1
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Schmidt FV, Schulz L, Zarzycki J, Prinz S, Oehlmann NN, Erb TJ, Rebelein JG. Structural insights into the iron nitrogenase complex. Nat Struct Mol Biol 2024; 31:150-158. [PMID: 38062208 PMCID: PMC10803253 DOI: 10.1038/s41594-023-01124-2] [Citation(s) in RCA: 4] [Impact Index Per Article: 4.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/30/2023] [Accepted: 09/12/2023] [Indexed: 01/24/2024]
Abstract
Nitrogenases are best known for catalyzing the reduction of dinitrogen to ammonia at a complex metallic cofactor. Recently, nitrogenases were shown to reduce carbon dioxide (CO2) and carbon monoxide to hydrocarbons, offering a pathway to recycle carbon waste into hydrocarbon products. Among the three nitrogenase isozymes, the iron nitrogenase has the highest wild-type activity for the reduction of CO2, but the molecular architecture facilitating these activities has remained unknown. Here, we report a 2.35-Å cryogenic electron microscopy structure of the ADP·AlF3-stabilized iron nitrogenase complex from Rhodobacter capsulatus, revealing an [Fe8S9C-(R)-homocitrate] cluster in the active site. The enzyme complex suggests that the iron nitrogenase G subunit is involved in cluster stabilization and substrate channeling and confers specificity between nitrogenase reductase and catalytic component proteins. Moreover, the structure highlights a different interface between the two catalytic halves of the iron and the molybdenum nitrogenase, potentially influencing the intrasubunit 'communication' and thus the nitrogenase mechanism.
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Affiliation(s)
- Frederik V Schmidt
- Microbial Metalloenzymes Research Group, Max Planck Institute for Terrestrial Microbiology, Marburg, Germany
| | - Luca Schulz
- Department of Biochemistry and Synthetic Metabolism, Max Planck Institute for Terrestrial Microbiology, Marburg, Germany
| | - Jan Zarzycki
- Department of Biochemistry and Synthetic Metabolism, Max Planck Institute for Terrestrial Microbiology, Marburg, Germany
| | - Simone Prinz
- Central Electron Microscopy Facility, Max Planck Institute of Biophysics, Frankfurt am Main, Germany
| | - Niels N Oehlmann
- Microbial Metalloenzymes Research Group, Max Planck Institute for Terrestrial Microbiology, Marburg, Germany
| | - Tobias J Erb
- Department of Biochemistry and Synthetic Metabolism, Max Planck Institute for Terrestrial Microbiology, Marburg, Germany
| | - Johannes G Rebelein
- Microbial Metalloenzymes Research Group, Max Planck Institute for Terrestrial Microbiology, Marburg, Germany.
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2
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Martin Del Campo JS, Rigsbee J, Bueno Batista M, Mus F, Rubio LM, Einsle O, Peters JW, Dixon R, Dean DR, Dos Santos PC. Overview of physiological, biochemical, and regulatory aspects of nitrogen fixation in Azotobacter vinelandii. Crit Rev Biochem Mol Biol 2023; 57:492-538. [PMID: 36877487 DOI: 10.1080/10409238.2023.2181309] [Citation(s) in RCA: 7] [Impact Index Per Article: 7.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 03/07/2023]
Abstract
Understanding how Nature accomplishes the reduction of inert nitrogen gas to form metabolically tractable ammonia at ambient temperature and pressure has challenged scientists for more than a century. Such an understanding is a key aspect toward accomplishing the transfer of the genetic determinants of biological nitrogen fixation to crop plants as well as for the development of improved synthetic catalysts based on the biological mechanism. Over the past 30 years, the free-living nitrogen-fixing bacterium Azotobacter vinelandii emerged as a preferred model organism for mechanistic, structural, genetic, and physiological studies aimed at understanding biological nitrogen fixation. This review provides a contemporary overview of these studies and places them within the context of their historical development.
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Affiliation(s)
| | - Jack Rigsbee
- Department of Chemistry, Wake Forest University, Winston-Salem, NC, USA
| | | | - Florence Mus
- Institute of Biological Chemistry, Washington State University, Pullman, WA, USA
| | - Luis M Rubio
- Centro de Biotecnología y Genómica de Plantas, Universidad Politécnica de Madrid (UPM) - Instituto Nacional de Investigación y Tecnología Agraria y Alimentaria (INIA/CSIC), Pozuelo de Alarcón, Spain
| | - Oliver Einsle
- Department of Biochemistry, University of Freiburg, Freiburg, Germany
| | - John W Peters
- Institute of Biological Chemistry, Washington State University, Pullman, WA, USA
| | - Ray Dixon
- Department of Molecular Microbiology, John Innes Centre, Norwich, UK
| | - Dennis R Dean
- Department of Biochemistry, Virginia Tech, Blacksburg, VA, USA
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3
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Decamps L, Rice DB, DeBeer S. An Fe 6 C Core in All Nitrogenase Cofactors. Angew Chem Int Ed Engl 2022; 61:e202209190. [PMID: 35975943 PMCID: PMC9826452 DOI: 10.1002/anie.202209190] [Citation(s) in RCA: 4] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/23/2022] [Indexed: 01/11/2023]
Abstract
The biological process of dinitrogen reduction to ammonium occurs at the cofactors of nitrogenases, the only enzymes that catalyze this challenging chemical reaction. Three types of nitrogenases have been described, named according to the heterometal in their cofactor: molybdenum, vanadium or iron nitrogenases. Spectroscopic and structural characterization allowed the unambiguous identification of the cofactors of molybdenum and vanadium nitrogenases and revealed a central μ6 -carbide in both of them. Although genetic studies suggested that the cofactor of the iron nitrogenase contains a similar Fe6 C core, this has not been experimentally demonstrated. Here we report Valence-to-Core X-ray Emission Spectroscopy providing experimental evidence that this cofactor contains a carbide, thereby making the Fe6 C core a feature of all nitrogenase cofactors.
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Affiliation(s)
- Laure Decamps
- Department of Inorganic SpectroscopyMax Planck Institute for Chemical Energy ConversionStiftstrasse 34–3645470Mülheim an derRuhrGermany
| | - Derek B. Rice
- Department of Inorganic SpectroscopyMax Planck Institute for Chemical Energy ConversionStiftstrasse 34–3645470Mülheim an derRuhrGermany
| | - Serena DeBeer
- Department of Inorganic SpectroscopyMax Planck Institute for Chemical Energy ConversionStiftstrasse 34–3645470Mülheim an derRuhrGermany
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4
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Decamps L, Rice D, DeBeer S. An Fe6C Core in All Nitrogenase Cofactors. Angew Chem Int Ed Engl 2022. [DOI: 10.1002/ange.202209190] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/11/2022]
Affiliation(s)
- Laure Decamps
- Max-Planck-Institute for Chemical Energy Conversion: Max-Planck-Institut fur chemische Energiekonversion Inorganic Spectroscopy GERMANY
| | - Derek Rice
- Max-Planck-Institute for Chemical Energy Conversion: Max-Planck-Institut fur chemische Energiekonversion Inorganic Spectroscopy GERMANY
| | - Serena DeBeer
- MPI CEC Molecular Theory and Spectroscopy Stidtstr. 34-36 45470 Muelheim an der Ruhr GERMANY
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5
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Lukoyanov DA, Harris DF, Yang ZY, Pérez-González A, Dean DR, Seefeldt LC, Hoffman BM. The One-Electron Reduced Active-Site FeFe-Cofactor of Fe-Nitrogenase Contains a Hydride Bound to a Formally Oxidized Metal-Ion Core. Inorg Chem 2022; 61:5459-5464. [PMID: 35357830 DOI: 10.1021/acs.inorgchem.2c00180] [Citation(s) in RCA: 11] [Impact Index Per Article: 5.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
Abstract
The nitrogenase active-site cofactor must accumulate 4e-/4H+ (E4(4H) state) before N2 can bind and be reduced. Earlier studies demonstrated that this E4(4H) state stores the reducing-equivalents as two hydrides, with the cofactor metal-ion core formally at its resting-state redox level. This led to the understanding that N2 binding is mechanistically coupled to reductive-elimination of the two hydrides that produce H2. The state having acquired 2e-/2H+ (E2(2H)) correspondingly contains one hydride with a resting-state core redox level. How the cofactor accommodates addition of the first e-/H+ (E1(H) state) is unknown. The Fe-nitrogenase FeFe-cofactor was used to address this question because it is EPR-active in the E1(H) state, unlike the FeMo-cofactor of Mo-nitrogenase, thus allowing characterization by EPR spectroscopy. The freeze-trapped E1(H) state of Fe-nitrogenase shows an S = 1/2 EPR spectrum with g = [1.965, 1.928, 1.779]. This state is photoactive, and under 12 K cryogenic intracavity, 450 nm photolysis converts to a new and likewise photoactive S = 1/2 state (denoted E1(H)*) with g = [2.009, 1.950, 1.860], which results in a photostationary state, with E1(H)* relaxing to E1(H) at temperatures above 145 K. An H/D kinetic isotope effect of 2.4 accompanies the 12 K E1(H)/E1(H)* photointerconversion. These observations indicate that the addition of the first e-/H+ to the FeFe-cofactor of Fe-nitrogenase produces an Fe-bound hydride, not a sulfur-bound proton. As a result, the cluster metal-ion core is formally one-electron oxidized relative to the resting state. It is proposed that this behavior applies to all three nitrogenase isozymes.
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Affiliation(s)
- Dmitriy A Lukoyanov
- Department of Chemistry, Northwestern University, Evanston, Illinois 60208, United States
| | - Derek F Harris
- Department of Chemistry and Biochemistry, Utah State University, Logan, Utah 84322, United States
| | - Zhi-Yong Yang
- Department of Chemistry and Biochemistry, Utah State University, Logan, Utah 84322, United States
| | - Ana Pérez-González
- Department of Biochemistry, Virginia Polytechnic Institute and State University, Blacksburg, Virginia 24061, United States
| | - Dennis R Dean
- Department of Biochemistry, Virginia Polytechnic Institute and State University, Blacksburg, Virginia 24061, United States
| | - Lance C Seefeldt
- Department of Chemistry and Biochemistry, Utah State University, Logan, Utah 84322, United States
| | - Brian M Hoffman
- Department of Chemistry, Northwestern University, Evanston, Illinois 60208, United States
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6
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Gee LB, Scott AD, Dapper CH, Newton WE, Cramer SP. Carbon monoxide binding to α-R277H Mo-nitrogenase – Evidence for multiple pH-dependent species from IR-monitored photolysis. J Inorg Biochem 2022; 232:111806. [DOI: 10.1016/j.jinorgbio.2022.111806] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/30/2021] [Revised: 02/28/2022] [Accepted: 03/21/2022] [Indexed: 10/18/2022]
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7
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Pérez‐González A, Jimenez‐Vicente E, Salinero‐Lanzarote A, Harris DF, Seefeldt LC, Dean DR. AnfO
controls fidelity of nitrogenase
FeFe
protein maturation by preventing misincorporation of
FeV
‐cofactor. Mol Microbiol 2022; 117:1080-1088. [PMID: 35220629 PMCID: PMC9310841 DOI: 10.1111/mmi.14890] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/13/2021] [Revised: 02/22/2022] [Accepted: 02/23/2022] [Indexed: 11/26/2022]
Abstract
Azotobacter vinelandii produces three genetically distinct, but structurally and mechanistically similar nitrogenase isozymes designated as Mo‐dependent, V‐dependent, or Fe‐only based on the heterometal contained within their associated active site cofactors. These catalytic cofactors, which provide the site for N2 binding and reduction, are, respectively, designated as FeMo‐cofactor, FeV‐cofactor, and FeFe‐cofactor. Fe‐only nitrogenase is a poor catalyst for N2 fixation, when compared to the Mo‐dependent and V‐dependent nitrogenases and is only produced when neither Mo nor V is available. Under conditions favoring the production of Fe‐only nitrogenase a gene product designated AnfO preserves the fidelity of Fe‐only nitrogenase by preventing the misincorporation of FeV‐cofactor, which results in the accumulation of a hybrid enzyme that cannot reduce N2. These results are interpreted to indicate that AnfO controls the fidelity of Fe‐only nitrogenase maturation during the physiological transition from conditions that favor V‐dependent nitrogenase utilization to Fe‐only nitrogenase utilization to support diazotrophic growth.
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Affiliation(s)
| | | | - Alvaro Salinero‐Lanzarote
- Centro de Biotecnología y Genómica de Plantas, Universidad Politécnica de Madrid, Instituto Nacional de Investigación y Tecnología Agraria y Alimentaria, Pozuelo de Alarcón, 28223 Madrid Spain
| | - Derek F. Harris
- Department of Chemistry and Biochemistry Utah State University Logan UT USA
| | - Lance C. Seefeldt
- Department of Chemistry and Biochemistry Utah State University Logan UT USA
| | - Dennis R. Dean
- Department of Biochemistry, Virginia Tech, Blacksburg Virginia USA
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8
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Spiller N, Bjornsson R, DeBeer S, Neese F. Carbon Monoxide Binding to the Iron-Molybdenum Cofactor of Nitrogenase: a Detailed Quantum Mechanics/Molecular Mechanics Investigation. Inorg Chem 2021; 60:18031-18047. [PMID: 34767349 PMCID: PMC8653219 DOI: 10.1021/acs.inorgchem.1c02649] [Citation(s) in RCA: 5] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Abstract
Carbon monoxide (CO) is a well-known inhibitor of nitrogenase activity. Under turnover conditions, CO binds to FeMoco, the active site of Mo nitrogenase. Time-resolved IR measurements suggest an initial terminal CO at 1904 cm-1 that converts to a bridging CO at 1715 cm-1, and an X-ray structure shows that CO can displace one of the bridging belt sulfides of FeMoco. However, the CO-binding redox state(s) of FeMoco (En) and the role of the protein environment in stabilizing specific CO-bound intermediates remain elusive. In this work, we carry out an in-depth analysis of the CO-FeMoco interaction based on quantum chemical calculations addressing different aspects of the electronic structure. (1) The local electronic structure of the Fe-CO bond is studied through diamagnetically substituted FeMoco. (2) A cluster model of FeMoco within a polarizable continuum illustrates how CO binding may affect the spin-coupling between the metal centers. (3) A QM/MM model incorporates the explicit influence of the amino acid residues surrounding FeMoco in the MoFe protein. The QM/MM model predicts both a terminal and a bridging CO in the E1 redox state. The scaled calculated CO frequencies (1922 and 1716 cm-1, respectively) are in good agreement with the experimentally observed IR bands supporting CO binding to the E1 state. Alternatively, an E2 state QM/MM model, which has the same atomic structure as the CO-bound X-ray structure, features a semi-bridging CO with a scaled calculated frequency (1718 cm-1) similar to the bridging CO in the E1 model.
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Affiliation(s)
- Nico Spiller
- Max-Planck-Institut für Kohlenforschung, Kaiser-Wilhelm-Platz 1, 45470 Mülheim an der Ruhr, Germany
| | - Ragnar Bjornsson
- Max Planck Institute for Chemical Energy Conversion, Stiftstr 34-36, 45470 Mülheim an der Ruhr, Germany
| | - Serena DeBeer
- Max Planck Institute for Chemical Energy Conversion, Stiftstr 34-36, 45470 Mülheim an der Ruhr, Germany
| | - Frank Neese
- Max-Planck-Institut für Kohlenforschung, Kaiser-Wilhelm-Platz 1, 45470 Mülheim an der Ruhr, Germany
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9
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Pessoa JC, Santos MF, Correia I, Sanna D, Sciortino G, Garribba E. Binding of vanadium ions and complexes to proteins and enzymes in aqueous solution. Coord Chem Rev 2021. [DOI: 10.1016/j.ccr.2021.214192] [Citation(s) in RCA: 17] [Impact Index Per Article: 5.7] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/20/2022]
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10
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Oehlmann NN, Rebelein JG. The Conversion of Carbon Monoxide and Carbon Dioxide by Nitrogenases. Chembiochem 2021; 23:e202100453. [PMID: 34643977 PMCID: PMC9298215 DOI: 10.1002/cbic.202100453] [Citation(s) in RCA: 5] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/27/2021] [Revised: 10/13/2021] [Indexed: 12/02/2022]
Abstract
Nitrogenases are the only known family of enzymes that catalyze the reduction of molecular nitrogen (N2) to ammonia (NH3). The N2 reduction drives biological nitrogen fixation and the global nitrogen cycle. Besides the conversion of N2, nitrogenases catalyze a whole range of other reductions, including the reduction of the small gaseous substrates carbon monoxide (CO) and carbon dioxide (CO2) to hydrocarbons. However, it remains an open question whether these ‘side reactivities’ play a role under environmental conditions. Nonetheless, these reactivities and particularly the formation of hydrocarbons have spurred the interest in nitrogenases for biotechnological applications. There are three different isozymes of nitrogenase: the molybdenum and the alternative vanadium and iron‐only nitrogenase. The isozymes differ in their metal content, structure, and substrate‐dependent activity, despite their homology. This minireview focuses on the conversion of CO and CO2 to methane and higher hydrocarbons and aims to specify the differences in activity between the three nitrogenase isozymes.
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Affiliation(s)
- Niels N Oehlmann
- Max Planck Institute for Terrestrial Microbiology, Karl-von-Frisch-Straße 10, 35043, Marburg, Germany
| | - Johannes G Rebelein
- Max Planck Institute for Terrestrial Microbiology, Karl-von-Frisch-Straße 10, 35043, Marburg, Germany
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11
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Specificity of NifEN and VnfEN for the Assembly of Nitrogenase Active Site Cofactors in Azotobacter vinelandii. mBio 2021; 12:e0156821. [PMID: 34281397 PMCID: PMC8406325 DOI: 10.1128/mbio.01568-21] [Citation(s) in RCA: 4] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022] Open
Abstract
The nitrogen-fixing microbe Azotobacter vinelandii has the ability to produce three genetically distinct, but mechanistically similar, components that catalyze nitrogen fixation. For two of these components, the Mo-dependent and V-dependent components, their corresponding metal-containing active site cofactors, designated FeMo-cofactor and FeV-cofactor, respectively, are preformed on separate molecular scaffolds designated NifEN and VnfEN, respectively. From prior studies, and the present work, it is now established that neither of these scaffolds can replace the other with respect to their in vivo cofactor assembly functions. Namely, a strain inactivated for NifEN cannot produce active Mo-dependent nitrogenase nor can a strain inactivated for VnfEN produce an active V-dependent nitrogenase. It is therefore proposed that metal specificities for FeMo-cofactor and FeV-cofactor formation are supplied by their respective assembly scaffolds. In the case of the third, Fe-only component, its associated active site cofactor, designated FeFe-cofactor, requires neither the NifEN nor VnfEN assembly scaffold for its formation. Furthermore, there are no other genes present in A. vinelandii that encode proteins having primary structure similarity to either NifEN or VnfEN. It is therefore concluded that FeFe-cofactor assembly is completed within its cognate catalytic protein partner without the aid of an intermediate assembly site. IMPORTANCE Biological nitrogen fixation is a complex process involving the nitrogenases. The biosynthesis of an active nitrogenase involves a large number of genes and the coordinated function of their products. Understanding the details of the assembly and activation of the different nitrogen fixation components, in particular the simplest one known so far, the Fe-only nitrogenase, would contribute to the goal of transferring the necessary genetic elements of bacterial nitrogen fixation to cereal crops to endow them with the capacity for self-fertilization. In this work, we show that there is no need for a scaffold complex for the assembly of the FeFe-cofactor, which provides the active site for Fe-only nitrogenase. These results are in agreement with previously reported genetic reconstruction experiments using a non-nitrogen-fixing microbe. In aggregate, these findings provide a high degree of confidence that the Fe-only system represents the simplest and, therefore, most attractive target for mobilizing nitrogen fixation into plants.
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12
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Rohde M, Laun K, Zebger I, Stripp ST, Einsle O. Two ligand-binding sites in CO-reducing V nitrogenase reveal a general mechanistic principle. SCIENCE ADVANCES 2021; 7:7/22/eabg4474. [PMID: 34049880 PMCID: PMC8163085 DOI: 10.1126/sciadv.abg4474] [Citation(s) in RCA: 24] [Impact Index Per Article: 8.0] [Reference Citation Analysis] [Abstract] [Grants] [Track Full Text] [Download PDF] [Figures] [Subscribe] [Scholar Register] [Received: 01/06/2021] [Accepted: 04/14/2021] [Indexed: 06/12/2023]
Abstract
Besides its role in biological nitrogen fixation, vanadium-containing nitrogenase also reduces carbon monoxide (CO) to hydrocarbons, in analogy to the industrial Fischer-Tropsch process. The protein yields 93% of ethylene (C2H4), implying a C-C coupling step that mandates the simultaneous binding of two CO at the active site FeV cofactor. Spectroscopic data indicated multiple CO binding events, but structural analyses of Mo and V nitrogenase only confirmed a single site. Here, we report the structure of a two CO-bound state of V nitrogenase at 1.05 Å resolution, with one μ-bridging and one terminal CO molecule. This additional, specific ligand binding site suggests a mechanistic route for CO reduction and hydrocarbon formation, as well as a second access pathway for protons required during the reaction. Moreover, carbonyls are strong-field ligands that are chemically similar to mechanistically relevant hydrides that may be formed and used in a fully analogous fashion.
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Affiliation(s)
- Michael Rohde
- Institute for Biochemistry, University of Freiburg, Albertstrasse 21, 79104 Freiburg, Germany
| | - Konstantin Laun
- Institute of Chemistry, Technical University of Berlin, Straße des 17. Juni 135, 10623 Berlin, Germany
| | - Ingo Zebger
- Institute of Chemistry, Technical University of Berlin, Straße des 17. Juni 135, 10623 Berlin, Germany
| | - Sven T Stripp
- Institute of Experimental Physics, Department of Physics, Free University of Berlin, Arnimallee 14, 14195 Berlin, Germany
| | - Oliver Einsle
- Institute for Biochemistry, University of Freiburg, Albertstrasse 21, 79104 Freiburg, Germany.
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13
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Yang ZY, Jimenez-Vicente E, Kallas H, Lukoyanov DA, Yang H, Martin Del Campo JS, Dean DR, Hoffman BM, Seefeldt LC. The electronic structure of FeV-cofactor in vanadium-dependent nitrogenase. Chem Sci 2021; 12:6913-6922. [PMID: 34123320 PMCID: PMC8153082 DOI: 10.1039/d0sc06561g] [Citation(s) in RCA: 14] [Impact Index Per Article: 4.7] [Reference Citation Analysis] [Abstract] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/30/2020] [Accepted: 03/26/2021] [Indexed: 01/01/2023] Open
Abstract
The electronic structure of the active-site metal cofactor (FeV-cofactor) of resting-state V-dependent nitrogenase has been an open question, with earlier studies indicating that it exhibits a broad S = 3/2 EPR signal (Kramers state) having g values of ∼4.3 and 3.8, along with suggestions that it contains metal-ions with valencies [1V3+, 3Fe3+, 4Fe2+]. In the present work, genetic, biochemical, and spectroscopic approaches were combined to reveal that the EPR signals previously assigned to FeV-cofactor do not correlate with active VFe-protein, and thus cannot arise from the resting-state of catalytically relevant FeV-cofactor. It, instead, appears resting-state FeV-cofactor is either diamagnetic, S = 0, or non-Kramers, integer-spin (S = 1, 2 etc.). When VFe-protein is freeze-trapped during high-flux turnover with its natural electron-donating partner Fe protein, conditions which populate reduced states of the FeV-cofactor, a new rhombic S = 1/2 EPR signal from such a reduced state is observed, with g = [2.18, 2.12, 2.09] and showing well-defined 51V (I = 7/2) hyperfine splitting, a iso = 110 MHz. These findings indicate a different assignment for the electronic structure of the resting state of FeV-cofactor: S = 0 (or integer-spin non-Kramers state) with metal-ion valencies, [1V3+, 4Fe3+, 3Fe2+]. Our findings suggest that the V3+ does not change valency throughout the catalytic cycle.
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Affiliation(s)
- Zhi-Yong Yang
- Department of Chemistry and Biochemistry, Utah State University Logan UT 84322 USA +1-435-797-3964
| | | | - Hayden Kallas
- Department of Chemistry and Biochemistry, Utah State University Logan UT 84322 USA +1-435-797-3964
| | - Dmitriy A Lukoyanov
- Department of Chemistry, Northwestern University Evanston IL 60208 USA +1-847-491-3104
| | - Hao Yang
- Department of Chemistry, Northwestern University Evanston IL 60208 USA +1-847-491-3104
| | | | - Dennis R Dean
- Department of Biochemistry, Virginia Tech Blacksburg VA 24061 USA +1-540-231-5895
| | - Brian M Hoffman
- Department of Chemistry, Northwestern University Evanston IL 60208 USA +1-847-491-3104
| | - Lance C Seefeldt
- Department of Chemistry and Biochemistry, Utah State University Logan UT 84322 USA +1-435-797-3964
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