1
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Gencic S, Duin EC, Grahame DA. The two-electron reduced A cluster in acetyl-CoA synthase: Preparation, characteristics and mechanistic implications. J Inorg Biochem 2023; 240:112098. [PMID: 36580832 DOI: 10.1016/j.jinorgbio.2022.112098] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/21/2022] [Revised: 12/05/2022] [Accepted: 12/07/2022] [Indexed: 12/14/2022]
Abstract
Acetyl-CoA synthase (ACS) is a central enzyme in the carbon and energy metabolism of certain anaerobic species of bacteria and archaea that catalyzes the direct synthesis and cleavage of the acetyl CC bond of acetyl-CoA by an unusual enzymatic mechanism of special interest for its use of organonickel intermediates. An Fe4S4 cluster associated with a proximal, reactive Nip and distal spectator Nid comprise the active site metal complex, known as the A cluster. Experimental and theoretical methods have uncovered much about the ACS mechanism, but have also opened new unanswered questions about the structure and reactivity of the A cluster in various intermediate forms. Here we report a method for large scale isolation of ACS with its A cluster in the acetylated state. Isolated acetyl-ACS and the two-electron reduced ACS, produced by acetyl-ACS reaction with CoA, were characterized by UV-visible and EPR spectroscopy. Reactivity with electron acceptors provided an assessment of the apparent Em for two-electron reduction of the A cluster. The results help to distinguish between alternative electronic states of the reduced cluster, provide evidence for a role of the Fe/S cluster in catalysis, and offer an explanation of why one-electron reductive activation is observed for a reaction cycle involving 2-electron chemistry.
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Affiliation(s)
- Simonida Gencic
- Department of Biochemistry and Molecular Biology, Uniformed Services University of the Health Sciences, Bethesda, MD 20814, USA
| | - Evert C Duin
- Department of Chemistry and Biochemistry, Auburn University, Auburn, AL 36849, USA
| | - David A Grahame
- Department of Biochemistry and Molecular Biology, Uniformed Services University of the Health Sciences, Bethesda, MD 20814, USA.
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2
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Biester A, Marcano-Delgado AN, Drennan CL. Structural Insights into Microbial One-Carbon Metabolic Enzymes Ni-Fe-S-Dependent Carbon Monoxide Dehydrogenases and Acetyl-CoA Synthases. Biochemistry 2022; 61:2797-2805. [PMID: 36137563 PMCID: PMC9782325 DOI: 10.1021/acs.biochem.2c00425] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/19/2023]
Abstract
Ni-Fe-S-dependent carbon monoxide dehydrogenases (CODHs) are enzymes that interconvert CO and CO2 by using their catalytic Ni-Fe-S C-cluster and their Fe-S B- and D-clusters for electron transfer. CODHs are important in the microbiota of animals such as humans, ruminants, and termites because they can facilitate the use of CO and CO2 as carbon sources and serve to maintain redox homeostasis. The bifunctional carbon monoxide dehydrogenase/acetyl-CoA synthase (CODH/ACS) is responsible for acetate production via the Wood-Ljungdahl pathway, where acetyl-CoA is assembled from two CO2-derived one-carbon units. A Ni-Fe-S A-cluster is key to this chemistry. Whereas acetogens use the A- and C-clusters of CODH/ACS to produce acetate from CO2, methanogens use A- and C-clusters of an acetyl-CoA decarbonylase/synthase complex (ACDS) to break down acetate en route to CO2 and methane production. Here we review some of the recent advances in understanding the structure and mechanism of CODHs, CODH/ACSs, and ACDSs, their unusual metallocofactors, and their unique metabolic roles in the human gut and elsewhere.
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Affiliation(s)
- Alison Biester
- Department
of Chemistry, Massachusetts Institute of
Technology, Cambridge, Massachusetts 02139, United States
| | - Andrea N. Marcano-Delgado
- Department
of Chemistry, Massachusetts Institute of
Technology, Cambridge, Massachusetts 02139, United States
| | - Catherine L. Drennan
- Department
of Chemistry, Massachusetts Institute of
Technology, Cambridge, Massachusetts 02139, United States,Department
of Biology, Massachusetts Institute of Technology, Cambridge, Massachusetts 02139, United States,Howard
Hughes Medical Institute, Massachusetts Institute of Technology, Cambridge, Massachusetts 02139, United States,Bio-inspired
Solar Energy Program, Canadian Institute
for Advanced Research, Toronto, ON M5G 1M1, Canada,
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3
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Thioester synthesis by a designed nickel enzyme models prebiotic energy conversion. Proc Natl Acad Sci U S A 2022; 119:e2123022119. [PMID: 35858422 PMCID: PMC9335327 DOI: 10.1073/pnas.2123022119] [Citation(s) in RCA: 4] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/21/2023] Open
Abstract
The formation of carbon-carbon bonds from prebiotic precursors such as carbon dioxide represents the foundation of all primordial life processes. In extant organisms, this reaction is carried out by the carbon monoxide dehydrogenase (CODH)/acetyl coenzyme A synthase (ACS) enzyme, which performs the cornerstone reaction in the ancient Wood-Ljungdahl metabolic pathway to synthesize the key biological metabolite, acetyl-CoA. Despite its significance, a fundamental understanding of this transformation is lacking, hampering efforts to harness analogous chemistry. To address these knowledge gaps, we have designed an artificial metalloenzyme within the azurin protein scaffold as a structural, functional, and mechanistic model of ACS. We demonstrate the intermediacy of the NiI species and requirement for ordered substrate binding in the bioorganometallic carbon-carbon bond-forming reaction from the one-carbon ACS substrates. The electronic and geometric structures of the nickel-acetyl intermediate have been characterized using time-resolved optical, electron paramagnetic resonance, and X-ray absorption spectroscopy in conjunction with quantum chemical calculations. Moreover, we demonstrate that the nickel-acetyl species is chemically competent for selective acyl transfer upon thiol addition to biosynthesize an activated thioester. Drawing an analogy to the native enzyme, a mechanism for thioester generation by this ACS model has been proposed. The fundamental insight into the enzymatic process provided by this rudimentary ACS model has implications for the evolution of primitive ACS-like proteins. Ultimately, these findings offer strategies for development of highly active catalysts for sustainable generation of liquid fuels from one-carbon substrates, with potential for broad applications across diverse fields ranging from energy storage to environmental remediation.
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4
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Theoretical Studies of Acetyl-CoA Synthase Catalytic Mechanism. Catalysts 2022. [DOI: 10.3390/catal12020195] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/10/2022] Open
Abstract
DFT calculations were performed for the A-cluster from the enzyme Acetyl-CoA synthase (ACS). The acid constants (pKa), reduction potentials, and pH-dependent reduction potential for the A-cluster with different oxidation states and ligands were calculated. Good agreement of the reduction potentials, dependent on pH in the experiment, was obtained. On the basis of the calculations, a mechanism for the methylation reaction involving two–electron reduction and protonation on the proximal nickel atom of the reduced A-cluster is proposed.
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5
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Rodríguez M A, Rache LY, Brijaldo MH, Romanelli GP, Luque R, Martinez JJ. Biocatalytic transformation of furfural into furfuryl alcohol using resting cells of Bacillus cereus. Catal Today 2021. [DOI: 10.1016/j.cattod.2021.01.011] [Citation(s) in RCA: 10] [Impact Index Per Article: 3.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/17/2022]
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6
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Kisgeropoulos EC, Manesis AC, Shafaat HS. Ligand Field Inversion as a Mechanism to Gate Bioorganometallic Reactivity: Investigating a Biochemical Model of Acetyl CoA Synthase Using Spectroscopy and Computation. J Am Chem Soc 2021; 143:849-867. [PMID: 33415980 DOI: 10.1021/jacs.0c10135] [Citation(s) in RCA: 13] [Impact Index Per Article: 4.3] [Reference Citation Analysis] [Abstract] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/30/2022]
Abstract
The biological global carbon cycle is largely regulated through microbial nickel enzymes, including carbon monoxide dehydrogenase (CODH), acetyl coenzyme A synthase (ACS), and methyl coenzyme M reductase (MCR). These systems are suggested to utilize organometallic intermediates during catalysis, though characterization of these species has remained challenging. We have established a mutant of nickel-substituted azurin as a scaffold upon which to develop protein-based models of enzymatic intermediates, including the organometallic states of ACS. In this work, we report the comprehensive investigation of the S = 1/2 Ni-CO and Ni-CH3 states using pulsed EPR spectroscopy and computational techniques. While the Ni-CO state shows conventional metal-ligand interactions and a classical ligand field, the Ni-CH3 hyperfine interactions between the methyl protons and the nickel indicate a closer distance than would be expected for an anionic methyl ligand. Structural analysis instead suggests a near-planar methyl ligand that can be best described as cationic. Consistent with this conclusion, the frontier molecular orbitals of the Ni-CH3 species indicate a ligand-centered LUMO, with a d9 population on the metal center, rather than the d7 population expected for a typical metal-alkyl species generated by oxidative addition. Collectively, these data support the presence of an inverted ligand field configuration for the Ni-CH3 Az species, in which the lowest unoccupied orbital is centered on the ligands rather than the more electropositive metal. These analyses provide the first evidence for an inverted ligand field within a biological system. The functional relevance of the electronic structures of both the Ni-CO and Ni-CH3 species are discussed in the context of native ACS, and an inverted ligand field is proposed as a mechanism by which to gate reactivity both within ACS and in other thiolate-containing metalloenzymes.
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Affiliation(s)
- Effie C Kisgeropoulos
- Department of Chemistry and Biochemistry and Ohio State Biochemistry Program, The Ohio State University, Columbus, Ohio 43210, United States
| | - Anastasia C Manesis
- Department of Chemistry and Biochemistry and Ohio State Biochemistry Program, The Ohio State University, Columbus, Ohio 43210, United States
| | - Hannah S Shafaat
- Department of Chemistry and Biochemistry and Ohio State Biochemistry Program, The Ohio State University, Columbus, Ohio 43210, United States
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7
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Elghobashi-Meinhardt N, Tombolelli D, Mroginski MA. QM/MM computations reveal details of the acetyl-CoA synthase catalytic center. Biochim Biophys Acta Gen Subj 2020; 1864:129579. [DOI: 10.1016/j.bbagen.2020.129579] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/18/2019] [Revised: 01/31/2020] [Accepted: 02/22/2020] [Indexed: 10/24/2022]
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8
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Manesis AC, Musselman BW, Keegan BC, Shearer J, Lehnert N, Shafaat HS. A Biochemical Nickel(I) State Supports Nucleophilic Alkyl Addition: A Roadmap for Methyl Reactivity in Acetyl Coenzyme A Synthase. Inorg Chem 2019; 58:8969-8982. [PMID: 30788970 PMCID: PMC6635881 DOI: 10.1021/acs.inorgchem.8b03546] [Citation(s) in RCA: 16] [Impact Index Per Article: 3.2] [Reference Citation Analysis] [Abstract] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/20/2023]
Abstract
![]()
Nickel-containing
enzymes such as methyl coenzyme M reductase (MCR) and carbon monoxide
dehydrogenase/acetyl coenzyme A synthase (CODH/ACS) play a critical
role in global energy conversion reactions, with significant contributions
to carbon-centered processes. These enzymes are implied to cycle through
a series of nickel-based organometallic intermediates during catalysis,
though identification of these intermediates remains challenging.
In this work, we have developed and characterized a nickel-containing
metalloprotein that models the methyl-bound organometallic intermediates
proposed in the native enzymes. Using a nickel(I)-substituted azurin
mutant, we demonstrate that alkyl binding occurs via nucleophilic
addition of methyl iodide as a methyl donor. The paramagnetic NiIII-CH3 species initially generated can be rapidly
reduced to a high-spin NiII-CH3 species in the
presence of exogenous reducing agent, following a reaction sequence
analogous to that proposed for ACS. These two distinct bioorganometallic
species have been characterized by optical, EPR, XAS, and MCD spectroscopy,
and the overall mechanism describing methyl reactivity with nickel
azurin has been quantitatively modeled using global kinetic simulations.
A comparison between the nickel azurin protein system and existing
ACS model compounds is presented. NiIII-CH3 Az
is only the second example of two-electron addition of methyl iodide
to a NiI center to give an isolable species and the first
to be formed in a biologically relevant system. These results highlight
the divergent reactivity of nickel across the two intermediates, with
implications for likely reaction mechanisms and catalytically relevant
states in the native ACS enzyme. A bioorganometallic model
for acetyl coenzyme A synthase has been developed. This model protein
is able to bind a cationic methyl group via direct addition to the
nickel(I) center. The resultant nickel(III)-methyl species has been
characterized via optical and electron paramagnetic resonance spectroscopy,
and the reduced nickel(II)-methyl state has been characterized using
magnetic circular dichroism and X-ray spectroscopy. Implications for
further reactivity with CO are gleaned from electronic structure analysis
of the nickel-methyl species.
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Affiliation(s)
- Anastasia C Manesis
- Department of Chemistry and Biochemistry , The Ohio State University , 100 W. 18th Avenue , Columbus , Ohio 43210 , United States
| | - Bradley W Musselman
- Department of Chemistry , University of Michigan , 930 N. University Avenue , Ann Arbor , Michigan 48109 , United States
| | - Brenna C Keegan
- Department of Chemistry , Trinity University , One Trinity Place , San Antonio , Texas 78212 , United States
| | - Jason Shearer
- Department of Chemistry , Trinity University , One Trinity Place , San Antonio , Texas 78212 , United States
| | - Nicolai Lehnert
- Department of Chemistry , University of Michigan , 930 N. University Avenue , Ann Arbor , Michigan 48109 , United States
| | - Hannah S Shafaat
- Department of Chemistry and Biochemistry , The Ohio State University , 100 W. 18th Avenue , Columbus , Ohio 43210 , United States
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9
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Bhandari A, Chandra Maji R, Mishra S, Kumar A, Barman SK, Das PP, Ghiassi KB, Olmstead MM, Patra AK. Model Complexes for the Nip Site of Acetyl Coenzyme A Synthase/Carbon Monoxide (CO) Dehydrogenase: Structure, Electrochemistry, and CO Reactivity. Inorg Chem 2018; 57:13713-13727. [DOI: 10.1021/acs.inorgchem.8b02276] [Citation(s) in RCA: 7] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
Affiliation(s)
- Anirban Bhandari
- Department of Chemistry, National Institute of Technology Durgapur, Mahatma Gandhi Avenue, Durgapur 713209, India
| | - Ram Chandra Maji
- Department of Chemistry, National Institute of Technology Durgapur, Mahatma Gandhi Avenue, Durgapur 713209, India
| | - Saikat Mishra
- Department of Chemistry, National Institute of Technology Durgapur, Mahatma Gandhi Avenue, Durgapur 713209, India
| | - Akhilesh Kumar
- Department of Chemistry, Indian Institute of Technology Kanpur, Kanpur 208016, India
| | - Suman Kumar Barman
- Department of Chemistry, Indian Institute of Technology Kanpur, Kanpur 208016, India
| | - Partha Pratim Das
- Department of Chemistry, Indian Institute of Technology Kanpur, Kanpur 208016, India
| | - Kamran B. Ghiassi
- Department of Chemistry, University of California, Davis, California 95616, United States
| | - Marilyn M. Olmstead
- Department of Chemistry, University of California, Davis, California 95616, United States
| | - Apurba K. Patra
- Department of Chemistry, National Institute of Technology Durgapur, Mahatma Gandhi Avenue, Durgapur 713209, India
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10
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Vitamin B 12 in the spotlight again. Curr Opin Chem Biol 2017; 37:63-70. [PMID: 28167430 DOI: 10.1016/j.cbpa.2017.01.013] [Citation(s) in RCA: 78] [Impact Index Per Article: 11.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/25/2016] [Revised: 01/07/2017] [Accepted: 01/17/2017] [Indexed: 11/21/2022]
Abstract
The ability of cobalamin to coordinate different upper axial ligands gives rise to a diversity of reactivity. Traditionally, adenosylcobalamin is associated with radical-based rearrangements, and methylcobalamin with methyl cation transfers. Recently, however, a new role for adenosylcobalamin has been discovered as a light sensor, and a methylcobalamin-dependent enzyme has been identified that is suggested to transfer a methyl anion. Additionally, recent studies have provided a wealth of new information about a third class of cobalamin-dependent enzymes that do not appear to use an upper ligand. They function in reductive dehalogenations and epoxide reduction reactions. Finally, mechanistic details are beginning to emerge about the cobalamin-dependent S-adenosylmethionine radical enzyme superfamily for which the role of cobalamin has been largely enigmatic.
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11
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Green Synthesis and Spectroscopic Characterization of Nanoparticles. NANOSCIENCE IN FOOD AND AGRICULTURE 1 2016. [DOI: 10.1007/978-3-319-39303-2_3] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 01/30/2023]
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12
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Manesis AC, Shafaat HS. Electrochemical, Spectroscopic, and Density Functional Theory Characterization of Redox Activity in Nickel-Substituted Azurin: A Model for Acetyl-CoA Synthase. Inorg Chem 2015; 54:7959-67. [PMID: 26234790 DOI: 10.1021/acs.inorgchem.5b01103] [Citation(s) in RCA: 27] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/09/2023]
Abstract
Nickel-containing enzymes are key players in global hydrogen, carbon dioxide, and methane cycles. Many of these enzymes rely on Ni(I) oxidation states in critical catalytic intermediates. However, due to the highly reactive nature of these species, their isolation within metalloenzymes has often proved elusive. In this report, we describe and characterize a model biological Ni(I) species that has been generated within the electron transfer protein, azurin. Replacement of the native copper cofactor with nickel is shown to preserve the redox activity of the protein. The Ni(II/I) couple is observed at -590 mV versus NHE, with an interfacial electron transfer rate of 70 s(-1). Chemical reduction of Ni(II)Az generates a stable species with strong absorption features at 350 nm and a highly anisotropic, axial EPR signal with principal g-values of 2.56 and 2.10. Density functional theory calculations provide insight into the electronic and geometric structure of the Ni(I) species, suggesting a trigonal planar coordination environment. The predicted spectroscopic features of this low-coordinate nickel site are in good agreement with the experimental data. Molecular orbital analysis suggests potential for both metal-centered and ligand-centered reactivity, highlighting the covalency of the metal-thiolate bond. Characterization of a stable Ni(I) species within a model protein has implications for understanding the mechanisms of complex enzymes, including acetyl coenzyme A synthase, and developing scaffolds for unique reactivity.
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13
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Bacteria in Nanoparticle Synthesis: Current Status and Future Prospects. INTERNATIONAL SCHOLARLY RESEARCH NOTICES 2014; 2014:359316. [PMID: 27355054 PMCID: PMC4897565 DOI: 10.1155/2014/359316] [Citation(s) in RCA: 125] [Impact Index Per Article: 12.5] [Reference Citation Analysis] [Abstract] [Download PDF] [Figures] [Subscribe] [Scholar Register] [Received: 03/26/2014] [Revised: 07/09/2014] [Accepted: 08/04/2014] [Indexed: 11/17/2022]
Abstract
Microbial metal reduction can be a strategy for remediation of metal contaminations and wastes. Bacteria are capable of mobilization and immobilization of metals and in some cases, the bacteria which can reduce metal ions show the ability to precipitate metals at nanometer scale. Biosynthesis of nanoparticles (NPs) using bacteria has emerged as rapidly developing research area in green nanotechnology across the globe with various biological entities being employed in synthesis of NPs constantly forming an impute alternative for conventional chemical and physical methods. Optimization of the processes can result in synthesis of NPs with desired morphologies and controlled sizes, fast and clean. The aim of this review is, therefore, to make a reflection on the current state and future prospects and especially the possibilities and limitations of the above mentioned bio-based technique for industries.
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14
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Can M, Armstrong F, Ragsdale SW. Structure, function, and mechanism of the nickel metalloenzymes, CO dehydrogenase, and acetyl-CoA synthase. Chem Rev 2014; 114:4149-74. [PMID: 24521136 PMCID: PMC4002135 DOI: 10.1021/cr400461p] [Citation(s) in RCA: 373] [Impact Index Per Article: 37.3] [Reference Citation Analysis] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/21/2013] [Indexed: 12/19/2022]
Affiliation(s)
- Mehmet Can
- Department
of Biological Chemistry, University of Michigan, Ann Arbor, Michigan 48109, United States
| | - Fraser
A. Armstrong
- Inorganic
Chemistry Laboratory, University of Oxford Oxford, OX1 3QR, United Kingdom
| | - Stephen W. Ragsdale
- Department
of Biological Chemistry, University of Michigan, Ann Arbor, Michigan 48109, United States
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15
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Chmielowska A, Lodowski P, Jaworska M. Redox Potentials and Protonation of the A-Cluster from Acetyl-CoA Synthase. A Density Functional Theory Study. J Phys Chem A 2013; 117:12484-96. [DOI: 10.1021/jp402616e] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/30/2023]
Affiliation(s)
| | - Piotr Lodowski
- Institute
of Chemistry, University of Silesia, Szkolna 9, 40-006 Katowice, Poland
| | - Maria Jaworska
- Institute
of Chemistry, University of Silesia, Szkolna 9, 40-006 Katowice, Poland
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16
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Appel AM, Bercaw JE, Bocarsly AB, Dobbek H, DuBois DL, Dupuis M, Ferry JG, Fujita E, Hille R, Kenis PJA, Kerfeld CA, Morris RH, Peden CHF, Portis AR, Ragsdale SW, Rauchfuss TB, Reek JNH, Seefeldt LC, Thauer RK, Waldrop GL. Frontiers, opportunities, and challenges in biochemical and chemical catalysis of CO2 fixation. Chem Rev 2013; 113:6621-58. [PMID: 23767781 PMCID: PMC3895110 DOI: 10.1021/cr300463y] [Citation(s) in RCA: 1277] [Impact Index Per Article: 116.1] [Reference Citation Analysis] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/17/2022]
Affiliation(s)
- Aaron M. Appel
- Institute for Integrated Catalysis, Pacific Northwest National Laboratory, P.O. Box 999, Richland, Washington 99352, United States
| | - John E. Bercaw
- Division of Chemistry and Chemical Engineering, California Institute of Technology, Pasadena, California 91125, United States
| | - Andrew B. Bocarsly
- Department of Chemistry, Princeton University, Princeton, New Jersey 08544, United States
| | - Holger Dobbek
- Institut für Biologie, Strukturbiologie/Biochemie, Humboldt Universität zu Berlin, Berlin, Germany
| | - Daniel L. DuBois
- Institute for Integrated Catalysis, Pacific Northwest National Laboratory, P.O. Box 999, Richland, Washington 99352, United States
| | - Michel Dupuis
- Institute for Integrated Catalysis, Pacific Northwest National Laboratory, P.O. Box 999, Richland, Washington 99352, United States
| | - James G. Ferry
- Department of Biochemistry and Molecular Biology, Pennsylvania State University, University Park, Pennsylvania 16801, United States
| | - Etsuko Fujita
- Chemistry Department, Brookhaven National Laboratory, Upton, New York 11973-5000, United States
| | - Russ Hille
- Department of Biochemistry, University of California, Riverside, California 92521, United States
| | - Paul J. A. Kenis
- Department of Chemical and Biochemical Engineering, University of Illinois, Urbana, Illinois 61801, United States
| | - Cheryl A. Kerfeld
- DOE Joint Genome Institute, 2800 Mitchell Drive Walnut Creek, California 94598, United States, and Department of Plant and Microbial Biology, University of California, Berkeley, 111 Koshland Hall Berkeley, California 94720, United States
| | - Robert H. Morris
- Department of Chemistry, University of Toronto, Toronto, Ontario M5S 3H6, Canada
| | - Charles H. F. Peden
- Institute for Integrated Catalysis, Pacific Northwest National Laboratory, P.O. Box 999, Richland, Washington 99352, United States
| | - Archie R. Portis
- Departments of Crop Sciences and Plant Biology, University of Illinois, Urbana, Illinois 61801, United States
| | - Stephen W. Ragsdale
- Department of Biological Chemistry, University of Michigan, Ann Arbor, Michigan 48109, United States
| | - Thomas B. Rauchfuss
- Department of Chemistry, University of Illinois, Urbana, Illinois 61801, United States
| | - Joost N. H. Reek
- van’t Hoff Institute for Molecular Sciences, University of Amsterdam, Science Park 904, 1098 XH, Amsterdam, The Netherlands
| | - Lance C. Seefeldt
- Department of Chemistry and Biochemistry, Utah State University, 0300 Old Main Hill, Logan, Utah 84322, United States
| | - Rudolf K. Thauer
- Max Planck Institute for Terrestrial Microbiology, Karl von Frisch Strasse 10, D-35043 Marburg, Germany
| | - Grover L. Waldrop
- Department of Biological Sciences, Louisiana State University, Baton Rouge, Louisiana 70803, United States
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17
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Gencic S, Kelly K, Ghebreamlak S, Duin EC, Grahame DA. Different Modes of Carbon Monoxide Binding to Acetyl-CoA Synthase and the Role of a Conserved Phenylalanine in the Coordination Environment of Nickel. Biochemistry 2013; 52:1705-16. [DOI: 10.1021/bi3016718] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/18/2023]
Affiliation(s)
- Simonida Gencic
- Department of Biochemistry and
Molecular Biology, Uniformed Services University of the Health Sciences, Bethesda, Maryland 20814, United States
| | - Kayla Kelly
- Holton-Arms School, Bethesda, Maryland 20817, United States
| | - Selamawit Ghebreamlak
- Department of Chemistry and Biochemistry, Auburn University, Auburn, Alabama 36849, United States
| | - Evert C. Duin
- Department of Chemistry and Biochemistry, Auburn University, Auburn, Alabama 36849, United States
| | - David A. Grahame
- Department of Biochemistry and
Molecular Biology, Uniformed Services University of the Health Sciences, Bethesda, Maryland 20814, United States
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18
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Abstract
Nickel-containing carbon monoxide dehydrogenases, acetyl-CoA synthases, nickel-iron hydrogenases, and diron hydrogenases are distinct metalloenzymes yet they share a number of important characteristics. All are O(2)-sensitive, with active-sites composed of iron and/or nickel ions coordinated primarily by sulfur ligands. In each case, two metals are juxtaposed at the "heart" of the active site, within range of forming metal-metal bonds. These active-site clusters exhibit multielectron redox abilities and must be reductively activated for catalysis. Reduction potentials are milder than expected based on formal oxidation state changes. When reductively activated, each cluster attacks an electrophilic substrate via an oxidative addition reaction. This affords a two-electron-reduced substrate bound to one or both metals of an oxidized cluster. M-M bonds have been established in hydrogenases where they serve to initiate the oxidative addition of protons and perhaps stabilize active sites in multiple redox states. The same may be true of the CODH and ACS active sites-Ni-Fe and Ni-Ni bonds in these sites may play critical roles in catalysis, stabilizing low-valence states and initiating oxidative addition of CO(2) and methyl group cations, respectively. In this article, the structural and functional commonalities of these metalloenzyme active sites are described, and the case is made for the formation and use of metal-metal bonds in each enzyme mentioned. As a post-script, the importance of Fe-Fe bonds in the nitrogenase FeMoco active site is discussed.
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Affiliation(s)
- Paul A Lindahl
- Department of Chemistry, Texas A&M University, College Station, TX 77843-3255, USA.
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19
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Bender G, Pierce E, Hill JA, Darty JE, Ragsdale SW. Metal centers in the anaerobic microbial metabolism of CO and CO2. Metallomics 2011; 3:797-815. [PMID: 21647480 PMCID: PMC3964926 DOI: 10.1039/c1mt00042j] [Citation(s) in RCA: 55] [Impact Index Per Article: 4.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/06/2023]
Abstract
Carbon dioxide and carbon monoxide are important components of the carbon cycle. Major research efforts are underway to develop better technologies to utilize the abundant greenhouse gas, CO(2), for harnessing 'green' energy and producing biofuels. One strategy is to convert CO(2) into CO, which has been valued for many years as a synthetic feedstock for major industrial processes. Living organisms are masters of CO(2) and CO chemistry and, here, we review the elegant ways that metalloenzymes catalyze reactions involving these simple compounds. After describing the chemical and physical properties of CO and CO(2), we shift focus to the enzymes and the metal clusters in their active sites that catalyze transformations of these two molecules. We cover how the metal centers on CO dehydrogenase catalyze the interconversion of CO and CO(2) and how pyruvate oxidoreductase, which contains thiamin pyrophosphate and multiple Fe(4)S(4) clusters, catalyzes the addition and elimination of CO(2) during intermediary metabolism. We also describe how the nickel center at the active site of acetyl-CoA synthase utilizes CO to generate the central metabolite, acetyl-CoA, as part of the Wood-Ljungdahl pathway, and how CO is channelled from the CO dehydrogenase to the acetyl-CoA synthase active site. We cover how the corrinoid iron-sulfur protein interacts with acetyl-CoA synthase. This protein uses vitamin B(12) and a Fe(4)S(4) cluster to catalyze a key methyltransferase reaction involving an organometallic methyl-Co(3+) intermediate. Studies of CO and CO(2) enzymology are of practical significance, and offer fundamental insights into important biochemical reactions involving metallocenters that act as nucleophiles to form organometallic intermediates and catalyze C-C and C-S bond formations.
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Affiliation(s)
- Güneş Bender
- Department of Biological Chemistry, University of Michigan, Ann Arbor, Michigan 48109-0606, USA. Fax: +1 734-763-4581; Tel: +1 734-615-4621
| | - Elizabeth Pierce
- Department of Biological Chemistry, University of Michigan, Ann Arbor, Michigan 48109-0606, USA. Fax: +1 734-763-4581; Tel: +1 734-615-4621
| | - Jeffrey A. Hill
- Department of Biological Chemistry, University of Michigan, Ann Arbor, Michigan 48109-0606, USA. Fax: +1 734-763-4581; Tel: +1 734-615-4621
| | - Joseph E. Darty
- Department of Biological Chemistry, University of Michigan, Ann Arbor, Michigan 48109-0606, USA. Fax: +1 734-763-4581; Tel: +1 734-615-4621
| | - Stephen W. Ragsdale
- Department of Biological Chemistry, University of Michigan, Ann Arbor, Michigan 48109-0606, USA. Fax: +1 734-763-4581; Tel: +1 734-615-4621
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Liu Y, Wang F, Li P, Tan X. Insights into the Mechanistic Role of the [Fe4S4] Cubane in the A-Cluster {[Fe4S4]-(SR)-[NipNid]} of Acetyl-Coenzyme A Synthase. Chembiochem 2011; 12:1417-21. [DOI: 10.1002/cbic.201100101] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/08/2011] [Indexed: 11/06/2022]
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Eser O, Eser B, Cosar M, Erdogan M, Aslan A, Yıldız H, Solak M, Haktanır A. Short aggrecan gene repetitive alleles associated with lumbar degenerative disc disease in Turkish patients. GENETICS AND MOLECULAR RESEARCH 2011; 10:1923-30. [DOI: 10.4238/vol10-3gmr1222] [Citation(s) in RCA: 11] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/03/2022]
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Bender G, Ragsdale SW. Evidence that ferredoxin interfaces with an internal redox shuttle in Acetyl-CoA synthase during reductive activation and catalysis. Biochemistry 2010; 50:276-86. [PMID: 21141812 DOI: 10.1021/bi101511r] [Citation(s) in RCA: 21] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/30/2022]
Abstract
Acetyl-CoA synthase (ACS), a subunit of the bifunctional CO dehydrogenase/acetyl-CoA synthase (CODH/ACS) complex of Moorella thermoacetica requires reductive activation in order to catalyze acetyl-CoA synthesis and related partial reactions, including the CO/[1-(14)C]-acetyl-CoA exchange reaction. We show that the M. thermoacetica ferredoxin(II) (Fd-II), which harbors two [4Fe-4S] clusters and is an electron acceptor for CODH, serves as a redox activator of ACS. The level of activation depends on the oxidation states of both ACS and Fd-II, which strongly suggests that Fd-II acts as a reducing agent. By the use of controlled potential enzymology, the midpoint reduction potential for the catalytic one-electron redox-active species in the CO/acetyl-CoA exchange reaction is -511 mV, which is similar to the midpoint reduction potential that was earlier measured for other reactions involving ACS. Incubation of ACS with Fd-II and CO leads to the formation of the NiFeC species, which also supports the role of Fd-II as a reductant for ACS. In addition to being a reductant, Fd-II can accept electrons from acetylated ACS, as observed by the increased intensity of the EPR spectrum of reduced Fd-II, indicating that there is a stored electron within an "electron shuttle" in the acetyl-Ni(II) form of ACS. This "shuttle" is proposed to serve as a redox mediator during activation and at different steps of the ACS catalytic cycle.
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Affiliation(s)
- Güneş Bender
- Department of Biological Chemistry, University of Michigan, Ann Arbor, 48109, United States
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Bender G, Stich TA, Yan L, Britt RD, Cramer SP, Ragsdale SW. Infrared and EPR spectroscopic characterization of a Ni(I) species formed by photolysis of a catalytically competent Ni(I)-CO intermediate in the acetyl-CoA synthase reaction. Biochemistry 2010; 49:7516-23. [PMID: 20669901 DOI: 10.1021/bi1010128] [Citation(s) in RCA: 31] [Impact Index Per Article: 2.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Abstract
Acetyl-CoA synthase (ACS) catalyzes the synthesis of acetyl-CoA from CO, coenzyme A (CoA), and a methyl group from the CH(3)-Co(3+) site in the corrinoid iron-sulfur protein (CFeSP). These are the key steps in the Wood-Ljungdahl pathway of anaerobic CO and CO(2) fixation. The active site of ACS is the A-cluster, which is an unusual nickel-iron-sulfur cluster. There is significant evidence for the catalytic intermediacy of a CO-bound paramagnetic Ni species, with an electronic configuration of [Fe(4)S(4)](2+)-(Ni(p)(+)-CO)-(Ni(d)(2+)), where Ni(p) and Ni(d) represent the Ni centers in the A-cluster that are proximal and distal to the [Fe(4)S(4)](2+) cluster, respectively. This well-characterized Ni(p)(+)-CO intermediate is often called the NiFeC species. Photolysis of the Ni(p)(+)-CO state generates a novel Ni(p)(+) species (A(red)*) with a rhombic electron paramagnetic resonance spectrum (g values of 2.56, 2.10, and 2.01) and an extremely low (1 kJ/mol) barrier for recombination with CO. We suggest that the photolytically generated A(red)* species is (or is similar to) the Ni(p)(+) species that binds CO (to form the Ni(p)(+)-CO species) and the methyl group (to form Ni(p)-CH(3)) in the ACS catalytic mechanism. The results provide support for a binding site (an "alcove") for CO near Ni(p), indicated by X-ray crystallographic studies of the Xe-incubated enzyme. We propose that, during catalysis, a resting Ni(p)(2+) state predominates over the active Ni(p)(+) species (A(red)*) that is trapped by the coupling of a one-electron transfer step to the binding of CO, which pulls the equilibrium toward Ni(p)(+)-CO formation.
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Affiliation(s)
- Güneş Bender
- Department of Biological Chemistry, University of Michigan, Ann Arbor, Michigan 48109-0606, USA
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Korbekandi H, Iravani S, Abbasi S. Production of nanoparticles using organisms. Crit Rev Biotechnol 2009; 29:279-306. [DOI: 10.3109/07388550903062462] [Citation(s) in RCA: 200] [Impact Index Per Article: 13.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/13/2022]
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Volbeda A, Darnault C, Tan X, Lindahl PA, Fontecilla-Camps JC. Novel domain arrangement in the crystal structure of a truncated acetyl-CoA synthase from Moorella thermoacetica. Biochemistry 2009; 48:7916-26. [PMID: 19650626 DOI: 10.1021/bi9003952] [Citation(s) in RCA: 11] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Abstract
Ni-dependent acetyl-CoA synthase (ACS) and CO dehydrogenase (CODH) constitute the central enzyme complex of the Wood-Ljungdahl pathway of acetyl-CoA formation. The crystal structure of a recombinant bacterial ACS lacking the N-terminal domain that interacts with CODH shows a large reorganization of the remaining two globular domains, producing a narrow cleft of suitable size, shape, and nature to bind CoA. Sequence comparisons with homologous archaeal enzymes that naturally lack the N-terminal domain show that many amino acids lining this cleft are conserved. Besides the typical [4Fe-4S] center, the A-cluster contains only one proximal metal ion that, according to anomalous scattering data, is most likely Cu or Zn. Incorporation of a functional Ni(2)Fe(4)S(4) A-cluster would require only minor structural rearrangements. Using available structures, a plausible model of the interaction between CODH and the smaller ACS in archaeal multienzyme complexes is presented, along with a discussion of evolutionary relationships of the archaeal and bacterial enzymes.
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Affiliation(s)
- Anne Volbeda
- Laboratoire de Cristallographie et Cristallogenèse des Protéines, Institut de Biologie Structurale Jean-Pierre Ebel, CEA, CNRS, Université Joseph Fourier, 41 Rue Jules Horowitz, F-38027 Grenoble, France.
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Ragsdale SW, Pierce E. Acetogenesis and the Wood-Ljungdahl pathway of CO(2) fixation. BIOCHIMICA ET BIOPHYSICA ACTA 2008; 1784:1873-98. [PMID: 18801467 PMCID: PMC2646786 DOI: 10.1016/j.bbapap.2008.08.012] [Citation(s) in RCA: 707] [Impact Index Per Article: 44.2] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 07/02/2008] [Revised: 08/12/2008] [Accepted: 08/13/2008] [Indexed: 01/04/2023]
Abstract
Conceptually, the simplest way to synthesize an organic molecule is to construct it one carbon at a time. The Wood-Ljungdahl pathway of CO(2) fixation involves this type of stepwise process. The biochemical events that underlie the condensation of two one-carbon units to form the two-carbon compound, acetate, have intrigued chemists, biochemists, and microbiologists for many decades. We begin this review with a description of the biology of acetogenesis. Then, we provide a short history of the important discoveries that have led to the identification of the key components and steps of this usual mechanism of CO and CO(2) fixation. In this historical perspective, we have included reflections that hopefully will sketch the landscape of the controversies, hypotheses, and opinions that led to the key experiments and discoveries. We then describe the properties of the genes and enzymes involved in the pathway and conclude with a section describing some major questions that remain unanswered.
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Affiliation(s)
- Stephen W Ragsdale
- Department of Biological Chemistry, MSRB III, 5301, 1150 W. Medical Center Drive, University of Michigan, Ann Arbor, MI 48109-0606, USA.
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Abstract
The biochemistry of acetogenesis is reviewed. The microbes that catalyze the reactions that are central to acetogenesis are described and the focus is on the enzymology of the process. These microbes play a key role in the global carbon cycle, producing over 10 trillion kilograms of acetic acid annually. Acetogens have the ability to anaerobically convert carbon dioxide and CO into acetyl-CoA by the Wood-Ljungdahl pathway, which is linked to energy conservation. They also can convert the six carbons of glucose stoichiometrically into 3 mol of acetate using this pathway. Acetogens and other anaerobic microbes (e.g., sulfate reducers and methanogens) use the Wood-Ljungdahl pathway for cell carbon synthesis. Important enzymes in this pathway that are covered in this review are pyruvate ferredoxin oxidoreductase, CO dehydrogenase/acetyl-CoA synthase, a corrinoid iron-sulfur protein, a methyltransferase, and the enzymes involved in the conversion of carbon dioxide to methyl-tetrahydrofolate.
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Affiliation(s)
- Stephen W Ragsdale
- Department of Biological Chemistry, University of Michigan, Ann Arbor, MI, USA.
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Tan X, Lindahl PA. Tunnel mutagenesis and Ni-dependent reduction and methylation of the alpha subunit of acetyl coenzyme A synthase/carbon monoxide dehydrogenase. J Biol Inorg Chem 2008; 13:771-8. [PMID: 18365259 DOI: 10.1007/s00775-008-0363-x] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/09/2007] [Accepted: 03/07/2008] [Indexed: 10/22/2022]
Abstract
Two isolated alpha subunit mutants (A110C and A222L) of the alpha(2)beta(2) acetyl coenzyme A synthase (ACS)/carbon monoxide dehydrogenase (CODH) from Moorella thermoacetica were designed to block the CO-migrating tunnel in the alpha subunit, allowing comparison with equivalent mutants in ACS/CODH. After Ni activation, both mutants exhibited electron paramagnetic resonance spectra indicating that the A-cluster was properly assembled. ACS activities were similar to those of the wild-type recombinant Ni-activated alpha subunit, suggesting that CO diffuses directly to the A-cluster from solvent rather than through the tunnel as is observed for the "majority" activity of ACS/CODH. Thus, CO appears to migrate to the A-cluster through two pathways, one involving and one not involving the tunnel. The kinetics and extent of reduction of the Fe(4)S(4) cubane in the apo-alpha subunit and the Ni-activated alpha subunit upon exposure to titanium(III) citrate were examined using the stopped-flow method. The extent of reduction was independent of Ni, whereas the kinetics of reduction was Ni-dependent. Apo-alpha subunit reduction was monophasic while Ni-activated alpha subunit reduction was biphasic, with the more rapid phase coincident with that of apo-alpha subunit reduction. Thus, binding of Ni to the A-cluster slows the reduction kinetics of the [Fe(4)S(4)](2+) cubane. An upper limit of two electrons per alpha subunit are transferred from titanium(III) citrate to the Ni subcomponent of the A-cluster during reductive activation. These electrons are accepted quickly relative to the reduction of the [Fe(4)S(4)](2+) cubane. This reduction is probably a prerequisite for methyl group transfer. CO appears to bind to reduced nonfunctional subunits, thereby inhibiting reduction (or promoting reoxidation) of the cubane subcomponent of the A-cluster.
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Affiliation(s)
- Xiangshi Tan
- Departments of Chemistry and of Biochemistry and Biophysics, Texas A&M University, College Station, TX, 77843-3255, USA
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Seravalli J, Ragsdale SW. Pulse-chase studies of the synthesis of acetyl-CoA by carbon monoxide dehydrogenase/acetyl-CoA synthase: evidence for a random mechanism of methyl and carbonyl addition. J Biol Chem 2008; 283:8384-94. [PMID: 18203715 DOI: 10.1074/jbc.m709470200] [Citation(s) in RCA: 43] [Impact Index Per Article: 2.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
Carbon monoxide dehydrogenase/acetyl-CoA synthase catalyzes acetyl-CoA synthesis from CO, CoA, and a methylated corrinoid iron-sulfur protein, which acts as a methyl donor. This reaction is the last step in the Wood-Ljungdahl pathway of anaerobic carbon fixation. The binding sequence for the three substrates has been debated for over a decade. Different binding orders imply different mechanisms (i.e. paramagnetic versus diamagnetic mechanisms). Ambiguity arises because CO and CoA can each undergo isotopic exchange with acetyl-CoA, suggesting that either of these two substrates could be the last to bind to the acetyl-CoA synthase active site. Furthermore, carbonylation, CoA binding, and methyl transfer can all occur in the absence of the other two substrates. Here, we report pulse-chase studies, which unambiguously establish the order in which the three substrates bind. Although a CoA pulse is substantially diluted by excess CoA in the chase, isotope recovery of a pulse of labeled CO or methyl group is unaffected by the presence of excess unlabeled CO or methyl group in the chase. These results demonstrate that CoA is the last substrate to bind and that CO and the methyl group bind randomly as the first substrate in acetyl-CoA synthesis. Up to 100% of the methyl groups and CoA and up to 60-70% of the CO employed in the pulse phase can be trapped in the product acetyl-CoA.
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Affiliation(s)
- Javier Seravalli
- Department of Biochemistry, University of Nebraska, Lincoln, NE 68588-0664, USA
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Tan X, Surovtsev IV, Lindahl PA. Kinetics of CO insertion and acetyl group transfer steps, and a model of the acetyl-CoA synthase catalytic mechanism. J Am Chem Soc 2007; 128:12331-8. [PMID: 16967985 PMCID: PMC2527582 DOI: 10.1021/ja0627702] [Citation(s) in RCA: 40] [Impact Index Per Article: 2.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
Abstract
Acetyl-CoA synthase/carbon monoxide dehydrogenase is a Ni-Fe-S-containing enzyme that catalyzes the synthesis of acetyl-CoA from CO, CoA, and a methyl group. The methyl group is transferred onto the enzyme from a corrinoid-iron-sulfur protein (CoFeSP). The kinetics of two steps within the catalytic mechanism were studied using the stopped-flow method, including the insertion of CO into a putative Ni(2+)-CH(3) bond and the transfer of the resulting acetyl group to CoA. Neither step had been studied previously. Reactions were monitored indirectly, starting with the methylated intermediate form of the enzyme. Resulting traces were analyzed by constructing a simple kinetic model describing the catalytic mechanism under reducing conditions. Besides methyl group transfer, CO insertion, and acetyl group transfer, fitting to experimental traces required the inclusion of an inhibitory step in which CO reversibly bound to the form of the enzyme obtained immediately after product release. Global simulation of the reported datasets afforded a consistent set of kinetic parameters. The equilibrium constant for the overall synthesis of acetyl-CoA was estimated and compared to the product of the individual equilibrium constants. Simulations obtained with the model duplicated the essential behavior of the enzyme, in terms of the variation of activity with [CO], and the time-dependent decay of the NiFeC EPR signal upon reaction with CoFeSP. Under standard assay conditions, the model suggests that the vast majority of active enzyme molecules in a population should be in the methylated form, suggesting that the subsequent catalytic step, namely CO insertion, is rate limiting. This conclusion is further supported by a sensitivity analysis showing that the rate is most sensitively affected by a change in the rate coefficient associated with the CO insertion step.
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Affiliation(s)
- Xiangshi Tan
- Department of Chemistry, Texas A&M University, College Station, Texas 77843, USA
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Affiliation(s)
- Stephen W Ragsdale
- Department of Biochemistry, Beadle Center, University of Nebraska, Lincoln, Nebraska 68588-0664, USA.
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Ragsdale SW. Nickel and the carbon cycle. J Inorg Biochem 2007; 101:1657-66. [PMID: 17716738 PMCID: PMC2100024 DOI: 10.1016/j.jinorgbio.2007.07.014] [Citation(s) in RCA: 99] [Impact Index Per Article: 5.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/24/2007] [Revised: 07/09/2007] [Accepted: 07/12/2007] [Indexed: 11/23/2022]
Abstract
This article, dedicated to Edward Stiefel, reviews three nickel enzymes that play important roles in the carbon cycle: CO dehydrogenase, acetyl-CoA synthase, and methyl-coenzyme M reductase. After a short discussion of the carbon cycle, the structures of the active centers of the proteins and their proposed mechanisms are discussed. A brief description of future research areas is presented for each enzyme system. A short perspective on future research on nickel enzymes ends this contribution.
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Affiliation(s)
- Stephen W Ragsdale
- Department of Biological Chemistry, 5301 MSRB III, 1150 W, Medical Center Drive, University of Michigan, Ann Arbor, MI 48109-0606, USA.
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Harrop TC, Olmstead MM, Mascharak PK. Synthetic analogues of the active site of the A-cluster of acetyl coenzyme A synthase/CO dehydrogenase: syntheses, structures, and reactions with CO. Inorg Chem 2007; 45:3424-36. [PMID: 16602803 PMCID: PMC4826277 DOI: 10.1021/ic0520465] [Citation(s) in RCA: 53] [Impact Index Per Article: 3.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Abstract
Two metallosynthons, namely (Et4N)2[Ni(NpPepS)] (1) and (Et4N)2[Ni(PhPepS)] (2) containing carboxamido-N and thiolato-S as donors have been used to model the bimetallic M(p)-Ni(d) subsite of the A-cluster of the enzyme acetyl coenzyme A synthase/CO dehydrogenase. A series of sulfur-bridged Ni/Cu dinuclear and trinuclear complexes (3-10) have been synthesized to explore their redox properties and affinity of the metal centers toward CO. The structures of (Et4N)2[Ni(PhPepS)] (2), (Et4N)[Cu(neo)Ni(NpPepS)] x 0.5 Et2O x 0.5 H2O (3 x 0.5 Et2O x 0.5 H2O), (Et4N)[Cu(neo)Ni(PhPepS)] x H2O (4 x H2O), (Et4N)2[Ni{Ni(NpPepS)}2] x DMF (5 x DMF), (Et4N)2[Ni(DMF)2{Ni(NpPepS)}2] x 3 DMF (6 x 3 DMF), (Et4N)2[Ni(DMF)2{Ni(PhPepS)}2] (8), and [Ni(dppe)Ni(PhPepS)] x CH2Cl2 (10 x CH2Cl2) have been determined by crystallography. The Ni(d) mimics 1 and 2 resist reduction and exhibit no affinity toward CO. In contrast, the sulfur-bridged Ni center (designated Ni(C)) in the trinuclear models 5-8 are amenable to reduction and binds CO in the Ni(I) state. Also, the sulfur-bridged Ni(C) center can be removed from the trimers (5-8) by treatment with 1,10-phenanthroline much like the "labile Ni" from the enzyme. The dinuclear Ni-Ni models 9 and 10 resemble the Ni(p)-Ni(d) subsite of the A-cluster more closely, and only the modeled Ni(p) site of the dimers can be reduced. The Ni(I)-Ni(II) species display EPR spectra typical of a Ni(I) center in distorted trigonal bipyramidal and distorted tetrahedral geometries for 9(red) and 10(red), respectively. Both species bind CO, and the CO-adducts 9(red)-CO and 10(red)-CO display strong nu(co) at 2044 and 1997 cm(-1), respectively. The reduction of 10 is reversible. The CO-affinity of 10 in the reduced state and the nu(co) value of 10(red)-CO closely resemble the CO-bound reduced A-cluster (nu(co) = 1996 cm(-1)).
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Affiliation(s)
- Todd C. Harrop
- Department of Chemistry and Biochemistry, University of California, Santa Cruz, CA 95064
| | | | - Pradip K. Mascharak
- Department of Chemistry and Biochemistry, University of California, Santa Cruz, CA 95064
- (P. K. Mascharak), Fax: + 1-831-459-2935 Tel: + 1-831-459-4251
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Bramlett MR, Stubna A, Tan X, Surovtsev IV, Münck E, Lindahl PA. Mössbauer and EPR study of recombinant acetyl-CoA synthase from Moorella thermoacetica. Biochemistry 2006; 45:8674-85. [PMID: 16834342 DOI: 10.1021/bi060003+] [Citation(s) in RCA: 28] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
Abstract
Mössbauer and EPR spectroscopies were used to study the electronic structure of the A-cluster from recombinant acetyl-CoA synthase (the alpha subunit of the alpha2beta2 acetyl-CoA synthase/CO dehydrogenase). Once activated with Ni, these subunits have properties mimicking those associated with the alpha2beta2 tetramer, including structural heterogeneities. The Fe4S4 portion of the A-cluster in oxidized, methylated, and acetylated states was in the 2+ core oxidation state. Upon reduction with dithionite or Ti3+ citrate, samples of Ni-activated alpha developed the ability to accept a methyl group. Corresponding Mössbauer spectra exhibited two populations of A-clusters; roughly, 70% contained [Fe4S4]1+ cubanes, while approximately 30% contained [Fe4S4]2+ cubanes, suggesting an extremely low [Fe4S4](1+/2+) reduction potential for the 30% portion (perhaps <-800 mV vs NHE). The same population ratio was observed when Ni-free unactivated alpha was used. The 70% fraction exhibited paramagnetic hyperfine structure in the absence of an applied magnetic field, excluding the possibility that it represents an [Fe4S4]1+ cluster coupled to a (proximal) Ni(p)1+. EPR spectra of dithionite-reduced, Ni-activated alpha exhibited features at g = 5.8 and g(ave) approximately 1.93, consistent with a physical mixture of {S = 3/2; S = 1/2} spin-states for A-clusters containing [Fe4S4]1+ clusters. Incubation of Ni-activated alpha with dithionite and CO converted 25% of alpha subunits into the S = 1/2 A(red)-CO state. Previous correlation of this state to functional A-clusters suggests that only the 30% fraction not reduced by dithionite or Ti3+ citrate represents functional A-clusters. Comparison of spin states in oxidized and methylated states suggests that two electrons are required for reductive activation, starting from the oxidized state containing Ni(p)2+. Refitting published activity-vs-potential data supports an n = 2 reductive activation. Enzyme starting in the methylated state exhibited catalytic activity in the absence of an external reductant, suggesting that the two electrons used in reductive activation are retained by the enzyme after each catalytic cycle and that the enzyme does not have to pass through the A(red)-CO state during catalysis. Taken together, our results suggest that a Ni(p)0 state may form upon reductive activation and reform after each catalytic cycle.
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Affiliation(s)
- Matthew R Bramlett
- Department of Biochemistry and Biophysics, Texas A&M University, College Station, Texas 77843, USA
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Harrop TC, Mascharak PK. Structural and spectroscopic models of the A-cluster of acetyl coenzyme a synthase/carbon monoxide dehydrogenase: Nature's Monsanto acetic acid catalyst. Coord Chem Rev 2005. [DOI: 10.1016/j.ccr.2005.04.019] [Citation(s) in RCA: 73] [Impact Index Per Article: 3.8] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/16/2022]
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Affiliation(s)
- Kenneth L Brown
- Department of Chemistry and Biochemistry, Ohio University, Athens, 45701, USA.
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Schenker R, Mock MT, Kieber-Emmons MT, Riordan CG, Brunold TC. Spectroscopic and computational studies on [Ni(tmc)CH3]OTf: implications for Ni-methyl bonding in the A cluster of acetyl-CoA synthase. Inorg Chem 2005; 44:3605-17. [PMID: 15877445 DOI: 10.1021/ic0483996] [Citation(s) in RCA: 12] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
Abstract
The five-coordinate high-spin (S = 1) Ni(2+) complex [Ni(tmc)CH(3)](+) (1) (tmc = 1,4,8,11-tetramethyl-1,4,8,11-tetraazacyclotetradecane) serves as a model for a viable reaction intermediate of the A cluster of acetyl-CoA synthase (ACS) in which the distal nickel center is methylated. Spectroscopic and density functional theory (DFT) computational studies afford a quantitative bonding description for 1 that reveals a highly covalent Ni-CH(3) bond. From a normal coordinate analysis of resonance Raman data obtained for 1, a value of k(Ni-C) = 1.44 mdyn/Angstroms is obtained for the Ni-C stretch force constant of this species. This value is smaller than k(Co)(-C) = 1.85 mdyn/Angstroms, which is reported for the Co-C stretch in the methylcobinamide cofactor (5) that serves as the methyl donor to the A cluster in the ACS catalytic cycle. Experimentally calibrated DFT computations on viable methylated A cluster models reveal that the methyl group binds to the proximal (Ni(p)) rather than the distal (Ni(d)) nickel center and afford a simple electronic argument for this preference. By correlating the experimental force constants with the computed bond orders of the M-C bonds in 1 and 5, the Ni(p)(2+)-CH(3) bond strength for an A cluster model with a square-planar Ni(p) conformation, which is the most probable structure of the methylated A cluster on the basis of steric and energetic considerations, is predicted to be similar to the Co(3+)-CH(3) bond strength in CH(3)-CoFeSP. This similarity could be a crucial thermodynamic prerequisite for the reversibility of the enzymatic transmethylation reaction.
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Affiliation(s)
- Ralph Schenker
- Department of Chemistry, University of Wisconsin-Madison, 53706, USA
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Amara P, Volbeda A, Fontecilla-Camps JC, Field MJ. A quantum chemical study of the reaction mechanism of acetyl-coenzyme a synthase. J Am Chem Soc 2005; 127:2776-84. [PMID: 15725036 DOI: 10.1021/ja0439221] [Citation(s) in RCA: 35] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/30/2022]
Abstract
Recent experimental and theoretical studies have focused on the mechanism of the A-cluster active site of acetyl-CoA synthase that produces acetyl-CoA from a methyl group, carbon monoxide, and CoA. Several proposals have been made concerning the redox states of the (Ni-Ni) bimetallic center and the iron-sulfur cluster connected to one of the metals. Using hybrid density functional theory, we have investigated putative intermediate states from the catalytic cycle. Among our conclusions are the following: (i) the zerovalent state proposed for the proximal metal is unlikely if the charge on the iron-sulfur cluster is +2; (ii) a mononuclear mechanism in which both CO and CH(3) bind the proximal nickel is favored over the binuclear mechanism in which CO and CH(3) bind the proximal and distal nickel ions, respectively; (iii) the formation of a disulfide bond in the active site could provide the two electrons necessary for the reaction but only if methylation occurs simultaneously; and (iv) the crystallographic closed form of the active site needs to open to accommodate ligands in the equatorial site.
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Affiliation(s)
- Patricia Amara
- Laboratoire de Dynamique Moléculaire and Laboratoire de Cristallographie et Cristallogenèse des Protéines, Institut de Biologie Structurale - Jean-Pierre Ebel, CEA/CNRS/UJF, 41, rue Jules Horowitz, F-38027 Grenoble Cedex 01, France
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40
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Tan X, Loke HK, Fitch S, Lindahl PA. The Tunnel of Acetyl-Coenzyme A Synthase/Carbon Monoxide Dehydrogenase Regulates Delivery of CO to the Active Site. J Am Chem Soc 2005; 127:5833-9. [PMID: 15839681 DOI: 10.1021/ja043701v] [Citation(s) in RCA: 43] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
Abstract
The effect of [CO] on acetyl-CoA synthesis activity of the isolated alpha subunit of acetyl-coenzyme A synthase/carbon monoxide dehydrogenase from Moorella thermoacetica was determined. In contrast to the complete alpha(2)beta(2) enzyme where multiple CO molecules exhibit strong cooperative inhibition, alpha was weakly inhibited, apparently by a single CO with K(I) = 1.5 +/- 0.5 mM; other parameters include k(cat) = 11 +/- 1 min(-)(1) and K(M) = 30 +/- 10 microM. The alpha subunit lacked the previously described "majority" activity of the complete enzyme but possessed its "residual" activity. The site affording cooperative inhibition may be absent or inoperative in isolated alpha subunits. Ni-activated alpha rapidly and reversibly accepted a methyl group from CH(3)-Co(3+)FeSP affording the equilibrium constant K(MT) = 10 +/- 4, demonstrating the superior nucleophilicity of alpha(red) relative to Co(1+)FeSP. CO inhibited this reaction weakly (K(I) = 540 +/- 190 microM). NiFeC EPR intensity of alpha developed in accordance with an apparent K(d) = 30 microM, suggesting that the state exhibiting this signal is not responsible for inhibiting catalysis or methyl group transfer and that it may be a catalytic intermediate. At higher [CO], signal intensity declined slightly. Attenuation of catalysis, methyl group transfer, and the NiFeC signal might reflect the same weak CO binding process. Three mutant alpha(2)beta(2) proteins designed to block the tunnel between the A- and C-clusters exhibited little/no activity with CO(2) as a substrate and no evidence of cooperative CO inhibition. This suggests that the tunnel was blocked by these mutations and that cooperative CO inhibition is related to tunnel operation. Numerous CO molecules might bind cooperatively to some region associated with the tunnel and institute a conformational change that abolishes the majority activity. Alternatively, crowding of CO in the tunnel may control flow through the tunnel and deliver CO to the A-cluster at the appropriate step of catalysis. Residual activity may involve CO from the solvent binding directly to the A-cluster.
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Affiliation(s)
- Xiangshi Tan
- Contribution from the Departments of Chemistry and of Biochemistry and Biophysics, Texas A and M University, College Station, Texas 77843, USA
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41
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Abstract
This review focuses on how microbes live on CO as a sole source of carbon and energy and with CO by generating carbon monoxide as a metabolic intermediate. The use of CO is a property of organisms that use the Wood-L jungdahl pathway of autotrophic growth. The review discusses when CO metabolism originated, when and how it was discovered, and what properties of CO are ideal for microbial growth. How CO sensing by a heme-containing transcriptional regulatory protein activates the expression of CO metabolism-linked genes is described. Two metalloenzymes are the cornerstones of growth with CO: CO dehydrogenase (CODH) and acetyl-CoA synthase (ACS). CODH oxidizes CO to CO2, providing low-potential electrons for the cell, or alternatively reduces CO2 to CO. The latter reaction, when coupled to ACS, forms a machine for generating acetyl-CoA from CO2 for cell carbon synthesis. The recently solved crystal structures of CODH and ACS along with spectroscopic measurements and computational studies provide insights into novel bio-organometallic catalytic mechanisms and into the nature of a 140 A gas channel that coordinates the generation and utilization of CO. The enzymes that are coupled to CODH/ACS are also described, with a focus on a corrinoid protein, a methyltransferase, and pyruvate ferredoxin oxidoreductase.
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Affiliation(s)
- Stephen W Ragsdale
- Department of Biochemistry, Beadle Center, University of Nebraska, Lincoln, NE 68588-0664, USA.
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42
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Abstract
The bifunctional enzyme carbon monoxide dehydrogenase/acetyl-coenzyme A (CoA) synthase (CODH/ACS) is a key enzyme in the Wood-Ljungdahl pathway of carbon fixation. Carbon monoxide is combined with a methyl group and ultimately converted to acetyl-CoA at a unique Ni-containing bimetallic site in the A-cluster of this enzyme. Despite years of extensive biochemical and spectroscopic studies and the recent report of three separate crystal structures, the mechanism by which acetyl-CoA is synthesized is still unknown. Over the past two years there have been a number of significant developments regarding ACS. This Account critically examines these recent developments and especially focuses on those areas that are still a matter of debate.
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Affiliation(s)
- Eric L Hegg
- Department of Chemistry, University of Utah, 315 South 1400 East, Salt Lake City, Utah 84112-0850, USA.
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Tan X, Bramlett MR, Lindahl PA. Effect of Zn on acetyl coenzyme a synthase: evidence for a conformational change in the alpha subunit during catalysis. J Am Chem Soc 2004; 126:5954-5. [PMID: 15137746 DOI: 10.1021/ja039600z] [Citation(s) in RCA: 16] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
Abstract
Acetyl coenzyme A synthase (ACS) is an alpha2beta2 tetramer in which the active-site A-cluster, located in the alpha subunits, consists of an Fe4S4 cubane bridged to a {Nip Nid} binuclear site. The alpha subunits exist in two conformations. In the open conformation, Nip is surface-exposed, while the proximal metal is buried in the closed conformation. Nip is labile and can be replaced by Cu. In this study, the effects of Zn are reported. ACS in which Zn replaced Nip was inactive and did not exhibit the so-called NiFeC EPR signal nor the ability to accept a methyl group from the corrinoid-iron-sulfur protein (CoFeSP). Once Zn-bound, it could not be replaced by subsequently adding Ni. The Zn-bound A-cluster cannot be reduced and bound with CO or become methylated, probably because Zn (like Cu) is insufficiently nucleophilic for these functions. Unexpectedly, Zn replaced Nip only while ACS was engaged in catalysis. Under these conditions, replacement occurred with kapp approximately 0.6 min-1. Replacement was blocked by including EDTA in the assay mix. Zn appears to replace Nip when ACS is in an intermediate state (or states) of catalysis but this(these) state(s) must not be present when ACS is reduced in CO alone, or in the presence of CoA, CoFeSP, or reduced methyl viologen. Nip appears susceptible to Zn-attack when the alpha subunit is in the open conformation and protected from attack when it is in the closed conformation. This is the first evidence that the structurally-characterized conformations of the alpha subunit change during catalysis, indicating a mechanistic role for this conformational change.
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Affiliation(s)
- Xiangshi Tan
- Department of Chemistry, Texas A & M University, College Station, Texas 77843, USA
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44
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Lindahl PA. Acetyl-coenzyme A synthase: the case for a Nip0-based mechanism of catalysis. J Biol Inorg Chem 2004; 9:516-24. [PMID: 15221478 DOI: 10.1007/s00775-004-0564-x] [Citation(s) in RCA: 89] [Impact Index Per Article: 4.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/15/2004] [Accepted: 05/21/2004] [Indexed: 11/30/2022]
Abstract
Acetyl-CoA synthase (also known as carbon monoxide dehydrogenase) is a bifunctional Ni-Fe-S-containing enzyme that catalyzes the reversible reduction of CO(2) to CO and the synthesis of acetyl-coenzyme A from CO, CoA, and a methyl group donated by a corrinoid iron-sulfur protein. The active site for the latter reaction, called the A-cluster, consists of an Fe(4)S(4) cubane bridged to the proximal Ni site (Ni(p)), which is bridged in turn to the so-called distal Ni site. In this review, evidence is presented that Ni(p) achieves a zero-valent state at low potentials and during catalysis. Ni(p) appears to be the metal to which CO and methyl groups bind and then react to form an acetyl-Ni(p) intermediate. Methyl group binding requires reductive activation, where two electrons reduce some site on the A-cluster. The coordination environment of the distal Ni suggests that it could not be stabilized in redox states lower than 2+. The rate at which the [Fe(4)S(4)](2+) cubane is reduced is far slower than that at which reductive activation occurs, suggesting that the cubane is not the site of reduction. An intriguing possibility is that Ni(p)(2+) might be reduced to the zero-valent state. Reinforcing this idea are Ni-organometallic complexes in which the Ni exhibits analogous reactivity properties when reduced to the zero-valent state. A zero-valent Ni stabilized exclusively with biological ligands would be remarkable and unprecedented in biology.
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Affiliation(s)
- Paul A Lindahl
- Departments of Chemistry and of Biochemistry and Biophysics, Texas A and M University, College Station, TX 77843-3255, USA.
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45
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Volbeda A, Fontecilla-Camps JC. Crystallographic evidence for a CO/CO(2) tunnel gating mechanism in the bifunctional carbon monoxide dehydrogenase/acetyl coenzyme A synthase from Moorella thermoacetica. J Biol Inorg Chem 2004; 9:525-32. [PMID: 15221479 DOI: 10.1007/s00775-004-0565-9] [Citation(s) in RCA: 39] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/27/2004] [Accepted: 05/21/2004] [Indexed: 11/30/2022]
Abstract
Acetyl coenzyme A synthase (ACS) acts in concert with carbon monoxide dehydrogenase (CODH) to catalyze the formation of acetyl-coenzyme A from CO(2)-derived CO and CH(3)(+) molecules. Recent crystal structures have shown that the three globular domains constituting the ACS subunit may be arranged in either a closed or an open conformation. A long hydrophobic tunnel network allows diffusion of CO between the CODH and the ACS active sites in the closed form, but it is blocked in the open form. On the other hand, the active site of ACS is only accessible for coenzyme A and the methyl donating protein in the open domain conformation. Although several metal compositions have been observed for this active site, present consensus is that it consists of a Ni-Ni-[Fe(4)S(4)] cluster. The observed conformational changes of ACS and the resulting different substrate accessibilities of the catalytic central nickel are reviewed here in the context of a putative CO(2)/CO tunnel gating mechanism.
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Affiliation(s)
- Anne Volbeda
- Laboratoire de Cristallographie et de Cristallogenèse des Protéines, Institut de Biologie Structurale J.P. Ebel, 41 rue Jules Horowitz, 38027 Cédex 1, Grenoble, France
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46
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Brunold TC. Spectroscopic and computational insights into the geometric and electronic properties of the A-cluster of acetyl-coenzyme A synthase. J Biol Inorg Chem 2004; 9:533-41. [PMID: 15221480 DOI: 10.1007/s00775-004-0566-8] [Citation(s) in RCA: 24] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/15/2004] [Accepted: 05/21/2004] [Indexed: 10/26/2022]
Abstract
For the last two decades, the bifunctional enzyme acetyl-coenzyme A synthase/carbon monoxide dehydrogenase (ACS/CODH) from Moorella thermoacetica has been the subject of considerable research aimed at elucidating the geometric and electronic properties of the A-cluster, which serves as the active site for ACS catalysis. While the recent success in obtaining high-resolution X-ray structures of this enzyme solved many of the mysteries regarding the number, identities, and coordination environments of the metal centers of the A-cluster, fundamental questions concerning the catalytic mechanism of this highly elaborate polynuclear active site have yet to be answered. This Commentary summarizes relevant information obtained from spectroscopic and computational studies on the oxidized, reduced, and CO-bound forms of the A-cluster and highlights some of the key issues regarding the electronic properties and reactivity of this cluster that need to be addressed in future studies.
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Affiliation(s)
- Thomas C Brunold
- Department of Chemistry, University of Wisconsin, Madison, WI 53706, USA.
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47
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Riordan CG. Synthetic chemistry and chemical precedents for understanding the structure and function of acetyl coenzyme A synthase. J Biol Inorg Chem 2004; 9:542-9. [PMID: 15221481 DOI: 10.1007/s00775-004-0567-7] [Citation(s) in RCA: 27] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/13/2004] [Accepted: 05/21/2004] [Indexed: 10/26/2022]
Abstract
Acetyl coenzyme A synthase (ACS), found in acetogenic and methanogenic organisms, is responsible for the synthesis and breakdown of acetate. The mechanism by which methylcob(III)alamin, CO and coenzyme A are assembled/disassembled at the active-site A-cluster involves a number of biologically unprecedented intermediates. In the past two years, two protein crystal structures have significantly enhanced the understanding of the structure of the active-site A-cluster, responsible for catalysis. The structure reports spawned a number of important questions regarding the metal ion constitution of the active enzyme, the structure(s) of the spectroscopically identified states and the details of the catalytic mechanism. This Commentary addresses these issues in the framework of existing synthetic and chemical precedent studies aimed at developing rational structure-function correlations and presents structural and reactivity targets for future studies.
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Affiliation(s)
- Charles G Riordan
- Department of Chemistry and Biochemistry, University of Delaware, Newark, DE 19716, USA.
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48
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Drennan CL, Doukov TI, Ragsdale SW. The metalloclusters of carbon monoxide dehydrogenase/acetyl-CoA synthase: a story in pictures. J Biol Inorg Chem 2004; 9:511-5. [PMID: 15221484 DOI: 10.1007/s00775-004-0563-y] [Citation(s) in RCA: 85] [Impact Index Per Article: 4.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/15/2004] [Accepted: 05/21/2004] [Indexed: 11/25/2022]
Abstract
Eight Ni proteins are known and three of these, CO dehydrogenase (CODH), acetyl-CoA synthase (ACS), and hydrogenase, are Ni-Fe-S proteins. In the last three years, the long-awaited structures of CODH and ACS have been solved. The bioinorganic community was shocked, as the structures of the active sites of CODH and ACS, the C- and A-cluster, respectively, which each had been predicted to consist of a [Fe(4)S(4)] cluster bridged to a single Ni, revealed unexpected compositions and arrangements. Crystal structures of ACS revealed major differences in protein conformation and in A-cluster composition; for example, a [Fe(4)S(4)] cluster bridged to a binuclear center in which one of the metal binding sites was occupied by Ni, Cu, or Zn. Recent studies have revealed Ni-Ni to be the active state, unveiled the source of the heterogeneity that had plagued studies of CODH/ACS for decades, and produced a metal-replacement strategy to generate highly active and nearly homogeneous enzyme.
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Affiliation(s)
- Catherine L Drennan
- Department of Chemistry, Massachusetts Institute of Technology, Cambridge, MA 02139, USA.
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49
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Krishnan R, Riordan CG. Cys-Gly-Cys Tripeptide Complexes of Nickel: Binuclear Analogues for the Catalytic Site in Acetyl Coenzyme A Synthase. J Am Chem Soc 2004; 126:4484-5. [PMID: 15070343 DOI: 10.1021/ja038086u] [Citation(s) in RCA: 62] [Impact Index Per Article: 3.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Abstract
The tripeptide, Ac-CysGlyCys-CONH2, is utilized as a ligand to bind Ni in a fashion identical to that found at the active site of acetyl coenzyme A synthase. The Ni-peptide construct is a suitable metalloligand for the preparation of larger structures formed via bridging Cys side chains. The complexes Ni(CysGlyCys)Ni(dppe) and Ni(CysGlyCys)Ni(depe) serve as close structural representations for the binuclear subcluster, exhibiting electrochemical properties that demonstrate facile access to the reduced mixed valent Ni(II)Ni(I) state, which binds CO.
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Affiliation(s)
- Rangan Krishnan
- Department of Chemistry and Biochemistry, University of Delaware, Newark, Delaware 19716, USA
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50
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Maynard EL, Tan X, Lindahl PA. Autocatalytic activation of acetyl-CoA synthase. J Biol Inorg Chem 2004; 9:316-22. [PMID: 15015040 DOI: 10.1007/s00775-004-0528-1] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/30/2003] [Accepted: 02/02/2004] [Indexed: 11/30/2022]
Abstract
Acetyl-CoA synthase (ACS identical with ACS/CODH identical with CODH/ACS) from Moorella thermoacetica catalyzes the synthesis of acetyl-CoA from CO, CoA, and a methyl group of a corrinoid-iron-sulfur protein (CoFeSP). A time lag prior to the onset of acetyl-CoA production, varying from 4 to 20 min, was observed in assay solutions lacking the low-potential electron-transfer agent methyl viologen (MV). No lag was observed when MV was included in the assay. The length of the lag depended on the concentrations of CO and ACS, with shorter lags found for higher [ACS] and sub-saturating [CO]. Lag length also depended on CoFeSP. Rate profiles of acetyl-CoA synthesis, including the lag phase, were numerically simulated assuming an autocatalytic mechanism. A similar reaction profile was monitored by UV-vis spectrophotometry, allowing the redox status of the CoFeSP to be evaluated during this process. At early stages in the lag phase, Co(2+)FeSP reduced to Co(+)FeSP, and this was rapidly methylated to afford CH(3)-Co(3+)FeSP. During steady-state synthesis of acetyl-CoA, CoFeSP was predominately in the CH(3)-Co(3+)FeSP state. As the synthesis rate declined and eventually ceased, the Co(+)FeSP state predominated. Three activation reductive reactions may be involved, including reduction of the A- and C-clusters within ACS and the reduction of the cobamide of CoFeSP. The B-, C-, and D-clusters in the beta subunit appear to be electronically isolated from the A-cluster in the connected alpha subunit, consistent with the ~70 A distance separating these clusters, suggesting the need for an in vivo reductant that activates ACS and/or CoFeSP.
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Affiliation(s)
- Ernest L Maynard
- Department of Biophysics and Biophysical Chemistry, The Johns Hopkins University School of Medicine, Baltimore, MD 21205, USA
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