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Hagen WR. Quantum Magnetism of the Iron Core in Ferritin Proteins-A Re-Evaluation of the Giant-Spin Model. Molecules 2024; 29:2254. [PMID: 38792115 PMCID: PMC11123763 DOI: 10.3390/molecules29102254] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/14/2024] [Revised: 05/04/2024] [Accepted: 05/09/2024] [Indexed: 05/26/2024] Open
Abstract
The electron-electron, or zero-field interaction (ZFI) in the electron paramagnetic resonance (EPR) of high-spin transition ions in metalloproteins and coordination complexes, is commonly described by a simple spin Hamiltonian that is second-order in the spin S: H=D[Sz2-SS+1/3+E(Sx2-Sy2). Symmetry considerations, however, allow for fourth-order terms when S ≥ 2. In metalloprotein EPR studies, these terms have rarely been explored. Metal ions can cluster via non-metal bridges, as, for example, in iron-sulfur clusters, in which exchange interaction can result in higher system spin, and this would allow for sixth- and higher-order ZFI terms. For metalloproteins, these have thus far been completely ignored. Single-molecule magnets (SMMs) are multi-metal ion high spin complexes, in which the ZFI usually has a negative sign, thus affording a ground state level pair with maximal spin quantum number mS = ±S, giving rise to unusual magnetic properties at low temperatures. The description of EPR from SMMs is commonly cast in terms of the 'giant-spin model', which assumes a magnetically isolated system spin, and in which fourth-order, and recently, even sixth-order ZFI terms have been found to be required. A special version of the giant-spin model, adopted for scaling-up to system spins of order S ≈ 103-104, has been applied to the ubiquitous iron-storage protein ferritin, which has an internal core containing Fe3+ ions whose individual high spins couple in a way to create a superparamagnet at ambient temperature with very high system spin reminiscent to that of ferromagnetic nanoparticles. This scaled giant-spin model is critically evaluated; limitations and future possibilities are explicitly formulated.
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Affiliation(s)
- Wilfred R Hagen
- Department of Biotechnology, Delft University of Technology, Building 58, Van der Maasweg 9, 2629 HZ Delft, The Netherlands
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2
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Abstract
The Fischer-Tropsch (FT) process converts a mixture of CO and H2 into liquid hydrocarbons as a major component of the gas-to-liquid technology for the production of synthetic fuels. Contrary to the energy-demanding chemical FT process, the enzymatic FT-type reactions catalyzed by nitrogenase enzymes, their metalloclusters, and synthetic mimics utilize H+ and e- as the reducing equivalents to reduce CO, CO2, and CN- into hydrocarbons under ambient conditions. The C1 chemistry exemplified by these FT-type reactions is underscored by the structural and electronic properties of the nitrogenase-associated metallocenters, and recent studies have pointed to the potential relevance of this reactivity to nitrogenase mechanism, prebiotic chemistry, and biotechnological applications. This review will provide an overview of the features of nitrogenase enzymes and associated metalloclusters, followed by a detailed discussion of the activities of various nitrogenase-derived FT systems and plausible mechanisms of the enzymatic FT reactions, highlighting the versatility of this unique reactivity while providing perspectives onto its mechanistic, evolutionary, and biotechnological implications.
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Affiliation(s)
- Yilin Hu
- Department of Molecular Biology and Biochemistry, University of California, Irvine, Irvine 92697-3900, USA
| | - Chi Chung Lee
- Department of Molecular Biology and Biochemistry, University of California, Irvine, Irvine 92697-3900, USA
| | - Mario Grosch
- Department of Molecular Biology and Biochemistry, University of California, Irvine, Irvine 92697-3900, USA
| | - Joseph B. Solomon
- Department of Chemistry, University of California, Irvine, CA 92697-2025, USA
| | - Wolfgang Weigand
- Institute of Inorganic and Analytical Chemistry, Friedrich Schiller University Jena, 07743 Jena, Germany
| | - Markus W. Ribbe
- Department of Molecular Biology and Biochemistry, University of California, Irvine, Irvine 92697-3900, USA
- Department of Chemistry, University of California, Irvine, CA 92697-2025, USA
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3
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Ye M, Brown AC, Suess DLM. Reversible Alkyl-Group Migration between Iron and Sulfur in [Fe 4S 4] Clusters. J Am Chem Soc 2022; 144:13184-13195. [PMID: 35830717 DOI: 10.1021/jacs.2c03195] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/08/2023]
Abstract
Synthetic [Fe4S4] clusters with Fe-R groups (R = alkyl/benzyl) are shown to release organic radicals on an [Fe4S4]3+-R/[Fe4S4]2+ redox couple, the same that has been proposed for a radical-generating intermediate in the superfamily of radical S-adenosyl-l-methionine (SAM) enzymes. In attempts to trap the immediate precursor to radical generation, a species in which the alkyl group has migrated from Fe to S is instead isolated. This S-alkylated cluster is a structurally faithful model of intermediates proposed in a variety of functionally diverse S transferase enzymes and features an "[Fe4S4]+-like" core that exists as a physical mixture of S = 1/2 and 7/2 states. The latter corresponds to an unusual, valence-localized electronic structure as indicated by distortions in its geometric structure and supported by computational analysis. Fe-to-S alkyl group migration is (electro)chemically reversible, and the preference for Fe vs S alkylation is dictated by the redox state of the cluster. These findings link the organoiron and organosulfur chemistry of Fe-S clusters and are discussed in the context of metalloenzymes that are proposed to make and break Fe-S and/or C-S bonds during catalysis.
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Affiliation(s)
- Mengshan Ye
- Department of Chemistry, Massachusetts Institute of Technology, Cambridge, Massachusetts 02139, United States
| | - Alexandra C Brown
- Department of Chemistry, Massachusetts Institute of Technology, Cambridge, Massachusetts 02139, United States
| | - Daniel L M Suess
- Department of Chemistry, Massachusetts Institute of Technology, Cambridge, Massachusetts 02139, United States
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4
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Sun C, Yang L, Ortuño MA, Wright AM, Chen T, Head AR, López N, Dincă M. Spectroscopic Evidence of Hyponitrite Radical Intermediate in NO Disproportionation at a MOF-Supported Mononuclear Copper Site. Angew Chem Int Ed Engl 2021; 60:7845-7850. [PMID: 33645907 DOI: 10.1002/anie.202015359] [Citation(s) in RCA: 6] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/17/2020] [Indexed: 12/11/2022]
Abstract
Dianionic hyponitrite (N2 O2 2- ) is often proposed, based on model complexes, as the key intermediate in reductive coupling of nitric oxide to nitrous oxide at the bimetallic active sites of heme-copper oxidases and nitric oxide reductases. In this work, we examine the gas-solid reaction of nitric oxide with the metal-organic framework CuI -ZrTpmC* with a suite of in situ spectroscopies and density functional theory simulations, and identify an unusual chelating N2 O2 .- intermediate. These results highlight the advantage provided by site-isolation in metal-organic frameworks (MOFs) for studying important reaction intermediates, and provide a mechanistic scenario compatible with the proposed one-electron couple in these enzymes.
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Affiliation(s)
- Chenyue Sun
- Department of Chemistry, Massachusetts Institute of Technology, 77 Massachusetts Avenue, Cambridge, MA, 02139, USA
| | - Luming Yang
- Department of Chemistry, Massachusetts Institute of Technology, 77 Massachusetts Avenue, Cambridge, MA, 02139, USA
| | - Manuel A Ortuño
- Institute of Chemical Research of Catalonia, The Barcelona Institute of Science and Technology, Av. Països Catalans 16, 43007, Tarragona, Spain
| | - Ashley M Wright
- Department of Chemistry, Massachusetts Institute of Technology, 77 Massachusetts Avenue, Cambridge, MA, 02139, USA
| | - Tianyang Chen
- Department of Chemistry, Massachusetts Institute of Technology, 77 Massachusetts Avenue, Cambridge, MA, 02139, USA
| | - Ashley R Head
- Center for Functional Nanomaterials, Brookhaven National Laboratory, Upton, NY, 11973, USA
| | - Núria López
- Institute of Chemical Research of Catalonia, The Barcelona Institute of Science and Technology, Av. Països Catalans 16, 43007, Tarragona, Spain
| | - Mircea Dincă
- Department of Chemistry, Massachusetts Institute of Technology, 77 Massachusetts Avenue, Cambridge, MA, 02139, USA
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6
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Sun C, Yang L, Ortuño MA, Wright AM, Chen T, Head AR, López N, Dincă M. Spectroscopic Evidence of Hyponitrite Radical Intermediate in NO Disproportionation at a MOF‐Supported Mononuclear Copper Site. Angew Chem Int Ed Engl 2021. [DOI: 10.1002/ange.202015359] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/22/2022]
Affiliation(s)
- Chenyue Sun
- Department of Chemistry Massachusetts Institute of Technology 77 Massachusetts Avenue Cambridge MA 02139 USA
| | - Luming Yang
- Department of Chemistry Massachusetts Institute of Technology 77 Massachusetts Avenue Cambridge MA 02139 USA
| | - Manuel A. Ortuño
- Institute of Chemical Research of Catalonia The Barcelona Institute of Science and Technology Av. Països Catalans 16 43007 Tarragona Spain
| | - Ashley M. Wright
- Department of Chemistry Massachusetts Institute of Technology 77 Massachusetts Avenue Cambridge MA 02139 USA
| | - Tianyang Chen
- Department of Chemistry Massachusetts Institute of Technology 77 Massachusetts Avenue Cambridge MA 02139 USA
| | - Ashley R. Head
- Center for Functional Nanomaterials Brookhaven National Laboratory Upton NY 11973 USA
| | - Núria López
- Institute of Chemical Research of Catalonia The Barcelona Institute of Science and Technology Av. Països Catalans 16 43007 Tarragona Spain
| | - Mircea Dincă
- Department of Chemistry Massachusetts Institute of Technology 77 Massachusetts Avenue Cambridge MA 02139 USA
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7
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Van Stappen C, Decamps L, Cutsail GE, Bjornsson R, Henthorn JT, Birrell JA, DeBeer S. The Spectroscopy of Nitrogenases. Chem Rev 2020; 120:5005-5081. [PMID: 32237739 PMCID: PMC7318057 DOI: 10.1021/acs.chemrev.9b00650] [Citation(s) in RCA: 115] [Impact Index Per Article: 28.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/14/2019] [Indexed: 01/08/2023]
Abstract
Nitrogenases are responsible for biological nitrogen fixation, a crucial step in the biogeochemical nitrogen cycle. These enzymes utilize a two-component protein system and a series of iron-sulfur clusters to perform this reaction, culminating at the FeMco active site (M = Mo, V, Fe), which is capable of binding and reducing N2 to 2NH3. In this review, we summarize how different spectroscopic approaches have shed light on various aspects of these enzymes, including their structure, mechanism, alternative reactivity, and maturation. Synthetic model chemistry and theory have also played significant roles in developing our present understanding of these systems and are discussed in the context of their contributions to interpreting the nature of nitrogenases. Despite years of significant progress, there is still much to be learned from these enzymes through spectroscopic means, and we highlight where further spectroscopic investigations are needed.
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Affiliation(s)
- Casey Van Stappen
- Max Planck Institute for
Chemical Energy Conversion, Stiftstrasse 34-36, 45470 Mülheim an der Ruhr, Germany
| | - Laure Decamps
- Max Planck Institute for
Chemical Energy Conversion, Stiftstrasse 34-36, 45470 Mülheim an der Ruhr, Germany
| | - George E. Cutsail
- Max Planck Institute for
Chemical Energy Conversion, Stiftstrasse 34-36, 45470 Mülheim an der Ruhr, Germany
| | - Ragnar Bjornsson
- Max Planck Institute for
Chemical Energy Conversion, Stiftstrasse 34-36, 45470 Mülheim an der Ruhr, Germany
| | - Justin T. Henthorn
- Max Planck Institute for
Chemical Energy Conversion, Stiftstrasse 34-36, 45470 Mülheim an der Ruhr, Germany
| | - James A. Birrell
- Max Planck Institute for
Chemical Energy Conversion, Stiftstrasse 34-36, 45470 Mülheim an der Ruhr, Germany
| | - Serena DeBeer
- Max Planck Institute for
Chemical Energy Conversion, Stiftstrasse 34-36, 45470 Mülheim an der Ruhr, Germany
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8
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Chiu CC, Cheng MC, Lin SH, Yan CW, Lee GH, Chang MC, Lin TS, Peng SM. Structure and magnetic properties of a novel heteroheptanuclear metal string complex [Ni 3Ru 2Ni 2(μ 7-teptra) 4(NCS) 2](PF 6). Dalton Trans 2020; 49:6635-6643. [PMID: 32367097 DOI: 10.1039/d0dt00156b] [Citation(s) in RCA: 6] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/28/2022]
Abstract
We report the synthesis of a novel heteroheptanuclear metal string complex (HMSC) [Ni3Ru2Ni2(μ7-teptra)4(NCS)2](PF6) 1 supported by tetra-pyridyl-tri-amine (H3teptra) ligands. We employed X-ray diffraction and other spectroscopic techniques to characterize the complex. The observed remarkably short Ru-Ru distance of 2.2499(3) Å for 1 is indicative of a unique metal-metal interaction in the mixed-valence [Ru2]5+ (S = 3/2) unit. The complex exhibits a relatively high magnetic moment value of 4.55 B.M. at 4 K, which increases rapidly to 6.00 B.M. at 30 K and remains at 6.11 B.M. from 50 to 300 K as shown by SQUID measurements, indicating a high spin (S≥ 3/2) system which is further supported by the analyses of EPR spectra at low temperatures. These magnetic behaviors can be ascribed to the result of spin-exchange interactions among multi-spin centers.
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Affiliation(s)
- Cheng-Chang Chiu
- Department of Chemistry, National Taiwan University, No. 1, Sec. 4, Roosevelt Rd., 10617 Taipei, Taiwan, Republic of China.
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9
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Zanello P. Structure and electrochemistry of proteins harboring iron-sulfur clusters of different nuclearities. Part V. Nitrogenases. Coord Chem Rev 2019. [DOI: 10.1016/j.ccr.2019.07.001] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/26/2022]
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10
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Abstract
Metals and metal clusters in proteins typically serve as important structural/functional motifs. Because of this reason, there is a wide range of techniques that specifically probe the structure and energy levels of metals in metalloproteins. One technique, magnetic circular dichroism (MCD) spectroscopy, is the focus of this chapter. MCD spectroscopy monitors the circular dichroism spectrum induced by a magnetic field and is an effective way of obtaining electronic and structural information of paramagnetic metal ions or clusters. The basic methodology of this technique is discussed along with examples of how MCD spectroscopy can be used to elucidate typical metal clusters in proteins. Special emphasis is placed on iron-sulfur (FeS) clusters.
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11
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Sánchez RH, Betley TA. Thermally Persistent High-Spin Ground States in Octahedral Iron Clusters. J Am Chem Soc 2018; 140:16792-16806. [PMID: 30403845 DOI: 10.1021/jacs.8b10181] [Citation(s) in RCA: 18] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
Abstract
Chemical oxidation and reduction of the all-ferrous (HL)2Fe6 in THF affords isostructural, coordinatively unsaturated clusters of the type [(HL)2Fe6] n: [(HL)2Fe6][BArF24] (1, n = +1; where [BArF24]- = tetrakis[(3,5-trifluoromethyl)phenyl]borate), [Bu4N][(HL)2Fe6] (2a, n = -1), [P][(HL)2Fe6] (2b, n = -1; where [P]+ = tributyl(1,3-dioxolan-2-ylmethyl)phosphonium), and [Bu4N]2[(HL)2Fe6] (3, n = -2). Each member of the redox-transfer series was characterized by zero-field 57Fe Mössbauer spectroscopy, near-infrared spectroscopy, single-crystal X-ray crystallography, and magnetometry. Redox-directed trends are observed when comparing the structural metrics within the [Fe6] core. The metal octahedron [Fe6] decreases marginally in volume as the molecular reduction state increases as gauged by the Fe-Feavg distance varying from 2.608(11) Å ( n = +1) to 2.573(3) ( n = -2). In contrast, the mean Fe-N distances and ∠Fe-N-Fe angles correlate linearly with the [Fe6] oxidation level, or alternatively, the changes observed within the local Fe-N4 coordination planes vary linearly with the aggregate spin ground state. In general, as the spin ground state ( S) increases, the Fe-N(H)avg distances also increase. The structural metric perturbations within the [Fe6] core and measured spin ground states were rationalized extending the previously proposed molecular orbital diagram derived for (HL)2Fe6. Chemical reduction of the (HL)2Fe6 cluster results in an abrupt increase in spin ground state from S = 6 for the all-ferrous cluster, to S = 19/2 in the monoanionic 2b and S = 11 for the dianionic 3. The observation of asymmetric intervalence charge transfer bands in 3 provides further evidence of the fully delocalized ground state observed by 57Fe Mössbauer spectroscopy for all species examined (1-3). For each of the clusters examined within the electron-transfer series, the observed spin ground states thermally persist to 300 K. In particular, the S = 11 in dianionic 3 and S = 19/2 in the monoanionic 2b represent the highest spin ground states isolated up to room temperature known to date. The increase in spin ground state results from population of the antibonding orbital band comprised of the Fe-N σ* interactions. As such, the thermally persistent ground states arise from population of the resultant single spin manifolds in accordance with Hund's rules. The large spin ground states, indicative of strong ferromagnetic electronic alignment of the valence electrons, result from strong direct exchange electronic coupling mediated by Fe-Fe orbital overlap within the [Fe6] cores, equivalent to a strong double exchange magnetic coupling B for 3 that was calculated to be 309 cm-1.
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Affiliation(s)
- Raúl Hernández Sánchez
- Department of Chemistry and Chemical Biology , Harvard University , 12 Oxford Street , Cambridge , Massachusetts 02138 , United States
| | - Theodore A Betley
- Department of Chemistry and Chemical Biology , Harvard University , 12 Oxford Street , Cambridge , Massachusetts 02138 , United States
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12
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Hagen WR, Hagedoorn PL, Honarmand Ebrahimi K. The workings of ferritin: a crossroad of opinions. Metallomics 2018; 9:595-605. [PMID: 28573266 DOI: 10.1039/c7mt00124j] [Citation(s) in RCA: 28] [Impact Index Per Article: 4.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/30/2022]
Abstract
Biochemistry of the essential element iron is complicated by radical chemistry associated with Fe(ii) ions and by the extremely low solubility of the Fe(iii) ion in near-neutral water. To mitigate these problems cells from all domains of life synthesize the protein ferritin to take up and oxidize Fe(ii) and to form a soluble storage of Fe(iii) from which iron can be made available for physiology. A long history of studies on ferritin has not yet resulted in a generally accepted mechanism of action of this enzyme. In fact strong disagreement exists between extant ideas on several key steps in the workings of ferritin. The scope of this review is to explain the experimental background of these controversies and to indicate directions towards their possible resolution.
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Affiliation(s)
- Wilfred R Hagen
- Delft University of Technology, Department of Biotechnology, van der Maasweg 9, 2629 HZ Delft, The Netherlands.
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Honarmand Ebrahimi K, Silveira C, Todorovic S. Evidence for the synthesis of an unusual high spin (S = 7/2) [Cu–3Fe–4S] cluster in the radical-SAM enzyme RSAD2 (viperin). Chem Commun (Camb) 2018; 54:8614-8617. [DOI: 10.1039/c8cc03565b] [Citation(s) in RCA: 8] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022]
Abstract
We demonstrate the synthesis of an unusual high spin [Cu–3Fe–4S] cluster in the radical S-adenosylmethionine enzyme RSAD2 (also known as viperin).
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Affiliation(s)
| | - C. Silveira
- Instituto de Tecnologia Química e Biológica António Xavier
- Universidade Nova de Lisboa
- Av da República
- 2780-157 Oeiras
- Portugal
| | - S. Todorovic
- Instituto de Tecnologia Química e Biológica António Xavier
- Universidade Nova de Lisboa
- Av da República
- 2780-157 Oeiras
- Portugal
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Sánchez RH, Zheng SL, Betley TA. Ligand Field Strength Mediates Electron Delocalization in Octahedral [((H)L)2Fe6(L')m](n+) Clusters. J Am Chem Soc 2015; 137:11126-43. [PMID: 26231520 PMCID: PMC5572642 DOI: 10.1021/jacs.5b06453] [Citation(s) in RCA: 42] [Impact Index Per Article: 4.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/24/2022]
Abstract
To assess the impact of terminal ligand binding on a variety of cluster properties (redox delocalization, ground-state stabilization, and breadth of redox state accessibility), we prepared three electron-transfer series based on the hexanuclear iron cluster [((H)L)2Fe6(L')m](n+) in which the terminal ligand field strength was modulated from weak to strong (L' = DMF, MeCN, CN). The extent of intracore M-M interactions is gauged by M-M distances, spin ground state persistence, and preference for mixed-valence states as determined by electrochemical comproportionation constants. Coordination of DMF to the [((H)L)2Fe6] core leads to weaker Fe-Fe interactions, as manifested by the observation of ground states populated only at lower temperatures (<100 K) and by the greater evidence of valence trapping within the mixed-valence states. Comproportionation constants determined electrochemically (Kc = 10(4)-10(8)) indicate that the redox series exhibits electronic delocalization (class II-III), yet no intervalence charge transfer (IVCT) bands are observable in the near-IR spectra. Ligation of the stronger σ donor acetonitrile results in stabilization of spin ground states to higher temperatures (∼300 K) and a high degree of valence delocalization (Kc = 10(2)-10(8)) with observable IVCT bands. Finally, the anionic cyanide-bound series reveals the highest degree of valence delocalization with the most intense IVCT bands (Kc = 10(12)-10(20)) and spin ground state population beyond room temperature. Across the series, at a given formal oxidation level, the capping ligand on the hexairon cluster dictates the overall properties of the aggregate, modulating the redox delocalization and the persistence of the intracore coupling of the metal sites.
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Affiliation(s)
- Raúl Hernández Sánchez
- Department of Chemistry and Chemical Biology, Harvard University, 12 Oxford Street, Cambridge, Massachusetts 02138, United States
| | - Shao-Liang Zheng
- Department of Chemistry and Chemical Biology, Harvard University, 12 Oxford Street, Cambridge, Massachusetts 02138, United States
| | - Theodore A. Betley
- Department of Chemistry and Chemical Biology, Harvard University, 12 Oxford Street, Cambridge, Massachusetts 02138, United States
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15
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Magnetic circular dichroism spectroscopy. Methods Mol Biol 2011. [PMID: 21833870 DOI: 10.1007/978-1-61779-194-9_14] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register]
Abstract
Being able to probe the structure and energy levels of metal ions in biological systems is an important goal of bioinorganic scientists. Several of the techniques used rely on the paramagnetic property of certain oxidation states of metal ions. MCD spectroscopy is one of those techniques and represents an effective way of obtaining structure/electronic information of paramagnetic metal ions. The basics of this technique are discussed along with examples of how MCD spectroscopy has been successfully used to elucidate the metal clusters of Nif proteins from nitrogen-fixing bacteria.
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16
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Danyal K, Yang ZY, Seefeldt LC. Electron paramagnetic resonance spectroscopy. METHODS IN MOLECULAR BIOLOGY (CLIFTON, N.J.) 2011; 766:191-205. [PMID: 21833869 DOI: 10.1007/978-1-61779-194-9_13] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Subscribe] [Scholar Register] [Indexed: 11/26/2022]
Abstract
EPR spectroscopy has been an important tool in nitrogenase research for the last 50 years. The three metalloclusters in nitrogenase, the Fe protein [4Fe-4S] cluster, and the MoFe protein P-cluster, and FeMo-cofactor, all have EPR spectra when poised in the appropriate paramagnetic states. EPR spectroscopy can probe changes in the electronic properties of each metal cluster, such as when substrates bind, and can provide a definitive method for observing changes in the redox states of the clusters. In this chapter, the methods for analysis of the three metal clusters of nitrogenase by EPR spectroscopy are described, along with methods for trapping substrate-derived intermediates on the active site that are amenable to characterization by EPR and other magnetic resonance spectroscopy techniques.
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Affiliation(s)
- Karamatullah Danyal
- Department of Chemistry and Biochemistry, Utah State University, Logan, UT 84322, USA.
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Abstract
Nitrogenase is the enzyme responsible for biological reduction of dinitrogen (N(2)) to ammonia, a form usable for life. Playing a central role in the global biogeochemical nitrogen cycle, this enzyme has been the focus of intensive research for over 60 years. This chapter provides an overview of the features of nitrogenase as a background to the subsequent chapters of this volume that detail the many methods that have been applied in an attempt to gain a deeper understanding of this complex enzyme.
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Affiliation(s)
- Zhi-Yong Yang
- Department of Chemistry and Biochemistry, Utah State University, Logan, UT 84322, USA.
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Ohki Y, Imada M, Murata A, Sunada Y, Ohta S, Honda M, Sasamori T, Tokitoh N, Katada M, Tatsumi K. Synthesis, Structures, and Electronic Properties of [8Fe-7S] Cluster Complexes Modeling the Nitrogenase P-Cluster. J Am Chem Soc 2009; 131:13168-78. [DOI: 10.1021/ja9055036] [Citation(s) in RCA: 54] [Impact Index Per Article: 3.6] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Affiliation(s)
- Yasuhiro Ohki
- Department of Chemistry, Graduate School of Science and Research Center for Materials Science, Nagoya University, Furo-cho, Chikusa-ku, Nagoya 464-8602, Japan, Institute for Chemical Research, Kyoto University, Gokasho, Uji, Kyoto 611-0011, Japan, and Graduate School of Science and Engineering, Tokyo Metropolitan University, Minami-ohsawa, Hachioji, Tokyo 192-0397, Japan
| | - Motosuke Imada
- Department of Chemistry, Graduate School of Science and Research Center for Materials Science, Nagoya University, Furo-cho, Chikusa-ku, Nagoya 464-8602, Japan, Institute for Chemical Research, Kyoto University, Gokasho, Uji, Kyoto 611-0011, Japan, and Graduate School of Science and Engineering, Tokyo Metropolitan University, Minami-ohsawa, Hachioji, Tokyo 192-0397, Japan
| | - Ayuro Murata
- Department of Chemistry, Graduate School of Science and Research Center for Materials Science, Nagoya University, Furo-cho, Chikusa-ku, Nagoya 464-8602, Japan, Institute for Chemical Research, Kyoto University, Gokasho, Uji, Kyoto 611-0011, Japan, and Graduate School of Science and Engineering, Tokyo Metropolitan University, Minami-ohsawa, Hachioji, Tokyo 192-0397, Japan
| | - Yusuke Sunada
- Department of Chemistry, Graduate School of Science and Research Center for Materials Science, Nagoya University, Furo-cho, Chikusa-ku, Nagoya 464-8602, Japan, Institute for Chemical Research, Kyoto University, Gokasho, Uji, Kyoto 611-0011, Japan, and Graduate School of Science and Engineering, Tokyo Metropolitan University, Minami-ohsawa, Hachioji, Tokyo 192-0397, Japan
| | - Shun Ohta
- Department of Chemistry, Graduate School of Science and Research Center for Materials Science, Nagoya University, Furo-cho, Chikusa-ku, Nagoya 464-8602, Japan, Institute for Chemical Research, Kyoto University, Gokasho, Uji, Kyoto 611-0011, Japan, and Graduate School of Science and Engineering, Tokyo Metropolitan University, Minami-ohsawa, Hachioji, Tokyo 192-0397, Japan
| | - Masaru Honda
- Department of Chemistry, Graduate School of Science and Research Center for Materials Science, Nagoya University, Furo-cho, Chikusa-ku, Nagoya 464-8602, Japan, Institute for Chemical Research, Kyoto University, Gokasho, Uji, Kyoto 611-0011, Japan, and Graduate School of Science and Engineering, Tokyo Metropolitan University, Minami-ohsawa, Hachioji, Tokyo 192-0397, Japan
| | - Takahiro Sasamori
- Department of Chemistry, Graduate School of Science and Research Center for Materials Science, Nagoya University, Furo-cho, Chikusa-ku, Nagoya 464-8602, Japan, Institute for Chemical Research, Kyoto University, Gokasho, Uji, Kyoto 611-0011, Japan, and Graduate School of Science and Engineering, Tokyo Metropolitan University, Minami-ohsawa, Hachioji, Tokyo 192-0397, Japan
| | - Norihiro Tokitoh
- Department of Chemistry, Graduate School of Science and Research Center for Materials Science, Nagoya University, Furo-cho, Chikusa-ku, Nagoya 464-8602, Japan, Institute for Chemical Research, Kyoto University, Gokasho, Uji, Kyoto 611-0011, Japan, and Graduate School of Science and Engineering, Tokyo Metropolitan University, Minami-ohsawa, Hachioji, Tokyo 192-0397, Japan
| | - Motomi Katada
- Department of Chemistry, Graduate School of Science and Research Center for Materials Science, Nagoya University, Furo-cho, Chikusa-ku, Nagoya 464-8602, Japan, Institute for Chemical Research, Kyoto University, Gokasho, Uji, Kyoto 611-0011, Japan, and Graduate School of Science and Engineering, Tokyo Metropolitan University, Minami-ohsawa, Hachioji, Tokyo 192-0397, Japan
| | - Kazuyuki Tatsumi
- Department of Chemistry, Graduate School of Science and Research Center for Materials Science, Nagoya University, Furo-cho, Chikusa-ku, Nagoya 464-8602, Japan, Institute for Chemical Research, Kyoto University, Gokasho, Uji, Kyoto 611-0011, Japan, and Graduate School of Science and Engineering, Tokyo Metropolitan University, Minami-ohsawa, Hachioji, Tokyo 192-0397, Japan
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21
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Abstract
Nitrogen-fixing bacteria catalyze the reduction of dinitrogen (N(2)) to two ammonia molecules (NH(3)), the major contribution of fixed nitrogen to the biogeochemical nitrogen cycle. The most widely studied nitrogenase is the molybdenum (Mo)-dependent enzyme. The reduction of N(2) by this enzyme involves the transient interaction of two component proteins, designated the iron (Fe) protein and the MoFe protein, and minimally requires 16 magnesium ATP (MgATP), eight protons, and eight electrons. The current state of knowledge on how these proteins and small molecules together effect the reduction of N(2) to ammonia is reviewed. Included is a summary of the roles of the Fe protein and MgATP hydrolysis, information on the roles of the two metal clusters contained in the MoFe protein in catalysis, insights gained from recent success in trapping substrates and inhibitors at the active-site metal cluster FeMo cofactor, and finally, considerations of the mechanism of N(2) reduction catalyzed by nitrogenase.
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Affiliation(s)
- Lance C Seefeldt
- Department of Chemistry and Biochemistry, Utah State University, Logan, UT 84322, USA.
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22
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Lee HI, Sørlie M, Christiansen J, Yang TC, Shao J, Dean DR, Hales BJ, Hoffman BM. Electron inventory, kinetic assignment (E(n)), structure, and bonding of nitrogenase turnover intermediates with C2H2 and CO. J Am Chem Soc 2006; 127:15880-90. [PMID: 16277531 DOI: 10.1021/ja054078x] [Citation(s) in RCA: 62] [Impact Index Per Article: 3.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
Abstract
Improved 1H ENDOR data from the S(EPR1) intermediate formed during turnover of the nitrogenase alpha-195Gln MoFe protein with C2(1,2)H2 in (1,2)H2O buffers, taken in context with the recent study of the intermediate formed from propargyl alcohol, indicate that S(EPR1) is a product complex, likely with C2H4 bound as a ferracycle to a single Fe of the FeMo-cofactor active site. 35 GHz CW and Mims pulsed 57Fe ENDOR of 57Fe-enriched S(EPR1) cofactor indicates that it exhibits the same valencies as those of the CO-bound cofactor of the lo-CO intermediate formed during turnover with CO, [Mo4+, Fe3+, Fe6(2+), S9(2-)(d43)](+1), reduced by m = 2 electrons relative to the resting-state cofactor. Consideration of 57Fe hyperfine coupling in S(EPR1) and lo-CO leads to a picture in which CO bridges two Fe of lo-CO, while the C2H4 of S(EPR1) binds to one of these. To correlate these and other intermediates with Lowe-Thorneley (LT) kinetic schemes for substrate reduction, we introduce the concept of an "electron inventory". It partitions the number of electrons a MoFe protein intermediate has accepted from the Fe protein (n) into the number transmitted to the substrate (s), the number that remain on the intermediate cofactor (m), and the additional number delivered to the cofactor from the P clusters (p): n = m + s - p (with p = 0 here). The cofactors of lo-CO and S(EPR1) both are reduced by m = 2 electrons, but the intermediates are not at the same LT reduction stage (E(n)): (n = 2; m = 2, s = 0) for lo-CO; (n = 4; s = 2, m = 2) for S(EPR1). This is the first proposed correlation of an LT E(n) kinetic state with a well-defined chemical state of the enzyme.
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Affiliation(s)
- Hong-In Lee
- Department of Chemistry Education, Kyungpook National University, Daegu, 702-701, Korea.
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23
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Abstract
Molecular paramagnetism pervades the bioinorganic chemistry of V, Mn, Fe, Co, Ni, Cu, Mo, W, and of a number of non-biological transition elements. To date we can look back at half a century of fruitful EPR studies on metalloproteins, and against this background evaluate the significance of modern EPR spectroscopy from the perspective of a biochemist, making a distinction between conventional continuous wave X-band spectroscopy as a reliable work horse with broad, established applicability even on crude preparations, vs. a diffuse set of "advanced EPR" technologies whose practical application typically calls for narrowly focused research hypotheses and very high quality samples. The type of knowledge on metalloproteins that is readily obtainable with EPR spectroscopy, is explained with illustrative examples, as is the relation between experimental complexity and the spin value of the system.
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Affiliation(s)
- Wilfred R Hagen
- Department of Biotechnology, Delft University of Technology, Julianalaan 67, 2628, BC Delft, The Netherlands.
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24
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Fisher K, Newton WE. Nitrogenase proteins from Gluconacetobacter diazotrophicus, a sugarcane-colonizing bacterium. BIOCHIMICA ET BIOPHYSICA ACTA-PROTEINS AND PROTEOMICS 2005; 1750:154-65. [PMID: 15925553 DOI: 10.1016/j.bbapap.2005.04.010] [Citation(s) in RCA: 9] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 03/14/2005] [Revised: 04/27/2005] [Accepted: 04/28/2005] [Indexed: 10/25/2022]
Abstract
Gluconacetobacter diazotrophicus Pal-5 grew well and expressed nitrogenase activity in the absence of NH4+ and at initial O2 concentrations greater than 5% in the culture atmosphere. G. diazotrophicus nitrogenase consisted of two components, Gd1 and Gd2, which were difficult to separate but were purified individually to homogeneity. Their compositions were very similar to those of Azotobacter vinelandii nitrogenase, however, all subunits were slightly smaller in size. The purified Gd1 protein contained a 12:1 Fe/Mo ratio as compared to 14:1 found for Av1 purified in parallel. Both Gd2 and Av2 contained 3.9 Fe atoms per molecule. Dithionite-reduced Gd1 exhibited EPR features at g=3.69, 3.96, and 4.16 compared with 3.64 and 4.27 for Av1. Gd2 gave an S=1/2 EPR signal identical to that of Av2. A Gd1 maximum specific activity of 1600 nmol H2 (min mg of protein)(-1) was obtained when complemented with either Gd2 or Av2, however, more Av2 was required. Gd2 had specific activities of 600 and 1100 nmol H2 (min mg protein)(-1) when complemented with Av1 and Gd1, respectively. The purified G. diazotrophicus nitrogenase exhibited a narrowed pH range for effective catalysis compared to the A. vinelandii nitrogenase, however, both exhibited maximum specific activity at about pH 7. The Gd-nitrogenase was more sensitive to ionic strength than the Av-nitrogenase.
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Affiliation(s)
- Karl Fisher
- Department of Biochemistry, The Virginia Polytechnic Institute and State University, Blacksburg, VA 24061, USA
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25
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Boll M. Key enzymes in the anaerobic aromatic metabolism catalysing Birch-like reductions. BIOCHIMICA ET BIOPHYSICA ACTA-BIOENERGETICS 2005; 1707:34-50. [PMID: 15721605 DOI: 10.1016/j.bbabio.2004.01.009] [Citation(s) in RCA: 72] [Impact Index Per Article: 3.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 04/28/2003] [Accepted: 01/23/2004] [Indexed: 11/16/2022]
Abstract
Several novel enzyme reactions have recently been discovered in the aromatic metabolism of anaerobic bacteria. Many of these reactions appear to be catalyzed by oxygen-sensitive enzymes by means of highly reactive radical intermediates. This contribution deals with two key reactions in this metabolism: the ATP-driven reductive dearomatisation of the benzene ring and the reductive removal of a phenolic hydroxyl group. The two reactions catalyzed by benzoyl-CoA reductase (BCR) and 4-hydroxybenzoyl-CoA reductase (4-HBCR) are both mechanistically difficult to achieve; both are considered to proceed in 'Birch-like' reductions involving single electron and proton transfer steps to the aromatic ring. The problem of both reactions is the extremely high redox barrier for the first electron transfer to the substrate (e.g., -1.9 V in case of a benzoyl-CoA (BCoA) analogue), which is solved in the two enzymes in different manners. Studying these enzymatic reactions provides insights into general principles of how oxygen-dependent reactions are replaced by alternative processes under anoxic conditions.
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Affiliation(s)
- Matthias Boll
- Institut für Biologie II, Universität Freiburg, Schänzlestr. 1, D-79104 Freiburg, Germany.
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26
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Blokesch M, Albracht SPJ, Matzanke BF, Drapal NM, Jacobi A, Böck A. The complex between hydrogenase-maturation proteins HypC and HypD is an intermediate in the supply of cyanide to the active site iron of [NiFe]-hydrogenases. J Mol Biol 2004; 344:155-67. [PMID: 15504408 DOI: 10.1016/j.jmb.2004.09.040] [Citation(s) in RCA: 85] [Impact Index Per Article: 4.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/06/2004] [Revised: 09/16/2004] [Accepted: 09/17/2004] [Indexed: 11/30/2022]
Abstract
Carbamoylphosphate has been shown to be the educt for the synthesis of the CN ligands of the NiFe metal centre of hydrogenases from Escherichia coli. In the absence of carbamoylphosphate, cells accumulate a complex of two hydrogenase maturation proteins, namely HypC and HypD for the synthesis of hydrogenase 3. A procedure for the purification of wild-type HypD protein or of a biologically active derivative carrying the Strep-tagII((R)) at the N terminus has been developed. HypD is a monomeric protein possessing about 4 mol of iron per mol of protein. Electron paramagnetic resonance (EPR) and Mossbauer spectroscopy demonstrated that the iron is present as a diamagnetic [4Fe-4S](2+) cluster. The complex between HypC and HypD can be cross-linked by a number of thiol and primary amine-specific linkers. When HypD and HypC were overproduced side-by-side with HypE, the HypC-HypD complex contained substoichiometric amounts of HypE whose proportion in the complex could be augmented when HypF was also overproduced. HypE trapped in this complex could be carbamoylated by protein HypF and after dehydration transferred the cyano group to the HypC-HypD part of the complex. Free HypC and HypD were not cyanated by HypE-CN. An active HypC-HypD complex from anaerobic cells was inactivated by incubation with K(3)[Fe(CN)(6)] but not with K(4)[Fe(CN)(6)]. The results suggest the existence of a dynamic complex between the hydrogenase maturation proteins HypD, HypC, HypE and HypF, which is the site of ligand biosynthesis and attachment to the iron atom of the NiFe site in hydrogenase 3.
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Affiliation(s)
- Melanie Blokesch
- Department I der Fakultät für Biologie, Ludwig-Maximilians-Universität München, Maria-Ward-Strasse 1a, D-80638 Münich, Germany
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27
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Benton PM, Mayer SM, Shao J, Hoffman BM, Dean DR, Seefeldt LC. Interaction of acetylene and cyanide with the resting state of nitrogenase alpha-96-substituted MoFe proteins. Biochemistry 2001; 40:13816-25. [PMID: 11705370 DOI: 10.1021/bi011571m] [Citation(s) in RCA: 27] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Abstract
The nitrogenase MoFe protein contains the active site metallocluster called FeMo-cofactor [7Fe-9S-Mo-homocitrate] that exhibits an S = 3/2 EPR signal in the resting state. No interaction with FeMo-cofactor is detected when either substrates or inhibitors are incubated with MoFe protein in the resting state. Rather, the detection of such interactions requires the incubation of the MoFe protein together with its obligate electron donor, called the Fe protein, and MgATP under turnover conditions. This indicates that a more reduced state of the MoFe protein is required to accommodate substrate or inhibitor interaction. In the present work, substitution of an arginine residue (alpha-96(Arg)) located next to the active site FeMo-cofactor in the MoFe protein by leucine, glutamine, alanine, or histidine is found to result in MoFe proteins that can interact with acetylene or cyanide in the as-isolated, resting state without the need for the Fe protein, or MgATP. The dithionite-reduced, resting states of the alpha-96(Leu)-, alpha-96(Gln)-, alpha-96(Ala)-, or alpha-96(His)-substituted MoFe proteins show an S = 3/2 EPR signal (g = 4.26, 3.67, 2.00) similar to that assigned to FeMo-cofactor in the wild-type MoFe protein. However, in contrast to the wild-type MoFe protein, the alpha-96-substituted MoFe proteins all exhibit changes in their EPR spectra upon incubation with acetylene or cyanide. The alpha-96(Leu)-substituted MoFe protein was representative of the other alpha-96-substituted MoFe proteins examined. The incubation of acetylene with the alpha-96(Leu) MoFe protein decreased the intensity of the normal FeMo-cofactor signal with the appearance of a new EPR signal having inflections at g = 4.50 and 3.50. Incubation of cyanide with the alpha-96(Leu) MoFe protein also decreased the FeMo-cofactor EPR signal with concomitant appearance of a new EPR signal having an inflection at g = 4.06. The acetylene- and cyanide-dependent EPR signals observed for the alpha-96(Leu)-substituted MoFe protein were found to follow Curie law 1/T dependence, consistent with a ground-state transition as observed for FeMo-cofactor. The microwave power dependence of the EPR signal intensity is shifted to higher power for the acetylene- and cyanide-dependent signals, consistent with a change in the relaxation properties of the spin system of FeMo-cofactor. Finally, the alpha-96(Leu)-substituted MoFe protein incubated with (13)C-labeled cyanide displays a (13)C ENDOR signal with an isotropic hyperfine coupling of 0.42 MHz in Q-band Mims pulsed ENDOR spectra. This indicates the existence of some spin density on the cyanide, and thus suggests that the new component of the cyanide-dependent EPR signals arise from the direct bonding of cyanide to the FeMo-cofactor. These data indicate that both acetylene and cyanide are able to interact with FeMo-cofactor contained within the alpha-96-substituted MoFe proteins in the resting state. These results support a model where effective interaction of substrates or inhibitors with FeMo-cofactor occurs as a consequence of both increased reactivity and accessibility of FeMo-cofactor under turnover conditions. We suggest that, for the wild-type MoFe protein, the alpha-96(Arg) side chain acts as a gatekeeper, moving during turnover in order to permit accessibility of acetylene or cyanide to a specific [4Fe-4S] face of FeMo-cofactor.
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Affiliation(s)
- P M Benton
- Department of Chemistry and Biochemistry, Utah State University, Logan, Utah 84322, USA
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28
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Christiansen J, Dean DR, Seefeldt LC. MECHANISTIC FEATURES OF THE MO-CONTAINING NITROGENASE. ANNUAL REVIEW OF PLANT PHYSIOLOGY AND PLANT MOLECULAR BIOLOGY 2001; 52:269-295. [PMID: 11337399 DOI: 10.1146/annurev.arplant.52.1.269] [Citation(s) in RCA: 130] [Impact Index Per Article: 5.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 11/09/2022]
Abstract
Nitrogenase is the complex metalloenzyme responsible for biological dinitrogen reduction. This reaction represents the single largest contributor to the reductive portion of the global nitrogen cycle. Recent developments in understanding the mechanism of the Mo-based nitrogenase are reviewed. Topics include how nucleotide binding and hydrolysis are coupled to electron transfer and substrate reduction, how electrons are accumulated and transferred within the MoFe-protein, and how substrates bind and are reduced at the active site metal cluster.
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Affiliation(s)
- Jason Christiansen
- Department of Biochemistry, Virginia Polytechnic Institute and State University, Blacksburg, Virginia 24061; e-mail: , Department of Chemistry and Biochemistry, Utah State University, Logan, Utah 84332; e-mail:
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29
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Boll M, Fuchs G, Meier C, Trautwein A, Lowe DJ. EPR and Mössbauer studies of benzoyl-CoA reductase. J Biol Chem 2000; 275:31857-68. [PMID: 10903310 DOI: 10.1074/jbc.m001508200] [Citation(s) in RCA: 33] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
Benzoyl-CoA reductase catalyzes the two-electron transfer from a reduced ferredoxin to the aromatic ring of benzoyl-CoA; this reaction is coupled to stoichiometrical ATP hydrolysis. A very low reduction potential (less than -1 V) is required for the first electron transfer to the aromatic ring. In this work the nature of the redox centers of purified benzoyl-CoA reductase from Thauera aromatica was studied by EPR and Mössbauer spectroscopy. The results obtained indicated the presence of three [4Fe-4S] clusters. Redox titration studies revealed that the reduction potentials of all three clusters were below -500 mV. The previously reported S = 7/2 state of the enzyme during benzoyl-CoA-independent ATPase activity (Boll, M., Albracht, S. J. P., and Fuchs, G. (1997) Eur. J. Biochem. 244, 840-851) was confirmed by Mössbauer spectroscopy. Inactivation by oxygen was associated with the irreversible conversion of part of the [4Fe-4S] clusters to [3Fe-4S] clusters. Acetylene stimulated the benzoyl-CoA-independent ATPase activity and induced novel EPR signals with g(av) >2. The presence of simple cubane clusters in benzoyl-CoA reductase as the sole redox-active metal centers demonstrates novel aspects of [4Fe-4S] clusters since they adopt the role of elemental sodium or lithium which are used as electron donors in the analogous chemical Birch reduction of aromatic rings.
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Affiliation(s)
- M Boll
- Biological Chemistry Department, John Innes Centre, Colney, Norwich NR4 7UH, United Kingdom.
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30
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Smith BE. Structure, Function, and Biosynthesis of the Metallosulfur Clusters in Nitrogenases. ADVANCES IN INORGANIC CHEMISTRY 1999. [DOI: 10.1016/s0898-8838(08)60078-1] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 10/22/2022]
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31
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Arendsen AF, Lindley PF. The Search for A “Prismane” Fe–S Protein. ADVANCES IN INORGANIC CHEMISTRY 1999. [DOI: 10.1016/s0898-8838(08)60079-3] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 11/30/2022]
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32
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Christiansen J, Goodwin PJ, Lanzilotta WN, Seefeldt LC, Dean DR. Catalytic and biophysical properties of a nitrogenase Apo-MoFe protein produced by a nifB-deletion mutant of Azotobacter vinelandii. Biochemistry 1998; 37:12611-23. [PMID: 9730834 DOI: 10.1021/bi981165b] [Citation(s) in RCA: 143] [Impact Index Per Article: 5.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/08/2023]
Abstract
A Zn-immobilized metal-affinity chromatography technique was used to purify a poly-histidine-tagged, FeMo-cofactorless MoFe protein (apo-MoFe protein) from a nifB-deletion mutant of Azotobacter vinelandii. Apo-MoFe protein prepared in this way was obtained in sufficient concentrations for detailed catalytic, kinetic, and spectroscopic analyses. Metal analysis and electron paramagnetic resonance spectroscopy (EPR) were used to show that the apo-MoFe protein does not contain FeMo-cofactor. The EPR of the as-isolated apo-MoFe protein is featureless except for a minor S = 1/2 signal probably arising from the presence of either a damaged P cluster or a P cluster precursor. The apo-MoFe protein has an alpha2beta2 subunit composition and can be activated to 80% of the theoretical MoFe protein value by the addition of isolated FeMo-cofactor. Oxidation of the as-isolated apo-MoFe protein by indigodisulfonate was used to elicit the parallel mode EPR signal indicative of the two-electron oxidized form of the P cluster (P2+). The midpoint potential of the PN/P2+ redox couple for the apo-MoFe protein was shown to be shifted by -63 mV when compared to the same redox couple for the intact MoFe protein. Although the apo-MoFe protein is not able to catalyze the reduction of substrates under turnover conditions, it does support the hydrolysis of MgATP at 60% of the rate supported by the MoFe protein when incubated in the presence of Fe protein. The ability of the apo-MoFe protein to specifically interact with the Fe protein was also shown by stopped-flow techniques and by formation of an apo-MoFe protein-Fe protein complex. Finally, the two-electron oxidized form of the apo-MoFe protein could be reduced to the one-electron oxidized form (P1+) in a reaction that required Fe protein and MgATP. These results are interpreted to indicate that the apo-MoFe protein produced in a nifB-deficient genetic background [corrected] contains intact P clusters and P cluster polypeptide environments. Small changes in the electronic properties of P clusters contained within the apo-MoFe protein are most likely caused by slight perturbations in their polypeptide environments.
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Affiliation(s)
- J Christiansen
- Department of Biochemistry, Fralin Biotechnology Center, Virginia Tech, Blacksburg, Virginia 24061, USA
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33
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Cameron LM, Hales BJ. Investigation of CO binding and release from Mo-nitrogenase during catalytic turnover. Biochemistry 1998; 37:9449-56. [PMID: 9649328 DOI: 10.1021/bi972667c] [Citation(s) in RCA: 43] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/08/2023]
Abstract
During enzymatic turnover in the presence of CO, Mo-nitrogenase has been shown to generate two different EPR signals termed lo-CO (PCO = 0.08 atm) and hi-CO (PCO = 0.5 atm). When the formation of hi-CO is monitored under the conditions of very low electron flux, a 2 min lag is observed prior to the initial detection of the signal followed by a near-linear rate of formation during which the S = 3/2 cofactor signal exhibits similar decay kinetics. Increasing the electron flux produces a significant increase in the rate of both the formation of hi-CO and the decay of the S = 3/2 cofactor. These results are interpreted in terms of a state of the enzyme (redox or structural) generated only during turnover which is needed to initially bind CO to the cofactor. Under high electron flux conditions, new EPR inflections are observed at g = 5.78, 5.15 and g = 1.95, 1.81 and tentatively assigned to S = 3/2 and 1/2 states of the CO-bound cofactor and 1 equiv of oxidized P cluster, respectively. Sudden removal of CO from the environment results in the slow decay (>10 min) of both the hi-CO signal and CO inhibition of acetylene reduction activity. The use of ethylene glycol to quench enzymatic activity strongly inhibits the decay of hi-CO (in the presence of CO) and the subsequent decay of lo-CO (after removal of CO) but does not prevent the reversible interconversion hi-CO left and right arrow lo-CO + CO.
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Affiliation(s)
- L M Cameron
- Department of Chemistry, Louisiana State University, Baton Rouge 70803-1804, USA
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34
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Boll M, Albracht SS, Fuchs G. Benzoyl-CoA reductase (dearomatizing), a key enzyme of anaerobic aromatic metabolism. A study of adenosinetriphosphatase activity, ATP stoichiometry of the reaction and EPR properties of the enzyme. EUROPEAN JOURNAL OF BIOCHEMISTRY 1997; 244:840-51. [PMID: 9108255 DOI: 10.1111/j.1432-1033.1997.00840.x] [Citation(s) in RCA: 69] [Impact Index Per Article: 2.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 02/04/2023]
Abstract
An enzyme was recently described, benzoyl-CoA reductase (dearomatizing), which catalyses the ATP-driven reduction of the aromatic ring of benzoyl-CoA yielding a non-aromatic CoA thioester, ADP and phosphate [Boll, M. & Fuchs, G. (1995) Eur. J. Biochem. 234, 921-933]. The 170-kDa enzyme consists of four different subunits and contains approximately 12 Fe and acid-labile sulfur/mol. Benzoyl-CoA reductase exhibits ATPase activity in the absence of substrate. It is shown that only the reduced form of this iron-sulfur protein has ATPase activity. ATPase activity is reversibly lost when the enzyme is oxidized by thionine; reduction of the enzyme fully restores ATPase and ring-reduction activity. 2 mol ATP are hydrolyzed/2 mol electrons transferred in the course of the reaction. The product ADP acts as competitive inhibitor (Ki = 1.1 mM) for ATP in benzoyl-CoA reduction; ADP inhibits ATPase activity to the same extent as ring-reduction activity. EPR investigation of the dithionite-reduced enzyme suggested the presence of two separate [2Fe-2S] clusters and two interacting [4Fe-4S] clusters. Addition of MgATP to the reduced enzyme resulted in a new isotropic signal at g = 5.15 and a weak signal at g = 12; in controls with MgADP only a minor signal at g = 5.15 was observed. The positions, shapes and temperature dependencies of these MgATP-induced signals are indicative for excited states of a S = 7/2 spin multiplet. The [2Fe-2S] signals were not affected by ATP, but one of the [4Fe-4S] clusters became slowly oxidized. Addition of both benzoyl-CoA and MgATP resulted in a major oxidation of the iron-sulfur clusters accompanied by the appearance of some minor signals of unknown origin in the g = 2.037-1.96 region. Neither the benzoyl-CoA plus MgATP-oxidized nor the thionine-oxidized enzyme showed the ATP-dependent formation of the high-spin signals of the reduced enzyme. At present we hypothesize that the S = 7/2 signal is due to an ATP-induced change of one of the [4Fe-4S] clusters. The data suggest that hydrolysis of MgATP is required to activate the enzyme; in the absence of substrate the energy involved in this activation dissipates. MgATP-driven formation of this excited state of the reduced enzyme rather than transfer of electrons from the reduced enzyme to the aromatic substrate appears to be the rate-limiting step in the catalytic cycle. We suggest that the excited state is required to overcome the high activation energy associated with the loss of the aromatic character and/or to render ring reduction irreversible.
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Affiliation(s)
- M Boll
- Mikrobiologie, Institut Biologie II, Universität Freiburg, Germany
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35
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36
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Eady RR. Structureminus signFunction Relationships of Alternative Nitrogenases. Chem Rev 1996; 96:3013-3030. [PMID: 11848850 DOI: 10.1021/cr950057h] [Citation(s) in RCA: 540] [Impact Index Per Article: 19.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
Affiliation(s)
- Robert R. Eady
- Nitrogen Fixation Laboratory, John Innes Institute, Colney Lane Norwich NR4 7UH U.K
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37
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Affiliation(s)
- Barbara K. Burgess
- Department of Molecular Biology and Biochemistry, University of California, Irvine, California 92717-3900, and Nitrogen Fixation Laboratory, John Innes Centre, Norwich Research Park, Colney, Norwich NR4 7UH, U.K
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38
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Eggen RI, van Kranenburg R, Vriesema AJ, Geerling AC, Verhagen MF, Hagen WR, de Vos WM. Carbon monoxide dehydrogenase from Methanosarcina frisia Gö1. Characterization of the enzyme and the regulated expression of two operon-like cdh gene clusters. J Biol Chem 1996; 271:14256-63. [PMID: 8662887 DOI: 10.1074/jbc.271.24.14256] [Citation(s) in RCA: 25] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/01/2023] Open
Abstract
Carbon monoxide dehydrogenase (Cdh) has been anaerobically purified from Methanosarcina frisia Gö1. The enzyme is a Ni2+-, Fe2+-, and S2--containing alpha2beta2 heterotetramer of 214 kDa with a pI of 5.2 and subunits of 94 and 19 kDa. It has a Vmax of 0.3 mmol of CO min-1 mg-1 and Km values for CO and methyl viologen of approximately 0.9 mM and 0.12 mM, respectively. EPR spectroscopy on the reduced enzyme showed two overlapping signals: one indicative for 2 (4Fe-4S)+ clusters and a second signal that is atypical for standard Fe/S clusters. The latter was, together with high-spin EPR signals of the oxidized enzyme tentatively assigned to an Fe/S cluster of high nuclearity.
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Affiliation(s)
- R I Eggen
- Department of Microbiology, Wageningen Agricultural University, Wageningen 6703 CT, The Netherlands
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39
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Duyvis MG, Wassink H, Haaker H. Formation and characterization of a transition state complex of Azotobacter vinelandii nitrogenase. FEBS Lett 1996; 380:233-6. [PMID: 8601431 DOI: 10.1016/0014-5793(96)00019-1] [Citation(s) in RCA: 46] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/31/2023]
Abstract
A stable complex is formed between the nitrogenase proteins of Azotobacter vinelandii, aluminium fluoride and MgADP. All nitrogenase activities are inhibited. The complex formation was found to be reversible. An incubation at 50 degrees C recovers nitrogenase activity. The complex has been characterized with respect to protein and nucleotide composition and redox state of the metal-sulfur clusters. Based on the inhibition by aluminium fluoride together with MgADP, it is proposed that a stable transition state complex with nitrogenase is isolated.
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Affiliation(s)
- M G Duyvis
- Department of Biochemistry, Agricultural University, Wageningen, The Netherlands
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40
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Tittsworth RC, Hales BJ. Oxidative titration of the nitrogenase VFe protein from Azotobacter vinelandii: an example of redox-gated electron flow. Biochemistry 1996; 35:479-87. [PMID: 8555218 DOI: 10.1021/bi951430i] [Citation(s) in RCA: 29] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/31/2023]
Abstract
The nitrogenase VFe protein of Azotobacter vinelandii (Av1') has been shown to exist in two forms called Av1'A, which has a primary alpha beta 2 trimeric structure, and Av1'B, which has an alpha 2 beta 2 tetrameric structure [Blanchard, C. Z., & Hales, B. J. (1996) Biochemistry 35, 472-478]. Both forms exhibit S = 5/2 EPR signals in the as-isolated state that may be assigned to 1-equiv-oxidized P clusters (P+). These signals are abolished by enzymatic reduction with the component 2 protein (Av2'). Stepwise oxidative titrations of enzymatically reduced Av1'B result in the restoration of the S = 5/2 P+ signals and the concurrent decrease of the S = 3/2 vanadium cofactor signal. Further oxidation results in the appearance of an integer spin signal assigned to the 2-equiv-oxidized P cluster (P2+). Unlike the analogous signal previously observed in Mo nitrogenase component 1 (Av1), which arises from an excited state, the integer spin P2+ signal in Av1'B originates from a ground-state doublet. Similar oxidative titrations of enzymatically reduced Av1'A show redox behavior dramatically different from that of Av1'B, as monitored by EPR spectroscopy. We observed spectral evidence for a redox-induced intramolecular electron transfer between the reduced P cluster and the oxidized FeV cofactor cluster during the titrations.
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Affiliation(s)
- R C Tittsworth
- Department of Chemistry, Louisiana State University, Baton Rouge 70803-1804, USA
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41
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Duyvis MG, Wassink H, Haaker H. Pre-steady-state MgATP-dependent proton production and electron transfer by nitrogenase from Azotobacter vinelandii. EUROPEAN JOURNAL OF BIOCHEMISTRY 1994; 225:881-90. [PMID: 7957225 DOI: 10.1111/j.1432-1033.1994.0881b.x] [Citation(s) in RCA: 10] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 01/28/2023]
Abstract
MgATP-dependent pre-steady-state proton production by nitrogenase from Azotobacter vinelandii was studied by monitoring the absorbance changes at 572 nm of the pH indicator o-cresolsulphonphtalein in a weakly buffered solution. The absorbance changes are characterized by a constant phase, a single exponential decrease and a linear decrease. The observed rate constant for the single exponential MgATP-dependent proton production by reduced nitrogenase proteins at 20.0 degrees C is 14 +/- 4 s-1. No proton production with a rate constant comparable to the observed rate constant of electron transfer (kobs approximately 100 s-1) was detected. The extent of the observed MgATP-dependent proton production is determined by the redox state of the nitrogenase proteins before mixing with MgATP; less protons are produced when more electrons are transferred from the Fe protein to the MoFe protein. Values of 2.7 +/- 0.3 mol H+produced/mol MoFe protein with oxidized Fe protein, and 1.1 +/- 0.1 mol H+produced/mol MoFe protein with reduced Fe protein, were found. The data are interpreted to mean that protons are taken up after electron transfer from the Fe protein to the MoFe protein; the ratio electrons(transferred)/H-uptake was calculated to be 1.2 +/- 0.2. After mixing the nitrogenase proteins with MgADP, proton production takes place as well. The proton-production curve did not have a constant phase and the observed rate constant of the single exponential reaction is higher, compared to MgATP-dependent proton production (kobs approximately 35 s-1). The amount of protons produced depends also on the redox state of the Fe protein; no proton production was observed with the oxidized Fe protein; with dithionite-reduced Fe protein a value of 3.1 +/- 0.4 mol H+produced/mol MoFe protein was found (or 0.5 +/- 0.1 mol H+/mol Fe protein). Similar results were obtained when only the Fe protein was mixed with MgADP, but the observed absorbance changes were smaller; mixing of dithionite-reduced Fe protein with MgADP resulted in the production of 0.17 +/- 0.05 mol H+/mol Fe protein. All reported absorbance changes were absent when the experiments were performed in a buffered solution. The series of events that occur after mixing of the nitrogenase proteins with MgATP will be presented and discussed. In the case of the reduced Fe protein, electron transfer takes place at a rate of 100 s-1, which is followed by H+ production (kobs approximately 14 s-1). When there is no electron transfer (oxidized Fe protein) the rate constant of the MgATP-induced proton production decreases.(ABSTRACT TRUNCATED AT 400 WORDS)
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Affiliation(s)
- M G Duyvis
- Department of Biochemistry, Agricultural University, Wageningen, The Netherlands
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42
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Mössbauer characterization of the metal clusters in Azotobacter vinelandii nitrogenase VFe protein. J Biol Chem 1994. [DOI: 10.1016/s0021-9258(17)31909-9] [Citation(s) in RCA: 41] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/24/2022] Open
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43
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van den Berg WA, Stevens AA, Verhagen MF, van Dongen WM, Hagen WR. Overproduction of the prismane protein from Desulfovibrio desulfuricans ATCC 27774 in Desulfovibrio vulgaris (Hildenborough) and EPR spectroscopy of the [6Fe-6S] cluster in different redox states. BIOCHIMICA ET BIOPHYSICA ACTA 1994; 1206:240-6. [PMID: 8003528 DOI: 10.1016/0167-4838(94)90214-3] [Citation(s) in RCA: 26] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 01/28/2023]
Abstract
The Desulfovibrio desulfuricans ATCC 27774 prismane protein was isolated from a Desulfovibrio vulgaris (Hildenborough) strain that contained the gene for this protein in expression vector pSUP104. A redox titration demonstrated that the [Fe-S] cluster in this protein may attain four different redox states, indicated as +3, +4, +5 and +6, with midpoint potentials for the transitions of approx. -220, +50/-25 and +370 mV, respectively. EPR spectra of the protein in the various redox states are reminiscent of those of the D. vulgaris prismane protein (Pierik et al. (1992) Eur. J. Biochem. 206, 705-719), but differ in details. In the +5-state, virtually all the iron is in a S = 9/2 spin state, indicative for a cluster that is more complex than common [4Fe-4S] or [2Fe-2S] clusters. Similarity of the EPR spectrum of the protein in the +3-state with those of inorganic [6Fe-6S] model compounds suggests that the cluster in the protein is also [6Fe-6S]. In the +4-state of the protein a broad signal due to an integer-spin system can be detected with normal-mode EPR. A dramatic sharpening-up and increase of intensity of this band (g = 14.7) is observed with parallel-mode EPR. In accordance with the chemically determined iron content of the protein (6.0 +/- 0.45 moles of iron/mole of protein), the spectroscopic data indicate one [6Fe-6S] cluster in this protein. We did not find evidence for a previous claim (Moura et al. (1992) J. Biol. Chem. 267, 4489-4496) that the D. desulfuricans protein contains two [6Fe-6S] clusters.
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Affiliation(s)
- W A van den Berg
- Department of Biochemistry, Wageningen Agricultural University, The Netherlands
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44
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Lowe DJ, Fisher K, Thorneley RN. Klebsiella pneumoniae nitrogenase: pre-steady-state absorbance changes show that redox changes occur in the MoFe protein that depend on substrate and component protein ratio; a role for P-centres in reducing dinitrogen? Biochem J 1993; 292 ( Pt 1):93-8. [PMID: 8389132 PMCID: PMC1134273 DOI: 10.1042/bj2920093] [Citation(s) in RCA: 60] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/30/2023]
Abstract
The pre-steady-state absorbance changes that occur during the first 0.6 s of reaction of the nitrogenase of Klebsiella pneumoniae can be simulated by associating redox changes with the different states of the MoFe protein described by our published kinetic model for nitrogenase [Lowe and Thorneley (1984) Biochem. J. 224, 877-886]. When the substrate is changed, from H+ to C2H2 (acetylene) or N2, or the nitrogenase component protein ratio is altered, these pre-steady-state absorbance changes are affected in a manner that is quantitatively predicted by our model. The results, together with parallel e.p.r. studies, are interpreted as showing that the P-clusters become oxidized when the MoFe protein is in the state where bound N2 is irreversibly committed to being reduced and is protonated to the hydrazido(2-) level.
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Affiliation(s)
- D J Lowe
- AFRC Institute of Plant Science Research, Nitrogen Fixation Laboratory, University of Sussex, Brighton, U.K
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45
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Pierik AJ, Wassink H, Haaker H, Hagen WR. Redox properties and EPR spectroscopy of the P clusters of Azotobacter vinelandii MoFe protein. EUROPEAN JOURNAL OF BIOCHEMISTRY 1993; 212:51-61. [PMID: 8383042 DOI: 10.1111/j.1432-1033.1993.tb17632.x] [Citation(s) in RCA: 110] [Impact Index Per Article: 3.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 01/30/2023]
Abstract
In Azotobacter vinelandii MoFe protein the oxidation of the P clusters to the S = 7/2 state is associated with a redox reaction with Em,7.5 = +90 +/- 10 mV (vs the normal hydrogen electrode), n = 1. A concomitant redox process is observed for a rhombic S = 1/2 EPR signal with g = 1.97, 1.88 and 1.68. This indicates that both S = 1/2 and S = 7/2 signals are associated with oxidized P clusters occurring as a physical mixture of spin states. The maximal intensity of the S = 1/2 and S = 7/2 signals in the mediated equilibrium redox titration is similar if not identical to that of solid-thionine-treated samples. Summation of the spin concentration of the S = 1/2 spin state (0.25 +/- 0.03 spin/alpha 2 beta 2) and the S = 7/2 spin state (1.3 +/- 0.2 spin/alpha 2 beta 2) confirms that the MoFe protein has absolutely no more than two P clusters. In spectra of enzyme fixed at potentials around -100 mV a very low-intensity g = 12 EPR signal was discovered. In parallel-mode EPR the signal sharpened and increased > 10-fold in intensity which allowed us to assign the g = 12 signal to a non-Kramers system (presumably S = 3). In contrast with the non-Kramers EPR signals of various metalloproteins and inorganic compounds, the sharp absorption-shaped g = 12 signal is not significantly broadened into zero field, implying that the zero field splitting of the non-Kramers doublet is smaller than the X-band microwave quantum. The temperature dependence of this g = 12 EPR signal indicates that it is from an excited state within the integer spin multiplet. A bell-shaped titration curve with Em,7.5 = -307 +/- 30 mV and +81 +/- 30 mV midpoint potentials is found for the g = 12 EPR signal. We propose that this signal represents an intermediate redox state of the P clusters between the diamagnetic, dithionite-reduced and the fully oxidized S = 7/2 and S = 1/2 state. Redox transitions of two electrons (-307 +/- 30 mV) and one electron (+90 +/- 10 mV) link the sequence S = 0<-->S = 3<-->(S = 7/2 and S = 1/2). We propose to name the latter paramagnetic oxidation states of the P clusters in nitrogenase POX1 and POX2, and to retain PN for the diamagnetic native redox state.(ABSTRACT TRUNCATED AT 400 WORDS)
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Affiliation(s)
- A J Pierik
- Department of Biochemistry, Wageningen Agricultural University, The Netherlands
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46
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Bolin JT, Ronco AE, Morgan TV, Mortenson LE, Xuong NH. The unusual metal clusters of nitrogenase: structural features revealed by x-ray anomalous diffraction studies of the MoFe protein from Clostridium pasteurianum. Proc Natl Acad Sci U S A 1993; 90:1078-82. [PMID: 8430077 PMCID: PMC45814 DOI: 10.1073/pnas.90.3.1078] [Citation(s) in RCA: 87] [Impact Index Per Article: 2.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/30/2023] Open
Abstract
Nitrogenase (EC 1.18.6.1) catalyzes the conversion of dinitrogen to ammonia, the central reaction of biological nitrogen fixation. X-ray anomalous diffraction data were analyzed to probe the structures of the metal clusters bound by nitrogenase MoFe protein. In addition to one FeMo cofactor, each half-molecule of MoFe protein binds one large FeS cluster of a type not previously observed in a protein. The FeS cluster contains roughly eight Fe atoms, comprises two subclusters, and is separated from the FeMo cofactor by an edge-to-edge distance of 14 A. The inorganic framework of the FeMo cofactor is not resolved into subclusters, but the Mo atom is located at its periphery. FeMo cofactors in different half-molecules are 70 A apart and cannot promote binuclear activation of dinitrogen by two Mo atoms.
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Affiliation(s)
- J T Bolin
- Department of Biological Sciences, Purdue University, West Lafayette, IN 47907
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47
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The Crystal Structure of the Nitrogenase MoFe Protein from Clostridium Pasteurianum. NEW HORIZONS IN NITROGEN FIXATION 1993. [DOI: 10.1007/978-94-017-2416-6_10] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 12/23/2022]
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48
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49
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Rees DC, Chan MK, Kim J. Structure and Function of Nitrogenase. ADVANCES IN INORGANIC CHEMISTRY 1993. [DOI: 10.1016/s0898-8838(08)60182-8] [Citation(s) in RCA: 77] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 11/26/2022]
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50
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Stokkermans JP, Houba PH, Pierik AJ, Hagen WR, van Dongen WM, Veeger C. Overproduction of prismane protein in Desulfovibrio vulgaris (Hildenborough): evidence for a second S = 1/2-spin system in the one-electron reduced state. EUROPEAN JOURNAL OF BIOCHEMISTRY 1992; 210:983-8. [PMID: 1336462 DOI: 10.1111/j.1432-1033.1992.tb17503.x] [Citation(s) in RCA: 19] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 12/26/2022]
Abstract
The gene encoding the prismane protein from Desulfovibrio vulgaris (Hildenborough) was inserted into broad-host-range vector pSUP104. The recombinant plasmid, pJSP104, was transferred to D. vulgaris by conjugal plasmid transfer. In the transconjugant D. vulgaris cells the prismane protein was 25-fold overproduced. The overproduced prismane protein was characterized by molecular mass, isoelectric point, iron content and spectroscopical properties. Both the iron content and the ultraviolet/visible spectrum are identical to the wild-type protein indicating that iron incorporation in the overproduced protein is complete. EPR spectra of the dithionite-reduced form of the overproduced protein indicated that the Fe-S cluster might occur in a similar structure as found in inorganic model compounds containing a [6Fe-6S] prismane core. The as-isolated overproduced protein showed the presence of a second S = 1/2 spin system that was also detected in the corresponding prismane protein from D. desulfuricans (ATCC 27774), but not in the protein from wild-type D. vulgaris. This additional signal was irreversibly transformed to the 'wild-type' high-spin and low-spin systems upon two reduction/re-oxidation cycles. It is shown that the EPR spectroscopy of the overproduced prismane protein is very similar to that of the D. desulfuricans enzyme and, with the exception of the second S = 1/2 spin system, to that of the prismane protein from wild-type D. vulgaris. Contrary to claims for the D. desulfuricans protein, it is shown here that all data can be fully explained assuming a single [6Fe-6S] cluster, that might be titrated into four different redox states and occurs in up to three different spin systems in the one-electron reduced state.
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Affiliation(s)
- J P Stokkermans
- Department of Biochemistry, Agricultural University, Wageningen, The Netherlands
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