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England J, Farquhar ER, Guo Y, Cranswick MA, Ray K, Münck E, Que L. Characterization of a tricationic trigonal bipyramidal iron(IV) cyanide complex, with a very high reduction potential, and its iron(II) and iron(III) congeners. Inorg Chem 2011; 50:2885-96. [PMID: 21381646 DOI: 10.1021/ic102094d] [Citation(s) in RCA: 24] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
Abstract
Currently, there are only a handful of synthetic S = 2 oxoiron(IV) complexes. These serve as models for the high-spin (S = 2) oxoiron(IV) species that have been postulated, and confirmed in several cases, as key intermediates in the catalytic cycles of a variety of nonheme oxygen activating enzymes. The trigonal bipyramidal complex [Fe(IV)(O)(TMG(3)tren)](2+) (1) was both the first S = 2 oxoiron(IV) model complex to be generated in high yield and the first to be crystallographically characterized. In this study, we demonstrate that the TMG(3)tren ligand is also capable of supporting a tricationic cyanoiron(IV) unit, [Fe(IV)(CN)(TMG(3)tren)](3+) (4). This complex was generated by electrolytic oxidation of the high-spin (S = 2) iron(II) complex [Fe(II)(CN)(TMG(3)tren)](+) (2), via the S = 5/2 complex [Fe(III)(CN)(TMG(3)tren)](2+) (3), the progress of which was conveniently monitored by using UV-vis spectroscopy to follow the growth of bathochromically shifting ligand-to-metal charge transfer (LMCT) bands. A combination of X-ray absorption spectroscopy (XAS), Mössbauer and NMR spectroscopies was used to establish that 4 has a S = 0 iron(IV) center. Consistent with its diamagnetic iron(IV) ground state, extended X-ray absorption fine structure (EXAFS) analysis of 4 indicated a significant contraction of the iron-donor atom bond lengths, relative to those of the crystallographically characterized complexes 2 and 3. Notably, 4 has an Fe(IV/III) reduction potential of ∼1.4 V vs Fc(+/o), the highest value yet observed for a monoiron complex. The relatively high stability of 4 (t(1/2) in CD(3)CN solution containing 0.1 M KPF(6) at 25 °C ≈ 15 min), as reflected by its high-yield accumulation via slow bulk electrolysis and amenability to (13)C NMR at -40 °C, highlights the ability of the sterically protecting, highly basic peralkylguanidyl donors of the TMG(3)tren ligand to support highly charged high-valent complexes.
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Affiliation(s)
- Jason England
- Department of Chemistry, University of Minnesota, Minneapolis, Minnesota 55455, USA
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Westenhoff S, Nazarenko E, Malmerberg E, Davidsson J, Katona G, Neutze R. Time-resolved structural studies of protein reaction dynamics: a smorgasbord of X-ray approaches. Acta Crystallogr A 2010; 66:207-19. [PMID: 20164644 PMCID: PMC2824530 DOI: 10.1107/s0108767309054361] [Citation(s) in RCA: 40] [Impact Index Per Article: 2.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/28/2009] [Accepted: 12/16/2009] [Indexed: 11/26/2022] Open
Abstract
Time-resolved structural studies of proteins have undergone several significant developments during the last decade. Recent developments using time-resolved X-ray methods, such as time-resolved Laue diffraction, low-temperature intermediate trapping, time-resolved wide-angle X-ray scattering and time-resolved X-ray absorption spectroscopy, are reviewed. Proteins undergo conformational changes during their biological function. As such, a high-resolution structure of a protein’s resting conformation provides a starting point for elucidating its reaction mechanism, but provides no direct information concerning the protein’s conformational dynamics. Several X-ray methods have been developed to elucidate those conformational changes that occur during a protein’s reaction, including time-resolved Laue diffraction and intermediate trapping studies on three-dimensional protein crystals, and time-resolved wide-angle X-ray scattering and X-ray absorption studies on proteins in the solution phase. This review emphasizes the scope and limitations of these complementary experimental approaches when seeking to understand protein conformational dynamics. These methods are illustrated using a limited set of examples including myoglobin and haemoglobin in complex with carbon monoxide, the simple light-driven proton pump bacteriorhodopsin, and the superoxide scavenger superoxide reductase. In conclusion, likely future developments of these methods at synchrotron X-ray sources and the potential impact of emerging X-ray free-electron laser facilities are speculated upon.
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Affiliation(s)
- Sebastian Westenhoff
- Department of Chemistry, Biochemistry and Biophysics, University of Gothenburg, Box 462, SE-40530 Gothenburg, Sweden
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Matsuura K, Yoshioka S, Takahashi S, Ishimori K, Mogi T, Hori H, Morishima I. Dioxygen reduction by bo-type quinol oxidase from Escherichia coli studied by submillisecond-resolved freeze-quench EPR spectroscopy. Biochemistry 2004; 43:2288-96. [PMID: 14979725 DOI: 10.1021/bi0355490] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/30/2022]
Abstract
The mechanism of the dioxygen (O(2)) reduction conducted by cytochrome bo-type quinol oxidase was investigated using submillisecond-resolved freeze-quench EPR spectroscopy. The fully reduced form of the wild-type enzyme (WT) with the bound ubiquinone-8 at the high-affinity quinone-binding site was mixed with an O(2)-saturated solution, and the subsequent reaction was quenched at different time intervals from 0.2 to 50 ms. The EPR signals derived from the binuclear center and heme b were weak in the time domain from 0.2 to 0.5 ms. The signals derived from the ferric heme b and hydroxide-bound ferric heme o increased simultaneously after 1 ms, indicating that the oxidation of heme b is coupled to the formation of hydroxy heme o. In contrast, the enzyme without the bound ubiquinone-8 (Delta UbiA) showed the faster oxidation of heme b and the slower formation of hydroxy heme o than WT. It is interpreted that the F(I) intermediate possessing ferryl-oxo heme o, cupric Cu(B), and ferric heme b is converted to the F(II) intermediate within 0.2 ms by an electron transfer from the bound ubiquinonol-8 to ferric heme b. The conversion of the F(II) intermediate to the hydroxy intermediate occurred after 1 ms and was accompanied by the one-electron transfer from heme b to the binuclear center. Finally, it is suggested that the hydroxy intermediate possesses no bridging ligand between heme o and Cu(B) and is the final intermediate in the turnover cycle of cytochrome bo under steady-state conditions.
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Affiliation(s)
- Koji Matsuura
- Department of Molecular Engineering, Graduate School of Engineering, Kyoto University, Nishikyo, Kyoto 615-8510, Japan
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Tanaka M, Matsuura K, Yoshioka S, Takahashi S, Ishimori K, Hori H, Morishima I. Activation of hydrogen peroxide in horseradish peroxidase occurs within approximately 200 micro s observed by a new freeze-quench device. Biophys J 2003; 84:1998-2004. [PMID: 12609902 PMCID: PMC1302769 DOI: 10.1016/s0006-3495(03)75008-5] [Citation(s) in RCA: 48] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/26/2022] Open
Abstract
To observe the formation process of compound I in horseradish peroxidase (HRP), we developed a new freeze-quench device with approximately 200 micro s of the mixing-to-freezing time interval and observed the reaction between HRP and hydrogen peroxide (H(2)O(2)). The developed device consists of a submillisecond solution mixer and rotating copper or silver plates cooled at 77 K; it freezes the small droplets of mixed solution on the surface of the rotating plates. The ultraviolet-visible spectra of the sample quenched at approximately 1 ms after the mixing of HRP and H(2)O(2) suggest the formation of compound I. The electron paramagnetic resonance spectra of the same reaction quenched at approximately 200 micro s show a convex peak at g = 2.00, which is identified as compound I due to its microwave power and temperature dependencies. The absence of ferric signals in the electron paramagnetic resonance spectra of the quenched sample indicates that compound I is formed within approximately 200 micro s after mixing HRP and H(2)O(2). We conclude that the activation of H(2)O(2) in HRP at ambient temperature completes within approximately 200 micro s. The developed device can be generally applied to investigate the electronic structures of short-lived intermediates of metalloenzymes.
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Affiliation(s)
- Motomasa Tanaka
- Department of Molecular Engineering, Graduate School of Engineering, Kyoto University, Japan
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Riggs-Gelasco PJ, Shu L, Chen S, Burdi D, Huynh BH, Que, L, Stubbe J. EXAFS Characterization of the Intermediate X Generated During the Assembly of the Escherichia coli Ribonucleotide Reductase R2 Diferric Tyrosyl Radical Cofactor. J Am Chem Soc 1998. [DOI: 10.1021/ja9718230] [Citation(s) in RCA: 97] [Impact Index Per Article: 3.7] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
Affiliation(s)
- Pamela J. Riggs-Gelasco
- Contribution from the Chemistry Department, Massachusetts Institute of Technology, 77 Massachusetts Avenue, Cambridge, Massachusetts 02139, Department of Chemistry, Center for Metals in Biocatalysis, University of Minnesota, Minneapolis, Minnesota 55455, and Physics Department, Emory University, Atlanta, Georgia 30322
| | - Lijin Shu
- Contribution from the Chemistry Department, Massachusetts Institute of Technology, 77 Massachusetts Avenue, Cambridge, Massachusetts 02139, Department of Chemistry, Center for Metals in Biocatalysis, University of Minnesota, Minneapolis, Minnesota 55455, and Physics Department, Emory University, Atlanta, Georgia 30322
| | - Shuxian Chen
- Contribution from the Chemistry Department, Massachusetts Institute of Technology, 77 Massachusetts Avenue, Cambridge, Massachusetts 02139, Department of Chemistry, Center for Metals in Biocatalysis, University of Minnesota, Minneapolis, Minnesota 55455, and Physics Department, Emory University, Atlanta, Georgia 30322
| | - Doug Burdi
- Contribution from the Chemistry Department, Massachusetts Institute of Technology, 77 Massachusetts Avenue, Cambridge, Massachusetts 02139, Department of Chemistry, Center for Metals in Biocatalysis, University of Minnesota, Minneapolis, Minnesota 55455, and Physics Department, Emory University, Atlanta, Georgia 30322
| | - Boi Hanh Huynh
- Contribution from the Chemistry Department, Massachusetts Institute of Technology, 77 Massachusetts Avenue, Cambridge, Massachusetts 02139, Department of Chemistry, Center for Metals in Biocatalysis, University of Minnesota, Minneapolis, Minnesota 55455, and Physics Department, Emory University, Atlanta, Georgia 30322
| | - Lawrence Que,
- Contribution from the Chemistry Department, Massachusetts Institute of Technology, 77 Massachusetts Avenue, Cambridge, Massachusetts 02139, Department of Chemistry, Center for Metals in Biocatalysis, University of Minnesota, Minneapolis, Minnesota 55455, and Physics Department, Emory University, Atlanta, Georgia 30322
| | - JoAnne Stubbe
- Contribution from the Chemistry Department, Massachusetts Institute of Technology, 77 Massachusetts Avenue, Cambridge, Massachusetts 02139, Department of Chemistry, Center for Metals in Biocatalysis, University of Minnesota, Minneapolis, Minnesota 55455, and Physics Department, Emory University, Atlanta, Georgia 30322
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