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Xia S, Hirao H. The Dissociation Process of NADP + from NADPH-Cytochrome P450 Reductase Studied by Molecular Dynamics Simulation. J Phys Chem B 2024. [PMID: 38991231 DOI: 10.1021/acs.jpcb.4c03329] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 07/13/2024]
Abstract
NADPH-cytochrome P450 reductase (CPR) plays a vital role as a redox partner for mammalian cytochrome P450 enzymes (P450s), facilitating the transfer of two electrons from NADPH to the P450 heme center in a sequential manner. Previous experimental studies revealed substantial domain movements of CPR, transitioning between closed and open states during the electron transfer (ET) cycle. These transitions are essential and are influenced by the binding of NADPH or the release of NADP+. However, the intricate molecular mechanisms governing the CPR-mediated ET cycle have largely remained elusive. This study employed molecular dynamics (MD) simulation techniques to explore the dissociation of NADP+ from CPR, a crucial step preceding the initial ET from CPR to a P450. Alongside the binding structure of NADP+ observed in a crystal structure (pose I), our MD simulations identified an alternative binding structure (pose II). Although pose II exhibits slightly lower stability than pose I, it can be formed through an approximate 210° counterclockwise rotation of the adenine group, with a free energy barrier of only 2.76 kcal/mol. The simulation results further suggest that NADP+ dissociation involves a tentative formation of pose II from pose I before complete dissociation, and that the binding of NADP+ to CPR is primarily governed by nonbonded interactions within the adenosine binding pocket.
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Affiliation(s)
- Songyan Xia
- Warshel Institute for Computational Biology, School of Medicine, The Chinese University of Hong Kong, Shenzhen, Guangdong 518172, P.R. China
| | - Hajime Hirao
- Warshel Institute for Computational Biology, School of Medicine, The Chinese University of Hong Kong, Shenzhen, Guangdong 518172, P.R. China
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2
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Bizet M, Byrne D, Biaso F, Gerbaud G, Etienne E, Briola G, Guigliarelli B, Urban P, Dorlet P, Kalai T, Truan G, Martinho M. Structural insights into the semiquinone form of human Cytochrome P450 reductase by DEER distance measurements between a native flavin and a spin labelled non-canonical amino acid. Chemistry 2024; 30:e202304307. [PMID: 38277424 DOI: 10.1002/chem.202304307] [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: 12/22/2023] [Revised: 01/25/2024] [Accepted: 01/26/2024] [Indexed: 01/28/2024]
Abstract
The flavoprotein Cytochrome P450 reductase (CPR) is the unique electron pathway from NADPH to Cytochrome P450 (CYPs). The conformational dynamics of human CPR in solution, which involves transitions from a "locked/closed" to an "unlocked/open" state, is crucial for electron transfer. To date, however, the factors guiding these changes remain unknown. By Site-Directed Spin Labelling coupled to Electron Paramagnetic Resonance spectroscopy, we have incorporated a non-canonical amino acid onto the flavin mononucleotide (FMN) and flavin adenine dinucleotide (FAD) domains of soluble human CPR, and labelled it with a specific nitroxide spin probe. Taking advantage of the endogenous FMN cofactor, we successfully measured for the first time, the distance distribution by DEER between the semiquinone state FMNH• and the nitroxide. The DEER data revealed a salt concentration-dependent distance distribution, evidence of an "open" CPR conformation at high salt concentrations exceeding previous reports. We also conducted molecular dynamics simulations which unveiled a diverse ensemble of conformations for the "open" semiquinone state of the CPR at high salt concentration. This study unravels the conformational landscape of the one electron reduced state of CPR, which had never been studied before.
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Affiliation(s)
- Maxime Bizet
- Aix Marseille Univ, CNRS, Bioénergétique et Ingénierie des Protéines, IMM, 13402, Marseille, France
| | - Deborah Byrne
- Protein Expression Facility, Aix Marseille Univ, CNRS, IMM, 13402, Marseille, France
| | - Frédéric Biaso
- Aix Marseille Univ, CNRS, Bioénergétique et Ingénierie des Protéines, IMM, 13402, Marseille, France
| | - Guillaume Gerbaud
- Aix Marseille Univ, CNRS, Bioénergétique et Ingénierie des Protéines, IMM, 13402, Marseille, France
| | - Emilien Etienne
- Aix Marseille Univ, CNRS, Bioénergétique et Ingénierie des Protéines, IMM, 13402, Marseille, France
| | - Giuseppina Briola
- Aix Marseille Univ, CNRS, Bioénergétique et Ingénierie des Protéines, IMM, 13402, Marseille, France
| | - Bruno Guigliarelli
- Aix Marseille Univ, CNRS, Bioénergétique et Ingénierie des Protéines, IMM, 13402, Marseille, France
| | - Philippe Urban
- TBI, Université de Toulouse, CNRS, INRAE, INSA, 31077, Toulouse, France
| | - Pierre Dorlet
- Aix Marseille Univ, CNRS, Bioénergétique et Ingénierie des Protéines, IMM, 13402, Marseille, France
| | - Tamas Kalai
- Department of Organic and Medicinal Chemistry, Faculty of Pharmacy, University of Pécs, PO Box 99 Szigeti st. 12, H-7602 7624, Pécs, Hungary
| | - Gilles Truan
- TBI, Université de Toulouse, CNRS, INRAE, INSA, 31077, Toulouse, France
| | - Marlène Martinho
- Aix Marseille Univ, CNRS, Bioénergétique et Ingénierie des Protéines, IMM, 13402, Marseille, France
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3
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Hubbard PA, Xia C, Shen AL, Kim JJP. Structural and kinetic investigations of the carboxy terminus of NADPH-cytochrome P450 oxidoreductase. Arch Biochem Biophys 2021; 701:108792. [PMID: 33556357 PMCID: PMC8020834 DOI: 10.1016/j.abb.2021.108792] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/18/2020] [Revised: 01/20/2021] [Accepted: 01/31/2021] [Indexed: 01/04/2023]
Abstract
The influence of the side chains and positioning of the carboxy-terminal residues of NADPH-cytochrome P450 oxidoreductase (CYPOR) on catalytic activity, structure of the carboxy terminus, and interaction with cofactors has been investigated. A tandem deletion of residues Asp675 and Val676, that was expected to shift the position of the functionally important Trp677, resulted in higher cytochrome c reductase activity than that expected from previous studies on the importance of Asp675 and Trp677 in catalysis. Crystallographic determination of the structure of this variant revealed two conformations of the carboxy terminus. In one conformation (Mol A), the last α-helix is partially unwound, resulting in repositioning of all subsequent residues in β-strand 21, from Arg671 to Leu674 (corresponding to Ser673 and Val676 in the wild type structure). This results in the two C-terminal residues, Trp677 and Ser678, being maintained in their wild type positions, with the indole ring of Trp677 stacked against the isoalloxazine ring of FAD as seen in the wild type structure, and Ser673 occupying a similar position to the catalytic residue, Asp675. The other, more disordered conformation is a mixture of the Mol A conformation and one in which the last α-helix is not unwound and the nicotinamide ring is in one of two conformations, out towards the protein surface as observed in the wild type structure (1AMO), or stacked against the flavin ring, similar to that seen in the W677X structure that lacks Trp677 and Ser678 (1JA0). Further kinetic analysis on additional variants showed deletion or substitution of alanine or glycine for Trp677 in conjunction with deletion of Ser678 produced alterations in interactions of CYPOR with NADP+, 2'5'-ADP, and 2'-AMP, as well as the pH dependence of cytochrome c reductase activity. We postulate that deletion of bulky residues at the carboxy terminus permits increased mobility leading to decreased affinity for the 2'5'-ADP and 2'-AMP moieties of NADP+ and subsequent domain movement.
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Affiliation(s)
- Paul A Hubbard
- Department of Biochemistry, Medical College of Wisconsin, Milwaukee, WI, 53226, USA
| | - Chuanwu Xia
- Department of Biochemistry, Medical College of Wisconsin, Milwaukee, WI, 53226, USA
| | - Anna L Shen
- McArdle Laboratory for Cancer Research, Department of Oncology, University of Wisconsin School of Medicine and Public Health, Madison, WI, 53706, USA
| | - Jung-Ja P Kim
- Department of Biochemistry, Medical College of Wisconsin, Milwaukee, WI, 53226, USA.
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4
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Xia C, Rwere F, Im S, Shen AL, Waskell L, Kim JJP. Structural and Kinetic Studies of Asp632 Mutants and Fully Reduced NADPH-Cytochrome P450 Oxidoreductase Define the Role of Asp632 Loop Dynamics in the Control of NADPH Binding and Hydride Transfer. Biochemistry 2018; 57:945-962. [PMID: 29308883 PMCID: PMC5967631 DOI: 10.1021/acs.biochem.7b01102] [Citation(s) in RCA: 8] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/07/2023]
Abstract
Conformational changes in NADPH-cytochrome P450 oxidoreductase (CYPOR) associated with electron transfer from NADPH to electron acceptors via FAD and FMN have been investigated via structural studies of the four-electron-reduced NADP+-bound enzyme and kinetic and structural studies of mutants that affect the conformation of the mobile Gly631-Asn635 loop (Asp632 loop). The structure of four-electron-reduced, NADP+-bound wild type CYPOR shows the plane of the nicotinamide ring positioned perpendicular to the FAD isoalloxazine with its carboxamide group forming H-bonds with N1 of the flavin ring and the Thr535 hydroxyl group. In the reduced enzyme, the C8-C8 atoms of the two flavin rings are ∼1 Å closer than in the fully oxidized and one-electron-reduced structures, which suggests that flavin reduction facilitates interflavin electron transfer. Structural and kinetic studies of mutants Asp632Ala, Asp632Phe, Asp632Asn, and Asp632Glu demonstrate that the carboxyl group of Asp632 is important for stabilizing the Asp632 loop in a retracted position that is required for the binding of the NADPH ribityl-nicotinamide in a hydride-transfer-competent conformation. Structures of the mutants and reduced wild type CYPOR permit us to identify a possible pathway for NADP(H) binding to and release from CYPOR. Asp632 mutants unable to form stable H-bonds with the backbone amides of Arg634, Asn635, and Met636 exhibit decreased catalytic activity and severely impaired hydride transfer from NADPH to FAD, but leave interflavin electron transfer intact. Intriguingly, the Arg634Ala mutation slightly increases the cytochrome P450 2B4 activity. We propose that Asp632 loop movement, in addition to facilitating NADP(H) binding and release, participates in domain movements modulating interflavin electron transfer.
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Affiliation(s)
- Chuanwu Xia
- Medical College of Wisconsin, Milwaukee, Wisconsin 53226
| | - Freeborn Rwere
- University of Michigan Medical School, Ann Arbor, Michigan 48105
| | - Sangchoul Im
- University of Michigan Medical School, Ann Arbor, Michigan 48105
| | - Anna L. Shen
- McArdle Laboratory for Cancer Research, University of Wisconsin-Madison, Madison, Wisconsin 53706
| | - Lucy Waskell
- University of Michigan Medical School, Ann Arbor, Michigan 48105,Corresponding Author: Correspondence should be addressed to Lucy Waskell, M.D., Ph.D., Department of Anesthesiology, University of Michigan, Mail Stop 151, 2215 Fuller Rd., Ann Arbor, MI 48109-0112. . OR Jung Ja Kim, Ph.D., Department of Biochemistry, Medical College of Wisconsin, 8701 Watertown Plank Rd., Milwaukee, WI 53226.
| | - Jung-Ja P. Kim
- Medical College of Wisconsin, Milwaukee, Wisconsin 53226,Corresponding Author: Correspondence should be addressed to Lucy Waskell, M.D., Ph.D., Department of Anesthesiology, University of Michigan, Mail Stop 151, 2215 Fuller Rd., Ann Arbor, MI 48109-0112. . OR Jung Ja Kim, Ph.D., Department of Biochemistry, Medical College of Wisconsin, 8701 Watertown Plank Rd., Milwaukee, WI 53226.
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5
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Chu WT, Nesbitt NM, Gnatenko DV, Li Z, Zhang B, Seeliger MA, Browne S, Mantle TJ, Bahou WF, Wang J. Enzymatic Activity and Thermodynamic Stability of Biliverdin IXβ Reductase Are Maintained by an Active Site Serine. Chemistry 2017; 23:1891-1900. [PMID: 27897348 DOI: 10.1002/chem.201604517] [Citation(s) in RCA: 10] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [Key Words] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/23/2016] [Indexed: 11/10/2022]
Abstract
Biliverdin reductase IXβ (BLVRB) is a crucial enzyme in heme metabolism. Recent studies in humans have identified a loss-of-function mutation (Ser111Leu) that unmasks a fundamentally important role in hematopoiesis. We have undertaken experimental and thermodynamic modeling studies to provide further insight into the role of the cofactor in substrate accessibility and protein folding properties regulating BLVRB catalytic mechanisms. Site-directed mutagenesis with molecular dynamic (MD) simulations establish the critical role of NAD(P)H-dependent conformational changes on substrate accessibility by forming the "hydrophobic pocket", along with identification of a single key residue (Arg35) modulating NADPH/NADH selectivity. Loop80 and Loop120 block the hydrophobic substrate binding pocket in apo BLVRB (open), whereas movement of these structures after cofactor binding results in the "closed" (catalytically active) conformation. Both enzymatic activity and thermodynamic stability are affected by mutation(s) involving Ser111, which is located in the core of the BLVRB active site. This work 1) elucidates the crucial role of Ser111 in enzymatic catalysis and thermodynamic stability by active site hydrogen bond network; 2) defines a dynamic model for apo BLVRB extending beyond the crystal structure of the binary BLVRB/NADP+ complex; 3) provides a structural basis for the "encounter" and "equilibrium" states of the binary complex, which are regulated by NAD(P)H.
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Affiliation(s)
- Wen-Ting Chu
- State Key Laboratory of Electroanalytical Chemistry, Changchun Institute of Applied Chemistry, Chinese Academy of Sciences, Changchun, Jilin, 130022, P. R. China
| | - Natasha M Nesbitt
- Department of Medicine, Stony Brook University, Stony Brook, NY, 11794, USA
| | - Dmitri V Gnatenko
- Department of Medicine, Stony Brook University, Stony Brook, NY, 11794, USA
| | - Zongdong Li
- Department of Medicine, Stony Brook University, Stony Brook, NY, 11794, USA
| | - Beibei Zhang
- Department of Biochemistry and Cell Biology, Stony Brook University, Stony Brook, NY, 11794, USA
| | - Markus A Seeliger
- Department of Pharmacological Sciences, Stony Brook University, Stony Brook, NY, 11794, USA
| | - Seamus Browne
- Department of Biochemistry, Trinity College, Dublin 2, Ireland
| | | | - Wadie F Bahou
- Department of Medicine, Stony Brook University, Stony Brook, NY, 11794, USA
| | - Jin Wang
- State Key Laboratory of Electroanalytical Chemistry, Changchun Institute of Applied Chemistry, Chinese Academy of Sciences, Changchun, Jilin, 130022, P. R. China.,Department of Chemistry and Physics, Stony Brook University, Stony Brook, NY, 11794, USA
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6
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Gillani TB, Rawling T, Murray M. Cytochrome P450-Mediated Biotransformation of Sorafenib and Its N-Oxide Metabolite: Implications for Cell Viability and Human Toxicity. Chem Res Toxicol 2014; 28:92-102. [DOI: 10.1021/tx500373g] [Citation(s) in RCA: 17] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/28/2022]
Affiliation(s)
- Tina B. Gillani
- Pharmacogenomics
and Drug Development Group, Discipline of Pharmacology, University of Sydney, Sydney, NSW 2006, Australia
| | - Tristan Rawling
- School
of Pharmacy, Graduate School of Health, University of Technology, Sydney, PO
Box 123, Broadway, Ultimo, NSW 2007, Australia
| | - Michael Murray
- Pharmacogenomics
and Drug Development Group, Discipline of Pharmacology, University of Sydney, Sydney, NSW 2006, Australia
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7
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Roston D, Kohen A, Doron D, Major DT. Simulations of remote mutants of dihydrofolate reductase reveal the nature of a network of residues coupled to hydride transfer. J Comput Chem 2014; 35:1411-7. [PMID: 24798860 DOI: 10.1002/jcc.23629] [Citation(s) in RCA: 17] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/09/2014] [Revised: 03/11/2014] [Accepted: 04/06/2014] [Indexed: 11/07/2022]
Abstract
Recent experimental and theoretical studies have proposed that enzymes involve networks of coupled residues throughout the protein that participate in motions accompanying chemical barrier crossing. Here, we have examined portions of a proposed network in dihydrofolate reductase (DHFR) using quantum mechanics/molecular mechanics simulations. The simulations use a hybrid quantum mechanics-molecular mechanics approach with a recently developed semiempirical AM1-SRP Hamiltonian that provides accurate results for this reaction. The simulations reproduce experimentally determined catalytic rates for the wild type and distant mutants of E. coli DHFR, underscoring the accuracy of the simulation protocol. Additionally, the simulations provide detailed insight into how residues remote from the active site affect the catalyzed chemistry, through changes in the thermally averaged properties along the reaction coordinate. The mutations do not greatly affect the structure of the transition state near the bond activation, but we observe differences somewhat removed from the point of C-H cleavage that affect the rate. The mutations have global effects on the thermally averaged structure that propagate throughout the enzyme and the current simulations highlight several interactions that appear to be particularly important.
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Affiliation(s)
- Daniel Roston
- Department of Chemistry, University of Iowa, Iowa City, Iowa, 52242
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8
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Doron D, Major DT, Kohen A, Thiel W, Wu X. Hybrid Quantum and Classical Simulations of the Dihydrofolate Reductase Catalyzed Hydride Transfer Reaction on an Accurate Semi-Empirical Potential Energy Surface. J Chem Theory Comput 2011; 7:3420-37. [PMID: 26598171 DOI: 10.1021/ct2004808] [Citation(s) in RCA: 45] [Impact Index Per Article: 3.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Abstract
Dihydrofolate reductase (DHFR) catalyzes the reduction of 7,8-dihydrofolate by nicotinamide adenine dinucleotide phosphate hydride (NADPH) to form 5,6,7,8-tetrahydrofolate and oxidized nicotinamide. DHFR is a small, flexible, monomeric protein with no metals or SS bonds and serves as one of the enzymes commonly used to examine basic aspects in enzymology. In the current work, we present extensive benchmark calculations for several model reactions in the gas phase that are relevant to the DHFR catalyzed hydride transfer. To this end, we employ G4MP2 and CBS-QB3 ab initio calculations as well as numerous density functional theory methods. Using these results, we develop two specific reaction parameter (SRP) Hamiltonians based on the semiempirical AM1 method. The first generation SRP Hamiltonian does not account for dispersion, while the second generation SRP accounts for dispersion implicitly via the AM1 core-repulsion functions. These SRP semiempirical Hamiltonians are subsequently used in hybrid quantum mechanics/molecular mechanics simulations of the DHFR catalyzed reaction. Finally, kinetic isotope effects are computed using a mass-perturbation-based path-integral approach.
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Affiliation(s)
- Dvir Doron
- Department of Chemistry, The Lise Meitner-Minerva Center of Computational Quantum Chemistry, Bar-Ilan University , Ramat-Gan 52900, Israel
| | - Dan Thomas Major
- Department of Chemistry, The Lise Meitner-Minerva Center of Computational Quantum Chemistry, Bar-Ilan University , Ramat-Gan 52900, Israel
| | - Amnon Kohen
- Department of Chemistry, University of Iowa , Iowa City, Iowa 52242, United States
| | - Walter Thiel
- Max-Planck-Institut für Kohlenforschung , Kaiser-Wilhelm-Platz 1, D-45470 Mülheim an der Ruhr, Germany
| | - Xin Wu
- Max-Planck-Institut für Kohlenforschung , Kaiser-Wilhelm-Platz 1, D-45470 Mülheim an der Ruhr, Germany
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9
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Traylor MJ, Chai J, Clark DS. Simultaneous measurement of CYP1A2 activity, regioselectivity, and coupling: Implications for environmental sensitivity of enzyme-substrate binding. Arch Biochem Biophys 2010; 505:186-93. [PMID: 20933493 DOI: 10.1016/j.abb.2010.10.002] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/25/2010] [Revised: 10/04/2010] [Accepted: 10/04/2010] [Indexed: 11/15/2022]
Abstract
The cytochrome P450 (CYP) reaction mechanism often yields a broad array of coupled and uncoupled products from a single substrate. While it is well known that reaction conditions can drastically affect the rate of P450 catalysis, their effects on regioselectivity and coupling are not well characterized. To investigate such effects, the CYP1A2 oxidation of 7-ethoxymethoxy-3-cyanocoumarin (EOMCC) was examined as a function of buffer type, buffer concentration, pH, and temperature. A high-throughput, optical method was developed to simultaneously measure the rate of substrate depletion, NADPH depletion, and generation of the O-dealkylated product. Increasing the phosphate buffer concentration and temperature increased both the NADPH and EOMCC depletion rates by 6-fold, whereas coupling was constant at 7.9% and the regioselectivity of O-dealkylation to other coupled pathways was constant at 21.7%. Varying the buffer type and pH increased NADPH depletion by 2.5-fold and EOMCC depletion by 3.5-fold; however, neither coupling nor regioselectivity was constant, with variations of 14.4% and 21.6%, respectively. Because the enzyme-substrate binding interaction is a primary determinant of both coupling and regioselectivity, it is reasonable to conclude that ionic strength, as varied by the buffer concentration, and temperature alter the rate without affecting binding while buffer type and pH alter both.
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Affiliation(s)
- Matthew J Traylor
- Department of Chemical and Biomolecular Engineering, University of California, Berkeley, 94720, United States
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10
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Brenner S, Hay S, Munro AW, Scrutton NS. Inter-flavin electron transfer in cytochrome P450 reductase - effects of solvent and pH identify hidden complexity in mechanism. FEBS J 2008; 275:4540-57. [PMID: 18681889 DOI: 10.1111/j.1742-4658.2008.06597.x] [Citation(s) in RCA: 36] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
Abstract
This study on human cytochrome P450 reductase (CPR) presents a comprehensive analysis of the thermodynamic and kinetic effects of pH and solvent on two- and four-electron reduction in this diflavin enzyme. pH-dependent redox potentiometry revealed that the thermodynamic equilibrium between various two-electron reduced enzyme species (FMNH*,FADH*; FMN,FADH2; FMNH2,FAD) is independent of pH. No shift from the blue, neutral di-semiquinone (FMNH*,FADH*) towards the red, anionic species is observed upon increasing the pH from 6.5 to 8.5. Spectrophotometric analysis of events following the mixing of oxidized CPR and NADPH (1 to 1) in a stopped-flow instrument demonstrates that the establishment of this thermodynamic equilibrium becomes a very slow process at elevated pH, indicative of a pH-gating mechanism. The final level of blue di-semiquinone formation is found to be pH independent. Stopped-flow experiments using excess NADPH over CPR provide evidence that both pH and solvent significantly influence the kinetic exposure of the blue di-semiquinone intermediate, yet the observed rate constants are essentially pH independent. Thus, the kinetic pH-gating mechanism under stoichiometric conditions is of no significant kinetic relevance for four-electron reduction, but rather modulates the observed semiquinone absorbance at 600 nm in a pH-dependent manner. The use of proton inventory experiments and primary kinetic isotope effects are described as kinetic tools to disentangle the intricate pH-dependent kinetic mechanism in CPR. Our analysis of the pH and isotope dependence in human CPR reveals previously hidden complexity in the mechanism of electron transfer in this complex flavoprotein.
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Affiliation(s)
- Sibylle Brenner
- Manchester Interdisciplinary Biocentre and Faculty of Life Sciences, University of Manchester, UK
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11
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Matsunaga T, Higuchi S, Watanabe K, Kageyama T, Ohmori S, Yamamoto I. Effective NADH-dependent oxidation of 7beta-hydroxy-delta8-tetrahydrocannabinol to the corresponding ketone by Japanese monkey hepatic microsomes. Biol Pharm Bull 2005; 28:646-51. [PMID: 15802803 DOI: 10.1248/bpb.28.646] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022]
Abstract
The NADH-dependent activity by hepatic microsomes of Japanese monkeys for 7-oxo-Delta(8)-tetrahydrocannabinol (7-oxo-Delta(8)-THC) formation from 7beta-hydroxy-Delta(8)-THC exhibited about 70% of the NADPH-dependent activity (100%) at the substrate concentration of 72.7 microM, although NADPH was an obligatory cofactor for maximal activity. Both NADH- and NADPH-dependent activities were significantly inhibited by the typical P450 inhibitors, such as SKF525-A and metyrapone. Both activities were almost completely inhibited by the NADPH-P450 reductase inhibitor diphenyliodonium chloride. The ratio of NADH- and NADPH-dependent activities varied significantly according to the substrate concentration. Interestingly, the NADH-dependent activity was higher than that of NADPH at low substrate concentrations of 13-50 microM. The ratio was also affected by the cofactor concentration. In the reconstituted system of CYP3A8 purified from hepatic microsomes of Japanese monkeys as a major enzyme responsible for the NADPH-dependent oxidation, NADH as well as NADPH could sustain the oxidation of 7beta-hydroxy-Delta(8)-THC to the corresponding ketone. The NADH-dependent oxidation of 7beta-hydroxy-Delta(8)-THC by monkey livers is mainly catalyzed by CYP3A8 as well as the NADPH-dependent oxidation. These results indicate that NADH as a cofactor may be also useful for the oxidation of 7beta-hydroxy-Delta(8)-THC, and that the cofactor requirement for the reaction is varied by the concentrations of substrate and/or cofactor.
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12
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Higashimoto Y, Sakamoto H, Hayashi S, Sugishima M, Fukuyama K, Palmer G, Noguchi M. Involvement of NADPH in the interaction between heme oxygenase-1 and cytochrome P450 reductase. J Biol Chem 2004; 280:729-37. [PMID: 15516695 DOI: 10.1074/jbc.m406203200] [Citation(s) in RCA: 37] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
Heme oxygenase-1 (HO-1) catalyzes the physiological degradation of heme at the expense of molecular oxygen using electrons donated by NADPH-cytochrome P450 reductase (CPR). In this study, we investigated the effect of NADP(H) on the interaction of HO-1 with CPR by surface plasmon resonance. We found that HO-1 associated with CPR more tightly in the presence of NADP(+) (K(D) = 0.5 microm) than in its absence (K(D) = 2.4 microm). The HO-1 mutants, K149A, K149A/K153A, and R185A, showed almost no heme degradation activity with NADPH-CPR, whereas they exhibited activity comparable to that of the wild type when sodium ascorbate was used. R185A showed a 100-fold decreased affinity for CPR compared with wild type, even in the presence of NADP(+) (K(D) = 36.3 microm). The affinities of K149A and K149A/K153A for CPR were decreased 7- and 9-fold (K(D) = 16.8 and 21.8 microm), respectively. In contrast to R185A, the affinities of K149A and K149A/K153A were improved by the addition of NADP(+) (K(D) = 5.2 and 9.6 microm, respectively), as was the case with wild type. Computer modeling of the HO-1/CPR complex showed that the guanidino group of Arg(185) is located within the hydrogen bonding distance of 2'-phosphate of NADPH, suggesting that Arg(185) contributes to the binding to CPR through an electrostatic interaction with the phosphate group. On the other hand, Lys(149) is close to a cluster of acidic amino acids near the FMN binding site of CPR. Thus, Lys(149) and Lys(153) appear to interact with CPR in such a way as to orient the redox partners for optimal electron transfer from FMN of CPR to heme of HO-1.
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Affiliation(s)
- Yuichiro Higashimoto
- Department of Medical Biochemistry, Kurume University School of Medicine, 67 Asahi-machi, Kurume 830-0011, Japan
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13
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Murataliev MB, Feyereisen R, Walker FA. Electron transfer by diflavin reductases. BIOCHIMICA ET BIOPHYSICA ACTA-PROTEINS AND PROTEOMICS 2004; 1698:1-26. [PMID: 15063311 DOI: 10.1016/j.bbapap.2003.10.003] [Citation(s) in RCA: 150] [Impact Index Per Article: 7.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 05/01/2003] [Revised: 08/20/2003] [Accepted: 10/14/2003] [Indexed: 11/25/2022]
Abstract
Diflavin reductases are enzymes which emerged as a gene fusion of ferredoxin (flavodoxin) reductase and flavodoxin. The enzymes of this family tightly bind two flavin cofactors, FAD and FMN, and catalyze transfer of the reducing equivalents from the two-electron donor NADPH to a variety of one-electron acceptors. Cytochrome P450 reductase (P450R), a flavoprotein subunit of sulfite reductase (SiR), and flavoprotein domains of naturally occurring flavocytochrome fusion enzymes like nitric oxide synthases (NOS) and the fatty acid hydroxylase from Bacillus megaterium are some of the enzymes of this family. In this review the results of the last decade of research are summarized, and some earlier results are reevaluated as well. The kinetic mechanism of cytochrome c reduction is analyzed in light of other results on flavoprotein interactions with nucleotides and cytochromes. The roles of the binding sites of the isoalloxazine rings of the flavin cofactors and conformational changes of the protein in electron transfer are discussed. It is proposed that minor conformational changes during catalysis can potentiate properties of the redox centers during the catalytic turnover. A function of the aromatic residue that shields the isoalloxazine ring of the FAD is also proposed.
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Affiliation(s)
- Marat B Murataliev
- Department of Chemistry, University of Arizona, P.O. Box 210041, Tucson, AZ 85721-0041, USA
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Gutierrez A, Munro AW, Grunau A, Wolf CR, Scrutton NS, Roberts GCK. Interflavin electron transfer in human cytochrome P450 reductase is enhanced by coenzyme binding. Relaxation kinetic studies with coenzyme analogues. EUROPEAN JOURNAL OF BIOCHEMISTRY 2003; 270:2612-21. [PMID: 12787027 DOI: 10.1046/j.1432-1033.2003.03633.x] [Citation(s) in RCA: 49] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 11/20/2022]
Abstract
The role of coenzyme binding in regulating interflavin electron transfer in human cytochrome P450 reductase (CPR) has been studied using temperature-jump spectroscopy. Previous studies [Gutierrez, A., Paine, M., Wolf, C.R., Scrutton, N.S., & Roberts, G.C.K. Biochemistry (2002) 41, 4626-4637] have shown that the observed rate, 1/tau, of interflavin electron transfer (FADsq - FMNsq-->FADox - FMNhq) in CPR reduced at the two-electron level with NADPH is 55 +/- 2 s-1, whereas with dithionite-reduced enzyme the observed rate is 11 +/- 0.5 s-1, suggesting that NADPH (or NADP+) binding has an important role in controlling the rate of internal electron transfer. In relaxation experiments performed with CPR reduced at the two-electron level with NADH, the observed rate of internal electron transfer (1/tau = 18 +/- 0.7 s-1) is intermediate in value between those seen with dithionite-reduced and NADPH-reduced enzyme, indicating that the presence of the 2'-phosphate is important for enhancing internal electron transfer. To investigate this further, temperature jump experiments were performed with dithionite-reduced enzyme in the presence of 2',5'-ADP and 2'-AMP. These two ligands increase the observed rate of interflavin electron transfer in two-electron reduced CPR from 1/tau = 11 s-1 to 35 +/- 0.2 s-1 and 32 +/- 0.6 s-1, respectively. Reduction of CPR at the two-electron level by NADPH, NADH or dithionite generates the same spectral species, consistent with an electron distribution that is equivalent regardless of reductant at the initiation of the temperature jump. Spectroelectrochemical experiments establish that the redox potentials of the flavins of CPR are unchanged on binding 2',5'-ADP, supporting the view that enhanced rates of interdomain electron transfer have their origin in a conformational change produced by binding NADPH or its fragments. Addition of 2',5'-ADP either to the isolated FAD-domain or to full-length CPR (in their oxidized and reduced forms) leads to perturbation of the optical spectra of both the flavins, consistent with a conformational change that alters the environment of these redox cofactors. The binding of 2',5'-ADP eliminates the unusual dependence of the observed flavin reduction rate on NADPH concentration (i.e. enhanced at low coenzyme concentration) observed in stopped-flow studies. The data are discussed in the context of previous kinetic studies and of the crystallographic structure of rat CPR.
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Affiliation(s)
- Aldo Gutierrez
- Department of Biochemistry and Biological NMR Centre, University of Leicester, UK
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Döhr O, Paine MJ, Friedberg T, Roberts GC, Wolf CR. Engineering of a functional human NADH-dependent cytochrome P450 system. Proc Natl Acad Sci U S A 2001; 98:81-6. [PMID: 11136248 PMCID: PMC14548 DOI: 10.1073/pnas.98.1.81] [Citation(s) in RCA: 72] [Impact Index Per Article: 3.1] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/18/2022] Open
Abstract
A functional human NADH-dependent cytochrome P450 system has been developed by altering the cofactor preference of human NADPH cytochrome P450 reductase (CPR), the redox partner for P450s. This has been achieved by a single amino acid change of the conserved aromatic amino acid Trp-676, which covers the re-side of the FAD isoalloxazine ring in the nicotinamide-binding site. Of the mutations made, the substitution of Trp-676 with alanine (W676A) resulted in a functional NADH-dependent enzyme, which catalyzed the reduction of cytochrome c and ferricyanide as well as facilitated the metabolism of 7-ethoxyresorufin by CYP1A2. Kinetic analysis measuring cytochrome c activity revealed that the NADH-dependent k(cat) of W676A is equivalent (90%) to the NADPH-dependent k(cat) of the wild-type enzyme, with W676A having an approximately 1,000-fold higher specificity for NADH. The apparent K(M)(NADPH) and K(M)(NADH) values of W676A are 80- and 150-fold decreased, respectively. In accordance with structural data, which show a bipartite binding mode of NADPH, substitution of Trp-676 does not affect 2'-AMP binding as seen by the inhibition of both wild-type CPR and the W676A mutant. Furthermore, NADPH was a potent inhibitor of the W676A NADH-dependent cytochrome c reduction and CYP1A2 activity. Overall, the results show that Trp-676 of human CPR plays a major role in cofactor discrimination, and substitution of this conserved aromatic residue with alanine results in an efficient NADH-dependent cytochrome P450 system.
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Affiliation(s)
- O Döhr
- Biomedical Research Center, University of Dundee, and Imperial Cancer Research Fund Molecular Pharmacology Unit, Ninewells Hospital and Medical School, Dundee, DD1 9SY, United Kingdom
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Murataliev MB, Feyereisen R. Mechanism of cytochrome P450 reductase from the house fly: evidence for an FMN semiquinone as electron donor. FEBS Lett 1999; 453:201-4. [PMID: 10403403 DOI: 10.1016/s0014-5793(99)00723-1] [Citation(s) in RCA: 16] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022]
Abstract
The interaction of recombinant house fly (Musca domestica) P450 reductase with NADPH and the role of the FMN semiquinone in reducing cytochrome c have been investigated. House fly P450 reductase can rapidly oxidize only one molecule of NADPH, whereas the rate of oxidation of a second molecule of NADPH is too slow to account for the observed rates of catalysis. This demonstrates that house fly P450 reductase does not require a priming reaction with NADPH for catalysis. Kinetics of cytochrome c reduction and EPR spectroscopy revealed that the enzyme forms two types of neutral FMN semiquinone. One serves as the catalytic intermediate of cytochrome c reduction, and another one is an 'airstable' semiquinone, which reduces cytochrome c 3000 times more slowly. The results show that the reduction state of the house fly P450 reductase during catalysis cycles in a 0-2-1-0 sequence.
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Affiliation(s)
- M B Murataliev
- Department of Entomology and Center for Toxicology, University of Arizona, Tucson 85721-0036, USA.
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Murataliev MB, Ariño A, Guzov VM, Feyereisen R. Kinetic mechanism of cytochrome P450 reductase from the house fly (Musca domestica). INSECT BIOCHEMISTRY AND MOLECULAR BIOLOGY 1999; 29:233-242. [PMID: 10319436 DOI: 10.1016/s0965-1748(98)00131-3] [Citation(s) in RCA: 21] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/23/2023]
Abstract
Recombinant house fly (Musca domestica) cytochrome P450 reductase has been purified by anion exchange and affinity chromatography. Steady-state kinetics of cytochrome c reductase activity revealed a random Bi-Bi mechanism with formation of a ternary P450 reductase-NADPH-electron acceptor complex as catalytic intermediate. NADP(H) binding is essential for fast hydride ion transfer to FAD, as well as for electron transfer from FMN to cytochrome c. Reduced cytochrome c had no effect on the enzyme activity, while NADP+ and 2'-AMP inhibited P450 reductase competitively with respect to NADPH and noncompetitively with respect to cytochrome c. The affinity of the P450 reductase to NADPH is 10 times higher than to NADP+ (Kd of 0.31 and 3.3 microM, respectively). Such an affinity change during catalysis could account for a +30 mV shift of the redox potential of FAD. Cys560 was substituted for Tyr by site-directed mutagenesis. This mutation decreased enzyme affinity to NADPH 35-fold by decreasing the bimolecular rate constant of nucleotide binding with no detectable effect on the kinetic mechanism. The affinity of the C560Y mutant enzyme to NADP+ decreased 9-fold compared to the wild-type enzyme, while the affinity to 2'-AMP was not significantly affected, suggesting that Cys560 is located in the nicotinamide binding site of the active, full-size enzyme in solution.
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Affiliation(s)
- M B Murataliev
- Department of Entomology, University of Arizona, Tucson 85721-0036, USA
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Shen AL, Sem DS, Kasper CB. Mechanistic studies on the reductive half-reaction of NADPH-cytochrome P450 oxidoreductase. J Biol Chem 1999; 274:5391-8. [PMID: 10026149 DOI: 10.1074/jbc.274.9.5391] [Citation(s) in RCA: 48] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
Site-directed mutagenesis has been employed to study the mechanism of hydride transfer from NADPH to NADPH-cytochrome P450 oxidoreductase. Specifically, Ser457, Asp675, and Cys630 have been selected because of their proximity to the isoalloxazine ring of FAD. Substitution of Asp675 with asparagine or valine decreased cytochrome c reductase activities 17- and 677-fold, respectively, while the C630A substitution decreased enzymatic activity 49-fold. Earlier studies had shown that the S457A mutation decreased cytochrome c reductase activity 90-fold and also lowered the redox potential of the FAD semiquinone (Shen, A., and Kasper, C. B. (1996) Biochemistry 35, 9451-9459). The S457A/D675N and S457A/D675N/C630A mutants produced roughly multiplicative decreases in cytochrome c reductase activity (774- and 22000-fold, respectively) with corresponding decreases in the rates of flavin reduction. For each mutation, increases were observed in the magnitudes of the primary deuterium isotope effects with NADPD, consistent with decreased rates of hydride transfer from NADPH to FAD and an increase in the relative rate limitation of hydride transfer. Asp675 substitutions lowered the redox potential of the FAD semiquinone. In addition, the C630A substitution shifted the pKa of an ionizable group previously identified as necessary for catalysis (Sem, D. S., and Kasper, C. B. (1993) Biochemistry 32, 11539-11547) from 6.9 to 7.8. These results are consistent with a model in which Ser457, Asp675, and Cys630 stabilize the transition state for hydride transfer. Ser457 and Asp675 interact to stabilize both the transition state and the FAD semiquinone, while Cys630 interacts with the nicotinamide ring and the fully reduced FAD, functioning as a proton donor/acceptor to FAD.
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Affiliation(s)
- A L Shen
- McArdle Laboratory for Cancer Research, Madison, Wisconsin 53706, USA
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Pérez-Pomares F, Ferrer J, Camacho M, Pire C, LLorca F, Bonete MJ. Amino acid residues involved in the catalytic mechanism of NAD-dependent glutamate dehydrogenase from Halobacterium salinarum. BIOCHIMICA ET BIOPHYSICA ACTA 1999; 1426:513-25. [PMID: 10076069 DOI: 10.1016/s0304-4165(98)00174-3] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 11/18/2022]
Abstract
The pH dependence of kinetic parameters for a competitive inhibitor (glutarate) was determined in order to obtain information on the chemical mechanism for NAD-dependent glutamate dehydrogenase from Halobacterium salinarum. The maximum velocity is pH dependent, decreasing at low pHs giving a pK value of 7.19+/-0.13, while the V/K for l-glutamate at 30 degrees C decreases at low and high pHs, yielding pK values of 7.9+/-0.2 and 9.8+/-0.2, respectively. The glutarate pKis profile decreases at high pHs, yielding a pK of 9. 59+/-0.09 at 30 degrees C. The values of ionization heat calculated from the change in pK with temperature are: 1.19 x 10(4), 5.7 x 10(3), 7 x 10(3), 6.6 x 10(3) cal mol-1, for the residues involved. All these data suggest that the groups required for catalysis and/or binding are lysine, histidine and tyrosine. The enzyme shows a time-dependent loss in glutamate oxidation activity when incubated with diethyl pyrocarbonate (DEPC). Inactivation follows pseudo-first-order kinetics with a second-order rate constant of 53 M-1min-1. The pKa of the titratable group was pK1=6.6+/-0.6. Inactivation with ethyl acetimidate also shows pseudo-first-order kinetics as well as inactivation with TNM yielding second-order constants of 1.2 M-1min-1 and 2.8 M-1min-1, and pKas of 8.36 and 9.0, respectively. The proposed mechanism involves hydrogen binding of each of the two carboxylic groups to tyrosyl residues; histidine interacts with one of the N-hydrogens of the l-glutamate amino group. We also corroborate the presence of a conservative lysine that has a remarkable ability to coordinate a water molecule that would act as general base.
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Affiliation(s)
- F Pérez-Pomares
- División de Bioquímica, Facultad de Ciencias, Universidad de Alicante, Ap. 99, E-03080, Alicante, Spain
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Didierjean C, Rahuel-Clermont S, Vitoux B, Dideberg O, Branlant G, Aubry A. A crystallographic comparison between mutated glyceraldehyde-3-phosphate dehydrogenases from Bacillus stearothermophilus complexed with either NAD+ or NADP+. J Mol Biol 1997; 268:739-59. [PMID: 9175858 DOI: 10.1006/jmbi.1997.0998] [Citation(s) in RCA: 34] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/04/2023]
Abstract
Mutations have been introduced in the cytosolic glyceraldehyde-3-phosphate dehydrogenase (GAPDH) from Bacillus stearothermophilus in order to convert its cofactor selectivity from a specificity towards NAD into a preference for NADP. In the B-S mutant, five mutations (L33T, T34G, D35G, L187A, P188S) were selected on the basis of a sequence alignment with NADP-dependent chloroplastic GAPDHs. In the D32G-S mutant, two of the five mutations mentioned above (L187A, P188S) have been used in combination with another one designed from electrostatic considerations (D32G). Both mutants exhibit a dual-cofactor selectivity at the advantage of either NAD (B-S) or NADP (D32G-S). In order to analyse the cofactor-binding site plasticity at the molecular level, crystal structures of these mutants have been solved, when complexed with either NAD+ (D32G-Sn, resolution 2.5 A, R = 13.9%; B-Sn, 2.45 A, 19.3%) or NADP+ (D32G-Sp, 2.2 A, 19.2%; B-Sp, 2.5 A, 14.4%). The four refined models are very similar to that of the wild-type GAPDH and as expected resemble more closely the holo form than the apo form. In the B-S mutant, the wild-type low affinity for NADP+ seems to be essentially retained because of repulsive electrostatic contacts between the extra 2'-phosphate and the unchanged carboxylate group of residue D32. Such an antideterminant effect is not well compensated by putative attractive interactions which had been expected to arise from the newly-introduced side-chains. In this mutant, recognition of NAD+ is slightly affected with respect to that known on the wild-type, because mutations only weakly destabilize hydrogen bonds and van der Waals contacts originally present in the natural enzyme. Thus, the B-S mutant does not mimic efficiently the chloroplastic GAPDHs, and long-range and/or second-layer effects, not easily predictable from visual inspection of three-dimensional structures, need to be taken into account for designing a true "chloroplastic-like" mutant of cytosolic GAPDH. In the case of the D32G-S mutant, the dissociation constants for NAD+ and NADP+ are practically reversed with respect to those of the wild-type. The strong alteration of the affinity for NAD+ obviously proceeds from the suppression of the two wild-type hydrogen bonds between the adenosine 2'- and 3'-hydroxyl positions and the D32 carboxylate group. As expected, the efficient recognition of NADP+ is partly promoted by the removal of intra-subunit electrostatic repulsion (D32G) and inter-subunit steric hindrance (L187A, P188S). Another interesting feature of the reshaped NADP+-binding site is provided by the local stabilization of the extra 2'-phosphate which forms a hydrogen bond with the side-chain hydroxyl group of the newly-introduced S188. When compared to the presently known natural NADP-binding clefts, this result clearly demonstrates that an absolute need for a salt-bridge involving the 2'-phosphate is not required to switch the cofactor selectivity from NAD to NADP. In fact, as it is the case in this mutant, only a moderately polar hydrogen bond can be sufficient to make the extra 2'-phosphate of NADP+ well recognized by a protein environment.
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Affiliation(s)
- C Didierjean
- Laboratoire de Cristallographie et Modélisation des Matériaux Minéraux et Biologiques, IFR Protéines, Université Henri Poincaré Nancy I (URA CNRS 809), Vandoeuvre-lès-Nancy, France
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Shen AL, Kasper CB. Role of Ser457 of NADPH-cytochrome P450 oxidoreductase in catalysis and control of FAD oxidation-reduction potential. Biochemistry 1996; 35:9451-9. [PMID: 8755724 DOI: 10.1021/bi960587n] [Citation(s) in RCA: 23] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/02/2023]
Abstract
Site-directed mutagenesis of Ser457 of NADPH-cytochrome P450 oxidoreductase demonstrates that this residue plays a major role in both hydride transfer from NADPH to FAD and modulation of FAD redox potential. Substitution of Ser457 with alanine or cysteine decreases the rates of reduction of the substrates cytochrome c and potassium ferricyanide approximately 100-fold, while substitution with threonine produces a 20-fold decrease in activity. No changes are observed in k(m)NADPH, KiNADP+, or flavin content, indicating that these substitutions have no effect on cofactor binding but affect catalysis only. k(m)cyt c values are decreased in parallel with the observed decreases in the rates of the reductive half-reaction. Stopped-flow studies with the S457A mutant show a 100-fold decrease in the rate of flavin reduction. The primary deuterium isotope effect on Kcat for cytochrome c reduction increases from 2.7 for the wild-type enzyme to 9.0 for the S457A mutant, consistent with a change in the rate-determining step from NADP+ release in the wild-type enzyme to hydride transfer in the S457A mutant. The primary deuterium isotope effect on K1 for flavin reduction at high ionic strength (I = 535 mM) increases from 12.2 for the wild-type enzyme to > 20 for the S457A mutant, consistent again with an increase in the relative rate limitation of hydride transfer. Furthermore, anaerobic titration of S457A indicates that the redox potential of the FAD semiquinone has been decreased. Data presented in this study support the hypothesis that Ser457 is involved in hydrogen bonding interactions which stabilize both the transition state for hydride transfer and the reduced FAD.
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Affiliation(s)
- A L Shen
- McArdle Laboratory for Cancer Research, Madison, Wisconsin 53706, USA
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Flynn TG, Green NC, Bhatia MB, el-Kabbani O. Structure and mechanism of aldehyde reductase. ADVANCES IN EXPERIMENTAL MEDICINE AND BIOLOGY 1995; 372:193-201. [PMID: 7484379 DOI: 10.1007/978-1-4615-1965-2_25] [Citation(s) in RCA: 15] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 01/25/2023]
Affiliation(s)
- T G Flynn
- Department of Biochemistry, Queen's University, Kingston, Ontario, Canada
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Sem DS, Kasper CB. Kinetic mechanism for the model reaction of NADPH-cytochrome P450 oxidoreductase with cytochrome c. Biochemistry 1994; 33:12012-21. [PMID: 7918420 DOI: 10.1021/bi00206a002] [Citation(s) in RCA: 21] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/27/2023]
Abstract
The kinetic mechanism of NADPH-cytochrome P450 oxidoreductase (P450R) has been determined for the model reaction with cytochrome c3+. Although initial velocity studies show parallel patterns, consistent with a classical (one-site) ping-pong mechanism that precludes the formation of a ternary NADPH-P450R-cytochrome c3+ complex, product and dead-end inhibition results suggest a nonclassical (two-site) ping-pong mechanism [Northrop, D. B. (1969) J. Biol. Chem. 244, 5808-5819]. This mechanism is a hybrid of the random sequential (ternary complex) and ping-pong mechanisms, since ternary complexes can form as well as intermediate, modified forms of the enzyme that can be present in the absence of any bound substrate. The complete rate equation is derived for this mechanism, and values for Vmax, (V/K)NADPH, (V/K)cytc, and the corresponding Michaelis constants are presented in terms of microscopic rate constants along with the expected product inhibition patterns (Appendix). Inhibition by NADP+ is competitive versus NADPH and uncompetitive versus cytochrome c3+, while inhibition by cytochrome c2+ is competitive versus cytochrome c3+ and noncompetitive versus NADPH. These inhibition patterns are consistent with the proposed two-site mechanism. This mechanism would give the same initial velocity patterns as the classical one-site ping-pong mechanism, but it allows for the formation of a ternary complex, with NADPH and cytochrome c3+ reacting independently at two separate sites on P450R. The D(V/K)NADPH isotope effect is not affected by cytochrome c3+ concentration, consistent with our assumption (in deriving the rate equation) that binding at the two sites is independent. At the high ionic strength used in this study (850 mM), the mechanism is two-site ping-pong, with the electron acceptor site itself reacting with cytochrome c3+ in a tetra uni ping-pong manner.
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Affiliation(s)
- D S Sem
- McArdle Laboratory for Cancer Research, Medical School, University of Wisconsin, Madison 53706
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