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Zhou J, Wang Z, Bian H, Jiang Y, Zhang R, Wang X. Structure of the Green Heme Isolated from Allylbenzene-Modified Chloroperoxidase: A Novel Heme Architecture Implicating the Mechanisms of CPO Inactivation and Epoxidation. Comput Struct Biotechnol J 2023; 21:2365-2372. [PMID: 37066123 PMCID: PMC10090953 DOI: 10.1016/j.csbj.2023.03.042] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/01/2022] [Revised: 03/21/2023] [Accepted: 03/24/2023] [Indexed: 03/29/2023] Open
Abstract
The chemical identification of the modified heme (the green heme) during chloroperoxidase catalyzed epoxidation of allylbenzene remains unestablished due to its high instability within the protein matrix, the absence of paramagnetically shifted signals, and the difficulty in obtaining crystals of the modified enzyme. We have established the unambiguous structure of the modified prosthetic heme group, which was extracted from the protein matrix using 2D NMR spectroscopy and LC-MS spectrometry. The modified heme was isolated as a µ-oxo dimer that can be quantitatively converted to the corresponding monomer. The depolymerized green heme displayed characteristic NMR signatures of iron porphyrin complexes, but no Nuclear Overhauser Effect was observable to assist in signal assignment. An alternative strategy was applied by removing the iron center of the green heme, resulting in a stable demetallated green porphyrin species. Complete assignment of all the NMR resonances in the demetallated green heme allowed us to establish the molecular architecture of the modified species as a novel N-alkylated heme. Decisive space correlations between the propyl protons of allylbenzene and the γ meso proton coupled with clear dipolar connectivities between the propyl-2H of the substrate and the β proton in the side chain of the propionic acid at carbon-6 of the porphyrin ring, clearly indicate that allylbenzene was covalently attached to the nitrogen atom of the pyrrole ring III of the prosthetic heme. In this study, the mechanism of green CPO formation and its relation to CPO catalyzed chiral transformations are also discussed. It is concluded that the double-phenyl clamp formed by two phenylalanine residues at the distal heme pocket plays a critical role in fine-tuning substrate orientation that determines the outcome of CPO catalyzed epoxidation of substituted styrenes.
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Affiliation(s)
- Jieying Zhou
- Department of Chemistry and Biochemistry, Florida International University, Miami, FL 33199, United States of America
| | - Zhonghua Wang
- Department of Chemistry and Biochemistry, Florida International University, Miami, FL 33199, United States of America
| | - Hedong Bian
- Key Laboratory of Chemistry and Engineering of Forest Products (State Ethnic Affairs Commission), Guangxi Collaborative Innovation Center for Chemistry and Engineering of Forest Products, School of Chemistry and Chemical Engineering, Guangxi University for Nationalities, Nanning, Guangxi 530006, PR China
| | - Yucheng Jiang
- School of Chemistry and Materials Science, Shaanxi Normal University, Xi’an 710062, PR China
| | - Rui Zhang
- Department of Chemistry and Biochemistry, Florida International University, Miami, FL 33199, United States of America
| | - Xiaotang Wang
- Department of Chemistry and Biochemistry, Florida International University, Miami, FL 33199, United States of America
- Corresponding author.
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2
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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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3
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Pribitzer S, Mannikko D, Stoll S. Determining electron-nucleus distances and Fermi contact couplings from ENDOR spectra. Phys Chem Chem Phys 2021; 23:8326-8335. [PMID: 33875997 DOI: 10.1039/d1cp00229e] [Citation(s) in RCA: 3] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/18/2022]
Abstract
The hyperfine coupling between an electron spin and a nuclear spin depends on the Fermi contact coupling aiso and, through dipolar coupling, the distance r between the electron and the nucleus. It is measured with electron-nuclear double resonance (ENDOR) spectroscopy and provides insight into the electronic and spatial structure of paramagnetic centers. The analysis and interpretation of ENDOR spectra is commonly done by ordinary least-squares fitting. As this is an ill-posed, inverse mathematical problem, this is challenging, in particular for spectra that show features from several nuclei or where the hyperfine coupling parameters are distributed. We introduce a novel Tikhonov-type regularization approach that analyzes an experimental ENDOR spectrum in terms of a complete non-parametric distribution over r and aiso. The approach uses a penalty function similar to the cross entropy between the fitted distribution and a Bayesian prior distribution that is derived from density functional theory calculations. Additionally, we show that smoothness regularization, commonly used for a similar purpose in double electron-electron resonance (DEER) spectroscopy, is not suited for ENDOR. We demonstrate that the novel approach is able to identify and quantitate ligand protons with electron-nucleus distances between 4 and 9 Å in a series of vanadyl porphyrin compounds.
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Affiliation(s)
- Stephan Pribitzer
- Department of Chemistry, University of Washington, Seattle, WA 98195, USA.
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4
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Tao L, Stich TA, Fugate CJ, Jarrett JT, Britt RD. EPR-Derived Structure of a Paramagnetic Intermediate Generated by Biotin Synthase BioB. J Am Chem Soc 2018; 140:12947-12963. [PMID: 30222930 PMCID: PMC6363123 DOI: 10.1021/jacs.8b07613] [Citation(s) in RCA: 10] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/26/2023]
Abstract
Biotin (vitamin B7) is an enzyme cofactor required by organisms from all branches of life but synthesized only in microbes and plants. In the final step of biotin biosynthesis, a radical S-adenosyl-l-methionine (SAM) enzyme, biotin synthase (BioB), converts the substrate dethiobiotin to biotin through the stepwise formation of two C-S bonds. Previous electron paramagnetic resonance (EPR) spectroscopic studies identified a semistable intermediate in the formation of the first C-S bond as 9-mercaptodethiobiotin linked to a paramagnetic [2Fe-2S] cluster through one of its bridging sulfides. Herein, we report orientation-selected pulse EPR spectroscopic results that reveal hyperfine interactions between the [2Fe-2S] cluster and a number of magnetic nuclei (e.g., 57Fe, 15N, 13C, and 2H) introduced in a site-specific manner via biosynthetic methods. Combining these results with quantum chemical modeling gives a structural model of the intermediate showing that C6, the target of the second hydrogen-atom abstraction, is now in close proximity to the nascent thioether sulfur and is ideally positioned for the second C-S bond forming event.
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Affiliation(s)
- Lizhi Tao
- Department of Chemistry, University of California, Davis, California 95616, United States
| | - Troy A. Stich
- Department of Chemistry, University of California, Davis, California 95616, United States
| | - Corey J. Fugate
- Department of Chemistry, University of Hawaii at Manoa, Honolulu, Hawaii 96822, United States
| | - Joseph T. Jarrett
- Department of Chemistry, University of Hawaii at Manoa, Honolulu, Hawaii 96822, United States
| | - R. David Britt
- Department of Chemistry, University of California, Davis, California 95616, United States
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5
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Van Doorslaer S. Understanding heme proteins with hyperfine spectroscopy. JOURNAL OF MAGNETIC RESONANCE (SAN DIEGO, CALIF. : 1997) 2017; 280:79-88. [PMID: 28579104 DOI: 10.1016/j.jmr.2017.01.008] [Citation(s) in RCA: 9] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 11/30/2016] [Revised: 01/10/2017] [Accepted: 01/11/2017] [Indexed: 06/07/2023]
Abstract
Heme proteins are versatile proteins that are involved in a large number of biological processes. Many spectroscopic methods are used to gain insight into the different mechanistic processes governing heme-protein functions. Since many (intermediate) states of heme proteins are paramagnetic, electron paramagnetic resonance (EPR) methods, such as hyperfine spectroscopy, offer unique tools for these investigations. This perspective gives an overview of the use of state-of-the-art hyperfine spectroscopy in heme research, focusing on the advantages, limits and challenges of the different techniques.
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Affiliation(s)
- Sabine Van Doorslaer
- BIMEF Laboratory, Department of Physics, University of Antwerp, B-2610 Antwerp, Belgium.
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6
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Liu Q, Zhang X, Zeng W, Wang J, Zhou Z. Origin of d-π Interaction in Cobalt(II) Porphyrins under Synergistic Effects of Core Contraction and Axial Ligation: Implications for a Ligand Effect of Natural Distorted Tetrapyrrole. CHINESE J CHEM 2016. [DOI: 10.1002/cjoc.201600226] [Citation(s) in RCA: 8] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/06/2023]
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7
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Kinney RA, Saouma CT, Peters JC, Hoffman BM. Modeling the signatures of hydrides in metalloenzymes: ENDOR analysis of a Di-iron Fe(μ-NH)(μ-H)Fe core. J Am Chem Soc 2012; 134:12637-47. [PMID: 22823933 PMCID: PMC3433054 DOI: 10.1021/ja303739g] [Citation(s) in RCA: 36] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
Abstract
The application of 35 GHz pulsed EPR and ENDOR spectroscopies has established that the biomimetic model complex L(3)Fe(μ-NH)(μ-H)FeL(3) (L(3) = [PhB(CH(2)PPh(2))(3)](-)) complex, 3, is a novel S = (1)/(2) type-III mixed-valence di-iron II/III species, in which the unpaired electron is shared equally between the two iron centers. (1,2)H and (14,15)N ENDOR measurements of the bridging imide are consistent with an allyl radical molecular orbital model for the two bridging ligands. Both the (μ-H) and the proton of the (μ-NH) of the crystallographically characterized 3 show the proposed signature of a 'bridging' hydride that is essentially equidistant between two 'anchor' metal ions: a rhombic dipolar interaction tensor, T ≈ [T, -T, 0]. The point-dipole model for describing the anisotropic interaction of a bridging H as the sum of the point-dipole couplings to the 'anchor' metal ions reproduces this signature with high accuracy, as well as the axial tensor of a terminal hydride, T ≈ [-T, -T, 2T], thus validating both the model and the signatures. This validation in turn lends strong support to the assignment, based on such a point-dipole analysis, that the molybdenum-iron cofactor of nitrogenase contains two [Fe-H(-)-Fe] bridging-hydride fragments in the catalytic intermediate that has accumulated four reducing equivalents (E(4)). Analysis further reveals a complementary similarity between the isotropic hyperfine couplings for the bridging hydrides in 3 and E(4). This study provides a foundation for spectroscopic study of hydrides in a variety of reducing metalloenzymes in addition to nitrogenase.
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Affiliation(s)
- R Adam Kinney
- Department of Chemistry, Northwestern University, Evanston, Illinois 60208, United States
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8
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Taxak N, Desai PV, Patel B, Mohutsky M, Klimkowski VJ, Gombar V, Bharatam PV. Metabolic-intermediate complex formation with cytochrome P450: theoretical studies in elucidating the reaction pathway for the generation of reactive nitroso intermediate. J Comput Chem 2012; 33:1740-7. [PMID: 22610824 DOI: 10.1002/jcc.23008] [Citation(s) in RCA: 27] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/12/2011] [Revised: 04/16/2012] [Accepted: 04/20/2012] [Indexed: 11/10/2022]
Abstract
Mechanism-based inhibition (MBI) of cytochrome P450 (CYP) can lead to drug-drug interactions and often to toxicity. Some aliphatic and aromatic amines can undergo biotransformation reactions to form reactive metabolites such as nitrosoalkanes, leading to MBI of CYPs. It has been proposed that the nitrosoalkanes coordinate with the heme iron, forming metabolic-intermediate complex (MIC), resulting in the quasi-irreversible inhibition of CYPs. Limited mechanistic details regarding the formation of reactive nitroso intermediate and its coordination with heme-iron have been reported. A quantum chemical analysis was performed to elucidate potential reaction pathways for the generation of nitroso intermediate and the formation of MIC. Elucidation of the energy profile along the reaction path, identification of three-dimensional structures of reactive intermediates and transition states, as well as charge and spin density analyses, were performed using the density functional B3LYP method. The study was performed using Cpd I [iron (IV-oxo] heme porphine with SH(-) as the axial ligand) to represent the catalytic domain of CYP, simulating the biotransformation process. Three pathways: (i) N-oxidation followed by proton shuttle, (ii) N-oxidation followed by 1,2-H shift, and (iii) H-abstraction followed by rebound mechanism, were studied. It was observed that the proton shuttle pathway was more favorable over the whole reaction leading to reactive nitroso intermediate. This study revealed that the MIC formation from a primary amine is a favorable exothermic process, involving eight different steps and preferably takes place on the doublet spin surface of Cpd I. The rate-determining step was identified to be the first N-oxidation of primary amine.
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Affiliation(s)
- Nikhil Taxak
- Department of Medicinal Chemistry, National Institute of Pharmaceutical Education and Research, S. A. S. Nagar, Mohali, Punjab, India
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9
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Xu W, Lees NS, Adedeji D, Wiesner J, Jomaa H, Hoffman BM, Duin EC. Paramagnetic Intermediates of (E)-4-Hydroxy-3-methylbut-2-enyl Diphosphate Synthase (GcpE/IspG) under Steady-State and Pre-Steady-State Conditions. J Am Chem Soc 2010; 132:14509-20. [DOI: 10.1021/ja101764w] [Citation(s) in RCA: 36] [Impact Index Per Article: 2.6] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Affiliation(s)
- Weiya Xu
- Department of Chemistry and Biochemistry, Auburn University, Auburn, Alabama 36849, Department of Chemistry, Northwestern University, Evanston, Illinois 60208, and Institut für Klinische Chemie und Pathobiochemie, Universitätsklinikum Giessen und Marburg, D-Giessen, 35392 Giessen, Germany
| | - Nicholas S. Lees
- Department of Chemistry and Biochemistry, Auburn University, Auburn, Alabama 36849, Department of Chemistry, Northwestern University, Evanston, Illinois 60208, and Institut für Klinische Chemie und Pathobiochemie, Universitätsklinikum Giessen und Marburg, D-Giessen, 35392 Giessen, Germany
| | - Dolapo Adedeji
- Department of Chemistry and Biochemistry, Auburn University, Auburn, Alabama 36849, Department of Chemistry, Northwestern University, Evanston, Illinois 60208, and Institut für Klinische Chemie und Pathobiochemie, Universitätsklinikum Giessen und Marburg, D-Giessen, 35392 Giessen, Germany
| | - Jochen Wiesner
- Department of Chemistry and Biochemistry, Auburn University, Auburn, Alabama 36849, Department of Chemistry, Northwestern University, Evanston, Illinois 60208, and Institut für Klinische Chemie und Pathobiochemie, Universitätsklinikum Giessen und Marburg, D-Giessen, 35392 Giessen, Germany
| | - Hassan Jomaa
- Department of Chemistry and Biochemistry, Auburn University, Auburn, Alabama 36849, Department of Chemistry, Northwestern University, Evanston, Illinois 60208, and Institut für Klinische Chemie und Pathobiochemie, Universitätsklinikum Giessen und Marburg, D-Giessen, 35392 Giessen, Germany
| | - Brian M. Hoffman
- Department of Chemistry and Biochemistry, Auburn University, Auburn, Alabama 36849, Department of Chemistry, Northwestern University, Evanston, Illinois 60208, and Institut für Klinische Chemie und Pathobiochemie, Universitätsklinikum Giessen und Marburg, D-Giessen, 35392 Giessen, Germany
| | - Evert C. Duin
- Department of Chemistry and Biochemistry, Auburn University, Auburn, Alabama 36849, Department of Chemistry, Northwestern University, Evanston, Illinois 60208, and Institut für Klinische Chemie und Pathobiochemie, Universitätsklinikum Giessen und Marburg, D-Giessen, 35392 Giessen, Germany
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10
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Structure and spin density of ferric low-spin heme complexes determined with high-resolution ESEEM experiments at 35 GHz. J Biol Inorg Chem 2010; 15:929-41. [DOI: 10.1007/s00775-010-0655-9] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/09/2009] [Accepted: 03/21/2010] [Indexed: 11/25/2022]
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11
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Myers WK, Scholes CP, Tierney DL. Anisotropic Fermi couplings due to large unquenched orbital angular momentum: Q-band (1)H, (14)N, and (11)B ENDOR of bis(trispyrazolylborate) cobalt(II). J Am Chem Soc 2009; 131:10421-9. [PMID: 19591466 DOI: 10.1021/ja900866y] [Citation(s) in RCA: 20] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
Abstract
We report Q-band ENDOR of (1)H, (14)N, and (11)B at the g( parallel) extreme of the EPR spectrum of bis(trispyrazolylborate) cobalt(II) [Co(Tp)(2)] and two structural analogs. This trigonally symmetric, high-spin (hs) S = 3/2 Co(II) complex shows large unquenched ground-state orbital angular momentum, which leads to highly anisotropic electronic g-values (g( parallel) = 8.48, g( perpendicular) = 1.02). The large g-anisotropy is shown to result in large dipolar couplings near g( parallel) and uniquely anisotropic (14)N Fermi couplings, which arise from spin transferred to the nitrogen 2s orbital (2.2%) via antibonding interactions with singly occupied metal d(x(2)-y(2)) and d(z(2)) orbitals. Large, well-resolved (1)H and (11)B dipolar couplings were also observed. Taken in concert with our previous X-band ENDOR measurements at g( perpendicular) ( Myers, W. K.; et al. Inorg. Chem. 2008, 47, 6701-6710 ), the present data allow a detailed analysis of the dipolar hyperfine tensors of two of the four symmetry distinct protons in the parent molecule. In the substituted analogs, changes in hyperfine coupling due to altered metal-proton distances give further evidence of an anisotropic Fermi contact interaction. For the pyrazolyl 3H proton, the data indicate a 0.2 MHz anisotropic contact interaction and approximately 4% transfer of spin away from Co(II). Dipolar coupling also dominates for the axial boron atoms, consistent with their distance from the Co(II) ion, and resolved (11)B quadrupolar coupling showed approximately 30% electronic inequivalence between the B-H and B-C sp(3) bonds. This is the first comprehensive ENDOR study of any hs Co(II) species and lays the foundation for future development.
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Affiliation(s)
- William K Myers
- Department of Chemistry and Chemical Biology, University of New Mexico, Albuquerque, New Mexico 87131, USA
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12
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Van Doorslaer S, Desmet F. The power of using continuous-wave and pulsed electron paramagnetic resonance methods for the structure analysis of ferric forms and nitric oxide-ligated ferrous forms of globins. Methods Enzymol 2008; 437:287-310. [PMID: 18433634 DOI: 10.1016/s0076-6879(07)37015-8] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 03/19/2023]
Abstract
For several decades now, electron paramagnetic resonance (EPR) has been a valuable spectroscopic tool for the characterization of globin proteins. In the early years, the majority of EPR studies were performed using standard continuous-wave EPR techniques at conventional microwave frequencies. In the last years, the field of EPR has known tremendous technological developments, including the introduction of advanced pulsed EPR and high-frequency EPR techniques. After a short overview of the basics of EPR and recent advances in the field, we will illustrate how these different EPR methods can provide information about the dynamics and geometric and electronic structures of heme proteins. Although the main focus of this chapter lies on the EPR analysis of nitric oxide-ligated ferrous heme proteins and ferric heme systems, we also briefly outline the possibility of site-directed spin labeling of heme proteins. The last section highlights the future potential and challenges in using this magnetic resonance technique in globin research.
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Affiliation(s)
- Sabine Van Doorslaer
- University of Antwerp, Department of Physics, SIBAC Laboratory, Antwerp, Belgium
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Van Doorslaer S, Vinck E. The strength of EPR and ENDOR techniques in revealing structure-function relationships in metalloproteins. Phys Chem Chem Phys 2007; 9:4620-38. [PMID: 17700864 DOI: 10.1039/b701568b] [Citation(s) in RCA: 60] [Impact Index Per Article: 3.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022]
Abstract
Recent technological and methodological advances have strongly increased the potential of electron paramagnetic resonance (EPR) and electron nuclear double resonance (ENDOR) techniques to characterize the structure and dynamics of metalloproteins. These developments include the introduction of powerful pulsed EPR/ENDOR methodologies and the development of spectrometers operating at very high microwave frequencies and high magnetic fields. This overview focuses on how valuable information about metalloprotein structure-function relations can be obtained using a combination of EPR and ENDOR techniques. After an overview of the historical development and a limited theoretical description of some of the key EPR and ENDOR techniques, their potential will be highlighted using selected examples of applications to iron-, nickel-, cobalt-, and copper-containing proteins. We will end with an outlook of future developments.
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Affiliation(s)
- Sabine Van Doorslaer
- SIBAC Laboratory, University of Antwerp, Universiteitsplein 1, B-2160, Wilrijk-Antwerp, Belgium.
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14
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Keliher EJ, Burrell RC, Chobanian HR, Conkrite KL, Shukla R, Baldwin JE. Efficient syntheses of four stable-isotope labeled (1R)-menthyl (1S,2S)-(+)-2-phenylcyclopropanecarboxylates. Org Biomol Chem 2006; 4:2777-84. [PMID: 16826303 DOI: 10.1039/b605912k] [Citation(s) in RCA: 9] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022]
Abstract
Many carbenoid cyclopropanation reactions promoted by chiral catalysts give product mixtures reflecting impressive diastereo- and enantioselectivities. Few provide a single chiral product efficiently. This limitation has been overcome in cyclopropanations of styrene and isotopically labeled styrenes with alpha-diazoacetates. Convenient syntheses on a 20 g scale of each of four chiral isotopically labeled (1R)-menthyl (1S,2S)-2-phenylcyclopropanecarboxylates (the 1-d-3-(13)C, 1,(3S)-d2, 1,2,(3S)-d3, and 1,3,3-d3 isotopomers) of better than 99% ee have been realized.
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Affiliation(s)
- Edmund J Keliher
- Department of Chemistry and Chemical Biology, Harvard University, 12 Oxford Street, Box 234, Cambridge, MA 02138, USA
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15
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Benda R, Schünemann V, Trautwein AX, Cai S, Reddy Polam J, Watson CT, Shokhireva TK, Walker FA. Models of the bis-histidine-coordinated ferricytochromes: Mössbauer and EPR spectroscopic studies of low-spin iron(III) tetrapyrroles of various electronic ground states and axial ligand orientations. J Biol Inorg Chem 2003; 8:787-801. [PMID: 12898323 DOI: 10.1007/s00775-003-0472-5] [Citation(s) in RCA: 23] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/25/2002] [Accepted: 05/19/2003] [Indexed: 10/26/2022]
Abstract
The EPR and magnetic Mössbauer spectra of a series of axial ligand complexes of tetrakis(2,6-dimethoxyphenyl)porphyrinatoiron(III), [(2,6-(OMe)(2))(4)TPPFeL(2)](+), where L= N-methylimidazole, 2-methylimidazole, or 4-(dimethylamino)pyridine, of one axial ligand complex of tetraphenylporphyrin, the bis(4-cyanopyridine) complex [TPPFe(4-CNPy)(2)](+), and of one axial ligand complex of tetraphenylchlorin, [TPCFe(ImH)(2)](+), where ImH=imidazole, have been investigated and compared to those of low-spin Fe(III) porphyrinates and ferriheme proteins reported in the literature. On the basis of this and previous complementary spectroscopic investigations, three types of complexes have been identified: those having (d(xy))(2)(d(xz),d(yz))(3) electronic ground states with axial ligands aligned in perpendicular planes (Type I), those having (d(xy))(2)(d(xz),d(yz))(3) electronic ground states with axial ligands aligned in parallel planes (Type II), and those having the novel (d(xz),d(yz))(4)(d(xy))(1) electronic ground state (Type III). A subset of the latter type, with planar axial ligands aligned parallel to each other or strong macrocycle asymmetry that yield rhombic EPR spectra, cannot be created using the porphyrinate ligand. Type I centers are characterized by "large g(max)" EPR spectra with g>3.2 and well-resolved, widely spread magnetic Mössbauer spectra having A(zz)/ g(N)mu(N)>680 kG, with A(xx) negative in sign but much smaller in magnitude than A(zz), while Type II centers have well-resolved rhombic EPR spectra with g(zz)=2.4-3.1 and also less-resolved magnetic Mössbauer spectra, and usually have A(zz)/ g(Nmu(N) in the range of 440-660 kG (but in certain cases as small as 180 kG) and A(xx) again negative in sign but only somewhat smaller (but occasionally larger in magnitude) than A(zz), and Type III centers have axial EPR spectra with g( upper left and right quadrants ) approximately 2.6 or smaller and g( vertical line )<1.0-1.95, but often not resolved, and less-resolved magnetic Mössbauer spectra having A(zz)/ g(N)mu(N) in the range of 270-400 kG, and A(xx) again negative in sign but much smaller in magnitude than A(zz). An exception to this rule is [TPPFe(4-CNPy)(2)](+), which has A(xx)/ g(N)mu(N)=-565 kG, A(yy)/ g(N)mu(N)=629 kG, and A(zz)/ g(N)mu(N)=4 kG. A subset of Type II complexes (Type II') have rhombicities ( V/Delta) much greater than 0.67 and A(zz)/ g(N)mu(N) ranging from 320 to 170 kG, with A(xx) also negative but with the magnitude of A(xx) significantly larger than that of A(zz). These classifications are also observed for a variety of ferriheme proteins, and they lead to linear correlations between A(zz) and either A(xx), g(zz), or V/Delta for Types I and II (but not for A(zz) versus V/Delta for Type II'). Not enough data are yet available on Type III complexes to determine what, if any, correlations may be observed.
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Affiliation(s)
- Rüdiger Benda
- Institut für Physik, Universität Lübeck, Ratzeburger Allee 160, 23538, Lübeck, Germany
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de Visser SP, Ogliaro F, Shaik S. How Does Ethene Inactivate Cytochrome P450 En Route to Its Epoxidation? A Density Functional Study. Angew Chem Int Ed Engl 2001; 40:2871-2874. [DOI: 10.1002/1521-3773(20010803)40:15<2871::aid-anie2871>3.0.co;2-r] [Citation(s) in RCA: 81] [Impact Index Per Article: 3.5] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/15/2000] [Indexed: 11/11/2022]
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de Visser SP, Ogliaro F, Shaik S. How Does Ethene Inactivate Cytochrome P450 En Route to Its Epoxidation? A Density Functional Study. Angew Chem Int Ed Engl 2001. [DOI: 10.1002/1521-3757(20010803)113:15<2955::aid-ange2955>3.0.co;2-5] [Citation(s) in RCA: 15] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022]
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Abstract
Pulsed electron paramagnetic resonance (EPR) methods such as ESEEM, PELDOR, relaxation time measurements, transient EPR, high-field/high-frequency EPR, and pulsed ENDOR, have been used successfully to investigate the local structure and dynamics of paramagnetic centers in biological samples. These methods allow different contributions to the EPR spectra to be distinguished and can help unravel complicated EPR spectra consisting of overlapping resonance lines, as are often found in disordered protein samples. The basic principles, specific potentials, technical requirements, and limitations of these advanced EPR techniques will be reviewed together with recent applications to metal centers, organic radicals, and spin labels in proteins.
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Affiliation(s)
- T Prisner
- Institute for Physical and Theoretical Chemistry, J. W. Goethe-University Frankfurt, Marie-Curie-Strasse 11, Frankfurt am Main, D-60439 Germany.
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Astashkin AV, Raitsimring AM, Walker FA. 1H pulsed ENDOR and ESEEM evidence that the bis-imidazole complexes of iron(III) tetraphenylchlorin and tetraphenylporphyrin have the same order of g values, and the same electronic ground state. J Am Chem Soc 2001; 123:1905-13. [PMID: 11456811 DOI: 10.1021/ja002777y] [Citation(s) in RCA: 31] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Abstract
The electronic structures of the bis-imidazole complexes of iron(III) tetraphenylporphyrin ([(TPP)Fe(ImH)(2)](+)) and iron(III) tetraphenylchlorin ([(TPC)Fe(ImH)(2)](+)) in frozen glassy solutions have been studied by the pulsed electron nuclear double resonance (ENDOR) technique of Mims and by electron spin-echo envelope modulation (ESEEM) spectroscopy. ESEEM spectra have been used to determine the orientation of the imidazole ligand planes with respect to the g tensor axes. In the ENDOR spectra, the manifestations of the implicit TRIPLE effect described and explained earlier by Doan et al. (J. Am. Chem. Soc. 1996, 118, 7014) were seen. In this work, the explicit expressions describing this effect were derived for the first time and used to successfully simulate the proton ENDOR spectra at the low- (LF) and high-field (HF) edges of the EPR spectrum. Using pulsed ENDOR, we have been able to determine the spin density distributions in the pi-systems of both tetrapyrroles and show that [(TPC)Fe(ImH)(2)](+) has the electronic orbital ground state (d(xy)())(2)(d(xz)(),d(yz)())(3), the same as that known for [(TPP)Fe(ImH)(2)](+), and the largest principal g value corresponds to the g tensor axis 3, which is normal to the heme plane. For the TPP complex, the g tensor axis 1, corresponding to the smallest principal g value, was found to be at an angle phi(1) of 30-35 degrees from the N-Fe-N axis, with the ligand planes rotated by the angle of 20-25 degrees in the opposite direction. For the TPC complex, phi(1) was found to be about 25 degrees from the direction N(I)-Fe-N(III), where N(I) corresponds to the nitrogen of the saturated pyrrole ring. The ligand planes in this complex were found to be oriented at an angle of about 10 degrees in the opposite direction.
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Affiliation(s)
- A V Astashkin
- Department of Chemistry, University of Arizona, Tucson, AZ 85721-0041, USA
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Rai GP, Zong Q, Hager LP. Isolation of directed evolution mutants of chloroperoxidase resistant to suicide inactivation by primary olefins. Isr J Chem 2000. [DOI: 10.1560/264g-uh9k-meyu-9yhy] [Citation(s) in RCA: 20] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/18/2022]
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Manoj KM, Yi X, Rai GP, Hager LP. A kinetic epoxidation assay for chloroperoxidase. Biochem Biophys Res Commun 1999; 266:301-3. [PMID: 10600497 DOI: 10.1006/bbrc.1999.1810] [Citation(s) in RCA: 19] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022]
Abstract
Chloroperoxidase exhibits a wide variety of enantioselective epoxidation reactions. Until now, the epoxidation activities have been mainly evaluated using elaborate gas chromatographic methods. This paper reports a rapid and convenient spectrophotometric assay for CPO. The disappearance of indene by catalytic epoxidation is monitored at 250 nm and this is used as an index of enzyme activity. This method will prove to be highly useful in large-scale screening of mutants.
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Affiliation(s)
- K M Manoj
- Department of Biochemistry, University of Illinois at Urbana-Champaign, 600 South Mathews Avenue, Urbana, Illinois 61801, USA
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Walker F. Magnetic spectroscopic (EPR, ESEEM, Mössbauer, MCD and NMR) studies of low-spin ferriheme centers and their corresponding heme proteins. Coord Chem Rev 1999. [DOI: 10.1016/s0010-8545(99)00029-6] [Citation(s) in RCA: 234] [Impact Index Per Article: 9.4] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/26/2022]
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Abstract
The past year has seen further structural characterisation of both nonmetal and vanadium haloperoxidase enzymes to add to that already known for the haem- and vanadium-containing enzymes. Exploitation of these enzymes for halogenation, sulfoxidation, epoxidation, oxidation of indoles and other biotransformations has increased as more information on their catalytic mechanism has been obtained.
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Affiliation(s)
- J Littlechild
- Schools of Chemistry and Biological Sciences, University of Exeter, Stocker Road, Exeter EX4 4QD, UK.
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