1
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Lewis LC, Sanabria-Gracia JA, Lee Y, Jenkins AJ, Shafaat HS. Electronic isomerism in a heterometallic nickel-iron-sulfur cluster models substrate binding and cyanide inhibition of carbon monoxide dehydrogenase. Chem Sci 2024; 15:5916-5928. [PMID: 38665523 PMCID: PMC11040638 DOI: 10.1039/d4sc00023d] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Grants] [Track Full Text] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/02/2024] [Accepted: 03/04/2024] [Indexed: 04/28/2024] Open
Abstract
The nickel-iron carbon monoxide dehydrogenase (CODH) enzyme uses a heterometallic nickel-iron-sulfur ([NiFe4S4]) cluster to catalyze the reversible interconversion of carbon dioxide (CO2) and carbon monoxide (CO). These reactions are essential for maintaining the global carbon cycle and offer a route towards sustainable greenhouse gas conversion but have not been successfully replicated in synthetic models, in part due to a poor understanding of the natural system. Though the general protein architecture of CODH is known, the electronic structure of the active site is not well-understood, and the mechanism of catalysis remains unresolved. To better understand the CODH enzyme, we have developed a protein-based model containing a heterometallic [NiFe3S4] cluster in the Pyrococcus furiosus (Pf) ferredoxin (Fd). This model binds small molecules such as carbon monoxide and cyanide, analogous to CODH. Multiple redox- and ligand-bound states of [NiFe3S4] Fd (NiFd) have been investigated using a suite of spectroscopic techniques, including resonance Raman, Ni and Fe K-edge X-ray absorption spectroscopy, and electron paramagnetic resonance, to resolve charge and spin delocalization across the cluster, site-specific electron density, and ligand activation. The facile movement of charge through the cluster highlights the fluidity of electron density within iron-sulfur clusters and suggests an electronic basis by which CN- inhibits the native system while the CO-bound state continues to elude isolation in CODH. The detailed characterization of isolable states that are accessible in our CODH model system provides valuable insight into unresolved enzymatic intermediates and offers design principles towards developing functional mimics of CODH.
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Affiliation(s)
- Luke C Lewis
- Department of Chemistry and Biochemistry, The Ohio State University Columbus OH 43210 USA
| | - José A Sanabria-Gracia
- Department of Chemistry and Biochemistry, The Ohio State University Columbus OH 43210 USA
| | - Yuri Lee
- Department of Chemistry and Biochemistry, The Ohio State University Columbus OH 43210 USA
- Department of Chemistry and Biochemistry, University of California, Los Angeles Los Angeles CA 90095 USA
| | - Adam J Jenkins
- Department of Chemistry and Biochemistry, The Ohio State University Columbus OH 43210 USA
| | - Hannah S Shafaat
- Department of Chemistry and Biochemistry, The Ohio State University Columbus OH 43210 USA
- Department of Chemistry and Biochemistry, University of California, Los Angeles Los Angeles CA 90095 USA
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2
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Solomon JB, Liu YA, Górecki K, Quechol R, Lee CC, Jasniewski AJ, Hu Y, Ribbe MW. Heterologous expression of a fully active Azotobacter vinelandii nitrogenase Fe protein in Escherichia coli. mBio 2023; 14:e0257223. [PMID: 37909748 PMCID: PMC10746259 DOI: 10.1128/mbio.02572-23] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/20/2023] [Accepted: 09/27/2023] [Indexed: 11/03/2023] Open
Abstract
IMPORTANCE The heterologous expression of a fully active Azotobacter vinelandii Fe protein (AvNifH) has never been accomplished. Given the functional importance of this protein in nitrogenase catalysis and assembly, the successful expression of AvNifH in Escherichia coli as reported herein supplies a key element for the further development of heterologous expression systems that explore the catalytic versatility of the Fe protein, either on its own or as a key component of nitrogenase, for nitrogenase-based biotechnological applications in the future. Moreover, the "clean" genetic background of the heterologous expression host allows for an unambiguous assessment of the effect of certain nif-encoded protein factors, such as AvNifM described in this work, in the maturation of AvNifH, highlighting the utility of this heterologous expression system in further advancing our understanding of the complex biosynthetic mechanism of nitrogenase.
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Affiliation(s)
- Joseph B. Solomon
- Department of Molecular Biology and Biochemistry, University of California, Irvine, California, USA
- Department of Chemistry, University of California, Irvine, California, USA
| | - Yiling A. Liu
- Department of Molecular Biology and Biochemistry, University of California, Irvine, California, USA
| | - Kamil Górecki
- Department of Molecular Biology and Biochemistry, University of California, Irvine, California, USA
| | - Robert Quechol
- Department of Molecular Biology and Biochemistry, University of California, Irvine, California, USA
| | - Chi Chung Lee
- Department of Molecular Biology and Biochemistry, University of California, Irvine, California, USA
| | - Andrew J. Jasniewski
- Department of Molecular Biology and Biochemistry, University of California, Irvine, California, USA
| | - Yilin Hu
- Department of Molecular Biology and Biochemistry, University of California, Irvine, California, USA
| | - Markus W. Ribbe
- Department of Molecular Biology and Biochemistry, University of California, Irvine, California, USA
- Department of Chemistry, University of California, Irvine, California, USA
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3
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Warmack RA, Rees DC. Nitrogenase beyond the Resting State: A Structural Perspective. Molecules 2023; 28:7952. [PMID: 38138444 PMCID: PMC10745740 DOI: 10.3390/molecules28247952] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/06/2023] [Revised: 11/30/2023] [Accepted: 12/01/2023] [Indexed: 12/24/2023] Open
Abstract
Nitrogenases have the remarkable ability to catalyze the reduction of dinitrogen to ammonia under physiological conditions. How does this happen? The current view of the nitrogenase mechanism focuses on the role of hydrides, the binding of dinitrogen in a reductive elimination process coupled to loss of dihydrogen, and the binding of substrates to a binuclear site on the active site cofactor. This review focuses on recent experimental characterizations of turnover relevant forms of the enzyme determined by cryo-electron microscopy and other approaches, and comparison of these forms to the resting state enzyme and the broader family of iron sulfur clusters. Emerging themes include the following: (i) The obligatory coupling of protein and electron transfers does not occur in synthetic and small-molecule iron-sulfur clusters. The coupling of these processes in nitrogenase suggests that they may involve unique features of the cofactor, such as hydride formation on the trigonal prismatic arrangement of irons, protonation of belt sulfurs, and/or protonation of the interstitial carbon. (ii) Both the active site cofactor and protein are dynamic under turnover conditions; the changes are such that more highly reduced forms may differ in key ways from the resting-state structure. Homocitrate appears to play a key role in coupling cofactor and protein dynamics. (iii) Structural asymmetries are observed in nitrogenase under turnover-relevant conditions by cryo-electron microscopy, although the mechanistic relevance of these states (such as half-of-sites reactivity) remains to be established.
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Affiliation(s)
- Rebeccah A. Warmack
- Division of Chemistry and Chemical Engineering, California Institute of Technology, Pasadena, CA 91125, USA
- Howard Hughes Medical Institute, California Institute of Technology, Pasadena, CA 91125, USA
| | - Douglas C. Rees
- Division of Chemistry and Chemical Engineering, California Institute of Technology, Pasadena, CA 91125, USA
- Howard Hughes Medical Institute, California Institute of Technology, Pasadena, CA 91125, USA
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4
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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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5
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Yang ZY, Badalyan A, Hoffman BM, Dean DR, Seefeldt LC. The Fe Protein Cycle Associated with Nitrogenase Catalysis Requires the Hydrolysis of Two ATP for Each Single Electron Transfer Event. J Am Chem Soc 2023; 145:5637-5644. [PMID: 36857604 DOI: 10.1021/jacs.2c09576] [Citation(s) in RCA: 5] [Impact Index Per Article: 5.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 03/03/2023]
Abstract
A central feature of the current understanding of dinitrogen (N2) reduction by the enzyme nitrogenase is the proposed coupling of the hydrolysis of two ATP, forming two ADP and two Pi, to the transfer of one electron from the Fe protein component to the MoFe protein component, where substrates are reduced. A redox-active [4Fe-4S] cluster associated with the Fe protein is the agent of electron delivery, and it is well known to have a capacity to cycle between a one-electron-reduced [4Fe-4S]1+ state and an oxidized [4Fe-4S]2+ state. Recently, however, it has been shown that certain reducing agents can be used to further reduce the Fe protein [4Fe-4S] cluster to a super-reduced, all-ferrous [4Fe-4S]0 state that can be either diamagnetic (S = 0) or paramagnetic (S = 4). It has been proposed that the super-reduced state might fundamentally alter the existing model for nitrogenase energy utilization by the transfer of two electrons per Fe protein cycle linked to hydrolysis of only two ATP molecules. Here, we measure the number of ATP consumed for each electron transfer under steady-state catalysis while the Fe protein cluster is in the [4Fe-4S]1+ state and when it is in the [4Fe-4S]0 state. Both oxidation states of the Fe protein are found to operate by hydrolyzing two ATP for each single-electron transfer event. Thus, regardless of its initial redox state, the Fe protein transfers only one electron at a time to the MoFe protein in a process that requires the hydrolysis of two ATP.
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Affiliation(s)
- Zhi-Yong Yang
- Department of Chemistry and Biochemistry, Utah State University, Logan, Utah 84322, United States
| | - Artavazd Badalyan
- Department of Chemistry and Biochemistry, Utah State University, Logan, Utah 84322, United States
| | - Brian M Hoffman
- Departments of Chemistry and Molecular Biosciences, Northwestern University, Evanston, Illinois 60208, United States
| | - Dennis R Dean
- Department of Biochemistry, Virginia Tech, Blacksburg, Virginia 24061, United States
| | - Lance C Seefeldt
- Department of Chemistry and Biochemistry, Utah State University, Logan, Utah 84322, United States
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6
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Ribbe MW, Górecki K, Grosch M, Solomon JB, Quechol R, Liu YA, Lee CC, Hu Y. Nitrogenase Fe Protein: A Multi-Tasking Player in Substrate Reduction and Metallocluster Assembly. Molecules 2022; 27:molecules27196743. [PMID: 36235278 PMCID: PMC9571451 DOI: 10.3390/molecules27196743] [Citation(s) in RCA: 2] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/31/2022] [Revised: 10/05/2022] [Accepted: 10/06/2022] [Indexed: 11/18/2022] Open
Abstract
The Fe protein of nitrogenase plays multiple roles in substrate reduction and metallocluster assembly. Best known for its function to transfer electrons to its catalytic partner during nitrogenase catalysis, the Fe protein is also a key player in the biosynthesis of the complex metalloclusters of nitrogenase. In addition, it can function as a reductase on its own and affect the ambient reduction of CO2 or CO to hydrocarbons. This review will provide an overview of the properties and functions of the Fe protein, highlighting the relevance of this unique FeS enzyme to areas related to the catalysis, biosynthesis, and applications of the fascinating nitrogenase system.
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Affiliation(s)
- Markus W. Ribbe
- Department of Molecular Biology and Biochemistry, University of California, Irvine, CA 92697-3900, USA
- Department of Chemistry, University of California, Irvine, CA 92697-2025, USA
- Correspondence: (M.W.R.); (Y.H.)
| | - Kamil Górecki
- Department of Molecular Biology and Biochemistry, University of California, Irvine, CA 92697-3900, USA
| | - Mario Grosch
- Department of Molecular Biology and Biochemistry, University of California, Irvine, CA 92697-3900, USA
| | - Joseph B. Solomon
- Department of Molecular Biology and Biochemistry, University of California, Irvine, CA 92697-3900, USA
- Department of Chemistry, University of California, Irvine, CA 92697-2025, USA
| | - Robert Quechol
- Department of Molecular Biology and Biochemistry, University of California, Irvine, CA 92697-3900, USA
| | - Yiling A. Liu
- Department of Molecular Biology and Biochemistry, University of California, Irvine, CA 92697-3900, USA
| | - Chi Chung Lee
- Department of Molecular Biology and Biochemistry, University of California, Irvine, CA 92697-3900, USA
| | - Yilin Hu
- Department of Molecular Biology and Biochemistry, University of California, Irvine, CA 92697-3900, USA
- Correspondence: (M.W.R.); (Y.H.)
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7
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Abstract
Synthetic iron-sulfur cubanes are models for biological cofactors, which are essential to delineate oxidation states in the more complex enzymatic systems. However, a complete series of [Fe4S4]n complexes spanning all redox states accessible by 1-electron transformations of the individual iron atoms (n = 0-4+) has never been prepared, deterring the methodical comparison of structure and spectroscopic signature. Here, we demonstrate that the use of a bulky arylthiolate ligand promoting the encapsulation of alkali-metal cations in the vicinity of the cubane enables the synthesis of such a series. Characterization by EPR, 57Fe Mössbauer spectroscopy, UV-visible electronic absorption, variable-temperature X-ray diffraction analysis, and cyclic voltammetry reveals key trends for the geometry of the Fe4S4 core as well as for the Mössbauer isomer shift, which both correlate systematically with oxidation state. Furthermore, we confirm the S = 4 electronic ground state of the most reduced member of the series, [Fe4S4]0, and provide electrochemical evidence that it is accessible within 0.82 V from the [Fe4S4]2+ state, highlighting its relevance as a mimic of the nitrogenase iron protein cluster.
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8
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Solomon JB, Tanifuji K, Lee CC, Jasniewski AJ, Hedman B, Hodgson KO, Hu Y, Ribbe MW. Characterization of a Nitrogenase Iron Protein Substituted with a Synthetic [Fe 4 Se 4 ] Cluster. Angew Chem Int Ed Engl 2022; 61:e202202271. [PMID: 35218104 PMCID: PMC9038695 DOI: 10.1002/anie.202202271] [Citation(s) in RCA: 2] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/10/2022] [Indexed: 11/08/2022]
Abstract
The Fe protein of nitrogenase plays multiple roles in substrate reduction and cluster maturation via its redox-active [Fe4 S4 ] cluster. Here we report the synthesis and characterization of a water-soluble [Fe4 Se4 ] cluster that is used to substitute the [Fe4 S4 ] cluster of the Azotobacter vinelandii Fe protein (AvNifH). Biochemical, EPR and XAS/EXAFS analyses demonstrate the ability of the [Fe4 Se4 ] cluster to adopt the super-reduced, all-ferrous state upon its incorporation into AvNifH. Moreover, these studies reveal that the [Fe4 Se4 ] cluster in AvNifH already assumes a partial all-ferrous state ([Fe4 Se4 ]0 ) in the presence of dithionite, where its [Fe4 S4 ] counterpart in AvNifH exists solely in the reduced state ([Fe4 S4 ]1+ ). Such a discrepancy in the redox properties of the AvNifH-associated [Fe4 Se4 ] and [Fe4 S4 ] clusters can be used to distinguish the differential redox requirements for the substrate reduction and cluster maturation of nitrogenase, pointing to the utility of chalcogen-substituted FeS clusters in future mechanistic studies of nitrogenase catalysis and assembly.
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Affiliation(s)
- Joseph B Solomon
- Department of Molecular Biology and Biochemistry, University of Califronia, Irvine, Irvine, CA 92697-3900, USA.,Department of Chemistry, University of California, Irvine, Irvine, CA 92697-2025, USA
| | - Kazuki Tanifuji
- Department of Molecular Biology and Biochemistry, University of Califronia, Irvine, Irvine, CA 92697-3900, USA.,Institute for Chemical Research, Kyoto University, Gokasho, Uji, Kyoto, 611-0011, Japan
| | - Chi Chung Lee
- Department of Molecular Biology and Biochemistry, University of Califronia, Irvine, Irvine, CA 92697-3900, USA
| | - Andrew J Jasniewski
- Department of Molecular Biology and Biochemistry, University of Califronia, Irvine, Irvine, CA 92697-3900, USA
| | - Britt Hedman
- Stanford Synchrotron Radiation Lightsource, SLAC National Accelerator Laboratory, Stanford University, Menlo Park, CA 94025, USA
| | - Keith O Hodgson
- Stanford Synchrotron Radiation Lightsource, SLAC National Accelerator Laboratory, Stanford University, Menlo Park, CA 94025, USA.,Department of Chemistry, Stanford University, Stanford, CA 94305, USA
| | - Yilin Hu
- Department of Molecular Biology and Biochemistry, University of Califronia, Irvine, Irvine, CA 92697-3900, USA
| | - Markus W Ribbe
- Department of Molecular Biology and Biochemistry, University of Califronia, Irvine, Irvine, CA 92697-3900, USA.,Department of Chemistry, University of California, Irvine, Irvine, CA 92697-2025, USA
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9
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Solomon J, Tanifuji K, Lee CC, Jasniewski A, Hedman B, Hodgson K, Hu Y, Ribbe M. Characterization of a Nitrogenase Iron Protein Substituted with a Synthetic [Fe4Se4] Cluster. Angew Chem Int Ed Engl 2022. [DOI: 10.1002/ange.202202271] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/08/2022]
Affiliation(s)
| | - Kazuki Tanifuji
- Kyoto University Institute for Chemical Research UNITED STATES
| | - Chi Chung Lee
- University of California Irvine Molecular Biology and Biochemistry UNITED STATES
| | - Andrew Jasniewski
- University of California Irvine Molecular Biology and Biochemistry UNITED STATES
| | - Britt Hedman
- Stanford University Stanford Synchrotron Radiation Lightsource, SLAC National Accelerator Laboratory UNITED STATES
| | | | - Yilin Hu
- University of California Irvine Molecular Biology and Biochemistry UNITED STATES
| | - Markus Ribbe
- Irvine Molecular Biology & Biochemistry 2236 McGaugh Hall 92697 Irvine UNITED STATES
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10
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Solomon J, Rasekh MF, Hiller CJ, Lee CC, Tanifuji K, Ribbe MW, Hu Y. Probing the All-Ferrous States of Methanogen Nitrogenase Iron Proteins. JACS AU 2021; 1:119-123. [PMID: 34467276 PMCID: PMC8395668 DOI: 10.1021/jacsau.0c00072] [Citation(s) in RCA: 6] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Figures] [Subscribe] [Scholar Register] [Indexed: 06/13/2023]
Abstract
The Fe protein of nitrogenase reduces two C1 substrates, CO2 and CO, under ambient conditions when its [Fe4S4] cluster adopts the all-ferrous [Fe4S4]0 state. Here, we show disparate reactivities of the nifH- and vnf-encoded Fe proteins from Methanosarcina acetivorans (designated MaNifH and MaVnfH) toward C1 substrates in the all-ferrous state, with the former capable of reducing both CO2 and CO to hydrocarbons, and the latter only capable of reducing CO to hydrocarbons at substantially reduced yields. EPR experiments conducted at varying solution potentials reveal that MaVnfH adopts the all-ferrous state at a more positive reduction potential than MaNifH, which could account for the weaker reactivity of the MaVnfH toward C1 substrates than MaNifH. More importantly, MaVnfH already displays the g = 16.4 parallel-mode EPR signal that is characteristic of the all-ferrous [Fe4S4]0 cluster at a reduction potential of -0.44 V, and the signal reaches 50% maximum intensity at a reduction potential of -0.59 V, suggesting the possibility of this Fe protein to access the all-ferrous [Fe4S4]0 state under physiological conditions. These results bear significant relevance to the long-lasting debate of whether the Fe protein can utilize the [Fe4S4]0/2+ redox couple to support a two-electron transfer during substrate turnover which, therefore, is crucial for expanding our knowledge of the reaction mechanism of nitrogenase and the cellular energetics of nitrogenase-based processes.
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Affiliation(s)
- Joseph
B. Solomon
- Department
of Molecular Biology and Biochemistry, University
of California, Irvine, California 92697-3900, United States
- Department
of Chemistry, University of California, Irvine, California 92697-2025, United States
| | - Mahtab F. Rasekh
- Department
of Molecular Biology and Biochemistry, University
of California, Irvine, California 92697-3900, United States
- Department
of Chemistry, University of California, Irvine, California 92697-2025, United States
| | - Caleb J. Hiller
- Department
of Physical Science, Southern Utah University, Cedar City, Utah 84720, United States
| | - Chi Chung Lee
- Department
of Molecular Biology and Biochemistry, University
of California, Irvine, California 92697-3900, United States
| | - Kazuki Tanifuji
- Department
of Molecular Biology and Biochemistry, University
of California, Irvine, California 92697-3900, United States
| | - Markus W. Ribbe
- Department
of Molecular Biology and Biochemistry, University
of California, Irvine, California 92697-3900, United States
- Department
of Chemistry, University of California, Irvine, California 92697-2025, United States
| | - Yilin Hu
- Department
of Molecular Biology and Biochemistry, University
of California, Irvine, California 92697-3900, United States
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11
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Abstract
Nitrogenase is the only enzyme capable of reducing N2 to NH3. This challenging reaction requires the coordinated transfer of multiple electrons from the reductase, Fe-protein, to the catalytic component, MoFe-protein, in an ATP-dependent fashion. In the last two decades, there have been significant advances in our understanding of how nitrogenase orchestrates electron transfer (ET) from the Fe-protein to the catalytic site of MoFe-protein and how energy from ATP hydrolysis transduces the ET processes. In this review, we summarize these advances, with focus on the structural and thermodynamic redox properties of nitrogenase component proteins and their complexes, as well as on new insights regarding the mechanism of ET reactions during catalysis and how they are coupled to ATP hydrolysis. We also discuss recently developed chemical, photochemical, and electrochemical methods for uncoupling substrate reduction from ATP hydrolysis, which may provide new avenues for studying the catalytic mechanism of nitrogenase.
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Affiliation(s)
- Hannah L Rutledge
- Department of Chemistry and Biochemistry, University of California, San Diego, 9500 Gilman Drive, La Jolla, California 92093-0340, United States
| | - F Akif Tezcan
- Department of Chemistry and Biochemistry, University of California, San Diego, 9500 Gilman Drive, La Jolla, California 92093-0340, United States
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12
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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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13
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Affiliation(s)
- Oliver Einsle
- Institute for Biochemistry, Albert-Ludwigs-University Freiburg, 79104 Freiburg, Germany
| | - Douglas C. Rees
- Division of Chemistry and Chemical Engineering, Howard Hughes Medical Institute, California Institute of Technology, Pasadena California 91125, United States
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14
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Abstract
As the only enzyme currently known to reduce dinitrogen (N2) to ammonia (NH3), nitrogenase is of significant interest for bio-inspired catalyst design and for new biotechnologies aiming to produce NH3 from N2. In order to reduce N2, nitrogenase must also hydrolyze at least 16 equivalents of adenosine triphosphate (MgATP), representing the consumption of a significant quantity of energy available to biological systems. Here, we review natural and engineered electron transfer pathways to nitrogenase, including strategies to redirect or redistribute electron flow in vivo towards NH3 production. Further, we also review strategies to artificially reduce nitrogenase in vitro, where MgATP hydrolysis is necessary for turnover, in addition to strategies that are capable of bypassing the requirement of MgATP hydrolysis to achieve MgATP-independent N2 reduction.
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15
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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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16
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Rettberg LA, Stiebritz MT, Kang W, Lee CC, Ribbe MW, Hu Y. Structural and Mechanistic Insights into CO 2 Activation by Nitrogenase Iron Protein. Chemistry 2019; 25:13078-13082. [PMID: 31402524 DOI: 10.1002/chem.201903387] [Citation(s) in RCA: 6] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/24/2019] [Revised: 08/06/2019] [Indexed: 11/09/2022]
Abstract
The Fe protein of nitrogenase catalyzes the ambient reduction of CO2 when its cluster is present in the all-ferrous, [Fe4 S4 ]0 oxidation state. Here, we report a combined structural and theoretical study that probes the unique reactivity of the all-ferrous Fe protein toward CO2 . Structural comparisons of the Azotobacter vinelandii Fe protein in the [Fe4 S4 ]0 and [Fe4 S4 ]+ states point to a possible asymmetric functionality of a highly conserved Arg pair in CO2 binding and reduction. Density functional theory (DFT) calculations provide further support for the asymmetric coordination of O by the "proximal" Arg and binding of C to a unique Fe atom of the all-ferrous cluster, followed by donation of protons by the proximate guanidinium group of Arg that eventually results in the scission of a C-O bond. These results provide important mechanistic and structural insights into CO2 activation by a surface-exposed, scaffold-held [Fe4 S4 ] cluster.
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Affiliation(s)
- Lee A Rettberg
- Department of Molecular Biology & Biochemistry, University of California, Irvine, CA, 92697-3900, USA
| | - Martin T Stiebritz
- Department of Molecular Biology & Biochemistry, University of California, Irvine, CA, 92697-3900, USA
| | - Wonchull Kang
- Department of Molecular Biology & Biochemistry, University of California, Irvine, CA, 92697-3900, USA
| | - Chi Chung Lee
- Department of Molecular Biology & Biochemistry, University of California, Irvine, CA, 92697-3900, USA
| | - Markus W Ribbe
- Department of Molecular Biology & Biochemistry, University of California, Irvine, CA, 92697-3900, USA.,Department Chemistry, University of California, Irvine, Irvine, CA, 92697-2025, USA
| | - Yilin Hu
- Department of Molecular Biology & Biochemistry, University of California, Irvine, CA, 92697-3900, USA
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17
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Abstract
Biological nitrogen fixation, the conversion of dinitrogen (N2) into ammonia (NH3), stands as a particularly challenging chemical process. As the entry point into a bioavailable form of nitrogen, biological nitrogen fixation is a critical step in the global nitrogen cycle. In Nature, only one enzyme, nitrogenase, is competent in performing this reaction. Study of this complex metalloenzyme has revealed a potent substrate reduction system that utilizes some of the most sophisticated metalloclusters known. This chapter discusses the structure and function of nitrogenase, covers methods that have proven useful in the elucidation of enzyme properties, and provides an overview of the three known nitrogenase variants.
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18
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Lee CC, Stiebritz MT, Hu Y. Reactivity of [Fe 4S 4] Clusters toward C1 Substrates: Mechanism, Implications, and Potential Applications. Acc Chem Res 2019; 52:1168-1176. [PMID: 30977994 DOI: 10.1021/acs.accounts.9b00063] [Citation(s) in RCA: 15] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/19/2022]
Abstract
FeS proteins are metalloproteins prevalent in the metabolic pathways of most organisms, playing key roles in a wide range of essential cellular processes. A member of this protein family, the Fe protein of nitrogenase, is a homodimer that contains a redox-active [Fe4S4] cluster at the subunit interface and an ATP-binding site within each subunit. During catalysis, the Fe protein serves as the obligate electron donor for its catalytic partner, transferring electrons concomitant with ATP hydrolysis to the cofactor site of the catalytic component to enable substrate reduction. The effectiveness of Fe protein in electron transfer is reflected by the unique reactivity of nitrogenase toward small-molecule substrates. Most notably, nitrogenase is capable of catalyzing the ambient reduction of N2 and CO into NH4+ and hydrocarbons, respectively, in reactions that parallel the important industrial Haber-Bosch and Fischer-Tropsch processes. Other than participating in nitrogenase catalysis, the Fe protein also functions as an essential factor in nitrogenase assembly, which again highlights its capacity as an effective, ATP-dependent electron donor. Recently, the Fe protein of a soil bacterium, Azotobacter vinelandii, was shown to act as a reductase on its own and catalyze the ambient conversion of CO2 to CO at its [Fe4S4] cluster either under in vitro conditions when a strong reductant is supplied or under in vivo conditions through the action of an unknown electron donor(s) in the cell. Subsequently, the Fe protein of a mesophilic methanogenic organism, Methanosarcina acetivorans, was shown to catalyze the in vitro reduction of CO2 and CO into hydrocarbons under ambient conditions, illustrating an impact of protein scaffold on the redox properties of the [Fe4S4] cluster and the reactivity of the cluster toward C1 substrates. This reactivity was further traced to the [Fe4S4] cluster itself, as a synthetic [Fe4S4] compound was shown to catalyze the reduction of CO2 and CO to hydrocarbons in solutions in the presence of a strong reductant. Together, these observations pointed to an inherent ability of the [Fe4S4] clusters and, possibly, the FeS clusters in general to catalyze C1-substrate reduction. Theoretical calculations have led to the proposal of a plausible reaction pathway that involves the formation of hydrocarbons via aldehyde-like intermediates, providing an important framework for further mechanistic investigations of FeS-based activation and reduction of C1 substrates. In this Account, we summarize the recent work leading to the discovery of C1-substrate reduction by protein-bound and free [Fe4S4] clusters as well as the current mechanistic understanding of this FeS-based reactivity. In addition, we briefly discuss the evolutionary implications of this discovery and potential applications that could be developed to enable FeS-based strategies for the ambient recycling of unwanted C1 waste into useful chemical commodities.
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Affiliation(s)
- Chi Chung Lee
- Department of Molecular Biology and Biochemistry, University of California, Irvine, California 92697-3900, United States
| | - Martin T. Stiebritz
- Department of Molecular Biology and Biochemistry, University of California, Irvine, California 92697-3900, United States
| | - Yilin Hu
- Department of Molecular Biology and Biochemistry, University of California, Irvine, California 92697-3900, United States
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19
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Wenke BB, Spatzal T, Rees DC. Site-Specific Oxidation State Assignments of the Iron Atoms in the [4Fe:4S] 2+/1+/0 States of the Nitrogenase Fe-Protein. Angew Chem Int Ed Engl 2019; 58:3894-3897. [PMID: 30698901 PMCID: PMC6519357 DOI: 10.1002/anie.201813966] [Citation(s) in RCA: 25] [Impact Index Per Article: 5.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/14/2018] [Indexed: 12/05/2022]
Abstract
The nitrogenase iron protein (Fe-protein) contains an unusual [4Fe:4S] iron-sulphur cluster that is stable in three oxidation states: 2+, 1+, and 0. Here, we use spatially resolved anomalous dispersion (SpReAD) refinement to determine oxidation assignments for the individual irons for each state. Additionally, we report the 1.13-Å resolution structure for the ADP bound Fe-protein, the highest resolution Fe-protein structure presently determined. In the dithionite-reduced [4Fe:4S]1+ state, our analysis identifies a solvent exposed, delocalized Fe2.5+ pair and a buried Fe2+ pair. We propose that ATP binding by the Fe-protein promotes an internal redox rearrangement such that the solvent-exposed Fe pair becomes reduced, thereby facilitating electron transfer to the nitrogenase molybdenum iron-protein. In the [4Fe:4S]0 and [4Fe:4S]2+ states, the SpReAD analysis supports oxidation states assignments for all irons in these clusters of Fe2+ and valence delocalized Fe2.5+ , respectively.
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Affiliation(s)
- Belinda B. Wenke
- Division of Chemistry and Chemical EngineeringCalifornia Institute of TechnologyPasadenaCA91125USA
| | - Thomas Spatzal
- Howard Hughes Medical InstituteCalifornia Institute of TechnologyPasadenaCA91125USA
- Division of Chemistry and Chemical EngineeringCalifornia Institute of TechnologyPasadenaCA91125USA
| | - Douglas C. Rees
- Howard Hughes Medical InstituteCalifornia Institute of TechnologyPasadenaCA91125USA
- Division of Chemistry and Chemical EngineeringCalifornia Institute of TechnologyPasadenaCA91125USA
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20
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Wenke BB, Spatzal T, Rees DC. Site‐Specific Oxidation State Assignments of the Iron Atoms in the [4Fe:4S]
2+/1+/0
States of the Nitrogenase Fe‐Protein. Angew Chem Int Ed Engl 2019. [DOI: 10.1002/ange.201813966] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/09/2022]
Affiliation(s)
- Belinda B. Wenke
- Division of Chemistry and Chemical EngineeringCalifornia Institute of Technology Pasadena CA 91125 USA
| | - Thomas Spatzal
- Howard Hughes Medical InstituteCalifornia Institute of Technology Pasadena CA 91125 USA
- Division of Chemistry and Chemical EngineeringCalifornia Institute of Technology Pasadena CA 91125 USA
| | - Douglas C. Rees
- Howard Hughes Medical InstituteCalifornia Institute of Technology Pasadena CA 91125 USA
- Division of Chemistry and Chemical EngineeringCalifornia Institute of Technology Pasadena CA 91125 USA
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21
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Todorovic S, Teixeira M. Resonance Raman spectroscopy of Fe-S proteins and their redox properties. J Biol Inorg Chem 2018; 23:647-661. [PMID: 29368020 PMCID: PMC6006211 DOI: 10.1007/s00775-018-1533-0] [Citation(s) in RCA: 17] [Impact Index Per Article: 2.8] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/23/2017] [Accepted: 12/14/2017] [Indexed: 12/02/2022]
Abstract
Resonance Raman spectra of Fe-S proteins are sensitive to the cluster type, structure and symmetry. Furthermore, bands that originate from bridging and terminal Fe-S vibrations in the 2Fe-2S, 3Fe-4S and 4Fe-4S clusters can be sensitively distinguished in the spectra, as well as the type of non-cysteinyl coordinating ligands, if present. For these reasons, resonance Raman spectroscopy has been playing an exceptionally active role in the studies of Fe-S proteins of diverse structures and functions. We provide here a concise overview of the structural information that can be obtained from resonance Raman spectroscopy on Fe-S clusters, and in parallel, refer to their thermodynamic properties (e.g., reduction potential), which together define the physiological roles of Fe-S proteins. We demonstrate how the knowledge gained over the past several decades on simple clusters nowadays enables studies of complex structures that include Fe-S clusters coupled to other centers and transient processes that involve cluster inter-conversion, biogenesis, disassembly and catalysis.
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Affiliation(s)
- Smilja Todorovic
- Instituto de Tecnologia Química e Biológica António Xavier, Universidade Nova de Lisboa, Av da República, 2780-157, Oeiras, Portugal.
| | - Miguel Teixeira
- Instituto de Tecnologia Química e Biológica António Xavier, Universidade Nova de Lisboa, Av da República, 2780-157, Oeiras, Portugal
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22
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Hiller CJ, Stiebritz MT, Lee CC, Liedtke J, Hu Y. Tuning Electron Flux through Nitrogenase with Methanogen Iron Protein Homologues. Chemistry 2017; 23:16152-16156. [PMID: 28984391 DOI: 10.1002/chem.201704378] [Citation(s) in RCA: 20] [Impact Index Per Article: 2.9] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/18/2017] [Indexed: 11/06/2022]
Abstract
Nitrogenase uses a reductase component called Fe protein to deliver electrons to its catalytic partner for substrate reduction. The essential role of Fe protein in catalysis makes it an ideal target for regulating the electron flux and enzymatic activity of nitrogenase without perturbing the cofactor site. This work reports that hybrids between the Fe protein homologs of Methanosarcina acetivorans and the catalytic components of Azotobacter vinelandii can trap substrate CO through reduced electron fluxes. In addition, homology modeling/in silico docking is used to define markers for binding energy and specificity between the component proteins that correlate with the experimentally determined activities. This homologue-based approach could be further developed to allow identification or design of hybrids between homologous nitrogenase components for mechanistic investigations of nitrogenase through capture of substrates/ intermediates or for transgenic expression of nitrogenase through synthetic biology.
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Affiliation(s)
- Caleb J Hiller
- Department of Molecular Biology and Biochemistry, University of California, Irvine, CA, 92697-3900, USA
| | - Martin T Stiebritz
- Department of Molecular Biology and Biochemistry, University of California, Irvine, CA, 92697-3900, USA
| | - Chi Chung Lee
- Department of Molecular Biology and Biochemistry, University of California, Irvine, CA, 92697-3900, USA
| | - Jasper Liedtke
- Department of Molecular Biology and Biochemistry, University of California, Irvine, CA, 92697-3900, USA
| | - Yilin Hu
- Department of Molecular Biology and Biochemistry, University of California, Irvine, CA, 92697-3900, USA
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23
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Sickerman NS, Hu Y, Ribbe MW. Activation of CO
2
by Vanadium Nitrogenase. Chem Asian J 2017; 12:1985-1996. [DOI: 10.1002/asia.201700624] [Citation(s) in RCA: 20] [Impact Index Per Article: 2.9] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/25/2017] [Indexed: 11/08/2022]
Affiliation(s)
- Nathaniel S. Sickerman
- Department of Molecular Biology and Biochemistry University of California, Irvine Irvine CA 92697-3900 USA
| | - Yilin Hu
- Department of Molecular Biology and Biochemistry University of California, Irvine Irvine CA 92697-3900 USA
| | - Markus W. Ribbe
- Department of Molecular Biology and Biochemistry University of California, Irvine Irvine CA 92697-3900 USA
- Department of Chemistry University of California, Irvine Irvine CA 92697-2025 USA
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24
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Zanello P. The competition between chemistry and biology in assembling iron–sulfur derivatives. Molecular structures and electrochemistry. Part V. {[Fe4S4](SCysγ)4} proteins. Coord Chem Rev 2017. [DOI: 10.1016/j.ccr.2016.10.003] [Citation(s) in RCA: 11] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/04/2023]
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25
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Activation and reduction of carbon dioxide by nitrogenase iron proteins. Nat Chem Biol 2016; 13:147-149. [PMID: 27893704 DOI: 10.1038/nchembio.2245] [Citation(s) in RCA: 39] [Impact Index Per Article: 4.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/11/2016] [Accepted: 09/16/2016] [Indexed: 01/24/2023]
Abstract
The iron (Fe) proteins of molybdenum (Mo) and vanadium (V) nitrogenases mimic carbon monoxide (CO) dehydrogenase in catalyzing the interconversion between CO2 and CO under ambient conditions. Catalytic reduction of CO2 to CO is achieved in vitro and in vivo upon redox changes of the Fe-protein-associated [Fe4S4] clusters. These observations establish the Fe protein as a model for investigation of CO2 activation while suggesting its biotechnological adaptability for recycling the greenhouse gas into useful products.
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26
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Roncaroli F, Bill E, Friedrich B, Lenz O, Lubitz W, Pandelia ME. Cofactor composition and function of a H 2-sensing regulatory hydrogenase as revealed by Mössbauer and EPR spectroscopy. Chem Sci 2015; 6:4495-4507. [PMID: 29142700 PMCID: PMC5665086 DOI: 10.1039/c5sc01560j] [Citation(s) in RCA: 32] [Impact Index Per Article: 3.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/29/2015] [Accepted: 05/26/2015] [Indexed: 01/22/2023] Open
Abstract
The regulatory hydrogenase (RH) from Ralstonia eutropha H16 acts as a sensor for the detection of environmental H2 and regulates gene expression related to hydrogenase-mediated cellular metabolism. In marked contrast to prototypical energy-converting [NiFe] hydrogenases, the RH is apparently insensitive to inhibition by O2 and CO. While the physiological function of regulatory hydrogenases is well established, little is known about the redox cycling of the [NiFe] center and the nature of the iron-sulfur (FeS) clusters acting as electron relay. The absence of any FeS cluster signals in EPR had been attributed to their particular nature, whereas the observation of essentially only two active site redox states, namely Ni-SI and Ni-C, invoked a different operant mechanism. In the present work, we employ a combination of Mössbauer, FTIR and EPR spectroscopic techniques to study the RH, and the results are consistent with the presence of three [4Fe-4S] centers in the small subunit. In the as-isolated, oxidized RH all FeS clusters reside in the EPR-silent 2+ state. Incubation with H2 leads to reduction of two of the [4Fe-4S] clusters, whereas only strongly reducing agents lead to reduction of the third cluster, which is ascribed to be the [4Fe-4S] center in 'proximal' position to the [NiFe] center. In the two different active site redox states, the low-spin FeII exhibits distinct Mössbauer features attributed to changes in the electronic and geometric structure of the catalytic center. The results are discussed with regard to the spectral characteristics and physiological function of H2-sensing regulatory hydrogenases.
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Affiliation(s)
- Federico Roncaroli
- Max-Planck-Institut für Chemische Energiekonversion , Stiftstraße 34-36 , 45470 Mülheim an der Ruhr , Germany . ; .,Department of Condensed Matter Physics , Centro Atómico Constituyentes , Comisión Nacional de Energía Atómica (CNEA) , Argentina
| | - Eckhard Bill
- Max-Planck-Institut für Chemische Energiekonversion , Stiftstraße 34-36 , 45470 Mülheim an der Ruhr , Germany . ;
| | - Bärbel Friedrich
- Institut für Biologie/Mikrobiologie , Humboldt-Universität zu Berlin , Chausseestraße 117 , 10115 Berlin , Germany
| | - Oliver Lenz
- Institut für Biologie/Mikrobiologie , Humboldt-Universität zu Berlin , Chausseestraße 117 , 10115 Berlin , Germany.,Institut für Chemie , Technische Universität Berlin , Max-Volmer-Laboratorium , Straße des 17. Juni 135 , 10623 Berlin , Germany
| | - Wolfgang Lubitz
- Max-Planck-Institut für Chemische Energiekonversion , Stiftstraße 34-36 , 45470 Mülheim an der Ruhr , Germany . ;
| | - Maria-Eirini Pandelia
- The Pennsylvania State University , Department of Chemistry , State College , PA 16802 , USA . .,Max-Planck-Institut für Chemische Energiekonversion , Stiftstraße 34-36 , 45470 Mülheim an der Ruhr , Germany . ;
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27
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Liu J, Chakraborty S, Hosseinzadeh P, Yu Y, Tian S, Petrik I, Bhagi A, Lu Y. Metalloproteins containing cytochrome, iron-sulfur, or copper redox centers. Chem Rev 2014; 114:4366-469. [PMID: 24758379 PMCID: PMC4002152 DOI: 10.1021/cr400479b] [Citation(s) in RCA: 559] [Impact Index Per Article: 55.9] [Reference Citation Analysis] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/02/2013] [Indexed: 02/07/2023]
Affiliation(s)
- Jing Liu
- Department of Chemistry, Department of Biochemistry, and Center for Biophysics
and Computational
Biology, University of Illinois at Urbana-Champaign, Urbana, Illinois 61801, United States
| | - Saumen Chakraborty
- Department of Chemistry, Department of Biochemistry, and Center for Biophysics
and Computational
Biology, University of Illinois at Urbana-Champaign, Urbana, Illinois 61801, United States
| | - Parisa Hosseinzadeh
- Department of Chemistry, Department of Biochemistry, and Center for Biophysics
and Computational
Biology, University of Illinois at Urbana-Champaign, Urbana, Illinois 61801, United States
| | - Yang Yu
- Department of Chemistry, Department of Biochemistry, and Center for Biophysics
and Computational
Biology, University of Illinois at Urbana-Champaign, Urbana, Illinois 61801, United States
| | - Shiliang Tian
- Department of Chemistry, Department of Biochemistry, and Center for Biophysics
and Computational
Biology, University of Illinois at Urbana-Champaign, Urbana, Illinois 61801, United States
| | - Igor Petrik
- Department of Chemistry, Department of Biochemistry, and Center for Biophysics
and Computational
Biology, University of Illinois at Urbana-Champaign, Urbana, Illinois 61801, United States
| | - Ambika Bhagi
- Department of Chemistry, Department of Biochemistry, and Center for Biophysics
and Computational
Biology, University of Illinois at Urbana-Champaign, Urbana, Illinois 61801, United States
| | - Yi Lu
- Department of Chemistry, Department of Biochemistry, and Center for Biophysics
and Computational
Biology, University of Illinois at Urbana-Champaign, Urbana, Illinois 61801, United States
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28
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Rupnik K, Lee CC, Wiig JA, Hu Y, Ribbe MW, Hales BJ. Nonenzymatic synthesis of the P-cluster in the nitrogenase MoFe protein: evidence of the involvement of all-ferrous [Fe4S4](0) intermediates. Biochemistry 2014; 53:1108-16. [PMID: 24520862 PMCID: PMC3970913 DOI: 10.1021/bi401699u] [Citation(s) in RCA: 14] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
Abstract
![]()
The
P-cluster in the nitrogenase MoFe protein is a [Fe8S7] cluster and represents the most complex FeS cluster
found in Nature. To date, the exact mechanism of the in vivo synthesis of the P-cluster remains unclear. What is known is that
the precursor to the P-cluster is a pair of neighboring [Fe4S4]-like clusters found on the ΔnifH MoFe protein, a protein expressed in the absence of the nitrogenase
Fe protein (NifH). Moreover, incubation of the ΔnifH MoFe protein with NifH and MgATP results in the synthesis of the
MoFe protein P-clusters. To improve our understanding of the mechanism
of this reaction, we conducted a magnetic circular dichroism (MCD)
spectroscopic study of the [Fe4S4]-like clusters
on the ΔnifH MoFe protein. Reducing the ΔnifH MoFe protein with Ti(III) citrate results in the quenching
of the S = 1/2 electron paramagnetic
resonance signal
associated with the [Fe4S4]+ state
of the clusters. MCD spectroscopy reveals this reduction results in
all four 4Fe clusters being converted into the unusual, all-ferrous
[Fe4S4]0 state. Subsequent increases
of the redox potential generate new clusters. Most significantly,
one of these newly formed clusters is the P-cluster, which represents
approximately 20–25% of the converted Fe concentration. The
other two clusters are an
X cluster, of unknown structure, and a classic [Fe4S4] cluster, which represents approximately 30–35% of
the Fe concentration. Diamagnetic FeS clusters may also have
been generated but, because of their low spectral intensity, would
not have been identified. These results demonstrate that the nitrogenase
P-cluster can be generated in the absence of NifH and MgATP.
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Affiliation(s)
- Kresimir Rupnik
- Department of Chemistry, Louisiana State University , Baton Rouge, Louisiana 70808, United States
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29
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Hoffman BM, Lukoyanov D, Yang ZY, Dean DR, Seefeldt LC. Mechanism of nitrogen fixation by nitrogenase: the next stage. Chem Rev 2014; 114:4041-62. [PMID: 24467365 PMCID: PMC4012840 DOI: 10.1021/cr400641x] [Citation(s) in RCA: 969] [Impact Index Per Article: 96.9] [Reference Citation Analysis] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/28/2022]
Affiliation(s)
- Brian M Hoffman
- Department of Chemistry and Biochemistry, Utah State University , 0300 Old Main Hill, Logan, Utah 84322, United States
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30
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Spatzal T, Einsle O, Andrade SLA. Analysis of the Magnetic Properties of Nitrogenase FeMo Cofactor by Single-Crystal EPR Spectroscopy. Angew Chem Int Ed Engl 2013; 52:10116-9. [DOI: 10.1002/anie.201303000] [Citation(s) in RCA: 20] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/10/2013] [Revised: 06/11/2013] [Indexed: 11/09/2022]
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31
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Spatzal T, Einsle O, Andrade SLA. Analyse der magnetischen Eigenschaften des FeMo-Cofaktors der Nitrogenase mittels Einkristall-EPR-Spektroskopie. Angew Chem Int Ed Engl 2013. [DOI: 10.1002/ange.201303000] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/07/2022]
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32
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Mitra D, George SJ, Guo Y, Kamali S, Keable S, Peters JW, Pelmenschikov V, Case DA, Cramer SP. Characterization of [4Fe-4S] cluster vibrations and structure in nitrogenase Fe protein at three oxidation levels via combined NRVS, EXAFS, and DFT analyses. J Am Chem Soc 2013; 135:2530-43. [PMID: 23282058 DOI: 10.1021/ja307027n] [Citation(s) in RCA: 38] [Impact Index Per Article: 3.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/30/2022]
Abstract
Azotobacter vinelandii nitrogenase Fe protein (Av2) provides a rare opportunity to investigate a [4Fe-4S] cluster at three oxidation levels in the same protein environment. Here, we report the structural and vibrational changes of this cluster upon reduction using a combination of NRVS and EXAFS spectroscopies and DFT calculations. Key to this work is the synergy between these three techniques as each generates highly complementary information and their analytical methodologies are interdependent. Importantly, the spectroscopic samples contained no glassing agents. NRVS and DFT reveal a systematic 10-30 cm(-1) decrease in Fe-S stretching frequencies with each added electron. The "oxidized" [4Fe-4S](2+) state spectrum is consistent with and extends previous resonance Raman spectra. For the "reduced" [4Fe-4S](1+) state in Fe protein, and for any "all-ferrous" [4Fe-4S](0) cluster, these NRVS spectra are the first available vibrational data. NRVS simulations also allow estimation of the vibrational disorder for Fe-S and Fe-Fe distances, constraining the EXAFS analysis and allowing structural disorder to be estimated. For oxidized Av2, EXAFS and DFT indicate nearly equal Fe-Fe distances, while addition of one electron decreases the cluster symmetry. However, addition of the second electron to form the all-ferrous state induces significant structural change. EXAFS data recorded to k = 21 Å(-1) indicates a 1:1 ratio of Fe-Fe interactions at 2.56 Å and 2.75 Å, a result consistent with DFT. Broken symmetry (BS) DFT rationalizes the interplay between redox state and the Fe-S and Fe-Fe distances as predominantly spin-dependent behavior inherent to the [4Fe-4S] cluster and perturbed by the Av2 protein environment.
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Affiliation(s)
- Devrani Mitra
- Department of Biochemistry and Molecular Biology, The University of Chicago, Chicago, Illinois 60637, USA
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33
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Rodriguez MM, Stubbert BD, Scarborough CC, Brennessel WW, Bill E, Holland PL. Isolation and characterization of stable iron(I) sulfide complexes. Angew Chem Int Ed Engl 2012; 51:8247-50. [PMID: 22821816 PMCID: PMC3970908 DOI: 10.1002/anie.201202211] [Citation(s) in RCA: 36] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/20/2012] [Indexed: 11/11/2022]
Affiliation(s)
| | - Bryan D. Stubbert
- Department of Chemistry University of Rochester Rochester, NY 14627 (USA)
| | | | | | - Eckhard Bill
- Max-Planck-Institut für Bioanorganische Chemie 45470 Mülheim an der Ruhr (Germany)
| | - Patrick L. Holland
- Department of Chemistry University of Rochester Rochester, NY 14627 (USA)
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34
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Rodriguez MM, Stubbert BD, Scarborough CC, Brennessel WW, Bill E, Holland PL. Isolation and Characterization of Stable Iron(I) Sulfide Complexes. Angew Chem Int Ed Engl 2012. [DOI: 10.1002/ange.201202211] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022]
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Seefeldt LC, Hoffman BM, Dean DR. Electron transfer in nitrogenase catalysis. Curr Opin Chem Biol 2012; 16:19-25. [PMID: 22397885 DOI: 10.1016/j.cbpa.2012.02.012] [Citation(s) in RCA: 70] [Impact Index Per Article: 5.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/11/2011] [Revised: 02/11/2012] [Accepted: 02/13/2012] [Indexed: 11/30/2022]
Abstract
Nitrogenase is a two-component enzyme that catalyzes the nucleotide-dependent reduction of N2 to 2NH3. This process involves three redox-active metal-containing cofactors including a [4Fe-4S] cluster, an eight-iron P cluster and a seven-iron plus molybdenum FeMo-cofactor, the site of substrate reduction. A deficit-spending model for electron transfer has recently been proposed that incorporates protein conformational gating that favors uni-directional electron transfer among the metalloclusters for the activation of the substrate-binding site. Also reviewed is a proposal that each of the metal clusters cycles through only two redox states of the metal-sulfur core as the system accumulates the multiple electrons required for substrate binding and reduction. In particular, it was suggested that as FeMo-cofactor acquires the four electrons necessary for optimal binding of N2, each successive pair of electrons is stored as an Fe-H--Fe bridging hydride, with the FeMo-cofactor metal-ion core retaining its resting redox state. We here broaden the discussion of stable intermediates that might form when FeMo-cofactor receives an odd number of electrons.
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Affiliation(s)
- Lance C Seefeldt
- Department of Chemistry and Biochemistry, Utah State University, 0300 Old Main Hill, Logan, UT 84322, USA.
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Danyal K, Dean DR, Hoffman BM, Seefeldt LC. Electron transfer within nitrogenase: evidence for a deficit-spending mechanism. Biochemistry 2011; 50:9255-63. [PMID: 21939270 DOI: 10.1021/bi201003a] [Citation(s) in RCA: 89] [Impact Index Per Article: 6.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/04/2023]
Abstract
The reduction of substrates catalyzed by nitrogenase utilizes an electron transfer (ET) chain comprised of three metalloclusters distributed between the two component proteins, designated as the Fe protein and the MoFe protein. The flow of electrons through these three metalloclusters involves ET from the [4Fe-4S] cluster located within the Fe protein to an [8Fe-7S] cluster, called the P cluster, located within the MoFe protein and ET from the P cluster to the active site [7Fe-9S-X-Mo-homocitrate] cluster called FeMo-cofactor, also located within the MoFe protein. The order of these two electron transfer events, the relevant oxidation states of the P-cluster, and the role(s) of ATP, which is obligatory for ET, remain unknown. In the present work, the electron transfer process was examined by stopped-flow spectrophotometry using the wild-type MoFe protein and two variant MoFe proteins, one having the β-188(Ser) residue substituted by cysteine and the other having the β-153(Cys) residue deleted. The data support a "deficit-spending" model of electron transfer where the first event (rate constant 168 s(-1)) is ET from the P cluster to FeMo-cofactor and the second, "backfill", event is fast ET (rate constant >1700 s(-1)) from the Fe protein [4Fe-4S] cluster to the oxidized P cluster. Changes in osmotic pressure reveal that the first electron transfer is conformationally gated, whereas the second is not. The data for the β-153(Cys) deletion MoFe protein variant provide an argument against an alternative two-step "hopping" ET model that reverses the two ET steps, with the Fe protein first transferring an electron to the P cluster, which in turn transfers an electron to FeMo-cofactor. The roles for ATP binding and hydrolysis in controlling the ET reactions were examined using βγ-methylene-ATP as a prehydrolysis ATP analogue and ADP + AlF(4)(-) as a posthydrolysis analogue (a mimic of ADP + P(i)).
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Affiliation(s)
- Karamatullah Danyal
- Department of Chemistry and Biochemistry, Utah State University, Logan, Utah 84322, United States
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Ohki Y, Tanifuji K, Yamada N, Imada M, Tajima T, Tatsumi K. Synthetic analogues of [Fe4S4(Cys)3(His)] in hydrogenases and [Fe4S4(Cys)4] in HiPIP derived from all-ferric [Fe4S4{N(SiMe3)2}4]. Proc Natl Acad Sci U S A 2011; 108:12635-40. [PMID: 21768339 PMCID: PMC3150945 DOI: 10.1073/pnas.1106472108] [Citation(s) in RCA: 34] [Impact Index Per Article: 2.6] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/18/2022] Open
Abstract
The all-ferric [Fe(4)S(4)](4+) cluster [Fe(4)S(4){N(SiMe(3))(2)}(4)] 1 and its one-electron reduced form [1](-) serve as convenient precursors for the synthesis of 31-site differentiated [Fe(4)S(4)] clusters and high-potential iron-sulfur protein (HiPIP) model clusters. The reaction of 1 with four equivalents (equiv) of the bulky thiol HSDmp (Dmp = 2,6-(mesityl)(2)C(6)H(3), mesityl = 2,4,6-Me(3)C(6)H(2)) followed by treatment with tetrahydrofuran (THF) resulted in the isolation of [Fe(4)S(4)(SDmp)(3)(THF)(3)] 2. Cluster 2 contains an octahedral iron atom with three THF ligands, and its Fe(S)(3)(O)(3) coordination environment is relevant to that in the active site of substrate-bound aconitase. An analogous reaction of [1](-) with four equiv of HSDmp gave [Fe(4)S(4)(SDmp)(4)](-) 3, which models the oxidized form of HiPIP. The THF ligands in 2 can be replaced by tetramethyl-imidazole (Me(4)Im) to give [Fe(4)S(4)(SDmp)(3)(Me(4)Im)] 4 modeling the [Fe(4)S(4)(Cys)(3)(His)] cluster in hydrogenases, and its one-electron reduced form [4](-) was synthesized from the reaction of 3 with Me(4)Im. The reversible redox couple between 3 and [3](-) was observed at E(1/2) = -820 mV vs. Ag/Ag(+), and the corresponding reversible couple for 4 and [4](-) is positively shifted by +440 mV. The cyclic voltammogram of 3 also exhibited a reversible oxidation couple, which indicates generation of the all-ferric [Fe(4)S(4)](4+) cluster, [Fe(4)S(4)(SDmp)(4)].
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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
| | - Kazuki Tanifuji
- Department of Chemistry, Graduate School of Science and Research Center for Materials Science, Nagoya University, Furo-cho, Chikusa-ku, Nagoya 464-8602, Japan
| | - Norihiro Yamada
- Department of Chemistry, Graduate School of Science and Research Center for Materials Science, Nagoya University, Furo-cho, Chikusa-ku, Nagoya 464-8602, 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
| | - Tomoyuki Tajima
- Department of Chemistry, Graduate School of Science and Research Center for Materials Science, Nagoya University, Furo-cho, Chikusa-ku, Nagoya 464-8602, 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
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Chakrabarti M, Münck E, Bominaar EL. Density functional theory study of an all ferrous 4Fe-4S cluster. Inorg Chem 2011; 50:4322-6. [PMID: 21476577 DOI: 10.1021/ic102287j] [Citation(s) in RCA: 18] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/30/2022]
Abstract
The all-ferrous, carbene-capped Fe(4)S(4) cluster, synthesized by Deng and Holm (DH complex), has been studied with density functional theory (DFT). The geometry of the complex was optimized for several electronic configurations. The lowest energy was obtained for the broken-symmetry (BS) configuration derived from the ferromagnetic state by reversing the spin projection of one of the high spin (S(i) = 2) irons. The optimized geometry of the latter configuration contains one unique and three equivalent iron sites, which are both structurally and electronically clearly distinguishable. For example, a distinctive feature of the unique iron site is the diagonal Fe···S distance, which is 0.3 Å longer than for the equivalent irons. The calculated (57)Fe hyperfine parameters show the same 1:3 pattern as observed in the Mössbauer spectra and are in good agreement with experiment. BS analysis of the exchange interactions in the optimized geometry for the 1:3, M(S) = 4, BS configuration confirms the prediction of an earlier study that the unique site is coupled to the three equivalent ones by strong antiferromagnetic exchange (J > 0 in J Σ(j<4)Ŝ(4)·Ŝ(j)) and that the latter are mutually coupled by ferromagnetic exchange (J' < 0 in J' Σ(i<j<4)Ŝ(i)·Ŝ(j)). In combination, these exchange couplings stabilize an S = 4 ground state in which the composite spin of the three equivalent sites (S(123) = 6) is antiparallel to the spin (S(4) = 2) of the unique site. Thus, DFT analysis supports the idea that the unprecedented high value of the spin of the DH complex and, by analogy, of the all-ferrous cluster of the Fe-protein of nitrogenase, results from a remarkably strong dependence of the exchange interactions on cluster core geometry. The structure dependence of the exchange-coupling constants in the Fe(II)-(μ(3)-S)(2)-Fe(II) moieties of the all-ferrous clusters is compared with the magneto-structural correlations observed in the data for dinuclear copper complexes. Finally, we discuss two all-ferric clusters in the light of the results for the all-ferrous cluster.
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Affiliation(s)
- Mrinmoy Chakrabarti
- Department of Chemistry, Carnegie Mellon University, 4400 Fifth Avenue, Pittsburgh, Pennsylvania 15213, USA
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Deng L, Bill E, Wieghardt K, Holm RH. Cubane-type Co4S4 clusters: synthesis, redox series, and magnetic ground states. J Am Chem Soc 2009; 131:11213-21. [PMID: 19722678 PMCID: PMC3170832 DOI: 10.1021/ja903847a] [Citation(s) in RCA: 27] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/30/2022]
Abstract
The recent demonstration that the carbene cluster [Fe(4)S(4)(Pr(i)(2)NHCMe(2))(4)] (9) is an accurate structural and electronic analogue of the fully reduced cluster of the iron protein of Azotobacter vinelandii nitrogenase, including a common S = 4 ground state, raises the issue of the existence and magnetism of other [M(4)S(4)L(4)](z) clusters, none of which are known with transition metals other than iron. The system CoCl(2)/Pr(i)(3)P/(Me(3)Si)(2)S/THF assembles [Co(4)S(4)(PPr(i)(3))(4)] (3), which is converted to [Co(4)S(4)(Pr(i)(2)NHCMe(2))(4)] (5) upon reaction with carbene. The clusters support the redox series [3](1-/0/1+) and [5](0/1+/2+); monocations (4, 6) have been isolated by chemical oxidation. Redox potentials and substitution reactions indicate that the carbene is the more effective electron donor to tetrahedral Fe(II) and Co(II) sites. Clusters 3-6 have the same overall cubane-type geometry as 9. Neutral clusters 3 and 5 have an S = 3 ground state. As with the S = 4 state of 9 with local spins S(Fe) = 2, the septet spin state can be described in terms of the coupling of three parallel and one antiparallel spins S(Co) = 3/2. The octanuclear clusters [Co(8)S(8)(PPr(i)(3))(6)](0,1+) were isolated as minor byproducts of the formation and chemical oxidation of 3. The clusters exhibit a rhomb-bridged noncubane (RBNC) structure, whereas clusters with the Fe(8)S(8) core possess edge-bridged double-cubane (EBDC) stereochemistry. There are two structural solutions for the M(8)S(8) core in the form of topological isomers whose stability may depend on valence electron count. A conceptual model for the RBNC <--> EBDC interconversion is presented. (Pr(i)(2)NHCMe(2) = C(11)H(20)N(2) = 1,3-diisopropyl-4,5-dimethylimidazol-2-ylidene).
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Affiliation(s)
- Liang Deng
- Department of Chemistry and Chemical Biology, Harvard University, Cambridge, Massachusetts 02138
| | - Eckhard Bill
- Max-Planck-Institut für Bioanorganische Chemie, Mülheim an der Ruhr, Germany
| | - Karl Wieghardt
- Max-Planck-Institut für Bioanorganische Chemie, Mülheim an der Ruhr, Germany
| | - R. H. Holm
- Department of Chemistry and Chemical Biology, Harvard University, Cambridge, Massachusetts 02138
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Chakrabarti M, Deng L, Holm RH, Münck E, Bominaar EL. Mössbauer, electron paramagnetic resonance, and theoretical studies of a carbene-based all-ferrous Fe4S4 cluster: electronic origin and structural identification of the unique spectroscopic site. Inorg Chem 2009; 48:2735-47. [PMID: 19326927 DOI: 10.1021/ic802192w] [Citation(s) in RCA: 38] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Abstract
It is well established that the cysteinate-coordinated [Fe(4)S(4)] cluster of the iron protein of nitrogenase from Azotobacter vinelandii (Av2) can attain the all-ferrous core oxidation state. Mössbauer and electron paramagnetic resonance (EPR) studies have shown that the all-ferrous cluster has a ground-state spin S = 4 and an effective 3:1 site symmetry in the spin structure and (57)Fe quadrupole interactions. Recently, Deng and Holm reported the synthesis of [Fe(4)S(4)(Pr(i)(2)NHCMe(2))(4)],(2) (1; Pr(i)(2)NHCMe(2) = 1,3-diisopropyl-4,5-dimethylimidazol-2-ylidene) and showed that the all-ferrous carbene-coordinated cluster is amenable to physicochemical studies. Mössbauer and EPR studies of 1, reported here, reveal that the electronic structure of this complex is strikingly similar to that of the protein-bound cluster, suggesting that the ground-state spin and the 3:1 site ratio are consequences of spontaneous distortions of the cluster core. To gain insight into the origin of the peculiar ground state of the all-ferrous clusters in 1 and Av2, we have studied a theoretical model that is based on a Heisenberg-Dirac-van Vleck Hamiltonian whose exchange-coupling constants are a function of the Fe-Fe distances. By combining the exchange energies with the elastic deformation energies in the harmonic approximation, we obtain for a T(2) distortion a minimum with spin S = 4 and a C(3v) core structure in which one iron is unique and three irons are equivalent. This minimum has all of the spectroscopic and structural characteristics of the all-ferrous clusters of 1 and Av2. Our analysis maps the unique spectroscopic iron site to a specific site in the X-ray structure of the [Fe(4)S(4)](0) core both in complex 1 and in Av2.
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Affiliation(s)
- Mrinmoy Chakrabarti
- Department of Chemistry, Carnegie Mellon University, Pittsburgh, Pennsylvania 15213, USA
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Hans M, Buckel W, Bill E. Spectroscopic evidence for an all-ferrous [4Fe-4S]0 cluster in the superreduced activator of 2-hydroxyglutaryl-CoA dehydratase from Acidaminococcus fermentans. J Biol Inorg Chem 2008; 13:563-74. [PMID: 18274792 PMCID: PMC2359827 DOI: 10.1007/s00775-008-0345-z] [Citation(s) in RCA: 41] [Impact Index Per Article: 2.6] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/02/2007] [Accepted: 01/28/2008] [Indexed: 11/30/2022]
Abstract
The key enzyme of the fermentation of glutamate by Acidaminococcus fermentans, 2-hydroxyglutaryl-coenzyme A dehydratase, catalyzes the reversible syn-elimination of water from (R)-2-hydroxyglutaryl-coenzyme A, resulting in (E)-glutaconylcoenzyme A. The dehydratase system consists of two oxygen-sensitive protein components, the activator (HgdC) and the actual dehydratase (HgdAB). Previous biochemical and spectroscopic studies revealed that the reduced [4Fe-4S]+ cluster containing activator transfers one electron to the dehydratase driven by ATP hydrolysis, which activates the enzyme. With a tenfold excess of titanium(III) citrate at pH 8.0 the activator can be further reduced, yielding about 50% of a superreduced [4Fe-4S]0 cluster in the all-ferrous state. This is inferred from the appearance of a new Mössbauer spectrum with parameters delta = 0.65 mm/s and deltaE(Q) = 1.51-2.19 mm/s at 140 K, which are typical of Fe(II)S4 sites. Parallel-mode electron paramagnetic resonance (EPR) spectroscopy performed at temperatures between 3 and 20 K showed two sharp signals at g = 16 and 12, indicating an integer-spin system. The X-band EPR spectra and magnetic Mössbauer spectra could be consistently simulated by adopting a total spin S(t) = 4 for the all-ferrous cluster with weak zero-field splitting parameters D = -0.66 cm(-1) and E/D = 0.17. The superreduced cluster has apparent spectroscopic similarities with the corresponding [4Fe-4S]0 cluster described for the nitrogenase Fe-protein, but in detail their properties differ. While the all-ferrous Fe-protein is capable of transferring electrons to the MoFe-protein for dinitrogen reduction, a similar physiological role is elusive for the superreduced activator. This finding supports our model that only one-electron transfer steps are involved in dehydratase catalysis. Nevertheless we discuss a common basic mechanism of the two diverse systems, which are so far the only described examples of the all-ferrous [4Fe-4S]0 cluster found in biology.
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Affiliation(s)
- Marcus Hans
- Laboratorium für Mikrobiologie, Fachbereich Biologie, Philipps-Universität, 35032 Marburg, Germany
- DSM Anti-Infectives, Dep. DAI/INNO Genetics (624-0270), P.O. Box 425, 2600 AK Delft, The Netherlands
| | - Wolfgang Buckel
- Laboratorium für Mikrobiologie, Fachbereich Biologie, Philipps-Universität, 35032 Marburg, Germany
| | - Eckhard Bill
- Max-Planck-Institut für Bioanorganische Chemie, Stiftstrasse 34–36, 45470 Mülheim/Ruhr, Germany
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Corbett MC, Hu Y, Fay AW, Tsuruta H, Ribbe MW, Hodgson KO, Hedman B. Conformational differences between Azotobacter vinelandii nitrogenase MoFe proteins as studied by small-angle X-ray scattering. Biochemistry 2007; 46:8066-74. [PMID: 17567155 DOI: 10.1021/bi7005064] [Citation(s) in RCA: 22] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/30/2022]
Abstract
The nitrogenase MoFe protein is a heterotetramer containing two unique high-nuclearity metalloclusters, FeMoco and the P-cluster. FeMoco is assembled outside the MoFe protein, whereas the P-cluster is assembled directly on the MoFe protein polypeptides. MoFe proteins isolated from different genetic backgrounds have been analyzed using biochemical and spectroscopic techniques in attempting to elucidate the pathway of P-cluster biosynthesis. The DeltanifH MoFe protein is less stable than other MoFe proteins and has been shown by extended X-ray absorption fine structure studies to contain a variant P-cluster that most likely exists as two separate [Fe4S4]-like clusters instead of the subunit-bridging [Fe8S7] cluster found in the wild-type and DeltanifB forms of the MoFe protein [Corbett, M. C., et al. (2004) J. Biol. Chem. 279, 28276-28282]. Here, a combination of small-angle X-ray scattering and Fe chelation studies is used to show that there is a correlation between the state of the P-cluster and the conformation of the MoFe protein. The DeltanifH MoFe protein is found to be larger than the wild-type or DeltanifB MoFe proteins, an increase in size that can be modeled well by an opening of the subunit interface consistent with P-cluster fragmentation and solvent exposure. Importantly, this opening would allow for the insertion of P-cluster precursors into a region of the MoFe protein that is buried in the wild-type conformation. Thus, DeltanifH MoFe protein could represent an early intermediate in MoFe protein biosynthesis where the P-cluster precursors have been inserted, but P-cluster condensation and tetramer stabilization have yet to occur.
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Affiliation(s)
- Mary C Corbett
- Department of Chemistry, Stanford University, Stanford, California 94305-5080, USA
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Fay AW, Hu Y, Schmid B, Ribbe MW. Molecular insights into nitrogenase FeMoco insertion--the role of His 274 and His 451 of MoFe protein alpha subunit. J Inorg Biochem 2007; 101:1630-41. [PMID: 17521738 PMCID: PMC2935933 DOI: 10.1016/j.jinorgbio.2007.03.013] [Citation(s) in RCA: 22] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/28/2007] [Revised: 03/21/2007] [Accepted: 03/23/2007] [Indexed: 11/30/2022]
Abstract
The final step of FeMo cofactor (FeMoco) assembly involves the insertion of FeMoco into its binding site in the molybdenum-iron (MoFe) protein of nitrogenase. Here we examine the role of His alpha274 and His alpha451 of Azotobacter vinelandii MoFe protein in this process. Our results from combined metal, activity, EPR, stability and insertion analyses show that mutations of His alpha274 and/or His alpha451, two of the histidines that belong to a so-called His triad, to small uncharged Ala specifically reduce the accumulation of FeMoco in MoFe protein. This observation indicates that the enrichment of histidines at the His triad is important for FeMoco insertion and that the His triad potentially serves as an intermediate docking point for FeMoco through transitory ligand coordination and/or electrostatic interaction.
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Affiliation(s)
- Aaron W. Fay
- Department of Molecular Biology and Biochemistry, University of California, Irvine, CA 92697-3900
| | - Yilin Hu
- Department of Molecular Biology and Biochemistry, University of California, Irvine, CA 92697-3900
| | - Benedikt Schmid
- Department of Biotechnology, Friedrich-Alexander-University Erlangen-Nürnberg, 91052 Erlangen, Germany
| | - Markus W. Ribbe
- Department of Molecular Biology and Biochemistry, University of California, Irvine, CA 92697-3900
- *Address correspondence to: Markus W. Ribbe, Department of Molecular Biology and Biochemistry, University of California-Irvine, Irvine, CA 92697-3900; Tel. (949) 824-9509; Fax. (949) 824-8551; E-Mail:
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Hu Y, Fay AW, Ribbe MW. Molecular insights into nitrogenase FeMo cofactor insertion: the role of His 362 of the MoFe protein alpha subunit in FeMo cofactor incorporation. J Biol Inorg Chem 2007; 12:449-60. [PMID: 17203313 DOI: 10.1007/s00775-006-0199-1] [Citation(s) in RCA: 16] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/04/2006] [Accepted: 11/29/2006] [Indexed: 10/23/2022]
Abstract
The assembly of the complex iron-molybdenum cofactor (FeMoco) of nitrogenase molybdenum-iron (MoFe) protein has served as one of the central topics in the field of bioinorganic chemistry for decades. Here we examine the role of a MoFe protein residue (His alpha362) in FeMoco insertion, the final step of FeMoco biosynthesis where FeMoco is incorporated into its binding site in the MoFe protein. Our data from combined metal, activity and electron paramagnetic resonance analyses show that mutations of His alpha362 to small uncharged Ala or negatively charged Asp result in significantly reduced FeMoco accumulation in MoFe protein, indicating that His alpha362 plays a key role in the process of FeMoco insertion. Given the strategic location of His alpha362 at the entry point of the FeMoco insertion funnel, this residue may serve as one of the initial docking points for FeMoco insertion through transient ligand coordination and/or electrostatic interaction.
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Affiliation(s)
- Yilin Hu
- Department of Molecular Biology and Biochemistry, University of California, Irvine, CA 92697-3900, USA
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Hu Y, Corbett MC, Fay AW, Webber JA, Hodgson KO, Hedman B, Ribbe MW. Nitrogenase Fe protein: A molybdate/homocitrate insertase. Proc Natl Acad Sci U S A 2006; 103:17125-30. [PMID: 17062756 PMCID: PMC1859896 DOI: 10.1073/pnas.0602651103] [Citation(s) in RCA: 75] [Impact Index Per Article: 4.2] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/31/2006] [Indexed: 11/18/2022] Open
Abstract
The Fe protein is indispensable for nitrogenase catalysis and biosynthesis. However, its function in iron-molybdenum cofactor (FeMoco) biosynthesis has not been clearly defined. Here we show that the Fe protein can act as a Mo/homocitrate insertase that mobilizes Mo/homocitrate for the maturation of FeMoco precursor on NifEN. Further, we establish that Mo/homocitrate mobilization by the Fe protein likely involves hydrolysis of MgATP and protein-protein interaction between the Fe protein and NifEN. Our findings not only clarify the role of the Fe protein in FeMoco assembly and assign another function to this multitask enzyme but also provide useful insights into a mechanism of metal trafficking required for the assembly of complex metalloproteins such as nitrogenase.
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Affiliation(s)
- Yilin Hu
- *Department of Molecular Biology and Biochemistry, University of California, Irvine, CA 92697-3900
| | - Mary C. Corbett
- Department of Chemistry, Stanford University, Stanford, CA 94305; and
| | - Aaron W. Fay
- *Department of Molecular Biology and Biochemistry, University of California, Irvine, CA 92697-3900
| | - Jerome A. Webber
- *Department of Molecular Biology and Biochemistry, University of California, Irvine, CA 92697-3900
| | - Keith O. Hodgson
- Department of Chemistry, Stanford University, Stanford, CA 94305; and
- Stanford Synchrotron Radiation Laboratory, Stanford Linear Accelerator Center, Stanford University, 2575 Sand Hill Road, MS 69, Menlo Park, CA 94025-7015
| | - Britt Hedman
- Stanford Synchrotron Radiation Laboratory, Stanford Linear Accelerator Center, Stanford University, 2575 Sand Hill Road, MS 69, Menlo Park, CA 94025-7015
| | - Markus W. Ribbe
- *Department of Molecular Biology and Biochemistry, University of California, Irvine, CA 92697-3900
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Lowery TJ, Wilson PE, Zhang B, Bunker J, Harrison RG, Nyborg AC, Thiriot D, Watt GD. Flavodoxin hydroquinone reduces Azotobacter vinelandii Fe protein to the all-ferrous redox state with a S = 0 spin state. Proc Natl Acad Sci U S A 2006; 103:17131-6. [PMID: 17085583 PMCID: PMC1859897 DOI: 10.1073/pnas.0603223103] [Citation(s) in RCA: 43] [Impact Index Per Article: 2.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/18/2022] Open
Abstract
Azotobacter vinelandii flavodoxin hydroquinone (FldHQ) is a physiological reductant to nitrogenase supporting catalysis that is twice as energy efficient (ATP/2e- = 2) as dithionite (ATP/2e- = 4). This catalytic efficiency results from reduction of Fe protein from A. vinelandii (Av2) to the all-ferrous oxidation state ([Fe4S4]0), in contrast to dithionite, which only reduces Av2 to the [Fe4S4]1+ state. Like FldHQ, Ti(III) citrate yields ATP/2e- = 2, and Ti(III)-reduced [Fe4S4]0 Av2 has a S = 4 spin state and characteristic Mossbauer spectrum, a parallel mode g = 16.4 EPR signal, and a shoulder at 520 nm in its UV-vis spectrum, each of which distinguish the S = 4 [Fe4S4]0 Av2 from other states. In this study, we demonstrate that FldHQ makes [Fe4S4]0 Av2, which is sufficiently characterized to demonstrate unique physical properties that distinguish it from the previously characterized Ti(III)-reduced [Fe4S4]0 Av2. In particular, Evans NMR magnetic susceptibility and EPR measurements indicate that FldHQ-reduced [Fe4S4]0 Av2 has an S = 0 spin state (like [Fe4S4]2+ Av2). There is no g = 16.4 EPR signal and no shoulder at 520 nm in its absorbance spectrum, which resembles that of [Fe4S4]1+ Av2. That the physiological reductant to Av2 is capable of forming [Fe4S4]0 Av2 has important implications for in vivo nitrogenase activity.
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Affiliation(s)
| | - Phillip E. Wilson
- Department of Chemistry and Biochemistry, Brigham Young University, Provo, UT 84602
| | - Bo Zhang
- Department of Chemistry and Biochemistry, Brigham Young University, Provo, UT 84602
| | | | - Roger G. Harrison
- Department of Chemistry and Biochemistry, Brigham Young University, Provo, UT 84602
| | - Andrew C. Nyborg
- Department of Chemistry and Biochemistry, Brigham Young University, Provo, UT 84602
| | - David Thiriot
- Department of Chemistry and Biochemistry, Brigham Young University, Provo, UT 84602
| | - Gerald D. Watt
- Department of Chemistry and Biochemistry, Brigham Young University, Provo, UT 84602
- To whom correspondence should be addressed. E-mail:
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48
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Scott TA, Berlinguette CP, Holm RH, Zhou HC. Initial synthesis and structure of an all-ferrous analogue of the fully reduced [Fe4S4]0 cluster of the nitrogenase iron protein. Proc Natl Acad Sci U S A 2005; 102:9741-4. [PMID: 15985547 PMCID: PMC1175011 DOI: 10.1073/pnas.0504258102] [Citation(s) in RCA: 52] [Impact Index Per Article: 2.7] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/18/2022] Open
Abstract
The synthetic cubane-type iron-sulfur clusters [Fe(4)S(4)(SR)(4)](z) form a four-member electron transfer series (z = 3-, 2-, 1-, and 0), all members of which except that with z = 0 have been isolated and characterized. They serve as accurate analogues of protein-bound [Fe(4)S(4)(SCys)(4)](z) redox centers, which, in terms of core oxidation states, exhibit the redox couples [Fe(4)S(4)](3+/2+) and [Fe(4)S(4)](2+/1+). Clusters with the all-ferrous core [Fe(4)S(4)](0) have never been isolated because of their oxidative sensitivity. Recent work on the Fe protein of Azotobacter vinelandii nitrogenase has demonstrated the formation of the all-ferrous state upon reaction with a strong reductant. Treatment of the cyanide cluster [Fe(4)S(4)(CN)(4)](3-) with K[Ph(2)CO] in acetonitrile/tetrahydrofuran affords the all-ferrous cluster [Fe(4)S(4)(CN)(4)](4-), isolated as the Bu(4)N(+) salt. The x-ray structure demonstrates retention of a cubane-type structure with idealized D(2)(d) symmetry. The Mössbauer spectrum unambiguously demonstrates the [Fe(4)S(4)](0) oxidation state. Bond distances, core volumes, (57)Fe isomer shifts, and visible absorption spectra make evident the high degree of structural and electronic similarity with the fully reduced Fe protein. The attribute of cyanide ligation causes positive [Fe(4)S(4)](2+/1+) and [Fe(4)S(4)](1+/0) redox potential shifts, facilitating the initial isolation of an analogue of the [Fe(4)S(4)](0) protein site.
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Affiliation(s)
- Thomas A Scott
- Department of Chemistry and Biochemistry, Miami University, Oxford, OH 45056, USA
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49
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Hu Y, Fay AW, Dos Santos PC, Naderi F, Ribbe MW. Characterization of Azotobacter vinelandii nifZ deletion strains. Indication of stepwise MoFe protein assembly. J Biol Chem 2004; 279:54963-71. [PMID: 15485884 DOI: 10.1074/jbc.m408983200] [Citation(s) in RCA: 46] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
The nifZ gene product (NifZ) of Azotobacter vinelandii has been implicated in MoFe protein maturation. However, its exact function in this process remains largely unknown. Here, we report a detailed biochemical/biophysical characterization of His-tagged MoFe proteins purified from A. vinelandii nifZ and nifZ/nifB deletion strains DJ1182 and YM6A (Delta nifZ and Delta nifZ Delta nifB MoFe proteins, respectively). Our data from EPR, metal, activity, and stability analyses indicate that one alpha beta subunit pair of the Delta nifZ MoFe protein contains a P cluster ([8Fe-7S]) and an iron-molybdenum cofactor (FeMoco) ([Mo-7Fe-9S-X-homocitrate]), whereas the other contains a presumed P cluster precursor, possibly comprising a pair of [4Fe-4S]-like clusters, and a vacant FeMoco site. Likewise, the Delta nifZ Delta nifB MoFe protein has the same composition as the Delta nifZ MoFe protein except for the absence of FeMoco, an effect caused by the deletion of the nifB gene. These results suggest that the MoFe protein is likely assembled stepwise, i.e. one alpha beta subunit pair of the tetrameric MoFe protein is assembled prior to the other, and that NifZ might act as a chaperone in the assembly of the second alpha beta subunit pair by facilitating a conformational rearrangement that is required for the formation of the P cluster through the condensation of two [4Fe-4S]-like clusters. The possibility of NifZ exercising its effect through the Fe protein was ruled out because the Fe proteins from nifZ and nifZ/nifB deletion strains are not defective in their normal functions. However, the detailed mechanism of how NifZ carries out its exact function in MoFe protein maturation awaits further investigation.
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Affiliation(s)
- Yilin Hu
- Department of Molecular Biology and Biochemistry, University of California, Irvine, California 92697-3900, USA
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50
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Abstract
Metallocluster-containing enzymes catalyze some of the most basic redox transformations in the biosphere. The reactions catalyzed by these enzymes typically involve small molecules such as N2, CO, and H2 that are used to generate both chemical building blocks and energy for metabolic purposes. During the past decade, structures have been established for the iron-sulfur-based metalloclusters present in the molybdenum nitrogenase, the iron-only hydrogenase, and the nickel-carbon monoxide dehydrogenase, and for the copper-sulfide-based cluster in nitrous oxide reductase. Although these clusters are built from interactions observed in simpler metalloproteins, they contain novel features that may be relevant for their catalytic function. The mechanisms of metallocluster-containing enzymes are still poorly defined, and represent substantial and continuing challenges to biochemists, biophysicists, and synthetic chemists. These proteins also provide a window into the union of the biological and inorganic worlds that may have been relevant to the early evolution of biochemical catalysis.
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Affiliation(s)
- Douglas C Rees
- Division of Chemistry and Chemical Engineering 147-75CH, Howard Hughes Medical Institute, California Institute of Technology, Pasadena, California 91125, USA.
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