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Gera R, De P, Singh KK, Jannuzzi SAV, Mohanty A, Velasco L, Kulbir, Kumar P, Marco JF, Nagarajan K, Pecharromán C, Rodríguez-Pascual PM, DeBeer S, Moonshiram D, Gupta SS, Dasgupta J. Trapping an Elusive Fe(IV)-Superoxo Intermediate Inside a Self-Assembled Nanocage in Water at Room Temperature. J Am Chem Soc 2024; 146:21729-21741. [PMID: 39078020 DOI: 10.1021/jacs.4c05849] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 07/31/2024]
Abstract
Molecular cavities that mimic natural metalloenzymes have shown the potential to trap elusive reaction intermediates. Here, we demonstrate the formation of a rare yet stable Fe(IV)-superoxo intermediate at room temperature subsequent to dioxygen binding at the Fe(III) site of a (Et4N)2[FeIII(Cl)(bTAML)] complex confined inside the hydrophobic interior of a water-soluble Pd6L412+ nanocage. Using a combination of electron paramagnetic resonance, Mössbauer, Raman/IR vibrational, X-ray absorption, and emission spectroscopies, we demonstrate that the cage-encapsulated complex has a Fe(IV) oxidation state characterized by a stable S = 1/2 spin state and a short Fe-O bond distance of ∼1.70 Å. We find that the O2 reaction in confinement is reversible, while the formed Fe(IV)-superoxo complex readily reacts when presented with substrates having weak C-H bonds, highlighting the lability of the O-O bond. We envision that such optimally trapped high-valent superoxos can show new classes of reactivities catalyzing both oxygen atom transfer and C-H bond activation reactions.
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Affiliation(s)
- Rahul Gera
- Department of Chemical Sciences, Tata Institute of Fundamental Research, Mumbai 400005, India
- Department of Education in Science and Mathematics, Regional Institute of Education - Mysuru, NCERT, Mysuru 570006, India
| | - Puja De
- Department of Chemical Sciences, Indian Institute of Science Education and Research Kolkata, Mohanpur, West Bengal 741246, India
| | - Kundan K Singh
- Chemical Engineering Division, CSIR-National Chemical Laboratory, Pune, Maharashtra 411008, India
- Chemistry Department, Indian Institute of Technology, Dharwad 580007, India
| | - Sergio A V Jannuzzi
- Department of Inorganic Spectroscopy, Max Planck Institute for Chemical Energy Conversion, Stiftstr. 34-36, Mülheim an der Ruhr 45470, Germany
| | - Aisworika Mohanty
- Department of Chemical Sciences, Tata Institute of Fundamental Research, Mumbai 400005, India
| | - Lucia Velasco
- Instituto de Ciencia de Materiales de Madrid Consejo Superior de Investigaciones Científicas Sor Juana Inés de la Cruz, 3, Madrid 28049, Spain
| | - Kulbir
- Department of Chemistry, Indian Institute of Science Education and Research (IISER), Tirupati 517507, India
| | - Pankaj Kumar
- Department of Chemistry, Indian Institute of Science Education and Research (IISER), Tirupati 517507, India
| | - J F Marco
- Instituto de Quimica Fisica Blas Cabrera, Consejo Superior de Investigaciones Científicas, Serrano 119, Madrid 28006, Spain
| | - Kalaivanan Nagarajan
- Department of Chemical Sciences, Tata Institute of Fundamental Research, Mumbai 400005, India
| | - Carlos Pecharromán
- Instituto de Ciencia de Materiales de Madrid Consejo Superior de Investigaciones Científicas Sor Juana Inés de la Cruz, 3, Madrid 28049, Spain
| | - P M Rodríguez-Pascual
- Instituto de Ciencia de Materiales de Madrid Consejo Superior de Investigaciones Científicas Sor Juana Inés de la Cruz, 3, Madrid 28049, Spain
| | - Serena DeBeer
- Department of Inorganic Spectroscopy, Max Planck Institute for Chemical Energy Conversion, Stiftstr. 34-36, Mülheim an der Ruhr 45470, Germany
| | - Dooshaye Moonshiram
- Instituto de Ciencia de Materiales de Madrid Consejo Superior de Investigaciones Científicas Sor Juana Inés de la Cruz, 3, Madrid 28049, Spain
| | - Sayam Sen Gupta
- Department of Chemical Sciences, Indian Institute of Science Education and Research Kolkata, Mohanpur, West Bengal 741246, India
| | - Jyotishman Dasgupta
- Department of Chemical Sciences, Tata Institute of Fundamental Research, Mumbai 400005, India
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2
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Bollmeyer MM, Coleman RE, Majer SH, Ferrao SD, Lancaster KM. Cytochrome P460 Cofactor Maturation Proceeds via Peroxide-Dependent Post-translational Modification. J Am Chem Soc 2023; 145:14404-14416. [PMID: 37338957 PMCID: PMC10431212 DOI: 10.1021/jacs.3c03608] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 06/21/2023]
Abstract
Cytochrome P460s are heme enzymes that oxidize hydroxylamine to nitrous oxide. They bear specialized "heme P460" cofactors that are cross-linked to their host polypeptides by a post-translationally modified lysine residue. Wild-type N. europaea cytochrome P460 may be isolated as a cross-link-deficient proenzyme following anaerobic overexpression in E. coli. When treated with peroxide, this proenzyme undergoes maturation to active enzyme with spectroscopic and catalytic properties that match wild-type cyt P460. This maturation reactivity requires no chaperones─it is intrinsic to the protein. This behavior extends to the broader cytochrome c'β superfamily. Accumulated data reveal key contributions from the secondary coordination sphere that enable selective, complete maturation. Spectroscopic data support the intermediacy of a ferryl species along the maturation pathway.
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Affiliation(s)
- Melissa M. Bollmeyer
- Department of Chemistry and Chemical Biology Cornell University, Baker Laboratory, 162 Sciences Drive, Ithaca, NY 14853, USA
| | - Rachael E. Coleman
- Department of Chemistry and Chemical Biology Cornell University, Baker Laboratory, 162 Sciences Drive, Ithaca, NY 14853, USA
| | - Sean H. Majer
- Department of Chemistry and Chemical Biology Cornell University, Baker Laboratory, 162 Sciences Drive, Ithaca, NY 14853, USA
| | - Silas D. Ferrao
- Department of Chemistry and Chemical Biology Cornell University, Baker Laboratory, 162 Sciences Drive, Ithaca, NY 14853, USA
| | - Kyle M. Lancaster
- Department of Chemistry and Chemical Biology Cornell University, Baker Laboratory, 162 Sciences Drive, Ithaca, NY 14853, USA
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3
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Davydov R, Herzog AE, Jodts RJ, Karlin KD, Hoffman BM. End-On Copper(I) Superoxo and Cu(II) Peroxo and Hydroperoxo Complexes Generated by Cryoreduction/Annealing and Characterized by EPR/ENDOR Spectroscopy. J Am Chem Soc 2022; 144:377-389. [PMID: 34981938 PMCID: PMC8785356 DOI: 10.1021/jacs.1c10252] [Citation(s) in RCA: 10] [Impact Index Per Article: 5.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/14/2023]
Abstract
In this report, we investigate the physical and chemical properties of monocopper Cu(I) superoxo and Cu(II) peroxo and hydroperoxo complexes. These are prepared by cryoreduction/annealing of the parent [LCuI(O2)]+ Cu(I) dioxygen adducts with the tripodal, N4-coordinating, tetradentate ligands L = PVtmpa, DMMtmpa, TMG3tren and are best described as [LCuII(O2•-)]+ Cu(II) complexes that possess end-on (η1-O2•-) superoxo coordination. Cryogenic γ-irradiation (77 K) of the EPR-silent parent complexes generates mobile electrons from the solvent that reduce the [LCuII(O2•-)]+ within the frozen matrix, trapping the reduced form fixed in the structure of the parent complex. Cryoannealing, namely progressively raising the temperature of a frozen sample in stages and then cooling back to low temperature at each stage for examination, tracks the reduced product as it relaxes its structure and undergoes chemical transformations. We employ EPR and ENDOR (electron-nuclear double resonance) as powerful spectroscopic tools for examining the properties of the states that form. Surprisingly, the primary products of reduction of the Cu(II) superoxo species are metastable cuprous superoxo [LCuI(O2•-)]+ complexes. During annealing to higher temperatures this state first undergoes internal electron transfer (IET) to form the end-on Cu(II) peroxo state, which is then protonated to form Cu(II)-OOH species. This is the first time these methods, which have been used to determine key details of metalloenzyme catalytic cycles and are a powerful tools for tracking PCET reactions, have been applied to copper coordination compounds.
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Affiliation(s)
- Roman Davydov
- Department of Chemistry, Northwestern University, Evanston, Illinois 60201, United States
| | - Austin E Herzog
- Department of Chemistry, Johns Hopkins University, Baltimore, Maryland 21218, United States
| | - Richard J Jodts
- Department of Chemistry, Northwestern University, Evanston, Illinois 60201, United States
| | - Kenneth D Karlin
- Department of Chemistry, Johns Hopkins University, Baltimore, Maryland 21218, United States
| | - Brian M Hoffman
- Department of Chemistry, Northwestern University, Evanston, Illinois 60201, United States
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4
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Kim H, Rogler PJ, Sharma SK, Schaefer AW, Solomon EI, Karlin KD. Ferric Heme Superoxide Reductive Transformations to Ferric Heme (Hydro)Peroxide Species: Spectroscopic Characterization and Thermodynamic Implications for H‐Atom Transfer (HAT). Angew Chem Int Ed Engl 2021. [DOI: 10.1002/ange.202013791] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022]
Affiliation(s)
- Hyun Kim
- Chemistry Department Johns Hopkins University Baltimore MD 21218 USA
| | - Patrick J. Rogler
- Chemistry Department Johns Hopkins University Baltimore MD 21218 USA
| | - Savita K. Sharma
- Chemistry Department Johns Hopkins University Baltimore MD 21218 USA
| | | | | | - Kenneth D. Karlin
- Chemistry Department Johns Hopkins University Baltimore MD 21218 USA
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5
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Kim H, Rogler PJ, Sharma SK, Schaefer AW, Solomon EI, Karlin KD. Ferric Heme Superoxide Reductive Transformations to Ferric Heme (Hydro)Peroxide Species: Spectroscopic Characterization and Thermodynamic Implications for H-Atom Transfer (HAT). Angew Chem Int Ed Engl 2021; 60:5907-5912. [PMID: 33348450 PMCID: PMC7920932 DOI: 10.1002/anie.202013791] [Citation(s) in RCA: 7] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/13/2020] [Indexed: 01/07/2023]
Abstract
A new end-on low-spin ferric heme peroxide, [(PIm )FeIII -(O22- )]- (PIm -P), and subsequently formed hydroperoxide species, [(PIm )FeIII -(OOH)] (PIm -HP) are generated utilizing the iron-porphyrinate PIm with its tethered axial base imidazolyl group. Measured thermodynamic parameters, the ferric heme superoxide [(PIm )FeIII -(O2⋅- )] (PIm -S) reduction potential (E°') and the PIm -HP pKa value, lead to the finding of the OO-H bond-dissociation free energy (BDFE) of PIm -HP as 69.5 kcal mol-1 using a thermodynamic square scheme and Bordwell relationship. The results are validated by the observed oxidizing ability of PIm -S via hydrogen-atom transfer (HAT) compared to that of the F8 superoxide complex, [(F8 )FeIII -(O2.- )] (S) (F8 =tetrakis(2,6-difluorophenyl)porphyrinate, without an internally appended axial base imidazolyl), as determined from reactivity comparison of superoxide complexes PIm -S and S with the hydroxylamine (O-H) substrates TEMPO-H and ABNO-H.
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Affiliation(s)
- Hyun Kim
- Chemistry Department, Johns Hopkins University, Baltimore, MD, 21218, USA
| | - Patrick J Rogler
- Chemistry Department, Johns Hopkins University, Baltimore, MD, 21218, USA
| | - Savita K Sharma
- Chemistry Department, Johns Hopkins University, Baltimore, MD, 21218, USA
| | | | - Edward I Solomon
- Chemistry Department, Stanford University, Stanford, CA, 94305, USA
| | - Kenneth D Karlin
- Chemistry Department, Johns Hopkins University, Baltimore, MD, 21218, USA
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6
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Kim H, Rogler PJ, Sharma SK, Schaefer AW, Solomon EI, Karlin KD. Heme-Fe III Superoxide, Peroxide and Hydroperoxide Thermodynamic Relationships: Fe III-O 2•- Complex H-Atom Abstraction Reactivity. J Am Chem Soc 2020; 142:3104-3116. [PMID: 31913628 PMCID: PMC7034651 DOI: 10.1021/jacs.9b12571] [Citation(s) in RCA: 30] [Impact Index Per Article: 7.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/23/2022]
Abstract
Establishing redox and thermodynamic relationships between metal-ion-bound O2 and its reduced (and protonated) derivatives is critically important for a full understanding of (bio)chemical processes involving dioxygen processing. Here, a ferric heme peroxide complex, [(F8)FeIII-(O22-)]- (P) (F8 = tetrakis(2,6-difluorophenyl)porphyrinate), and a superoxide complex, [(F8)FeIII-(O2•-)] (S), are shown to be redox interconvertible. Using Cr(η-C6H6)2, an equilibrium state where S and P are present is established in tetrahydrofuran (THF) at -80 °C, allowing determination of the reduction potential of S as -1.17 V vs Fc+/0. P could be protonated with 2,6-lutidinium triflate, yielding the low-spin ferric hydroperoxide species, [(F8)FeIII-(OOH)] (HP). Partial conversion of HP back to P using a derivatized phosphazene base gave a P/HP equilibrium mixture, leading to the determination of pKa = 28.8 for HP (THF, -80 °C). With the measured reduction potential and pKa, the O-H bond dissociation free energy (BDFE) of hydroperoxide species HP was calculated to be 73.5 kcal/mol, employing the thermodynamic square scheme and Bordwell relationship. This calculated O-H BDFE of HP, in fact, lines up with an experimental demonstration of the oxidizing ability of S via hydrogen atom transfer (HAT) from TEMPO-H (2,2,6,6-tetramethylpiperdine-N-hydroxide, BDFE = 66.5 kcal/mol in THF), forming the hydroperoxide species HP and TEMPO radical. Kinetic studies carried out with TEMPO-H(D) reveal second-order behavior, kH = 0.5, kD = 0.08 M-1 s-1 (THF, -80 °C); thus, the hydrogen/deuterium kinetic isotope effect (KIE) = 6, consistent with H-atom abstraction by S being the rate-determining step. This appears to be the first case where experimentally derived thermodynamics lead to a ferric heme hydroperoxide OO-H BDFE determination, that FeIII-OOH species being formed via HAT reactivity of the partner ferric heme superoxide complex.
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Affiliation(s)
- Hyun Kim
- Department of Chemistry , Johns Hopkins University , Baltimore , Maryland 21218 , United States
| | - Patrick J Rogler
- Department of Chemistry , Johns Hopkins University , Baltimore , Maryland 21218 , United States
| | - Savita K Sharma
- Department of Chemistry , Johns Hopkins University , Baltimore , Maryland 21218 , United States
| | - Andrew W Schaefer
- Department of Chemistry , Stanford University , Stanford , California 94305 , United States
| | - Edward I Solomon
- Department of Chemistry , Stanford University , Stanford , California 94305 , United States
| | - Kenneth D Karlin
- Department of Chemistry , Johns Hopkins University , Baltimore , Maryland 21218 , United States
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7
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Affiliation(s)
- Kazuo Kobayashi
- The Institute of Scientific and Industrial Research, Osaka University, Mihogaoka 8-1, Ibaraki, Osaka 567-0047, Japan
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8
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Fukuzumi S, Lee YM, Nam W. Structure and reactivity of the first-row d-block metal-superoxo complexes. Dalton Trans 2019; 48:9469-9489. [DOI: 10.1039/c9dt01402k] [Citation(s) in RCA: 42] [Impact Index Per Article: 8.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/12/2022]
Abstract
This review discusses the structure and reactivity of metal-superoxo complexes covering all ten first-row d-block metals from Sc to Zn.
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Affiliation(s)
- Shunichi Fukuzumi
- Department of Chemistry and Nano Science
- Ewha Womans University
- Seoul 03760
- Korea
- Graduate School of Science and Technology
| | - Yong-Min Lee
- Department of Chemistry and Nano Science
- Ewha Womans University
- Seoul 03760
- Korea
- Research Institute for Basic Sciences
| | - Wonwoo Nam
- Department of Chemistry and Nano Science
- Ewha Womans University
- Seoul 03760
- Korea
- State Key Laboratory for Oxo Synthesis and Selective Oxidation
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9
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Adam SM, Wijeratne GB, Rogler PJ, Diaz DE, Quist DA, Liu JJ, Karlin KD. Synthetic Fe/Cu Complexes: Toward Understanding Heme-Copper Oxidase Structure and Function. Chem Rev 2018; 118:10840-11022. [PMID: 30372042 PMCID: PMC6360144 DOI: 10.1021/acs.chemrev.8b00074] [Citation(s) in RCA: 132] [Impact Index Per Article: 22.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/18/2022]
Abstract
Heme-copper oxidases (HCOs) are terminal enzymes on the mitochondrial or bacterial respiratory electron transport chain, which utilize a unique heterobinuclear active site to catalyze the 4H+/4e- reduction of dioxygen to water. This process involves a proton-coupled electron transfer (PCET) from a tyrosine (phenolic) residue and additional redox events coupled to transmembrane proton pumping and ATP synthesis. Given that HCOs are large, complex, membrane-bound enzymes, bioinspired synthetic model chemistry is a promising approach to better understand heme-Cu-mediated dioxygen reduction, including the details of proton and electron movements. This review encompasses important aspects of heme-O2 and copper-O2 (bio)chemistries as they relate to the design and interpretation of small molecule model systems and provides perspectives from fundamental coordination chemistry, which can be applied to the understanding of HCO activity. We focus on recent advancements from studies of heme-Cu models, evaluating experimental and computational results, which highlight important fundamental structure-function relationships. Finally, we provide an outlook for future potential contributions from synthetic inorganic chemistry and discuss their implications with relevance to biological O2-reduction.
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Affiliation(s)
- Suzanne M. Adam
- Department of Chemistry, Johns Hopkins University, Baltimore, Maryland 21218, United States
| | - Gayan B. Wijeratne
- Department of Chemistry, Johns Hopkins University, Baltimore, Maryland 21218, United States
| | - Patrick J. Rogler
- Department of Chemistry, Johns Hopkins University, Baltimore, Maryland 21218, United States
| | - Daniel E. Diaz
- Department of Chemistry, Johns Hopkins University, Baltimore, Maryland 21218, United States
| | - David A. Quist
- Department of Chemistry, Johns Hopkins University, Baltimore, Maryland 21218, United States
| | - Jeffrey J. Liu
- Department of Chemistry, Johns Hopkins University, Baltimore, Maryland 21218, United States
| | - Kenneth D. Karlin
- Department of Chemistry, Johns Hopkins University, Baltimore, Maryland 21218, United States
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10
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Araki I, Fukui K, Fujii H. Preparation, Characterization and Reactivity of a Bis-hypochlorite Adduct of a Chiral Manganese(IV) Salen Complex. Inorg Chem 2018; 57:1685-1688. [DOI: 10.1021/acs.inorgchem.7b02661] [Citation(s) in RCA: 7] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Affiliation(s)
- Ikuko Araki
- Department of Chemistry, Graduate School
of Humanities and Sciences, Nara Women’s University, Kitauoyanishi, Nara 630-8506, Japan
| | - Kaoru Fukui
- Department of Chemistry, Graduate School
of Humanities and Sciences, Nara Women’s University, Kitauoyanishi, Nara 630-8506, Japan
| | - Hiroshi Fujii
- Department of Chemistry, Graduate School
of Humanities and Sciences, Nara Women’s University, Kitauoyanishi, Nara 630-8506, Japan
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11
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Zhu Q, Mak PJ, Tuckey RC, Kincaid JR. Active Site Structures of CYP11A1 in the Presence of Its Physiological Substrates and Alterations upon Binding of Adrenodoxin. Biochemistry 2017; 56:5786-5797. [PMID: 28991453 PMCID: PMC6541926 DOI: 10.1021/acs.biochem.7b00766] [Citation(s) in RCA: 11] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
Abstract
The rate-limiting step in the steroid synthesis pathway is catalyzed by CYP11A1 through three sequential reactions. The first two steps involve hydroxylations at positions 22 and 20, generating 20(R),22(R)-dihydroxycholesterol (20R,22R-DiOHCH), with the third stage leading to a C20-C22 bond cleavage, forming pregnenolone. This work provides detailed information about the active site structure of CYP11A1 in the resting state and substrate-bound ferric forms as well as the CO-ligated adducts. In addition, high-quality resonance Raman spectra are reported for the dioxygen complexes, providing new insight into the status of Fe-O-O fragments encountered during the enzymatic cycle. Results show that the three natural substrates of CYP11A1 have quite different effects on the active site structure, including variations of spin state populations, reorientations of heme peripheral groups, and, most importantly, substrate-mediated distortions of Fe-CO and Fe-O2 fragments, as revealed by telltale shifts of the observed vibrational modes. Specifically, the vibrational mode patterns observed for the Fe-O-O fragments with the first and third substrates are consistent with H-bonding interactions with the terminal oxygen, a structural feature that tends to promote O-O bond cleavage to form the Compound I intermediate. Furthermore, such spectral data are acquired for complexes with the natural redox partner, adrenodoxin (Adx), revealing protein-protein-induced active site structural perturbations. While this work shows that Adx has an only weak effect on ferric and ferrous CO states, it has a relatively stronger impact on the Fe-O-O fragments of the functionally relevant oxy complexes.
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Affiliation(s)
- Qianhong Zhu
- Department of Chemistry, Marquette University , Milwaukee, Wisconsin 53233, United States
| | - Piotr J Mak
- Department of Chemistry, Marquette University , Milwaukee, Wisconsin 53233, United States
| | - Robert C Tuckey
- School of Molecular Sciences, The University of Western Australia , Perth, WA 6009, Australia
| | - James R Kincaid
- Department of Chemistry, Marquette University , Milwaukee, Wisconsin 53233, United States
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12
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Burger RM, Grigoryants VM, Scholes CP. Exchangeable proton ENDOR as a probe of the redox-active iron center in activated bleomycin and ferric bleomycin. Dalton Trans 2017; 46:13263-13272. [PMID: 28715026 DOI: 10.1039/c7dt01354j] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022]
Abstract
Activated bleomycin (ABLM) is a drug-Fe(iii)-hydroperoxide complex kinetically competent in DNA attack (via H4' abstraction). This intermediate is relatively stable, but its spontaneous conversion to ferric bleomycin (Fe(iii)·BLM) is poorly characterized because no observable intermediate product accumulates. The Fe(iii)·BLM formed cryophotolytically from ABLM and kept at 77 K was remarkably similar by EPR and ENDOR criteria to Fe(iii)·BLM formed from Fe(iii) + BLM solution. The notable ENDOR criteria were the ENDOR frequencies and features of orientation-selected, strongly hyperfine-coupled, exchangeable protons associated with the environs of the iron within <3.5 Å of paramagnetic Fe(iii) in Fe(iii)·BLM and ABLM. Cryophotolytic conversion of activated bleomycin to its ferric bleomycin product in the frozen solid is a sign that the reaction requires only constrained local proton rearrangements. We have characterized the metal-proton distances and orientations of the protons in that rearrangement, especially noting that these protons are of mechanistic importance in the ambient temperature conversion of ABLM to Fe(iii)·BLM in concert with a directed radical-forming attack on DNA.
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13
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Gain S, Das RS, Banerjee R, Mukhopadhyay S. Kinetics and mechanism of oxidation of thiourea by a bridging superoxide in the presence of Ellman’s reagent. J COORD CHEM 2016. [DOI: 10.1080/00958972.2016.1206198] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/21/2022]
Affiliation(s)
- Sekhar Gain
- Department of Chemistry, Ramakrishna Mission Vidyamandira, Howrah, India
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14
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Ohta T, Liu JG, Nagaraju P, Ogura T, Naruta Y. A cryo-generated ferrous-superoxo porphyrin: EPR, resonance Raman and DFT studies. Chem Commun (Camb) 2016; 51:12407-10. [PMID: 26144219 DOI: 10.1039/c5cc03520a] [Citation(s) in RCA: 10] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022]
Abstract
The resonance Raman analysis of cryo-generated ferrous-superoxy heme has been performed for the first time, and its structure and the reaction mechanism are rationalized by DFT calculations. The presence of another electronic tautomer of ferrous-superoxy heme is predicted computationally.
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Affiliation(s)
- Takehiro Ohta
- Picobiology Institute, Graduate School of Life Science, University of Hyogo, Hyogo 679-5148, Japan.
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15
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Sengupta K, Chatterjee S, Dey A. Catalytic H2O2 Disproportionation and Electrocatalytic O2 Reduction by a Functional Mimic of Heme Catalase: Direct Observation of Compound 0 and Compound I in Situ. ACS Catal 2016. [DOI: 10.1021/acscatal.5b02668] [Citation(s) in RCA: 44] [Impact Index Per Article: 5.5] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/30/2022]
Affiliation(s)
- Kushal Sengupta
- Department
of Inorganic Chemistry, Indian Association for the Cultivation of Science, Kolkata, India 700032
| | - Sudipta Chatterjee
- Department
of Inorganic Chemistry, Indian Association for the Cultivation of Science, Kolkata, India 700032
| | - Abhishek Dey
- Department
of Inorganic Chemistry, Indian Association for the Cultivation of Science, Kolkata, India 700032
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16
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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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17
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Davydov R, Strushkevich N, Smil D, Yantsevich A, Gilep A, Usanov S, Hoffman BM. Evidence That Compound I Is the Active Species in Both the Hydroxylase and Lyase Steps by Which P450scc Converts Cholesterol to Pregnenolone: EPR/ENDOR/Cryoreduction/Annealing Studies. Biochemistry 2015; 54:7089-97. [PMID: 26603348 DOI: 10.1021/acs.biochem.5b00903] [Citation(s) in RCA: 28] [Impact Index Per Article: 3.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
Abstract
Cytochrome P450scc (CYP 11A1) catalyzes the conversion of cholesterol (Ch) to pregnenolone, the precursor to steroid hormones. This process proceeds via three sequential monooxygenation reactions: two hydroxylations of Ch first form 22(R)-hydroxycholesterol (HC) and then 20α,22(R)-dihydroxycholesterol (DHC); a lyase reaction then cleaves the C20-C22 bond to form pregnenolone. Recent cryoreduction/annealing studies that employed electron paramagnetic resonance (EPR)/electron nuclear double resonance (ENDOR) spectroscopy [Davydov, R., et al. (2012) J. Am. Chem. Soc. 134, 17149] showed that compound I (Cpd I) is the active intermediate in the first step, hydroxylation of Ch. Herein, we have employed EPR and ENDOR spectroscopy to characterize the intermediates in the second and third steps of the enzymatic process, as conducted by 77 K radiolytic one-electron cryoreduction and subsequent annealing of the ternary oxy-cytochrome P450scc complexes with HC and DHC. This procedure is validated by showing that the cryoreduced ternary complexes of oxy-cytochrome P450scc with HC and DHC are catalytically competent and during annealing generate DHC and pregnenolone, respectively. Cryoreduction of the oxy-P450scc-HC ternary complex trapped at 77K produces the superoxo-ferrous P450scc intermediate along with a minor fraction of ferric hydroperoxo intermediates. The superoxo-ferrous intermediate converts into a ferric-hydroperoxo species after annealing at 145 K. During subsequent annealing at 170-180 K, the ferric-hydroperoxo intermediate converts to the primary product complex with the large solvent kinetic isotope effect that indicates Cpd I is being formed, and (1)H ENDOR measurements of the primary product formed in D2O demonstrate that Cpd I is the active species. They show that the primary product contains Fe(III) coordinated to the 20-O(1)H of DHC with the (1)H derived from substrate, the signature of the Cpd I reaction. Hydroperoxo ferric intermediates are the primary species formed during cryoreduction of the oxy-P450scc-DHC ternary complex, and they decay at 185 K with a strong solvent kinetic isotope effect to form low-spin ferric P450scc. Together, these observations indicated that Cpd I also is the active intermediate in the C20,22 lyase final step. In combination with our previous results, this study thus indicates that Cpd I is the active species in each of the three sequential monooxygenation reactions by which P450scc catalytically converts Ch to pregnenolone.
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Affiliation(s)
- Roman Davydov
- Department of Chemistry, Northwestern University , Evanston, Illinois 60208-3113, United States
| | - Natallia Strushkevich
- Institute of Bioorganic Chemistry, National Academy of Sciences of Belarus , Kuprevicha Street 5/2, Minsk 220141, Belarus
| | - David Smil
- Structural Genomics Consortium, University of Toronto , 101 College Street, Toronto, ON, Canada M5G 1L7
| | - Aliaksei Yantsevich
- Institute of Bioorganic Chemistry, National Academy of Sciences of Belarus , Kuprevicha Street 5/2, Minsk 220141, Belarus
| | - Andrey Gilep
- Institute of Bioorganic Chemistry, National Academy of Sciences of Belarus , Kuprevicha Street 5/2, Minsk 220141, Belarus
| | - Sergey Usanov
- Institute of Bioorganic Chemistry, National Academy of Sciences of Belarus , Kuprevicha Street 5/2, Minsk 220141, Belarus
| | - Brian M Hoffman
- Department of Chemistry, Northwestern University , Evanston, Illinois 60208-3113, United States
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18
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Hedegård ED, Kongsted J, Sauer SPA. Validating and Analyzing EPR Hyperfine Coupling Constants with Density Functional Theory. J Chem Theory Comput 2013; 9:2380-8. [PMID: 26583728 DOI: 10.1021/ct400171c] [Citation(s) in RCA: 27] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/30/2022]
Affiliation(s)
- Erik D Hedegård
- Department of Physics, Chemistry and Pharmacy, University of Southern Denmark
| | - Jacob Kongsted
- Department of Physics, Chemistry and Pharmacy, University of Southern Denmark
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19
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Abstract
All but a few bacterial species have an absolute need for heme, and most are able to synthesize it via a pathway that is highly conserved among all life domains. Because heme is a rich source for iron, many pathogenic bacteria have also evolved processes for sequestering heme from their hosts. The heme biosynthesis pathways are well understood at the genetic and structural biology levels. In comparison, much less is known about the heme acquisition, trafficking, and degradation processes in bacteria. Gram-positive and Gram-negative bacteria have evolved similar strategies but different tactics for importing and degrading heme, likely as a consequence of their different cellular architectures. The differences are manifested in distinct structures for molecules that perform similar functions. Consequently, the aim of this chapter is to provide an overview of the structural biology of proteins and protein-protein interactions that enable Gram-positive and Gram-negative bacteria to sequester heme from the extracellular milieu, import it to the cytosol, and degrade it to mine iron.
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Affiliation(s)
- David R Benson
- Department of Chemistry, University of Kansas, Multidisciplinary Research Building, 2030 Becker Dr., Lawrence, KS, 66047, USA,
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20
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Ohta T, Liu JG, Naruta Y. Resonance Raman characterization of mononuclear heme-peroxo intermediate models. Coord Chem Rev 2013. [DOI: 10.1016/j.ccr.2012.05.009] [Citation(s) in RCA: 41] [Impact Index Per Article: 3.7] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
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21
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Cong Z, Yanagisawa S, Kurahashi T, Ogura T, Nakashima S, Fujii H. Synthesis, Characterization, and Reactivity of Hypochloritoiron(III) Porphyrin Complexes. J Am Chem Soc 2012; 134:20617-20. [DOI: 10.1021/ja3108774] [Citation(s) in RCA: 37] [Impact Index Per Article: 3.1] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Affiliation(s)
- Zhiqi Cong
- Institute for Molecular Science and Okazaki Institute for Integrative Bioscience, National Institutes of Natural Sciences, Myodaiji, Okazaki 444-8787, Japan
| | - Sachiko Yanagisawa
- Department of Life Science and Picobiology Institute, Graduate School of Life Science, University of Hyogo, Koto, Kamigori, Ako, Hyogo 678-1297, Japan
| | - Takuya Kurahashi
- Institute for Molecular Science and Okazaki Institute for Integrative Bioscience, National Institutes of Natural Sciences, Myodaiji, Okazaki 444-8787, Japan
| | - Takashi Ogura
- Department of Life Science and Picobiology Institute, Graduate School of Life Science, University of Hyogo, Koto, Kamigori, Ako, Hyogo 678-1297, Japan
| | - Satoru Nakashima
- Department of Life Science and Picobiology Institute, Graduate School of Life Science, University of Hyogo, Koto, Kamigori, Ako, Hyogo 678-1297, Japan
| | - Hiroshi Fujii
- Institute for Molecular Science and Okazaki Institute for Integrative Bioscience, National Institutes of Natural Sciences, Myodaiji, Okazaki 444-8787, Japan
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22
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Hedegård ED, Kongsted J, Sauer SPA. Improving the calculation of Electron Paramagnetic Resonance hyperfine coupling tensors for d-block metals. Phys Chem Chem Phys 2012; 14:10669-76. [PMID: 22785432 DOI: 10.1039/c2cp40969k] [Citation(s) in RCA: 26] [Impact Index Per Article: 2.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/11/2022]
Abstract
Calculation of hyperfine coupling constants (HFCs) of Electron Paramagnetic Resonance from first principles can be a beneficial complement to experimental data in cases where the molecular structure is unknown. We have recently investigated basis set convergence of HFCs in d-block complexes and obtained a set of basis functions for the elements Sc-Zn, which were saturated with respect to both the Fermi contact and spin-dipolar components of the hyperfine coupling tensor [Hedegård et al., J. Chem. Theory Comput., 2011, 7, 4077-4087]. Furthermore, a contraction scheme was proposed leading to very accurate, yet efficient basis sets for the elements Sc-Zn. Here this scheme is tested against a larger test set of molecules and a wider range of DFT functionals. We further investigate the regular aug-cc-pVTZ and core-valence correlation aug-cc-pCVTZ basis sets as well as another core-property basis set, CP(PPP). While aug-cc-pVTZ-J provides hyperfine coupling constants that are almost identical to the converged series (aug-cc-pVTZ-Juc), we observe that not only the regular but also the core-valence correlation basis sets provide results far from the converged results. The usage of specialized core-basis sets leads to a large and highly significant improvement of the calculated hyperfine couplings in comparison with experimental data.
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Affiliation(s)
- Erik D Hedegård
- University of Southern Denmark, Institute for Physics, Chemistry and Pharmacy, Campusvej 55, Odense, Denmark.
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23
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Davydov R, Gilep AA, Strushkevich NV, Usanov SA, Hoffman BM. Compound I is the reactive intermediate in the first monooxygenation step during conversion of cholesterol to pregnenolone by cytochrome P450scc: EPR/ENDOR/cryoreduction/annealing studies. J Am Chem Soc 2012; 134:17149-56. [PMID: 23039857 DOI: 10.1021/ja3067226] [Citation(s) in RCA: 36] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/30/2022]
Abstract
Cytochrome P450scc (CYP11A1) catalyzes conversion of cholesterol (CH) to pregnenolone, the precursor to all steroid hormones. This process proceeds via three sequential monooxygenation reactions: two stereospecific hydroxylations with formation first of 22R-hydroxycholesterol (22-HC) and then 20α,22R-dihydroxycholesterol (20,22-DHC), followed by C20-C22 bond cleavage. Herein we have employed EPR and ENDOR spectroscopy to characterize the intermediates in the first hydroxylation step by 77 K radiolytic one-electron cryoreduction and subsequent annealing of the ternary oxy-cytochrome P450scc-cholesterol complex. This approach is fully validated by the demonstration that the cryoreduced ternary complex of oxy-P450scc-CH is catalytically competent and hydroxylates cholesterol to form 22-HC with no detectable formation of 20-HC, just as occurs under physiological conditions. Cryoreduction of the ternary complex trapped at 77 K produces predominantly the hydroperoxy-ferriheme P450scc intermediate, along with a minor fraction of peroxo-ferriheme intermediate that converts into a new hydroperoxo-ferriheme species at 145 K. This behavior reveals that the distal pocket of the parent oxy-P450scc-cholesterol complex exhibits an efficient proton delivery network, with an ordered water molecule H-bonded to the distal oxygen of the dioxygen ligand. During annealing of the hydroperoxy-ferric P450scc intermediates at 185 K, they convert to the primary product complex in which CH has been converted to 22-HC. In this process, the hydroperoxy-ferric intermediate decays with a large solvent kinetic isotope effect, as expected when proton delivery to the terminal O leads to formation of Compound I (Cpd I). (1)H ENDOR measurements of the primary product formed in deuterated solvent show that the heme Fe(III) is coordinated to the 22R-O(1)H of 22-HC, where the (1)H is derived from substrate and exchanges to D after annealing at higher temperatures. These observations establish that Cpd I is the agent that hydroxylates CH, rather than the hydroperoxy-ferric heme.
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Affiliation(s)
- Roman Davydov
- Department of Chemistry, Northwestern University, 2145 Sheridan Road, Evanston, Illinois 60208, USA
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24
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Cong Z, Kurahashi T, Fujii H. Formation of Iron(III) meso-Chloro-isoporphyrin as a Reactive Chlorinating Agent from Oxoiron(IV) Porphyrin π-Cation Radical. J Am Chem Soc 2012; 134:4469-72. [DOI: 10.1021/ja209985v] [Citation(s) in RCA: 39] [Impact Index Per Article: 3.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Affiliation(s)
- Zhiqi Cong
- Institute
for Molecular Science and Okazaki Institute
for Integrative Bioscience, National Institutes of Natural Sciences, Myodaiji, Okazaki 444-8787, Japan
| | - Takuya Kurahashi
- Institute
for Molecular Science and Okazaki Institute
for Integrative Bioscience, National Institutes of Natural Sciences, Myodaiji, Okazaki 444-8787, Japan
| | - Hiroshi Fujii
- Institute
for Molecular Science and Okazaki Institute
for Integrative Bioscience, National Institutes of Natural Sciences, Myodaiji, Okazaki 444-8787, Japan
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25
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Hedegård ED, Kongsted J, Sauer SPA. Optimized Basis Sets for Calculation of Electron Paramagnetic Resonance Hyperfine Coupling Constants: aug-cc-pVTZ-J for the 3d Atoms Sc-Zn. J Chem Theory Comput 2011; 7:4077-87. [PMID: 26598353 DOI: 10.1021/ct200587k] [Citation(s) in RCA: 68] [Impact Index Per Article: 5.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/16/2022]
Abstract
The hyperfine coupling tensor of electron paramagnetic resonance (EPR), describing the interaction between an electron and a given nuclei, depends strongly on the electron density at the nucleus. With standard Gaussian-type orbital basis sets (GTOs), employed in most calculations, it is difficult to obtain converged results of the hyperfine coupling tensor, and basis sets with more flexible core regions have therefore been devised. To this class of core property basis sets belong the aug-cc-pVTZ-J basis sets developed for the s- and p-block atoms. Here, we extend the aug-cc-pVTZ-J basis sets to include the 3d elements Sc-Zn. The converged optimal basis sets are throughout the series described by a (25s17p10d3f2g)/[17s10p7d3f2g] contraction scheme, where four tight s-, one tight p-, and one tight d-type function have been added to the original aug-cc-pVTZ basis sets. The basis sets are generally contracted, and molecular orbital coefficients are used as contraction coefficients. By validation studies with different functionals and compounds, it is shown that the values of the contraction coefficient are effectively independent of the compound used in their generation and the exchange-correlation functional employed in the calculation.
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Affiliation(s)
- Erik Donovan Hedegård
- Department of Chemistry and Physics, University of Southern Denmark , Odense, Denmark
| | - Jacob Kongsted
- Department of Chemistry and Physics, University of Southern Denmark , Odense, Denmark
| | - Stephan P A Sauer
- Department of Chemistry, University of Copenhagen , Copenhagen, Denmark
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26
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Duerr K, Troeppner O, Olah J, Li J, Zahl A, Drewello T, Jux N, Harvey JN, Ivanović-Burmazović I. Solution behavior of iron(III) and iron(II) porphyrins in DMSO and reaction with superoxide. Effect of neighboring positive charge on thermodynamics, kinetics and nature of iron-(su)peroxo product. Dalton Trans 2011; 41:546-57. [PMID: 22045167 DOI: 10.1039/c1dt11521a] [Citation(s) in RCA: 16] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022]
Abstract
The solution behavior of iron(III) and iron(II) complexes of 5(4),10(4),15(4),20(4)-tetra-tert-butyl-5,10,15,20-tetraphenylporphyrin (H(2)tBuTPP) and the reaction with superoxide (KO(2)) in DMSO have been studied in detail. Applying temperature and pressure dependent NMR studies, the thermodynamics of the low-spin/high-spin equilibrium between bis- and mono-DMSO Fe(II) forms have been quantified (K(DMSO) = 0.082 ± 0.002 at 298.2 K, ΔH° = +36 ± 1 kJ mol(-1), ΔS° = +101 ± 4 J K(-1) mol(-1), ΔV° = +16 ± 2 cm(3) mol(-1)). This is a key activation step for substitution and inner-sphere electron transfer. The superoxide binding constant to the iron(II) form of the studied porphyrin complex was found to be (9 ± 0.5) × 10(3) M(-1), and does not change significantly in the presence of the externally added crown ether in DMSO (11 ± 4) × 10(3) M(-1). The rate constants for the superoxide binding (k(on) = (1.30 ± 0.01) × 10(5) M(-1) s(-1)) and release (k(off) = 11.6 ± 0.7 s(-1)) are not affected by the presence of the external crown ether in solution. The resulting iron(II)-superoxide adduct has been characterized (mass spectrometry, EPR, high-pressure UV/Vis spectroscopy) and upon controlled addition of a proton source it regenerates the starting iron(II) complex. Based on DFT calculations, the reaction product without neighboring positive charge has iron(II)-superoxo character in both high-spin side-on and low-spin end-on forms. The results are compared to those obtained for the analogous complex with covalently attached crown ether, and more general conclusions regarding the spin-state equilibrium of iron(II) porphyrins, their reaction with superoxide and the electronic structure of the product species are drawn.
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Affiliation(s)
- K Duerr
- Department of Chemistry and Pharmacy, University of Erlangen-Nürnberg, Egerlandstr. 1, 91058, Erlangen, Germany
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27
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Lyakin OY, Bryliakov KP, Talsi EP. EPR, 1H and 2H NMR, and reactivity studies of the iron-oxygen intermediates in bioinspired catalyst systems. Inorg Chem 2011; 50:5526-38. [PMID: 21598909 DOI: 10.1021/ic200088e] [Citation(s) in RCA: 92] [Impact Index Per Article: 7.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
Abstract
Complexes [(BPMEN)Fe(II)(CH(3)CN)(2)](ClO(4))(2) (1, BPMEN = N,N'-dimethyl-N,N'-bis(2-pyridylmethyl)-1,2-diaminoethane) and [(TPA)Fe(II)(CH(3)CN)(2)](ClO(4))(2) (2, TPA = tris(2-pyridylmethyl)amine) are among the best nonheme iron-based catalysts for bioinspired oxidation of hydrocarbons. Using EPR and (1)H and (2)H NMR spectroscopy, the iron-oxygen intermediates formed in the catalyst systems 1,2/H(2)O(2); 1,2/H(2)O(2)/CH(3)COOH; 1,2/CH(3)CO(3)H; 1,2/m-CPBA; 1,2/PhIO; 1,2/(t)BuOOH; and 1,2/(t)BuOOH/CH(3)COOH have been studied (m-CPBA is m-chloroperbenzoic acid). The following intermediates have been observed: [(L)Fe(III)(OOR)(S)](2+), [(L)Fe(IV)═O(S)](2+) (L = BPMEN or TPA, R = H or (t)Bu, S = CH(3)CN or H(2)O), and the iron-oxygen species 1c (L = BPMEN) and 2c (L = TPA). It has been shown that 1c and 2c directly react with cyclohexene to yield cyclohexene oxide, whereas [(L)Fe(IV)═O(S)](2+) react with cyclohexene to yield mainly products of allylic oxidation. [(L)Fe(III)(OOR)(S)](2+) are inert in this reaction. The analysis of EPR and reactivity data shows that only those catalyst systems which display EPR spectra of 1c and 2c are able to selectively epoxidize cyclohexene, thus bearing strong evidence in favor of the key role of 1c and 2c in selective epoxidation. 1c and 2c were tentatively assigned to the oxoiron(V) intermediates.
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Affiliation(s)
- Oleg Y Lyakin
- Boreskov Institute of Catalysis, Siberian Branch of the Russian Academy of Sciences, Pr. Lavrentieva 5, Novosibirsk 630090, Russian Federation
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28
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Dürr K, Jux N, Zahl A, van Eldik R, Ivanović-Burmazović I. Volume Profile Analysis for the Reversible Binding of Superoxide to Form Iron(II)-Superoxo/Iron(III)-Peroxo Porphyrin Complexes. Inorg Chem 2010; 49:11254-60. [DOI: 10.1021/ic102092h] [Citation(s) in RCA: 15] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
Affiliation(s)
- Katharina Dürr
- Department of Chemistry and Pharmacy, University of Erlangen-Nürnberg, Egerlandstrasse 1, 91058 Erlangen, Germany
| | - Norbert Jux
- Department of Chemistry and Pharmacy, University of Erlangen-Nürnberg, Egerlandstrasse 1, 91058 Erlangen, Germany
| | - Achim Zahl
- Department of Chemistry and Pharmacy, University of Erlangen-Nürnberg, Egerlandstrasse 1, 91058 Erlangen, Germany
| | - Rudi van Eldik
- Department of Chemistry and Pharmacy, University of Erlangen-Nürnberg, Egerlandstrasse 1, 91058 Erlangen, Germany
| | - Ivana Ivanović-Burmazović
- Department of Chemistry and Pharmacy, University of Erlangen-Nürnberg, Egerlandstrasse 1, 91058 Erlangen, Germany
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29
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Davydov R, Osborne RL, Shanmugam M, Du J, Dawson JH, Hoffman BM. Probing the oxyferrous and catalytically active ferryl states of Amphitrite ornata dehaloperoxidase by cryoreduction and EPR/ENDOR spectroscopy. Detection of compound I. J Am Chem Soc 2010; 132:14995-5004. [PMID: 20925340 PMCID: PMC2978736 DOI: 10.1021/ja1059747] [Citation(s) in RCA: 40] [Impact Index Per Article: 2.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
Abstract
Dehaloperoxidase (DHP) from Amphitrite ornata is a heme protein that can function both as a hemoglobin and as a peroxidase. This report describes the use of 77 K cryoreduction EPR/ENDOR techniques to study both functions of DHP. Cryoreduced oxyferrous [Fe(II)-O(2)] DHP exhibits two EPR signals characteristic of a peroxoferric [Fe(III)-O(2)(2-)] heme species, reflecting the presence of conformational substates in the oxyferrous precursor. (1)H ENDOR spectroscopy of the cryogenerated substates shows that H-bonding interactions between His N(ε)H and heme-bound O(2) in these conformers are similar to those in the β-chain of oxyferrous hemoglobin A (HbA) and oxyferrous myoglobin, respectively. Decay of cryogenerated peroxoferric heme DHP intermediates upon annealing at temperatures above 180 K is accompanied by the appearance of a new paramagnetic species with an axial EPR signal with g(⊥) = 3.75 and g(∥) = 1.96, characteristic of an S = 3/2 spin state. This species is assigned to Compound I (Cpd I), in which a porphyrin π-cation radical is ferromagnetically coupled with an S = 1 ferryl [Fe(IV)═O] ion. This species was also trapped by rapid freeze-quench of the ambient-temperature reaction mixture of ferric [Fe(III)] DHP and H(2)O(2). However, in the latter case Cpd I is reduced very rapidly by a nearby tyrosine to form Cpd ES [(Fe(IV)═O)(porphyrin)/Tyr(•)]. Addition of the substrate analogue 2,4,6-trifluorophenol (F(3)PhOH) suppresses formation of the Cpd I intermediate during annealing of cryoreduced oxyferrous DHP at 190 K but has no effect on the spectroscopic properties of the remaining cryoreduced oxyferrous DHP intermediates and kinetics of their decay. These observations indicate that substrate (i) binds to oxyferrous DHP outside of the distal pocket and (ii) can reduce Cpd I to Cpd II [Fe(IV)═O]. These assumptions are also supported by the observation that F(3)PhOH has only a small effect on the EPR properties of radiolytically cryooxidized and cryoreduced ferrous [Fe(II)] DHP. EPR spectra of cryoreduced ferrous DHP disclose the multiconformational nature of the ferrous DHP precursor. The observation and characterization of Cpds I, II, and ES in the absence and in the presence of F(3)PhOH provides definitive evidence of a mechanism involving consecutive one-electron steps and clarifies the role of all intermediates formed during turnover.
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Affiliation(s)
- Roman Davydov
- Department of Chemistry, Northwestern University, Evanston, Illinois 60208
| | - Robert L. Osborne
- Department of Chemistry and Biochemistry University of South Carolina, Columbia, South Carolina 29208
| | | | - Jing Du
- Department of Chemistry and Biochemistry University of South Carolina, Columbia, South Carolina 29208
| | - John H. Dawson
- Department of Chemistry and Biochemistry University of South Carolina, Columbia, South Carolina 29208
- School of Medicine University of South Carolina, Columbia, South Carolina 29208
| | - Brian M. Hoffman
- Department of Chemistry, Northwestern University, Evanston, Illinois 60208
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30
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Active intermediates in heme monooxygenase reactions as revealed by cryoreduction/annealing, EPR/ENDOR studies. Arch Biochem Biophys 2010; 507:36-43. [PMID: 20854788 DOI: 10.1016/j.abb.2010.09.013] [Citation(s) in RCA: 51] [Impact Index Per Article: 3.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/06/2010] [Revised: 09/13/2010] [Accepted: 09/14/2010] [Indexed: 11/21/2022]
Abstract
This review describes the use of cryoreduction/annealing EPR/ENDOR techniques for determining the active oxidizing species in reactions catalyzed by heme monooxygenases. The three candidate heme states are: ferric peroxo, ferric hydroperoxo and compound I intermediates. The enzymes discussed include cytochromes P450, nitric oxide synthase and heme oxygenase.
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Napoli F, Chiesa M, Giamello E, Preda G, Di Valentin C, Pacchioni G. Formation of superoxo species by interaction of O(2) with Na atoms deposited on MgO powders: a combined continuous-wave EPR (CW-EPR), hyperfine sublevel correlation (HYSCORE) and DFT study. Chemistry 2010; 16:6776-85. [PMID: 20514645 DOI: 10.1002/chem.201000546] [Citation(s) in RCA: 15] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/08/2022]
Abstract
The formation of O(2) (-) radical anions by contact of O(2) molecules with a Na pre-covered MgO surface is studied by a combined EPR and quantum chemical approach. Na atoms deposited on polycrystalline MgO samples are brought into contact with O(2). The typical EPR signal of isolated Na atoms disappears when the reaction with O(2) takes place and new paramagnetic species are observed, which are attributed to different surface-stabilised O(2) (-) radicals. Hyperfine sublevel correlation (HYSCORE) spectroscopy allows the superhyperfine interaction tensor of O(2) (-)Na(+) species to be determined, demonstrating the direct coordination of the O(2) (-) adsorbate to surface Na(+) cations. DFT calculations enable the structural details of the formed species to be determined. Matrix-isolated alkali superoxides are used as a standard to enable comparison of the formed species, revealing important and unexpected contributions of the MgO matrix in determining the electronic structure of the surface-stabilised Na(+)-O(2) (-) complexes.
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Affiliation(s)
- Francesco Napoli
- Dipartimento di Chimica IFM, Università di Torino and NIS, Nanostructured Interfaces and Surfaces Centre of Excellence, Via P. Giuria 7, I - 10125 Torino, Italy
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Liu JG, Shimizu Y, Ohta T, Naruta Y. Formation of an end-on ferric peroxo intermediate upon one-electron reduction of a ferric superoxo heme. J Am Chem Soc 2010; 132:3672-3. [PMID: 20196593 DOI: 10.1021/ja1001955] [Citation(s) in RCA: 63] [Impact Index Per Article: 4.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Abstract
The low-spin end-on ferric peroxo heme intermediate has been proposed as an alternative reactive intermediate involved in the catalytic cycles of enzymes such as nitric oxide synthase and cytochrome P450. This transient heme intermediate has never been captured using synthetic heme models. We demonstrate herein our success in the solution preparation of such an end-on ferric peroxo intermediate derived from a heme model, which features both a group hanging over the porphyrin macrocycle and a covalently appended axial imidazole ligand, through one-electron reduction of its ferric superoxo precursor. The obtained ferric peroxo intermediate was further transformed into the corresponding ferric hydroperoxo species upon protonation. This heme model compound provides a convenient system for sequential preparation of the important and biologically relevant superoxo/peroxo/hydroperoxo heme intermediates through an oxygenation/one-electron reduction/protonation process similar to the mechanisms used by enzyme systems.
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Affiliation(s)
- Jin-Gang Liu
- Institute for Materials Chemistry and Engineering, Kyushu University, Higashi-ku, Fukuoka 812-8581, Japan
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A computational analysis of electromerism in hemoprotein Fe(I) models. J Biol Inorg Chem 2010; 15:977-86. [PMID: 20437065 DOI: 10.1007/s00775-010-0659-5] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/13/2009] [Accepted: 04/11/2010] [Indexed: 10/19/2022]
Abstract
The electronic structures of formally Fe(I) centers in thiolate- and imidazole-ligated hemoproteins are examined with density functional theory. The S = 1/2 spin state of the imidazole-ligated model apparently features a net total of one unpaired electron on the porphyrin, suggestive of a macrocycle-centered reductive process; however, this spin density originates from two different orbitals, each carrying 0.5 spin units on the porphyrin. Under these conditions, the system may be described as S = 3/2 Fe(I) (d(xy)(2)d(xz)(1)d(yz)(1)dz2(1)) antiferromagnetically coupled to a porphyrin triplet state; nevertheless, there is still the caveat that the iron d (xz) and d (yz) orbitals are strongly mixed with porphyrin orbitals, to such an extent that they each harbor 0.5 spin units and hence an alternative description as Fe(II) or Fe(III) cannot be ruled out. Electromerism phenomena are described in the formally Fe(I) systems examined here, with electronic structures varying between Fe(II) and Fe(III) in various spin states, coupled either ferro- or antiferromagnetically to porphyrin radicals. The main factors controlling this electromerism appear to be the identity of the axial ligand, the iron-axial ligand bond length, and the overall spin state; heme deformations, ligand charge, or medium polarity do not appear to qualitatively affect the electronic structures of these systems.
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Davydov RM, Chauhan N, Thackray SJ, Anderson JLR, Papadopoulou ND, Mowat CG, Chapman SK, Raven EL, Hoffman BM. Probing the ternary complexes of indoleamine and tryptophan 2,3-dioxygenases by cryoreduction EPR and ENDOR spectroscopy. J Am Chem Soc 2010; 132:5494-500. [PMID: 20353179 PMCID: PMC2903012 DOI: 10.1021/ja100518z] [Citation(s) in RCA: 43] [Impact Index Per Article: 3.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/20/2010] [Indexed: 11/30/2022]
Abstract
We have applied cryoreduction/EPR/ENDOR techniques to characterize the active-site structure of the ferrous-oxy complexes of human (hIDO) and Shewanella oneidensis (sIDO) indoleamine 2,3-dioxygenases, Xanthomonas campestris (XcTDO) tryptophan 2,3-dioxygenase, and the H55S variant of XcTDO in the absence and in the presence of the substrate L-Trp and a substrate analogue, L-Me-Trp. The results reveal the presence of multiple conformations of the binary ferrous-oxy species of the IDOs. In more populated conformers, most likely a water molecule is within hydrogen-bonding distance of the bound ligand, which favors protonation of a cryogenerated ferric peroxy species at 77 K. In contrast to the binary complexes, cryoreduction of all of the studied ternary [enzyme-O(2)-Trp] dioxygenase complexes generates a ferric peroxy heme species with very similar EPR and (1)H ENDOR spectra in which protonation of the basic peroxy ligand does not occur at 77 K. Parallel studies with L-Me-Trp, in which the proton of the indole nitrogen is replaced with a methyl group, eliminate the possibility that the indole NH group of the substrate acts as a hydrogen bond donor to the bound O(2), and we suggest instead that the ammonium group of the substrate hydrogen-bonds to the dioxygen ligand. The present data show that substrate binding, primarily through this H-bond, causes the bound dioxygen to adopt a new conformation, which presumably is oriented for insertion of O(2) into the C(2)-C(3) double bond of the substrate. This substrate interaction further helps control the reactivity of the heme-bound dioxygen by "shielding" it from water.
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Liu JG, Ohta T, Yamaguchi S, Ogura T, Sakamoto S, Maeda Y, Naruta Y. Spectroscopic characterization of a hydroperoxo-heme intermediate: conversion of a side-on peroxo to an end-on hydroperoxo complex. Angew Chem Int Ed Engl 2010; 48:9262-7. [PMID: 19882613 DOI: 10.1002/anie.200904572] [Citation(s) in RCA: 84] [Impact Index Per Article: 6.0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/05/2022]
Affiliation(s)
- Jin-Gang Liu
- Institute for Materials Chemistry and Engineering, Kyushu University, Higashi-ku, Fukuoka, 812-8581, Japan
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Duerr K, Olah J, Davydov R, Kleimann M, Li J, Lang N, Puchta R, Hübner E, Drewello T, Harvey JN, Jux N, Ivanović-Burmazović I. Studies on an iron(iii)-peroxo porphyrin. Iron(iii)-peroxo or iron(ii)-superoxo? Dalton Trans 2010; 39:2049-56. [DOI: 10.1039/b920237d] [Citation(s) in RCA: 32] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022]
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Liu JG, Ohta T, Yamaguchi S, Ogura T, Sakamoto S, Maeda Y, Naruta Y. Spectroscopic Characterization of a HydroperoxoâHeme Intermediate: Conversion of a Side-On Peroxo to an End-On Hydroperoxo Complex. Angew Chem Int Ed Engl 2009. [DOI: 10.1002/ange.200904572] [Citation(s) in RCA: 19] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/10/2022]
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Davydov R, Sudhamsu J, Lees NS, Crane BR, Hoffman BM. EPR and ENDOR characterization of the reactive intermediates in the generation of NO by cryoreduced oxy-nitric oxide synthase from Geobacillus stearothermophilus. J Am Chem Soc 2009; 131:14493-507. [PMID: 19754116 DOI: 10.1021/ja906133h] [Citation(s) in RCA: 55] [Impact Index Per Article: 3.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
Abstract
Cryoreduction EPR/ENDOR/step-annealing measurements with substrate complexes of oxy-gsNOS (3; gsNOS is nitric oxide synthase from Geobacillus stearothermophilus) confirm that Compound I (6) is the reactive heme species that carries out the gsNOS-catalyzed (Stage I) oxidation of L-arginine to N-hydroxy-L-arginine (NOHA), whereas the active species in the (Stage II) oxidation of NOHA to citrulline and HNO/NO(-) is the hydroperoxy-ferric form (5). When 3 is reduced by tetrahydrobiopterin (BH4), instead of an externally supplied electron, the resulting BH4(+) radical oxidizes HNO/NO(-) to NO. In this report, radiolytic one-electron reduction of 3 and its complexes with Arg, Me-Arg, and NO(2)Arg was shown by EPR and (1)H and (14,15)N ENDOR spectroscopies to generate 5; in contrast, during cryoreduction of 3/NOHA, the peroxo-ferric-gsNOS intermediate (4/NOHA) was trapped. During annealing at 145 K, ENDOR shows that 5/Arg and 5/Me-Arg (but not 5/NO(2)Arg) generate a Stage I primary product species in which the OH group of the hydroxylated substrate is coordinated to Fe(III), characteristic of 6 as the active heme center. Analysis shows that hydroxylation of Arg and Me-Arg is quantitative. Annealing of 4/NOHA at 160 K converts it first to 5/NOHA and then to the Stage II primary enzymatic product. The latter contains Fe(III) coordinated by water, characteristic of 5 as the active heme center. It further contains quantitative amounts of citrulline and HNO/NO(-); the latter reacts with the ferriheme to form the NO-ferroheme upon further annealing. Stage I delivery of the first proton of catalysis to the (unobserved) 4 formed by cryoreduction of 3 involves a bound water that may convey a proton from L-Arg, while the second proton likely derives from the carboxyl side chain of Glu 248 or the heme carboxylates; the process also involves proton delivery by water(s). In the Stage II oxidation of NOHA, the proton that converts 4/NOHA to 5/NOHA likely is derived from NOHA itself, a conclusion supported by the pH invariance of the process. The present results illustrate how the substrate itself modulates the nature and reactivity of intermediates along the monooxygenase reaction pathway.
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Affiliation(s)
- Roman Davydov
- Chemistry Department, Northwestern University, Evanston, Illinois 60208-3113, USA
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Davydov R, Razeghifard R, Im SC, Waskell L, Hoffman BM. Characterization of the microsomal cytochrome P450 2B4 O2 activation intermediates by cryoreduction and electron paramagnetic resonance. Biochemistry 2008; 47:9661-6. [PMID: 18700729 DOI: 10.1021/bi800926x] [Citation(s) in RCA: 44] [Impact Index Per Article: 2.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/30/2022]
Abstract
The oxy-ferrous complex of cytochrome P450 2B4 (2B4) has been prepared at -40 degrees C with and without bound substrate [butylated hydroxytoluene (BHT)] and radiolytically one-electron cryoreduced at 77 K. Electron paramagnetic resonance (EPR) shows that in both cases the observed product of cryoreduction is the hydroperoxo-ferriheme species, indicating that the microsomal P450 contains an efficient distal-pocket proton-delivery network. In the absence of substrate, two distinct hydroperoxo-ferriheme signals are observed, reflecting the presence of two major conformational substates in the oxy-ferrous precursor. Only one species is observed when BHT is bound, indicating a more ordered active site. BHT binding also changes the g-tensor components of the hydroperoxo-ferric 2B4 intermediate, indicating that the substrate modulates the properties of this intermediate. Step annealing the cryoreduced ternary 2B4 complex at >or=175 K causes the loss of hydroperoxo-ferric 2B4 and the parallel appearance of high-spin ferric 2B4; liquid chromatography-tandem mass spectroscopy (LC-MS/MS) analysis shows that in this process BHT is quantitatively converted to two products, hydroxymethyl BHT (1) and 3-hydroxy- tert-butyl BHT (2). This implies that the hydroperoxo-ferric 2B4 prepared by cryoreduction is catalytically active and that the high-spin state observed after annealing contains an enzyme-bound product of BHT monooxygenation. The ratio of products generated during cryoreduction and annealing (6.2/1) is significantly different from the ratio (2.5/1) at ambient temperature. These findings suggest that substrate is held more rigidly relative to the oxidizing species at low temperatures and/or that dissociation of FeOOH is inhibited at low temperature. As in experiments under ambient conditions, product formation is not observed with the inactive F429H 2B4 mutant.
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Affiliation(s)
- Roman Davydov
- Department of Chemistry, Northwestern University, 2145 Sheridan Road, Tech K148, Evanston, Illinois 60208-3113, USA
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Davydov R, Osborne RL, Kim SH, Dawson JH, Hoffman BM. EPR and ENDOR studies of cryoreduced compounds II of peroxidases and myoglobin. Proton-coupled electron transfer and protonation status of ferryl hemes. Biochemistry 2008; 47:5147-55. [PMID: 18407661 DOI: 10.1021/bi702514d] [Citation(s) in RCA: 53] [Impact Index Per Article: 3.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
Abstract
The nature of the [Fe(IV)-O] center in hemoprotein Compounds II has recently received considerable attention, as several experimental and theoretical investigations have suggested that this group is not necessarily the traditionally assumed ferryl ion, [Fe(IV)=O]2+, but can be the protonated ferryl, [Fe(IV)-OH]3+. We show here that cryoreduction of the EPR-silent Compound II by gamma-irradiation at 77 K produces Fe(III) species retaining the structure of the precursor [Fe(IV)=O]2+ or [Fe(IV)-OH]3+, and that the properties of the cryogenerated species provide a report on structural features and the protonation state of the parent Compound II when studied by EPR and 1H and 14N ENDOR spectroscopies. To give the broadest view of the properties of Compounds II we have carried out such measurements on cryoreduced Compounds II of HRP, Mb, DHP and CPO and on CCP Compound ES. EPR and ENDOR spectra of cryoreduced HRP II, CPO II and CCP ES are characteristic of low-spin hydroxy-Fe(III) heme species. In contrast, cryoreduced "globins", Mb II, Hb II, and DHP II, show EPR spectra having lower rhombicity. In addition the cryogenerated ferric "globin" species display strongly coupled exchangeable (1)H ENDOR signals, with A max approximately 20 MHz and a iso approximately 14 MHz, both substantially greater than for hydroxide/water ligand protons. Upon annealing at T > 180 K the cryoreduced globin compounds II relax to the low-spin hydroxy-ferric form with a solvent kinetic isotope effect, KIE > 6. The results presented here together with published resonance Raman and Mossbauer data suggest that the high-valent iron center of globin and HRP compounds II, as well as of CCP ES, is [Fe(IV)=O]2+, and that its cryoreduction produces [Fe(III)-O]+. Instead, as proposed by Green and co-workers, CPO II contains [Fe(IV)-OH]3+ which forms [Fe(III)-OH]2+ upon radiolysis. The [Fe(III)-O]+ generated by cryoreduction of HRP II and CCP ES protonate at 77 K, presumably because the heme is linked to a distal-pocket hydrogen bonding/proton-delivery network through an H-bond to the "oxide" ligand. The data also indicate that Mb and HRP compounds II exist as two major conformational substates.
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Affiliation(s)
- Roman Davydov
- Department of Chemistry, Northwestern University, 2145 Sheridan Road, Tech K148, Evanston, Illinois 60208-3113, USA
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Silaghi-Dumitrescu R, Reeder B, Nicholls P, Cooper C, Wilson M. Ferryl haem protonation gates peroxidatic reactivity in globins. Biochem J 2007; 403:391-5. [PMID: 17214588 PMCID: PMC1876371 DOI: 10.1042/bj20061421] [Citation(s) in RCA: 67] [Impact Index Per Article: 3.9] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/18/2006] [Revised: 01/02/2007] [Accepted: 01/10/2007] [Indexed: 02/04/2023]
Abstract
Ferryl (Fe(IV)=O) species are involved in key enzymatic processes with direct biomedical relevance; among others, the uncontrolled reactivities of ferryl Mb (myoglobin) and Hb (haemoglobin) have been reported to be central to the pathology of rhabdomyolysis and subarachnoid haemorrhage. Rapid-scan stopped-flow methods have been used to monitor the spectra of the ferryl species in Mb and Hb as a function of pH. The ferryl forms of both proteins display an optical transition with pK approximately 4.7, and this is assigned to protonation of the ferryl species itself. We also demonstrate for the first time a direct correlation between Hb/Mb ferryl reactivity and ferryl protonation status, simultaneously informing on chemical mechanism and toxicity and with broader biochemical implications.
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Affiliation(s)
- Radu Silaghi-Dumitrescu
- *Department of Biological Sciences, University of Essex, Colchester CO4 3SQ, U.K
- †Domeniul Chimie, Universitatea Babeş-Bolyai, Str. Arany János 11, RO-3400 Cluj-Napoca, Romania
| | - Brandon J. Reeder
- *Department of Biological Sciences, University of Essex, Colchester CO4 3SQ, U.K
| | - Peter Nicholls
- *Department of Biological Sciences, University of Essex, Colchester CO4 3SQ, U.K
| | - Chris E. Cooper
- *Department of Biological Sciences, University of Essex, Colchester CO4 3SQ, U.K
| | - Michael T. Wilson
- *Department of Biological Sciences, University of Essex, Colchester CO4 3SQ, U.K
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Silaghi-Dumitrescu R, Cooper CE. Transient species involved in catalytic dioxygen/peroxide activation by hemoproteins: possible involvement of protonated Compound I species. Dalton Trans 2005:3477-82. [PMID: 16234928 DOI: 10.1039/b505440k] [Citation(s) in RCA: 28] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022]
Abstract
Interaction of hemoproteins with peroxide leads in several cases to transient formation of ferric peroxo, ferric hydroperoxo, and "high-valent", formally Fev, oxo or hydroxo Compound species. Here, density functional calculations on ferric peroxo, ferric hydroperoxo, Compound and protonated Compound heme active site models are reported. The theoretical results, including calculated isotropic Fermi contact couplings and anisotropic spin dipole couplings, are found to generally correlate well with experimental EPR/ENDOR data. Hydrogen bonding and solvation affect the ferric-peroxo/ferrous-superoxo electromerism. The transition between the two electromers appears smooth, but neither hydrogen bonding to up to two water molecules, nor solvation appear able to dramatically alter the redox state of the superoxo ligand or of the iron. The presence of almost one full unpaired electron on the iron and of one full unpaired electron on the dioxygenic ligand in the "ferric-peroxo" state suggests a possible description of non-protonated "ferric-peroxo" as {ferric-superoxo+porphyrin radical}. Emerging from the DFT data is the possibility that a protonated Compound has already been detected in ENDOR experiments on cytochrome P450. The general feasibility of a protonated Compound in P450 monooxygenases is probed in light of these findings. To encompass the multiple mechanisms available in P450 for substrate oxidation, we define "mechanistic promiscuity" as the feature allowing an enzyme to perform the same reaction, with the same product, using more than one mechanism.
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Denisov IG, Makris TM, Sligar SG, Schlichting I. Structure and Chemistry of Cytochrome P450. Chem Rev 2005; 105:2253-77. [PMID: 15941214 DOI: 10.1021/cr0307143] [Citation(s) in RCA: 1510] [Impact Index Per Article: 79.5] [Reference Citation Analysis] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/30/2022]
Affiliation(s)
- Ilia G Denisov
- Department of Biochemistry, Center for Biophysics and Computational Biology, University of Illinois, Urbana-Champaign, 61801, USA
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Kim SH, Yang TC, Perera R, Jin S, Bryson TA, Sono M, Davydov R, Dawson JH, Hoffman BM. Cryoreduction EPR and 13C, 19F ENDOR study of substrate-bound substates and solvent kinetic isotope effects in the catalytic cycle of cytochrome P450cam and its T252A mutant. Dalton Trans 2005:3464-9. [PMID: 16234926 DOI: 10.1039/b506764m] [Citation(s) in RCA: 28] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022]
Abstract
We recently used cryoreduction EPR/ENDOR techniques to show that a substrate can modulate the properties of both the monooxygenase active-oxygen intermediates and of the proton-delivery network which encompasses them. In the present report we use Q-band pulsed 19F ENDOR (Mims 3-pulse sequence) to examine the substrate binding geometries of camphor, through use of the 5,5'--difluorocamphor, and 13C ENDOR to examine the binding of 5-methylenyl camphor labeled with 13C at C11. These probes are examined in multiple states of the catalytic cycle of P450cam and its T252A mutant. As part of this investigation we further report a new cryoreduction reaction, the reduction of a ferroheme to the EPR-visible Fe(I) state, and use it to probe the substrate binding to the EPR-silent ferroheme state. Finally we report the solvent kinetic isotope effect on the decay of the camphor complex of the hydroperoxo-ferric intermediate, the first such measurement on an individual step within the P450cam reaction cycle. Following reduction of oxyferrous-P450cam, this step is the rate-limiting step in camphor hydroxylation, and its solv-KIE of 1.8 at 190 K establishes that it involves activation of the hydroperoxo moiety by transfer of the 'second' proton of catalysis. We suggest that the finding that the heme pocket can exist in multiple substates, including multiple substrate binding locations, even in P450cam, along with the established possibility that the hydroperoxo-ferriheme intermediate can react with substrate, may explain the formation of multiple products by P450s.
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Affiliation(s)
- Sun Hee Kim
- Department of Chemistry, Northwestern University, Evanston, IL 60208, USA
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Giangiacomo L, Ilari A, Boffi A, Morea V, Chiancone E. The truncated oxygen-avid hemoglobin from Bacillus subtilis: X-ray structure and ligand binding properties. J Biol Chem 2004; 280:9192-202. [PMID: 15590662 DOI: 10.1074/jbc.m407267200] [Citation(s) in RCA: 64] [Impact Index Per Article: 3.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
The group II truncated hemoglobin from Bacillus subtilis has been cloned, expressed, purified, and characterized. B. subtilis truncated hemoglobin is a monomeric protein endowed with an unusually high oxygen affinity (in the nanomolar range) such that the apparent thermodynamic binding constant for O2 exceeds that for CO by 1 order of magnitude. The kinetic basis of the high oxygen affinity resides mainly in the very slow rate of ligand release. The extremely stable ferrous oxygenated adduct is resistant to oxidation, which can be achieved only with oxidant in large excess, e.g. ferricyanide in 50-fold molar excess. The three-dimensional crystal structure of the cyano-Met derivative was determined at 2.15 A resolution. Although the overall fold resembles that of other truncated hemoglobins, the distal heme pocket displays a unique array of hydrophilic side chains in the topological positions that dominate the steric interaction with iron-bound ligands. In fact, the Tyr-B10, Thr-E7, and Gln-E11 oxygens on one side of the heme pocket and the Trp-G8 indole NE1 nitrogen on the other form a novel pattern of the "ligand-inclusive hydrogen bond network" described for mycobacterial HbO. On the proximal side, the histidine residue is in an unstrained conformation, and the iron-His bond is unusually short (1.91 A).
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Affiliation(s)
- Laura Giangiacomo
- Department of Biochemical Sciences and CNR Institute of Molecular Biology and Pathology, University of Rome La Sapienza, Piazzale Aldo Moro 5, 00185 Rome, Italy
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Hlavica P. Models and mechanisms of O-O bond activation by cytochrome P450. A critical assessment of the potential role of multiple active intermediates in oxidative catalysis. ACTA ACUST UNITED AC 2004; 271:4335-60. [PMID: 15560776 DOI: 10.1111/j.1432-1033.2004.04380.x] [Citation(s) in RCA: 80] [Impact Index Per Article: 4.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
Abstract
Cytochrome P450 enzymes promote a number of oxidative biotransformations including the hydroxylation of unactivated hydrocarbons. Whereas the long-standing consensus view of the P450 mechanism implicates a high-valent iron-oxene species as the predominant oxidant in the radicalar hydrogen abstraction/oxygen rebound pathway, more recent studies on isotope partitioning, product rearrangements with 'radical clocks', and the impact of threonine mutagenesis in P450s on hydroxylation rates support the notion of the nucleophilic and/or electrophilic (hydro)peroxo-iron intermediate(s) to be operative in P450 catalysis in addition to the electrophilic oxenoid-iron entity; this may contribute to the remarkable versatility of P450s in substrate modification. Precedent to this mechanistic concept is given by studies with natural and synthetic P450 biomimics. While the concept of an alternative electrophilic oxidant necessitates C-H hydroxylation to be brought about by a cationic insertion process, recent calculations employing density functional theory favour a 'two-state reactivity' scenario, implicating the usual ferryl-dependent oxygen rebound pathway to proceed via two spin states (doublet and quartet); state crossing is thought to be associated with either an insertion or a radicalar mechanism. Hence, challenge to future strategies should be to fold the disparate and sometimes contradictory data into a harmonized overall picture.
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Affiliation(s)
- Peter Hlavica
- Walther-Straub-Institut für Pharmakologie und Toxikologie der LMU, München, Germany.
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