101
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Kiesel S, Wätzlich D, Lange C, Reijerse E, Bröcker MJ, Rüdiger W, Lubitz W, Scheer H, Moser J, Jahn D. Iron-sulfur cluster-dependent catalysis of chlorophyllide a oxidoreductase from Roseobacter denitrificans. J Biol Chem 2015; 290:1141-54. [PMID: 25422320 PMCID: PMC4294481 DOI: 10.1074/jbc.m114.617761] [Citation(s) in RCA: 16] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/11/2014] [Revised: 11/18/2014] [Indexed: 11/06/2022] Open
Abstract
Bacteriochlorophyll a biosynthesis requires the stereo- and regiospecific two electron reduction of the C7-C8 double bond of chlorophyllide a by the nitrogenase-like multisubunit metalloenzyme, chlorophyllide a oxidoreductase (COR). ATP-dependent COR catalysis requires interaction of the protein subcomplex (BchX)2 with the catalytic (BchY/BchZ)2 protein to facilitate substrate reduction via two redox active iron-sulfur centers. The ternary COR enzyme holocomplex comprising subunits BchX, BchY, and BchZ from the purple bacterium Roseobacter denitrificans was trapped in the presence of the ATP transition state analog ADP·AlF4(-). Electron paramagnetic resonance experiments revealed a [4Fe-4S] cluster of subcomplex (BchX)2. A second [4Fe-4S] cluster was identified on (BchY/BchZ)2. Mutagenesis experiments indicated that the latter is ligated by four cysteines, which is in contrast to the three cysteine/one aspartate ligation pattern of the closely related dark-operative protochlorophyllide a oxidoreductase (DPOR). In subsequent mutagenesis experiments a DPOR-like aspartate ligation pattern was implemented for the catalytic [4Fe-4S] cluster of COR. Artificial cluster formation for this inactive COR variant was demonstrated spectroscopically. A series of chemically modified substrate molecules with altered substituents on the individual pyrrole rings and the isocyclic ring were tested as COR substrates. The COR enzyme was still able to reduce the B ring of substrates carrying modified substituents on ring systems A, C, and E. However, substrates with a modification of the distantly located propionate side chain were not accepted. A tentative substrate binding mode was concluded in analogy to the related DPOR system.
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Affiliation(s)
- Svenja Kiesel
- From the Institute of Microbiology, Technische Universität Braunschweig, Spielmannstrasse 7, D-38106 Braunschweig, Germany
| | - Denise Wätzlich
- From the Institute of Microbiology, Technische Universität Braunschweig, Spielmannstrasse 7, D-38106 Braunschweig, Germany
| | - Christiane Lange
- From the Institute of Microbiology, Technische Universität Braunschweig, Spielmannstrasse 7, D-38106 Braunschweig, Germany
| | - Edward Reijerse
- Max-Planck-Institute for Chemical Energy Conversion, D-45470 Mülheim, Germany
| | - Markus J Bröcker
- Department of Molecular Biophysics and Biochemistry, Yale University New Haven, Connecticut 06520, and
| | - Wolfhart Rüdiger
- Department Biology I, Botany, Ludwig-Maximilians-Universität München, D-80638 München, Germany
| | - Wolfgang Lubitz
- Max-Planck-Institute for Chemical Energy Conversion, D-45470 Mülheim, Germany
| | - Hugo Scheer
- Department Biology I, Botany, Ludwig-Maximilians-Universität München, D-80638 München, Germany
| | - Jürgen Moser
- From the Institute of Microbiology, Technische Universität Braunschweig, Spielmannstrasse 7, D-38106 Braunschweig, Germany,
| | - Dieter Jahn
- From the Institute of Microbiology, Technische Universität Braunschweig, Spielmannstrasse 7, D-38106 Braunschweig, Germany
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102
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Tezcan FA, Kaiser JT, Howard JB, Rees DC. Structural evidence for asymmetrical nucleotide interactions in nitrogenase. J Am Chem Soc 2014; 137:146-9. [PMID: 25522159 PMCID: PMC4304452 DOI: 10.1021/ja511945e] [Citation(s) in RCA: 39] [Impact Index Per Article: 3.9] [Reference Citation Analysis] [Abstract] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Abstract
![]()
The
roles of ATP hydrolysis in electron-transfer (ET) reactions
of the nitrogenase catalytic cycle remain obscure. Here, we present
a new structure of a nitrogenase complex crystallized with MgADP and
MgAMPPCP, an ATP analogue. In this structure the two nucleotides are
bound asymmetrically by the Fe-protein subunits connected to the two
different MoFe-protein subunits. This binding mode suggests that ATP
hydrolysis and phosphate release may proceed by a stepwise mechanism.
Through the associated Fe-protein conformational changes, a stepwise
mechanism is anticipated to prolong the lifetime of the Fe-protein-MoFe-protein
complex and, in turn, could orchestrate the sequence of intracomplex
ET required for substrate reduction.
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Affiliation(s)
- F Akif Tezcan
- Department of Chemistry and Biochemistry, University of California, San Diego , La Jolla, California 92093-0356, United States
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103
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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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104
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Spatzal T, Perez KA, Einsle O, Howard JB, Rees DC. Ligand binding to the FeMo-cofactor: structures of CO-bound and reactivated nitrogenase. Science 2014; 345:1620-3. [PMID: 25258081 PMCID: PMC4205161 DOI: 10.1126/science.1256679] [Citation(s) in RCA: 280] [Impact Index Per Article: 28.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/02/2022]
Abstract
The mechanism of nitrogenase remains enigmatic, with a major unresolved issue concerning how inhibitors and substrates bind to the active site. We report a crystal structure of carbon monoxide (CO)-inhibited nitrogenase molybdenum-iron (MoFe)-protein at 1.50 angstrom resolution, which reveals a CO molecule bridging Fe2 and Fe6 of the FeMo-cofactor. The μ2 binding geometry is achieved by replacing a belt-sulfur atom (S2B) and highlights the generation of a reactive iron species uncovered by the displacement of sulfur. The CO inhibition is fully reversible as established by regain of enzyme activity and reappearance of S2B in the 1.43 angstrom resolution structure of the reactivated enzyme. The substantial and reversible reorganization of the FeMo-cofactor accompanying CO binding was unanticipated and provides insights into a catalytically competent state of nitrogenase.
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Affiliation(s)
- Thomas Spatzal
- Howard Hughes Medical Institute and Division of Chemistry and Chemical Engineering, MailCode 114-96, California Institute of Technology, Pasadena, CA 91125, USA.
| | - Kathryn A Perez
- Howard Hughes Medical Institute and Division of Chemistry and Chemical Engineering, MailCode 114-96, California Institute of Technology, Pasadena, CA 91125, USA
| | - Oliver Einsle
- Institut für Biochemie, Albert-Ludwigs-Universität Freiburg, 79104 Freiburg, Germany. BIOSS Centre for Biological Signalling Studies, Albert-Ludwigs-Universität Freiburg, 79104 Freiburg, Germany
| | - James B Howard
- Howard Hughes Medical Institute and Division of Chemistry and Chemical Engineering, MailCode 114-96, California Institute of Technology, Pasadena, CA 91125, USA. Department of Biochemistry, Molecular Biology and Biophysics, University of Minnesota, Minneapolis, MN 55455, USA
| | - Douglas C Rees
- Howard Hughes Medical Institute and Division of Chemistry and Chemical Engineering, MailCode 114-96, California Institute of Technology, Pasadena, CA 91125, USA.
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105
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Rebelein JG, Hu Y, Ribbe MW. Differential reduction of CO₂ by molybdenum and vanadium nitrogenases. Angew Chem Int Ed Engl 2014; 53:11543-6. [PMID: 25205285 DOI: 10.1002/anie.201406863] [Citation(s) in RCA: 58] [Impact Index Per Article: 5.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/03/2014] [Revised: 08/04/2014] [Indexed: 11/06/2022]
Abstract
The molybdenum and vanadium nitrogenases are two homologous enzymes with distinct structural and catalytic features. Previously, it was demonstrated that the V nitrogenase was nearly 700 times more active than its Mo counterpart in reducing CO to hydrocarbons. Herein, a similar discrepancy between the two nitrogenases in the reduction of CO2 is reported, with the V nitrogenase being capable of reducing CO2 to CO, CD4, C2D4, and C2D6, and its Mo counterpart only capable of reducing CO2 to CO. Furthermore, it is shown that the V nitrogenase may direct the formation of CD4 in part via CO2-derived CO, but that it does not catalyze the formation of C2D4 and C2D6 along this route. The exciting observation of a V nitrogenase-catalyzed C-C coupling with CO2 as the origin of the building blocks adds another interesting reaction to the catalytic repertoire of this unique enzyme system. The differential activities of the V and Mo nitrogenases in CO2 reduction provide an important framework for systematic investigations of this reaction in the future.
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Affiliation(s)
- Johannes G Rebelein
- Department of Molecular Biology and Biochemistry, University of California, Irvine (USA)
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106
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Rebelein JG, Hu Y, Ribbe MW. Differential Reduction of CO2by Molybdenum and Vanadium Nitrogenases. Angew Chem Int Ed Engl 2014. [DOI: 10.1002/ange.201406863] [Citation(s) in RCA: 16] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/09/2022]
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107
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Buckel W, Kung JW, Boll M. The benzoyl-coenzyme a reductase and 2-hydroxyacyl-coenzyme a dehydratase radical enzyme family. Chembiochem 2014; 15:2188-94. [PMID: 25204868 DOI: 10.1002/cbic.201402270] [Citation(s) in RCA: 36] [Impact Index Per Article: 3.6] [Reference Citation Analysis] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/28/2014] [Indexed: 11/10/2022]
Affiliation(s)
- Wolfgang Buckel
- Laboratorium für Mikrobiologie, Fachbereich Biologie, Philipps-Universität Marburg, Karl-von-Frisch-Strasse 8, 35043 Marburg (Germany)
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108
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Abstract
From the catalytic reactions that sustain the global oxygen, nitrogen, and carbon cycles to the stabilization of DNA processing proteins, transition metal ions and metallocofactors play key roles in biology. Although the exquisite interplay between metal ions and protein scaffolds has been studied extensively, the fact that the biological roles of the metals often stem from their placement in the interfaces between proteins and protein subunits is not always recognized. Interfacial metal ions stabilize permanent or transient protein-protein interactions, enable protein complexes involved in cellular signaling to adopt distinct conformations in response to environmental stimuli, and catalyze challenging chemical reactions that are uniquely performed by multisubunit protein complexes. This review provides a structural survey of transition metal ions and metallocofactors found in protein-protein interfaces, along with a series of selected examples that illustrate their diverse biological utility and significance.
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Affiliation(s)
- Woon Ju Song
- Department of Chemistry and Biochemistry, University of California, San Diego, La Jolla, California 92093; emails: , ,
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109
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ATP-induced electron transfer by redox-selective partner recognition. Nat Commun 2014; 5:4626. [PMID: 25109607 DOI: 10.1038/ncomms5626] [Citation(s) in RCA: 17] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/22/2014] [Accepted: 07/08/2014] [Indexed: 11/08/2022] Open
Abstract
Thermodynamically unfavourable electron transfers are enabled by coupling to an energy-supplying reaction. How the energy is transduced from the exergonic to the endergonic process is largely unknown. Here we provide the structural basis for an energy transduction process in the reductive activation of B12-dependent methyltransferases. The transfer of one electron from an activating enzyme to the cobalamin cofactor is energetically uphill and relies on coupling to an ATPase reaction. Our results demonstrate that the key to coupling is, besides the oxidation state-dependent complex formation, the conformational gating of the electron transfer. Complex formation induces a substitution of the ligand at the electron-accepting Co ion. Addition of ATP initiates electron transfer by provoking conformational changes that destabilize the complex. We show how remodelling of the electron-accepting Co(2+) promotes ATP-dependent electron transfer; an efficient strategy not seen in other electron-transferring ATPases.
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110
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Liu J, Chakraborty S, Hosseinzadeh P, Yu Y, Tian S, Petrik I, Bhagi A, Lu Y. Metalloproteins containing cytochrome, iron-sulfur, or copper redox centers. Chem Rev 2014; 114:4366-469. [PMID: 24758379 PMCID: PMC4002152 DOI: 10.1021/cr400479b] [Citation(s) in RCA: 560] [Impact Index Per Article: 56.0] [Reference Citation Analysis] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/02/2013] [Indexed: 02/07/2023]
Affiliation(s)
- Jing Liu
- Department of Chemistry, Department of Biochemistry, and Center for Biophysics
and Computational
Biology, University of Illinois at Urbana-Champaign, Urbana, Illinois 61801, United States
| | - Saumen Chakraborty
- Department of Chemistry, Department of Biochemistry, and Center for Biophysics
and Computational
Biology, University of Illinois at Urbana-Champaign, Urbana, Illinois 61801, United States
| | - Parisa Hosseinzadeh
- Department of Chemistry, Department of Biochemistry, and Center for Biophysics
and Computational
Biology, University of Illinois at Urbana-Champaign, Urbana, Illinois 61801, United States
| | - Yang Yu
- Department of Chemistry, Department of Biochemistry, and Center for Biophysics
and Computational
Biology, University of Illinois at Urbana-Champaign, Urbana, Illinois 61801, United States
| | - Shiliang Tian
- Department of Chemistry, Department of Biochemistry, and Center for Biophysics
and Computational
Biology, University of Illinois at Urbana-Champaign, Urbana, Illinois 61801, United States
| | - Igor Petrik
- Department of Chemistry, Department of Biochemistry, and Center for Biophysics
and Computational
Biology, University of Illinois at Urbana-Champaign, Urbana, Illinois 61801, United States
| | - Ambika Bhagi
- Department of Chemistry, Department of Biochemistry, and Center for Biophysics
and Computational
Biology, University of Illinois at Urbana-Champaign, Urbana, Illinois 61801, United States
| | - Yi Lu
- Department of Chemistry, Department of Biochemistry, and Center for Biophysics
and Computational
Biology, University of Illinois at Urbana-Champaign, Urbana, Illinois 61801, United States
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111
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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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112
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Smith D, Danyal K, Raugei S, Seefeldt LC. Substrate channel in nitrogenase revealed by a molecular dynamics approach. Biochemistry 2014; 53:2278-85. [PMID: 24654842 DOI: 10.1021/bi401313j] [Citation(s) in RCA: 22] [Impact Index Per Article: 2.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/12/2022]
Abstract
Mo-dependent nitrogenase catalyzes the biological reduction of N2 to two NH3 molecules at FeMo-cofactor buried deep inside the MoFe protein. Access of substrates, such as N2, to the active site is likely restricted by the surrounding protein, requiring substrate channels that lead from the surface to the active site. Earlier studies on crystallographic structures of the MoFe protein have suggested three putative substrate channels. Here, we have utilized submicrosecond atomistic molecular dynamics simulations to allow the nitrogenase MoFe protein to explore its conformational space in an aqueous solution at physiological ionic strength, revealing a putative substrate channel. The viability of this observed channel was tested by examining the free energy of passage of N2 from the surface through the channel to FeMo-cofactor, resulting in the discovery of a very low energy barrier. These studies point to a viable substrate channel in nitrogenase that appears during thermal motions of the protein in an aqueous environment and that approaches a face of FeMo-cofactor earlier implicated in substrate binding.
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Affiliation(s)
- Dayle Smith
- Pacific Northwestern National Laboratory , Richland, Washington 99352, United States
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113
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Nitrogen fertilization has a stronger effect on soil nitrogen-fixing bacterial communities than elevated atmospheric CO2. Appl Environ Microbiol 2014; 80:3103-12. [PMID: 24610855 DOI: 10.1128/aem.04034-13] [Citation(s) in RCA: 66] [Impact Index Per Article: 6.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022] Open
Abstract
Biological nitrogen fixation is the primary supply of N to most ecosystems, yet there is considerable uncertainty about how N-fixing bacteria will respond to global change factors such as increasing atmospheric CO2 and N deposition. Using the nifH gene as a molecular marker, we studied how the community structure of N-fixing soil bacteria from temperate pine, aspen, and sweet gum stands and a brackish tidal marsh responded to multiyear elevated CO2 conditions. We also examined how N availability, specifically, N fertilization, interacted with elevated CO2 to affect these communities in the temperate pine forest. Based on data from Sanger sequencing and quantitative PCR, the soil nifH composition in the three forest systems was dominated by species in the Geobacteraceae and, to a lesser extent, Alphaproteobacteria. The N-fixing-bacterial-community structure was subtly altered after 10 or more years of elevated atmospheric CO2, and the observed shifts differed in each biome. In the pine forest, N fertilization had a stronger effect on nifH community structure than elevated CO2 and suppressed the diversity and abundance of N-fixing bacteria under elevated atmospheric CO2 conditions. These results indicate that N-fixing bacteria have complex, interacting responses that will be important for understanding ecosystem productivity in a changing climate.
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114
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Sydor AM, Lebrette H, Ariyakumaran R, Cavazza C, Zamble DB. Relationship between Ni(II) and Zn(II) coordination and nucleotide binding by the Helicobacter pylori [NiFe]-hydrogenase and urease maturation factor HypB. J Biol Chem 2014; 289:3828-41. [PMID: 24338018 PMCID: PMC3924253 DOI: 10.1074/jbc.m113.502781] [Citation(s) in RCA: 46] [Impact Index Per Article: 4.6] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/23/2013] [Revised: 12/01/2013] [Indexed: 12/23/2022] Open
Abstract
The pathogen Helicobacter pylori requires two nickel-containing enzymes, urease and [NiFe]-hydrogenase, for efficient colonization of the human gastric mucosa. These enzymes possess complex metallocenters that are assembled by teams of proteins in multistep pathways. One essential accessory protein is the GTPase HypB, which is required for Ni(II) delivery to [NiFe]-hydrogenase and participates in urease maturation. Ni(II) or Zn(II) binding to a site embedded in the GTPase domain of HypB modulates the enzymatic activity, suggesting a mechanism of regulation. In this study, biochemical and structural analyses of H. pylori HypB (HpHypB) revealed an intricate link between nucleotide and metal binding. HpHypB nickel coordination, stoichiometry, and affinity were modulated by GTP and GDP, an effect not observed for zinc, and biochemical evidence suggests that His-107 coordination to nickel toggles on and off in a nucleotide-dependent manner. These results are consistent with the crystal structure of HpHypB loaded with Ni(II), GDP, and Pi, which reveals a nickel site distinct from that of zinc-loaded Methanocaldococcus jannaschii HypB as well as subtle changes to the protein structure. Furthermore, Cys-142, a metal ligand from the Switch II GTPase motif, was identified as a key component of the signal transduction between metal binding and the enzymatic activity. Finally, potassium accelerated the enzymatic activity of HpHypB but had no effect on the other biochemical properties of the protein. Altogether, this molecular level information about HpHypB provides insight into its cellular function and illuminates a possible mechanism of metal ion discrimination.
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Affiliation(s)
- Andrew M. Sydor
- From the Department of Chemistry, University of Toronto, 80 St. George Street, Toronto, Ontario M5S 3H6, Canada and
| | - Hugo Lebrette
- University Grenoble Alpes, Institut de Biologie Structurale (IBS), CEA, DSV, IBS and CNRS, IBS, F-38000 Grenoble, France
| | - Rishikesh Ariyakumaran
- From the Department of Chemistry, University of Toronto, 80 St. George Street, Toronto, Ontario M5S 3H6, Canada and
| | - Christine Cavazza
- University Grenoble Alpes, Institut de Biologie Structurale (IBS), CEA, DSV, IBS and CNRS, IBS, F-38000 Grenoble, France
| | - Deborah B. Zamble
- From the Department of Chemistry, University of Toronto, 80 St. George Street, Toronto, Ontario M5S 3H6, Canada and
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115
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Hoffman BM, Lukoyanov D, Yang ZY, Dean DR, Seefeldt LC. Mechanism of nitrogen fixation by nitrogenase: the next stage. Chem Rev 2014; 114:4041-62. [PMID: 24467365 PMCID: PMC4012840 DOI: 10.1021/cr400641x] [Citation(s) in RCA: 979] [Impact Index Per Article: 97.9] [Reference Citation Analysis] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/28/2022]
Affiliation(s)
- Brian M Hoffman
- Department of Chemistry and Biochemistry, Utah State University , 0300 Old Main Hill, Logan, Utah 84322, United States
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116
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Yang KY, Haynes CA, Spatzal T, Rees DC, Howard JB. Turnover-dependent inactivation of the nitrogenase MoFe-protein at high pH. Biochemistry 2014; 53:333-43. [PMID: 24392967 PMCID: PMC3932303 DOI: 10.1021/bi4014769] [Citation(s) in RCA: 19] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Abstract] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Abstract
![]()
Proton uptake accompanies the reduction
of all known substrates
by nitrogenase. As a consequence, a higher pH should limit the availability
of protons as a substrate essential for turnover, thereby increasing
the proportion of more highly reduced forms of the enzyme for further
study. The utility of the high-pH approach would appear to be problematic
in view of the observation reported by Pham and Burgess [(1993) Biochemistry 32, 13725–13731] that the MoFe-protein
undergoes irreversible protein denaturation above pH 8.65. In contrast,
we found by both enzyme activity and crystallographic analyses that
the MoFe-protein is stable when incubated at pH 9.5. We did observe,
however, that at higher pHs and under turnover conditions, the MoFe-protein
is slowly inactivated. While a normal, albeit low, level of substrate
reduction occurs under these conditions, the MoFe-protein undergoes
a complex transformation; initially, the enzyme is reversibly inhibited
for substrate reduction at pH 9.5, yet in a second, slower process,
the MoFe-protein becomes irreversibly inactivated as measured by substrate
reduction activity at the optimal pH of 7.8. The final inactivated
MoFe-protein has an increased hydrodynamic radius compared to that
of the native MoFe-protein, yet it has a full complement of iron and
molybdenum. Significantly, the modified MoFe-protein retains the ability
to specifically interact with its nitrogenase partner, the Fe-protein,
as judged by the support of ATP hydrolysis and by formation of a tight
complex with the Fe-protein in the presence of ATP and aluminum fluoride.
The turnover-dependent inactivation coupled to conformational change
suggests a mechanism-based transformation that may provide a new probe
of nitrogenase catalysis.
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Affiliation(s)
- Kun-Yun Yang
- Division of Chemistry and Chemical Engineering 114-96, California Institute of Technology , Pasadena, California 91125, United States
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117
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Cleaving the n,n triple bond: the transformation of dinitrogen to ammonia by nitrogenases. Met Ions Life Sci 2014; 14:147-76. [PMID: 25416394 DOI: 10.1007/978-94-017-9269-1_7] [Citation(s) in RCA: 11] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/23/2022]
Abstract
Biological nitrogen fixation is a natural process that converts atmospheric nitrogen (N2) to bioavailable ammonia (NH3). This reaction not only plays a key role in supplying bio-accessible nitrogen to all life forms on Earth, but also embodies the powerful chemistry of cleaving the inert N,N triple bond under ambient conditions. The group of enzymes that carry out this reaction are called nitrogenases and typically consist of two redox active protein components, each containing metal cluster(s) that are crucial for catalysis. In the past decade, a number of crystal structures, including several at high resolutions, have been solved. However, the catalytic mechanism of nitrogenase, namely, how the N,N triple bond is cleaved by this enzyme under ambient conditions, has remained elusive. Nevertheless, recent biochemical and spectroscopic studies have led to a better understanding of the potential intermediates of N2 reduction by the molybdenum (Mo)-nitrogenase. In addition, it has been demonstrated that carbon monoxide (CO), which was thought to be an inhibitor of N2 reduction, could also be reduced by the vanadium (V)-nitrogenase to small alkanes and alkenes. This chapter will begin with an introduction to biological nitrogen fixation and Mo-nitrogenase, continue with a discussion of the catalytic mechanism of N2 reduction by Mo-nitrogenase, and conclude with a survey of the current knowledge of N2- and CO-reduction by V-nitrogenase and how V-nitrogenase compares to its Mo-counterpart in these catalytic activities.
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118
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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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119
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Howard JB, Kechris KJ, Rees DC, Glazer AN. Multiple amino acid sequence alignment nitrogenase component 1: insights into phylogenetics and structure-function relationships. PLoS One 2013; 8:e72751. [PMID: 24019874 PMCID: PMC3760896 DOI: 10.1371/journal.pone.0072751] [Citation(s) in RCA: 20] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/17/2013] [Accepted: 07/18/2013] [Indexed: 02/05/2023] Open
Abstract
Amino acid residues critical for a protein's structure-function are retained by natural selection and these residues are identified by the level of variance in co-aligned homologous protein sequences. The relevant residues in the nitrogen fixation Component 1 α- and β-subunits were identified by the alignment of 95 protein sequences. Proteins were included from species encompassing multiple microbial phyla and diverse ecological niches as well as the nitrogen fixation genotypes, anf, nif, and vnf, which encode proteins associated with cofactors differing at one metal site. After adjusting for differences in sequence length, insertions, and deletions, the remaining >85% of the sequence co-aligned the subunits from the three genotypes. Six Groups, designated Anf, Vnf , and Nif I-IV, were assigned based upon genetic origin, sequence adjustments, and conserved residues. Both subunits subdivided into the same groups. Invariant and single variant residues were identified and were defined as “core” for nitrogenase function. Three species in Group Nif-III, Candidatus Desulforudis audaxviator, Desulfotomaculum kuznetsovii, and Thermodesulfatator indicus, were found to have a seleno-cysteine that replaces one cysteinyl ligand of the 8Fe:7S, P-cluster. Subsets of invariant residues, limited to individual groups, were identified; these unique residues help identify the gene of origin (anf, nif, or vnf) yet should not be considered diagnostic of the metal content of associated cofactors. Fourteen of the 19 residues that compose the cofactor pocket are invariant or single variant; the other five residues are highly variable but do not correlate with the putative metal content of the cofactor. The variable residues are clustered on one side of the cofactor, away from other functional centers in the three dimensional structure. Many of the invariant and single variant residues were not previously recognized as potentially critical and their identification provides the bases for new analyses of the three-dimensional structure and for mutagenesis studies.
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Affiliation(s)
- James B. Howard
- Department of Biochemistry, Molecular Biology, and Biophysics, University of Minnesota, Minneapolis, Minnesota, United States of America
- Division of Chemistry and Chemical Engineering, California Institute of Technology, Pasadena, California, United States of America
- * E-mail: (JBH); (KJK); (DCR); (ANG)
| | - Katerina J. Kechris
- Department of Biostatistics and Informatics, Colorado School of Public Health, Aurora, Colorado, United States of America
- * E-mail: (JBH); (KJK); (DCR); (ANG)
| | - Douglas C. Rees
- Division of Chemistry and Chemical Engineering, Howard Hughes Medical Institute, California Institute of Technology, Pasadena, California, United States of America
- * E-mail: (JBH); (KJK); (DCR); (ANG)
| | - Alexander N. Glazer
- Department of Molecular and Cell Biology, University of California, Berkeley, California, United States of America
- * E-mail: (JBH); (KJK); (DCR); (ANG)
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120
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Crystalline and solution chemistry of tetrameric and dimeric molybdenum(VI) citrato complexes. Inorganica Chim Acta 2013. [DOI: 10.1016/j.ica.2013.06.032] [Citation(s) in RCA: 20] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/18/2022]
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121
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Nomata J, Kondo T, Itoh S, Fujita Y. Nicotinamide is a specific inhibitor of dark-operative protochlorophyllide oxidoreductase, a nitrogenase-like enzyme, from Rhodobacter capsulatus. FEBS Lett 2013; 587:3142-7. [PMID: 23954297 DOI: 10.1016/j.febslet.2013.07.054] [Citation(s) in RCA: 10] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/06/2013] [Revised: 07/30/2013] [Accepted: 07/31/2013] [Indexed: 11/18/2022]
Abstract
Dark-operative protochlorophyllide oxidoreductase (DPOR) is a nitrogenase-like enzyme consisting of two components, L-protein as a reductase component and NB-protein as a catalytic component. Elucidation of the crystal structures of NB-protein (Muraki et al., Nature 2010, 465: 110-114) has enabled us to study its reaction mechanism in combination with biochemical analysis. Here we demonstrate that nicotinamide (NA) inhibits DPOR activity by blocking the electron transfer from L-protein to NB-protein. A reaction scheme of DPOR, in which the binding of protochlorophyllide (Pchlide) to the NB-protein precedes the electron transfer from the L-protein, is proposed based on the NA effects.
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Affiliation(s)
- Jiro Nomata
- Graduate School of Bioagricultural Sciences, Nagoya University, Nagoya 464-8601, Japan
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122
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New Synthetic Routes to Metal-Sulfur Clusters Relevant to the Nitrogenase Metallo-Clusters. Z Anorg Allg Chem 2013. [DOI: 10.1002/zaac.201300081] [Citation(s) in RCA: 33] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/07/2022]
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123
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Nordlund S, Högbom M. ADP-ribosylation, a mechanism regulating nitrogenase activity. FEBS J 2013; 280:3484-90. [PMID: 23574616 DOI: 10.1111/febs.12279] [Citation(s) in RCA: 27] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/15/2013] [Revised: 03/26/2013] [Accepted: 04/08/2013] [Indexed: 11/29/2022]
Abstract
Nitrogen fixation is the vital biochemical process in which atmospheric molecular nitrogen is made available to the biosphere. The process is highly energetically costly and thus tightly regulated. The activity of the key enzyme, nitrogenase, is controlled by reversible mono-ADP-ribosylation of one of its components, the Fe protein. This protein provides the other component, the MoFe protein, with the electrons required for the reduction of molecular nitrogen. The Fe-protein is ADP-ribosylated and de-ADP-ribosylated by dinitrogenase reductase ADP-ribosyl transferase and dinitrogenase reductase activating glycohydrolase, respectively. Here we review the current biochemical and structural knowledge of this central regulatory reaction.
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Affiliation(s)
- Stefan Nordlund
- Department of Biochemistry and Biophysics, Stockholm University, Stockholm, Sweden.
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124
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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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125
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Yang HC, Fu HL, Lin YF, Rosen BP. Pathways of arsenic uptake and efflux. CURRENT TOPICS IN MEMBRANES 2013; 69:325-58. [PMID: 23046656 DOI: 10.1016/b978-0-12-394390-3.00012-4] [Citation(s) in RCA: 124] [Impact Index Per Article: 11.3] [Reference Citation Analysis] [Abstract] [Subscribe] [Scholar Register] [Indexed: 10/27/2022]
Abstract
Arsenic is the most prevalent environmental toxic substance and ranks first on the U.S. Environmental Protection Agency's Superfund List. Arsenic is a carcinogen and a causative agent of numerous human diseases. Paradoxically arsenic is used as a chemotherapeutic agent for treatment of acute promyelocytic leukemia. Inorganic arsenic has two biological important oxidation states: As(V) (arsenate) and As(III) (arsenite). Arsenic uptake is adventitious because the arsenate and arsenite are chemically similar to required nutrients. Arsenate resembles phosphate and is a competitive inhibitor of many phosphate-utilizing enzymes. Arsenate is taken up by phosphate transport systems. In contrast, at physiological pH, the form of arsenite is As(OH)(3), which resembles organic molecules such as glycerol. Consequently, arsenite is taken into cells by aquaglyceroporin channels. Arsenic efflux systems are found in nearly every organism and evolved to rid cells of this toxic metalloid. These efflux systems include members of the multidrug resistance protein family and the bacterial exchangers Acr3 and ArsB. ArsB can also be a subunit of the ArsAB As(III)-translocating ATPase, an ATP-driven efflux pump. The ArsD metallochaperone binds cytosolic As(III) and transfers it to the ArsA subunit of the efflux pump. Knowledge of the pathways and transporters for arsenic uptake and efflux is essential for understanding its toxicity and carcinogenicity and for rational design of cancer chemotherapeutic drugs.
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Affiliation(s)
- Hung-Chi Yang
- Department of Medical Biotechnology and Laboratory Sciences, Chang-Gung University, Tao-Yuan, Taiwan
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126
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Sasaki D, Watanabe S, Matsumi R, Shoji T, Yasukochi A, Tagashira K, Fukuda W, Kanai T, Atomi H, Imanaka T, Miki K. Identification and structure of a novel archaeal HypB for [NiFe] hydrogenase maturation. J Mol Biol 2013; 425:1627-40. [PMID: 23399544 DOI: 10.1016/j.jmb.2013.02.004] [Citation(s) in RCA: 19] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/03/2012] [Revised: 02/01/2013] [Accepted: 02/04/2013] [Indexed: 11/17/2022]
Abstract
HypB (metal-binding GTPase) and HypA (nickel metallochaperone) are required for nickel insertion into [NiFe] hydrogenase. However, the HypB homolog proteins are not found in some archaeal species including Thermococcales. In this article, we identify a novel archaeal Mrp/MinD family ATPase-type HypB from Thermococcus kodakarensis (Tk-mmHypB) and determine its crystal structure. The mmhypB gene is conserved among species lacking the hypB gene and is located adjacent to the hypA gene on their genome. Deletion of the mmhypB gene leads to a significant reduction in hydrogen-dependent growth of T. kodakarensis, which is restored by nickel supplementation. The monomer structure of Tk-mmHypB is similar to those of the Mrp/MinD family ATPases. The ADP molecules are tightly bound to the protein. Isothermal titration calorimetry shows that Tk-mmHypB binds ATP with a K(d) value of 84 nM. ADP binds more tightly than does ATP, with a K(d) value of 15 nM. The closed Tk-mmHypB dimer in the crystallographic asymmetric unit is consistent with the ATP-hydrolysis-deficient dimer of the Mrp/MinD family Soj/MinD proteins. Structural comparisons with these proteins suggest the ATP-binding dependent conformational change and rearrangement of the Tk-mmHypB dimer. These observations imply that the nickel insertion process during the [NiFe] hydrogenase maturation is performed by HypA, mmHypB, and a nucleotide exchange factor in these archaea.
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Affiliation(s)
- Daisuke Sasaki
- Department of Chemistry, Graduate School of Science, Kyoto University, Kyoto 606-8502, Japan
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127
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Structure of ADP-aluminium fluoride-stabilized protochlorophyllide oxidoreductase complex. Proc Natl Acad Sci U S A 2013; 110:2094-8. [PMID: 23341615 DOI: 10.1073/pnas.1218303110] [Citation(s) in RCA: 53] [Impact Index Per Article: 4.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/18/2022] Open
Abstract
Photosynthesis uses chlorophylls for the conversion of light into chemical energy, the driving force of life on Earth. During chlorophyll biosynthesis in photosynthetic bacteria, cyanobacteria, green algae and gymnosperms, dark-operative protochlorophyllide oxidoreductase (DPOR), a nitrogenase-like metalloenzyme, catalyzes the chemically challenging two-electron reduction of the fully conjugated ring system of protochlorophyllide a. The reduction of the C-17=C-18 double bond results in the characteristic ring architecture of all chlorophylls, thereby altering the absorption properties of the molecule and providing the basis for light-capturing and energy-transduction processes of photosynthesis. We report the X-ray crystallographic structure of the substrate-bound, ADP-aluminium fluoride-stabilized (ADP·AlF(3)-stabilized) transition state complex between the DPOR components L(2) and (NB)(2) from the marine cyanobacterium Prochlorococcus marinus. Our analysis permits a thorough investigation of the dynamic interplay between L(2) and (NB)(2). Upon complex formation, substantial ATP-dependent conformational rearrangements of L(2) trigger the protein-protein interactions with (NB)(2) as well as the electron transduction via redox-active [4Fe-4S] clusters. We also present the identification of artificial "small-molecule substrates" of DPOR in correlation with those of nitrogenase. The catalytic differences and similarities between DPOR and nitrogenase have broad implications for the energy transduction mechanism of related multiprotein complexes that are involved in the reduction of chemically stable double and/or triple bonds.
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129
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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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130
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The nitrogenase regulatory enzyme dinitrogenase reductase ADP-ribosyltransferase (DraT) is activated by direct interaction with the signal transduction protein GlnB. J Bacteriol 2012; 195:279-86. [PMID: 23144248 DOI: 10.1128/jb.01517-12] [Citation(s) in RCA: 16] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022] Open
Abstract
Fe protein (dinitrogenase reductase) activity is reversibly inactivated by dinitrogenase reductase ADP-ribosyltransferase (DraT) in response to an increase in the ammonium concentration or a decrease in cellular energy in Azospirillum brasilense, Rhodospirillum rubrum, and Rhodobacter capsulatus. The ADP-ribosyl is removed by the dinitrogenase reductase-activating glycohydrolase (DraG), promoting Fe protein reactivation. The signaling pathway leading to DraT activation by ammonium is still not completely understood, but the available evidence shows the involvement of direct interaction between the enzyme and the nitrogen-signaling P(II) proteins. In A. brasilense, two P(II) proteins, GlnB and GlnZ, were identified. We used Fe protein from Azotobacter vinelandii as the substrate to assess the activity of A. brasilense DraT in vitro complexed or not with P(II) proteins. Under our conditions, GlnB was necessary for DraT activity in the presence of Mg-ADP. The P(II) effector 2-oxoglutarate, in the presence of Mg-ATP, inhibited DraT-GlnB activity, possibly by inducing complex dissociation. DraT was also activated by GlnZ and by both uridylylated P(II) proteins, but not by a GlnB variant carrying a partial deletion of the T loop. Kinetics studies revealed that the A. brasilense DraT-GlnB complex was at least 18-fold more efficient than DraT purified from R. rubrum, but with a similar K(m) value for NAD(+). Our results showed that ADP-ribosylation of the Fe protein does not affect the electronic state of its metal cluster and prevents association between the Fe and MoFe proteins, thus inhibiting electron transfer.
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131
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Ohta S, Ohki Y, Hashimoto T, Cramer RE, Tatsumi K. A Nitrogenase Cluster Model [Fe8S6O] with an Oxygen Unsymmetrically Bridging Two Proto-Fe4S3 Cubes: Relevancy to the Substrate Binding Mode of the FeMo Cofactor. Inorg Chem 2012; 51:11217-9. [DOI: 10.1021/ic301348f] [Citation(s) in RCA: 47] [Impact Index Per Article: 3.9] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/30/2022]
Affiliation(s)
- Shun Ohta
- Department of Chemistry, Graduate School of Science, and Research Center for Meterials Science, Nagoya University, Furo-cho, Chikusa-ku, Nagoya 464-8602,
Japan
| | - Yasuhiro Ohki
- Department of Chemistry, Graduate School of Science, and Research Center for Meterials Science, Nagoya University, Furo-cho, Chikusa-ku, Nagoya 464-8602,
Japan
| | - Takayoshi Hashimoto
- Department of Chemistry, Graduate School of Science, and Research Center for Meterials Science, Nagoya University, Furo-cho, Chikusa-ku, Nagoya 464-8602,
Japan
| | - Roger E. Cramer
- Department
of Chemistry, University of Hawaii, Honolulu, Hawaii
96822, United States
| | - Kazuyuki Tatsumi
- Department of Chemistry, Graduate School of Science, and Research Center for Meterials Science, Nagoya University, Furo-cho, Chikusa-ku, Nagoya 464-8602,
Japan
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132
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Knauer SH, Buckel W, Dobbek H. On the ATP-dependent activation of the radical enzyme (R)-2-hydroxyisocaproyl-CoA dehydratase. Biochemistry 2012; 51:6609-22. [PMID: 22827463 DOI: 10.1021/bi300571z] [Citation(s) in RCA: 17] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/19/2023]
Abstract
Members of the 2-hydroxyacyl-CoA dehydratase enzyme family catalyze the β,α-dehydration of various CoA-esters in the fermentation of amino acids by clostridia. Abstraction of the nonacidic β-proton of the 2-hydroxyacyl-CoA compounds is achieved by the reductive generation of ketyl radicals on the substrate, which is initiated by the transfer of an electron at low redox potentials. The highly energetic electron needed on the dehydratase is donated by a [4Fe-4S] cluster containing ATPase, termed activator. We investigated the activator of the 2-hydroxyisocaproyl-CoA dehydratase from Clostridium difficile. The activator is a homodimeric protein structurally related to acetate and sugar kinases, Hsc70 and actin, and has a [4Fe-4S] cluster bound in the dimer interface. The crystal structures of the Mg-ADP, Mg-ADPNP, and nucleotide-free states of the reduced activator have been solved at 1.6-3.0 Å resolution, allowing us to define the position of Mg(2+) and water molecules in the vicinity of the nucleotides and the [4Fe-4S] cluster. The structures reveal redox- and nucleotide dependent changes agreeing with the modulation of the reduction potential of the [4Fe-4S] cluster by conformational changes. We also investigated the propensity of the activator to form a complex with its cognate dehydratase in the presence of Mg-ADP and Mg-ADPNP and together with the structural data present a refined mechanistic scheme for the ATP-dependent electron transfer between activator and dehydratase.
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Affiliation(s)
- Stefan H Knauer
- Institut für Biologie, Strukturbiologie/Biochemie, Humboldt-Universität zu Berlin, D-10099 Berlin, Germany
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133
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Park KT, Wu W, Lovell S, Lutkenhaus J. Mechanism of the asymmetric activation of the MinD ATPase by MinE. Mol Microbiol 2012; 85:271-81. [PMID: 22651575 DOI: 10.1111/j.1365-2958.2012.08110.x] [Citation(s) in RCA: 43] [Impact Index Per Article: 3.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/30/2022]
Abstract
MinD is a component of the Min system involved in the spatial regulation of cell division. It is an ATPase in the MinD/ParA/Mrp deviant Walker A motif family which is within the P loop GTPase superfamily. Its ATPase activity is stimulated by MinE; however, the mechanism of this activation is unclear. MinD forms a symmetric dimer with two binding sites for MinE; however, a recent model suggested that MinE occupying one site was sufficient for ATP hydrolysis. By generating heterodimers with one binding site for MinE we show that one binding site is sufficient for stimulation of the MinD ATPase. Furthermore, comparison of structures of MinD and related proteins led us to examine the role of N45 in the switch I region. An asparagine at this position is conserved in four of the deviant Walker A motif subfamilies (MinD, chromosomal ParAs, Get3 and FleN) and we find that N45 in MinD is essential for MinE-stimulated ATPase activity and suggest that it is a key residue affected by MinE binding.
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Affiliation(s)
- Kyung-Tae Park
- Department of Microbiology, Molecular Genetics and Immunology, University of Kansas Medical Center, Kansas City, KS 66160, USA
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134
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Lutkenhaus J. The ParA/MinD family puts things in their place. Trends Microbiol 2012; 20:411-8. [PMID: 22672910 DOI: 10.1016/j.tim.2012.05.002] [Citation(s) in RCA: 135] [Impact Index Per Article: 11.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/03/2012] [Revised: 05/01/2012] [Accepted: 05/04/2012] [Indexed: 01/09/2023]
Abstract
Bacteria must segregate their DNA and position a septum to grow and divide. In many bacteria, MinD is involved in spatial regulation of the cytokinetic Z ring, and ParAs are involved in chromosome and plasmid segregation. The use of the MinD/ParA family to provide positional information for spatial organization continues to expand with the recognition that orphan ParAs are required for segregating cytoplasmic protein clusters and the polar localization of chemotaxis proteins, conjugative transfer machinery, type IV pili, and cellulose synthesis. Also, some bacteria lacking MinD use orphan ParAs to regulate cell division. Positioning of MinD/ParA proteins is either due to self-organization on a surface or reliance on a landmark protein that functions as a molecular beacon.
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Affiliation(s)
- Joe Lutkenhaus
- Department of Microbiology, Molecular Genetics and Immunology, University of Kansas Medical Center, Kansas City, KS 66160, USA.
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135
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Siddique A, Figurski DH. Different phenotypes of Walker-like A box mutants of ParA homolog IncC of broad-host-range IncP plasmids. Plasmid 2012; 68:93-104. [PMID: 22579980 DOI: 10.1016/j.plasmid.2012.04.003] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/17/2011] [Revised: 03/27/2012] [Accepted: 04/02/2012] [Indexed: 11/30/2022]
Abstract
The promiscuous IncPα plasmids RK2 and R995 encode a broad-host-range partition system, whose essential components include the incC and korB genes and a DNA site (O(B)) to which the korB product binds. IncC2, the smaller of the two incC products, is sufficient for stabilization of R995ΔincC. It is a member of the type Ia ParA family of partition ATPases. To better understand the role of ATP in partition, we constructed three alanine-substitution mutants of IncC2. Each mutation changed a different residue of the Walker-like ATP-binding and hydrolysis motif, including a lysine (K10) conserved solely among members of the ParA and MinD families. All three IncC2 mutants were defective in plasmid partition, but they differed from one another in other respects. The IncC2 T16A mutant, predicted to be defective in Mg²⁺ coordination, was severely impaired in all activities tested. IncC2 K10A, predicted to be defective in ATP hydrolysis, mediated enhanced incompatibility with R995 derivatives. IncC2 K15A, predicted to be defective in ATP binding, exhibited two distinct incompatibility properties depending on the genotype of the target plasmid. When in trans to plasmids carrying a complementable incC deletion, IncC2 K15A caused dramatic plasmid loss, even at low levels of expression. In trans to wild-type R995 or to R995ΔincC carrying a functional P1 partition system, IncC2 K15A-mediated incompatibility was significantly less than that caused by wild-type IncC2. All three Walker-like A box mutants were also defective for the host toxicity that normally results from co-overexpression of incC and korB. The phenotypes of the mutants support a model in which nucleotide hydrolysis is required for separation of paired plasmid complexes and possible interaction with a host factor.
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Affiliation(s)
- Azeem Siddique
- Department of Microbiology and Immunology, College of Physicians and Surgeons, Columbia University, New York, NY 10032, USA
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136
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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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137
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Huergo LF, Pedrosa FO, Muller-Santos M, Chubatsu LS, Monteiro RA, Merrick M, Souza EM. PII signal transduction proteins: pivotal players in post-translational control of nitrogenase activity. MICROBIOLOGY-SGM 2012; 158:176-190. [PMID: 22210804 DOI: 10.1099/mic.0.049783-0] [Citation(s) in RCA: 57] [Impact Index Per Article: 4.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 01/27/2023]
Abstract
The fixation of atmospheric nitrogen by the prokaryotic enzyme nitrogenase is an energy- expensive process and consequently it is tightly regulated at a variety of levels. In many diazotrophs this includes post-translational regulation of the enzyme's activity, which has been reported in both bacteria and archaea. The best understood response is the short-term inactivation of nitrogenase in response to a transient rise in ammonium levels in the environment. A number of proteobacteria species effect this regulation through reversible ADP-ribosylation of the enzyme, but other prokaryotes have evolved different mechanisms. Here we review current knowledge of post-translational control of nitrogenase and show that, for the response to ammonium, the P(II) signal transduction proteins act as key players.
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Affiliation(s)
- Luciano F Huergo
- Instituto Nacional de Ciência e Tecnologia da Fixação Biológica de Nitrogênio, Departamento de Bioquímica e Biologia Molecular, UFPR Curitiba, PR, Brazil
| | - Fábio O Pedrosa
- Instituto Nacional de Ciência e Tecnologia da Fixação Biológica de Nitrogênio, Departamento de Bioquímica e Biologia Molecular, UFPR Curitiba, PR, Brazil
| | - Marcelo Muller-Santos
- Instituto Nacional de Ciência e Tecnologia da Fixação Biológica de Nitrogênio, Departamento de Bioquímica e Biologia Molecular, UFPR Curitiba, PR, Brazil
| | - Leda S Chubatsu
- Instituto Nacional de Ciência e Tecnologia da Fixação Biológica de Nitrogênio, Departamento de Bioquímica e Biologia Molecular, UFPR Curitiba, PR, Brazil
| | - Rose A Monteiro
- Instituto Nacional de Ciência e Tecnologia da Fixação Biológica de Nitrogênio, Departamento de Bioquímica e Biologia Molecular, UFPR Curitiba, PR, Brazil
| | - Mike Merrick
- Department of Molecular Microbiology, John Innes Centre, Norwich Research Park, UK
| | - Emanuel M Souza
- Instituto Nacional de Ciência e Tecnologia da Fixação Biológica de Nitrogênio, Departamento de Bioquímica e Biologia Molecular, UFPR Curitiba, PR, Brazil
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138
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ATP-independent substrate reduction by nitrogenase P-cluster variant. Proc Natl Acad Sci U S A 2012; 109:6922-6. [PMID: 22509042 DOI: 10.1073/pnas.1202429109] [Citation(s) in RCA: 22] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/18/2022] Open
Abstract
The P-cluster of nitrogenase is largely known for its function to mediate electron transfer to the active cofactor site during catalysis. Here, we show that a P-cluster variant (designated P*-cluster), which consists of paired [Fe(4)S(4)]-like clusters, can catalyze ATP-independent substrate reduction in the presence of a strong reductant, europium(II) diethylenetriaminepentaacetate [Eu(II)-DTPA]. The observation of a decrease of activity in the rank ΔnifH, ΔnifBΔnifZ, and ΔnifB MoFe protein, which corresponds to a decrease of the amount of P*-clusters in these cofactor-deficient proteins, firmly establishes P*-cluster as a catalytically active metal center in Eu(II)-DTPA-driven reactions. More excitingly, the fact that P*-cluster is not only capable of catalyzing the two-electron reduction of proton, acetylene, ethylene, and hydrazine, but also capable of reducing cyanide, carbon monoxide, and carbon dioxide to alkanes and alkenes, points to a possibility of developing biomimetic catalysts for hydrocarbon production under ambient conditions.
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139
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Harel A, Falkowski P, Bromberg Y. TrAnsFuSE refines the search for protein function: oxidoreductases. Integr Biol (Camb) 2012; 4:765-77. [DOI: 10.1039/c2ib00131d] [Citation(s) in RCA: 9] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022]
Affiliation(s)
- Arye Harel
- Environmental Biophysics and Molecular Ecology Program, Institute of Marine and Coastal Science, Rutgers the State University of New Jersey, 71 Dudley Road, New Brunswick, NJ 08901 USA. Fax: +1 732 9324083; Tel: +1 732 8489323 x412
- Department of Biochemistry and Microbiology, Rutgers the State University of New Jersey, Lipman Hall 218, New Brunswick, NJ 08901, USA. Fax: +1 732 9328965; Tel: +1 732 9329763 x203
| | - Paul Falkowski
- Environmental Biophysics and Molecular Ecology Program, Institute of Marine and Coastal Science, Rutgers the State University of New Jersey, 71 Dudley Road, New Brunswick, NJ 08901 USA. Fax: +1 732 9324083; Tel: +1 732 8489323 x412
| | - Yana Bromberg
- Department of Biochemistry and Microbiology, Rutgers the State University of New Jersey, Lipman Hall 218, New Brunswick, NJ 08901, USA. Fax: +1 732 9328965; Tel: +1 732 9329763 x203
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140
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Kiekebusch D, Michie KA, Essen LO, Löwe J, Thanbichler M. Localized dimerization and nucleoid binding drive gradient formation by the bacterial cell division inhibitor MipZ. Mol Cell 2012; 46:245-59. [PMID: 22483621 PMCID: PMC3355305 DOI: 10.1016/j.molcel.2012.03.004] [Citation(s) in RCA: 86] [Impact Index Per Article: 7.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/12/2011] [Revised: 12/11/2011] [Accepted: 03/08/2012] [Indexed: 11/26/2022]
Abstract
Protein gradients play a central role in the spatial organization of cells, but the mechanisms of their formation are incompletely understood. This study analyzes the determinants responsible for establishing bipolar gradients of the ATPase MipZ, a key regulator of division site placement in Caulobacter crescentus. We have solved the crystal structure of MipZ in different nucleotide states, dissected its ATPase cycle, and investigated its interaction with FtsZ, ParB, and the nucleoid. Our results suggest that the polar ParB complexes locally stimulate the formation of ATP-bound MipZ dimers, which are then retained near the cell poles through association with chromosomal DNA. Due to their intrinsic ATPase activity, dimers eventually dissociate into freely diffusible monomers that undergo spontaneous nucleotide exchange and are recaptured by ParB. These findings clarify the molecular function of a conserved gradient-forming system and reveal mechanistic principles that might be commonly used to sustain protein gradients within cells.
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Affiliation(s)
- Daniela Kiekebusch
- Max Planck Institute for Terrestrial Microbiology, 35043 Marburg, Germany
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141
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Chartron JW, Clemons WM, Suloway CJM. The complex process of GETting tail-anchored membrane proteins to the ER. Curr Opin Struct Biol 2012; 22:217-24. [PMID: 22444563 DOI: 10.1016/j.sbi.2012.03.001] [Citation(s) in RCA: 54] [Impact Index Per Article: 4.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/28/2012] [Accepted: 03/01/2012] [Indexed: 10/28/2022]
Abstract
Biosynthesis of membrane proteins requires that hydrophobic transmembrane (TM) regions be shielded from the cytoplasm while being directed to the correct membrane. Tail-anchored (TA) membrane proteins, characterized by a single C-terminal TM, pose an additional level of complexity because they must be post-translationally targeted. In eukaryotes, the GET pathway shuttles TA-proteins to the endoplasmic reticulum. The key proteins required in yeast (Sgt2 and Get1-5) have been under extensive structural and biochemical investigation during recent years. The central protein Get3 utilizes nucleotide linked conformational changes to facilitate substrate loading and targeting. Here we analyze this complex process from a structural perspective, as understood in yeast, and further postulate on similar pathways in other domains of life.
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Affiliation(s)
- Justin W Chartron
- Division of Chemistry and Chemical Engineering, California Institute of Technology, Pasadena, CA 91125, United States
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142
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Redox-dependent complex formation by an ATP-dependent activator of the corrinoid/iron-sulfur protein. Proc Natl Acad Sci U S A 2012; 109:5235-40. [PMID: 22431597 DOI: 10.1073/pnas.1117126109] [Citation(s) in RCA: 34] [Impact Index Per Article: 2.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/18/2022] Open
Abstract
Movement, cell division, protein biosynthesis, electron transfer against an electrochemical gradient, and many more processes depend on energy conversions coupled to the hydrolysis of ATP. The reduction of metal sites with low reduction potentials (E(0') < -500 mV) is possible by connecting an energetical uphill electron transfer with the hydrolysis of ATP. The corrinoid-iron/sulfur protein (CoFeSP) operates within the reductive acetyl-CoA pathway by transferring a methyl group from methyltetrahydrofolate bound to a methyltransferase to the [Ni-Ni-Fe(4)S(4)] cluster of acetyl-CoA synthase. Methylation of CoFeSP only occurs in the low-potential Co(I) state, which can be sporadically oxidized to the inactive Co(II) state, making its reductive reactivation necessary. Here we show that an open-reading frame proximal to the structural genes of CoFeSP encodes an ATP-dependent reductive activator of CoFeSP. Our biochemical and structural analysis uncovers a unique type of reductive activator distinct from the electron-transferring ATPases found to reduce the MoFe-nitrogenase and 2-hydroxyacyl-CoA dehydratases. The CoFeSP activator contains an ASKHA domain (acetate and sugar kinases, Hsp70, and actin) harboring the ATP-binding site, which is also present in the activator of 2-hydroxyacyl-CoA dehydratases and a ferredoxin-like [2Fe-2S] cluster domain acting as electron donor. Complex formation between CoFeSP and its activator depends on the oxidation state of CoFeSP, which provides evidence for a unique strategy to achieve unidirectional electron transfer between two redox proteins.
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143
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Lee CC, Hu Y, Ribbe MW. ATP-independent formation of hydrocarbons catalyzed by isolated nitrogenase cofactors. Angew Chem Int Ed Engl 2012; 51:1947-9. [PMID: 22253035 DOI: 10.1002/anie.201108916] [Citation(s) in RCA: 51] [Impact Index Per Article: 4.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/18/2011] [Revised: 01/03/2012] [Indexed: 11/12/2022]
Affiliation(s)
- Chi Chung Lee
- Molecular Biology and Biochemistry, University of California, Irvine, 2236/2448 McGaugh Hall, Irvine, CA 92697-3900, USA
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144
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Lee CC, Hu Y, Ribbe MW. ATP-Independent Formation of Hydrocarbons Catalyzed by Isolated Nitrogenase Cofactors. Angew Chem Int Ed Engl 2012. [DOI: 10.1002/ange.201108916] [Citation(s) in RCA: 20] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/11/2022]
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145
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Perez-Cheeks BA, Planet PJ, Sarkar IN, Clock SA, Xu Q, Figurski DH. The product of tadZ, a new member of the parA/minD superfamily, localizes to a pole in Aggregatibacter actinomycetemcomitans. Mol Microbiol 2012; 83:694-711. [PMID: 22239271 DOI: 10.1111/j.1365-2958.2011.07955.x] [Citation(s) in RCA: 26] [Impact Index Per Article: 2.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/08/2023]
Abstract
Aggregatibacter actinomycetemcomitans establishes a tenacious biofilm that is important for periodontal disease. The tad locus encodes the components for the secretion and biogenesis of Flp pili, which are necessary for the biofilm to form. TadZ is required, but its function has been elusive. We show that tadZ genes belong to the parA/minD superfamily of genes and that TadZ from A. actinomycetemcomitans (AaTadZ) forms a polar focus in the cell independent of any other tad locus protein. Mutations indicate that regions in AaTadZ are required for polar localization and biofilm formation. We show that AaTadZ dimerizes and that all TadZ proteins are predicted to have a Walker-like A box. However, they all lack the conserved lysine at position 6 (K6) present in the canonical Walker-like A box. When the alanine residue (A6) in the atypical Walker-like A box of AaTadZ was converted to lysine, the mutant protein remained able to dimerize and localize, but it was unable to allow the formation of a biofilm. Another essential biofilm protein, the ATPase (AaTadA), also localizes to a pole. However, its correct localization depends on the presence of AaTadZ. We suggest that the TadZ proteins mediate polar localization of the Tad secretion apparatus.
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Affiliation(s)
- Brenda A Perez-Cheeks
- Department of Microbiology & Immunology, College of Physicians & Surgeons, Columbia University, New York, NY 10032, USA
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146
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Enzyme catalyzed radical dehydrations of hydroxy acids. BIOCHIMICA ET BIOPHYSICA ACTA-PROTEINS AND PROTEOMICS 2011; 1824:1278-90. [PMID: 22178228 DOI: 10.1016/j.bbapap.2011.11.009] [Citation(s) in RCA: 24] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 09/11/2011] [Accepted: 11/28/2011] [Indexed: 11/24/2022]
Abstract
BACKGROUND The steadily increasing field of radical biochemistry is dominated by the large family of S-adenosylmethionine dependent enzymes, the so-called radical SAM enzymes, of which several new members are discovered every year. Here we report on 2- and 4-hydroxyacyl-CoA dehydratases which apply a very different method of radical generation. In these enzymes ketyl radicals are formed by one-electron reduction or oxidation and are recycled after each turnover without further energy input. Earlier reviews on 2-hydroxyacyl-CoA dehydratases were published in 2004 [J. Kim, M. Hetzel, C.D. Boiangiu, W. Buckel, FEMS Microbiol. Rev. 28 (2004) 455-468. W. Buckel, M. Hetzel, J. Kim, Curr. Opin. Chem. Biol. 8 (2004) 462-467.] SCOPE OF REVIEW The review focuses on four types of 2-hydroxyacyl-CoA dehydratases that are involved in the fermentation of amino acids by anaerobic bacteria, especially clostridia. These enzymes require activation by one-electron transfer from an iron-sulfur protein driven by hydrolysis of ATP. The review further describes the proposed mechanism that is highlighted by the identification of the allylic ketyl radical intermediate and the elucidation of the crystal structure of 2-hydroxyisocapryloyl-CoA dehydratase. With 4-hydroxybutyryl-CoA dehydratase the crystal structure, the complete stereochemistry and the function of several conserved residues around the active site could be identified. Finally potential biotechnological applications of the radical dehydratases are presented. GENERAL SIGNIFICANCE The action of the activator as an 'Archerase' shooting electrons into difficultly reducible acceptors becomes an emerging principle in anaerobic metabolism. The dehydratases may provide useful tools in biotechnology. This article is part of a Special Issue entitled: Radical SAM enzymes and Radical Enzymology.
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147
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Tail-anchor targeting by a Get3 tetramer: the structure of an archaeal homologue. EMBO J 2011; 31:707-19. [PMID: 22124326 PMCID: PMC3273380 DOI: 10.1038/emboj.2011.433] [Citation(s) in RCA: 34] [Impact Index Per Article: 2.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/03/2011] [Accepted: 11/09/2011] [Indexed: 11/09/2022] Open
Abstract
Efficient delivery of membrane proteins is a critical cellular process. The recently elucidated GET (Guided Entry of TA proteins) pathway is responsible for the targeted delivery of tail-anchored (TA) membrane proteins to the endoplasmic reticulum. The central player is the ATPase Get3, which in its free form exists as a dimer. Biochemical evidence suggests a role for a tetramer of Get3. Here, we present the first crystal structure of an archaeal Get3 homologue that exists as a tetramer and is capable of TA protein binding. The tetramer generates a hydrophobic chamber that we propose binds the TA protein. We use small-angle X-ray scattering to provide the first structural information of a fungal Get3/TA protein complex showing that the overall molecular envelope is consistent with the archaeal tetramer structure. Moreover, we show that this fungal tetramer complex is capable of TA insertion. This allows us to suggest a model where a tetramer of Get3 sequesters a TA protein during targeting to the membrane.
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148
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Abstract
Nitrogenase catalyzes the biological conversion of atmospheric dinitrogen to bioavailable ammonia. The molybdenum (Mo)- and vanadium (V)-dependent nitrogenases are two homologous members of this metalloenzyme family. However, despite their similarities in structure and function, the characterization of V-nitrogenase has taken a much longer and more winding path than that of its Mo-counterpart. From the initial discovery of this nitrogen-fixing system, to the recent finding of its CO-reducing capacity, V-nitrogenase has proven to be a two-hit wonder in the over-a-century-long research of nitrogen fixation. This perspective provides a brief account of the catalytic function and structural basis of V-nitrogenase, as well as a short discussion of the theoretical and practical potentials of this unique metalloenzyme.
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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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149
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Yamamoto H, Kurumiya S, Ohashi R, Fujita Y. Functional evaluation of a nitrogenase-like protochlorophyllide reductase encoded by the chloroplast DNA of Physcomitrella patens in the cyanobacterium Leptolyngbya boryana. PLANT & CELL PHYSIOLOGY 2011; 52:1983-1993. [PMID: 21949030 DOI: 10.1093/pcp/pcr132] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/31/2023]
Abstract
Dark-operative protochlorophyllide (Pchlide) oxidoreductase (DPOR) is a nitrogenase-like enzyme consisting of the two components, L-protein (a ChlL dimer) and NB-protein (a ChlN-ChlB heterotetramer), to catalyze Pchlide reduction in Chl biosynthesis. While nitrogenase is distributed only among certain prokaryotes, the probable structural genes for DPOR are encoded by chloroplast DNA in lower plants. Here we show functional evaluation of DPOR encoded by chloroplast DNA in a moss Physcomitrella patens by the complementation analysis of the cyanobacterium Leptolyngbya boryana and the heterologous reconstitution of the moss L-protein and the cyanobacterial NB-protein. Two shuttle vectors to overexpress chlL and chlN-chlB from P. patens were introduced into the cyanobacterial chlL- and chlB-lacking mutants, respectively. Both transformants restored the ability to perform Chl biosynthesis in the dark, indicating that the chloroplast-encoded DPOR components form an active complex with the cyanobacterial components. The L-protein of P. patens was purified from the cyanobacterial transformant, and DPOR activity was reconstituted in a heterologous combination with the cyanobacterial NB-protein. The specific activity of the L-protein from P. patens was determined to be 118 nmol min(-1) mg (-1), which is even higher than that of the cyanobacterial L-protein (76 nmol min(-1) mg (-1)). Upon exposure to air, the activity of the L-protein from P. patens decayed with a half-life of 30 s, which was eight times faster than that of the cyanobacterial L-protein (240 s). These results suggested that the chloroplast-encoded L-protein functions as efficiently as the cyanobacterial L-protein but is more oxygen labile than the cyanobacterial L-protein.
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Affiliation(s)
- Haruki Yamamoto
- School of Bioagricultural Sciences, Nagoya University, Nagoya 464-8601, Japan
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150
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Danyal K, Dean DR, Hoffman BM, Seefeldt LC. Electron transfer within nitrogenase: evidence for a deficit-spending mechanism. Biochemistry 2011; 50:9255-63. [PMID: 21939270 DOI: 10.1021/bi201003a] [Citation(s) in RCA: 89] [Impact Index Per Article: 6.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/04/2023]
Abstract
The reduction of substrates catalyzed by nitrogenase utilizes an electron transfer (ET) chain comprised of three metalloclusters distributed between the two component proteins, designated as the Fe protein and the MoFe protein. The flow of electrons through these three metalloclusters involves ET from the [4Fe-4S] cluster located within the Fe protein to an [8Fe-7S] cluster, called the P cluster, located within the MoFe protein and ET from the P cluster to the active site [7Fe-9S-X-Mo-homocitrate] cluster called FeMo-cofactor, also located within the MoFe protein. The order of these two electron transfer events, the relevant oxidation states of the P-cluster, and the role(s) of ATP, which is obligatory for ET, remain unknown. In the present work, the electron transfer process was examined by stopped-flow spectrophotometry using the wild-type MoFe protein and two variant MoFe proteins, one having the β-188(Ser) residue substituted by cysteine and the other having the β-153(Cys) residue deleted. The data support a "deficit-spending" model of electron transfer where the first event (rate constant 168 s(-1)) is ET from the P cluster to FeMo-cofactor and the second, "backfill", event is fast ET (rate constant >1700 s(-1)) from the Fe protein [4Fe-4S] cluster to the oxidized P cluster. Changes in osmotic pressure reveal that the first electron transfer is conformationally gated, whereas the second is not. The data for the β-153(Cys) deletion MoFe protein variant provide an argument against an alternative two-step "hopping" ET model that reverses the two ET steps, with the Fe protein first transferring an electron to the P cluster, which in turn transfers an electron to FeMo-cofactor. The roles for ATP binding and hydrolysis in controlling the ET reactions were examined using βγ-methylene-ATP as a prehydrolysis ATP analogue and ADP + AlF(4)(-) as a posthydrolysis analogue (a mimic of ADP + P(i)).
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Affiliation(s)
- Karamatullah Danyal
- Department of Chemistry and Biochemistry, Utah State University, Logan, Utah 84322, United States
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