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Lee CC, Górecki K, Stang M, Ribbe MW, Hu Y. Cofactor maturase NifEN: A prototype ancient nitrogenase? SCIENCE ADVANCES 2024; 10:eado6169. [PMID: 38865457 PMCID: PMC11168457 DOI: 10.1126/sciadv.ado6169] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 02/11/2024] [Accepted: 05/07/2024] [Indexed: 06/14/2024]
Abstract
Nitrogenase plays a key role in the global nitrogen cycle; yet, the evolutionary history of nitrogenase and, particularly, the sequence of appearance between the homologous, yet distinct NifDK (the catalytic component) and NifEN (the cofactor maturase) of the extant molybdenum nitrogenase, remains elusive. Here, we report the ability of NifEN to reduce N2 at its surface-exposed L-cluster ([Fe8S9C]), a structural/functional homolog of the M-cluster (or cofactor; [(R-homocitrate)MoFe7S9C]) of NifDK. Furthermore, we demonstrate the ability of the L-cluster-bound NifDK to mimic its NifEN counterpart and enable N2 reduction. These observations, coupled with phylogenetic, ecological, and mechanistic considerations, lead to the proposal of a NifEN-like, L-cluster-carrying protein as an ancient nitrogenase, the exploration of which could shed crucial light on the evolutionary origin of nitrogenase and related enzymes.
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Affiliation(s)
- Chi Chung Lee
- Department of Molecular Biology and Biochemistry, University of California, Irvine, CA 92697- 3900, USA
| | - Kamil Górecki
- Department of Molecular Biology and Biochemistry, University of California, Irvine, CA 92697- 3900, USA
| | - Martin Stang
- Department of Chemistry, University of California, Irvine, CA 92697-2025, USA
| | - 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
| | - Yilin Hu
- Department of Molecular Biology and Biochemistry, University of California, Irvine, CA 92697- 3900, USA
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Körner D, Schäfer NM, Lagares Jr. A, Birmes L, Oehlmann NN, Addison H, Pöhl S, Thanbichler M, Rebelein JG, Petersen J, Becker A. Modular Low-Copy-Number Plasmid Vectors for Rhodobacterales with Extended Host Range in Alphaproteobacteria. ACS Synth Biol 2024; 13:1537-1548. [PMID: 38718218 PMCID: PMC11107812 DOI: 10.1021/acssynbio.4c00062] [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: 01/30/2024] [Revised: 03/27/2024] [Accepted: 04/15/2024] [Indexed: 05/18/2024]
Abstract
Members of the alphaproteobacterial order Rhodobacterales are metabolically diverse and highly abundant in the ocean. They are becoming increasingly interesting for marine biotechnology, due to their ecological adaptability, wealth of versatile low-copy-number plasmids, and their ability to produce secondary metabolites. However, molecular tools for engineering strains of this bacterial lineage are limited. Here, we expand the genetic toolbox by establishing standardized, modular repABC-based plasmid vectors of four well-characterized compatibility groups from the Roseobacter group applicable in the Rhodobacterales, and likely in further alphaproteobacterial orders (Hyphomicrobiales, Rhodospirillales, Caulobacterales). We confirmed replication of these newly constructed pABC vectors in two members of Rhodobacterales, namely, Dinoroseobacter shibae DFL 12 and Rhodobacter capsulatus B10S, as well as in two members of the alphaproteobacterial order Hyphomicrobiales (synonym: Rhizobiales; Ensifer meliloti 2011 and "Agrobacterium fabrum" C58). Maintenance of the pABC vectors in the biotechnologically valuable orders Rhodobacterales and Hyphomicrobiales facilitates the shuttling of genetic constructs between alphaproteobacterial genera and orders. Additionally, plasmid replication was verified in one member of Rhodospirillales (Rhodospirillum rubrum S1) as well as in one member of Caulobacterales (Caulobacter vibrioides CB15N). The modular construction of pABC vectors and the usage of four compatible replication systems, which allows their coexistence in a host cell, are advantageous features for future implementations of newly designed synthetic pathways. The vector applicability was demonstrated by functional complementation of a nitrogenase mutant phenotype by two complementary pABC-based plasmids in R. capsulatus.
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Affiliation(s)
- Désirée Körner
- Center
for Synthetic Microbiology (SYNMIKRO) and Department of Biology, Philipps-Universität Marburg, Marburg 35043, Germany
| | - Niklas M. Schäfer
- Center
for Synthetic Microbiology (SYNMIKRO) and Department of Biology, Philipps-Universität Marburg, Marburg 35043, Germany
| | - Antonio Lagares Jr.
- Center
for Synthetic Microbiology (SYNMIKRO) and Department of Biology, Philipps-Universität Marburg, Marburg 35043, Germany
| | - Lukas Birmes
- Leibniz-Institut
DSMZ - Deutsche Sammlung von Mikroorganismen und Zellkulturen GmbH, Braunschweig 38124, Germany
| | - Niels N. Oehlmann
- Max
Planck Institute for Terrestrial Microbiology, Marburg 35043, Germany
| | - Holly Addison
- Max
Planck Institute for Terrestrial Microbiology, Marburg 35043, Germany
| | - Sebastian Pöhl
- Center
for Synthetic Microbiology (SYNMIKRO) and Department of Biology, Philipps-Universität Marburg, Marburg 35043, Germany
| | - Martin Thanbichler
- Center
for Synthetic Microbiology (SYNMIKRO) and Department of Biology, Philipps-Universität Marburg, Marburg 35043, Germany
- Max
Planck Institute for Terrestrial Microbiology, Marburg 35043, Germany
| | - Johannes G. Rebelein
- Center
for Synthetic Microbiology (SYNMIKRO) and Department of Biology, Philipps-Universität Marburg, Marburg 35043, Germany
- Max
Planck Institute for Terrestrial Microbiology, Marburg 35043, Germany
| | - Jörn Petersen
- Leibniz-Institut
DSMZ - Deutsche Sammlung von Mikroorganismen und Zellkulturen GmbH, Braunschweig 38124, Germany
| | - Anke Becker
- Center
for Synthetic Microbiology (SYNMIKRO) and Department of Biology, Philipps-Universität Marburg, Marburg 35043, Germany
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Dobrzyńska K, Pérez-González A, Echavarri-Erasun C, Coroian D, Salinero-Lanzarote A, Veldhuizen M, Dean DR, Burén S, Rubio LM. Nitrogenase cofactor biosynthesis using proteins produced in mitochondria of Saccharomyces cerevisiae. mBio 2024; 15:e0308823. [PMID: 38126768 PMCID: PMC10865832 DOI: 10.1128/mbio.03088-23] [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: 11/14/2023] [Accepted: 11/20/2023] [Indexed: 12/23/2023] Open
Abstract
Biological nitrogen fixation, the conversion of inert N2 to metabolically tractable NH3, is only performed by certain microorganisms called diazotrophs and is catalyzed by the nitrogenases. A [7Fe-9S-C-Mo-R-homocitrate]-cofactor, designated FeMo-co, provides the catalytic site for N2 reduction in the Mo-dependent nitrogenase. Thus, achieving FeMo-co formation in model eukaryotic organisms, such as Saccharomyces cerevisiae, represents an important milestone toward endowing them with a capacity for Mo-dependent biological nitrogen fixation. A central player in FeMo-co assembly is the scaffold protein NifEN upon which processing of NifB-co, an [8Fe-9S-C] precursor produced by NifB, occurs. Prior work established that NifB-co can be produced in S. cerevisiae mitochondria. In the present work, a library of nifEN genes from diverse diazotrophs was expressed in S. cerevisiae, targeted to mitochondria, and surveyed for their ability to produce soluble NifEN protein complexes. Many such NifEN variants supported FeMo-co formation when heterologously produced in the diazotroph A. vinelandii. However, only three of them accumulated in soluble forms in mitochondria of aerobically cultured S. cerevisiae. Of these, two variants were active in the in vitro FeMo-co synthesis assay. NifEN, NifB, and NifH proteins from different species, all of them produced in and purified from S. cerevisiae mitochondria, were combined to establish successful FeMo-co biosynthetic pathways. These findings demonstrate that combining diverse interspecies nitrogenase FeMo-co assembly components could be an effective and, perhaps, the only approach to achieve and optimize nitrogen fixation in a eukaryotic organism.IMPORTANCEBiological nitrogen fixation, the conversion of inert N2 to metabolically usable NH3, is a process exclusive to diazotrophic microorganisms and relies on the activity of nitrogenases. The assembly of the nitrogenase [7Fe-9S-C-Mo-R-homocitrate]-cofactor (FeMo-co) in a eukaryotic cell is a pivotal milestone that will pave the way to engineer cereals with nitrogen fixing capabilities and therefore independent of nitrogen fertilizers. In this study, we identified NifEN protein complexes that were functional in the model eukaryotic organism Saccharomyces cerevisiae. NifEN is an essential component of the FeMo-co biosynthesis pathway. Furthermore, the FeMo-co biosynthetic pathway was recapitulated in vitro using only proteins expressed in S. cerevisiae. FeMo-co biosynthesis was achieved by combining nitrogenase FeMo-co assembly components from different species, a promising strategy to engineer nitrogen fixation in eukaryotic organisms.
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Affiliation(s)
- Katarzyna Dobrzyńska
- Centro de Biotecnología y Genómica de Plantas, Universidad Politécnica de Madrid (UPM), Instituto Nacional de Investigación y Tecnología Agraria y Alimentaria (INIA/CSIC), Pozuelo de Alarcón, Spain
- Departamento de Biotecnología-Biología Vegetal, Escuela Técnica Superior de Ingeniería Agronómica, Alimentaría y de Biosistemas, Universidad Politécnica de Madrid, Madrid, Spain
| | | | - Carlos Echavarri-Erasun
- Centro de Biotecnología y Genómica de Plantas, Universidad Politécnica de Madrid (UPM), Instituto Nacional de Investigación y Tecnología Agraria y Alimentaria (INIA/CSIC), Pozuelo de Alarcón, Spain
- Departamento de Biotecnología-Biología Vegetal, Escuela Técnica Superior de Ingeniería Agronómica, Alimentaría y de Biosistemas, Universidad Politécnica de Madrid, Madrid, Spain
| | - Diana Coroian
- Centro de Biotecnología y Genómica de Plantas, Universidad Politécnica de Madrid (UPM), Instituto Nacional de Investigación y Tecnología Agraria y Alimentaria (INIA/CSIC), Pozuelo de Alarcón, Spain
| | - Alvaro Salinero-Lanzarote
- Centro de Biotecnología y Genómica de Plantas, Universidad Politécnica de Madrid (UPM), Instituto Nacional de Investigación y Tecnología Agraria y Alimentaria (INIA/CSIC), Pozuelo de Alarcón, Spain
| | - Marcel Veldhuizen
- Centro de Biotecnología y Genómica de Plantas, Universidad Politécnica de Madrid (UPM), Instituto Nacional de Investigación y Tecnología Agraria y Alimentaria (INIA/CSIC), Pozuelo de Alarcón, Spain
| | - Dennis R. Dean
- Department of Biochemistry, Virginia Tech, Blacksburg, Virginia, USA
| | - Stefan Burén
- Centro de Biotecnología y Genómica de Plantas, Universidad Politécnica de Madrid (UPM), Instituto Nacional de Investigación y Tecnología Agraria y Alimentaria (INIA/CSIC), Pozuelo de Alarcón, Spain
- Departamento de Biotecnología-Biología Vegetal, Escuela Técnica Superior de Ingeniería Agronómica, Alimentaría y de Biosistemas, Universidad Politécnica de Madrid, Madrid, Spain
| | - Luis M. Rubio
- Centro de Biotecnología y Genómica de Plantas, Universidad Politécnica de Madrid (UPM), Instituto Nacional de Investigación y Tecnología Agraria y Alimentaria (INIA/CSIC), Pozuelo de Alarcón, Spain
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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] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/20/2023] [Accepted: 09/27/2023] [Indexed: 11/03/2023] Open
Abstract
The functional versatility of the Fe protein, the reductase component of nitrogenase, makes it an appealing target for heterologous expression, which could facilitate future biotechnological adaptations of nitrogenase-based production of valuable chemical commodities. Yet, the heterologous synthesis of a fully active Fe protein of Azotobacter vinelandii (AvNifH) in Escherichia coli has proven to be a challenging task. Here, we report the successful synthesis of a fully active AvNifH protein upon co-expression of this protein with AvIscS/U and AvNifM in E. coli. Our metal, activity, electron paramagnetic resonance, and X-ray absorption spectroscopy/extended X-ray absorption fine structure (EXAFS) data demonstrate that the heterologously expressed AvNifH protein has a high [Fe4S4] cluster content and is fully functional in nitrogenase catalysis and assembly. Moreover, our phylogenetic analyses and structural predictions suggest that AvNifM could serve as a chaperone and assist the maturation of a cluster-replete AvNifH protein. Given the crucial importance of the Fe protein for the functionality of nitrogenase, this work establishes an effective framework for developing a heterologous expression system of the complete, two-component nitrogenase system; additionally, it provides a useful tool for further exploring the intricate biosynthetic mechanism of this structurally unique and functionally important metalloenzyme. 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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5
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Quechol R, Solomon JB, Liu YA, Lee CC, Jasniewski AJ, Górecki K, Oyala P, Hedman B, Hodgson KO, Ribbe MW, Hu Y. Heterologous synthesis of the complex homometallic cores of nitrogenase P- and M-clusters in Escherichia coli. Proc Natl Acad Sci U S A 2023; 120:e2314788120. [PMID: 37871225 PMCID: PMC10622910 DOI: 10.1073/pnas.2314788120] [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: 08/26/2023] [Accepted: 09/28/2023] [Indexed: 10/25/2023] Open
Abstract
Nitrogenase is an active target of heterologous expression because of its importance for areas related to agronomy, energy, and environment. One major hurdle for expressing an active Mo-nitrogenase in Escherichia coli is to generate the complex metalloclusters (P- and M-clusters) within this enzyme, which involves some highly unique bioinorganic chemistry/metalloenzyme biochemistry that is not generally dealt with in the heterologous expression of proteins via synthetic biology; in particular, the heterologous synthesis of the homometallic P-cluster ([Fe8S7]) and M-cluster core (or L-cluster; [Fe8S9C]) on their respective protein scaffolds, which represents two crucial checkpoints along the biosynthetic pathway of a complete nitrogenase, has yet to be demonstrated by biochemical and spectroscopic analyses of purified metalloproteins. Here, we report the heterologous formation of a P-cluster-containing NifDK protein upon coexpression of Azotobacter vinelandii nifD, nifK, nifH, nifM, and nifZ genes, and that of an L-cluster-containing NifB protein upon coexpression of Methanosarcina acetivorans nifB, nifS, and nifU genes alongside the A. vinelandii fdxN gene, in E. coli. Our metal content, activity, EPR, and XAS/EXAFS data provide conclusive evidence for the successful synthesis of P- and L-clusters in a nondiazotrophic host, thereby highlighting the effectiveness of our metallocentric, divide-and-conquer approach that individually tackles the key events of nitrogenase biosynthesis prior to piecing them together into a complete pathway for the heterologous expression of nitrogenase. As such, this work paves the way for the transgenic expression of an active nitrogenase while providing an effective tool for further tackling the biosynthetic mechanism of this important metalloenzyme.
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Affiliation(s)
- Robert Quechol
- Department of Molecular Biology and Biochemistry, University of California, Irvine, CA92697-3900
| | - Joseph B. Solomon
- Department of Molecular Biology and Biochemistry, University of California, Irvine, CA92697-3900
- Department of Chemistry, University of California, Irvine, CA92697-2025
| | - Yiling A. Liu
- Department of Molecular Biology and Biochemistry, University of California, Irvine, CA92697-3900
| | - Chi Chung Lee
- Department of Molecular Biology and Biochemistry, University of California, Irvine, CA92697-3900
| | - Andrew J. Jasniewski
- Department of Molecular Biology and Biochemistry, University of California, Irvine, CA92697-3900
| | - Kamil Górecki
- Department of Molecular Biology and Biochemistry, University of California, Irvine, CA92697-3900
| | - Paul Oyala
- Department of Chemistry and Chemical Engineering, California Institute of Technology, Pasadena, CA91125
| | - Britt Hedman
- Stanford Synchrotron Radiation Lightsource, Stanford Linear Accelerator Center National Accelerator Laboratory, Stanford University, Menlo Park, CA94025
| | - Keith O. Hodgson
- Stanford Synchrotron Radiation Lightsource, Stanford Linear Accelerator Center National Accelerator Laboratory, Stanford University, Menlo Park, CA94025
- Department of Chemistry, Stanford University, Stanford, CA94305
| | - Markus W. Ribbe
- Department of Molecular Biology and Biochemistry, University of California, Irvine, CA92697-3900
- Department of Chemistry, University of California, Irvine, CA92697-2025
| | - Yilin Hu
- Department of Molecular Biology and Biochemistry, University of California, Irvine, CA92697-3900
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Li X, Li Z. What determines symbiotic nitrogen fixation efficiency in rhizobium: recent insights into Rhizobium leguminosarum. Arch Microbiol 2023; 205:300. [PMID: 37542687 DOI: 10.1007/s00203-023-03640-7] [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: 06/01/2023] [Revised: 07/21/2023] [Accepted: 07/24/2023] [Indexed: 08/07/2023]
Abstract
Symbiotic nitrogen fixation (SNF) by rhizobium, a Gram-negative soil bacterium, is an essential component in the nitrogen cycle and is a sustainable green way to maintain soil fertility without chemical energy consumption. SNF, which results from the processes of nodulation, rhizobial infection, bacteroid differentiation and nitrogen-fixing reaction, requires the expression of various genes from both symbionts with adaptation to the changing environment. To achieve successful nitrogen fixation, rhizobia and their hosts cooperate closely for precise regulation of symbiotic genes, metabolic processes and internal environment homeostasis. Many researches have progressed to reveal the ample information about regulatory aspects of SNF during recent decades, but the major bottlenecks regarding improvement of nitrogen-fixing efficiency has proven to be complex. In this mini-review, we summarize recent advances that have contributed to understanding the rhizobial regulatory aspects that determine SNF efficiency, focusing on the coordinated regulatory mechanism of symbiotic genes, oxygen, carbon metabolism, amino acid metabolism, combined nitrogen, non-coding RNAs and internal environment homeostasis. Unraveling regulatory determinants of SNF in the nitrogen-fixing protagonist rhizobium is expected to promote an improvement of nitrogen-fixing efficiency in crop production.
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Affiliation(s)
- Xiaofang Li
- Institute of Biopharmaceuticals, Taizhou University, 1139 Shifu Avenue, Taizhou, 318000, China.
- School of Pharmaceutical Sciences, Taizhou University, 1139 Shifu Avenue, Taizhou, 318000, China.
| | - Zhangqun Li
- School of Pharmaceutical Sciences, Taizhou University, 1139 Shifu Avenue, Taizhou, 318000, China
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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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Liu YA, Quechol R, Solomon JB, Lee CC, Ribbe MW, Hu Y, Hedman B, Hodgson KO. Radical SAM-dependent formation of a nitrogenase cofactor core on NifB. J Inorg Biochem 2022; 233:111837. [PMID: 35550498 PMCID: PMC9526504 DOI: 10.1016/j.jinorgbio.2022.111837] [Citation(s) in RCA: 2] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/31/2021] [Revised: 04/10/2022] [Accepted: 04/14/2022] [Indexed: 11/15/2022]
Abstract
Nitrogenase is a versatile metalloenzyme that reduces N2, CO and CO2 at its cofactor site. Designated the M-cluster, this complex cofactor has a composition of [(R-homocitrate)MoFe7S9C], and it is assembled through the generation of a unique [Fe8S9C] core prior to the insertion of Mo and homocitrate. NifB is a radical S-adenosyl-L-methionine (SAM) enzyme that is essential for nitrogenase cofactor assembly. This review focuses on the recent work that sheds light on the role of NifB in the formation of the [Fe8S9C] core of the nitrogenase cofactor, highlighting the structure, function and mechanism of this unique radical SAM methyltransferase.
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Affiliation(s)
- Yiling A Liu
- Department of Molecular Biology and Biochemistry, University of California, Irvine, CA 92697-3900, United States of America
| | - Robert Quechol
- Department of Molecular Biology and Biochemistry, University of California, Irvine, CA 92697-3900, United States of America
| | - Joseph B Solomon
- Department of Molecular Biology and Biochemistry, University of California, Irvine, CA 92697-3900, United States of America; Department of Chemistry, University of California, Irvine, CA 92697-2025, United States of America
| | - Chi Chung Lee
- Department of Molecular Biology and Biochemistry, University of California, Irvine, CA 92697-3900, United States of America
| | - Markus W Ribbe
- Department of Molecular Biology and Biochemistry, University of California, Irvine, CA 92697-3900, United States of America; Department of Chemistry, University of California, Irvine, CA 92697-2025, United States of America.
| | - Yilin Hu
- Department of Molecular Biology and Biochemistry, University of California, Irvine, CA 92697-3900, United States of America.
| | - Britt Hedman
- Stanford Synchrotron Radiation Lightsource, SLAC National Accelerator Laboratory, Stanford University, Menlo Park, CA 94025, United States of America.
| | - Keith O Hodgson
- Stanford Synchrotron Radiation Lightsource, SLAC National Accelerator Laboratory, Stanford University, Menlo Park, CA 94025, United States of America; Department of Chemistry, Stanford University, Stanford, CA 94305, United States of America.
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Specificity of NifEN and VnfEN for the Assembly of Nitrogenase Active Site Cofactors in Azotobacter vinelandii. mBio 2021; 12:e0156821. [PMID: 34281397 PMCID: PMC8406325 DOI: 10.1128/mbio.01568-21] [Citation(s) in RCA: 4] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022] Open
Abstract
The nitrogen-fixing microbe Azotobacter vinelandii has the ability to produce three genetically distinct, but mechanistically similar, components that catalyze nitrogen fixation. For two of these components, the Mo-dependent and V-dependent components, their corresponding metal-containing active site cofactors, designated FeMo-cofactor and FeV-cofactor, respectively, are preformed on separate molecular scaffolds designated NifEN and VnfEN, respectively. From prior studies, and the present work, it is now established that neither of these scaffolds can replace the other with respect to their in vivo cofactor assembly functions. Namely, a strain inactivated for NifEN cannot produce active Mo-dependent nitrogenase nor can a strain inactivated for VnfEN produce an active V-dependent nitrogenase. It is therefore proposed that metal specificities for FeMo-cofactor and FeV-cofactor formation are supplied by their respective assembly scaffolds. In the case of the third, Fe-only component, its associated active site cofactor, designated FeFe-cofactor, requires neither the NifEN nor VnfEN assembly scaffold for its formation. Furthermore, there are no other genes present in A. vinelandii that encode proteins having primary structure similarity to either NifEN or VnfEN. It is therefore concluded that FeFe-cofactor assembly is completed within its cognate catalytic protein partner without the aid of an intermediate assembly site. IMPORTANCE Biological nitrogen fixation is a complex process involving the nitrogenases. The biosynthesis of an active nitrogenase involves a large number of genes and the coordinated function of their products. Understanding the details of the assembly and activation of the different nitrogen fixation components, in particular the simplest one known so far, the Fe-only nitrogenase, would contribute to the goal of transferring the necessary genetic elements of bacterial nitrogen fixation to cereal crops to endow them with the capacity for self-fertilization. In this work, we show that there is no need for a scaffold complex for the assembly of the FeFe-cofactor, which provides the active site for Fe-only nitrogenase. These results are in agreement with previously reported genetic reconstruction experiments using a non-nitrogen-fixing microbe. In aggregate, these findings provide a high degree of confidence that the Fe-only system represents the simplest and, therefore, most attractive target for mobilizing nitrogen fixation into plants.
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10
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Chen Y, Nishihara A, Haruta S. Nitrogen-fixing Ability and Nitrogen Fixation-related Genes of Thermophilic Fermentative Bacteria in the Genus Caldicellulosiruptor. Microbes Environ 2021; 36. [PMID: 34108360 PMCID: PMC8209448 DOI: 10.1264/jsme2.me21018] [Citation(s) in RCA: 8] [Impact Index Per Article: 2.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/19/2022] Open
Abstract
Fermentative nitrogen-fixing bacteria have not yet been examined in detail in thermal environments. In the present study, we isolated the thermophilic fermentative bacterium, strain YA01 from a hot spring. This strain grew at temperatures up to 78°C. A phylogenetic analysis based on its 16S rRNA gene sequence indicated that strain YA01 belonged to the genus Caldicellulosiruptor, which are fermentative bacteria in the phylum Firmicutes, with 97.7–98.0% sequence identity to its closest relatives. Strain YA01 clearly exhibited N2-dependent growth at 70°C. We also confirmed N2-dependent growth in the relatives of strain YA01, Caldicellulosiruptor hydrothermalis 108 and Caldicellulosiruptor kronotskyensis 2002. The nitrogenase activities of these three strains were examined using the acetylene reduction assay. Similar activities were detected for all tested strains, and were slightly suppressed by the addition of ammonium. A genome analysis revealed that strain YA01, as well as other Caldicellulosiruptor, possessed a gene set for nitrogen fixation, but lacked the nifN gene, which encodes a nitrogenase iron-molybdenum cofactor biosynthesis protein that is commonly detected in nitrogen-fixing bacteria. The amino acid sequences of nitrogenase encoded by nifH, nifD, and nifK shared 92–98% similarity in Caldicellulosiruptor. A phylogenetic tree of concatenated NifHDK sequences showed that NifHDK of Caldicellulosiruptor was in the deepest clade. To the best of our knowledge, this is the first study to demonstrate the nitrogen-fixing ability of fermentative bacteria at 70°C. Caldicellulosiruptor may have retained an ancient nitrogen-fixing enzyme system.
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Affiliation(s)
- Yuxin Chen
- Department of Biological Sciences, Tokyo Metropolitan University
| | - Arisa Nishihara
- Department of Biological Sciences, Tokyo Metropolitan University.,Bioproduction Research Institute, National Institute of Advanced Industrial Science and Technology (AIST)
| | - Shin Haruta
- Department of Biological Sciences, Tokyo Metropolitan University
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11
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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: 111] [Impact Index Per Article: 27.8] [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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12
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Tanifuji K, Ohki Y. Metal–Sulfur Compounds in N2 Reduction and Nitrogenase-Related Chemistry. Chem Rev 2020; 120:5194-5251. [DOI: 10.1021/acs.chemrev.9b00544] [Citation(s) in RCA: 66] [Impact Index Per Article: 16.5] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/21/2022]
Affiliation(s)
- Kazuki Tanifuji
- Department of Molecular Biology and Biochemistry, University of California, Irvine, Irvine, California 92697-3900, United States
| | - Yasuhiro Ohki
- Department of Chemsitry, Graduate School of Science, Nagoya University, Furo-cho, Chikusa-ku, Nagoya 464-8602, Japan
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13
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Garcia AK, McShea H, Kolaczkowski B, Kaçar B. Reconstructing the evolutionary history of nitrogenases: Evidence for ancestral molybdenum-cofactor utilization. GEOBIOLOGY 2020; 18:394-411. [PMID: 32065506 PMCID: PMC7216921 DOI: 10.1111/gbi.12381] [Citation(s) in RCA: 32] [Impact Index Per Article: 8.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 07/25/2019] [Revised: 12/23/2019] [Accepted: 01/22/2020] [Indexed: 05/08/2023]
Abstract
The nitrogenase metalloenzyme family, essential for supplying fixed nitrogen to the biosphere, is one of life's key biogeochemical innovations. The three forms of nitrogenase differ in their metal dependence, each binding either a FeMo-, FeV-, or FeFe-cofactor where the reduction of dinitrogen takes place. The history of nitrogenase metal dependence has been of particular interest due to the possible implication that ancient marine metal availabilities have significantly constrained nitrogenase evolution over geologic time. Here, we reconstructed the evolutionary history of nitrogenases, and combined phylogenetic reconstruction, ancestral sequence inference, and structural homology modeling to evaluate the potential metal dependence of ancient nitrogenases. We find that active-site sequence features can reliably distinguish extant Mo-nitrogenases from V- and Fe-nitrogenases and that inferred ancestral sequences at the deepest nodes of the phylogeny suggest these ancient proteins most resemble modern Mo-nitrogenases. Taxa representing early-branching nitrogenase lineages lack one or more biosynthetic nifE and nifN genes that both contribute to the assembly of the FeMo-cofactor in studied organisms, suggesting that early Mo-nitrogenases may have utilized an alternate and/or simplified pathway for cofactor biosynthesis. Our results underscore the profound impacts that protein-level innovations likely had on shaping global biogeochemical cycles throughout the Precambrian, in contrast to organism-level innovations that characterize the Phanerozoic Eon.
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Affiliation(s)
- Amanda K. Garcia
- Department of Molecular and Cellular BiologyUniversity of ArizonaTucsonArizona
| | - Hanon McShea
- Department of Earth System ScienceStanford UniversityStanfordCalifornia
| | - Bryan Kolaczkowski
- Department of Microbiology and Cell ScienceUniversity of FloridaGainesvilleFlorida
| | - Betül Kaçar
- Department of Molecular and Cellular BiologyUniversity of ArizonaTucsonArizona
- Steward Observatory and the Lunar and Planetary LaboratoryUniversity of ArizonaTucsonArizona
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14
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Solomon JB, Lee CC, Jasniewski AJ, Rasekh MF, Ribbe MW, Hu Y. Heterologous Expression and Engineering of the Nitrogenase Cofactor Biosynthesis Scaffold NifEN. Angew Chem Int Ed Engl 2020. [DOI: 10.1002/ange.201916598] [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)
- Joseph B. Solomon
- Department of Molecular Biology & Biochemistry University of California, Irvine Irvine CA 92697-3900 USA
- Department Chemistry University of California, Irvine Irvine CA 92697-2025 USA
| | - Chi Chung Lee
- Department of Molecular Biology & Biochemistry University of California, Irvine Irvine CA 92697-3900 USA
| | - Andrew J. Jasniewski
- Department of Molecular Biology & Biochemistry University of California, Irvine Irvine CA 92697-3900 USA
| | - Mahtab F. Rasekh
- Department of Molecular Biology & Biochemistry University of California, Irvine Irvine CA 92697-3900 USA
- Department Chemistry University of California, Irvine Irvine CA 92697-2025 USA
| | - Markus W. Ribbe
- Department of Molecular Biology & Biochemistry University of California, Irvine 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 Irvine CA 92697-3900 USA
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15
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Ghebreamlak SM, Mansoorabadi SO. Divergent Members of the Nitrogenase Superfamily: Tetrapyrrole Biosynthesis and Beyond. Chembiochem 2020; 21:1723-1728. [PMID: 32180329 DOI: 10.1002/cbic.201900782] [Citation(s) in RCA: 9] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/24/2019] [Revised: 02/13/2020] [Indexed: 11/06/2022]
Abstract
The nitrogenase superfamily constitutes a large and diverse ensemble of two-component metalloenzymes. These systems couple the hydrolysis of ATP to the reduction of disparate substrates from diatomic gases (Mo and alternative nitrogenases) to photosynthetic pigments (protochlorophyllide and chlorophyllide oxidoreductases). Only very recently have the activities of the highly divergent and paraphyletic Group IV nitrogenases begun to be uncovered. This review highlights the first characterized member of this group, which was found to catalyze an unprecedented reaction in the coenzyme F430 biosynthetic pathway, and the catalytic potential of a superfamily that has yet to be fully explored.
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Affiliation(s)
- Selamawit M Ghebreamlak
- Department of Chemistry and Biochemistry, Auburn University 179 Chemistry Building, Auburn, AL, 36849, USA
| | - Steven O Mansoorabadi
- Department of Chemistry and Biochemistry, Auburn University 179 Chemistry Building, Auburn, AL, 36849, USA
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16
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Solomon JB, Lee CC, Jasniewski AJ, Rasekh MF, Ribbe MW, Hu Y. Heterologous Expression and Engineering of the Nitrogenase Cofactor Biosynthesis Scaffold NifEN. Angew Chem Int Ed Engl 2020; 59:6887-6893. [PMID: 32022452 DOI: 10.1002/anie.201916598] [Citation(s) in RCA: 9] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/26/2019] [Indexed: 01/01/2023]
Abstract
NifEN plays a crucial role in the biosynthesis of nitrogenase, catalyzing the final step of cofactor maturation prior to delivering the cofactor to NifDK, the catalytic component of nitrogenase. The difficulty in expressing NifEN, a complex, heteromultimeric metalloprotein sharing structural/functional homology with NifDK, is a major challenge in the heterologous expression of nitrogenase. Herein, we report the expression and engineering of Azotobacter vinelandii NifEN in Escherichia coli. Biochemical and spectroscopic analyses demonstrate the integrity of the heterologously expressed NifEN in composition and functionality and, additionally, the ability of an engineered NifEN variant to mimic NifDK in retaining the matured cofactor at an analogous cofactor-binding site. This is an important step toward piecing together a viable pathway for the heterologous expression of nitrogenase and identifying variants for the mechanistic investigation of this enzyme.
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Affiliation(s)
- Joseph B Solomon
- Department of Molecular Biology & Biochemistry, University of California, Irvine, Irvine, CA, 92697-3900, USA.,Department Chemistry, University of California, Irvine, Irvine, CA, 92697-2025, USA
| | - Chi Chung Lee
- Department of Molecular Biology & Biochemistry, University of California, Irvine, Irvine, CA, 92697-3900, USA
| | - Andrew J Jasniewski
- Department of Molecular Biology & Biochemistry, University of California, Irvine, Irvine, CA, 92697-3900, USA
| | - Mahtab F Rasekh
- Department of Molecular Biology & Biochemistry, University of California, Irvine, Irvine, CA, 92697-3900, USA.,Department Chemistry, University of California, Irvine, Irvine, CA, 92697-2025, USA
| | - Markus W Ribbe
- Department of Molecular Biology & Biochemistry, University of California, Irvine, 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, Irvine, CA, 92697-3900, USA
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17
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Abstract
![]()
Nitrogenase harbors three distinct
metal prosthetic groups that
are required for its activity. The simplest one is a [4Fe-4S] cluster
located at the Fe protein nitrogenase component. The MoFe protein
component carries an [8Fe-7S] group called P-cluster and a [7Fe-9S-C-Mo-R-homocitrate] group called FeMo-co. Formation of nitrogenase
metalloclusters requires the participation of the structural nitrogenase
components and many accessory proteins, and occurs both in
situ, for the P-cluster, and in external assembly sites for
FeMo-co. The biosynthesis of FeMo-co is performed stepwise and involves
molecular scaffolds, metallochaperones, radical chemistry, and novel
and unique biosynthetic intermediates. This review provides a critical
overview of discoveries on nitrogenase cofactor structure, function,
and activity over the last four decades.
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Affiliation(s)
- Stefan Burén
- Centro de Biotecnologı́a y Genómica de Plantas, Universidad Politécnica de Madrid (UPM), Instituto Nacional de Investigación y Tecnologı́a Agraria y Alimentaria (INIA), Pozuelo de Alarcón, 28223 Madrid, Spain
| | - Emilio Jiménez-Vicente
- Department of Biochemistry, Virginia Polytechnic Institute, Blacksburg, Virginia 24061, United States
| | - Carlos Echavarri-Erasun
- Centro de Biotecnologı́a y Genómica de Plantas, Universidad Politécnica de Madrid (UPM), Instituto Nacional de Investigación y Tecnologı́a Agraria y Alimentaria (INIA), Pozuelo de Alarcón, 28223 Madrid, Spain
| | - Luis M Rubio
- Centro de Biotecnologı́a y Genómica de Plantas, Universidad Politécnica de Madrid (UPM), Instituto Nacional de Investigación y Tecnologı́a Agraria y Alimentaria (INIA), Pozuelo de Alarcón, 28223 Madrid, Spain
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18
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Lydon BR, Lee CC, Tanifuji K, Sickerman NS, Newcomb MP, Hu Y, Ribbe MW, Yang JY. Electrochemical Characterization of Isolated Nitrogenase Cofactors from Azotobacter vinelandii. Chembiochem 2019; 21:1773-1778. [PMID: 31392810 DOI: 10.1002/cbic.201900425] [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: 07/01/2019] [Indexed: 11/09/2022]
Abstract
The nitrogenase cofactors are structurally and functionally unique in biological chemistry. Despite a substantial amount of spectroscopic characterization of protein-bound and isolated nitrogenase cofactors, electrochemical characterization of these cofactors and their related species is far from complete. Herein we present voltammetric studies of three isolated nitrogenase cofactor species: the iron-molybdenum cofactor (M-cluster), iron-vanadium cofactor (V-cluster), and a homologue to the iron-iron cofactor (L-cluster). We observe two reductive events in the redox profiles of all three cofactors. Of the three, the V-cluster is the most reducing. The reduction potentials of the isolated cofactors are significantly more negative than previously measured values within the molybdenum-iron and vanadium-iron proteins. The outcome of this study provides insight into the importance of the heterometal identity, the overall ligation of the cluster, and the impact of the protein scaffolds on the overall electronic structures of the cofactors.
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Affiliation(s)
- Brian R Lydon
- Department of Chemistry, University of California, 1102 Natural Sciences II, Irvine, CA, 92697, USA
| | - Chi Chung Lee
- Department of Molecular Biology and Biochemistry, University of California, 3205 McGaugh Hall, Irvine, CA, 92697, USA
| | - Kazuki Tanifuji
- Department of Molecular Biology and Biochemistry, University of California, 3205 McGaugh Hall, Irvine, CA, 92697, USA
| | - Nathaniel S Sickerman
- Department of Molecular Biology and Biochemistry, University of California, 3205 McGaugh Hall, Irvine, CA, 92697, USA
| | - Megan P Newcomb
- Department of Chemistry, University of California, 1102 Natural Sciences II, Irvine, CA, 92697, USA
| | - Yilin Hu
- Department of Molecular Biology and Biochemistry, University of California, 3205 McGaugh Hall, Irvine, CA, 92697, USA
| | - Markus W Ribbe
- Department of Chemistry, University of California, 1102 Natural Sciences II, Irvine, CA, 92697, USA.,Department of Molecular Biology and Biochemistry, University of California, 3205 McGaugh Hall, Irvine, CA, 92697, USA
| | - Jenny Y Yang
- Department of Chemistry, University of California, 1102 Natural Sciences II, Irvine, CA, 92697, USA
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19
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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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20
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Abstract
Electron paramagnetic resonance (EPR) is a spectroscopic technique that is sensitive to the presence of unpaired electrons and, therefore, is a powerful tool for the study of proteins containing complex metallocofactors. When a magnetic field is applied to a transition metal-containing system with unpaired electrons and the sample is irradiated with microwaves, a spin transition can be observed. Through detailed analysis of the resulting EPR spectrum, one can extract parameters that can provide information about the electronic environment of the unpaired electrons found on the metal centers. Here, a basic introduction to the theory of EPR and the instrumentation is presented along with procedures for obtaining EPR spectra of sensitive metalloprotein species.
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21
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Abstract
A major hurdle in the studies of nitrogenase, one of the most complicated metalloenzymes known to date, is to obtain large amounts of intact, active proteins. Nitrogenase and related proteins are often multimeric and consist of metal centers that are critical for their activities. Most notably, the well-studied MoFe protein of Mo-nitrogenase is a heterotetramer that houses two of the most complicated metal clusters found in nature, the P-cluster and the FeMoco (or M-cluster). The structural complexity of these proteins and the oxygen sensitivity of their associated metal clusters, along with the demand for large amounts of high-quality proteins in most downstream analyses, make large-scale, high-yield purification of fully competent nitrogenase proteins a formidable task and yet, at the same time, a prerequisite for the success of nitrogenase research. This chapter highlights several methods that have been developed over the past few decades chiefly for the purification of naturally expressed nitrogenase in the diazotroph Azotobacter vinelandii. In addition, purification and Fe-S reconstitution strategies are also outlined for the heterologously expressed nitrogenase proteins in Escherichia coli.
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Affiliation(s)
- Chi-Chung Lee
- Department of Molecular Biology and Biochemistry, University of California, Irvine, Irvine, CA, USA
| | - Markus W Ribbe
- Department of Molecular Biology and Biochemistry, University of California, Irvine, Irvine, CA, USA.
- Department of Chemistry, University of California, Irvine, Irvine, CA, USA.
| | - Yilin Hu
- Department of Molecular Biology and Biochemistry, University of California, Irvine, Irvine, CA, USA.
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22
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Abstract
The biological reduction of nitrogen gas to ammonia is limited to a select group of nitrogen-fixing prokaryotes. While nitrogenase is the catalyst of nitrogen fixation in these biological systems, a consortium of additional gene products is required for the synthesis, activation, and catalytic competency of this oxygen-sensitive metalloenzyme. Thus, the biochemical complexity of this process often requires functional studies and isolation of gene products from the native nitrogen-fixing organisms. The strict aerobe Azotobacter vinelandii is the best-studied model bacterium among diazotrophs. This chapter provides a description of procedures for targeted genomic manipulation and isolation of A. vinelandii strains. These methods have enabled identification and characterization of gene products with roles in nitrogen fixation and other related aspects of metabolism. The ability to modify and control expression levels of targeted sequences provides a biotechnological tool to uncover molecular details associated with nitrogen fixation, as well as to exploit this model system as a host for expression of oxygen-sensitive proteins.
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24
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Rettberg L, Tanifuji K, Jasniewski A, Ribbe MW, Hu Y. Radical S-Adenosyl-l-Methionine (SAM) Enzyme Involved in the Maturation of the Nitrogenase Cluster. Methods Enzymol 2018; 606:341-361. [PMID: 30097098 DOI: 10.1016/bs.mie.2018.04.009] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/07/2023]
Abstract
Nitrogenase is the only known enzymatic system that converts atmospheric dinitrogen (N2) into bioavailable ammonia (NH3). The active-site cofactor responsible for this reactivity is a [(R-homocitrate)MoFe7S9C] cluster that is designated as the M-cluster. This important cofactor is assembled stepwise from a pair of [Fe4S4] clusters that become fused into a [Fe8S9C] core before additional refinements take place to complete the biosynthesis. NifB, a member of the radical S-adenosyl-l-methionine (SAM) superfamily, facilitates the conversion of the [Fe4S4] clusters (called the K-cluster) to the [Fe8S9C] core (called the L-cluster). This transformation includes a SAM-dependent carbide insertion with concomitant incorporation of an additional sulfur. While difficulties with the purification of NifB have historically prevented detailed biochemical analyses, we have developed a heterologous expression system in Escherichia coli that yields stable NifB proteins from various N2-fixing methanogenic organisms that can be used for studies. This chapter details the procedures necessary to prepare an active NifB protein. The methods used for the biochemical characterization of the SAM-dependent carbide insertion reactions are also described.
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Affiliation(s)
- Lee Rettberg
- Department of Molecular Biology and Biochemistry, University of California, Irvine, CA, United States
| | - Kazuki Tanifuji
- Department of Molecular Biology and Biochemistry, University of California, Irvine, CA, United States
| | - Andrew Jasniewski
- Department of Molecular Biology and Biochemistry, University of California, Irvine, CA, United States
| | - Markus Walter Ribbe
- Department of Molecular Biology and Biochemistry, University of California, Irvine, CA, United States; Department of Chemistry, University of California, Irvine, CA, United States.
| | - Yilin Hu
- Department of Molecular Biology and Biochemistry, University of California, Irvine, CA, United States
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25
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Abstract
Although the nitrogen-fixing enzyme nitrogenase critically requires both a reductase component (Fe protein) and a catalytic component, considerably more work has focused on the latter species. Properties of the catalytic component, which contains two highly complex metallocofactors and catalyzes the reduction of N2 into ammonia, understandably making it the “star” of nitrogenase. However, as its obligate redox partner, the Fe protein is a workhorse with multiple supporting roles in both cofactor maturation and catalysis. In particular, the nitrogenase Fe protein utilizes nucleotide binding and hydrolysis in concert with electron transfer to accomplish several tasks of critical importance. Aside from the ATP-coupled transfer of electrons to the catalytic component during substrate reduction, the Fe protein also functions in a maturase and insertase capacity to facilitate the biosynthesis of the two-catalytic component metallocofactors: fusion of the [Fe8S7] P-cluster and insertion of Mo and homocitrate to form the matured [(homocitrate)MoFe7S9C] M-cluster. These and key structural-functional relationships of the indispensable Fe protein and its complex with the catalytic component will be covered in this review.
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26
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Abstract
Nitrogenase is known for its remarkable ability to catalyze the reduction of N2 to NH3, and C1 substrates to short-chain hydrocarbon products, under ambient conditions. The best-studied Mo-nitrogenase utilizes a complex metallocofactor as the site of substrate binding and reduction. Designated the M-cluster, this [MoFe7S9C(R-homocitrate)] cluster can be viewed as [MoFe3S3] and [Fe4S3] subclusters bridged by three μ2-sulfides and one μ6-interstitial carbide, with its Mo end further coordinated by an R-homocitrate moiety. The unique cofactor has attracted considerable attention ever since its discovery; however, the complexity of its structure has hindered mechanistic understanding and chemical synthesis of this cofactor. Motivated by the pressing questions related to the structure and function of the nitrogenase cofactor, one major thrust of our research has been to unravel the key biosynthetic steps of this metallocluster to cultivate a deeper understanding of these reactions and their effects on functionalizing the cofactor. In this Account, we will discuss our recent work that provides insights into how simple Fe and S atoms, along with a single C atom, a heterometallic Mo atom and an organic homocitrate entity, are assembled into one of the most complex metalloclusters known in Nature. Combined biochemical, spectroscopic and structural studies have led us to a working model of M-cluster assembly, which starts with the sequential synthesis of small [Fe2S2] and [Fe4S4] units by NifS/U, followed by the coupling and rearrangement of two [Fe4S4] clusters on NifB concomitant with the insertion of an interstitial carbide and a "9th sulfur" that give rise to a [Fe8S9C] core that is nearly indistinguishable in structure to the M-cluster except for the absence of Mo and homocitrate. This 8Fe core is then matured into an M-cluster on NifEN upon substitution of a Mo-homocitrate conjugate for one terminal Fe atom of the cluster prior to transfer of the M-cluster to its target binding site in the catalytic component of Mo-nitrogenase. Taking stock of the elemental inventory during the cofactor assembly process, the core Fe and S atoms are derived from modular fusion of FeS building blocks, going through 2Fe, 4Fe and 8Fe stages to generate an 8Fe core of the cofactor. However, such a flow of Fe/S along the biosynthetic pathway of the M-cluster is "intervened" by the insertion of C and Mo, which renders the cofactor unique in structure and reactivity. Insertion of C occurs through a novel, radical SAM-dependent mechanism, which involves SN2-type methyl transfer from SAM to a [Fe4S4] cluster pair, hydrogen abstraction of the transferred methyl group by a SAM-derived 5'-dA· radical, and further deprotonation of the resultant methylene radical concomitant with radical chemistry-based coupling and rearrangement of the [Fe4S4] cluster pair into an [Fe8S9C] core. Insertion of Mo, on the other hand, employs an ATPase-dependent mechanism that parallels metal trafficking in the biosynthesis of molybdopterin and CO dehydrogenase cofactors. These findings provide a nice framework for further exploration of the "black box" of nitrogenase cofactor assembly and function.
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Affiliation(s)
- Nathaniel S. Sickerman
- 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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27
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Abstract
Nitrogenase is a metalloenzyme system that plays a critical role in biological nitrogen fixation, and the study of how its metallocenters are assembled into functional entities to facilitate the catalytic reduction of dinitrogen to ammonia is an active area of interest. The diazotroph Azotobacter vinelandii is especially amenable to culturing and genetic manipulation, and this organism has provided the basis for many insights into the assembly of nitrogenase proteins and their respective metallocofactors. This chapter will cover the basic procedures necessary for growing A. vinelandii cultures and subsequent recombinant transformation and protein expression techniques. Furthermore, protocols for nitrogenase protein purification and substrate reduction activity assays are described. These methods provide a solid framework for the assessment of nitrogenase assembly and catalysis.
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Affiliation(s)
| | - Yilin Hu
- University of California, Irvine, Irvine, CA, United States.
| | - Markus W Ribbe
- University of California, Irvine, Irvine, CA, United States.
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28
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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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29
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Nickerson LA, Huynh V, Balmond EI, Cramer SP, Shaw JT. Asymmetric Synthesis of Homocitric Acid Lactone. J Org Chem 2016; 81:11404-11408. [PMID: 27685496 DOI: 10.1021/acs.joc.6b01997] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
Abstract
A short, diastereoselective synthesis of homocitric acid lactone is described. The key step is a bioinspired aldol addition to set the stereogenic center in an intermediate that requires only modest oxidation state manipulation to complete the synthesis. This approach enables rapid generation of isotopomers in which carbon and hydrogen can be replaced by heavier nuclei at nearly every position.
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Affiliation(s)
- Leslie A Nickerson
- Department of Chemistry, University of California , One Shields Avenue, Davis, California 95616, United States
| | - Valerie Huynh
- Department of Chemistry, University of California , One Shields Avenue, Davis, California 95616, United States
| | - Edward I Balmond
- Department of Chemistry, University of California , One Shields Avenue, Davis, California 95616, United States
| | - Stephen P Cramer
- Department of Chemistry, University of California , One Shields Avenue, Davis, California 95616, United States
| | - Jared T Shaw
- Department of Chemistry, University of California , One Shields Avenue, Davis, California 95616, United States
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30
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Affiliation(s)
- Yilin Hu
- Department of Molecular Biology and Biochemistry and
| | - Markus W. Ribbe
- Department of Molecular Biology and Biochemistry and
- Department of Chemistry, University of California, Irvine, California 92697-2025; ,
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31
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Affiliation(s)
- Yilin Hu
- Department of Molecular Biology and Biochemistry;, Department of Chemistry University of California, Irvine Irvine CA 92697-3900 USA
| | - Markus W. Ribbe
- Department of Molecular Biology and Biochemistry;, Department of Chemistry University of California, Irvine Irvine CA 92697-3900 USA
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32
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Abstract
Named after its ability to catalyze the reduction of nitrogen to ammonia, nitrogenase has a surprising rapport with carbon-both through the interstitial carbide that resides in the central cavity of its cofactor and through its ability to catalyze the reductive carbon-carbon coupling of small carbon compounds into hydrocarbon products. Recently, a radical-SAM-dependent pathway was revealed for the insertion of carbide, which signifies a novel biosynthetic route to complex bridged metalloclusters. Moreover, a sulfur-displacement mechanism was proposed for the activation of carbon monoxide by nitrogenase, which suggests an essential role of the interstitial carbide in maintaining the stability while permitting a certain flexibility of the cofactor structure during substrate turnover.
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Affiliation(s)
- Yilin Hu
- Department of Molecular Biology and Biochemistry, Department of Chemistry, University of California, Irvine, Irvine, CA, 92697-3900, USA.
| | - Markus W Ribbe
- Department of Molecular Biology and Biochemistry, Department of Chemistry, University of California, Irvine, Irvine, CA, 92697-3900, USA.
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33
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Hu Y, Ribbe MW. Maturation of nitrogenase cofactor-the role of a class E radical SAM methyltransferase NifB. Curr Opin Chem Biol 2016; 31:188-94. [PMID: 26969410 DOI: 10.1016/j.cbpa.2016.02.016] [Citation(s) in RCA: 20] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/14/2015] [Revised: 02/23/2016] [Accepted: 02/24/2016] [Indexed: 10/22/2022]
Abstract
Nitrogenase catalyzes the important reactions of N2-reduction, CO-reduction and CO2-reduction at its active cofactor site. Designated the M-cluster, this complex metallocofactor is assembled through the generation of a characteristic 8Fe-core before the insertion of Mo and homocitrate that completes the stoichiometry of the M-cluster. NifB catalyzes the crucial step of radical SAM-dependent carbide insertion that occurs concomitant with the insertion a '9th' sulfur and the rearrangement/coupling of two 4Fe-clusters into a complete 8Fe-core of the M-cluster. Further categorization of a family of NifB proteins as a new class of radical SAM methyltransferases suggests a general function of these proteins in complex metallocofactor assembly and provides a new platform for unveiling unprecedented chemical reactions catalyzed by biological systems.
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Affiliation(s)
- Yilin Hu
- Department of Molecular Biology and Biochemistry, University of California, Irvine, CA 92697-3900, United States.
| | - Markus W Ribbe
- Department of Molecular Biology and Biochemistry, University of California, Irvine, CA 92697-3900, United States; Department of Chemistry, University of California, Irvine, CA 92697-2025, United States.
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34
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Identification and characterization of functional homologs of nitrogenase cofactor biosynthesis protein NifB from methanogens. Proc Natl Acad Sci U S A 2015; 112:14829-33. [PMID: 26627238 DOI: 10.1073/pnas.1510409112] [Citation(s) in RCA: 47] [Impact Index Per Article: 5.2] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/18/2022] Open
Abstract
Nitrogenase biosynthesis protein NifB catalyzes the radical S-adenosyl-L-methionine (SAM)-dependent insertion of carbide into the M cluster, the cofactor of the molybdenum nitrogenase from Azotobacter vinelandii. Here, we report the identification and characterization of two naturally "truncated" homologs of NifB from Methanosarcina acetivorans (NifB(Ma)) and Methanobacterium thermoautotrophicum (NifB(Mt)), which contain a SAM-binding domain at the N terminus but lack a domain toward the C terminus that shares homology with NifX, an accessory protein in M cluster biosynthesis. NifB(Ma) and NifB(Mt) are monomeric proteins containing a SAM-binding [Fe4S4] cluster (designated the SAM cluster) and a [Fe4S4]-like cluster pair (designated the K cluster) that can be processed into an [Fe8S9] precursor to the M cluster (designated the L cluster). Further, the K clusters in NifB(Ma) and NifB(Mt) can be converted to L clusters upon addition of SAM, which corresponds to their ability to heterologously donate L clusters to the biosynthetic machinery of A. vinelandii for further maturation into the M clusters. Perhaps even more excitingly, NifB(Ma) and NifB(Mt) can catalyze the removal of methyl group from SAM and the abstraction of hydrogen from this methyl group by 5'-deoxyadenosyl radical that initiates the radical-based incorporation of methyl-derived carbide into the M cluster. The successful identification of NifB(Ma) and NifB(Mt) as functional homologs of NifB not only enabled classification of a new subset of radical SAM methyltransferases that specialize in complex metallocluster assembly, but also provided a new tool for further characterization of the distinctive, NifB-catalyzed methyl transfer and conversion to an iron-bound carbide.
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35
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Abstract
The L-cluster is an all-iron homolog of nitrogenase cofactors. Driven by europium(II) diethylenetriaminepentaacetate [Eu(II)-DTPA], the isolated L-cluster is capable of ATP-independent reduction of CO and CN− to C1 to C4 and C1 to C6 hydrocarbons, respectively. Compared to its cofactor homologs, the L-cluster generates considerably more CH4 from the reduction of CO and CN−, which could be explained by the presence of a “free” Fe atom that is “unmasked” by homocitrate as an additional site for methanation. Moreover, the elevated CH4 formation is accompanied by a decrease in the amount of longer hydrocarbons and/or the lengths of the hydrocarbon products, illustrating a competition between CH4 formation/release and C−C coupling/chain extension. These observations suggest the possibility of designing simpler synthetic clusters for hydrocarbon formation while establishing the L-cluster as a platform for mechanistic investigations of CO and CN− reduction without complications originating from the heterometal and homocitrate components. Nitrogenase is a metalloenzyme that is highly complex in structure and uniquely versatile in function. It catalyzes two reactions that parallel two important industrial processes: the reduction of nitrogen to ammonia, which parallels the Haber-Bosch process in ammonia production, and the reduction of carbon monoxide to hydrocarbons, which parallels the Fischer-Tropsch process in fuel production. Thus, the significance of nitrogenase can be appreciated from the perspective of the useful products it generates: (i) ammonia, the “fixed” nitrogen that is essential for the existence of the entire human population; and (ii) hydrocarbons, the “recycled” carbon fuel that could be used to directly address the worldwide energy shortage. This article provides initial insights into the catalytic characteristics of various nitrogenase cofactors in hydrocarbon formation. The reported assay system provides a useful tool for mechanistic investigations of this reaction while suggesting the possibility of designing bioinspired catalysts based on nitrogenase cofactors.
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36
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Lee CC, Hu Y, Ribbe MW. Catalytic reduction of CN-, CO, and CO2 by nitrogenase cofactors in lanthanide-driven reactions. Angew Chem Int Ed Engl 2015; 54:1219-22. [PMID: 25420957 PMCID: PMC4300254 DOI: 10.1002/anie.201410412] [Citation(s) in RCA: 48] [Impact Index Per Article: 5.3] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/23/2014] [Indexed: 12/19/2022]
Abstract
Nitrogenase cofactors can be extracted into an organic solvent to catalyze the reduction of cyanide (CN(-)), carbon monoxide (CO), and carbon dioxide (CO2) without using adenosine triphosphate (ATP), when samarium(II) iodide (SmI2) and 2,6-lutidinium triflate (Lut-H) are employed as a reductant and a proton source, respectively. Driven by SmI2, the cofactors catalytically reduce CN(-) or CO to C1-C4 hydrocarbons, and CO2 to CO and C1-C3 hydrocarbons. The C-C coupling from CO2 indicates a unique Fischer-Tropsch-like reaction with an atypical carbonaceous substrate, whereas the catalytic turnover of CN(-), CO, and CO2 by isolated cofactors suggests the possibility to develop nitrogenase-based electrocatalysts for the production of hydrocarbons from these carbon-containing compounds.
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Affiliation(s)
| | - Yilin Hu
- Department of Molecular Biology and Biochemistry
| | - Markus W. Ribbe
- Department of Molecular Biology and Biochemistry; Department of Chemistry, University of California, Irvine, Irvine, CA 92697-3900
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37
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Hu Y, Ribbe MW. Nitrogenase and homologs. J Biol Inorg Chem 2014; 20:435-45. [PMID: 25491285 DOI: 10.1007/s00775-014-1225-3] [Citation(s) in RCA: 73] [Impact Index Per Article: 7.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/19/2014] [Accepted: 11/24/2014] [Indexed: 11/24/2022]
Abstract
Nitrogenase catalyzes biological nitrogen fixation, a key step in the global nitrogen cycle. Three homologous nitrogenases have been identified to date, along with several structural and/or functional homologs of this enzyme that are involved in nitrogenase assembly, bacteriochlorophyll biosynthesis and methanogenic process, respectively. In this article, we provide an overview of the structures and functions of nitrogenase and its homologs, which highlights the similarity and disparity of this uniquely versatile group of enzymes.
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Affiliation(s)
- Yilin Hu
- Department of Molecular Biology and Biochemistry, 2230 McGaugh Hall, University of California, Irvine, CA, 92697-3900, USA,
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38
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Lee CC, Hu Y, Ribbe MW. Catalytic Reduction of CN−, CO, and CO2by Nitrogenase Cofactors in Lanthanide-Driven Reactions. Angew Chem Int Ed Engl 2014. [DOI: 10.1002/ange.201410412] [Citation(s) in RCA: 18] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/10/2022]
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39
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Broderick JB, Duffus B, Duschene KS, Shepard EM. Radical S-adenosylmethionine enzymes. Chem Rev 2014; 114:4229-317. [PMID: 24476342 PMCID: PMC4002137 DOI: 10.1021/cr4004709] [Citation(s) in RCA: 576] [Impact Index Per Article: 57.6] [Reference Citation Analysis] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/25/2013] [Indexed: 12/22/2022]
Affiliation(s)
- Joan B. Broderick
- Department of Chemistry and
Biochemistry, Montana State University, Bozeman, Montana 59717, United States
| | - Benjamin
R. Duffus
- Department of Chemistry and
Biochemistry, Montana State University, Bozeman, Montana 59717, United States
| | - Kaitlin S. Duschene
- Department of Chemistry and
Biochemistry, Montana State University, Bozeman, Montana 59717, United States
| | - Eric M. Shepard
- Department of Chemistry and
Biochemistry, Montana State University, Bozeman, Montana 59717, United States
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40
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Hu Y, Ribbe MW. A journey into the active center of nitrogenase. J Biol Inorg Chem 2014; 19:731-6. [PMID: 24752864 DOI: 10.1007/s00775-014-1137-2] [Citation(s) in RCA: 23] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/27/2014] [Accepted: 04/08/2014] [Indexed: 11/25/2022]
Abstract
Nitrogenase catalyzes the reduction of N2 to NH3, a key step in the global nitrogen cycle. This article describes our journey toward the definition of a complete molecular structure of the active site of nitrogenase, with an emphasis on the discovery of the interstitial carbide and the radical SAM-dependent insertion of this atom into the active FeMo cofactor site of nitrogenase.
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Affiliation(s)
- Yilin Hu
- Department of Molecular Biology and Biochemistry, University of California, 2230 McGaugh Hall, Irvine, CA, 92697-3900, USA,
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41
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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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42
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Ribbe MW, Hu Y, Hodgson KO, Hedman B. Biosynthesis of nitrogenase metalloclusters. Chem Rev 2013; 114:4063-80. [PMID: 24328215 DOI: 10.1021/cr400463x] [Citation(s) in RCA: 99] [Impact Index Per Article: 9.0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/28/2022]
Affiliation(s)
- Markus W Ribbe
- Department of Molecular Biology and Biochemistry, University of California , Irvine, California 92697-3900, United States
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43
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Boyd ES, Peters JW. New insights into the evolutionary history of biological nitrogen fixation. Front Microbiol 2013; 4:201. [PMID: 23935594 PMCID: PMC3733012 DOI: 10.3389/fmicb.2013.00201] [Citation(s) in RCA: 108] [Impact Index Per Article: 9.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/03/2013] [Accepted: 06/26/2013] [Indexed: 12/03/2022] Open
Abstract
Nitrogenase, which catalyzes the ATP-dependent reduction of dinitrogen (N2) to ammonia (NH3), accounts for roughly half of the bioavailable nitrogen supporting extant life. The fundamental requirement for fixed forms of nitrogen for life on Earth, both at present and in the past, has led to broad and significant interest in the origin and evolution of biological N2 fixation. One key question is whether the limited availability of fixed nitrogen was a factor in life's origin or whether there were ample sources of fixed nitrogen produced by abiotic processes or delivered through the weathering of bolide impact materials to support this early life. If the latter, the key questions become what were the characteristics of the environment that precipitated the evolution of this oxygen sensitive process, when did this occur, and how was its subsequent evolutionary history impacted by the advent of oxygenic photosynthesis and the rise of oxygen in the Earth's biosphere. Since the availability of fixed sources of nitrogen capable of supporting early life is difficult to glean from the geologic record, there are limited means to get direct insights into these questions. Indirect insights, however, can be gained through phylogenetic studies of nitrogenase structural gene products and additional gene products involved in the biosynthesis of the complex metal-containing prosthetic groups associated with this enzyme complex. Insights gained from such studies, as reviewed herein, challenge traditional models for the evolution of biological nitrogen fixation and provide the basis for the development of new conceptual models that explain the stepwise evolution of this highly complex life sustaining process.
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Affiliation(s)
- Eric S Boyd
- Department of Chemistry and Biochemistry and Department of Microbiology, Montana State University Bozeman, MT, USA
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44
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Abstract
The iron-molybdenum cofactor (the M-cluster) serves as the active site of molybdenum nitrogenase. Arguably one of the most complex metal cofactors in biological systems, the M-cluster is assembled through the formation of an 8Fe core prior to the insertion of molybdenum and homocitrate into this core. Here, we review the recent progress in the research area of M-cluster assembly, with an emphasis on our work that provides useful insights into the mechanistic details of this process.
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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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45
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Hu Y, Ribbe MW. Nitrogenase assembly. BIOCHIMICA ET BIOPHYSICA ACTA-BIOENERGETICS 2012; 1827:1112-22. [PMID: 23232096 DOI: 10.1016/j.bbabio.2012.12.001] [Citation(s) in RCA: 58] [Impact Index Per Article: 4.8] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 10/17/2012] [Revised: 12/02/2012] [Accepted: 12/03/2012] [Indexed: 11/18/2022]
Abstract
Nitrogenase contains two unique metalloclusters: the P-cluster and the M-cluster. The assembly processes of P- and M-clusters are arguably the most complicated processes in bioinorganic chemistry. There is considerable interest in decoding the biosynthetic mechanisms of the P- and M-clusters, because these clusters are not only biologically important, but also chemically unprecedented. Understanding the assembly mechanisms of these unique metalloclusters is crucial for understanding the structure-function relationship of nitrogenase. Here, we review the recent advances in this research area, with an emphasis on our work that provide important insights into the biosynthetic pathways of these high-nuclearity metal centers. This article is part of a Special Issue entitled: Metals in Bioenergetics and Biomimetics Systems.
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Affiliation(s)
- Yilin Hu
- Department of Molecular Biology and Biochemistry, University of California, Irvine, CA 92687-3900, USA.
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46
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Wiig JA, Hu Y, Chung Lee C, Ribbe MW. Radical SAM-dependent carbon insertion into the nitrogenase M-cluster. Science 2012; 337:1672-5. [PMID: 23019652 PMCID: PMC3836454 DOI: 10.1126/science.1224603] [Citation(s) in RCA: 193] [Impact Index Per Article: 16.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/02/2022]
Abstract
The active site of nitrogenase, the M-cluster, is a metal-sulfur cluster containing a carbide at its core. Using radiolabeling experiments, we show that this carbide originates from the methyl group of S-adenosylmethionine (SAM) and that it is inserted into the M-cluster by the assembly protein NifB. Our SAM cleavage and deuterium substitution analyses suggest a similarity between the mechanism of carbon insertion by NifB and the proposed mechanism of RNA methylation by the radical SAM enzymes RlmN and Cfr, which involves methyl transfer from one SAM equivalent, followed by hydrogen atom abstraction from the methyl group by a 5'-deoxyadenosyl radical generated from a second SAM equivalent. This work is an initial step toward unraveling the importance of the interstitial carbide and providing insights into the nitrogenase mechanism.
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Affiliation(s)
- Jared A. Wiig
- Department of Molecular Biology & Biochemistry, University of California, Irvine 92697-3900
| | - Yilin Hu
- Department of Molecular Biology & Biochemistry, University of California, Irvine 92697-3900
| | - Chi Chung Lee
- Department of Molecular Biology & Biochemistry, University of California, Irvine 92697-3900
| | - Markus W. Ribbe
- Department of Molecular Biology & Biochemistry, University of California, Irvine 92697-3900
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47
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Abstract
Nitrogenase catalyzes a key step in the global nitrogen cycle, the nucleotide-dependent reduction of atmospheric dinitrogen to bioavailable ammonia. There is a substantial amount of interest in elucidating the biosynthetic mechanisms of the FeMoco and the P-cluster of nitrogenase, because these clusters are not only biologically important but also chemically unprecedented. In this review, we summarize the recent advances in this research area, with an emphasis on our work that aims at providing structural and spectroscopic insights into the assembly of these complex metalloclusters.
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48
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Peters JW, Broderick JB. Emerging paradigms for complex iron-sulfur cofactor assembly and insertion. Annu Rev Biochem 2012; 81:429-50. [PMID: 22482905 DOI: 10.1146/annurev-biochem-052610-094911] [Citation(s) in RCA: 73] [Impact Index Per Article: 6.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/09/2022]
Abstract
[FeFe]-hydrogenses and molybdenum (Mo)-nitrogenase are evolutionarily unrelated enzymes with unique complex iron-sulfur cofactors at their active sites. The H cluster of [FeFe]-hydrogenases and the FeMo cofactor of Mo-nitrogenase require specific maturation machinery for their proper synthesis and insertion into the structural enzymes. Recent insights reveal striking similarities in the biosynthetic pathways of these complex cofactors. For both systems, simple iron-sulfur cluster precursors are modified on assembly scaffolds by the activity of radical S-adenosylmethionine (SAM) enzymes. Radical SAM enzymes are responsible for the synthesis and insertion of the unique nonprotein ligands presumed to be key structural determinants for their respective catalytic activities. Maturation culminates in the transfer of the intact cluster assemblies to a cofactor-less structural protein recipient. Required roles for nucleotide binding and hydrolysis have been implicated in both systems, but the specific role for these requirements remain unclear. In this review, we highlight the progress on [FeFe]-hydrogenase H cluster and nitrogenase FeMo-cofactor assembly in the context of these emerging paradigms.
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Affiliation(s)
- John W Peters
- Department of Chemistry and Biochemistry and the Astrobiology Biogeocatalysis Research Center, Montana State University, Bozeman, Montana 59717, USA.
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Abstract
Advances in sequencing technology in the past decade have enabled the sequencing of genomes of thousands of organisms including diazotrophs. Genomics have enabled thorough analysis of the gene organization of nitrogen-fixing species, the identification of new genes involved in nitrogen fixation, and the identification of new diazotrophic species. This chapter reviews key characteristics of nitrogen-fixing genomes and methods to identify and analyze genomes of new diazotrophs using genome scanning. This chapter refers to Azotobacter vinelandii, a well-studied nitrogen-fixing organism, as a model for studying nitrogen-fixing genomes. We discuss the main nitrogen fixation genes as well as accessory genes that contribute to diazotrophy. We also review approaches that can be used to modify genomes in order to study nitrogen fixation at the genetic, biochemical, and biophysical level.
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Lancaster KM, Roemelt M, Ettenhuber P, Hu Y, Ribbe MW, Neese F, Bergmann U, DeBeer S. X-ray emission spectroscopy evidences a central carbon in the nitrogenase iron-molybdenum cofactor. Science 2011; 334:974-7. [PMID: 22096198 PMCID: PMC3800678 DOI: 10.1126/science.1206445] [Citation(s) in RCA: 613] [Impact Index Per Article: 47.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/02/2022]
Abstract
Nitrogenase is a complex enzyme that catalyzes the reduction of dinitrogen to ammonia. Despite insight from structural and biochemical studies, its structure and mechanism await full characterization. An iron-molybdenum cofactor (FeMoco) is thought to be the site of dinitrogen reduction, but the identity of a central atom in this cofactor remains unknown. Fe Kβ x-ray emission spectroscopy (XES) of intact nitrogenase MoFe protein, isolated FeMoco, and the FeMoco-deficient nifB protein indicates that among the candidate atoms oxygen, nitrogen, and carbon, it is carbon that best fits the XES data. The experimental XES is supported by computational efforts, which show that oxidation and spin states do not affect the assignment of the central atom to C(4-). Identification of the central atom will drive further studies on its role in catalysis.
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Affiliation(s)
- Kyle M. Lancaster
- Department of Chemistry and Chemical Biology, Cornell University, Ithaca, NY 14853, USA
| | - Michael Roemelt
- Institut für Physikalische und Theoretische Chemie, Universität Bonn, D-53115 Bonn, Germany
| | - Patrick Ettenhuber
- Institut für Physikalische und Theoretische Chemie, Universität Bonn, D-53115 Bonn, Germany
| | - Yilin Hu
- Department of Molecular Biology and Biochemistry, University of California, Irvine, CA 92697, USA
| | - Markus W. Ribbe
- Department of Molecular Biology and Biochemistry, University of California, Irvine, CA 92697, USA
| | - Frank Neese
- Institut für Physikalische und Theoretische Chemie, Universität Bonn, D-53115 Bonn, Germany
- Max-Planck-Institut für Bioanorganische Chemie, Stiftstrasse 34-36, D-45470 Mülheim an der Ruhr, Germany
| | - Uwe Bergmann
- Linac Coherent Light Source, SLAC National Accelerator Laboratory, Menlo Park, CA 94025, USA
| | - Serena DeBeer
- Department of Chemistry and Chemical Biology, Cornell University, Ithaca, NY 14853, USA
- Max-Planck-Institut für Bioanorganische Chemie, Stiftstrasse 34-36, D-45470 Mülheim an der Ruhr, Germany
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