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Li G, Field JA, Zeng C, Madeira CL, Nguyen CH, Jog KV, Speed D, Sierra-Alvarez R. Diazole and triazole inhibition of nitrification process in return activated sludge. CHEMOSPHERE 2020; 241:124993. [PMID: 31600622 DOI: 10.1016/j.chemosphere.2019.124993] [Citation(s) in RCA: 5] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 02/24/2019] [Revised: 09/18/2019] [Accepted: 09/27/2019] [Indexed: 06/10/2023]
Abstract
Azoles are emerging contaminants that are resistant to biodegradation during wastewater treatment. Their presence has been widely reported in wastewater effluents and receiving waters. In this work, the potential inhibition of nitrification process by six different azole compounds in wastewater treatment plants was investigated in batch bioassays. The azoles studied included three diazoles: pyrazole (Pz); 1-methylpyrazole (MePz); 3,5-dimethylpyrazole (DMePz); and three triazoles: 1,2,4-triazole (Tz); benzotriazole (BTz); and 5-methyl benzotriazole (MeBTz). The concentration of azoles causing 50% inhibition (IC50) increased (azoles became less inhibitory) in the following order (mg L-1): BTz (1.99) < MeBTz (2.18) < Pz (2.69) < Tz (3.53) < DMePz (17.3) < MePz (49.6). No clear structure-inhibitory relationships were found using Log P and pKa as structural properties. The toxicity of any given azole may be related to the role of substituent groups on disabling/enabling binding to the active sites of metallo-enzymes in nitrifying microorganisms. This is exemplified by the low toxicity of MePz, which has a cyclic N blocked by a methyl group. The observed inhibition caused to nitrifying bacteria is more severe than their cytotoxicity to other target organisms (e.g., methanogens and heterotrophic bacteria), suggesting a specific inhibition to the copper-containing enzyme, ammonium monooxygenase, in ammonia oxidizing nitrifying microorganisms.
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Affiliation(s)
- Guangbin Li
- Department of Chemical and Environmental Engineering, University of Arizona, P.O. Box 210011, Tucson, AZ, 85721, USA.
| | - James A Field
- Department of Chemical and Environmental Engineering, University of Arizona, P.O. Box 210011, Tucson, AZ, 85721, USA
| | - Chao Zeng
- Department of Chemical and Environmental Engineering, University of Arizona, P.O. Box 210011, Tucson, AZ, 85721, USA
| | - Camila Leite Madeira
- Department of Chemical and Environmental Engineering, University of Arizona, P.O. Box 210011, Tucson, AZ, 85721, USA
| | - Chi Huynh Nguyen
- Department of Chemical and Environmental Engineering, University of Arizona, P.O. Box 210011, Tucson, AZ, 85721, USA
| | - Kalyani Vikas Jog
- Department of Chemical and Environmental Engineering, University of Arizona, P.O. Box 210011, Tucson, AZ, 85721, USA
| | | | - Reyes Sierra-Alvarez
- Department of Chemical and Environmental Engineering, University of Arizona, P.O. Box 210011, Tucson, AZ, 85721, USA
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Keiblinger KM, Zehetner F, Mentler A, Zechmeister-Boltenstern S. Biochar application increases sorption of nitrification inhibitor 3,4-dimethylpyrazole phosphate in soil. ENVIRONMENTAL SCIENCE AND POLLUTION RESEARCH INTERNATIONAL 2018; 25:11173-11177. [PMID: 29520552 PMCID: PMC5895663 DOI: 10.1007/s11356-018-1658-2] [Citation(s) in RCA: 8] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 11/21/2017] [Accepted: 02/28/2018] [Indexed: 06/01/2023]
Abstract
Biochar (BC) application to soils is of growing interest as a strategy to improve soil fertility and mitigate climate change. However, BC-induced alterations in the soil N cycle are currently under debate. BC has recently been shown to accelerate the emissions of N2O via the biotic ammonium oxidation pathway, which results in lower nitrogen use efficiency and environmentally harmful losses of NO3 and/ or N2O. To avoid these potential losses, the use of nitrification inhibitor (NI) could provide a useful mitigation strategy for BC-amended agricultural fields. Here, we tested the sorption behavior of a model NI, the synthetic 3,4-dimethylpyrazole phosphate (DMPP) on 15-month-aged soil-BC mixtures. We saw that BC additions increased DMPP sorption to varying extents depending on BC feedstock type and pyrolysis temperature. The highest sorption was found for BC pyrolyzed at a lower temperature. BC effects on soil physico-chemical characteristics (i.e., hydrophobicity) seem to be important factors.
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Affiliation(s)
- Katharina M Keiblinger
- Institute of Soil Research, Department of Forest and Soil Sciences, University of Natural Resources and Life Sciences Vienna (BOKU), Peter Jordan Strasse 82, A-1190, Vienna, Austria.
| | - Franz Zehetner
- Institute of Soil Research, Department of Forest and Soil Sciences, University of Natural Resources and Life Sciences Vienna (BOKU), Peter Jordan Strasse 82, A-1190, Vienna, Austria
| | - Axel Mentler
- Institute of Soil Research, Department of Forest and Soil Sciences, University of Natural Resources and Life Sciences Vienna (BOKU), Peter Jordan Strasse 82, A-1190, Vienna, Austria
| | - Sophie Zechmeister-Boltenstern
- Institute of Soil Research, Department of Forest and Soil Sciences, University of Natural Resources and Life Sciences Vienna (BOKU), Peter Jordan Strasse 82, A-1190, Vienna, Austria
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Mak PJ, Denisov IG. Spectroscopic studies of the cytochrome P450 reaction mechanisms. BIOCHIMICA ET BIOPHYSICA ACTA. PROTEINS AND PROTEOMICS 2018; 1866:178-204. [PMID: 28668640 PMCID: PMC5709052 DOI: 10.1016/j.bbapap.2017.06.021] [Citation(s) in RCA: 44] [Impact Index Per Article: 7.3] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 05/02/2017] [Accepted: 06/22/2017] [Indexed: 10/19/2022]
Abstract
The cytochrome P450 monooxygenases (P450s) are thiolate heme proteins that can, often under physiological conditions, catalyze many distinct oxidative transformations on a wide variety of molecules, including relatively simple alkanes or fatty acids, as well as more complex compounds such as steroids and exogenous pollutants. They perform such impressive chemistry utilizing a sophisticated catalytic cycle that involves a series of consecutive chemical transformations of heme prosthetic group. Each of these steps provides a unique spectral signature that reflects changes in oxidation or spin states, deformation of the porphyrin ring or alteration of dioxygen moieties. For a long time, the focus of cytochrome P450 research was to understand the underlying reaction mechanism of each enzymatic step, with the biggest challenge being identification and characterization of the powerful oxidizing intermediates. Spectroscopic methods, such as electronic absorption (UV-Vis), electron paramagnetic resonance (EPR), nuclear magnetic resonance (NMR), electron nuclear double resonance (ENDOR), Mössbauer, X-ray absorption (XAS), and resonance Raman (rR), have been useful tools in providing multifaceted and detailed mechanistic insights into the biophysics and biochemistry of these fascinating enzymes. The combination of spectroscopic techniques with novel approaches, such as cryoreduction and Nanodisc technology, allowed for generation, trapping and characterizing long sought transient intermediates, a task that has been difficult to achieve using other methods. Results obtained from the UV-Vis, rR and EPR spectroscopies are the main focus of this review, while the remaining spectroscopic techniques are briefly summarized. This article is part of a Special Issue entitled: Cytochrome P450 biodiversity and biotechnology, edited by Erika Plettner, Gianfranco Gilardi, Luet Wong, Vlada Urlacher, Jared Goldstone.
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Affiliation(s)
- Piotr J Mak
- Department of Chemistry, Saint Louis University, St. Louis, MO, United States.
| | - Ilia G Denisov
- Department of Biochemistry, University of Illinois Urbana-Champaign, Urbana, IL, United States.
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Hartman JH, Kozal JS, Di Giulio RT, Meyer JN. Zebrafish have an ethanol-inducible hepatic 4-nitrophenol hydroxylase that is not CYP2E1-like. ENVIRONMENTAL TOXICOLOGY AND PHARMACOLOGY 2017; 54:142-145. [PMID: 28728133 PMCID: PMC5563387 DOI: 10.1016/j.etap.2017.07.004] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 07/06/2017] [Accepted: 07/07/2017] [Indexed: 06/07/2023]
Abstract
Zebrafish are an attractive model organism for toxicology; however, an important consideration in translating between species is xenobiotic metabolism/bioactivation. CYP2E1 metabolizes small hydrophobic molecules, e.g. ethanol, cigarette smoke, and diesel exhaust components. CYP2E1 is thought to only be conserved in mammals, but recent reports identified homologous zebrafish cytochrome P450s. Herein, ex vivo biochemical measurements show that unlike mammals, zebrafish possess a low-affinity 4-nitrophenol hydroxylase (Km ∼0.6 mM) in hepatic microsomes and mitochondria that is inducible only 1.5- to 2-fold by ethanol and is insensitive to 4-methylpyrazole inhibition. In closing, we suggest creating improved models to study CYP2E1 in zebrafish.
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Affiliation(s)
- Jessica H Hartman
- Nicholas School of the Environment, Duke University, Durham, NC, United States.
| | - Jordan S Kozal
- Nicholas School of the Environment, Duke University, Durham, NC, United States
| | - Richard T Di Giulio
- Nicholas School of the Environment, Duke University, Durham, NC, United States
| | - Joel N Meyer
- Nicholas School of the Environment, Duke University, Durham, NC, United States
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Challenges in assignment of allosteric effects in cytochrome P450-catalyzed substrate oxidations to structural dynamics in the hemoprotein architecture. J Inorg Biochem 2017; 167:100-115. [DOI: 10.1016/j.jinorgbio.2016.11.025] [Citation(s) in RCA: 12] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/06/2016] [Revised: 10/17/2016] [Accepted: 11/22/2016] [Indexed: 12/19/2022]
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Venkatachalam A, Parashar A, Manoj KM. Functioning of drug-metabolizing microsomal cytochrome P450s: In silico probing of proteins suggests that the distal heme 'active site' pocket plays a relatively 'passive role' in some enzyme-substrate interactions. In Silico Pharmacol 2016; 4:2. [PMID: 26894412 PMCID: PMC4760962 DOI: 10.1186/s40203-016-0016-7] [Citation(s) in RCA: 19] [Impact Index Per Article: 2.4] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/07/2015] [Accepted: 02/05/2016] [Indexed: 01/01/2023] Open
Abstract
PURPOSE The currently held mechanistic understanding of microsomal cytochrome P450s (CYPs) seeks that diverse drug molecules bind within the deep-seated distal heme pocket and subsequently react at the heme centre. To explain a bevy of experimental observations and meta-analyses, we indulge a hypothesis that involves a "diffusible radical mediated" mechanism. This new hypothesis posits that many substrates could also bind at alternate loci on/within the enzyme and be reacted without the pertinent moiety accessing a bonding proximity to the purported catalytic Fe-O enzyme intermediate. METHODS Through blind and heme-distal pocket centered dockings of various substrates and non-substrates (drug molecules of diverse sizes, classes, topographies etc.) of microsomal CYPs, we explored the possibility of access of substrates via the distal channels, its binding energies, docking orientations, distance of reactive moieties (or molecule per se) to/from the heme centre, etc. We investigated specific cases like- (a) large drug molecules as substrates, (b) classical marker drug substrates, (c) class of drugs as substrates (Sartans, Statins etc.), (d) substrate preferences between related and unrelated CYPs, (e) man-made site-directed mutants' and naturally occurring mutants' reactivity and metabolic disposition, (f) drug-drug interactions, (g) overall affinities of drug substrate versus oxidized product, (h) meta-analysis of in silico versus experimental binding constants and reaction/residence times etc. RESULTS It was found that heme-centered dockings of the substrate/modulator drug molecules with the available CYP crystal structures gave poor docking geometries and distances from Fe-heme centre. In conjunction with several other arguments, the findings discount the relevance of erstwhile hypothesis in many CYP systems. Consequently, the newly proposed hypothesis is deemed a viable alternate, as it satisfies Occam's razor. CONCLUSIONS The new proposal affords expanded scope for explaining the mechanism, kinetics and overall phenomenology of CYP mediated drug metabolism. It is now understood that the heme-iron and the hydrophobic distal pocket of CYPs serve primarily to stabilize the reactive intermediate (diffusible radical) and the surface or crypts of the apoprotein bind to the xenobiotic substrate (and in some cases, the heme distal pocket could also serve the latter function). Thus, CYPs enhance reaction rates and selectivity/specificity via a hitherto unrecognized modality.
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Affiliation(s)
- Avanthika Venkatachalam
- Formerly at PSG Institute of Advanced Studies, Avinashi Road, Peelamedu, Coimbatore, Tamil Nadu, 641004, India.
| | - Abhinav Parashar
- Formerly at Hemoproteins Lab, School of Bio Sciences and Technology, VIT University, Vellore, Tamil Nadu, India, 632014.
| | - Kelath Murali Manoj
- Formerly at PSG Institute of Advanced Studies, Avinashi Road, Peelamedu, Coimbatore, Tamil Nadu, 641004, India.
- Formerly at Hemoproteins Lab, School of Bio Sciences and Technology, VIT University, Vellore, Tamil Nadu, India, 632014.
- Satyamjayatu: The Science & Ethics Foundation, Kulappully, Shoranur-2 (PO), Kerala, 679122, India.
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Nair PC, McKinnon RA, Miners JO. Cytochrome P450 structure–function: insights from molecular dynamics simulations. Drug Metab Rev 2016; 48:434-52. [DOI: 10.1080/03602532.2016.1178771] [Citation(s) in RCA: 48] [Impact Index Per Article: 6.0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/21/2022]
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Hartman JH, Martin HC, Caro AA, Pearce AR, Miller GP. Subcellular localization of rat CYP2E1 impacts metabolic efficiency toward common substrates. Toxicology 2015; 338:47-58. [PMID: 26463279 DOI: 10.1016/j.tox.2015.10.001] [Citation(s) in RCA: 13] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/14/2015] [Revised: 09/22/2015] [Accepted: 10/06/2015] [Indexed: 01/12/2023]
Abstract
Cytochrome P450 2E1 (CYP2E1) detoxifies or bioactivates many low molecular-weight compounds. Most knowledge about CYP2E1 activity relies on studies of the enzyme localized to endoplasmic reticulum (erCYP2E1); however, CYP2E1 undergoes transport to mitochondria (mtCYP2E1) and becomes metabolically active. We report the first comparison of in vitro steady-state kinetic profiles for erCYP2E1 and mtCYP2E1 oxidation of probe substrate 4-nitrophenol and pollutants styrene and aniline using subcellular fractions from rat liver. For all substrates, metabolic efficiency changed with substrate concentration for erCYP2E1 reflected in non-hyperbolic kinetic profiles but not for mtCYP2E1. Hyperbolic kinetic profiles for the mitochondrial enzyme were consistent with Michaelis-Menten mechanism in which metabolic efficiency was constant. By contrast, erCYP2E1 metabolism of 4-nitrophenol led to a loss of enzyme efficiency at high substrate concentrations when substrate inhibited the reaction. Similarly, aniline metabolism by erCYP2E1 demonstrated negative cooperativity as metabolic efficiency decreased with increasing substrate concentration. The opposite was observed for erCYP2E1 oxidation of styrene; the sigmoidal kinetic profile indicated increased efficiency at higher substrate concentrations. These mechanisms and CYP2E1 levels in mitochondria and endoplasmic reticulum were used to estimate the impact of CYP2E1 subcellular localization on metabolic flux of pollutants. Those models showed that erCYP2E1 mainly carries out aniline metabolism at all aniline concentrations. Conversely, mtCYP2E1 dominates styrene oxidation at low styrene concentrations and erCYP2E1 at higher concentrations. Taken together, subcellular localization of CYP2E1 results in distinctly different enzyme activities that could impact overall metabolic clearance and/or activation of substrates and thus impact the interpretation and prediction of toxicological outcomes.
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Affiliation(s)
- Jessica H Hartman
- Biochemistry and Molecular Biology, University of Arkansas for Medical Sciences, Little Rock, AR, United States
| | - H Cass Martin
- Biochemistry and Molecular Biology, University of Arkansas for Medical Sciences, Little Rock, AR, United States; Department of Chemistry, University of Central Arkansas, Conway, AR, United States
| | - Andres A Caro
- Department of Chemistry, Hendrix College, Conway, AR, United States
| | - Amy R Pearce
- Arkansas Biosciences Institute, United States; Psychology & Counseling, Arkansas State University, Jonesboro, AR, United States
| | - Grover P Miller
- Biochemistry and Molecular Biology, University of Arkansas for Medical Sciences, Little Rock, AR, United States.
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Hartman JH, Letzig LG, Roberts DW, James LP, Fifer EK, Miller GP. Cooperativity in CYP2E1 metabolism of acetaminophen and styrene mixtures. Biochem Pharmacol 2015. [PMID: 26225832 DOI: 10.1016/j.bcp.2015.07.026] [Citation(s) in RCA: 10] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/16/2023]
Abstract
Risk assessment for exposure to mixtures of drugs and pollutants relies heavily on in vitro characterization of their bioactivation and/or metabolism individually and extrapolation to mixtures assuming no interaction. Herein, we demonstrated that in vitro CYP2E1 metabolic activation of acetaminophen and styrene mixtures could not be explained through the Michaelis-Menten mechanism or any models relying on that premise. As a baseline for mixture studies with styrene, steady-state analysis of acetaminophen oxidation revealed a biphasic kinetic profile that was best described by negative cooperativity (Hill coefficient=0.72). The best-fit mechanism for this relationship involved two binding sites with differing affinities (Ks=830μM and Kss=32mM). Introduction of styrene inhibited that reaction less than predicted by simple competition and thus provided evidence for a cooperative mechanism within the mixture. Likewise, acetaminophen acted through a mixed-type inhibition mechanism to impact styrene epoxidation. In this case, acetaminophen competed with styrene for CYP2E1 (Ki=830μM and Ksi=180μM for catalytic and effector sites, respectively) and resulted in cooperative impacts on binding and catalysis. Based on modeling of in vivo clearance, cooperative interactions between acetaminophen and styrene resulted in profoundly increased styrene activation at low styrene exposure levels and therapeutic acetaminophen levels. Current Michaelis-Menten based toxicological models for mixtures such as styrene and acetaminophen would fail to detect this concentration-dependent relationship. Hence, future studies must assess the role of alternate CYP2E1 mechanisms in bioactivation of compounds to improve the accuracy of interpretations and predictions of toxicity.
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Affiliation(s)
- Jessica H Hartman
- Department of Biochemistry and Molecular Biology, College of Medicine, University of Arkansas for Medical Sciences, Little Rock, AR, United States
| | - Lynda G Letzig
- Department of Pediatrics, College of Medicine, University of Arkansas for Medical Sciences, Little Rock, AR, United States
| | - Dean W Roberts
- Department of Pediatrics, College of Medicine, University of Arkansas for Medical Sciences, Little Rock, AR, United States
| | - Laura P James
- Department of Pediatrics, College of Medicine, University of Arkansas for Medical Sciences, Little Rock, AR, United States
| | - E Kim Fifer
- Department of Pharmaceutical Sciences, College of Pharmacy, University of Arkansas for Medical Sciences, Little Rock, AR, United States
| | - Grover P Miller
- Department of Biochemistry and Molecular Biology, College of Medicine, University of Arkansas for Medical Sciences, Little Rock, AR, United States.
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Structural basis for cooperative binding of azoles to CYP2E1 as interpreted through guided molecular dynamics simulations. J Mol Graph Model 2014; 56:43-52. [PMID: 25544389 DOI: 10.1016/j.jmgm.2014.11.013] [Citation(s) in RCA: 14] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/11/2014] [Revised: 10/21/2014] [Accepted: 11/30/2014] [Indexed: 01/20/2023]
Abstract
CYP2E1 metabolizes a wide array of small, hydrophobic molecules, resulting in their detoxification or activation into carcinogens through Michaelis-Menten as well as cooperative mechanisms. Nevertheless, the molecular determinants for CYP2E1 specificity and metabolic efficiency toward these compounds are still unknown. Herein, we employed computational docking studies coupled to molecular dynamics simulations to provide a critical perspective for understanding a structural basis for cooperativity observed for an array of azoles from our previous binding and catalytic studies (Hartman et al., 2014). The resulting 28 CYP2E1 complexes in this study revealed a common passageway for azoles that included a hydrophobic steric barrier causing a pause in movement toward the active site. The entrance to the active site acted like a second sieve to restrict access to the inner chamber. Collectively, these interactions impacted the final orientation of azoles reaching the active site and hence could explain differences in their biochemical properties observed in our previous studies, such as the consequences of methylation at position 5 of the azole ring. The association of a second azole demonstrated significant differences in interactions stabilizing the bound complex than observed for the first binding event. Intermolecular interactions occurred between the two azoles as well as CYP2E1 residue side chains and backbone and involved both hydrophobic contacts and hydrogen bonds. The relative importance of these interactions depended on the structure of the respective azoles indicating the absence of specific defining criteria for binding unlike the well-characterized dominant role of hydrophobicity in active site binding. Consequently, the structure activity relationships described here and elsewhere are necessary to more accurately identify factors impacting the observation and significance of cooperativity in CYP2E1 binding and catalysis toward drugs, dietary compounds, and pollutants.
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Wang M, Baaden M, Wang J, Liang Z. A cooperative mechanism of clotrimazoles in P450 revealed by the dissociation picture of clotrimazole from P450. J Chem Inf Model 2014; 54:1218-25. [PMID: 24611729 DOI: 10.1021/ci400660e] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
Abstract
The dissociation processes of clotrimazole (CLT) in several models are comparatively investigated by molecular dynamics simulations to explore the cooperative mechanism of clotrimazoles in P450. Our results suggest that when P450 only accommodates the active CLT (CLT1), CLT1 continually diffuses away from heme, and the partial BC loop (residues 73-88) and the extended FG loop (residues 173-186) first close and then open. When the enzyme binds to two CLT molecules, CLT1 basically keeps close to heme, and the partial BC loop and the extended FG loop move close to each other. Clearly, the effector CLT (CLT2) plays a cooperative role in the inhibition of CLT1 on P450. CLT2 restrains the dissociation of CLT1 first through direct π-π stacking interactions and then through the rearranged binding site induced by CLT2. The presence of CLT1 can help to stabilize the protein structure around CLT2 by interacting with M86, Q173, and M174.
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Affiliation(s)
- Mian Wang
- School of Chemistry and Chemical Engineering, Guangxi University , Nanning 530004, China
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12
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Hartman JH, Knott K, Miller GP. CYP2E1 hydroxylation of aniline involves negative cooperativity. Biochem Pharmacol 2014; 87:523-33. [DOI: 10.1016/j.bcp.2013.12.003] [Citation(s) in RCA: 20] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/21/2013] [Revised: 11/28/2013] [Accepted: 12/02/2013] [Indexed: 11/24/2022]
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13
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Pianalto KM, Hartman JH, Boysen G, Miller GP. Differences in butadiene adduct formation between rats and mice not due to selective inhibition of CYP2E1 by butadiene metabolites. Toxicol Lett 2013; 223:221-7. [PMID: 24021170 PMCID: PMC3831829 DOI: 10.1016/j.toxlet.2013.08.025] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/04/2013] [Revised: 08/29/2013] [Accepted: 08/30/2013] [Indexed: 10/26/2022]
Abstract
CYP2E1 metabolizes 1,3-butadiene (BD) into genotoxic and possibly carcinogenic 1,2-epoxy-3-butene (EB), 1,2:3,4-diepoxybutane (DEB), and 1,2-epoxy-3,4-butanediol (EB-diol). The dose response of DNA and protein adducts derived from BD metabolites increases linearly at low BD exposures and then saturates at higher exposures in rats, but not mice. It was hypothesized that differences in adduct formation between rodents reflect more efficient BD oxidation in mice than rats. Herein, we assessed whether BD-derived metabolites selectively inhibit rat but not mouse CYP2E1 activity using B6C3F1 mouse and Fisher 344 rat liver microsomes. Basal CYP2E1 activities toward 4-nitrophenol were similar between rodents. Through IC50 studies, EB was the strongest inhibitor (IC50 54μM, mouse; 98μM, rat), BD-diol considerably weaker (IC50 1200μM, mouse; 1000μM, rat), and DEB inhibition nonexistent (IC50>25mM). Kinetic studies showed that in both species EB and BD-diol inhibited 4-nitrophenol oxidation through two-site mechanisms in which inhibition constants reflected trends observed in IC50 studies. None of the reactive epoxide metabolites inactivated CYP2E1 irreversibly. Thus, there was no selective inhibition or inactivation of rat CYP2E1 by BD metabolites relative to mouse Cyp2e1, and it can be inferred that CYP2E1 activity toward BD between rodent species would similarly not be impacted by the presence of BD metabolites. Inhibition of CYP2E1 by BD metabolites is then not responsible for the reported species difference in BD metabolism, formation of BD-derived DNA and protein adducts, mutagenicity and tumorigenesis.
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Affiliation(s)
- Kaila M. Pianalto
- Department of Chemistry and Biochemistry, University of Arkansas at Fayetteville, Fayetteville, AR 72701, USA
| | - Jessica H. Hartman
- Department of Biochemistry and Molecular Biology, University of Arkansas for Medical Sciences, Little Rock, AR 72205, USA
| | - Gunnar Boysen
- Department of Environmental and Occupational Health, University of Arkansas for Medical Sciences, Little Rock, AR 72205, USA
| | - Grover P. Miller
- Department of Biochemistry and Molecular Biology, University of Arkansas for Medical Sciences, Little Rock, AR 72205, USA
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