify a transient Compound I species as a reaction intermediate. The results provide the first direct evidence that covalent heme linkage formation occurs as an H2O2-dependent process that involves Compound I formation. A mechanism that is consistent with the data is presented.
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Affiliation(s)
- Clive L Metcalfe
- Department of Chemistry, University of Leicester, University Road, Leicester LE1 7RH, UK
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32
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Colas C, De Montellano PRO. Horseradish Peroxidase Mutants That Autocatalytically Modify Their Prosthetic Heme Group. J Biol Chem 2004; 279:24131-40. [PMID: 15039425 DOI: 10.1074/jbc.m401687200] [Citation(s) in RCA: 29] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/05/2023] Open
Abstract
The mammalian peroxidases, including myeloperoxidase and lactoperoxidase, bind their prosthetic heme covalently through ester bonds to two of the heme methyl groups. These bonds are autocatalytically formed. No other peroxidase is known to form such bonds. To determine whether features other than an appropriately placed carboxylic acid residue are important for covalent heme binding, we have introduced aspartate and/or glutamic acid residues into horseradish peroxidase, a plant enzyme that exhibits essentially no sequence identity with the mammalian peroxidases. Based on superposition of the horseradish peroxidase and myeloperoxidase structures, the mutated residues were Leu(37), Phe(41), Gly(69), and Ser(73). The F41E mutant was isolated with no covalently bound heme, but the heme was completely covalently bound upon incubation with H(2)O(2). As predicted, the modified heme released from the protein was 3-hydroxymethylheme. The S73E mutant did not covalently bind its heme but oxidized it to the 8-hydroxymethyl derivative. The hydroxyl group in this modified heme derived from the medium. The other mutations gave unstable proteins. The rate of compound I formation for the F41E mutant was 100 times faster after covalent bond formation, but the reduction of compound I to compound II was similar with and without the covalent bond. The results clearly establish that an appropriately situated carboxylic acid group is sufficient for covalent heme attachment, strengthen the proposed mechanism, and suggest that covalent heme attachment in the mammalian peroxidases relates to peroxidase biology or stability rather than to intrinsic catalytic properties.
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Affiliation(s)
- Christophe Colas
- Department of Pharmaceutical Chemistry, University of California, San Francisco, California 94143-2280, USA
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Xu F, Falck JR, Ortiz de Montellano PR, Kroetz DL. Catalytic Activity and Isoform-Specific Inhibition of Rat Cytochrome P450 4F Enzymes. J Pharmacol Exp Ther 2003; 308:887-95. [PMID: 14634044 DOI: 10.1124/jpet.103.059626] [Citation(s) in RCA: 60] [Impact Index Per Article: 2.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022] Open
Abstract
Arachidonic acid is omega-hydroxylated to 20-hydroxyeicosatetraenoic acid (20-HETE), which has effects on vasoactivity and renal tubular transport and has been implicated in the regulation of blood pressure. Cytochrome p450 (p450) 4A isoforms are generally considered the major arachidonic acid omega-hydroxylases; however, little is known about the role of rat CYP4F isoforms in 20-HETE formation. The rat CYP4F isoforms, CYP4F1, CYP4F4, CYP4F5, and CYP4F6, were heterologously expressed in Escherichia coli, and their substrate specificity in fatty acid metabolism was characterized. Substrate-binding assays indicated that leukotriene B(4) (LTB(4)) and arachidonic acid bound CYP4F1 and CYP4F4 in a type-I manner with a K(s) of 25 to 59 microM, and lauric acid bound CYP4F4 poorly. Reconstituted CYP4F1 and CYP4F4 catalyzed the omega-hydroxylation of LTB(4) with a K(m) of 24 and 31 microM, respectively, and CYP4F5 had minor activity in LTB(4) metabolism. Importantly, CYP4F1 and CYP4F4 catalyzed the omega-hydroxylation of arachidonic acid with an apparent k(cat) of 9 and 11 min(-1), respectively. Lauric acid was a poor substrate for all of the CYP4F isoforms, and CYP4F6 had no detectable fatty acid omega-hydroxylase activity. The p450 omega-hydroxylase inhibitors 17-octadecynoic acid, 10-undecynyl sulfate, and N-methylsulfonyl-12,12-dibromododec-11-enamide showed isoform-specific inhibition of CYP4F1- and CYP4F4-catalyzed omega-hydroxylation of arachidonic acid and potency differences between the CYP4A and CYP4F isoforms. These data support a significant role for CYP4F1 and CYP4F4 in the formation of 20-HETE and identify p450 inhibitors that can be used to understand the relative contribution of the CYP4A and CYP4F isoforms to renal 20-HETE formation.
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Affiliation(s)
- Fengyun Xu
- Department of Biopharmaceutical Sciences, University of California, San Francisco, CA 94143-0446, USA
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Colas C, Ortiz de Montellano PR. Autocatalytic radical reactions in physiological prosthetic heme modification. Chem Rev 2003; 103:2305-32. [PMID: 12797831 DOI: 10.1021/cr0204303] [Citation(s) in RCA: 119] [Impact Index Per Article: 5.7] [Reference Citation Analysis] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/23/2022]
Affiliation(s)
- Christophe Colas
- Department of Pharmaceutical Chemistry, School of Pharmacy, University of California, San Francisco, California 94143-0446, USA
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Carr BA, Ramakanth S, Dannan GA, Yost GS. Characterization of pulmonary CYP4B2, specific catalyst of methyl oxidation of 3-methylindole. Mol Pharmacol 2003; 63:1137-47. [PMID: 12695542 DOI: 10.1124/mol.63.5.1137] [Citation(s) in RCA: 22] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022] Open
Abstract
The selective toxicity of chemicals to lung tissues is predominantly mediated by the selective expression of certain pulmonary cytochrome P450 enzymes. This report describes the purification, cloning, and characterization of a unique enzyme, CYP4B2, from goat lung. The purified P450 enzyme was isolated by multistep ion exchange chromatography to electrophoretic homogeneity with an apparent molecular mass of 55,000 Da. Western blotting studies demonstrated that CYP4B enzymes were selectively expressed in lung tissues of rabbits, rats, and mice. Two cDNAs, CYP4B2 and CYP4B2v, were cloned from goat lung tissue. CYP4B2 was predicted to be 511 amino acids and approximately 82% similar to the four known CYP4B1 proteins. Concurrently, a variant of the known human CYP4B1 cDNA, that contained a S207 insertion, was cloned from human lung tissue. The modified recombinant goat CYP4B2 was expressed in Escherichia coli and the enzyme catalyzed the N-hydroxylation of the prototypical substrate 2AF. CYP4B2 preferentially dehydrogenated, rather than hydroxylated, the pneumotoxicant 3-methylindole (3MI) (V(max) = 4.61 versus 0.83 nmol/nmol of P450/min, respectively). To investigate the relevance of covalent heme binding of CYP4 enzymes in CYP4B2-mediated metabolism of 3MI, a site-directed mutant (CYP4B2/A315E) was evaluated. The mutation had little effect on the V(max) of either dehydrogenation or hydroxylation but increased the K(m), which decreased the catalytic efficiency (V/K) for 3MI. The A315E mutation shifted the absorbance maximum of the enzyme from 448 to 451 nm, suggesting that the electron density of the heme was altered. These results demonstrate that CYP4B2 is highly specific for methyl group oxidation of 3MI, without formation of ring-oxidized metabolites, and seems to be predominately responsible for the highly organ-specific toxicity of 3MI in goats.
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Affiliation(s)
- Brian A Carr
- Department of Pharmacology and Toxicology, University of Utah Salt Lake City, 84112-5820, USA
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