1
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Amaya JA, Manley OM, Bian JC, Rutland CD, Leschinsky N, Ratigan SC, Makris TM. Enhancing ferryl accumulation in H 2O 2-dependent cytochrome P450s. J Inorg Biochem 2024; 252:112458. [PMID: 38141432 DOI: 10.1016/j.jinorgbio.2023.112458] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/02/2023] [Revised: 12/08/2023] [Accepted: 12/16/2023] [Indexed: 12/25/2023]
Abstract
A facile strategy is presented to enhance the accumulation of ferryl (iron(IV)-oxo) species in H2O2 dependent cytochrome P450s (CYPs) of the CYP152 family. We report the characterization of a highly chemoselective CYP decarboxylase from Staphylococcus aureus (OleTSA) that is soluble at high concentrations. Examination of OleTSA Compound I (CpdI) accumulation with a variety of fatty acid substrates reveals a dependence on resting spin-state equilibrium. Alteration of this equilibrium through targeted mutagenesis of the proximal pocket favors the high-spin form, and as a result, enhances Cpd-I accumulation to nearly stoichiometric yields.
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Affiliation(s)
- Jose A Amaya
- Department of Chemistry and Biochemistry, University of South Carolina, Columbia, SC 29208, United States of America
| | - Olivia M Manley
- Department of Chemistry and Biochemistry, University of South Carolina, Columbia, SC 29208, United States of America; Department of Structural and Molecular Biochemistry, North Carolina State University, Raleigh, NC 27695, United States of America
| | - Julia C Bian
- Department of Chemistry and Biochemistry, University of South Carolina, Columbia, SC 29208, United States of America
| | - Cooper D Rutland
- Department of Chemistry and Biochemistry, University of South Carolina, Columbia, SC 29208, United States of America
| | - Nicholas Leschinsky
- Department of Chemistry and Biochemistry, University of South Carolina, Columbia, SC 29208, United States of America
| | - Steven C Ratigan
- Department of Chemistry and Biochemistry, University of South Carolina, Columbia, SC 29208, United States of America
| | - Thomas M Makris
- Department of Chemistry and Biochemistry, University of South Carolina, Columbia, SC 29208, United States of America; Department of Structural and Molecular Biochemistry, North Carolina State University, Raleigh, NC 27695, United States of America; Department of Chemistry, North Carolina State University, Raleigh, NC 27695, United States of America.
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2
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Mohamed H, Ghith A, Bell SG. The binding of nitrogen-donor ligands to the ferric and ferrous forms of cytochrome P450 enzymes. J Inorg Biochem 2023; 242:112168. [PMID: 36870164 DOI: 10.1016/j.jinorgbio.2023.112168] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/01/2022] [Revised: 01/24/2023] [Accepted: 02/21/2023] [Indexed: 02/27/2023]
Abstract
The cytochrome P450 superfamily of heme-thiolate monooxygenase enzymes can catalyse various oxidation reactions. The addition of a substrate or an inhibitor ligand induces changes in the absorption spectrum of these enzymes and UV-visible (UV-vis) absorbance spectroscopy is the most common and readily available technique used to interrogate their heme and active site environment. Nitrogen-containing ligands can inhibit the catalytic cycle of heme enzymes by interacting with the heme. Here we evaluate the binding of imidazole and pyridine-based ligands to the ferric and ferrous forms of a selection of bacterial cytochrome P450 enzymes using UV-visible absorbance spectroscopy. The majority of these ligands interact with the heme as one would expect for type II nitrogen directly coordinated to a ferric heme-thiolate species. However, the spectroscopic changes observed in the ligand-bound ferrous forms indicated differences in the heme environment across these P450 enzyme/ligand combinations. Multiple species were observed in the UV-vis spectra of the ferrous ligand-bound P450s. None of the enzymes gave rise to the isolation of a single species with a Soret band at ∼442-447 nm, indicative of a 6-coordinate ferrous thiolate species with a nitrogen-donor ligand. A ferrous species with Soret band at ∼427 nm coupled with an α-band of increased intensity was observed with the imidazole ligands. With some enzyme-ligand combinations reduction resulted in breaking of the iron‑nitrogen bond yielding a 5-coordinate high-spin ferrous species. In other instances, the ferrous form was readily oxidised back to the ferric form on addition of the ligand.
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Affiliation(s)
- Hebatalla Mohamed
- Department of Chemistry, University Adelaide, Adelaide, SA 5005, Australia
| | - Amna Ghith
- Department of Chemistry, University Adelaide, Adelaide, SA 5005, Australia
| | - Stephen G Bell
- Department of Chemistry, University Adelaide, Adelaide, SA 5005, Australia.
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3
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Verde C, Giordano D, Bruno S. NO and Heme Proteins: Cross-Talk between Heme and Cysteine Residues. Antioxidants (Basel) 2023; 12:antiox12020321. [PMID: 36829880 PMCID: PMC9952723 DOI: 10.3390/antiox12020321] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/23/2022] [Revised: 01/19/2023] [Accepted: 01/24/2023] [Indexed: 01/31/2023] Open
Abstract
Heme proteins are a diverse group that includes several unrelated families. Their biological function is mainly associated with the reactivity of the heme group, which-among several other reactions-can bind to and react with nitric oxide (NO) and other nitrogen compounds for their production, scavenging, and transport. The S-nitrosylation of cysteine residues, which also results from the reaction with NO and other nitrogen compounds, is a post-translational modification regulating protein activity, with direct effects on a variety of signaling pathways. Heme proteins are unique in exhibiting this dual reactivity toward NO, with reported examples of cross-reactivity between the heme and cysteine residues within the same protein. In this work, we review the literature on this interplay, with particular emphasis on heme proteins in which heme-dependent nitrosylation has been reported and those for which both heme nitrosylation and S-nitrosylation have been associated with biological functions.
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Affiliation(s)
- Cinzia Verde
- Institute of Biosciences and BioResources (IBBR), National Research Council (CNR), Via Pietro Castellino 111, 80131 Napoli, Italy
- Department of Marine Biotechnology, Stazione Zoologica Anton Dohrn (SZN), Villa Comunale, 80121 Napoli, Italy
| | - Daniela Giordano
- Institute of Biosciences and BioResources (IBBR), National Research Council (CNR), Via Pietro Castellino 111, 80131 Napoli, Italy
- Department of Marine Biotechnology, Stazione Zoologica Anton Dohrn (SZN), Villa Comunale, 80121 Napoli, Italy
| | - Stefano Bruno
- Department of Food and Drug, University of Parma, 43124 Parma, Italy
- Biopharmanet-TEC, University of Parma, 43124 Parma, Italy
- Correspondence:
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4
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Schrage BR, Zhou W, Harrison LA, Nevonen DE, Thompson JR, Prosser KE, Walsby CJ, Ziegler CJ, Leznoff DB, Nemykin VN. Resolving a Half-Century-Long Controversy between (Magneto)optical and EPR Spectra of Single-Electron-Reduced [PcFe] −, [PcFeL] −, and [PcFeX] 2– Complexes: Story of a Double Flip. Inorg Chem 2022; 61:20177-20199. [DOI: 10.1021/acs.inorgchem.2c03456] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/12/2022]
Affiliation(s)
- Briana R. Schrage
- Department of Chemistry, University of Tennessee, Knoxville, Tennessee37996, United States
| | - Wen Zhou
- Department of Chemistry, Simon Fraser University, Burnaby, British ColumbiaV5A 1S6, Canada
| | - Laurel A. Harrison
- Department of Chemistry, University of Tennessee, Knoxville, Tennessee37996, United States
| | - Dustin E. Nevonen
- Department of Chemistry, University of Tennessee, Knoxville, Tennessee37996, United States
| | - John R. Thompson
- Department of Chemistry, Simon Fraser University, Burnaby, British ColumbiaV5A 1S6, Canada
| | - Kathleen E. Prosser
- Department of Chemistry, Simon Fraser University, Burnaby, British ColumbiaV5A 1S6, Canada
| | - Charles J. Walsby
- Department of Chemistry, Simon Fraser University, Burnaby, British ColumbiaV5A 1S6, Canada
| | | | - Daniel B. Leznoff
- Department of Chemistry, Simon Fraser University, Burnaby, British ColumbiaV5A 1S6, Canada
| | - Victor N. Nemykin
- Department of Chemistry, University of Tennessee, Knoxville, Tennessee37996, United States
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5
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Nevonen DE, Ferch LS, Schrage BR, Nemykin VN. Charge-Transfer Spectroscopy of Bisaxially Coordinated Iron(II) Phthalocyanines through the Prism of the Lever's EL Parameters Scale, MCD Spectroscopy, and TDDFT Calculations. Inorg Chem 2022; 61:8250-8266. [PMID: 35549169 DOI: 10.1021/acs.inorgchem.2c00721] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Abstract
The position of the experimentally observed (in the UV-vis and magnetic circular dichroism (MCD) spectra) low-energy metal-to-ligand charge-transfer (MLCT) band in low-spin iron(II) phthalocyanine complexes of general formula PcFeL2, PcFeL'L″, and [PcFeX2]2- (L, L', or L″ are neutral and X- is an anionic axial ligand) was correlated with the Lever's electrochemical EL scale values for the axial ligands. The time-dependent density functional theory (TDDFT)-predicted UV-vis spectra are in very good agreement with the experimental data for all complexes. In the majority of compounds, TDDFT predicts that the first degenerate MLCT band that correlates with the MCD A-term observed between 360 and 480 nm is dominated by an eg (Fe, dπ) → b1u (Pc, π*) single-electron excitation (in traditional D4h point group notation) and agrees well with the previous assignment discussed by Stillman and co-workers[ Inorg. Chem. 1994, 33, 573-583]. The TDDFT calculations also suggest a small energy gap for b1u/b2u (Pc, π*) orbital splitting and closeness of the MLCT1 eg (Fe, dπ) → b1u (Pc, π*) and MLCT2 eg (Fe, dπ) → b2u (Pc, π*) transitions. In the case of the PcFeL2 complexes with phosphines as the axial ligands, additional degenerate charge-transfer transitions were observed between 450 and 500 nm. These transitions are dominated by a2u (Pc + L, π) → eg (Pc, π*) single-electron excitations and are unique for the PcFe(PR3)2 complexes. The energy of the phthalocyanine-based a2u orbital has large axial ligand dependency and is the reason for a large energy deviation for B1 a2u (Pc + L, π) → eg (Pc, π*) transition. The energies of the axial ligand-to-iron, axial ligand-to-phthalocyanine, iron-to-axial ligand, and phthalocyanine-to-axial ligand charge-transfer transitions were discussed on the basis of TDDFT calculations.
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Affiliation(s)
- Dustin E Nevonen
- Department of Chemistry, University of Manitoba, Winnipeg, Manitoba R3T 2N2, Canada
| | - Laura S Ferch
- Department of Chemistry, University of Manitoba, Winnipeg, Manitoba R3T 2N2, Canada
| | - Briana R Schrage
- Department of Chemistry, University of Tennessee, Knoxville, Tennessee 37996, United States
| | - Victor N Nemykin
- Department of Chemistry, University of Manitoba, Winnipeg, Manitoba R3T 2N2, Canada.,Department of Chemistry, University of Tennessee, Knoxville, Tennessee 37996, United States
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6
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Lehnert N, Kim E, Dong HT, Harland JB, Hunt AP, Manickas EC, Oakley KM, Pham J, Reed GC, Alfaro VS. The Biologically Relevant Coordination Chemistry of Iron and Nitric Oxide: Electronic Structure and Reactivity. Chem Rev 2021; 121:14682-14905. [PMID: 34902255 DOI: 10.1021/acs.chemrev.1c00253] [Citation(s) in RCA: 101] [Impact Index Per Article: 33.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/14/2023]
Abstract
Nitric oxide (NO) is an important signaling molecule that is involved in a wide range of physiological and pathological events in biology. Metal coordination chemistry, especially with iron, is at the heart of many biological transformations involving NO. A series of heme proteins, nitric oxide synthases (NOS), soluble guanylate cyclase (sGC), and nitrophorins, are responsible for the biosynthesis, sensing, and transport of NO. Alternatively, NO can be generated from nitrite by heme- and copper-containing nitrite reductases (NIRs). The NO-bearing small molecules such as nitrosothiols and dinitrosyl iron complexes (DNICs) can serve as an alternative vehicle for NO storage and transport. Once NO is formed, the rich reaction chemistry of NO leads to a wide variety of biological activities including reduction of NO by heme or non-heme iron-containing NO reductases and protein post-translational modifications by DNICs. Much of our understanding of the reactivity of metal sites in biology with NO and the mechanisms of these transformations has come from the elucidation of the geometric and electronic structures and chemical reactivity of synthetic model systems, in synergy with biochemical and biophysical studies on the relevant proteins themselves. This review focuses on recent advancements from studies on proteins and model complexes that not only have improved our understanding of the biological roles of NO but also have provided foundations for biomedical research and for bio-inspired catalyst design in energy science.
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Affiliation(s)
- Nicolai Lehnert
- Department of Chemistry and Department of Biophysics, University of Michigan, Ann Arbor, Michigan 48109-1055, United States
| | - Eunsuk Kim
- Department of Chemistry, Brown University, Providence, Rhode Island 02912, United States
| | - Hai T Dong
- Department of Chemistry and Department of Biophysics, University of Michigan, Ann Arbor, Michigan 48109-1055, United States
| | - Jill B Harland
- Department of Chemistry and Department of Biophysics, University of Michigan, Ann Arbor, Michigan 48109-1055, United States
| | - Andrew P Hunt
- Department of Chemistry and Department of Biophysics, University of Michigan, Ann Arbor, Michigan 48109-1055, United States
| | - Elizabeth C Manickas
- Department of Chemistry and Department of Biophysics, University of Michigan, Ann Arbor, Michigan 48109-1055, United States
| | - Kady M Oakley
- Department of Chemistry, Brown University, Providence, Rhode Island 02912, United States
| | - John Pham
- Department of Chemistry, Brown University, Providence, Rhode Island 02912, United States
| | - Garrett C Reed
- Department of Chemistry and Department of Biophysics, University of Michigan, Ann Arbor, Michigan 48109-1055, United States
| | - Victor Sosa Alfaro
- Department of Chemistry and Department of Biophysics, University of Michigan, Ann Arbor, Michigan 48109-1055, United States
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7
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Hunt AP, Samanta S, Dent MR, Milbauer MW, Burstyn JN, Lehnert N. Model Complexes Elucidate the Role of the Proximal Hydrogen-Bonding Network in Cytochrome P450s. Inorg Chem 2020; 59:8034-8043. [DOI: 10.1021/acs.inorgchem.0c00245] [Citation(s) in RCA: 4] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
Affiliation(s)
- Andrew P. Hunt
- Department of Chemistry and Department of Biophysics, University of Michigan, Ann Arbor, Michigan 48109-1055, United States
| | - Subhra Samanta
- Department of Chemistry and Department of Biophysics, University of Michigan, Ann Arbor, Michigan 48109-1055, United States
| | - Matthew R. Dent
- Department of Chemistry, University of Wisconsin, Madison, Wisconsin 53706, United States
| | - Michael W. Milbauer
- Department of Chemistry, University of Wisconsin, Madison, Wisconsin 53706, United States
| | - Judith N. Burstyn
- Department of Chemistry, University of Wisconsin, Madison, Wisconsin 53706, United States
| | - Nicolai Lehnert
- Department of Chemistry and Department of Biophysics, University of Michigan, Ann Arbor, Michigan 48109-1055, United States
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8
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Dorazio SJ, Vogel A, Dechert S, Nevonen DE, Nemykin VN, Brückner C, Meyer F. Siamese-Twin Porphyrin Goes Platinum: Group 10 Monometallic, Homobimetallic, and Heterobimetallic Complexes. Inorg Chem 2020; 59:7290-7305. [PMID: 32374995 DOI: 10.1021/acs.inorgchem.0c00714] [Citation(s) in RCA: 6] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/08/2023]
Abstract
A series of PtII-based monometallic (H2PtL), homobimetallic (Pt2L), and heterobimetallic (NiPtL and PdPtL) group 10 complexes of the previously established expanded twin porphyrin (H4L) were prepared. Structural characterization of the bimetallic PtII series (Pt2L, NiPtL, and PdPtL) revealed their similar general structures, with slight differences correlated to the ion size. An improvement of the metal-ion insertion process also allowed efficient preparation of the known Pd2L complex, and the novel heterobimetallic NiPdL complex was also structurally characterized. UV-vis spectroscopy, NMR spectroscopy, magnetic circular dichroism (MCD), and (spectro)electrochemistry were used to characterize the complexes; the electronic properties followed largely established lines for metal complexes of the twin porphyrin, except that the PtII-based systems exhibited more complex UV-vis spectral signatures. MCD spectra accompanied by density functional theory (DFT)/time-dependent DFT computations (TDDFT) rationalize the origins of the optical features of the twin porphyrin. The presence of the nonplanar, nonaromatic macrocyclic π system with conjugation pathways confined to each half of the molecule could be visualized. Significant pyrazole(π) → pyrrole(π*) charge-transfer character was predicted for several transitions in the visible region. This study adds to our fundamental understanding of the formation, structure, and electronic structure of bimetallic complexes of this class of expanded metalloporphyrins containing nonpyrrolic moieties.
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Affiliation(s)
- Sarina J Dorazio
- Institute for Inorganic Chemistry, University of Göttingen, Tammannstraße 4, D-37077 Göttingen, Germany.,Department of Chemistry, University of Connecticut, Storrs, Connecticut 06269-3060, United States
| | - Anastasia Vogel
- Institute for Inorganic Chemistry, University of Göttingen, Tammannstraße 4, D-37077 Göttingen, Germany
| | - Sebastian Dechert
- Institute for Inorganic Chemistry, University of Göttingen, Tammannstraße 4, D-37077 Göttingen, Germany
| | - Dustin E Nevonen
- Department of ChemistryUniversity of Manitoba, 360 Parker Building, Winnipeg, Manitoba R3T 2N2, Canada
| | - Victor N Nemykin
- Department of ChemistryUniversity of Manitoba, 360 Parker Building, Winnipeg, Manitoba R3T 2N2, Canada
| | - Christian Brückner
- Department of Chemistry, University of Connecticut, Storrs, Connecticut 06269-3060, United States
| | - Franc Meyer
- Institute for Inorganic Chemistry, University of Göttingen, Tammannstraße 4, D-37077 Göttingen, Germany
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9
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Galinato MGI, Brocious EP, Paulat F, Martin S, Skodack J, Harland JB, Lehnert N. Elucidating the Electronic Structure of High-Spin [MnIII(TPP)Cl] Using Magnetic Circular Dichroism Spectroscopy. Inorg Chem 2020; 59:2144-2162. [DOI: 10.1021/acs.inorgchem.9b02599] [Citation(s) in RCA: 10] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Affiliation(s)
- Mary Grace I. Galinato
- Department of Chemistry, University of Michigan, Ann Arbor, Michigan 48109-1055, United States
- School of Science-Chemistry, Penn State Behrend, Erie, Pennsylvania 16563, United States
| | - Emily P. Brocious
- School of Science-Chemistry, Penn State Behrend, Erie, Pennsylvania 16563, United States
| | - Florian Paulat
- Department of Chemistry, University of Michigan, Ann Arbor, Michigan 48109-1055, United States
| | - Sherri Martin
- Department of Chemistry, University of Michigan, Ann Arbor, Michigan 48109-1055, United States
| | - Joshua Skodack
- Department of Chemistry, University of Michigan, Ann Arbor, Michigan 48109-1055, United States
| | - Jill B. Harland
- Department of Chemistry, University of Michigan, Ann Arbor, Michigan 48109-1055, United States
| | - Nicolai Lehnert
- Department of Chemistry, University of Michigan, Ann Arbor, Michigan 48109-1055, United States
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10
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Dent MR, Milbauer MW, Hunt AP, Aristov MM, Guzei IA, Lehnert N, Burstyn JN. Electron Paramagnetic Resonance Spectroscopy as a Probe of Hydrogen Bonding in Heme-Thiolate Proteins. Inorg Chem 2019; 58:16011-16027. [PMID: 31786931 PMCID: PMC11160398 DOI: 10.1021/acs.inorgchem.9b02506] [Citation(s) in RCA: 8] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/14/2023]
Abstract
Despite utilizing a common cofactor binding motif, hemoproteins bearing a cysteine-derived thiolate ligand (heme-thiolate proteins) are involved in a diverse array of biological processes ranging from drug metabolism to transcriptional regulation. Though the origin of heme-thiolate functional divergence is not well understood, growing evidence suggests that the hydrogen bonding (H-bonding) environment surrounding the Fe-coordinating thiolate influences protein function. Outside of X-ray crystallography, few methods exist to characterize these critical H-bonding interactions. Electron paramagnetic resonance (EPR) spectra of heme-thiolate proteins bearing a six-coordinate, Fe(III) heme exhibit uniquely narrow low-spin (S = 1/2), rhombic signals, which are sensitive to changes in the heme-thiolate H-bonding environment. To establish a well-defined relationship between the magnitude of g-value dispersion in this unique EPR signal and the strength of the heme-thiolate H-bonding environment, we synthesized and characterized of a series of six-coordinate, aryl-thiolate-ligated Fe(III) porphyrin complexes bearing a tunable intramolecular H-bond. Spectroscopic investigation of these complexes revealed a direct correlation between H-bond strength and g-value dispersion in the rhombic EPR signal. Using density functional theory (DFT), we elucidated the electronic origins of the narrow, rhombic EPR signal in heme-thiolates, which arises from an Fe-S pπ-dπ bonding interaction. Computational analysis of the intramolecularly H-bonded heme-thiolate models revealed that H-bond donation to the coordinating thiolate reduces thiolate donor strength and weakens this Fe-S interaction, giving rise to larger g-value dispersion. By defining the relationship between heme-thiolate electronic structure and rhombic EPR signal, it is possible to compare thiolate donor strengths among heme-thiolate proteins through analysis of low-spin, Fe(III) EPR spectra. Thus, this study establishes EPR spectroscopy as a valuable tool for exploring how second coordination sphere effects influence heme-thiolate protein function.
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Affiliation(s)
- Matthew R. Dent
- Department of Chemistry, University of Wisconsin-Madison, 1101 University Avenue, Madison, Wisconsin 53706, United States
| | - Michael W. Milbauer
- Department of Chemistry, University of Wisconsin-Madison, 1101 University Avenue, Madison, Wisconsin 53706, United States
| | - Andrew P. Hunt
- Department of Chemistry, University of Michigan, 930 North University Avenue, Ann Arbor, Michigan 48109, United States
| | - Michael M. Aristov
- Department of Chemistry, University of Wisconsin-Madison, 1101 University Avenue, Madison, Wisconsin 53706, United States
| | - Ilia A. Guzei
- Department of Chemistry, University of Wisconsin-Madison, 1101 University Avenue, Madison, Wisconsin 53706, United States
| | - Nicolai Lehnert
- Department of Chemistry, University of Michigan, 930 North University Avenue, Ann Arbor, Michigan 48109, United States
| | - Judith N. Burstyn
- Department of Chemistry, University of Wisconsin-Madison, 1101 University Avenue, Madison, Wisconsin 53706, United States
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11
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Slater JW, Marguet SC, Gray ME, Monaco HA, Sotomayor M, Shafaat HS. Power of the Secondary Sphere: Modulating Hydrogenase Activity in Nickel-Substituted Rubredoxin. ACS Catal 2019. [DOI: 10.1021/acscatal.9b01720] [Citation(s) in RCA: 20] [Impact Index Per Article: 4.0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
Affiliation(s)
- Jeffrey W. Slater
- The Ohio State University, 100 West 18th Avenue, Columbus, Ohio 43210, United States
| | - Sean C. Marguet
- The Ohio State University, 100 West 18th Avenue, Columbus, Ohio 43210, United States
| | - Michelle E. Gray
- The Ohio State University, 100 West 18th Avenue, Columbus, Ohio 43210, United States
| | - Haleigh A. Monaco
- The Ohio State University, 100 West 18th Avenue, Columbus, Ohio 43210, United States
| | - Marcos Sotomayor
- The Ohio State University, 100 West 18th Avenue, Columbus, Ohio 43210, United States
| | - Hannah S. Shafaat
- The Ohio State University, 100 West 18th Avenue, Columbus, Ohio 43210, United States
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12
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Hunt AP, Lehnert N. The Thiolate Trans Effect in Heme {FeNO}6 Complexes and Beyond: Insight into the Nature of the Push Effect. Inorg Chem 2019; 58:11317-11332. [DOI: 10.1021/acs.inorgchem.9b00091] [Citation(s) in RCA: 20] [Impact Index Per Article: 4.0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/17/2022]
Affiliation(s)
- Andrew P. Hunt
- Department of Chemistry, University of Michigan, 930 North University Avenue, Ann Arbor, Michigan 48109, United States
| | - Nicolai Lehnert
- Department of Chemistry, University of Michigan, 930 North University Avenue, Ann Arbor, Michigan 48109, United States
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13
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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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14
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Belosludov RV, Nevonen D, Rhoda HM, Sabin JR, Nemykin VN. Simultaneous Prediction of the Energies of Qx and Qy Bands and Intramolecular Charge-Transfer Transitions in Benzoannulated and Non-Peripherally Substituted Metal-Free Phthalocyanines and Their Analogues: No Standard TDDFT Silver Bullet Yet. J Phys Chem A 2018; 123:132-152. [DOI: 10.1021/acs.jpca.8b07647] [Citation(s) in RCA: 18] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/29/2023]
Affiliation(s)
- Rodion V. Belosludov
- Institute for Materials Research, Tohoku University, Katahira 2-1-1,
Aoba-ku Sendai 980-8577, Japan
| | - Dustin Nevonen
- Department of Chemistry, University of Manitoba, Winnipeg, Manitoba R3T 2N2, Canada
| | - Hannah M. Rhoda
- Department of Chemistry & Biochemistry, University of Minnesota Duluth, Duluth, Minnesota 55812, United States
| | - Jared R. Sabin
- Department of Chemistry & Biochemistry, University of Minnesota Duluth, Duluth, Minnesota 55812, United States
| | - Victor N. Nemykin
- Department of Chemistry, University of Manitoba, Winnipeg, Manitoba R3T 2N2, Canada
- Department of Chemistry & Biochemistry, University of Minnesota Duluth, Duluth, Minnesota 55812, United States
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15
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Wolf MW, Rizzolo K, Elliott SJ, Lehnert N. Resonance Raman, Electron Paramagnetic Resonance, and Magnetic Circular Dichroism Spectroscopic Investigation of Diheme Cytochrome c Peroxidases from Nitrosomonas europaea and Shewanella oneidensis. Biochemistry 2018; 57:6416-6433. [PMID: 30335984 DOI: 10.1021/acs.biochem.8b00732] [Citation(s) in RCA: 12] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/30/2022]
Abstract
Cytochrome c peroxidases (bCcPs) are diheme enzymes required for the reduction of H2O2 to water in bacteria. There are two classes of bCcPs: one is active in the diferric form (constitutively active), and the other requires the reduction of the high-potential heme (H-heme) before catalysis commences (reductively activated) at the low-potential heme (L-heme). To improve our understanding of the mechanisms and heme electronic structures of these different bCcPs, a constitutively active bCcP from Nitrosomonas europaea ( NeCcP) and a reductively activated bCcP from Shewanella oneidensis ( SoCcP) were characterized in both the diferric and semireduced states by electron paramagnetic resonance (EPR), resonance Raman (rRaman), and magnetic circular dichroism (MCD) spectroscopy. In contrast to some previous crystallographic studies, EPR and rRaman spectra do not indicate the presence of significant amounts of a five-coordinate, high-spin ferric heme in NeCcP or SoCcP in either the diferric or semireduced state in solution. This observation points toward a mechanism of activation in which the active site L-heme is not in a static, five-coordinate state but where the activation is more subtle and likely involves formation of a six-coordinate hydroxo complex, which could then react with hydrogen peroxide in an acid-base-type reaction to create Compound 0, the ferric hydroperoxo complex. This mechanism lies in stark contrast to the diheme enzyme MauG that exhibits a static, five-coordinate open heme site at the peroxidatic heme and that forms a more stable FeIV═O intermediate.
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Affiliation(s)
- Matthew W Wolf
- Department of Chemistry and Department of Biophysics , University of Michigan , Ann Arbor , Michigan 48109 , United States
| | - Kimberly Rizzolo
- Department of Chemistry , Boston University , 590 Commonwealth Avenue , Boston , Massachusetts 02215 , United States
| | - Sean J Elliott
- Department of Chemistry , Boston University , 590 Commonwealth Avenue , Boston , Massachusetts 02215 , United States
| | - Nicolai Lehnert
- Department of Chemistry and Department of Biophysics , University of Michigan , Ann Arbor , Michigan 48109 , United States
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16
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Albertolle ME, Peter Guengerich F. The relationships between cytochromes P450 and H 2O 2: Production, reaction, and inhibition. J Inorg Biochem 2018; 186:228-234. [PMID: 29990746 PMCID: PMC6084448 DOI: 10.1016/j.jinorgbio.2018.05.014] [Citation(s) in RCA: 56] [Impact Index Per Article: 9.3] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/02/2018] [Revised: 04/25/2018] [Accepted: 05/23/2018] [Indexed: 12/26/2022]
Abstract
In this review we address the relationship between cytochromes P450 (P450) and H2O2. This association can affect biology in three distinct ways. First, P450s produce H2O2 as a byproduct either during catalysis or when no substrate is present. This reaction, known as uncoupling, releases reactive oxygen species that may have implications in disease. Second, H2O2 is used as an oxygen-donating co-substrate in peroxygenase and peroxidase reactions catalyzed by P450s. This activity has proven to be important mainly in reactions involving prokaryotic P450s, and investigators have harnessed this reaction with the aim of adaptation for industrial use. Third, H2O2-dependent inhibition of human P450s has been studied in our laboratory, demonstrating heme destruction and also the inactivating oxidation of the heme-thiolate ligand to a sulfenic acid (-SOH). This reversible oxidative modification of P450s may have implications in the prevention of uncoupling and may give new insights into the oxidative regulation of these enzymes. Research has elucidated many of the chemical mechanisms involved in the relationship between P450 and H2O2, but the application to biology is difficult to evaluate. Further studies are needed reveal both the harmful and protective natures of reactive oxygen species in an organismal context.
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Affiliation(s)
- Matthew E Albertolle
- Department of Biochemistry, Vanderbilt University School of Medicine, Nashville, TN 37232-0146, United States
| | - F Peter Guengerich
- Department of Biochemistry, Vanderbilt University School of Medicine, Nashville, TN 37232-0146, United States.
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17
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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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18
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Creutz SE, Peters JC. Exploring secondary-sphere interactions in Fe-N x H y complexes relevant to N 2 fixation. Chem Sci 2017; 8:2321-2328. [PMID: 28451336 PMCID: PMC5363375 DOI: 10.1039/c6sc04805f] [Citation(s) in RCA: 47] [Impact Index Per Article: 6.7] [Reference Citation Analysis] [Abstract] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/31/2016] [Accepted: 12/07/2016] [Indexed: 12/11/2022] Open
Abstract
Hydrogen bonding and other types of secondary-sphere interactions are ubiquitous in metalloenzyme active sites and are critical to the transformations they mediate. Exploiting secondary sphere interactions in synthetic catalysts to study the role(s) they might play in biological systems, and to develop increasingly efficient catalysts, is an important challenge. Whereas model studies in this broad context are increasingly abundant, as yet there has been relatively little progress in the area of synthetic catalysts for nitrogen fixation that incorporate secondary sphere design elements. Herein we present our first study of Fe-N x H y complexes supported by new tris(phosphine)silyl ligands, abbreviated as [SiPNMe3] and [SiPiPr2PNMe], that incorporate remote tertiary amine hydrogen-bond acceptors within a tertiary phosphine/amine 6-membered ring. These remote amine sites facilitate hydrogen-bonding interactions via a boat conformation of the 6-membered ring when certain nitrogenous substrates (e.g., NH3 and N2H4) are coordinated to the apical site of a trigonal bipyramidal iron complex, and adopt a chair conformation when no H-bonding is possible (e.g., N2). Countercation binding at the cyclic amine is also observed for anionic {Fe-N2}- complexes. Reactivity studies in the presence of proton/electron sources show that the incorporated amine functionality leads to rapid generation of catalytically inactive Fe-H species, thereby substantiating a hydride termination pathway that we have previously proposed deactivates catalysts of the type [EPR3]FeN2 (E = Si, C).
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Affiliation(s)
- Sidney E Creutz
- California Institute of Technology , Division , of Chemistry and Chemical Engineering , Pasadena , California 91125 , USA .
| | - Jonas C Peters
- California Institute of Technology , Division , of Chemistry and Chemical Engineering , Pasadena , California 91125 , USA .
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19
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Christoforidis KC, Pantazis DA, Bonilla LL, Bletsa E, Louloudi M, Deligiannakis Y. Axial ligand effect on the catalytic activity of biomimetic Fe-porphyrin catalyst: An experimental and DFT study. J Catal 2016. [DOI: 10.1016/j.jcat.2016.08.013] [Citation(s) in RCA: 12] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/22/2023]
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20
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McQuarters AB, Speelman AL, Chen L, Elmore BO, Fan W, Feng C, Lehnert N. Exploring second coordination sphere effects in nitric oxide synthase. J Biol Inorg Chem 2016; 21:997-1008. [PMID: 27686338 DOI: 10.1007/s00775-016-1396-1] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/17/2016] [Accepted: 09/15/2016] [Indexed: 11/28/2022]
Abstract
Second coordination sphere (SCS) effects in proteins are modulated by active site residues and include hydrogen bonding, electrostatic/dipole interactions, steric interactions, and π-stacking of aromatic residues. In Cyt P450s, extended H-bonding networks are located around the proximal cysteinate ligand of the heme, referred to as the 'Cys pocket'. These hydrogen bonding networks are generally believed to regulate the Fe-S interaction. Previous work identified the S(Cys) → Fe σ CT transition in the high-spin (hs) ferric form of Cyt P450cam and corresponding Cys pocket mutants by low-temperature (LT) MCD spectroscopy [Biochemistry 50:1053, 2011]. In this work, we have investigated the effect of the hydrogen bond from W409 to the axial Cys ligand of the heme in the hs ferric state (with H4B and L-Arg bound) of rat neuronal nitric oxide synthase oxygenase construct (nNOSoxy) using MCD spectroscopy. For this purpose, wt enzyme and W409 mutants were investigated where the H-bonding network with the axial Cys ligand is perturbed. Overall, the results are similar to Cyt P450cam and show the intense S(Cys) → Fe σ CT band in the LT MCD spectrum at about 27,800 cm-1, indicating that this feature is a hallmark of {heme-thiolate} active sites. The discovery of this MCD feature could constitute a new approach to classify {heme-thiolate} sites in hs ferric proteins. Finally, the W409 mutants show that the hydrogen bond from this group only has a small effect on the Fe-S(Cys) bond strength, at least in the hs ferric form of the protein studied here. Low-temperature MCD spectroscopy is used to investigate the effect of the hydrogen bond from W409 to the axial Cys ligand of the heme in neuronal nitric oxide synthase. The intense S(Cys) → Fe σ-CT band is monitored to identify changes in the Fe-S(Cys) bond in wild-type protein and W409 mutants.
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Affiliation(s)
- Ashley B McQuarters
- Department of Chemistry, University of Michigan, Ann Arbor, MI, 48109, USA.,Department of Biophysics, University of Michigan, Ann Arbor, MI, 48109, USA
| | - Amy L Speelman
- Department of Chemistry, University of Michigan, Ann Arbor, MI, 48109, USA.,Department of Biophysics, University of Michigan, Ann Arbor, MI, 48109, USA
| | - Li Chen
- College of Pharmacy, University of New Mexico, Albuquerque, NM, 87131, USA
| | - Bradley O Elmore
- College of Pharmacy, University of New Mexico, Albuquerque, NM, 87131, USA
| | - Weihong Fan
- College of Pharmacy, University of New Mexico, Albuquerque, NM, 87131, USA
| | - Changjian Feng
- College of Pharmacy, University of New Mexico, Albuquerque, NM, 87131, USA
| | - Nicolai Lehnert
- Department of Chemistry, University of Michigan, Ann Arbor, MI, 48109, USA. .,Department of Biophysics, University of Michigan, Ann Arbor, MI, 48109, USA.
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21
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Morozov AN, Chatfield DC. How the Proximal Pocket May Influence the Enantiospecificities of Chloroperoxidase-Catalyzed Epoxidations of Olefins. Int J Mol Sci 2016; 17:E1297. [PMID: 27517911 PMCID: PMC5000694 DOI: 10.3390/ijms17081297] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/27/2016] [Revised: 07/28/2016] [Accepted: 08/01/2016] [Indexed: 11/16/2022] Open
Abstract
Chloroperoxidase-catalyzed enantiospecific epoxidations of olefins are of significant biotechnological interest. Typical enantiomeric excesses are in the range of 66%-97% and translate into free energy differences on the order of 1 kcal/mol. These differences are generally attributed to the effect of the distal pocket. In this paper, we show that the influence of the proximal pocket on the electron transfer mechanism in the rate-limiting event may be just as significant for a quantitatively accurate account of the experimentally-measured enantiospecificities.
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Affiliation(s)
- Alexander N Morozov
- Department of Chemistry and Biochemistry, Florida International University, 11200 SW 8th St., Miami, FL 33199, USA.
| | - David C Chatfield
- Department of Chemistry and Biochemistry, Florida International University, 11200 SW 8th St., Miami, FL 33199, USA.
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22
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Bostelaar T, Vitvitsky V, Kumutima J, Lewis BE, Yadav PK, Brunold TC, Filipovic M, Lehnert N, Stemmler TL, Banerjee R. Hydrogen Sulfide Oxidation by Myoglobin. J Am Chem Soc 2016; 138:8476-88. [PMID: 27310035 PMCID: PMC5464954 DOI: 10.1021/jacs.6b03456] [Citation(s) in RCA: 106] [Impact Index Per Article: 13.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/22/2022]
Abstract
Enzymes in the sulfur network generate the signaling molecule, hydrogen sulfide (H2S), from the amino acids cysteine and homocysteine. Since it is toxic at elevated concentrations, cells are equipped to clear H2S. A canonical sulfide oxidation pathway operates in mitochondria, converting H2S to thiosulfate and sulfate. We have recently discovered the ability of ferric hemoglobin to oxidize sulfide to thiosulfate and iron-bound hydropolysulfides. In this study, we report that myoglobin exhibits a similar capacity for sulfide oxidation. We have trapped and characterized iron-bound sulfur intermediates using cryo-mass spectrometry and X-ray absorption spectroscopy. Further support for the postulated intermediates in the chemically challenging conversion of H2S to thiosulfate and iron-bound catenated sulfur products is provided by EPR and resonance Raman spectroscopy in addition to density functional theory computational results. We speculate that the unusual sensitivity of skeletal muscle cytochrome c oxidase to sulfide poisoning in ethylmalonic encephalopathy, resulting from the deficiency in a mitochondrial sulfide oxidation enzyme, might be due to the concentration of H2S by myoglobin in this tissue.
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Affiliation(s)
- Trever Bostelaar
- Department of Biological Chemistry, University of Michigan,
Ann Arbor, Michigan 48109, United States
| | - Victor Vitvitsky
- Department of Biological Chemistry, University of Michigan,
Ann Arbor, Michigan 48109, United States
| | - Jacques Kumutima
- Department of Chemistry and Department of Biophysics,
University of Michigan, Ann Arbor, Michigan 48109, United States
| | - Brianne E. Lewis
- Department of Pharmaceutical Science, Wayne State
University, Detroit, Michigan 48201-2417, United States
| | - Pramod K. Yadav
- Department of Biological Chemistry, University of Michigan,
Ann Arbor, Michigan 48109, United States
| | - Thomas C. Brunold
- Department of Chemistry, University of Wisconsin, Madison,
Wisconsin 53706, United States
| | - Milos Filipovic
- University of Bordeaux, IBGC, and CNRS, IBGC, UMR 5095,
F-33077 Bordeaux, France
| | - Nicolai Lehnert
- Department of Chemistry and Department of Biophysics,
University of Michigan, Ann Arbor, Michigan 48109, United States
| | - Timothy L. Stemmler
- Department of Pharmaceutical Science, Wayne State
University, Detroit, Michigan 48201-2417, United States
| | - Ruma Banerjee
- Department of Biological Chemistry, University of Michigan,
Ann Arbor, Michigan 48109, United States
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23
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Met104 is the CO-replaceable ligand at Fe(II) heme in the CO-sensing transcription factor BxRcoM-1. J Biol Inorg Chem 2016; 21:559-69. [DOI: 10.1007/s00775-016-1368-5] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/07/2016] [Accepted: 06/01/2016] [Indexed: 10/21/2022]
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Abstract
CytP450s have a cysteine-bound heme cofactor that, in its as-isolated resting (oxidized) form, can be conclusively described as a ferric thiolate species. Unlike the native enzyme, most synthetic thiolate-bound ferric porphyrins are unstable in air unless the axial thiolate ligand is sterically protected. Spectroscopic investigations on a series of synthetic mimics of cytP450 indicate that a thiolate-bound ferric porphyrin coexists in organic solutions at room temperature (RT) with a thiyl-radical bound ferrous porphyrin, i.e., its valence tautomer. The ferric thiolate state is favored by greater enthalpy and is air stable. The ferrous thiyl state is favored by entropy, populates at RT, and degrades in air. These ground states can be reversibly interchanged at RT by the addition or removal of water to the apolar medium. It is concluded that hydrogen bonding and local electrostatics protect the resting oxidized cytP450 active site from degradation in air by stabilizing the ferric thiolate ground state in contrast to its synthetic analogs.
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25
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Davydov R, Im S, Shanmugam M, Gunderson WA, Pearl NM, Hoffman BM, Waskell L. Role of the Proximal Cysteine Hydrogen Bonding Interaction in Cytochrome P450 2B4 Studied by Cryoreduction, Electron Paramagnetic Resonance, and Electron-Nuclear Double Resonance Spectroscopy. Biochemistry 2016; 55:869-83. [PMID: 26750753 DOI: 10.1021/acs.biochem.5b00744] [Citation(s) in RCA: 24] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Abstract
Crystallographic studies have shown that the F429H mutation of cytochrome P450 2B4 introduces an H-bond between His429 and the proximal thiolate ligand, Cys436, without altering the protein fold but sharply decreases the enzymatic activity and stabilizes the oxyferrous P450 2B4 complex. To characterize the influence of this hydrogen bond on the states of the catalytic cycle, we have used radiolytic cryoreduction combined with electron paramagnetic resonance (EPR) and (electron-nuclear double resonance (ENDOR) spectroscopy to study and compare their characteristics for wild-type (WT) P450 2B4 and the F429H mutant. (i) The addition of an H-bond to the axial Cys436 thiolate significantly changes the EPR signals of both low-spin and high-spin heme-iron(III) and the hyperfine couplings of the heme-pyrrole (14)N but has relatively little effect on the (1)H ENDOR spectra of the water ligand in the six-coordinate low-spin ferriheme state. These changes indicate that the H-bond introduced between His and the proximal cysteine decreases the extent of S → Fe electron donation and weakens the Fe(III)-S bond. (ii) The added H-bond changes the primary product of cryoreduction of the Fe(II) enzyme, which is trapped in the conformation of the parent Fe(II) state. In the wild-type enzyme, the added electron localizes on the porphyrin, generating an S = (3)/2 state with the anion radical exchange-coupled to the Fe(II). In the mutant, it localizes on the iron, generating an S = (1)/2 Fe(I) state. (iii) The additional H-bond has little effect on g values and (1)H-(14)N hyperfine couplings of the cryogenerated, ferric hydroperoxo intermediate but noticeably slows its decay during cryoannealing. (iv) In both the WT and the mutant enzyme, this decay shows a significant solvent kinetic isotope effect, indicating that the decay reflects a proton-assisted conversion to Compound I (Cpd I). (v) We confirm that Cpd I formed during the annealing of the cryogenerated hydroperoxy intermediate and that it is the active hydroxylating species in both WT P450 2B4 and the F429H mutant. (vi) Our data also indicate that the added H-bond of the mutation diminishes the reactivity of Cpd I.
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Affiliation(s)
- Roman Davydov
- Department of Chemistry, Northwestern University , 2145 Sheridan Road, Evanston, Illinois 60208-3113, United States
| | - Sangchoul Im
- Department of Anesthesiology, University of Michigan, and VA Medical Center , 2215 Fuller Road, Ann Arbor, Michigan 48105, United States
| | - Muralidharan Shanmugam
- Department of Chemistry, Northwestern University , 2145 Sheridan Road, Evanston, Illinois 60208-3113, United States
| | - William A Gunderson
- Department of Chemistry, Northwestern University , 2145 Sheridan Road, Evanston, Illinois 60208-3113, United States
| | - Naw May Pearl
- Department of Anesthesiology, University of Michigan, and VA Medical Center , 2215 Fuller Road, Ann Arbor, Michigan 48105, United States
| | - Brian M Hoffman
- Department of Chemistry, Northwestern University , 2145 Sheridan Road, Evanston, Illinois 60208-3113, United States
| | - Lucy Waskell
- Department of Anesthesiology, University of Michigan, and VA Medical Center , 2215 Fuller Road, Ann Arbor, Michigan 48105, United States
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26
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Mittra K, Sengupta K, Singha A, Bandyopadhyay S, Chatterjee S, Rana A, Samanta S, Dey A. Second sphere control of spin state: Differential tuning of axial ligand bonds in ferric porphyrin complexes by hydrogen bonding. J Inorg Biochem 2016; 155:82-91. [DOI: 10.1016/j.jinorgbio.2015.11.013] [Citation(s) in RCA: 17] [Impact Index Per Article: 2.1] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/22/2015] [Revised: 10/02/2015] [Accepted: 11/10/2015] [Indexed: 11/16/2022]
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27
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Morozov AN, Pardillo AD, Chatfield DC. Chloroperoxidase-Catalyzed Epoxidation of Cis-β-Methylstyrene: NH-S Hydrogen Bonds and Proximal Helix Dipole Change the Catalytic Mechanism and Significantly Lower the Reaction Barrier. J Phys Chem B 2015; 119:14350-63. [PMID: 26452587 DOI: 10.1021/acs.jpcb.5b06731] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Abstract
Proximal hydrogen bonding of the axial sulfur with the backbone amides (NH-S) is a conserved feature of heme-thiolate enzymes such as chloroperoxidase (CPO) and cytochrome P450 (P450). In CPO, the effect of NH-S bonds is amplified by the dipole moment of the proximal helix. Our gas-phase DFT studies show that the proximal pocket effect significantly enhances CPO's reactivity toward the epoxidation of olefinic substrates. Comparison of models with and without proximal pocket residues shows that with them, the barrier for Cβ-O bond formation is lowered by about ∼4.6 kcal/mol, while Cα-O-Cβ ring closure becomes barrierless. The dipole moment of the proximal helix was estimated to contribute 1/3 of the decrease, while the rest is attributed to the effect of NH-S bonds. The decrease of the reaction barrier correlates with increased electron density transfer to residues of the proximal pocket. The effect is most pronounced on the doublet spin surface and involves a change in the electron-transfer mechanism. A full enzyme QMMM study on the doublet spin surface gives about the same barrier as the gas-phase DFT study. The free-energy barrier was estimated to be in agreement with the experimental results for the CPO-catalyzed epoxidation of styrene.
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Affiliation(s)
- Alexander N Morozov
- Department of Chemistry and Biochemistry, Florida International University , 11200 Southwest Eighth Street, Miami, Florida 33199, United States
| | - Armando D Pardillo
- Department of Chemistry and Biochemistry, Florida International University , 11200 Southwest Eighth Street, Miami, Florida 33199, United States
| | - David C Chatfield
- Department of Chemistry and Biochemistry, Florida International University , 11200 Southwest Eighth Street, Miami, Florida 33199, United States
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Pardillo AD, Morozov AN, Chatfield DC. Proximal Pocket Hydrogen Bonds Significantly Influence the Mechanism of Chloroperoxidase Compound I Formation. J Phys Chem B 2015; 119:12590-602. [DOI: 10.1021/acs.jpcb.5b06324] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/30/2022]
Affiliation(s)
- Armando D. Pardillo
- Department of Chemistry and
Biochemistry, Florida International University, 11200 SW 8th Street, Miami, Florida 33199, United States
| | - Alexander N. Morozov
- Department of Chemistry and
Biochemistry, Florida International University, 11200 SW 8th Street, Miami, Florida 33199, United States
| | - David C. Chatfield
- Department of Chemistry and
Biochemistry, Florida International University, 11200 SW 8th Street, Miami, Florida 33199, United States
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29
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Significantly shorter Fe-S bond in cytochrome P450-I is consistent with greater reactivity relative to chloroperoxidase. Nat Chem 2015; 7:696-702. [PMID: 26291940 PMCID: PMC4580274 DOI: 10.1038/nchem.2306] [Citation(s) in RCA: 78] [Impact Index Per Article: 8.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/27/2015] [Accepted: 06/19/2015] [Indexed: 11/16/2022]
Abstract
Cytochrome P450 (P450) and chloroperoxidase (CPO) are thiolate ligated heme proteins that catalyze the activation of carbon hydrogen bonds. The principal intermediate in these reactions is a ferryl radical species called compound I. P450 compound I (P450-I) is significantly more reactive than CPO-I, which only cleaves activated C-H bonds. To provide insight into the differing reactivities of these intermediates, we examined CPO-I and P450-I with variable temperature Mössbauer and X-ray absorption spectroscopies. These measurements indicate that the Fe-S bond is significantly shorter in P450-I than in CPO-I. This difference in Fe-S bond lengths can be understood in terms of variations in hydrogen bonding patterns within the “cys-pocket” (a portion of the proximal helix that encircles the thiolate ligand). Weaker hydrogen bonding in P450-I results in a shorter Fe-S bond, which enables greater electron donation from the axial-thiolate ligand. This observation may in part explain P450's greater propensity for C-H bond activation.
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Ye S, Xue G, Krivokapic I, Petrenko T, Bill E, Que Jr L, Neese F. Magnetic circular dichroism and computational study of mononuclear and dinuclear iron(IV) complexes. Chem Sci 2015; 6:2909-2921. [PMID: 26417426 PMCID: PMC4583211 DOI: 10.1039/c4sc03268c] [Citation(s) in RCA: 23] [Impact Index Per Article: 2.6] [Reference Citation Analysis] [Abstract] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/24/2014] [Accepted: 02/26/2015] [Indexed: 12/13/2022] Open
Abstract
High-valent iron(IV)-oxo species are key intermediates in the catalytic cycles of a range of O2-activating iron enzymes. This work presents a detailed study of the electronic structures of mononuclear ([FeIV(O)(L)(NCMe)]2+, 1, L = tris(3,5-dimethyl-4-methoxylpyridyl-2-methyl)amine) and dinuclear ([(L)FeIV(O)(μ-O)FeIV(OH)(L)]3+, 2) iron(IV) complexes using absorption (ABS), magnetic circular dichroism (MCD) spectroscopy and wave-function-based quantum chemical calculations. For complex 1, the experimental MCD spectra at 2-10 K are dominated by a broad positive C-term band between 12000 and 18000 cm-1. As the temperature increases up to ~20 K, this feature is gradually replaced by a derivative-shaped signal. The computed MCD spectra are in excellent agreement with experiment, which reproduce not only the excitation energies and the MCD signs of key transitions but also their temperature-dependent intensity variations. To further corroborate the assignments suggested by the calculations, the individual MCD sign for each transition is independently determined from the corresponding electron donating and accepting orbitals. Thus, unambiguous assignments can be made for the observed transitions in 1. The ABS/MCD data of complex 2 exhibit ten features that are assigned as ligand-field transitions or oxo- or hydroxo-to-metal charge transfer bands, based on MCD/ABS intensity ratios, calculated excitation energies, polarizations, and MCD signs. In comparison with complex 1, the electronic structure of the FeIV=O site is not significantly perturbed by the binding to another iron(IV) center. This may explain the experimental finding that complexes 1 and 2 have similar reactivities toward C-H bond activation and O-atom transfer.
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Affiliation(s)
- Shengfa Ye
- Max-Planck Institut für Chemische Energiekonversion , Stiftstraße 34-36 , D-45470 Mülheim an der Ruhr , Germany . ; ;
| | - Genqiang Xue
- Department of Chemistry , Center for Metals in Biocatalysis , University of Minnesota , 207 Pleasant St. SE , Minneapolis , Minnesota 55455 , USA .
| | - Itana Krivokapic
- Max-Planck Institut für Chemische Energiekonversion , Stiftstraße 34-36 , D-45470 Mülheim an der Ruhr , Germany . ; ;
| | - Taras Petrenko
- Max-Planck Institut für Chemische Energiekonversion , Stiftstraße 34-36 , D-45470 Mülheim an der Ruhr , Germany . ; ;
| | - Eckhard Bill
- Max-Planck Institut für Chemische Energiekonversion , Stiftstraße 34-36 , D-45470 Mülheim an der Ruhr , Germany . ; ;
| | - Lawrence Que Jr
- Department of Chemistry , Center for Metals in Biocatalysis , University of Minnesota , 207 Pleasant St. SE , Minneapolis , Minnesota 55455 , USA .
| | - Frank Neese
- Max-Planck Institut für Chemische Energiekonversion , Stiftstraße 34-36 , D-45470 Mülheim an der Ruhr , Germany . ; ;
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31
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Smith AT, Pazicni S, Marvin KA, Stevens DJ, Paulsen KM, Burstyn JN. Functional divergence of heme-thiolate proteins: a classification based on spectroscopic attributes. Chem Rev 2015; 115:2532-58. [PMID: 25763468 DOI: 10.1021/cr500056m] [Citation(s) in RCA: 43] [Impact Index Per Article: 4.8] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Affiliation(s)
- Aaron T Smith
- †Department of Molecular Biosciences, Northwestern University, 2205 Tech Drive, Evanston, Illinois 60208, United States
| | - Samuel Pazicni
- ‡Department of Chemistry, University of New Hampshire, 23 Academic Way, Durham, New Hampshire 03824, United States
| | - Katherine A Marvin
- §Department of Chemistry, Hendrix College, 1600 Washington Avenue, Conway, Arkansas 72032, United States
| | - Daniel J Stevens
- ∥Department of Chemistry, University of Wisconsin-Madison, 1101 University Avenue, Madison, Wisconsin 53706, United States
| | - Katherine M Paulsen
- ∥Department of Chemistry, University of Wisconsin-Madison, 1101 University Avenue, Madison, Wisconsin 53706, United States
| | - Judith N Burstyn
- ∥Department of Chemistry, University of Wisconsin-Madison, 1101 University Avenue, Madison, Wisconsin 53706, United States
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32
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Bandyopadhyay S, Rana A, Mittra K, Samanta S, Sengupta K, Dey A. Effect of Axial Ligand, Spin State, and Hydrogen Bonding on the Inner-Sphere Reorganization Energies of Functional Models of Cytochrome P450. Inorg Chem 2014; 53:10150-8. [PMID: 25238648 DOI: 10.1021/ic501112a] [Citation(s) in RCA: 21] [Impact Index Per Article: 2.1] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/06/2023]
Affiliation(s)
- Sabyasachi Bandyopadhyay
- Indian Association for the Cultivation of Science, 2A & 2B Raja S. C. Mullick Road, Jadavpur, Kolkata, West Bengal 700032, India
| | - Atanu Rana
- Indian Association for the Cultivation of Science, 2A & 2B Raja S. C. Mullick Road, Jadavpur, Kolkata, West Bengal 700032, India
| | - Kaustuv Mittra
- Indian Association for the Cultivation of Science, 2A & 2B Raja S. C. Mullick Road, Jadavpur, Kolkata, West Bengal 700032, India
| | - Subhra Samanta
- Indian Association for the Cultivation of Science, 2A & 2B Raja S. C. Mullick Road, Jadavpur, Kolkata, West Bengal 700032, India
| | - Kushal Sengupta
- Indian Association for the Cultivation of Science, 2A & 2B Raja S. C. Mullick Road, Jadavpur, Kolkata, West Bengal 700032, India
| | - Abhishek Dey
- Indian Association for the Cultivation of Science, 2A & 2B Raja S. C. Mullick Road, Jadavpur, Kolkata, West Bengal 700032, India
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33
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Maligaspe E, Hauwiller MR, Zatsikha YV, Hinke JA, Solntsev PV, Blank DA, Nemykin VN. Redox and Photoinduced Electron-Transfer Properties in Short Distance Organoboryl Ferrocene-Subphthalocyanine Dyads. Inorg Chem 2014; 53:9336-47. [DOI: 10.1021/ic5014544] [Citation(s) in RCA: 30] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Affiliation(s)
- Eranda Maligaspe
- Department of Chemistry and Biochemistry, University of Minnesota Duluth, 1039 University Drive, Duluth, Minnesota 55812, United States
| | - Matthew R. Hauwiller
- Department of Chemistry, University of Minnesota, 207 Pleasant Street SE, Minneapolis, Minnesota 55455, United States
| | - Yuriy V. Zatsikha
- Department of Chemistry and Biochemistry, University of Minnesota Duluth, 1039 University Drive, Duluth, Minnesota 55812, United States
- Institute of Organic Chemistry, National Academy of Sciences of Ukraine, 5 Murmanska str., 02660 Kyiv, Ukraine
| | - Jonathan A. Hinke
- Department of Chemistry, University of Minnesota, 207 Pleasant Street SE, Minneapolis, Minnesota 55455, United States
| | - Pavlo V. Solntsev
- Department of Chemistry and Biochemistry, University of Minnesota Duluth, 1039 University Drive, Duluth, Minnesota 55812, United States
- Department of Chemistry, University of Minnesota, 207 Pleasant Street SE, Minneapolis, Minnesota 55455, United States
| | - David A. Blank
- Department of Chemistry, University of Minnesota, 207 Pleasant Street SE, Minneapolis, Minnesota 55455, United States
| | - Victor N. Nemykin
- Department of Chemistry and Biochemistry, University of Minnesota Duluth, 1039 University Drive, Duluth, Minnesota 55812, United States
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34
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Yang Y, Zhang H, Usharani D, Bu W, Im S, Tarasev M, Rwere F, Pearl NM, Meagher J, Sun C, Stuckey J, Shaik S, Waskell L. Structural and functional characterization of a cytochrome P450 2B4 F429H mutant with an axial thiolate-histidine hydrogen bond. Biochemistry 2014; 53:5080-91. [PMID: 25029089 PMCID: PMC4131899 DOI: 10.1021/bi5003794] [Citation(s) in RCA: 13] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/28/2014] [Revised: 07/15/2014] [Indexed: 02/02/2023]
Abstract
The structural basis of the regulation of microsomal cytochrome P450 (P450) activity was investigated by mutating the highly conserved heme binding motif residue, Phe429, on the proximal side of cytochrome P450 2B4 to a histidine. Spectroscopic, pre-steady-state and steady-state kinetic, thermodynamic, theoretical, and structural studies of the mutant demonstrate that formation of an H-bond between His429 and the unbonded electron pair of the Cys436 axial thiolate significantly alters the properties of the enzyme. The mutant lost >90% of its activity; its redox potential was increased by 87 mV, and the half-life of the oxyferrous mutant was increased ∼37-fold. Single-crystal electronic absorption and resonance Raman spectroscopy demonstrated that the mutant was reduced by a small dose of X-ray photons. The structure revealed that the δN atom of His429 forms an H-bond with the axial Cys436 thiolate whereas the εN atom forms an H-bond with the solvent and the side chain of Gln357. The amide of Gly438 forms the only other H-bond to the tetrahedral thiolate. Theoretical quantification of the histidine-thiolate interaction demonstrates a significant electron withdrawing effect on the heme iron. Comparisons of structures of class I-IV P450s demonstrate that either a phenylalanine or tryptophan is often found at the location corresponding to Phe429. Depending on the structure of the distal pocket heme, the residue at this location may or may not regulate the thermodynamic properties of the P450. Regardless, this residue appears to protect the thiolate from solvent, oxidation, protonations, and other deleterious reactions.
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Affiliation(s)
- Yuting Yang
- Department
of Anesthesiology, University of Michigan
and VA Medical Center, 2215 Fuller Road, Building 31, Room 225, Ann
Arbor, Michigan 48105, United States
| | - Haoming Zhang
- Department
of Anesthesiology, University of Michigan
and VA Medical Center, 2215 Fuller Road, Building 31, Room 225, Ann
Arbor, Michigan 48105, United States
| | - Dandamudi Usharani
- Institute
of Chemistry and Lise Meitner-Minerva Center for Computational Quantum
Chemistry, Hebrew University of Jerusalem, 91904 Jerusalem, Israel
| | - Weishu Bu
- Department
of Anesthesiology, University of Michigan
and VA Medical Center, 2215 Fuller Road, Building 31, Room 225, Ann
Arbor, Michigan 48105, United States
| | - Sangchoul Im
- Department
of Anesthesiology, University of Michigan
and VA Medical Center, 2215 Fuller Road, Building 31, Room 225, Ann
Arbor, Michigan 48105, United States
| | - Michael Tarasev
- Department
of Anesthesiology, University of Michigan
and VA Medical Center, 2215 Fuller Road, Building 31, Room 225, Ann
Arbor, Michigan 48105, United States
| | - Freeborn Rwere
- Department
of Anesthesiology, University of Michigan
and VA Medical Center, 2215 Fuller Road, Building 31, Room 225, Ann
Arbor, Michigan 48105, United States
| | - Naw May Pearl
- Department
of Anesthesiology, University of Michigan
and VA Medical Center, 2215 Fuller Road, Building 31, Room 225, Ann
Arbor, Michigan 48105, United States
| | - Jennifer Meagher
- Life
Science Institute, University of Michigan, 210 Washtenaw Avenue, Ann Arbor, Michigan 48109, United States
| | - Cuthbert Sun
- Department
of Anesthesiology, University of Michigan
and VA Medical Center, 2215 Fuller Road, Building 31, Room 225, Ann
Arbor, Michigan 48105, United States
| | - Jeanne Stuckey
- Life
Science Institute, University of Michigan, 210 Washtenaw Avenue, Ann Arbor, Michigan 48109, United States
| | - Sason Shaik
- Institute
of Chemistry and Lise Meitner-Minerva Center for Computational Quantum
Chemistry, Hebrew University of Jerusalem, 91904 Jerusalem, Israel
| | - Lucy Waskell
- Department
of Anesthesiology, University of Michigan
and VA Medical Center, 2215 Fuller Road, Building 31, Room 225, Ann
Arbor, Michigan 48105, United States
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35
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Redox-dependent stability, protonation, and reactivity of cysteine-bound heme proteins. Proc Natl Acad Sci U S A 2014; 111:E306-15. [PMID: 24398520 DOI: 10.1073/pnas.1317173111] [Citation(s) in RCA: 39] [Impact Index Per Article: 3.9] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/21/2023] Open
Abstract
Cysteine-bound hemes are key components of many enzymes and biological sensors. Protonation (deprotonation) of the Cys ligand often accompanies redox transformations of these centers. To characterize these phenomena, we have engineered a series of Thr78Cys/Lys79Gly/Met80X mutants of yeast cytochrome c (cyt c) in which Cys78 becomes one of the axial ligands to the heme. At neutral pH, the protonation state of the coordinated Cys differs for the ferric and ferrous heme species, with Cys binding as a thiolate and a thiol, respectively. Analysis of redox-dependent stability and alkaline transitions of these model proteins, as well as comparisons to Cys binding studies with the minimalist heme peptide microperoxidase-8, demonstrate that the protein scaffold and solvent interactions play important roles in stabilizing a particular Cys-heme coordination. The increased stability of ferric thiolate compared with ferrous thiol arises mainly from entropic factors. This robust cyt c model system provides access to all four forms of Cys-bound heme, including the ferric thiol. Protein motions control the rates of heme redox reactions, and these effects are amplified at low pH, where the proteins are less stable. Thermodynamic signatures and redox reactivity of the model Cys-bound hemes highlight the critical role of the protein scaffold and its dynamics in modulating redox-linked transitions between thiols and thiolates.
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36
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Blusch LK, Craigo KE, Martin-Diaconescu V, McQuarters AB, Bill E, Dechert S, DeBeer S, Lehnert N, Meyer F. Hidden Non-Innocence in an Expanded Porphyrin: Electronic Structure of the Siamese-Twin Porphyrin’s Dicopper Complex in Different Oxidation States. J Am Chem Soc 2013; 135:13892-9. [DOI: 10.1021/ja406176e] [Citation(s) in RCA: 46] [Impact Index Per Article: 4.2] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
Affiliation(s)
- Lina K. Blusch
- Institut für
Anorganische Chemie, Georg-August-Universität, Tammannstr. 4, 37077 Göttingen, Germany
| | - Kathryn E. Craigo
- Department of Chemistry, University of Michigan, Ann Arbor, Michigan 48109-1055, United States
| | - Vlad Martin-Diaconescu
- MPI für Chemische Energiekonversion, Stiftstraße
34-36, 45470 Mülheim
an der Ruhr, Germany
| | - Ashley B. McQuarters
- Department of Chemistry, University of Michigan, Ann Arbor, Michigan 48109-1055, United States
| | - Eckhard Bill
- MPI für Chemische Energiekonversion, Stiftstraße
34-36, 45470 Mülheim
an der Ruhr, Germany
| | - Sebastian Dechert
- Institut für
Anorganische Chemie, Georg-August-Universität, Tammannstr. 4, 37077 Göttingen, Germany
| | - Serena DeBeer
- MPI für Chemische Energiekonversion, Stiftstraße
34-36, 45470 Mülheim
an der Ruhr, Germany
- Department of
Chemistry and Chemical Biology, Cornell University, Ithaca, New York 14853, United States
| | - Nicolai Lehnert
- Department of Chemistry, University of Michigan, Ann Arbor, Michigan 48109-1055, United States
| | - Franc Meyer
- Institut für
Anorganische Chemie, Georg-August-Universität, Tammannstr. 4, 37077 Göttingen, Germany
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37
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Wang X, Peter S, Ullrich R, Hofrichter M, Groves JT. Driving Force for Oxygen‐Atom Transfer by Heme‐Thiolate Enzymes. Angew Chem Int Ed Engl 2013. [DOI: 10.1002/ange.201302137] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/04/2023]
Affiliation(s)
- Xiaoshi Wang
- Department of Chemistry, Princeton University, Princeton, NJ 08544 (USA)
| | - Sebastian Peter
- Department of Bio‐ and Environmental Sciences, International Graduate School of Zittau, 02763 Zittau (Germany)
| | - René Ullrich
- Department of Bio‐ and Environmental Sciences, International Graduate School of Zittau, 02763 Zittau (Germany)
| | - Martin Hofrichter
- Department of Bio‐ and Environmental Sciences, International Graduate School of Zittau, 02763 Zittau (Germany)
| | - John T. Groves
- Department of Chemistry, Princeton University, Princeton, NJ 08544 (USA)
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38
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Wang X, Peter S, Ullrich R, Hofrichter M, Groves JT. Driving force for oxygen-atom transfer by heme-thiolate enzymes. Angew Chem Int Ed Engl 2013; 52:9238-41. [PMID: 23825007 DOI: 10.1002/anie.201302137] [Citation(s) in RCA: 39] [Impact Index Per Article: 3.5] [Reference Citation Analysis] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/13/2013] [Revised: 04/18/2013] [Indexed: 11/06/2022]
Affiliation(s)
- Xiaoshi Wang
- Department of Chemistry, Princeton University, Princeton, NJ 08544, USA
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39
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Complexes of ferriheme nitrophorin 4 with low-molecular weight thiol(ate)s occurring in blood plasma. J Inorg Biochem 2013; 122:38-48. [DOI: 10.1016/j.jinorgbio.2013.01.012] [Citation(s) in RCA: 9] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/22/2012] [Revised: 01/14/2013] [Accepted: 01/14/2013] [Indexed: 11/17/2022]
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40
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Zhao M, Wang HB, Ji LN, Mao ZW. Insights into metalloenzyme microenvironments: biomimetic metal complexes with a functional second coordination sphere. Chem Soc Rev 2013; 42:8360-75. [DOI: 10.1039/c3cs60162e] [Citation(s) in RCA: 149] [Impact Index Per Article: 13.5] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/21/2023]
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41
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Mak PJ, Yang Y, Im S, Waskell LA, Kincaid JR. Experimental Documentation of the Structural Consequences of Hydrogen-Bonding Interactions to the Proximal Cysteine of a Cytochrome P450. Angew Chem Int Ed Engl 2012. [DOI: 10.1002/ange.201205912] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/12/2022]
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42
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Mak PJ, Yang Y, Im S, Waskell LA, Kincaid JR. Experimental documentation of the structural consequences of hydrogen-bonding interactions to the proximal cysteine of a cytochrome P450. Angew Chem Int Ed Engl 2012; 51:10403-7. [PMID: 22968976 DOI: 10.1002/anie.201205912] [Citation(s) in RCA: 22] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/24/2012] [Indexed: 11/09/2022]
Affiliation(s)
- Piotr J Mak
- Department of Chemistry, Marquette University, Milwaukee, WI 53233, USA
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43
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Kuter D, Venter GA, Naidoo KJ, Egan TJ. Experimental and time-dependent density functional theory characterization of the UV-visible spectra of monomeric and μ-oxo dimeric ferriprotoporphyrin IX. Inorg Chem 2012; 51:10233-50. [PMID: 22963249 DOI: 10.1021/ic301154e] [Citation(s) in RCA: 20] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/05/2023]
Abstract
Speciation of ferriprotoporphyrin IX, Fe(III)PPIX, in aqueous solution is complex. Despite the use of its characteristic spectroscopic features for identification, the theoretical basis of the unique UV-visible absorbance spectrum of μ-[Fe(III)PPIX](2)O has not been explored. To investigate this and to establish a structural and spectroscopic model for Fe(III)PPIX species, density functional theory (DFT) calculations were undertaken for H(2)O-Fe(III)PPIX and μ-[Fe(III)PPIX](2)O. The models agreed with related Fe(III)porphyrin crystal structures and reproduced vibrational spectra well. The UV-visible absorbance spectra of H(2)O-Fe(III)PPIX and μ-[Fe(III)PPIX](2)O were calculated using time-dependent DFT and reproduced major features of the experimental spectra of both. Transitions contributing to calculated excitations have been identified. The features of the electronic spectrum calculated for μ-[Fe(III)PPIX](2)O were attributed to delocalization of electron density between the two porphyrin rings of the dimer, the weaker ligand field of the axial ligand, and antiferromagnetic coupling of the Fe(III) centers. Room temperature magnetic circular dichroism (MCD) spectra have been recorded and are shown to be useful in distinguishing between these two Fe(III)PPIX species. Bands underlying major spectroscopic features were identified through simultaneous deconvolution of UV-visible and MCD spectra. Computed UV-visible spectra were compared to deconvoluted spectra. Interpretation of the prominent bands of H(2)O-Fe(III)PPIX largely conforms to previous literature. Owing to the weak paramagnetism of μ-[Fe(III)PPIX](2)O at room temperature and the larger number of underlying excitations, interpretation of its experimental UV-visible spectrum was necessarily tentative. Nonetheless, comparison with the calculated spectra of antiferromagnetically coupled and paramagnetic forms of the μ-oxo dimer of Fe(III)porphine suggested that the composition of the Soret band involves a mixture of π→π* and π→d(π) charge transfer transitions. The Q-band and charge transfer bands appear to amalgamate into a mixed low energy envelope consisting of excitations with heavily admixed π→π* and charge transfer transitions.
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Affiliation(s)
- David Kuter
- Department of Chemistry, Department of Chemistry, University of Cape Town, Private Bag, Rondebosch 7701 South Africa
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44
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Smith AT, Su Y, Stevens DJ, Majtan T, Kraus JP, Burstyn JN. Effect of the disease-causing R266K mutation on the heme and PLP environments of human cystathionine β-synthase. Biochemistry 2012; 51:6360-70. [PMID: 22738154 DOI: 10.1021/bi300421z] [Citation(s) in RCA: 23] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
Abstract
Cystathionine β-synthase (CBS) is an essential pyridoxal 5'-phosphate (PLP)-dependent enzyme of the transsulfuration pathway that condenses serine with homocysteine to form cystathionine; intriguingly, human CBS also contains a heme b cofactor of unknown function. Herein we describe the enzymatic and spectroscopic properties of a disease-associated R266K hCBS variant, which has an altered hydrogen-bonding environment. The R266K hCBS contains a low-spin, six-coordinate Fe(III) heme bearing a His/Cys ligation motif, like that of WT hCBS; however, there is a geometric distortion that exists at the R266K heme. Using rR spectroscopy, we show that the Fe(III)-Cys(thiolate) bond is longer and weaker in R266K, as evidenced by an 8 cm(-1) downshift in the ν(Fe-S) resonance. Presence of this longer and weaker Fe(III)-Cys(thiolate) bond is correlated with alteration of the fluorescence spectrum of the active PLP ketoenamine tautomer. Activity data demonstrate that, relative to WT, the R266K variant is more impaired in the alternative cysteine-synthesis reaction than in the canonical cystathionine-synthesis reaction. This diminished cysteine synthesis activity and a greater sensitivity to exogenous PLP correlate with the change in PLP environment. Fe-S(Cys) bond weakening causes a nearly 300-fold increase in the rate of ligand switching upon reduction of the R266K heme. Combined, these data demonstrate cross talk between the heme and PLP active sites, consistent with previous proposals, revealing that alteration of the Arg(266)-Cys(52) interaction affects PLP-dependent activity and dramatically destabilizes the ferrous thiolate-ligated heme complex, underscoring the importance of this hydrogen-bonding residue pair.
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Affiliation(s)
- Aaron T Smith
- Department of Chemistry, University of Wisconsin-Madison, 1101 University Avenue, Madison, WI 53706, USA
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45
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Solntsev PV, Spurgin KL, Sabin JR, Heikal AA, Nemykin VN. Photoinduced charge transfer in short-distance ferrocenylsubphthalocyanine dyads. Inorg Chem 2012; 51:6537-47. [PMID: 22651219 DOI: 10.1021/ic3000608] [Citation(s) in RCA: 61] [Impact Index Per Article: 5.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Abstract
Two new ferrocenylsubphthalocyanine dyads with ferrocenylmethoxide (2) and ferrocenecarboxylate (3) substituents directly attached to the subphthalocyanine ligand via the axial position have been prepared and characterized using NMR, UV-vis, and magnetic circular dichroism (MCD) spectroscopies as well as X-ray crystallography. The redox properties of the ferrocenyl-containing dyads 2 and 3 were investigated using the cyclic voltammetry (CV) approach and compared to those of the parent subphthalocyanine 1. CV data reveal that the first reversible oxidation is ferrocene-centered, while the second oxidation and the first reduction are localized on the subphthalocyanine ligand. The electronic structures and nature of the optical bands observed in the UV-vis and MCD spectra of all target compounds were investigated by a density functional theory polarized continuum model (DFT-PCM) and time-dependent (TD)DFT-PCM approaches. It has been found that in both dyads the highest occupied molecular orbital (HOMO) to HOMO-2 are ferrocene-centered molecular orbitals, while HOMO-3 as well as lowest unoccupied molecular orbital (LUMO) and LUMO+1 are localized on the subphthalocyanine ligand. TDDFT-PCM data on complexes 1-3 are consistent with the experimental observations, which indicate the dominance of π-π* transitions in the UV-vis spectra of 1-3. The excited-state dynamics of the dyads 2 and 3 were investigated using time-correlated single photon counting, which indicates that fluorescence quenching is more efficient in dyad 3 compared to dyad 2. These fluorescence lifetime measurements were interpreted on the basis of DFT-PCM calculations.
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Affiliation(s)
- Pavlo V Solntsev
- Department of Chemistry and Biochemistry, University of Minnesota-Duluth, 1039 University Drive, Duluth, Minnesota 55812, USA
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46
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Lehnert N. Elucidating second coordination sphere effects in heme proteins using low-temperature magnetic circular dichroism spectroscopy. J Inorg Biochem 2012; 110:83-93. [PMID: 22516139 DOI: 10.1016/j.jinorgbio.2012.02.033] [Citation(s) in RCA: 17] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/07/2011] [Revised: 02/27/2012] [Accepted: 02/28/2012] [Indexed: 11/29/2022]
Abstract
This paper reviews recent findings on how the second coordination sphere of heme proteins fine-tunes the properties of the heme active site via hydrogen bonding. This insight is obtained from low-temperature magnetic circular dichroism (MCD) spectroscopy. In the case of high-spin ferric hemes, MCD spectroscopy allows for the identification of a multitude of charge-transfer (CT) transitions. Using optically-detected magnetic saturation curves, out-of-plane polarized CT transitions between the heme and its axial ligand(s) can be identified. In the case of ferric Cytochrome P450cam, the corresponding S(σ)→Fe(III) CT transition can be used as a probe for the {Fe(III)-axial ligand} interaction, indicating that the hydrogen bonding network of the proximal Cys only plays a limited role for fine-tuning the Fe(III)-S(Cys) interaction. In the case of high-spin ferrous hemes with axial His/imidazole coordination, our MCD-spectroscopic investigations have uncovered a direct correlation between the strength of the hydrogen bond to the proximal imidazole ligand and the ground state of the complexes. With neutral imidazole coordination, the doubly occupied d-orbital of high-spin iron(II) is of d(π) character, located orthogonal to the heme plane. As the strength of the hydrogen bond increases, this orbital rotates into the heme plane, changing the ground state of the complex.
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Affiliation(s)
- Nicolai Lehnert
- Department of Chemistry, The University of Michigan, 930 North University Avenue, Ann Arbor, MI 48109-1055, USA.
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Feng C. Mechanism of Nitric Oxide Synthase Regulation: Electron Transfer and Interdomain Interactions. Coord Chem Rev 2012; 256:393-411. [PMID: 22523434 PMCID: PMC3328867 DOI: 10.1016/j.ccr.2011.10.011] [Citation(s) in RCA: 69] [Impact Index Per Article: 5.8] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/26/2023]
Abstract
Nitric oxide synthase (NOS), a flavo-hemoprotein, tightly regulates nitric oxide (NO) synthesis and thereby its dual biological activities as a key signaling molecule for vasodilatation and neurotransmission at low concentrations, and also as a defensive cytotoxin at higher concentrations. Three NOS isoforms, iNOS, eNOS and nNOS (inducible, endothelial, and neuronal NOS), achieve their key biological functions by tight regulation of interdomain electron transfer (IET) process via interdomain interactions. In particular, the FMN-heme IET is essential in coupling electron transfer in the reductase domain with NO synthesis in the heme domain by delivery of electrons required for O(2) activation at the catalytic heme site. Compelling evidence indicates that calmodulin (CaM) activates NO synthesis in eNOS and nNOS through a conformational change of the FMN domain from its shielded electron-accepting (input) state to a new electron-donating (output) state, and that CaM is also required for proper alignment of the domains. Another exciting recent development in NOS enzymology is the discovery of importance of the the FMN domain motions in modulating reactivity and structure of the catalytic heme active site (in addition to the primary role of controlling the IET processes). In the absence of a structure of full-length NOS, an integrated approach of spectroscopic (e.g. pulsed EPR, MCD, resonance Raman), rapid kinetics (laser flash photolysis and stopped flow) and mutagenesis methods is critical to unravel the molecular details of the interdomain FMN/heme interactions. This is to investigate the roles of dynamic conformational changes of the FMN domain and the docking between the primary functional FMN and heme domains in regulating NOS activity. The recent developments in understanding of mechanisms of the NOS regulation that are driven by the combined approach are the focuses of this review. An improved understanding of the role of interdomain FMN/heme interaction and CaM binding may serve as the basis for the design of new selective inhibitors of NOS isoforms.
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Affiliation(s)
- Changjian Feng
- Department of Pharmaceutical Sciences, University of New Mexico, Albuquerque, NM 87131 (USA) , Tel: 505-925-4326
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48
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Crawford JA, Li W, Pierce BS. Single turnover of substrate-bound ferric cysteine dioxygenase with superoxide anion: enzymatic reactivation, product formation, and a transient intermediate. Biochemistry 2011; 50:10241-53. [PMID: 21992268 DOI: 10.1021/bi2011724] [Citation(s) in RCA: 57] [Impact Index Per Article: 4.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Abstract
Cysteine dioxygenase (CDO) is a non-heme mononuclear iron enzyme that catalyzes the O(2)-dependent oxidation of L-cysteine (Cys) to produce cysteine sulfinic acid (CSA). In this study we demonstrate that the catalytic cycle of CDO can be "primed" by one electron through chemical oxidation to produce CDO with ferric iron in the active site (Fe(III)-CDO, termed 2). While catalytically inactive, the substrate-bound form of Fe(III)-CDO (2a) is more amenable to interrogation by UV-vis and EPR spectroscopy than the 'as-isolated' Fe(II)-CDO enzyme (1). Chemical-rescue experiments were performed in which superoxide (O(2)(•-)) anions were introduced to 2a to explore the possibility that a Fe(III)-superoxide species represents the first intermediate within the catalytic pathway of CDO. In principle, O(2)(•-) can serve as a suitable acceptor for the remaining 3-electrons necessary for CSA formation and regeneration of the active Fe(II)-CDO enzyme (1). Indeed, addition of O(2)(•-) to 2a resulted in the rapid formation of a transient species (termed 3a) observable at 565 nm by UV-vis spectroscopy. The subsequent decay of 3a is kinetically matched to CSA formation. Moreover, a signal attributed to 3a was also identified using parallel mode X-band EPR spectroscopy (g ~ 11). Spectroscopic simulations, observed temperature dependence, and the microwave power saturation behavior of 3a are consistent with a ground state S = 3 from a ferromagnetically coupled (J ~ -8 cm(-1)) high-spin ferric iron (S(A) = 5/2) with a bound radical (S(B) = 1/2), presumably O(2)(•-). Following treatment with O(2)(•-), the specific activity of recovered CDO increased to ~60% relative to untreated enzyme.
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Affiliation(s)
- Joshua A Crawford
- Department of Chemistry and Biochemistry, College of Sciences, The University of Texas at Arlington, Arlington, Texas 76019, United States
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49
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Lang J, Santolini J, Couture M. The conserved Trp-Cys hydrogen bond dampens the "push effect" of the heme cysteinate proximal ligand during the first catalytic cycle of nitric oxide synthase. Biochemistry 2011; 50:10069-81. [PMID: 22023145 DOI: 10.1021/bi200965e] [Citation(s) in RCA: 23] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/14/2023]
Abstract
Residues surrounding and interacting with the heme proximal ligand are important for efficient catalysis by heme proteins. The nitric oxide synthases (NOSs) are thiolate-coordinated enzymes that catalyze the hydroxylation of l-Arg in the first of the two catalytic cycles needed to synthesize nitric oxide. In NOSs, the indole NH group of a conserved tryptophan [W56 of the bacterial NOS-like protein from Staphylococcus aureus (saNOS)] forms a hydrogen bond with the heme proximal cysteinate ligand. The purpose of this study was to determine the impact of increasing (W56F and W56Y variants) or decreasing (W56H variant) the electron density of the proximal cysteinate ligand on molecular oxygen (O(2)) activation using saNOS as a model. We show that the removal of the indole NH···S(-) bond for W56F and W56Y caused an increase in the electron density of the cysteinate. This was probed by the decrease of the midpoint reduction potential (E(1/2)) along with weakened σ-bonding and strengthened π-backbonding with distal ligands (CO and O(2)). On the other hand, the W56H variant showed stronger Fe-OO and Fe-CO bonds (strengthened σ-bonding) along with an elevated E(1/2), which is consistent with the formation of a strong NH···S(-) hydrogen bond from H56. We also show here that changing the electron density of the proximal thiolate controls its "push effect"; whereas the rates of both O(2) activation and autoxidation of the Fe(II)O(2) complex increase with the stronger push effect created by removing the indole NH···S(-) hydrogen bond (W56F and W56Y variants), the W56H variant showed an increased stability of the complex against autoxidation and a slower rate of O(2) activation. These results are discussed with regard to the roles played by the conserved tryptophan-cysteinate interaction in the first catalytic cycle of NOS.
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Affiliation(s)
- Jérôme Lang
- Département de biochimie, de microbiologie et de bioinformatique, PROTEO and IBIS, pavillon Charles-Eugène Marchand, room 3163, Université Laval, Québec, Canada G1V 0A6
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50
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Sempombe J, Galinato MGI, Elmore BO, Fan W, Guillemette JG, Lehnert N, Kirk ML, Feng C. Mutation in the flavin mononucleotide domain modulates magnetic circular dichroism spectra of the iNOS ferric cyano complex in a substrate-specific manner. Inorg Chem 2011; 50:6859-61. [PMID: 21718007 DOI: 10.1021/ic200952c] [Citation(s) in RCA: 12] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/01/2023]
Abstract
We have obtained low-temperature magnetic circular dichroism (MCD) spectra for ferric cyano complexes of the wild type and E546N mutant of a human inducible nitric oxide synthase (iNOS) oxygenase/flavin mononucleotide (oxyFMN) construct. The mutation at the FMN domain has previously been shown to modulate the MCD spectra of the l-arginine-bound ferric iNOS heme (Sempombe, J.; et al. J. Am. Chem. Soc. 2009, 131, 6940-6941). The addition of l-arginine to the wild-type protein causes notable changes in the CN(-)-adduct MCD spectrum, while the E546N mutant spectrum is not perturbed. Moreover, the MCD spectral perturbation observed with l-arginine is absent in the CN(-) complexes incubated with N-hydroxy-L-arginine, which is the substrate for the second step of NOS catalysis. These results indicate that interdomain FMN-heme interactions exert a long-range effect on key heme axial ligand-substrate interactions that determine substrate oxidation pathways of NOS.
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Affiliation(s)
- Joseph Sempombe
- Department of Chemistry and Chemical Biology, The University of New Mexico, New Mexico 87131, USA
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