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Blanford J, Zhai Z, Baer MD, Guo G, Liu H, Liu Q, Raugei S, Shanklin J. Molecular mechanism of trehalose 6-phosphate inhibition of the plant metabolic sensor kinase SnRK1. Sci Adv 2024; 10:eadn0895. [PMID: 38758793 PMCID: PMC11100557 DOI: 10.1126/sciadv.adn0895] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 11/28/2023] [Accepted: 04/15/2024] [Indexed: 05/19/2024]
Abstract
SUCROSE-NON-FERMENTING1-RELATED PROTEIN KINASE1 (SnRK1), a central plant metabolic sensor kinase, phosphorylates its target proteins, triggering a global shift from anabolism to catabolism. Molecular modeling revealed that upon binding of KIN10 to GEMINIVIRUS REP-INTERACTING KINASE1 (GRIK1), KIN10's activation T-loop reorients into GRIK1's active site, enabling its phosphorylation and activation. Trehalose 6-phosphate (T6P) is a proxy for cellular sugar status and a potent inhibitor of SnRK1. T6P binds to KIN10, a SnRK1 catalytic subunit, weakening its affinity for GRIK1. Here, we investigate the molecular details of T6P inhibition of KIN10. Molecular dynamics simulations and in vitro phosphorylation assays identified and validated the T6P binding site on KIN10. Under high-sugar conditions, T6P binds to KIN10, blocking the reorientation of its activation loop and preventing its phosphorylation and activation by GRIK1. Under these conditions, SnRK1 maintains only basal activity levels, minimizing phosphorylation of its target proteins, thereby facilitating a general shift from catabolism to anabolism.
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Affiliation(s)
- Jantana Blanford
- Department of Biology, Brookhaven National Laboratory, Upton, NY 11973, USA
| | - Zhiyang Zhai
- Department of Biology, Brookhaven National Laboratory, Upton, NY 11973, USA
| | - Marcel D. Baer
- Physical and Computational Sciences Directorate, Pacific Northwest National Laboratory, Richland, WA 99354, USA
| | - Gongrui Guo
- Department of Biology, Brookhaven National Laboratory, Upton, NY 11973, USA
| | - Hui Liu
- Department of Biology, Brookhaven National Laboratory, Upton, NY 11973, USA
| | - Qun Liu
- Department of Biology, Brookhaven National Laboratory, Upton, NY 11973, USA
| | - Simone Raugei
- Physical and Computational Sciences Directorate, Pacific Northwest National Laboratory, Richland, WA 99354, USA
| | - John Shanklin
- Department of Biology, Brookhaven National Laboratory, Upton, NY 11973, USA
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2
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Shisler KA, Kincannon WM, Mattice JR, Larson J, Valaydon-Pillay A, Mus F, Flusche T, Kumar Nath A, Stoian SA, Raugei S, Bothner B, DuBois JL, Peters JW. Homologous acetone carboxylases select Fe(II) or Mn(II) as the catalytic cofactor. mBio 2024; 15:e0298723. [PMID: 38126751 PMCID: PMC10865871 DOI: 10.1128/mbio.02987-23] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/13/2023] [Accepted: 11/16/2023] [Indexed: 12/23/2023] Open
Abstract
Acetone carboxylases (ACs) catalyze the metal- and ATP-dependent conversion of acetone and bicarbonate to form acetoacetate. Interestingly, two homologous ACs that have been biochemically characterized have been reported to have different metal complements, implicating different metal dependencies in catalysis. ACs from proteobacteria Xanthobacter autotrophicus and Aromatoleum aromaticum share 68% sequence identity but have been proposed to have different catalytic metals. In this work, the two ACs were expressed under the same conditions in Escherichia coli and were subjected to parallel chelation and reconstitution experiments with Mn(II) or Fe(II). Electron paramagnetic and Mössbauer spectroscopies identified signatures, respectively, of Mn(II) or Fe(II) bound at the active site. These experiments showed that the respective ACs, without the assistance of chaperones, second metal sites, or post-translational modifications facilitate correct metal incorporation, and despite the expected thermodynamic preference for Fe(II), each preferred a distinct metal. Catalysis was likewise associated uniquely with the cognate metal, though either could potentially serve the proposed Lewis acidic role. Subtle differences in the protein structure are implicated in serving as a selectivity filter for Mn(II) or Fe(II).IMPORTANCEThe Irving-Williams series refers to the predicted stabilities of transition metal complexes where the observed general stability for divalent first-row transition metal complexes increase across the row. Acetone carboxylases (ACs) use a coordinated divalent metal at their active site in the catalytic conversion of bicarbonate and acetone to form acetoacetate. Highly homologous ACs discriminate among different divalent metals at their active sites such that variations of the enzyme prefer Mn(II) over Fe(II), defying Irving-Williams-predicted behavior. Defining the determinants that promote metal discrimination within the first-row transition metals is of broad fundamental importance in understanding metal-mediated catalysis and metal catalyst design.
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Affiliation(s)
- Krista A. Shisler
- Institute of Biological Chemistry, Washington State University, Pullman, Washington, USA
| | - William M. Kincannon
- Department of Chemistry and Biochemistry, Montana State University, Bozeman, Montana, USA
| | - Jenna R. Mattice
- Department of Chemistry and Biochemistry, Montana State University, Bozeman, Montana, USA
| | - James Larson
- Department of Chemistry and Biochemistry, Montana State University, Bozeman, Montana, USA
| | | | - Florence Mus
- Institute of Biological Chemistry, Washington State University, Pullman, Washington, USA
- Department of Chemistry and Biochemistry, University of Oklahoma, Norman, Oklahoma, USA
| | - Tamara Flusche
- Department of Chemistry and Biochemistry, University of Oklahoma, Norman, Oklahoma, USA
| | - Arnab Kumar Nath
- Department of Chemistry and Biochemistry, Montana State University, Bozeman, Montana, USA
| | | | - Simone Raugei
- Physical Sciences Division, Pacific Northwest National Laboratory, Richland, Washington, USA
| | - Brian Bothner
- Department of Chemistry and Biochemistry, Montana State University, Bozeman, Montana, USA
| | - Jennifer L. DuBois
- Department of Chemistry and Biochemistry, Montana State University, Bozeman, Montana, USA
| | - John W. Peters
- Institute of Biological Chemistry, Washington State University, Pullman, Washington, USA
- Department of Chemistry and Biochemistry, University of Oklahoma, Norman, Oklahoma, USA
- Physical Sciences Division, Pacific Northwest National Laboratory, Richland, Washington, USA
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3
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Tokmina-Lukaszewska M, Huang Q, Berry L, Kallas H, Peters JW, Seefeldt LC, Raugei S, Bothner B. Fe protein docking transduces conformational changes to MoFe nitrogenase active site in a nucleotide-dependent manner. Commun Chem 2023; 6:254. [PMID: 37980448 PMCID: PMC10657360 DOI: 10.1038/s42004-023-01046-6] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/07/2023] [Accepted: 10/30/2023] [Indexed: 11/20/2023] Open
Abstract
The reduction of dinitrogen to ammonia catalyzed by nitrogenase involves a complex series of events, including ATP hydrolysis, electron transfer, and activation of metal clusters for N2 reduction. Early evidence shows that an essential part of the mechanism involves transducing information between the nitrogenase component proteins through conformational dynamics. Here, millisecond time-resolved hydrogen-deuterium exchange mass spectrometry was used to unravel peptide-level protein motion on the time scale of catalysis of Mo-dependent nitrogenase from Azotobacter vinelandii. Normal mode analysis calculations complemented this data, providing insights into the specific signal transduction pathways that relay information across protein interfaces at distances spanning 100 Å. Together, these results show that conformational changes induced by protein docking are rapidly transduced to the active site, suggesting a specific mechanism for activating the metal cofactor in the enzyme active site.
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Affiliation(s)
| | - Qi Huang
- Physical and Computational Sciences Directorate, Pacific Northwest National Laboratory, Richland, WA, USA
| | - Luke Berry
- Department of Chemistry and Biochemistry, Montana State University, Bozeman, MT, USA
| | - Hayden Kallas
- Department of Chemistry and Biochemistry, Utah State University, Logan, UT, USA
| | - John W Peters
- Institute of Biological Chemistry, The University of Oklahoma, Norman, OK, USA
| | - Lance C Seefeldt
- Department of Chemistry and Biochemistry, Utah State University, Logan, UT, USA
| | - Simone Raugei
- Physical and Computational Sciences Directorate, Pacific Northwest National Laboratory, Richland, WA, USA
| | - Brian Bothner
- Department of Chemistry and Biochemistry, Montana State University, Bozeman, MT, USA.
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4
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Baer MD, Raugei S, Shanklin J. Regioselectivity of the Thunbergia alata Δ6-16:0-acyl carrier protein desaturase by molecular dynamics. Biophys J 2023; 122:184a. [PMID: 36782875 DOI: 10.1016/j.bpj.2022.11.1136] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/12/2023] Open
Affiliation(s)
- Marcel D Baer
- Physical and Computational Sciences Directorate, Pacific Northwest National Laboratory, Richland, WA, USA
| | - Simone Raugei
- Pacific Northwest National Laboratory, Richland, WA, USA
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5
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Lukoyanov DA, Yang ZY, Shisler K, Peters JW, Raugei S, Dean DR, Seefeldt LC, Hoffman BM. A Conformational Equilibrium in the Nitrogenase MoFe Protein with an α-V70I Amino Acid Substitution Illuminates the Mechanism of H 2 Formation. Faraday Discuss 2023. [PMID: 37021412 DOI: 10.1039/d2fd00153e] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/15/2023]
Abstract
Study of α-V70I-substituted nitrogenase MoFe protein identified Fe6 of FeMo-cofactor (Fe7S9MoC-homocitrate) as a critical N2 binding/reduction site. Freeze-trapping this enzyme during Ar turnover captured the key catalytic intermediate in high...
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Affiliation(s)
- Dmitriy A Lukoyanov
- Department of Chemistry and Molecular Biosciences, Northwestern University, Evanston, Illinois 60208, USA
| | - Zhi-Yong Yang
- Department of Chemistry and Biochemistry, Utah State University, Logan, Utah 84322, USA
| | - Krista Shisler
- Institute of Biological Sciences, Washington State University, Pullman, Washington, 99164, USA
| | - John W Peters
- Department of Chemistry and Biochemistry, University of Oklahoma, Norman, Oklahoma, 73019, USA
| | - Simone Raugei
- Physical and Computational Sciences Directorate, Pacific Northwest National Laboratory, Richland, Washington, 99352, USA
| | - Dennis R Dean
- Biochemistry Department, Virginia Tech, Blacksburg, Virginia, 24061, USA
| | - Lance C Seefeldt
- Department of Chemistry and Biochemistry, Utah State University, Logan, Utah 84322, USA
| | - Brian M Hoffman
- Department of Chemistry and Molecular Biosciences, Northwestern University, Evanston, Illinois 60208, USA
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6
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Kim H, Hauner D, Laureanti JA, Agustin K, Raugei S, Kumar N. Mechanistic investigation of SARS-CoV-2 main protease to accelerate design of covalent inhibitors. Sci Rep 2022; 12:21037. [PMID: 36470873 PMCID: PMC9722715 DOI: 10.1038/s41598-022-23570-6] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Track Full Text] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/29/2022] [Accepted: 11/02/2022] [Indexed: 12/12/2022] Open
Abstract
Targeted covalent inhibition represents one possible strategy to block the function of SARS-CoV-2 Main Protease (MPRO), an enzyme that plays a critical role in the replication of the novel SARS-CoV-2. Toward the design of covalent inhibitors, we built a covalent inhibitor dataset using deep learning models followed by high throughput virtual screening of these candidates against MPRO. Two top-ranking inhibitors were selected for mechanistic investigations-one with an activated ester warhead that has a piperazine core and the other with an acrylamide warhead. Specifically, we performed a detailed analysis of the free energetics of covalent inhibition by hybrid quantum mechanics/molecular mechanics simulations. Cleavage of a fragment of the non-structured protein (NSP) from the SARS-CoV-2 genome was also simulated for reference. Simulations show that both candidates form more stable enzyme-inhibitor (E-I) complexes than the chosen NSP. It was found that both the NSP fragment and the activated ester inhibitor react with CYS145 of MPRO in a concerted manner, whereas the acrylamide inhibitor follows a stepwise mechanism. Most importantly, the reversible reaction and the subsequent hydrolysis reaction from E-I complexes are less probable when compared to the reactions with an NSP fragment, showing promise for these candidates to be the base for efficient MPRO inhibitors.
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Affiliation(s)
- Hoshin Kim
- grid.451303.00000 0001 2218 3491Physical and Computational Science Directorate, Pacific Northwest National Laboratory, Richland, WA 99352 USA
| | - Darin Hauner
- grid.451303.00000 0001 2218 3491Earth and Biological Science Directorate, Pacific Northwest National Laboratory, Richland, WA 99352 USA
| | - Joseph A. Laureanti
- grid.451303.00000 0001 2218 3491Physical and Computational Science Directorate, Pacific Northwest National Laboratory, Richland, WA 99352 USA
| | - Kruel Agustin
- grid.451303.00000 0001 2218 3491Earth and Biological Science Directorate, Pacific Northwest National Laboratory, Richland, WA 99352 USA
| | - Simone Raugei
- grid.451303.00000 0001 2218 3491Physical and Computational Science Directorate, Pacific Northwest National Laboratory, Richland, WA 99352 USA
| | - Neeraj Kumar
- grid.451303.00000 0001 2218 3491Earth and Biological Science Directorate, Pacific Northwest National Laboratory, Richland, WA 99352 USA
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7
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Makoś MZ, Gurunathan PK, Raugei S, Kowalski K, Glezakou VA, Rousseau R. Modeling Absolute Redox Potentials of Ferrocene in the Condensed Phase. J Phys Chem Lett 2022; 13:10005-10010. [PMID: 36264148 DOI: 10.1021/acs.jpclett.2c02447] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 06/16/2023]
Abstract
Absolute thermodynamic quantities for critical chemical reactions are needed to determine the role of solvents and reactive environments in catalysis and electrocatalysis. Theoretical methods can provide such quantification but are often hindered by the innate complexity of electron correlation and dynamic relaxation of solvent environments. We present and validate a protocol for calculating the redox potentials of the ferrocene/ferrocenium redox pair in acetonitrile. Equation-of-motion and effective fragment potential (EFP) methods are used to characterize the adiabatic and vertical ionization potentials as well as the electron affinity processes. We benchmark molecular mechanics against the EFP model to show the differences in the ferrocene electronic polarizability in two redox states. Our best estimate of the redox potential (4.94 eV) agrees well with the experimental value (4.93 eV). This demonstrates the ability of modern computational methods to predict absolute redox potentials quantitatively and to quantify the correlation of dynamic effects, which underlie their origin.
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Affiliation(s)
- Małgorzata Zofia Makoś
- Physical Sciences Division, Pacific Northwest National Laboratory, Richland, Washington 99354, United States
| | - Pradeep Kumar Gurunathan
- Physical Sciences Division, Pacific Northwest National Laboratory, Richland, Washington 99354, United States
| | - Simone Raugei
- Physical Sciences Division, Pacific Northwest National Laboratory, Richland, Washington 99354, United States
| | - Karol Kowalski
- Physical Sciences Division, Pacific Northwest National Laboratory, Richland, Washington 99354, United States
| | | | - Roger Rousseau
- Physical Sciences Division, Pacific Northwest National Laboratory, Richland, Washington 99354, United States
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8
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Lukoyanov DA, Yang ZY, Pérez-González A, Raugei S, Dean DR, Seefeldt LC, Hoffman BM. 13C ENDOR Characterization of the Central Carbon within the Nitrogenase Catalytic Cofactor Indicates That the CFe 6 Core Is a Stabilizing "Heart of Steel". J Am Chem Soc 2022; 144:18315-18328. [PMID: 36166637 DOI: 10.1021/jacs.2c06149] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Abstract
Substrates and inhibitors of Mo-dependent nitrogenase bind and react at Fe ions of the active-site FeMo-cofactor [7Fe-9S-C-Mo-homocitrate] contained within the MoFe protein α-subunit. The cofactor contains a CFe6 core, a carbon centered within a trigonal prism of six Fe, whose role in catalysis is unknown. Targeted 13C labeling of the carbon enables electron-nuclear double resonance (ENDOR) spectroscopy to sensitively monitor the electronic properties of the Fe-C bonds and the spin-coupling scheme adopted by the FeMo-cofactor metal ions. This report compares 13CFe6 ENDOR measurements for (i) the wild-type protein resting state (E0; α-Val70) to those of (ii) α-Ile70, (iii) α-Ala70-substituted proteins; (iv) crystallographically characterized CO-inhibited "hi-CO" state; (v) E4(4H) Janus intermediate, activated for N2 binding/reduction by accumulation of 4[e-/H+]; (vi) E4(2H)* state containing a doubly reduced FeMo-cofactor without Fe-bound substrates; and (vii) propargyl alcohol reduction intermediate having allyl alcohol bound as a ferracycle to FeMo-cofactor Fe6. All states examined, both S = 1/2 and 3/2 exhibited near-zero 13C isotropic hyperfine coupling constants, Ca = [-1.3 ↔ +2.7] MHz. Density functional theory computations and natural bond orbital analysis of the Fe-C bonds show that this occurs because a (3 spin-up/3 spin-down) spin-exchange configuration of CFe6 Fe-ion spins produces cancellation of large spin-transfers to carbon in each Fe-C bond. Previous X-ray diffraction and DFT both indicate that trigonal-prismatic geometry around carbon is maintained with high precision in all these states. The persistent structure and Fe-C bonding of the CFe6 core indicate that it does not provide a functionally dynamic (hemilabile) "beating heart"─instead it acts as "a heart of steel", stabilizing the structure of the FeMo-cofactor-active site during nitrogenase catalysis.
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Affiliation(s)
- Dmitriy A Lukoyanov
- Departments of Chemistry and Molecular Biosciences, Northwestern University, Evanston, Illinois60208, United States
| | - Zhi-Yong Yang
- Department of Chemistry and Biochemistry, Utah State University, Logan, Utah84322, United States
| | - Ana Pérez-González
- Biochemistry Department, Virginia Tech, Blacksburg, Virginia24061, United States
| | - Simone Raugei
- Physical and Computational Sciences Directorate, Pacific Northwest National Laboratory, Richland, Washington99352, United States
| | - Dennis R Dean
- Biochemistry Department, Virginia Tech, Blacksburg, Virginia24061, United States
| | - Lance C Seefeldt
- Department of Chemistry and Biochemistry, Utah State University, Logan, Utah84322, United States
| | - Brian M Hoffman
- Departments of Chemistry and Molecular Biosciences, Northwestern University, Evanston, Illinois60208, United States
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9
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Dunn PL, Barona M, Johnson SI, Raugei S, Bullock RM. Hydrogen Atom Abstraction from an Os II(NH 3) 2 Complex Generates an Os IV(NH 2) 2 Complex: Experimental and Computational Analysis of the N-H Bond Dissociation Free Energies and Reactivity. Inorg Chem 2022; 61:15325-15334. [PMID: 36121917 DOI: 10.1021/acs.inorgchem.2c00708] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Abstract
Double hydrogen atom abstraction from (TMP)OsII(NH3)2 (TMP = tetramesitylporphyrin) with phenoxyl or nitroxyl radicals leads to (TMP)OsIV(NH2)2. This unusual bis(amide) complex is diamagnetic and displays an N-H resonance at 12.0 ppm in its 1H NMR spectrum. 1H-15N correlation experiments identified a 15N NMR spectroscopic resonance signal at -267 ppm. Experimental reactivity studies and density functional theory calculations support relatively weak N-H bonds of 73.3 kcal/mol for (TMP)OsII(NH3)2 and 74.2 kcal/mol for (TMP)OsIII(NH3)(NH2). Cyclic voltammetry experiments provide an estimate of the pKa of [(TMP)OsIII(NH3)2]+. In the presence of Barton's base, a current enhancement is observed at the Os(III/II) couple, consistent with an ECE event. Spectroscopic experiments confirmed (TMP)OsIV(NH2)2 as the product of bulk electrolysis. Double hydrogen atom abstraction is influenced by π donation from the amides of (TMP)OsIV(NH2)2 into the d orbitals of the Os center, favoring the formation of (TMP)OsIV(NH2)2 over N-N coupling. This π donation leads to a Jahn-Teller distortion that splits the energy levels of the dxz and dyz orbitals of Os, results in a low-spin electron configuration, and leads to minimal aminyl character on the N atoms, rendering (TMP)OsIV(NH2)2 unreactive toward amide-amide coupling.
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Affiliation(s)
- Peter L Dunn
- Center for Molecular Electrocatalysis, Pacific Northwest National Laboratory, Richland, Washington 99352, United States
| | - Melissa Barona
- Center for Molecular Electrocatalysis, Pacific Northwest National Laboratory, Richland, Washington 99352, United States
| | - Samantha I Johnson
- Center for Molecular Electrocatalysis, Pacific Northwest National Laboratory, Richland, Washington 99352, United States
| | - Simone Raugei
- Center for Molecular Electrocatalysis, Pacific Northwest National Laboratory, Richland, Washington 99352, United States
| | - R Morris Bullock
- Center for Molecular Electrocatalysis, Pacific Northwest National Laboratory, Richland, Washington 99352, United States
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10
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Hutchison P, Rice PS, Warburton RE, Raugei S, Hammes-Schiffer S. Multilevel Computational Studies Reveal the Importance of Axial Ligand for Oxygen Reduction Reaction on Fe-N-C Materials. J Am Chem Soc 2022; 144:16524-16534. [PMID: 36001092 DOI: 10.1021/jacs.2c05779] [Citation(s) in RCA: 26] [Impact Index Per Article: 13.0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/09/2023]
Abstract
The systematic improvement of Fe-N-C materials for fuel cell applications has proven challenging, due in part to an incomplete atomistic understanding of the oxygen reduction reaction (ORR) under electrochemical conditions. Herein, a multilevel computational approach, which combines ab initio molecular dynamics simulations and constant potential density functional theory calculations, is used to assess proton-coupled electron transfer (PCET) processes and adsorption thermodynamics of key ORR intermediates. These calculations indicate that the potential-limiting step for ORR on Fe-N-C materials is the formation of the FeIII-OOH intermediate. They also show that an active site model with a water molecule axially ligated to the iron center throughout the catalytic cycle produces results that are consistent with the experimental measurements. In particular, reliable prediction of the ORR onset potential and the Fe(III/II) redox potential associated with the conversion of FeIII-OH to FeII and desorbed H2O requires an axial H2O co-adsorbed to the iron center. The observation of a five-coordinate rather than four-coordinate active site has significant implications for the thermodynamics and mechanism of ORR. These findings highlight the importance of solvent-substrate interactions and surface charge effects for understanding the PCET reaction mechanisms and transition-metal redox couples under realistic electrochemical conditions.
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Affiliation(s)
- Phillips Hutchison
- Department of Chemistry, Yale University, New Haven, Connecticut 06520, United States
| | - Peter S Rice
- Center for Molecular Electrocatalysis, Pacific Northwest National Laboratory, Richland, Washington 99352, United States
| | - Robert E Warburton
- Department of Chemistry, Yale University, New Haven, Connecticut 06520, United States
| | - Simone Raugei
- Center for Molecular Electrocatalysis, Pacific Northwest National Laboratory, Richland, Washington 99352, United States
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11
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Cook BJ, Barona M, Johnson SI, Raugei S, Bullock RM. Weakening the N-H Bonds of NH 3 Ligands: Triple Hydrogen-Atom Abstraction to Form a Chromium(V) Nitride. Inorg Chem 2022; 61:11165-11172. [PMID: 35829761 DOI: 10.1021/acs.inorgchem.2c01115] [Citation(s) in RCA: 4] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Abstract
Weakening and cleaving N-H bonds is crucial for improving molecular ammonia (NH3) oxidation catalysts. We report the synthesis and H-atom-abstraction reaction of bis(ammonia)chromium porphyrin complexes Cr(TPP)(NH3)2 and Cr(TMP)(NH3)2 (TPP = 5,10,15,20-tetraphenyl-meso-porphyrin and TMP = 5,10,15,20-tetramesityl-meso-porphyrin) using bulky aryloxyl radicals. The triple H-atom-abstraction reaction results in the formation of CrV(por)(≡N), with the nitride derived from NH3, as indicated by UV-vis and IR and single-crystal structural determination of Cr(TPP)(≡N). Subsequent oxidation of this chromium(V) nitrido complex results in the formation of CrIII(por), with scission of the Cr≡N bond. Computational analysis illustrates the progression from CrII to CrV and evaluates the energetics of abstracting H atoms from CrII-NH3 to generate CrV≡N. The formation and isolation of CrV(por)(≡N) illustrates the stability of these species and the need to chemically activate the nitride ligand for atom transfer or N-N coupling reactivity.
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Affiliation(s)
- Brian J Cook
- Center for Molecular Electrocatalysis, Pacific Northwest National Laboratory, Richland, Washington 99352, United States
| | - Melissa Barona
- Center for Molecular Electrocatalysis, Pacific Northwest National Laboratory, Richland, Washington 99352, United States
| | - Samantha I Johnson
- Center for Molecular Electrocatalysis, Pacific Northwest National Laboratory, Richland, Washington 99352, United States
| | - Simone Raugei
- Center for Molecular Electrocatalysis, Pacific Northwest National Laboratory, Richland, Washington 99352, United States
| | - R Morris Bullock
- Center for Molecular Electrocatalysis, Pacific Northwest National Laboratory, Richland, Washington 99352, United States
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12
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Kim H, Srividya N, Lange I, Huchala EW, Ginovska B, Lange BM, Raugei S. Determinants of Selectivity for the Formation of Monocyclic and Bicyclic Products in Monoterpene Synthases. ACS Catal 2022. [DOI: 10.1021/acscatal.2c01836] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
Affiliation(s)
- Hoshin Kim
- Physical and Computational Sciences Division, Pacific Northwest National Laboratory, Richland, Washington 99352, United States
| | - Narayanan Srividya
- Institute of Biological Chemistry and M. J. Murdock Metabolomics Laboratory, Washington State University, Pullman, Washington 99164-7411, United States
| | - Iris Lange
- Institute of Biological Chemistry and M. J. Murdock Metabolomics Laboratory, Washington State University, Pullman, Washington 99164-7411, United States
| | - Eden W. Huchala
- Physical and Computational Sciences Division, Pacific Northwest National Laboratory, Richland, Washington 99352, United States
- Department of Biochemistry, University of Washington, Seattle, Washington 98195, United States
| | - Bojana Ginovska
- Physical and Computational Sciences Division, Pacific Northwest National Laboratory, Richland, Washington 99352, United States
| | - B. Markus Lange
- Institute of Biological Chemistry and M. J. Murdock Metabolomics Laboratory, Washington State University, Pullman, Washington 99164-7411, United States
| | - Simone Raugei
- Physical and Computational Sciences Division, Pacific Northwest National Laboratory, Richland, Washington 99352, United States
- Institute of Biological Chemistry and M. J. Murdock Metabolomics Laboratory, Washington State University, Pullman, Washington 99164-7411, United States
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13
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Abstract
Pendant amines play an invaluable role in chemical reactivity, especially for molecular catalysts based on earth-abundant metals. As inspired by [FeFe]-hydrogenases, which contain a pendant amine positioned for cooperative bifunctionality, synthetic catalysts have been developed to emulate this multifunctionality through incorporation of a pendant amine in the second coordination sphere. Cyclic diphosphine ligands containing two amines serve as the basis for a class of catalysts that have been extensively studied and used to demonstrate the impact of a pendant base. These 1,5-diaza-3,7-diphosphacyclooctanes, now often referred to as "P2N2" ligands, have profound effects on the reactivity of many catalysts. The resulting [Ni(PR2NR'2)2]2+ complexes are electrocatalysts for both the oxidation and production of H2. Achieving the optimal benefit of the pendant amine requires that it has suitable basicity and is properly positioned relative to the metal center. In addition to the catalytic efficacy demonstrated with [Ni(PR2NR'2)2]2+ complexes for the oxidation and production of H2, catalysts with diphosphine ligands containing pendant amines have also been demonstrated for several metals for many different reactions, both in solution and immobilized on surfaces. The impact of pendant amines in catalyst design continues to expand.
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14
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Guy JE, Cai Y, Baer MD, Whittle E, Chai J, Yu XH, Lindqvist Y, Raugei S, Shanklin J. Regioselectivity mechanism of the Thunbergia alata Δ6-16:0-acyl carrier protein desaturase. Plant Physiol 2022; 188:1537-1549. [PMID: 34893899 PMCID: PMC8896614 DOI: 10.1093/plphys/kiab577] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 11/09/2021] [Accepted: 11/13/2021] [Indexed: 05/12/2023]
Abstract
Plant plastidial acyl-acyl carrier protein (ACP) desaturases are a soluble class of diiron-containing enzymes that are distinct from the diiron-containing integral membrane desaturases found in plants and other organisms. The archetype of this class is the stearoyl-ACP desaturase which converts stearoyl-ACP into oleoyl (18:1Δ9cis)-ACP. Several variants expressing distinct regioselectivity have been described including a Δ6-16:0-ACP desaturase from black-eyed Susan vine (Thunbergia alata). We solved a crystal structure of the T. alata desaturase at 2.05 Å resolution. Using molecular dynamics (MD) simulations, we identified a low-energy complex between 16:0-ACP and the desaturase that would position C6 and C7 of the acyl chain adjacent to the diiron active site. The model complex was used to identify mutant variants that could convert the T. alata Δ6 desaturase to Δ9 regioselectivity. Additional modeling between ACP and the mutant variants confirmed the predicted regioselectivity. To validate the in-silico predictions, we synthesized two variants of the T. alata desaturase and analyzed their reaction products using gas chromatography-coupled mass spectrometry. Assay results confirmed that mutants designed to convert T. alata Δ6 to Δ9 selectivity exhibited the predicted changes. In complementary experiments, variants of the castor desaturase designed to convert Δ9 to Δ6 selectivity lost some of their Δ9 desaturation ability and gained the ability to desaturate at the Δ6 position. The computational workflow for revealing the mechanistic understanding of regioselectivity presented herein lays a foundation for designing acyl-ACP desaturases with novel selectivities to increase the diversity of monoenes available for bioproduct applications.
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Affiliation(s)
- Jodie E Guy
- Division of Molecular Structural Biology, Department of Medical Biochemistry and Biophysics, Karolinska Institutet, S-171 77 Stockholm, Sweden
| | - Yuanheng Cai
- Biochemistry and Cell Biology Department, Stony Brook University, Stony Brook, New York 11794, USA
| | - Marcel D Baer
- Physical and Computational Sciences Directorate, Pacific Northwest National Laboratory, Richland, Washington 99354, USA
| | - Edward Whittle
- Brookhaven National Laboratory, Department of Biology, Upton, New York 11973, USA
| | - Jin Chai
- Brookhaven National Laboratory, Department of Biology, Upton, New York 11973, USA
| | - Xiao-Hong Yu
- Biochemistry and Cell Biology Department, Stony Brook University, Stony Brook, New York 11794, USA
| | - Ylva Lindqvist
- Division of Molecular Structural Biology, Department of Medical Biochemistry and Biophysics, Karolinska Institutet, S-171 77 Stockholm, Sweden
| | - Simone Raugei
- Physical and Computational Sciences Directorate, Pacific Northwest National Laboratory, Richland, Washington 99354, USA
| | - John Shanklin
- Brookhaven National Laboratory, Department of Biology, Upton, New York 11973, USA
- Author for communication:
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15
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Barona M, Johnson SI, Mbea M, Bullock RM, Raugei S. Computational Investigations of the Reactivity of Metalloporphyrins for Ammonia Oxidation. Top Catal 2022. [DOI: 10.1007/s11244-021-01511-3] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [What about the content of this article? (0)] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/02/2023]
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16
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Johnson SI, Baer MD, Raugei S. Protonation of Serine in Gas and Condensed and Microsolvated States in Aqueous Solution. J Phys Chem A 2021; 126:44-52. [PMID: 34941278 DOI: 10.1021/acs.jpca.1c08795] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Abstract
Identification of molecules and elucidation of their chemical structure are ubiquitous problems in chemistry. Mass spectrometry (MS) can be used due to its sensitivity and versatility. For detection to occur, analytes must be ionized and transferred to the gas phase. Soft ionization processes such as electrospray ionization are popular; however, resulting microsolvated phases can alter the chemistry of analytes and therefore detection and identification. To understand these processes, we use computational methods to probe the ionization propensity of serine in the gas phase, aqueous microsolvated clusters, and aqueous solution. We show that the tautomeric form of serine is altered by the presence of water, as five water molecules can stabilize the zwitterionic tautomer. Inclusion of cosolutes such as ions can stabilize the zwitterion with as few as one or two water molecules present. We demonstrate that ionization propensity, as measured by gas phase bacisity, can increase by over 100 kJ/mol when placed in a small water-serine cluster, showing the sensitivity of the chemistry of microsolvated analytes. Finally, detailed analysis reveals that small droplets (less than seven water molecules) are extremely sensitive to addition of further water molecules. Beyond this limit, structural and electronic properties change little with droplet size.
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Affiliation(s)
- Samantha I Johnson
- Pacific Northwest National Laboratory, Richland, Washington 99354, United States
| | - Marcel D Baer
- Pacific Northwest National Laboratory, Richland, Washington 99354, United States
| | - Simone Raugei
- Pacific Northwest National Laboratory, Richland, Washington 99354, United States
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17
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Tzeli D, Raugei S, Xantheas SS. Quantitative Account of the Bonding Properties of a Rubredoxin Model Complex [Fe(SCH 3) 4] q, q = -2, -1, +2, +3. J Chem Theory Comput 2021; 17:6080-6091. [PMID: 34546757 DOI: 10.1021/acs.jctc.1c00485] [Citation(s) in RCA: 3] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
Abstract
Iron-sulfur clusters play important roles in biology as parts of electron-transfer chains and catalytic cofactors. Here, we report a detailed computational analysis of a structural model of the simplest natural iron-sulfur cluster of rubredoxin and its cationic counterparts. Specifically, we investigated adiabatic reduction energies, dissociation energies, and bonding properties of the low-lying electronic states of the complexes [Fe(SCH3)4]2-/1-/2+/3+ using multireference (CASSCF, MRCISD), and coupled cluster [CCSD(T)] methodologies. We show that the nature of the Fe-S chemical bond and the magnitude of the ionization potentials in the anionic and cationic [Fe(SCH3)4] complexes offer a physical rationale for the relative stabilization, structure, and speciation of these complexes. Anionic and cationic complexes present different types of chemical bonds: prevalently ionic in [Fe(SCH3)4]2-/1- complexes and covalent in [Fe(SCH3)4]2+/3+ complexes. The ionic bonds result in an energy gain for the transition [Fe(SCH3)4]2- → [Fe(SCH3)4]- (i.e., FeII → FeIII) of 1.5 eV, while the covalent bonds result in an energy loss for the transition [Fe(SCH3)4]2+ → [Fe(SCH3)4]3+ of 16.6 eV, almost half of the ionization potential of Fe2+. The ionic versus covalent bond character influences the Fe-S bond strength and length, that is, ionic Fe-S bonds are longer than covalent ones by about 0.2 Å (for FeII) and 0.04 Å (for FeII). Finally, the average Fe-S heterolytic bond strength is 6.7 eV (FeII) and 14.6 eV (FeIII) at the RCCSD(T) level of theory.
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Affiliation(s)
- Demeter Tzeli
- Laboratory of Physical Chemistry, Department of Chemistry, National and Kapodistrian University of Athens, Panepistimiopolis Zografou, Athens 157 84, Greece.,Theoretical and Physical Chemistry Institute, National Hellenic Research Foundation, 48 Vassileos Constantinou Avenue, Athens 116 35, Greece
| | - Simone Raugei
- Physical Sciences Division, Pacific Northwest National Laboratory, 902 Battelle Boulevard, P.O. Box 999, MS K1-83, Richland, Washington 99352, United States
| | - Sotiris S Xantheas
- Advanced Computing, Mathematics and Data Division, Pacific Northwest National Laboratory, 902 Battelle Boulevard, P.O. Box 999, MS K1-83, Richland, Washington 99352, United States.,Department of Chemistry, University of Washington, Seattle, Washington 98195, United States
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18
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Patwardhan A, Sarangi R, Ginovska B, Raugei S, Ragsdale SW. Nickel-Sulfonate Mode of Substrate Binding for Forward and Reverse Reactions of Methyl-SCoM Reductase Suggest a Radical Mechanism Involving Long-Range Electron Transfer. J Am Chem Soc 2021; 143:5481-5496. [PMID: 33761259 DOI: 10.1021/jacs.1c01086] [Citation(s) in RCA: 7] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/20/2023]
Abstract
Methyl-coenzyme M reductase (MCR) catalyzes both the synthesis and the anaerobic oxidation of methane (AOM). Its catalytic site contains Ni at the core of cofactor F430. The Ni ion, in its low-valent Ni(I) state, lights the fuse leading to homolysis of the C-S bond of methyl-coenzyme M (methyl-SCoM) to generate a methyl radical, which abstracts a hydrogen atom from coenzyme B (HSCoB) to generate methane and the mixed disulfide CoMSSCoB. Direct reversal of this reaction activates methane to initiate anaerobic methane oxidation. On the basis of the crystal structures, which reveal a Ni-thiol interaction between Ni(II)-MCR and inhibitor CoMSH, a Ni(I)-thioether complex with substrate methyl-SCoM has been transposed to canonical MCR mechanisms. Similarly, a Ni(I)-disulfide with CoMSSCoB is proposed for the reverse reaction. However, this Ni(I)-sulfur interaction poses a conundrum for the proposed hydrogen-atom abstraction reaction because the >6 Å distance between the thiol group of SCoB and the thiol of SCoM observed in the structures appears to be too long for such a reaction. The spectroscopic, kinetic, structural, and computational studies described here establish that both methyl-SCoM and CoMSSCoB bind to the active Ni(I) state of MCR through their sulfonate groups, forming a hexacoordinate Ni(I)-N/O complex, not Ni(I)-S. These studies rule out direct Ni(I)-sulfur interactions in both substrate-bound states. As a solution to the mechanistic conundrum, we propose that both the forward and the reverse MCR reactions emanate through long-range electron transfer from the Ni(I)-sulfonate complexes with methyl-SCoM and CoMSSCoB, respectively.
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Affiliation(s)
- Anjali Patwardhan
- Department of Biological Chemistry, University of Michigan Medical School, Ann Arbor, Michigan 48103, United States
| | - Ritimukta Sarangi
- Stanford Synchrotron Radiation Lightsource, SLAC National Accelerator Laboratory, Menlo Park, California 94025, United States
| | - Bojana Ginovska
- Pacific Northwest National Laboratory, Richland, Washington 99354, United States
| | - Simone Raugei
- Pacific Northwest National Laboratory, Richland, Washington 99354, United States
| | - Stephen W Ragsdale
- Department of Biological Chemistry, University of Michigan Medical School, Ann Arbor, Michigan 48103, United States
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19
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Baer MD, Shanklin J, Raugei S. Atomistic insight on structure and dynamics of spinach acyl carrier protein with substrate length. Biophys J 2021; 120:3841-3853. [PMID: 33631202 PMCID: PMC8456182 DOI: 10.1016/j.bpj.2020.12.036] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/11/2020] [Revised: 12/08/2020] [Accepted: 12/10/2020] [Indexed: 01/02/2023] Open
Abstract
The plant acyl-acyl carrier protein (ACP) desaturases are a family of soluble enzymes that convert saturated fatty acyl-ACPs into their cis-monounsaturated equivalents in an oxygen-dependent reaction. These enzymes play a key role in biosynthesis of monounsaturated fatty acids in plants. ACPs are central proteins in fatty acid biosynthesis that deliver acyl chains to desaturases. They have been reported to show a varying degree of local dynamics and structural variability depending on the acyl chain size. It has been suggested that substrate-specific changes in ACP structure and dynamics have a crucial impact on the desaturase enzymatic activity. Using molecular dynamics simulations, we investigated the intrinsic solution structure and dynamics of ACP from spinach with four different acyl chains: capric (C10), myristic (C14), palmitic (C16), and stearic (C18) acids. We found that the fatty acids can adopt two distinct structural binding motifs, which feature different binding free energies and influence the ACP dynamics in a different manner. Docking simulations of ACP to castor Δ9-desaturase and ivy Δ4-desaturase suggest that ACP desaturase interactions could lead to a preferential selection between the motifs.
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Affiliation(s)
- Marcel D Baer
- Pacific Northwest National Laboratory, Physical and Computational Sciences Directorate, Richland, Washington.
| | - John Shanklin
- Biology Department, Brookhaven National Laboratory, Upton, New York
| | - Simone Raugei
- Pacific Northwest National Laboratory, Physical and Computational Sciences Directorate, Richland, Washington
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20
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Baer MD, Shanklin J, Raugei S. Atomistic Insights on Structure and Dynamics of Spinach Acyl Carrier Protein with Substrate Length. Biophys J 2021. [DOI: 10.1016/j.bpj.2020.11.941] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/25/2022] Open
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21
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Fantuzzi F, Nascimento MAC, Ginovska B, Bullock RM, Raugei S. Splitting of multiple hydrogen molecules by bioinspired diniobium metal complexes: a DFT study. Dalton Trans 2021; 50:840-849. [PMID: 33237062 DOI: 10.1039/d0dt03411h] [Citation(s) in RCA: 4] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/01/2023]
Abstract
Splitting of molecular hydrogen (H2) into bridging and terminal hydrides is a common step in transition metal chemistry. Herein, we propose a novel organometallic platform for cleavage of multiple H2 molecules, which combines metal centers capable of stabilizing multiple oxidation states, and ligands bearing positioned pendant basic groups. Using quantum chemical modeling, we show that low-valent, early transition metal diniobium(ii) complexes with diphosphine ligands featuring pendant amines can favorably uptake up to 8 hydrogen atoms, and that the energetics are favored by the formation of intramolecular dihydrogen bonds. This result suggests new possible strategies for the development of hydrogen scavenger molecules that are able to perform reversible splitting of multiple H2 molecules.
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Affiliation(s)
- Felipe Fantuzzi
- Instituto de Química, Universidade Federal do Rio de Janeiro, Av. Athos da Silveira Ramos 149, 21941.909, Rio de Janeiro, Brazil.
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22
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Abstract
Cataytic bias refers to the propensity of a reaction catalyst to effect a different rate acceleration in one direction versus the other in a chemical reaction under non-equilibrium conditions. In biocatalysis, the inherent bias of an enzyme is often advantagous to augment the innate thermodynamics of a reaction to promote efficiency and fidelity in the coordination of catabolic and anabolic pathways. In industrial chemical catalysis a directional cataltyic bias is a sought after property in facilitating the engineering of systems that couple catalysis with harvest and storage of for example fine chemicals or energy compounds. Interestingly, there is little information about catalytic bias in biocatalysis likely in large part due to difficulties in developing tractible assays sensitive enough to study detailed kinetics. For oxidation-reduction reactions, colorimetric redox indicators exist in a range of reduction potentials to provide a mechanism to study both directions of reactions in a fairly facile manner. The current short review attempts to define catalytic bias conceptually and to develop model systems for defining the parameters that control catalytic bias in enzyme catalyzed oxidation-reduction catalysis.
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Affiliation(s)
- David W Mulder
- Biosciences Center, National Renewable Energy Laboratory, Golden, CO 80401, USA
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23
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Lukoyanov DA, Yang ZY, Dean DR, Seefeldt LC, Raugei S, Hoffman BM. Electron Redistribution within the Nitrogenase Active Site FeMo-Cofactor During Reductive Elimination of H 2 to Achieve N≡N Triple-Bond Activation. J Am Chem Soc 2020; 142:21679-21690. [PMID: 33326225 DOI: 10.1021/jacs.0c07914] [Citation(s) in RCA: 19] [Impact Index Per Article: 4.8] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
Abstract
Nitrogen fixation by nitrogenase begins with the accumulation of four reducing equivalents at the active-site FeMo-cofactor (FeMo-co), generating a state (denoted E4(4H)) with two [Fe-H-Fe] bridging hydrides. Recently, photolytic reductive elimination (re) of the E4(4H) hydrides showed that enzymatic re of E4(4H) hydride yields an H2-bound complex (E4(H2,2H)), in a process corresponding to a formal 2-electron reduction of the metal-ion core of FeMo-co. The resulting electron-density redistribution from Fe-H bonds to the metal ions themselves enables N2 to bind with concomitant H2 release, a process illuminated here by QM/MM molecular dynamics simulations. What is the nature of this redistribution? Although E4(H2,2H) has not been trapped, cryogenic photolysis of E4(4H) provides a means to address this question. Photolysis of E4(4H) causes hydride-re with release of H2, generating doubly reduced FeMo-co (denoted E4(2H)*), the extreme limit of the electron-density redistribution upon formation of E4(H2,2H). Here we examine the doubly reduced FeMo-co core of the E4(2H)* limiting-state by 1H, 57Fe, and 95Mo ENDOR to illuminate the partial electron-density redistribution upon E4(H2,2H) formation during catalysis, complementing these results with corresponding DFT computations. Inferences from the E4(2H)* ENDOR results as extended by DFT computations include (i) the Mo-site participates negligibly, and overall it is unlikely that Mo changes valency throughout the catalytic cycle; and (ii) two distinctive E4(4H) 57Fe signals are suggested as associated with structurally identified "anchors" of one bridging hydride, two others with identified anchors of the second, with NBO-analysis further identifying one anchor of each hydride as a major recipient of electrons released upon breaking Fe-H bonds.
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Affiliation(s)
- Dmitriy A Lukoyanov
- Department of Chemistry, Northwestern University, Evanston, Illinois 60208, United States
| | - Zhi-Yong Yang
- Department of Chemistry and Biocemistry, Utah State University, Logan, Utah 84322, United States
| | - Dennis R Dean
- Department of Biochemistry, Virginia Polytechnic Institute and State University, Blacksburg, Virginia 24061, United States
| | - Lance C Seefeldt
- Department of Chemistry and Biochemistry, Utah State University, Logan, Utah 84322, United States
| | - Simone Raugei
- Pacific Northwest National Laboratory, Richland, Washington 99352, United States
| | - Brian M Hoffman
- Department of Chemistry, Northwestern University, Evanston, Illinois 60208, United States
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24
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Martin DJ, Johnson SI, Mercado BQ, Raugei S, Mayer JM. Intramolecular Electrostatic Effects on O2, CO2, and Acetate Binding to a Cationic Iron Porphyrin. Inorg Chem 2020; 59:17402-17414. [DOI: 10.1021/acs.inorgchem.0c02703] [Citation(s) in RCA: 15] [Impact Index Per Article: 3.8] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
Affiliation(s)
- Daniel J. Martin
- Department of Chemistry, Yale University, New Haven, Connecticut 06520, United States
| | - Samantha I. Johnson
- Pacific Northwest National Laboratory (PNNL), Richland, Washington 99352, United States
| | - Brandon Q. Mercado
- Department of Chemistry, Yale University, New Haven, Connecticut 06520, United States
| | - Simone Raugei
- Pacific Northwest National Laboratory (PNNL), Richland, Washington 99352, United States
| | - James M. Mayer
- Department of Chemistry, Yale University, New Haven, Connecticut 06520, United States
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25
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Abstract
Nitrogenase is the enzyme that catalyzes biological N2 reduction to NH3. This enzyme achieves an impressive rate enhancement over the uncatalyzed reaction. Given the high demand for N2 fixation to support food and chemical production and the heavy reliance of the industrial Haber-Bosch nitrogen fixation reaction on fossil fuels, there is a strong need to elucidate how nitrogenase achieves this difficult reaction under benign conditions as a means of informing the design of next generation synthetic catalysts. This Review summarizes recent progress in addressing how nitrogenase catalyzes the reduction of an array of substrates. New insights into the mechanism of N2 and proton reduction are first considered. This is followed by a summary of recent gains in understanding the reduction of a number of other nitrogenous compounds not considered to be physiological substrates. Progress in understanding the reduction of a wide range of C-based substrates, including CO and CO2, is also discussed, and remaining challenges in understanding nitrogenase substrate reduction are considered.
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Affiliation(s)
- Lance C Seefeldt
- Department of Chemistry and Biochemistry, Utah State University, Logan, Utah 84322, United States
| | - Zhi-Yong Yang
- Department of Chemistry and Biochemistry, Utah State University, Logan, Utah 84322, United States
| | - Dmitriy A Lukoyanov
- Department of Chemistry, Northwestern University, Evanston, Illinois 60208, United States
| | - Derek F Harris
- Department of Chemistry and Biochemistry, Utah State University, Logan, Utah 84322, United States
| | - Dennis R Dean
- Biochemistry Department, Virginia Tech, Blacksburg, Virginia 24061, United States
| | - Simone Raugei
- Physical and Computational Sciences Directorate, Pacific Northwest National Laboratory, Richland, Washington 99352, United States
| | - Brian M Hoffman
- Department of Chemistry, Northwestern University, Evanston, Illinois 60208, United States
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26
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Abstract
The oxygen reduction reaction (ORR) is the cathode reaction in fuel cells and its selectivity for water over hydrogen peroxide production is important for these technologies. Iron porphyrin catalysts have long been studied for the ORR, but the origins of their selectivity are not well understood because the selectivity-determining step(s) usually occur after the rate-determining step. We report here the effects of acid concentration, as well as other solution conditions such as acid pKa, on the H2O2/H2O selectivity in electrocatalytic ORR by iron(tetramesitylporphyrin) (Fe(TMP)) in DMF. The results show that selectivity reflects a kinetic competition in which the dependence on [HX] is one order greater for the production of H2O than H2O2. Based on such experimental results and computational studies, we propose that the selectivity is governed by competition between protonation of the hydroperoxo intermediate, FeIII(TMP)(OOH), to produce water versus dissociation of the HOO- ligand to yield H2O2. The data rule out a bifurcation based on the regioselectivity of protonation of the hydroperoxide, as suggested in the enzymatic systems. Furthermore, the analysis developed in this report should be generally valuable to the study of selectivity in other multi-proton/multi-electron electrocatalytic reactions.
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Affiliation(s)
- Anna C. Brezny
- Department of Chemistry, Yale University, New Haven, Connecticut 06520
| | - Samantha I. Johnson
- Center for Molecular Electrocatalysis, Pacific Northwest National Laboratory, Richland, Washington 99352
| | - Simone Raugei
- Center for Molecular Electrocatalysis, Pacific Northwest National Laboratory, Richland, Washington 99352
| | - James M. Mayer
- Department of Chemistry, Yale University, New Haven, Connecticut 06520
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27
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Hoeke V, Tociu L, Case DA, Seefeldt LC, Raugei S, Hoffman BM. Correction to "High-Resolution ENDOR Spectroscopy Combined with Quantum Chemical Calculations Reveals the Structure of Nitrogenase Janus Intermediate E 4(4H)". J Am Chem Soc 2019; 141:19950. [PMID: 31820971 DOI: 10.1021/jacs.9b13035] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [What about the content of this article? (0)] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/30/2022]
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28
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Artz JH, Zadvornyy OA, Mulder DW, Keable SM, Cohen AE, Ratzloff MW, Williams SG, Ginovska B, Kumar N, Song J, McPhillips SE, Davidson CM, Lyubimov AY, Pence N, Schut GJ, Jones AK, Soltis SM, Adams MWW, Raugei S, King PW, Peters JW. Tuning Catalytic Bias of Hydrogen Gas Producing Hydrogenases. J Am Chem Soc 2019; 142:1227-1235. [PMID: 31816235 PMCID: PMC8653774 DOI: 10.1021/jacs.9b08756] [Citation(s) in RCA: 39] [Impact Index Per Article: 7.8] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
Abstract
Hydrogenases display a wide range of catalytic rates and biases in reversible hydrogen gas oxidation catalysis. The interactions of the iron-sulfur-containing catalytic site with the local protein environment are thought to contribute to differences in catalytic reactivity, but this has not been demonstrated. The microbe Clostridium pasteurianum produces three [FeFe]-hydrogenases that differ in "catalytic bias" by exerting a disproportionate rate acceleration in one direction or the other that spans a remarkable 6 orders of magnitude. The combination of high-resolution structural work, biochemical analyses, and computational modeling indicates that protein secondary interactions directly influence the relative stabilization/destabilization of different oxidation states of the active site metal cluster. This selective stabilization or destabilization of oxidation states can preferentially promote hydrogen oxidation or proton reduction and represents a simple yet elegant model by which a protein catalytic site can confer catalytic bias.
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Affiliation(s)
- Jacob H. Artz
- Institute of Biological Chemistry, Washington State University, Pullman, Washington 99164, United States
- Biosciences Center, National Renewable Energy Laboratory, Golden, Colorado 80401, United States
| | - Oleg A. Zadvornyy
- Institute of Biological Chemistry, Washington State University, Pullman, Washington 99164, United States
| | - David W. Mulder
- Biosciences Center, National Renewable Energy Laboratory, Golden, Colorado 80401, United States
| | - Stephen M. Keable
- Department of Chemistry and Biochemistry, Montana State University, Bozeman, Montana 59717, United States
| | - Aina E. Cohen
- Stanford Synchrotron Radiation Lightsource, SLAC National Accelerator Laboratory, Menlo Park, California 94025, United States
| | - Michael W. Ratzloff
- Biosciences Center, National Renewable Energy Laboratory, Golden, Colorado 80401, United States
| | - S. Garrett Williams
- School of Molecular Sciences, Arizona State University, Tempe, Arizona 85287, United States
| | - Bojana Ginovska
- Pacific Northwest National Laboratory, Richland, Washington 99352, United States
| | - Neeraj Kumar
- Pacific Northwest National Laboratory, Richland, Washington 99352, United States
| | - Jinhu Song
- Stanford Synchrotron Radiation Lightsource, SLAC National Accelerator Laboratory, Menlo Park, California 94025, United States
| | - Scott E. McPhillips
- Stanford Synchrotron Radiation Lightsource, SLAC National Accelerator Laboratory, Menlo Park, California 94025, United States
| | - Catherine M. Davidson
- Stanford Synchrotron Radiation Lightsource, SLAC National Accelerator Laboratory, Menlo Park, California 94025, United States
| | - Artem Y. Lyubimov
- Stanford Synchrotron Radiation Lightsource, SLAC National Accelerator Laboratory, Menlo Park, California 94025, United States
| | - Natasha Pence
- Institute of Biological Chemistry, Washington State University, Pullman, Washington 99164, United States
| | - Gerrit J. Schut
- Department of Biochemistry and Molecular Biology, University of Georgia, Athens, Georgia 30602, United States
| | - Anne K. Jones
- School of Molecular Sciences, Arizona State University, Tempe, Arizona 85287, United States
| | - S. Michael Soltis
- Stanford Synchrotron Radiation Lightsource, SLAC National Accelerator Laboratory, Menlo Park, California 94025, United States
| | - Michael W. W. Adams
- Department of Biochemistry and Molecular Biology, University of Georgia, Athens, Georgia 30602, United States
| | - Simone Raugei
- Institute of Biological Chemistry, Washington State University, Pullman, Washington 99164, United States
- Pacific Northwest National Laboratory, Richland, Washington 99352, United States
| | - Paul W. King
- Biosciences Center, National Renewable Energy Laboratory, Golden, Colorado 80401, United States
| | - John W. Peters
- Institute of Biological Chemistry, Washington State University, Pullman, Washington 99164, United States
- Department of Chemistry and Biochemistry, Montana State University, Bozeman, Montana 59717, United States
- Pacific Northwest National Laboratory, Richland, Washington 99352, United States
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Hoeke V, Tociu L, Case DA, Seefeldt LC, Raugei S, Hoffman BM. High-Resolution ENDOR Spectroscopy Combined with Quantum Chemical Calculations Reveals the Structure of Nitrogenase Janus Intermediate E 4(4H). J Am Chem Soc 2019; 141:11984-11996. [PMID: 31310109 DOI: 10.1021/jacs.9b04474] [Citation(s) in RCA: 46] [Impact Index Per Article: 9.2] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/08/2023]
Abstract
We have shown that the key state in N2 reduction to two NH3 molecules by the enzyme nitrogenase is E4(4H), the "Janus" intermediate, which has accumulated four [e-/H+] and is poised to undergo reductive elimination of H2 coupled to N2 binding and activation. Initial 1H and 95Mo ENDOR studies of freeze-trapped E4(4H) revealed that the catalytic multimetallic cluster (FeMo-co) binds two Fe-bridging hydrides, [Fe-H-Fe]. However, the analysis failed to provide a satisfactory picture of the relative spatial relationships of the two [Fe-H-Fe]. Our recent density functional theory (DFT) study yielded a lowest-energy form, denoted as E4(4H)(a), with two parallel Fe-H-Fe planes bridging pairs of "anchor" Fe on the Fe2,3,6,7 face of FeMo-co. However, the relative energies of structures E4(4H)(b), with one bridging and one terminal hydride, and E4(4H)(c), with one pair of anchor Fe supporting two bridging hydrides, were not beyond the uncertainties in the calculation. Moreover, a structure of V-dependent nitrogenase resulted in a proposed structure analogous to E4(4H)(c), and additional structures have been proposed in the DFT studies of others. To resolve the nature of hydride binding to the Janus intermediate, we performed exhaustive, high-resolution CW-stochastic 1H-ENDOR experiments using improved instrumentation, Mims 2H ENDOR, and a recently developed pulsed-ENDOR protocol ("PESTRE") to obtain absolute hyperfine interaction signs. These measurements are coupled to DFT structural models through an analytical point-dipole Hamiltonian for the hydride electron-nuclear dipolar coupling to its "anchoring" Fe ions, an approach that overcomes limitations inherent in both experimental interpretation and computational accuracy. The result is the freeze-trapped, lowest-energy Janus intermediate structure, E4(4H)(a).
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Affiliation(s)
- Veronika Hoeke
- Department of Chemistry , Northwestern University , Evanston , Illinois 60208 , United States
| | - Laura Tociu
- Department of Chemistry , University of Chicago , Chicago , Illinois 60637 , United States
| | - David A Case
- Department of Chemistry and Chemical Biology , Rutgers University , Piscataway , New Jersey 08854 , United States
| | - Lance C Seefeldt
- Department of Chemistry and Biochemistry , Utah State University , Logan , Utah 84322 , United States
| | - Simone Raugei
- Physical Sciences Division , Pacific Northwestern National Laboratory , Richland , Washington 99352 , United States
| | - Brian M Hoffman
- Department of Chemistry , Northwestern University , Evanston , Illinois 60208 , United States
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30
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Pegis ML, Martin DJ, Wise CF, Brezny AC, Johnson SI, Johnson LE, Kumar N, Raugei S, Mayer JM. Mechanism of Catalytic O 2 Reduction by Iron Tetraphenylporphyrin. J Am Chem Soc 2019; 141:8315-8326. [PMID: 31042028 DOI: 10.1021/jacs.9b02640] [Citation(s) in RCA: 56] [Impact Index Per Article: 11.2] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/16/2023]
Abstract
The catalytic reduction of O2 to H2O is important for energy transduction in both synthetic and natural systems. Herein, we report a kinetic and thermochemical study of the oxygen reduction reaction (ORR) catalyzed by iron tetraphenylporphyrin (Fe(TPP)) in N, N'-dimethylformamide using decamethylferrocene as a soluble reductant and para-toluenesulfonic acid ( pTsOH) as the proton source. This work identifies and characterizes catalytic intermediates and their thermochemistry, providing a detailed mechanistic understanding of the system. Specifically, reduction of the ferric porphyrin, [FeIII(TPP)]+, forms the ferrous porphyrin, FeII(TPP), which binds O2 reversibly to form the ferric-superoxide porphyrin complex, FeIII(TPP)(O2•-). The temperature dependence of both the electron transfer and O2 binding equilibrium constants has been determined. Kinetic studies over a range of concentrations and temperatures show that the catalyst resting state changes during the course of each catalytic run, necessitating the use of global kinetic modeling to extract rate constants and kinetic barriers. The rate-determining step in oxygen reduction is the protonation of FeIII(TPP)(O2•-) by pTsOH, which proceeds with a substantial kinetic barrier. Computational studies indicate that this barrier for proton transfer arises from an unfavorable preassociation of the proton donor with the superoxide adduct and a transition state that requires significant desolvation of the proton donor. Together, these results are the first example of oxygen reduction by iron tetraphenylporphyrin where the pre-equilibria among ferric, ferrous, and ferric-superoxide intermediates have been quantified under catalytic conditions. This work gives a generalizable model for the mechanism of iron porphyrin-catalyzed ORR and provides an unusually complete mechanistic study of an ORR reaction. More broadly, this study also highlights the kinetic challenges for proton transfer to catalytic intermediates in organic media.
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Affiliation(s)
- Michael L Pegis
- Department of Chemistry , Yale University , P.O Box 208107, New Haven , Connecticut 06520-8107 , United States
| | - Daniel J Martin
- Department of Chemistry , Yale University , P.O Box 208107, New Haven , Connecticut 06520-8107 , United States
| | - Catherine F Wise
- Department of Chemistry , Yale University , P.O Box 208107, New Haven , Connecticut 06520-8107 , United States
| | - Anna C Brezny
- Department of Chemistry , Yale University , P.O Box 208107, New Haven , Connecticut 06520-8107 , United States
| | | | - Lewis E Johnson
- Department of Chemistry , University of Washington , Box 351700 Seattle , Washington 98195-1700 , United States
| | | | | | - James M Mayer
- Department of Chemistry , Yale University , P.O Box 208107, New Haven , Connecticut 06520-8107 , United States
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31
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Johnson LE, Ginovska B, Fenton AW, Raugei S. Chokepoints in Mechanical Coupling Associated with Allosteric Proteins: The Pyruvate Kinase Example. Biophys J 2019; 116:1598-1608. [PMID: 31010662 DOI: 10.1016/j.bpj.2019.03.026] [Citation(s) in RCA: 7] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/28/2019] [Revised: 03/14/2019] [Accepted: 03/21/2019] [Indexed: 12/14/2022] Open
Abstract
Although the critical role of allostery in controlling enzymatic processes is well appreciated, there is a current dearth in our understanding of its underlying mechanisms, including communication between binding sites. One potential key aspect of intersite communication is the mechanical coupling between residues in a protein. Here, we introduce a graph-based computational approach to investigate the mechanical coupling between distant parts of a protein, highlighting effective pathways via which protein motion can transfer energy between sites. In this method, each residue is treated as a node on a weighted, undirected graph, in which the edges are defined by locally correlated motions of those residues and weighted by the strength of the correlation. The method was validated against experimental data on allosteric regulation in the human liver pyruvate kinase as obtained from full-protein alanine-scanning mutagenesis (systematic mutation) studies, as well as computational data on two G-protein-coupled receptors. The method provides semiquantitative information on the regulatory importance of specific structural elements. It is shown that these elements are key for the mechanical coupling between distant parts of the protein by providing effective pathways for energy transfer. It is also shown that, although there are a multitude of energy transfer pathways between distant parts of a protein, these pathways share a few common nodes that represent effective "chokepoints" for the communication.
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Affiliation(s)
- Lewis E Johnson
- Department of Chemistry, University of Washington, Seattle, Washington; Physical and Computational Sciences Directorate, Pacific Northwestern National Laboratory, Richland, Washington
| | - Bojana Ginovska
- Physical and Computational Sciences Directorate, Pacific Northwestern National Laboratory, Richland, Washington
| | - Aron W Fenton
- Department of Biochemistry and Molecular Biology, The University of Kansas Medical Center, Kansas City, Kansas
| | - Simone Raugei
- Physical and Computational Sciences Directorate, Pacific Northwestern National Laboratory, Richland, Washington.
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32
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Chambers GM, Johnson SI, Raugei S, Bullock RM. Anion control of tautomeric equilibria: Fe-H vs. N-H influenced by NH···F hydrogen bonding. Chem Sci 2019; 10:1410-1418. [PMID: 30842818 PMCID: PMC6369578 DOI: 10.1039/c8sc04239j] [Citation(s) in RCA: 12] [Impact Index Per Article: 2.4] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/23/2018] [Accepted: 10/04/2018] [Indexed: 12/21/2022] Open
Abstract
Addition of excess BF4– to the iron hydride [Fe(PEtNMePEt)(CO)3H]+[B(C6F5)4]– leads to the NH tautomer, due to NH···F hydrogen bonding.
Counterions can play an active role in chemical reactivity, modulating reaction pathways, energetics and selectivity. We investigated the tautomeric equilibrium resulting from protonation of Fe(PEtNMePEt)(CO)3 (PEtNMePEt = (Et2PCH2)2NMe) at Fe or N. Protonation of Fe(PEtNMePEt)(CO)3 by [(Et2O)2H]+[B(C6F5)4]– occurs at the metal to give the iron hydride [Fe(PEtNMePEt)(CO)3H]+[B(C6F5)4]–. In contrast, treatment with HBF4·OEt2 gives protonation at the iron and at the pendant amine. Both the FeH and NH tautomers were characterized by single crystal X-ray diffraction. Addition of excess BF4– to the equilibrium mixture leads to the NH tautomer being exclusively observed, due to NH···F hydrogen bonding. A quantum chemical analysis of the bonding properties of these systems provided a quantification of hydrogen bonding of the NH to BF4– and to OTf–. Treatment of Fe(PEtNMePEt)(CO)3 with excess HOTf gives a dicationic complex where both the iron and nitrogen are protonated. Isomerization of the dicationic complex was studied by NOESY NMR spectroscopy.
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Affiliation(s)
- Geoffrey M Chambers
- Center for Molecular Electrocatalysis , Pacific Northwest National Laboratory , Richland , Washington 99352 , USA .
| | - Samantha I Johnson
- Center for Molecular Electrocatalysis , Pacific Northwest National Laboratory , Richland , Washington 99352 , USA .
| | - Simone Raugei
- Center for Molecular Electrocatalysis , Pacific Northwest National Laboratory , Richland , Washington 99352 , USA .
| | - R Morris Bullock
- Center for Molecular Electrocatalysis , Pacific Northwest National Laboratory , Richland , Washington 99352 , USA .
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33
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Kumar N, Darmon JM, Weiss CJ, Helm ML, Raugei S, Morris Bullock R. Outer Coordination Sphere Proton Relay Base and Proximity Effects on Hydrogen Oxidation with Iron Electrocatalysts. Organometallics 2019. [DOI: 10.1021/acs.organomet.8b00805] [Citation(s) in RCA: 6] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Affiliation(s)
- Neeraj Kumar
- Center for Molecular Electrocatalysis, Pacific Northwest National Laboratory, P.O. Box 999, K2-12, Richland, Washington 99352, United States
| | - Jonathan M. Darmon
- Center for Molecular Electrocatalysis, Pacific Northwest National Laboratory, P.O. Box 999, K2-12, Richland, Washington 99352, United States
| | - Charles J. Weiss
- Center for Molecular Electrocatalysis, Pacific Northwest National Laboratory, P.O. Box 999, K2-12, Richland, Washington 99352, United States
| | - Monte L. Helm
- Center for Molecular Electrocatalysis, Pacific Northwest National Laboratory, P.O. Box 999, K2-12, Richland, Washington 99352, United States
| | - Simone Raugei
- Center for Molecular Electrocatalysis, Pacific Northwest National Laboratory, P.O. Box 999, K2-12, Richland, Washington 99352, United States
| | - R. Morris Bullock
- Center for Molecular Electrocatalysis, Pacific Northwest National Laboratory, P.O. Box 999, K2-12, Richland, Washington 99352, United States
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34
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Johnson SI, Heins SP, Klug CM, Wiedner ES, Bullock RM, Raugei S. Design and reactivity of pentapyridyl metal complexes for ammonia oxidation. Chem Commun (Camb) 2019; 55:5083-5086. [DOI: 10.1039/c9cc01249d] [Citation(s) in RCA: 21] [Impact Index Per Article: 4.2] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/12/2023]
Abstract
Computational and experimental work shows that Mo pentapyridal complexes can oxidize ammonia in the presence of a chemical mediator and evolve N2.
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Affiliation(s)
- Samantha I. Johnson
- Center for Molecular Electrocatalysis
- Pacific Northwest National Laboratory
- Richland
- USA
| | - Spencer P. Heins
- Center for Molecular Electrocatalysis
- Pacific Northwest National Laboratory
- Richland
- USA
| | - Christina M. Klug
- Center for Molecular Electrocatalysis
- Pacific Northwest National Laboratory
- Richland
- USA
| | - Eric S. Wiedner
- Center for Molecular Electrocatalysis
- Pacific Northwest National Laboratory
- Richland
- USA
| | - R. Morris Bullock
- Center for Molecular Electrocatalysis
- Pacific Northwest National Laboratory
- Richland
- USA
| | - Simone Raugei
- Center for Molecular Electrocatalysis
- Pacific Northwest National Laboratory
- Richland
- USA
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35
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Abstract
Nitrogenase is a complicated two-component enzyme system that uses ATP binding and hydrolysis energy to achieve one of the most difficult chemical reactions in nature, the reduction of N2 to NH3. One component of the Mo-based nitrogenase system, Fe protein, delivers electrons one at a time to the second component, the catalytic MoFe protein. This process occurs through a series of synchronized events collectively called the "Fe protein cycle". Elucidating details of the events associated with this cycle has constituted an important challenge in understanding the nitrogenase mechanism. Electron delivery is a multistep process involving three metal clusters with intra- and interprotein events. It is proposed that the first electron transfer event is a gated intraprotein transfer of one electron from the MoFe protein P-cluster to the FeMo cofactor. Measurement of the effect of osmotic pressure on the rate of this electron transfer process revealed that it is gated by protein conformational changes. This first electron transfer is activated by binding of the Fe protein containing two bound ATP molecules. The mechanism of how this protein-protein association triggers electron transfer remains unknown. The second electron transfer event is proposed to be a rapid interprotein "backfill" with transfer of one electron from the reduced Fe protein 4Fe-4S cluster to the oxidized P-cluster. In this way, electron delivery can be viewed as a case of "deficit spending". Such a deficit-spending electron transfer process can be envisioned as a way to achieve one-direction electron flow, limiting the potential for back electron flow. Hydrolysis of two ATP molecules associated with the Fe protein occurs after the electron transfer and therefore is not used to directly drive the electron transfer. Rather, ATP hydrolysis is proposed to contribute to relaxation of the "activated" conformational state associated with the ATP form of the complex, with the free energy from ATP hydrolysis being used to pay back energy associated with component protein association and electron transfer. Release of inorganic phosphate (Pi) and protein-protein dissociation follow electron transfer and ATP hydrolysis. The rate-limiting step for the Fe protein cycle is not dissociation of the two proteins, as previously believed, but rather is release of Pi after ATP hydrolysis, which is then followed by rapid protein-protein complex dissociation. Nitrogenase is composed of two catalytic halves that do not function independently but rather exhibit anticooperative nuclear motion in which electron transfer in one-half of the complex partially inhibits electron transfer and ATP hydrolysis in the other half. Calculations indicated the existence of anticooperative interactions across the entire nitrogenase complex, suggesting a mechanism for the control of events on opposite ends of this large complex. The mechanistic necessity for this anticooperative process remains unknown. This Account presents a working model for how all of these processes work together in the nitrogenase "machine" to transduce the energy from ATP binding and hydrolysis to drive N2 reduction.
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Affiliation(s)
- Lance C. Seefeldt
- Department of Chemistry and Biochemistry, Utah State University, Logan, Utah 84322, United States
- Pacific Northwest National Laboratory, Richland, Washington 99352, United States
| | - Brian M. Hoffman
- Department of Chemistry, Northwestern University, Evanston, Illinois 60208, United States
| | - John W. Peters
- Pacific Northwest National Laboratory, Richland, Washington 99352, United States
- Institute of Biological Chemistry, Washington State University, Pullman, Washington 99163, United States
| | - Simone Raugei
- Pacific Northwest National Laboratory, Richland, Washington 99352, United States
- Institute of Biological Chemistry, Washington State University, Pullman, Washington 99163, United States
| | - David N. Beratan
- Department of Chemistry and Department of Physics, Duke University, Durham, North Carolina 27708, United States
- Department of Biochemistry, Duke University, Durham, North Carolina 27710, United States
| | - Edwin Antony
- Department of Biological Sciences, Marquette University, Milwaukee, Wisconsin 53201, United States
| | - Dennis R. Dean
- Department of Biochemistry, Virginia Tech, Blacksburg, Virginia 24061, United States
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36
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Seefeldt LC, Peters JW, Beratan DN, Bothner B, Minteer SD, Raugei S, Hoffman BM. Control of electron transfer in nitrogenase. Curr Opin Chem Biol 2018; 47:54-59. [PMID: 30205289 DOI: 10.1016/j.cbpa.2018.08.011] [Citation(s) in RCA: 28] [Impact Index Per Article: 4.7] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/11/2018] [Revised: 07/06/2018] [Accepted: 08/21/2018] [Indexed: 11/30/2022]
Abstract
The bacterial enzyme nitrogenase achieves the reduction of dinitrogen (N2) to ammonia (NH3) utilizing electrons, protons, and energy from the hydrolysis of ATP. Building on earlier foundational knowledge, recent studies provide molecular-level details on how the energy of ATP hydrolysis is utilized, the sequencing of multiple electron transfer events, and the nature of energy transduction across this large protein complex. Here, we review the state of knowledge about energy transduction in nitrogenase.
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Affiliation(s)
- Lance C Seefeldt
- Department of Chemistry and Biochemistry, Utah State University, 0300 Old Main Hill, Logan, UT 84322, USA.
| | - John W Peters
- Institute of Biological Chemistry, Washington State University, 287 Clark Hall, Pullman, WA 99164, USA
| | - David N Beratan
- Departments of Chemistry, Physics, and Biochemistry, Duke University, Durham, NC 27708 and 27710, USA
| | - Brian Bothner
- Department of Chemistry and Biochemistry, Montana State University, Bozeman, MT 59717, USA
| | - Shelley D Minteer
- Departments of Chemistry and Materials Science & Engineering, University of Utah, 315 S 1400 E, Salt Lake City, UT 84112, USA
| | - Simone Raugei
- Physical and Computational Sciences, Pacific Northwestern National Laboratory, 602 Battelle Blvd, Richland, WA 99352, USA
| | - Brian M Hoffman
- Department of Chemistry, Northwestern University, Evanston, IL 60208, USA
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37
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Peters JW, Beratan DN, Bothner B, Dyer RB, Harwood CS, Heiden ZM, Hille R, Jones AK, King PW, Lu Y, Lubner CE, Minteer SD, Mulder DW, Raugei S, Schut GJ, Seefeldt LC, Tokmina-Lukaszewska M, Zadvornyy OA, Zhang P, Adams MW. A new era for electron bifurcation. Curr Opin Chem Biol 2018; 47:32-38. [PMID: 30077080 DOI: 10.1016/j.cbpa.2018.07.026] [Citation(s) in RCA: 41] [Impact Index Per Article: 6.8] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/16/2018] [Revised: 06/16/2018] [Accepted: 07/18/2018] [Indexed: 11/17/2022]
Abstract
Electron bifurcation, or the coupling of exergonic and endergonic oxidation-reduction reactions, was discovered by Peter Mitchell and provides an elegant mechanism to rationalize and understand the logic that underpins the Q cycle of the respiratory chain. Thought to be a unique reaction of respiratory complex III for nearly 40 years, about a decade ago Wolfgang Buckel and Rudolf Thauer discovered that flavin-based electron bifurcation is also an important component of anaerobic microbial metabolism. Their discovery spawned a surge of research activity, providing a basis to understand flavin-based bifurcation, forging fundamental parallels with Mitchell's Q cycle and leading to the proposal of metal-based bifurcating enzymes. New insights into the mechanism of electron bifurcation provide a foundation to establish the unifying principles and essential elements of this fascinating biochemical phenomenon.
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Affiliation(s)
- John W Peters
- Institute of Biological Chemistry, Washington State University, Pullman WA 99163, United States; Pacific Northwest National Laboratory, Richland, WA 99352, United States.
| | - David N Beratan
- Department of Chemistry and Department of Physics, Duke University, Durham, NC 27708, United States; Department of Biochemistry, Duke University, Durham, NC 27710, United States
| | - Brian Bothner
- Department of Chemistry and Biochemistry, Montana State University, Bozeman, MT 59717, United States
| | - R Brian Dyer
- Department of Chemistry, Emory University, Atlanta, GA 30322, United States
| | - Caroline S Harwood
- Department of Microbiology, University of Washington, Seattle, WA 98195, United States
| | - Zachariah M Heiden
- Department of Chemistry, Washington State University, Pullman WA 99163, United States
| | - Russ Hille
- Biochemistry Department, University of California at Riverside, Riverside, CA 92521, United States
| | - Anne K Jones
- School of Molecular Sciences, Arizona State University, Tempe, AZ 85287, United States
| | - Paul W King
- National Renewable Energy Laboratory, Golden, CO 8040, United States
| | - Yi Lu
- Pacific Northwest National Laboratory, Richland, WA 99352, United States; Department of Chemistry, University of Illinois at Urbana-Champaign, Urbana, IL 61801, United States
| | - Carolyn E Lubner
- National Renewable Energy Laboratory, Golden, CO 8040, United States
| | - Shelley D Minteer
- Department of Chemistry, University of Utah, Salt Lake City, UT 84112, United States
| | - David W Mulder
- National Renewable Energy Laboratory, Golden, CO 8040, United States
| | - Simone Raugei
- Institute of Biological Chemistry, Washington State University, Pullman WA 99163, United States; Pacific Northwest National Laboratory, Richland, WA 99352, United States
| | - Gerrit J Schut
- Department of Biochemistry & Molecular Biology, University of Georgia, Athens, GA 30602, United States
| | - Lance C Seefeldt
- Pacific Northwest National Laboratory, Richland, WA 99352, United States; Department of Chemistry and Biochemistry, Utah State University, Logan, UT 84322, United States
| | | | - Oleg A Zadvornyy
- Institute of Biological Chemistry, Washington State University, Pullman WA 99163, United States
| | - Peng Zhang
- Department of Biochemistry, Duke University, Durham, NC 27710, United States
| | - Michael Ww Adams
- Department of Biochemistry & Molecular Biology, University of Georgia, Athens, GA 30602, United States
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38
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Keable SM, Zadvornyy OA, Johnson LE, Ginovska B, Rasmussen AJ, Danyal K, Eilers BJ, Prussia GA, LeVan AX, Raugei S, Seefeldt LC, Peters JW. Structural characterization of the P 1+ intermediate state of the P-cluster of nitrogenase. J Biol Chem 2018; 293:9629-9635. [PMID: 29720402 PMCID: PMC6016482 DOI: 10.1074/jbc.ra118.002435] [Citation(s) in RCA: 27] [Impact Index Per Article: 4.5] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/14/2018] [Revised: 04/26/2018] [Indexed: 01/07/2023] Open
Abstract
Nitrogenase is the enzyme that reduces atmospheric dinitrogen (N2) to ammonia (NH3) in biological systems. It catalyzes a series of single-electron transfers from the donor iron protein (Fe protein) to the molybdenum-iron protein (MoFe protein) that contains the iron-molybdenum cofactor (FeMo-co) sites where N2 is reduced to NH3 The P-cluster in the MoFe protein functions in nitrogenase catalysis as an intermediate electron carrier between the external electron donor, the Fe protein, and the FeMo-co sites of the MoFe protein. Previous work has revealed that the P-cluster undergoes redox-dependent structural changes and that the transition from the all-ferrous resting (PN) state to the two-electron oxidized P2+ state is accompanied by protein serine hydroxyl and backbone amide ligation to iron. In this work, the MoFe protein was poised at defined potentials with redox mediators in an electrochemical cell, and the three distinct structural states of the P-cluster (P2+, P1+, and PN) were characterized by X-ray crystallography and confirmed by computational analysis. These analyses revealed that the three oxidation states differ in coordination, implicating that the P1+ state retains the serine hydroxyl coordination but lacks the backbone amide coordination observed in the P2+ states. These results provide a complete picture of the redox-dependent ligand rearrangements of the three P-cluster redox states.
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Affiliation(s)
- Stephen M. Keable
- From the Department of Chemistry and Biochemistry, Montana State University, Bozeman, Montana 59717
| | - Oleg A. Zadvornyy
- Institute of Biological Chemistry, Washington State University, Pullman, Washington 99163
| | - Lewis E. Johnson
- Pacific Northwest National Laboratory, Richland, Washington 99352, and
| | - Bojana Ginovska
- Pacific Northwest National Laboratory, Richland, Washington 99352, and
| | - Andrew J. Rasmussen
- Department of Chemistry and Biochemistry, Utah State University, Logan, Utah 84322
| | - Karamatullah Danyal
- Department of Chemistry and Biochemistry, Utah State University, Logan, Utah 84322
| | - Brian J. Eilers
- From the Department of Chemistry and Biochemistry, Montana State University, Bozeman, Montana 59717
| | - Gregory A. Prussia
- From the Department of Chemistry and Biochemistry, Montana State University, Bozeman, Montana 59717
| | - Axl X. LeVan
- From the Department of Chemistry and Biochemistry, Montana State University, Bozeman, Montana 59717
| | - Simone Raugei
- Institute of Biological Chemistry, Washington State University, Pullman, Washington 99163, ,Pacific Northwest National Laboratory, Richland, Washington 99352, and
| | - Lance C. Seefeldt
- Pacific Northwest National Laboratory, Richland, Washington 99352, and ,Department of Chemistry and Biochemistry, Utah State University, Logan, Utah 84322, To whom correspondence may be addressed:
Dept. of Chemistry and Biochemistry, Utah State University, Logan, UT 84322. Tel.:
435-797-3964; E-mail:
| | - John W. Peters
- From the Department of Chemistry and Biochemistry, Montana State University, Bozeman, Montana 59717, ,Institute of Biological Chemistry, Washington State University, Pullman, Washington 99163, ,Pacific Northwest National Laboratory, Richland, Washington 99352, and , To whom correspondence may be addressed:
Institute of Biological Chemistry, Washington State University, Pullman, WA 99163. Tel.:
509-335-3412; E-mail:
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39
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Khadka N, Milton RD, Shaw S, Lukoyanov D, Dean DR, Minteer SD, Raugei S, Hoffman BM, Seefeldt LC. Mechanism of Nitrogenase H 2 Formation by Metal-Hydride Protonation Probed by Mediated Electrocatalysis and H/D Isotope Effects. J Am Chem Soc 2017; 139:13518-13524. [PMID: 28851217 DOI: 10.1021/jacs.7b07311] [Citation(s) in RCA: 37] [Impact Index Per Article: 5.3] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/12/2023]
Abstract
Nitrogenase catalyzes the reduction of dinitrogen (N2) to two ammonia (NH3) at its active site FeMo-cofactor through a mechanism involving reductive elimination of two [Fe-H-Fe] bridging hydrides to make H2. A competing reaction is the protonation of the hydride [Fe-H-Fe] to make H2. The overall nitrogenase rate-limiting step is associated with ATP-driven electron delivery from Fe protein, precluding isotope effect measurements on substrate reduction steps. Here, we use mediated bioelectrocatalysis to drive electron delivery to the MoFe protein allowing examination of the mechanism of H2 formation by the metal-hydride protonation reaction. The ratio of catalytic current in mixtures of H2O and D2O, the proton inventory, was found to change linearly with the D2O/H2O ratio, revealing that a single H/D is involved in the rate-limiting step of H2 formation. Kinetic models, along with measurements that vary the electron/proton delivery rate and use different substrates, reveal that the rate-limiting step under these conditions is the H2 formation reaction. Altering the chemical environment around the active site FeMo-cofactor in the MoFe protein, either by substituting nearby amino acids or transferring the isolated FeMo-cofactor into a different peptide matrix, changes the net isotope effect, but the proton inventory plot remains linear, consistent with an unchanging rate-limiting step. Density functional theory predicts a transition state for H2 formation where the S-H+ bond breaks and H+ attacks the Fe-hydride, and explains the observed H/D isotope effect. This study not only reveals the nitrogenase mechanism of H2 formation by hydride protonation, but also illustrates a strategy for mechanistic study that can be applied to other oxidoreductase enzymes and to biomimetic complexes.
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Affiliation(s)
- Nimesh Khadka
- Department of Chemistry and Biochemistry, Utah State University , Logan, Utah 84322, United States
| | - Ross D Milton
- Department of Chemistry, University of Utah , Salt Lake City, Utah 84112, United States
| | - Sudipta Shaw
- Department of Chemistry and Biochemistry, Utah State University , Logan, Utah 84322, United States
| | - Dmitriy Lukoyanov
- Department of Chemistry, Northwestern University , Evanston, Illinois 60208, United States
| | - Dennis R Dean
- Department of Biochemistry, Virginia Tech , Blacksburg, Virginia 24061, United States
| | - Shelley D Minteer
- Department of Chemistry, University of Utah , Salt Lake City, Utah 84112, United States
| | - Simone Raugei
- Pacific Northwest National Laboratory , Richland, Washington 99352, United States
| | - Brian M Hoffman
- Department of Chemistry, Northwestern University , Evanston, Illinois 60208, United States
| | - Lance C Seefeldt
- Department of Chemistry and Biochemistry, Utah State University , Logan, Utah 84322, United States
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40
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Abstract
Methanogens are masters of CO2 reduction. They conserve energy by coupling H2 oxidation to the reduction of CO2 to CH4, the primary constituent of natural gas. They also generate methane by the reduction of acetic acid, methanol, methane thiol, and methylamines. Methanogens produce 109 tons of methane per year and are the major source of the earth’s atmospheric methane. Reverse methanogenesis or anaerobic methane oxidation, which is catalyzed by methanotrophic archaea living in consortia among bacteria that can act as an electron acceptor, is responsible for annual oxidation of 108 tons of methane to CO2. This chapter briefly describes the overall process of methanogenesis and then describes the enzymatic mechanism of the nickel enzyme, methyl-CoM reductase (MCR), the key enzyme in methane synthesis and oxidation. MCR catalyzes the formation of methane and the heterodisulfide (CoBSSCoM) from methyl-coenzyme M (methyl-CoM) and coenzyme B (HSCoB). Uncovering the mechanistic and molecular details of MCR catalysis is critical since methane is an abundant and important fuel and is the second (to CO2) most prevalent greenhouse gas.
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Affiliation(s)
- Stephen W. Ragsdale
- Department of Biological Chemistry, University of Michigan Medical School 1150 W. Medical Center Dr., 5301 MSRB III Ann Arbor MI 48109-0606 USA
| | - Simone Raugei
- Physical Sciences Division, Pacific Northwest National Laboratory, Post Office Box 999 K1-83 Richland WA 99352 USA
| | - Bojana Ginovska
- Physical Sciences Division, Pacific Northwest National Laboratory, Post Office Box 999 K1-83 Richland WA 99352 USA
| | - Thanyaporn Wongnate
- School of Bioresources and Technology and Excellent Center of Waste Utilization and Management (ECoWaste), King Mongkut's University of Technology Thonburi Bangkhunthian, Bangkok 10140 Thailand
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41
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Bhattacharya P, Heiden ZM, Wiedner ES, Raugei S, Piro NA, Kassel WS, Bullock RM, Mock MT. Ammonia Oxidation by Abstraction of Three Hydrogen Atoms from a Mo–NH3 Complex. J Am Chem Soc 2017; 139:2916-2919. [DOI: 10.1021/jacs.7b00002] [Citation(s) in RCA: 48] [Impact Index Per Article: 6.9] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/30/2022]
Affiliation(s)
- Papri Bhattacharya
- Center
for Molecular Electrocatalysis, Pacific Northwest National Laboratory, P.O. Box 999, Richland, Washington 99352, United States
| | - Zachariah M. Heiden
- Department
of Chemistry, Washington State University, Pullman, Washington 99164, United States
| | - Eric S. Wiedner
- Center
for Molecular Electrocatalysis, Pacific Northwest National Laboratory, P.O. Box 999, Richland, Washington 99352, United States
| | - Simone Raugei
- Center
for Molecular Electrocatalysis, Pacific Northwest National Laboratory, P.O. Box 999, Richland, Washington 99352, United States
| | - Nicholas A. Piro
- Department
of Chemistry, Villanova University, Villanova, Pennsylvania 19085, United States
| | - W. Scott Kassel
- Department
of Chemistry, Villanova University, Villanova, Pennsylvania 19085, United States
| | - R. Morris Bullock
- Center
for Molecular Electrocatalysis, Pacific Northwest National Laboratory, P.O. Box 999, Richland, Washington 99352, United States
| | - Michael T. Mock
- Center
for Molecular Electrocatalysis, Pacific Northwest National Laboratory, P.O. Box 999, Richland, Washington 99352, United States
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42
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Lukoyanov D, Khadka N, Dean DR, Raugei S, Seefeldt LC, Hoffman BM. Photoinduced Reductive Elimination of H 2 from the Nitrogenase Dihydride (Janus) State Involves a FeMo-cofactor-H 2 Intermediate. Inorg Chem 2017; 56:2233-2240. [PMID: 28177622 DOI: 10.1021/acs.inorgchem.6b02899] [Citation(s) in RCA: 36] [Impact Index Per Article: 5.1] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/21/2022]
Abstract
N2 reduction by nitrogenase involves the accumulation of four reducing equivalents at the active site FeMo-cofactor to form a state with two [Fe-H-Fe] bridging hydrides (denoted E4(4H), the Janus intermediate), and we recently demonstrated that the enzyme is activated to cleave the N≡N triple bond by the reductive elimination (re) of H2 from this state. We are exploring a photochemical approach to obtaining atomic-level details of the re activation process. We have shown that, when E4(4H) at cryogenic temperatures is subjected to 450 nm irradiation in an EPR cavity, it cleanly undergoes photoinduced re of H2 to give a reactive doubly reduced intermediate, denoted E4(2H)*, which corresponds to the intermediate that would form if thermal dissociative re loss of H2 preceded N2 binding. Experiments reported here establish that photoinduced re primarily occurs in two steps. Photolysis of E4(4H) generates an intermediate state that undergoes subsequent photoinduced conversion to [E4(2H)* + H2]. The experiments, supported by DFT calculations, indicate that the trapped intermediate is an H2 complex on the ground adiabatic potential energy suface that connects E4(4H) with [E4(2H)* + H2]. We suggest that this complex, denoted E4(H2; 2H), is a thermally populated intermediate in the catalytically central re of H2 by E4(4H) and that N2 reacts with this complex to complete the activated conversion of [E4(4H) + N2] into [E4(2N2H) + H2].
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Affiliation(s)
- Dmitriy Lukoyanov
- Department of Chemistry, Northwestern University , Evanston, Illinois 60208, United States
| | - Nimesh Khadka
- Department of Chemistry and Biochemistry, Utah State University , Logan, Utah 84322, United States
| | - Dennis R Dean
- Department of Biochemistry, Virginia Tech , 110 Fralin Hall, Blacksburg, Virginia 24061, United States
| | - Simone Raugei
- Pacific Northwestern National Laboratory , Richland, Washington 99352, United States
| | - Lance C Seefeldt
- Department of Chemistry and Biochemistry, Utah State University , Logan, Utah 84322, United States
| | - Brian M Hoffman
- Department of Chemistry, Northwestern University , Evanston, Illinois 60208, United States
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43
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Pegis M, McKeown BA, Kumar N, Lang K, Wasylenko D, Zhang XP, Raugei S, Mayer JM. Homogenous Electrocatalytic Oxygen Reduction Rates Correlate with Reaction Overpotential in Acidic Organic Solutions. ACS Cent Sci 2016; 2:850-856. [PMID: 27924314 PMCID: PMC5126711 DOI: 10.1021/acscentsci.6b00261] [Citation(s) in RCA: 127] [Impact Index Per Article: 15.9] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 09/01/2016] [Indexed: 05/12/2023]
Abstract
Improved electrocatalysts for the oxygen reduction reaction (ORR) are critical for the advancement of fuel cell technologies. Herein, we report a series of 11 soluble iron porphyrin ORR electrocatalysts that possess turnover frequencies (TOFs) from 3 s-1 to an unprecedented value of 2.2 × 106 s-1. These TOFs correlate with the ORR overpotential, which can be modulated by changing the E1/2 of the catalyst using different ancillary ligands, by changing the solvent and solution acidity, and by changing the catalyst's protonation state. The overpotential is well-defined for these homogeneous electrocatalysts by the E1/2 of the catalyst and the proton activity of the solution. This is the first such correlation for homogeneous ORR electrocatalysis, and it demonstrates that the remarkably fast TOFs are a consequence of high overpotential. The correlation with overpotential is surprising since the turnover limiting steps involve oxygen binding and protonation, as opposed to turnover limiting electron transfer commonly found in Tafel analysis of heterogeneous ORR materials. Computational studies show that the free energies for oxygen binding to the catalyst and for protonation of the superoxide complex are in general linearly related to the catalyst E1/2, and that this is the origin of the overpotential correlations. This analysis thus provides detailed understanding of the ORR barriers. The best catalysts involve partial decoupling of the influence of the second coordination sphere from the properties of the metal center, which is suggested as new molecular design strategy to avoid the limitations of the traditional scaling relationships for these catalysts.
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Affiliation(s)
- Michael
L. Pegis
- Department
of Chemistry, Yale University, New Haven, Connecticut 06520, United States
| | - Bradley A. McKeown
- Department
of Chemistry, Yale University, New Haven, Connecticut 06520, United States
| | - Neeraj Kumar
- Pacific
Northwest National Laboratory (PNNL), Richland, Washington 99352, United States
| | - Kai Lang
- Department
of Chemistry, University of South Florida, Tampa, Florida 33620, United States
| | - Derek
J. Wasylenko
- Department
of Chemistry, University of Washington, Seattle, Washington 98195-1700, United States
| | - X. Peter Zhang
- Department
of Chemistry, Merkert Chemistry Center, Boston College, Chestnut Hill, Massachusetts 02467, United States
| | - Simone Raugei
- Pacific
Northwest National Laboratory (PNNL), Richland, Washington 99352, United States
| | - James M. Mayer
- Department
of Chemistry, Yale University, New Haven, Connecticut 06520, United States
- E-mail:
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44
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Cardenas AJP, Ginovska B, Kumar N, Hou J, Raugei S, Helm ML, Appel AM, Bullock RM, O'Hagan M. Controlling Proton Delivery through Catalyst Structural Dynamics. Angew Chem Int Ed Engl 2016; 55:13509-13513. [PMID: 27677094 DOI: 10.1002/anie.201607460] [Citation(s) in RCA: 45] [Impact Index Per Article: 5.6] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/02/2016] [Indexed: 01/12/2023]
Abstract
The fastest synthetic molecular catalysts for H2 production and oxidation emulate components of the active site of hydrogenases. The critical role of controlled structural dynamics is recognized for many enzymes, including hydrogenases, but is largely neglected in designing synthetic catalysts. Our results demonstrate the impact of controlling structural dynamics on H2 production rates for [Ni(PPh2 NC6H4R2 )2 ]2+ catalysts (R=n-hexyl, n-decyl, n-tetradecyl, n-octadecyl, phenyl, or cyclohexyl). The turnover frequencies correlate inversely with the rates of chair-boat ring inversion of the ligand, since this dynamic process governs protonation at either catalytically productive or non-productive sites. These results demonstrate that the dynamic processes involved in proton delivery can be controlled through modification of the outer coordination sphere, in a manner similar to the role of the protein architecture in many enzymes. As a design parameter, controlling structural dynamics can increase H2 production rates by three orders of magnitude with a minimal increase in overpotential.
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Affiliation(s)
- Allan Jay P Cardenas
- Center for Molecular Electrocatalysis, Pacific Northwest National Laboratory, P.O. Box 999, K2-57, Richland, WA, 99352, USA.,221 Science Center, State University of New York at Fredonia, Fredonia, NY, 14063, USA
| | - Bojana Ginovska
- Center for Molecular Electrocatalysis, Pacific Northwest National Laboratory, P.O. Box 999, K2-57, Richland, WA, 99352, USA
| | - Neeraj Kumar
- Center for Molecular Electrocatalysis, Pacific Northwest National Laboratory, P.O. Box 999, K2-57, Richland, WA, 99352, USA
| | - Jianbo Hou
- Center for Molecular Electrocatalysis, Pacific Northwest National Laboratory, P.O. Box 999, K2-57, Richland, WA, 99352, USA
| | - Simone Raugei
- Center for Molecular Electrocatalysis, Pacific Northwest National Laboratory, P.O. Box 999, K2-57, Richland, WA, 99352, USA
| | - Monte L Helm
- Center for Molecular Electrocatalysis, Pacific Northwest National Laboratory, P.O. Box 999, K2-57, Richland, WA, 99352, USA
| | - Aaron M Appel
- Center for Molecular Electrocatalysis, Pacific Northwest National Laboratory, P.O. Box 999, K2-57, Richland, WA, 99352, USA
| | - R Morris Bullock
- Center for Molecular Electrocatalysis, Pacific Northwest National Laboratory, P.O. Box 999, K2-57, Richland, WA, 99352, USA
| | - Molly O'Hagan
- Center for Molecular Electrocatalysis, Pacific Northwest National Laboratory, P.O. Box 999, K2-57, Richland, WA, 99352, USA.
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45
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Cardenas AJP, Ginovska B, Kumar N, Hou J, Raugei S, Helm ML, Appel AM, Bullock RM, O'Hagan M. Controlling Proton Delivery through Catalyst Structural Dynamics. Angew Chem Int Ed Engl 2016. [DOI: 10.1002/ange.201607460] [Citation(s) in RCA: 12] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/09/2022]
Affiliation(s)
- Allan Jay P. Cardenas
- Center for Molecular Electrocatalysis; Pacific Northwest National Laboratory; P.O. Box 999, K2-57 Richland WA 99352 USA
- 221 Science Center; State University of New York at Fredonia; Fredonia NY 14063 USA
| | - Bojana Ginovska
- Center for Molecular Electrocatalysis; Pacific Northwest National Laboratory; P.O. Box 999, K2-57 Richland WA 99352 USA
| | - Neeraj Kumar
- Center for Molecular Electrocatalysis; Pacific Northwest National Laboratory; P.O. Box 999, K2-57 Richland WA 99352 USA
| | - Jianbo Hou
- Center for Molecular Electrocatalysis; Pacific Northwest National Laboratory; P.O. Box 999, K2-57 Richland WA 99352 USA
| | - Simone Raugei
- Center for Molecular Electrocatalysis; Pacific Northwest National Laboratory; P.O. Box 999, K2-57 Richland WA 99352 USA
| | - Monte L. Helm
- Center for Molecular Electrocatalysis; Pacific Northwest National Laboratory; P.O. Box 999, K2-57 Richland WA 99352 USA
| | - Aaron M. Appel
- Center for Molecular Electrocatalysis; Pacific Northwest National Laboratory; P.O. Box 999, K2-57 Richland WA 99352 USA
| | - R. Morris Bullock
- Center for Molecular Electrocatalysis; Pacific Northwest National Laboratory; P.O. Box 999, K2-57 Richland WA 99352 USA
| | - Molly O'Hagan
- Center for Molecular Electrocatalysis; Pacific Northwest National Laboratory; P.O. Box 999, K2-57 Richland WA 99352 USA
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46
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Abstract
The reduction of N2 to NH3 by Mo-dependent nitrogenase at its active-site metal cluster FeMo-cofactor utilizes reductive elimination of Fe-bound hydrides with obligatory loss of H2 to activate the enzyme for binding/reduction of N2. Earlier work showed that wild-type nitrogenase and a nitrogenase with amino acid substitutions in the MoFe protein near FeMo-cofactor can catalytically reduce CO2 by two or eight electrons/protons to carbon monoxide (CO) and methane (CH4) at low rates. Here, it is demonstrated that nitrogenase preferentially reduces CO2 by two electrons/protons to formate (HCOO(-)) at rates >10 times higher than rates of CO2 reduction to CO and CH4. Quantum mechanical calculations on the doubly reduced FeMo-cofactor with a Fe-bound hydride and S-bound proton (E2(2H) state) favor a direct reaction of CO2 with the hydride ("direct hydride transfer" reaction pathway), with facile hydride transfer to CO2 yielding formate. In contrast, a significant barrier is observed for reaction of Fe-bound CO2 with the hydride ("associative" reaction pathway), which leads to CO and CH4. Remarkably, in the direct hydride transfer pathway, the Fe-H behaves as a hydridic hydrogen, whereas in the associative pathway it acts as a protic hydrogen. MoFe proteins with amino acid substitutions near FeMo-cofactor (α-70(Val→Ala), α-195(His→Gln)) are found to significantly alter the distribution of products between formate and CO/CH4.
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Affiliation(s)
- Nimesh Khadka
- Department of Chemistry and Biochemistry, Utah State University, Logan, Utah 84322
| | - Dennis R. Dean
- Department of Biochemistry, Virginia Tech, Blacksburg, Virginia 24061
| | | | - Brian M. Hoffman
- Department of Chemistry, Northwestern University, Evanston, Illinois 60208
| | - Simone Raugei
- Pacific Northwestern National Laboratory, Richland, Washington 99352
| | - Lance C. Seefeldt
- Department of Chemistry and Biochemistry, Utah State University, Logan, Utah 84322
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47
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Priyadarshani N, Dutta A, Ginovska B, Buchko GW, O’Hagan M, Raugei S, Shaw WJ. Achieving Reversible H2/H+ Interconversion at Room Temperature with Enzyme-Inspired Molecular Complexes: A Mechanistic Study. ACS Catal 2016. [DOI: 10.1021/acscatal.6b01433] [Citation(s) in RCA: 43] [Impact Index Per Article: 5.4] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/16/2022]
Affiliation(s)
- Nilusha Priyadarshani
- Pacific Northwest National Laboratory, P.O. Box 999, Richland, Washington 99352, United States
| | - Arnab Dutta
- Pacific Northwest National Laboratory, P.O. Box 999, Richland, Washington 99352, United States
| | - Bojana Ginovska
- Pacific Northwest National Laboratory, P.O. Box 999, Richland, Washington 99352, United States
| | - Garry W. Buchko
- Pacific Northwest National Laboratory, P.O. Box 999, Richland, Washington 99352, United States
| | - Molly O’Hagan
- Pacific Northwest National Laboratory, P.O. Box 999, Richland, Washington 99352, United States
| | - Simone Raugei
- Pacific Northwest National Laboratory, P.O. Box 999, Richland, Washington 99352, United States
| | - Wendy J. Shaw
- Pacific Northwest National Laboratory, P.O. Box 999, Richland, Washington 99352, United States
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48
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Wongnate T, Sliwa D, Ginovska B, Smith D, Wolf MW, Lehnert N, Raugei S, Ragsdale SW. The radical mechanism of biological methane synthesis by methyl-coenzyme M reductase. Science 2016; 352:953-8. [PMID: 27199421 DOI: 10.1126/science.aaf0616] [Citation(s) in RCA: 108] [Impact Index Per Article: 13.5] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/11/2015] [Accepted: 04/05/2016] [Indexed: 12/16/2022]
Abstract
Methyl-coenzyme M reductase, the rate-limiting enzyme in methanogenesis and anaerobic methane oxidation, is responsible for the biological production of more than 1 billion tons of methane per year. The mechanism of methane synthesis is thought to involve either methyl-nickel(III) or methyl radical/Ni(II)-thiolate intermediates. We employed transient kinetic, spectroscopic, and computational approaches to study the reaction between the active Ni(I) enzyme and substrates. Consistent with the methyl radical-based mechanism, there was no evidence for a methyl-Ni(III) species; furthermore, magnetic circular dichroism spectroscopy identified the Ni(II)-thiolate intermediate. Temperature-dependent transient kinetics also closely matched density functional theory predictions of the methyl radical mechanism. Identifying the key intermediate in methanogenesis provides fundamental insights to develop better catalysts for producing and activating an important fuel and potent greenhouse gas.
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Affiliation(s)
- Thanyaporn Wongnate
- Department of Biological Chemistry, University of Michigan, Ann Arbor, MI 48109-0606, USA
| | - Dariusz Sliwa
- Department of Biological Chemistry, University of Michigan, Ann Arbor, MI 48109-0606, USA
| | - Bojana Ginovska
- Physical Sciences Division, Pacific Northwest National Laboratory, Post Office Box 999, K1-83, Richland, WA 99352, USA
| | - Dayle Smith
- Physical Sciences Division, Pacific Northwest National Laboratory, Post Office Box 999, K1-83, Richland, WA 99352, USA
| | - Matthew W Wolf
- Department of Chemistry and Department of Biophysics, University of Michigan, Ann Arbor, MI 48109-1055, USA
| | - Nicolai Lehnert
- Department of Chemistry and Department of Biophysics, University of Michigan, Ann Arbor, MI 48109-1055, USA
| | - Simone Raugei
- Physical Sciences Division, Pacific Northwest National Laboratory, Post Office Box 999, K1-83, Richland, WA 99352, USA
| | - Stephen W Ragsdale
- Department of Biological Chemistry, University of Michigan, Ann Arbor, MI 48109-0606, USA.
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49
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Cornish AJ, Ginovska B, Thelen A, da Silva JCS, Soares TA, Raugei S, Dupuis M, Shaw WJ, Hegg EL. Single-Amino Acid Modifications Reveal Additional Controls on the Proton Pathway of [FeFe]-Hydrogenase. Biochemistry 2016; 55:3165-73. [PMID: 27186945 DOI: 10.1021/acs.biochem.5b01044] [Citation(s) in RCA: 21] [Impact Index Per Article: 2.6] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
Abstract
The proton pathway of [FeFe]-hydrogenase is essential for enzymatic H2 production and oxidation and is composed of four residues and a water molecule. A computational analysis of this pathway in the [FeFe]-hydrogenase from Clostridium pasteurianum revealed that the solvent-exposed residue of the pathway (Glu282) forms hydrogen bonds to two residues outside of the pathway (Arg286 and Ser320), implying that these residues could function in regulating proton transfer. In this study, we show that substituting Arg286 with leucine eliminates hydrogen bonding with Glu282 and results in an ∼3-fold enhancement of H2 production activity when methyl viologen is used as an electron donor, suggesting that Arg286 may help control the rate of proton delivery. In contrast, substitution of Ser320 with alanine reduces the rate ∼5-fold, implying that it either acts as a member of the pathway or influences Glu282 to permit proton transfer. Interestingly, quantum mechanics/molecular mechanics and molecular dynamics calculations indicate that Ser320 does not play a structural role or indirectly influence the barrier for proton movement at the entrance of the channel. Rather, it may act as an additional proton acceptor for the pathway or serve in a regulatory role. While further studies are needed to elucidate the role of Ser320, collectively these data provide insights into the complex proton transport process.
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Affiliation(s)
- Adam J Cornish
- Department of Biochemistry & Molecular Biology, Michigan State University , East Lansing, Michigan 48824, United States.,Great Lakes Bioenergy Research Center, Michigan State University , East Lansing, Michigan 48824, United States
| | - Bojana Ginovska
- Physical Sciences Division, Pacific Northwest National Laboratory , Richland, Washington 99352, United States
| | - Adam Thelen
- Department of Biochemistry & Molecular Biology, Michigan State University , East Lansing, Michigan 48824, United States
| | - Julio C S da Silva
- Department of Fundamental Chemistry, Federal University of Pernambuco , Cidade Universitária,50740-560 Recife, PE, Brazil
| | - Thereza A Soares
- Department of Fundamental Chemistry, Federal University of Pernambuco , Cidade Universitária,50740-560 Recife, PE, Brazil
| | - Simone Raugei
- Physical Sciences Division, Pacific Northwest National Laboratory , Richland, Washington 99352, United States
| | - Michel Dupuis
- Physical Sciences Division, Pacific Northwest National Laboratory , Richland, Washington 99352, United States
| | - Wendy J Shaw
- Physical Sciences Division, Pacific Northwest National Laboratory , Richland, Washington 99352, United States
| | - Eric L Hegg
- Department of Biochemistry & Molecular Biology, Michigan State University , East Lansing, Michigan 48824, United States.,Great Lakes Bioenergy Research Center, Michigan State University , East Lansing, Michigan 48824, United States
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50
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Dutta A, Ginovska B, Raugei S, Roberts JAS, Shaw WJ. Optimizing conditions for utilization of an H2 oxidation catalyst with outer coordination sphere functionalities. Dalton Trans 2016; 45:9786-93. [DOI: 10.1039/c6dt00280c] [Citation(s) in RCA: 23] [Impact Index Per Article: 2.9] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/19/2023]
Abstract
[Ni(PCy2NArginine2)2]2+ (CyArg) or [Ni(PCy2NBenzyl2)2]2+ (CyBn) were evaluated for H2 oxidation as a function of temperature, pressure, and solvent. 70 °C and 100 atm H2 result in a TOF of 1.1 × 106 s−1 and an overpotential of 240 mV for CyArg in water. In methanol the rates were 280 s−1 for CyArg and 80 s−1 for CyBn, demonstrating the importance of water and the outer coordination sphere (OCS).
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Affiliation(s)
- Arnab Dutta
- Pacific Northwest National Laboratory
- Richland
- USA
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