1
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Le LN, Joyce JP, Oyala PH, DeBeer S, Agapie T. Highly Activated Terminal Carbon Monoxide Ligand in an Iron-Sulfur Cluster Model of FeMco with Intermediate Local Spin State at Fe. J Am Chem Soc 2024; 146:5045-5050. [PMID: 38358932 PMCID: PMC10910499 DOI: 10.1021/jacs.3c12025] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/27/2023] [Revised: 01/29/2024] [Accepted: 01/30/2024] [Indexed: 02/17/2024]
Abstract
Nitrogenases, the enzymes that convert N2 to NH3, also catalyze the reductive coupling of CO to yield hydrocarbons. CO-coordinated species of nitrogenase clusters have been isolated and used to infer mechanistic information. However, synthetic FeS clusters displaying CO ligands remain rare, which limits benchmarking. Starting from a synthetic cluster that models a cubane portion of the FeMo cofactor (FeMoco), including a bridging carbyne ligand, we report a heterometallic tungsten-iron-sulfur cluster with a single terminal CO coordination in two oxidation states with a high level of CO activation (νCO = 1851 and 1751 cm-1). The local Fe coordination environment (2S, 1C, 1CO) is identical to that in the protein making this system a suitable benchmark. Computational studies find an unusual intermediate spin electronic configuration at the Fe sites promoted by the presence the carbyne ligand. This electronic feature is partly responsible for the high degree of CO activation in the reduced cluster.
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Affiliation(s)
- Linh N.
V. Le
- Division
of Chemistry and Chemical Engineering, California
Institute of Technology, Pasadena, California 91125, United States
| | - Justin P. Joyce
- Max
Planck Institute for Chemical Energy Conversion, Stiftstraße 34-36, 45470 Mülheim an der Ruhr, Germany
| | - Paul H. Oyala
- Division
of Chemistry and Chemical Engineering, California
Institute of Technology, Pasadena, California 91125, United States
| | - Serena DeBeer
- Max
Planck Institute for Chemical Energy Conversion, Stiftstraße 34-36, 45470 Mülheim an der Ruhr, Germany
| | - Theodor Agapie
- Division
of Chemistry and Chemical Engineering, California
Institute of Technology, Pasadena, California 91125, United States
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2
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Barchenko M, O’Malley PJ, de Visser SP. Mechanism of Nitrogen Reduction to Ammonia in a Diiron Model of Nitrogenase. Inorg Chem 2023; 62:14715-14726. [PMID: 37650683 PMCID: PMC10498488 DOI: 10.1021/acs.inorgchem.3c02089] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/23/2023] [Indexed: 09/01/2023]
Abstract
Nitrogenase is a fascinating enzyme in biology that reduces dinitrogen from air to ammonia through stepwise reduction and protonation. Despite it being studied in detail by experimental and computational groups, there are still many unknown factors in the catalytic cycle of nitrogenase, especially related to the addition of protons and electrons and their order. A recent biomimetic study characterized a potential dinitrogen-bridged diiron cluster as a synthetic model of nitrogenase. Using strong acid and reductants, the dinitrogen was converted into ammonia molecules, but details of the mechanism remains unknown. In particular, it was unclear from the experimental studies whether the proton and electron transfer steps are sequential or alternating. Moreover, the work failed to establish what the function of the diiron core is and whether it split into mononuclear iron fragments during the reaction. To understand the structure and reactivity of the biomimetic dinitrogen-bridged diiron complex [(P2P'PhFeH)2(μ-N2)] with triphenylphosphine ligands, we performed a density functional theory study. Our computational methods were validated against experimental crystal structure coordinates, Mössbauer parameters, and vibrational frequencies and show excellent agreement. Subsequently, we investigated the alternating and consecutive addition of electrons and protons to the system. The calculations identify a number of possible reaction channels, namely, same-site protonation, alternating protonation, and complex dissociation into mononuclear iron centers. The calculations show that the overall mechanism is not a pure sequential set of electron and proton transfers but a mixture of alternating and consecutive steps. In particular, the first reaction steps will start with double proton transfer followed by an electron transfer, while thereafter, there is another proton transfer and a second electron transfer to give a complex whereby ammonia can split off with a low energetic barrier. The second channel starts with alternating protonation of the two nitrogen atoms, whereafter the initial double proton transfer, electrons and protons are added sequentially to form a hydrazine-bound complex. The latter split off ammonia spontaneously after further protonation. The various reaction channels are analyzed with valence bond and orbital diagrams. We anticipate the nitrogenase enzyme to operate with mixed alternating and consecutive protonation and electron transfer steps.
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Affiliation(s)
- Maxim Barchenko
- Manchester
Institute of Biotechnology, The University
of Manchester, 131 Princess Street, Manchester M1 7DN, U.K.
- Department
of Chemistry, The University of Manchester, Oxford Road, Manchester M13 9PL, U.K.
| | - Patrick J. O’Malley
- Department
of Chemistry, The University of Manchester, Oxford Road, Manchester M13 9PL, U.K.
| | - Sam P. de Visser
- Manchester
Institute of Biotechnology, The University
of Manchester, 131 Princess Street, Manchester M1 7DN, U.K.
- Department
of Chemical Engineering, The University
of Manchester, Oxford
Road, Manchester M13 9PL, U.K.
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3
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Lu Y, Sen K, Yong C, Gunn DSD, Purton JA, Guan J, Desmoutier A, Abdul Nasir J, Zhang X, Zhu L, Hou Q, Jackson-Masters J, Watts S, Hanson R, Thomas HN, Jayawardena O, Logsdail AJ, Woodley SM, Senn HM, Sherwood P, Catlow CRA, Sokol AA, Keal TW. Multiscale QM/MM modelling of catalytic systems with ChemShell. Phys Chem Chem Phys 2023; 25:21816-21835. [PMID: 37097706 DOI: 10.1039/d3cp00648d] [Citation(s) in RCA: 8] [Impact Index Per Article: 8.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 04/26/2023]
Abstract
Hybrid quantum mechanical/molecular mechanical (QM/MM) methods are a powerful computational tool for the investigation of all forms of catalysis, as they allow for an accurate description of reactions occurring at catalytic sites in the context of a complicated electrostatic environment. The scriptable computational chemistry environment ChemShell is a leading software package for QM/MM calculations, providing a flexible, high performance framework for modelling both biomolecular and materials catalysis. We present an overview of recent applications of ChemShell to problems in catalysis and review new functionality introduced into the redeveloped Python-based version of ChemShell to support catalytic modelling. These include a fully guided workflow for biomolecular QM/MM modelling, starting from an experimental structure, a periodic QM/MM embedding scheme to support modelling of metallic materials, and a comprehensive set of tutorials for biomolecular and materials modelling.
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Affiliation(s)
- You Lu
- STFC Scientific Computing, Daresbury Laboratory, Keckwick Lane, Daresbury, Warrington, WA4 4AD, UK.
| | - Kakali Sen
- STFC Scientific Computing, Daresbury Laboratory, Keckwick Lane, Daresbury, Warrington, WA4 4AD, UK.
| | - Chin Yong
- STFC Scientific Computing, Daresbury Laboratory, Keckwick Lane, Daresbury, Warrington, WA4 4AD, UK.
| | - David S D Gunn
- STFC Scientific Computing, Daresbury Laboratory, Keckwick Lane, Daresbury, Warrington, WA4 4AD, UK.
| | - John A Purton
- STFC Scientific Computing, Daresbury Laboratory, Keckwick Lane, Daresbury, Warrington, WA4 4AD, UK.
| | - Jingcheng Guan
- Kathleen Lonsdale Materials Chemistry, Department of Chemistry, University College London, 20 Gordon Street, London, WC1H 0AJ, UK
| | - Alec Desmoutier
- Kathleen Lonsdale Materials Chemistry, Department of Chemistry, University College London, 20 Gordon Street, London, WC1H 0AJ, UK
| | - Jamal Abdul Nasir
- Kathleen Lonsdale Materials Chemistry, Department of Chemistry, University College London, 20 Gordon Street, London, WC1H 0AJ, UK
| | - Xingfan Zhang
- Kathleen Lonsdale Materials Chemistry, Department of Chemistry, University College London, 20 Gordon Street, London, WC1H 0AJ, UK
| | - Lei Zhu
- Kathleen Lonsdale Materials Chemistry, Department of Chemistry, University College London, 20 Gordon Street, London, WC1H 0AJ, UK
| | - Qing Hou
- Kathleen Lonsdale Materials Chemistry, Department of Chemistry, University College London, 20 Gordon Street, London, WC1H 0AJ, UK
| | - Joe Jackson-Masters
- Cardiff Catalysis Institute, School of Chemistry, Cardiff University, Cardiff CF10 3AT, UK
| | - Sam Watts
- Cardiff Catalysis Institute, School of Chemistry, Cardiff University, Cardiff CF10 3AT, UK
| | - Rowan Hanson
- Cardiff Catalysis Institute, School of Chemistry, Cardiff University, Cardiff CF10 3AT, UK
| | - Harry N Thomas
- Cardiff Catalysis Institute, School of Chemistry, Cardiff University, Cardiff CF10 3AT, UK
| | - Omal Jayawardena
- Cardiff Catalysis Institute, School of Chemistry, Cardiff University, Cardiff CF10 3AT, UK
| | - Andrew J Logsdail
- Cardiff Catalysis Institute, School of Chemistry, Cardiff University, Cardiff CF10 3AT, UK
| | - Scott M Woodley
- Kathleen Lonsdale Materials Chemistry, Department of Chemistry, University College London, 20 Gordon Street, London, WC1H 0AJ, UK
| | - Hans M Senn
- School of Chemistry, University of Glasgow, Joseph Black Building, Glasgow G12 8QQ, UK
| | - Paul Sherwood
- Department of Chemistry, Lancaster University, Lancaster, LA1 4YB, UK
| | - C Richard A Catlow
- Kathleen Lonsdale Materials Chemistry, Department of Chemistry, University College London, 20 Gordon Street, London, WC1H 0AJ, UK
- Cardiff Catalysis Institute, School of Chemistry, Cardiff University, Cardiff CF10 3AT, UK
| | - Alexey A Sokol
- Kathleen Lonsdale Materials Chemistry, Department of Chemistry, University College London, 20 Gordon Street, London, WC1H 0AJ, UK
| | - Thomas W Keal
- STFC Scientific Computing, Daresbury Laboratory, Keckwick Lane, Daresbury, Warrington, WA4 4AD, UK.
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4
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Pang Y, Bjornsson R. The E3 state of FeMoco: one hydride, two hydrides or dihydrogen? Phys Chem Chem Phys 2023; 25:21020-21036. [PMID: 37522223 DOI: 10.1039/d3cp01106b] [Citation(s) in RCA: 2] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 08/01/2023]
Abstract
Hydrides are present in the reduced states of the iron-molybdenum cofactor (FeMoco) of Mo nitrogenase and are believed to play a key mechanistic role in the dinitrogen reduction reaction catalyzed by the enzyme. Two hydrides are present in the E4 state according to 1H ENDOR and there is likely a single hydride in the E2 redox state. The 2-hydride E4 state has been experimentally observed to bind N2 and it has been speculated that E3 may bind N2 as well. However, the E3 state has not been directly observed and very little is known about its molecular and electronic structure or reactivity. In recent computational studies, we have explored the energy surfaces of the E2 and E4 by QM/MM modelling, and found that the most stable hydride isomers contain bridging or partially bridging hydrides with an open protonated belt sulfide-bridge. In this work we systematically explore the energy surface of the E3 redox state, comparing single hydride and two-hydride isomers with varying coordination and bridging vs. terminal sulfhydryl groups. We also include a model featuring a triply protonated carbide. The results are only mildly dependent on the QM-region size. The three most stable E3 isomers at the r2SCAN level of theory have in common: an open belt sulfide-bridge (terminal sulfhydryl group on Fe6) and either 2 bridging hydrides (between Fe2 and Fe6), 1 bridging-1-terminal hydride (around Fe2 and Fe6) or a dihydrogen ligand bound at the Fe2 site. Analyzing the functional dependency of the results, we find that functionals previously found to predict accurate structures of spin-coupled Fe/Mo dimers and FeMoco (TPSSh, B97-D3, r2SCAN, and B3LYP*) are in generally good agreement about the stability of these 3 E3 isomers. However, B3LYP*, similar to its parent B3LYP method, predicts a triply protonated carbide isomer as the most stable isomer, an unlikely scenario in view of the lack of experimental evidence for carbide protonation occurring in reduced FeMoco states. Distinguishing further between the 3 hydride isomers is difficult and this flexible coordination nature of hydrides suggests that multiple hydride isomers could be present during experimental conditions. N2 binding was explored and resulted in geometries with 2 bridging hydrides and N2 bound to either Fe2 or Fe6 with a local low-spin state on the Fe. N2 binding is predicted to be mildly endothermic, similar to the E2 state, and it seems unlikely that the E3 state is capable of binding N2.
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Affiliation(s)
- Yunjie Pang
- College of Chemistry, Beijing Normal University, 100875, Beijing, China
- Max-Planck Institute for Chemical Energy Conversion, Stiftstrasse 34-36, 45470 Mülheim an der Ruhr, Germany
| | - Ragnar Bjornsson
- Max-Planck Institute for Chemical Energy Conversion, Stiftstrasse 34-36, 45470 Mülheim an der Ruhr, Germany
- Univ. Grenoble Alpes, CNRS, CEA, IRIG, Laboratoire de Chimie et Biologie des Métaux, 17 Rue des Martyrs, F-38054 Grenoble, Cedex, France.
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5
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Nemykin VN, Sabin JR, Kail BW, Upadhyay A, Hendrich MP, Basu P. Influence of the ligand-field on EPR parameters of cis- and trans-isomers in Mo V systems relevant to molybdenum enzymes: Experimental and density functional theory study. J Inorg Biochem 2023; 245:112228. [PMID: 37149488 PMCID: PMC10330323 DOI: 10.1016/j.jinorgbio.2023.112228] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/13/2022] [Revised: 04/12/2023] [Accepted: 04/12/2023] [Indexed: 05/08/2023]
Abstract
The electron paramagnetic resonance (EPR) investigation of mononuclear cis- and trans-(L1O)MoOCl2 complexes [L1OH = bis(3,5-dimethylpyrazolyl)-3-tert-butyl-2-hydroxy-5-methylphenyl)methane] reveals a significant difference in their spin Hamiltonian parameters which reflect different equatorial and axial ligand fields created by the heteroscorpionate donor atoms. Density functional theory (DFT) was used to calculate the values of principal components and relative orientations of the g and A tensors, and the molecular framework in four pairs of isomeric mononuclear oxo‑molybdenum(V) complexes (cis- and trans-(L1O)MoOCl2, cis,cis- and cis,trans-(L-N2S2)MoOCl [L-N2S2H2 = N,N'-dimethyl-N,N'-bis(mercaptophenyl)ethylenediamine], cis,cis- and cis,trans-(L-N2S2)MoO(SCN), and cis- and trans-[(dt)2MoO(OMe)]2- [dtH2 = 2,3-dimercapto-2-butene]). Scalar relativistic DFT calculations were conducted using three different exchange-correlation functionals. It was found that the use of hybrid exchange-correlation functional with 25% of the Hartree-Fock exchange leads to the best quantitative agreement between theory and experiment. A simplified ligand-field approach was used to analyze the influence of the ligand fields in all cis- and trans-isomers on energies and contributions of molybdenum d-orbital manifold to g and A tensors and relative orientations. Specifically, contributions that originated from the spin-orbit coupling of the dxz, dyz, and dx2-y2 orbitals into the ground state have been discussed. The new findings are discussed in the context of the experimental data of mononuclear molybdoenzyme, DMSO reductase.
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Affiliation(s)
- Victor N Nemykin
- Department of Chemistry, University of Tennessee - Knoxville, Knoxville, TN 37996, USA; Department of Chemistry and Biochemistry, University of Minnesota Duluth, Duluth, MN 55812, USA.
| | - Jared R Sabin
- Department of Chemistry and Biochemistry, University of Minnesota Duluth, Duluth, MN 55812, USA
| | - Brian W Kail
- Department of Chemistry and Biochemistry, Duquesne University, Pittsburgh, PA 15216, USA
| | - Anup Upadhyay
- Department of Chemistry, Carnegie Mellon University, Pittsburgh, PA 15213, USA
| | - Michael P Hendrich
- Department of Chemistry, Carnegie Mellon University, Pittsburgh, PA 15213, USA.
| | - Partha Basu
- Department of Chemistry and Biochemistry, Duquesne University, Pittsburgh, PA 15216, USA; Department of Chemistry and Chemical Biology, Indiana University Purdue University Indianapolis, Indianapolis, IN 46202, USA.
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6
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Dance I. The HD Reaction of Nitrogenase: a Detailed Mechanism. Chemistry 2023; 29:e202202502. [PMID: 36274057 PMCID: PMC10099629 DOI: 10.1002/chem.202202502] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/11/2022] [Indexed: 11/06/2022]
Abstract
Nitrogenase is the enzyme that converts N2 to NH3 under ambient conditions. The chemical mechanism of this catalysis at the active site FeMo-co [Fe7 S9 CMo(homocitrate)] is unknown. An obligatory co-product is H2 , while exogenous H2 is a competitive inhibitor. Isotopic substitution using exogenous D2 revealed the N2 -dependent reaction D2 +2H+ +2e- →2HD (the 'HD reaction'), together with a collection of additional experimental characteristics and requirements. This paper describes a detailed mechanism for the HD reaction, developed and elaborated using density functional simulations with a 486-atom model of the active site and surrounding protein. First D2 binds at one Fe atom (endo-Fe6 coordination position), where it is flanked by H-Fe6 (exo position) and H-Fe2 (endo position). Then there is synchronous transfer of these two H atoms to bound D2 , forming one HD bound to Fe2 and a second HD bound to Fe6. These two HD dissociate sequentially. The final phase is recovery of the two flanking H atoms. These H atoms are generated, sequentially, by translocation of a proton from the protein surface to S3B of FeMo-co and combination with introduced electrons. The first H atom migrates from S3B to exo-Fe6 and the second from S3B to endo-Fe2. Reaction energies and kinetic barriers are reported for all steps. This mechanism accounts for the experimental data: (a) stoichiometry; (b) the N2 -dependence results from promotional N2 bound at exo-Fe2; (c) different N2 binding Km for the HD reaction and the NH3 formation reaction results from involvement of two different sites; (d) inhibition by CO; (e) the non-occurrence of 2HD→H2 +D2 results from the synchronicity of the two transfers of H to D2 ; (f) inhibition of HD production at high pN2 is by competitive binding of N2 at endo-Fe6; (g) the non-leakage of D to solvent follows from the hydrophobic environment and irreversibility of proton introduction.
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Affiliation(s)
- Ian Dance
- School of Chemistry, UNSW, Sydney, Australia
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7
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Dance I. Understanding the tethered unhooking and rehooking of S2B in the reaction domain of FeMo-co, the active site of nitrogenase. Dalton Trans 2022; 51:15538-15554. [PMID: 36168836 DOI: 10.1039/d2dt02571j] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022]
Abstract
The active site of the nitrogen fixing enzyme nitrogenase is an Fe7MoS9C cluster, and investigations of the enigmatic chemical mechanism of the enzyme have focussed on a pair of Fe atoms, Fe2 and Fe6, and the S2B atom that bridges them. There are three proposals for the status of the Fe2-S2B-Fe6 bridge during the catalytic cycle: one that it remains intact, another that it is completely labile and absent during catalysis, and a third that S2B is hemilabile, unhooking one of its bonds to Fe2 or Fe6. This report examines the tethered unhooking of S2B and factors that affect it, using DFT calculations of 50 geometric/electronic possibilities with a 485 atom model including all relevant parts of surrounding protein. The outcomes are: (a) unhooking the S2B-Fe2 bond is feasible and favourable, but alternative unhooking of the S2B-Fe6 bond is unlikely for steric reasons, (b) energy differences between hooked and unhooked isomers are generally <10 kcal mol-1, usually with unhooked more stable, (c) ligation at the exo-Fe6 position inhibits unhooking, (d) unhooking of hydrogenated S2B is more favourable than that of bare S2B, (e) hydrogen bonding from the NεH function of His195 to S2B occurs in hooked and unhooked forms, and possibly stabilises unhooking, (f) unhooking is reversible with kinetic barriers ranging 10-13 kcal mol-1. The conclusion is that energetically accessible reversible unhooking of S2B or S2BH, as an intrinsic property of FeMo-co, needs to be considered in the formulation of mechanisms for the reactions of nitrogenase.
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Affiliation(s)
- Ian Dance
- School of Chemistry, UNSW Sydney, Australia.
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8
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Gee LB, Myers WK, Nack-Lehman PA, Scott AD, Yan L, George SJ, Dong W, Dapper CH, Newton WE, Cramer SP. Nitrogenase Chemistry at 10 Kelvin─Phototautomerization and Recombination of CO-Inhibited α-H195Q Enzyme. Inorg Chem 2022; 61:11509-11513. [PMID: 35856737 DOI: 10.1021/acs.inorgchem.2c00818] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Abstract
CO-bound forms of nitrogenase are N2-reduction inhibited and likely intermediates in Fischer-Tropsch chemistry. Visible-light photolysis at 7 K was used to interrogate all three known CO-related EPR-active forms as exhibited by the α-H195Q variant of Azotobacter vinelandii nitrogenase MoFe protein. The hi(5)-CO EPR signal converted to the hi-CO EPR signal, which reverted at 10 K. FT-IR monitoring revealed an exquisitely light-sensitive "Hi-2" species with bands at 1932 and 1866 cm-1 that yielded "Hi-1" with bands at 1969 and 1692 cm-1, which reverted to "Hi-2". The similarities of photochemical behavior and recombination kinetics showed, for the first time, that hi-CO EPR and "Hi-1" IR signals arise from one chemical species. hi(5)-CO EPR and "Hi-2" IR signals are from a second species, and lo-CO EPR and "Lo-2" IR signals, formed after prolonged illumination, are from a third species. Comparing FT-IR data with CO-inhibited MoFe-protein crystal structures allowed assignment of CO-bonding geometries in these species.
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Affiliation(s)
- Leland B Gee
- Department of Chemistry, University of California, Davis, California 95616, United States.,LCLS, SLAC National Accelerator Laboratory, Menlo Park, California 94025, United States
| | - William K Myers
- Department of Chemistry, University of Oxford, Oxford 3QR OX1, United Kingdom
| | - Patrick A Nack-Lehman
- Department of Chemistry, University of California, Davis, California 95616, United States
| | - Aubrey D Scott
- Department of Chemistry, University of California, Davis, California 95616, United States
| | - Lifen Yan
- Department of Chemistry, University of California, Davis, California 95616, United States
| | - Simon J George
- Department of Chemistry, University of California, Davis, California 95616, United States
| | - Weibing Dong
- Department of Chemistry, University of California, Davis, California 95616, United States
| | - Christie H Dapper
- Department of Biochemistry, Virginia Tech, Blacksburg, Virginia 24061, United States
| | - William E Newton
- Department of Biochemistry, Virginia Tech, Blacksburg, Virginia 24061, United States
| | - Stephen P Cramer
- Department of Chemistry, University of California, Davis, California 95616, United States.,SETI Institute, Mountain View, California 94043, United States
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9
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Kisgeropoulos EC, Gan YJ, Greer SM, Hazel JM, Shafaat HS. Pulsed Multifrequency Electron Paramagnetic Resonance Spectroscopy Reveals Key Branch Points for One- vs Two-Electron Reactivity in Mn/Fe Proteins. J Am Chem Soc 2022; 144:11991-12006. [PMID: 35786920 DOI: 10.1021/jacs.1c13738] [Citation(s) in RCA: 5] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Abstract
Traditionally, the ferritin-like superfamily of proteins was thought to exclusively use a diiron active site in catalyzing a diverse array of oxygen-dependent reactions. In recent years, novel redox-active cofactors featuring heterobimetallic Mn/Fe active sites have been discovered in both the radical-generating R2 subunit of class Ic (R2c) ribonucleotide reductases (RNRs) and the related R2-like ligand-binding oxidases (R2lox). However, the protein-specific factors that differentiate the radical reactivity of R2c from the C-H activation reactions of R2lox remain unknown. In this work, multifrequency pulsed electron paramagnetic resonance (EPR) spectroscopy and ligand hyperfine techniques in conjunction with broken-symmetry density functional theory calculations are used to characterize the molecular and electronic structures of two EPR-active intermediates trapped during aerobic assembly of the R2lox Mn/Fe cofactor. A MnIII(μ-O)(μ-OH)FeIII species is identified as the first EPR-active species and represents a common state between the two classes of redox-active Mn/Fe proteins. The species downstream from the MnIII(μ-O)(μ-OH)FeIII state exhibits unique EPR properties, including unprecedented spectral breadth and isotope-dependent g-tensors, which are attributed to a weakly coupled, hydrogen-bonded MnIII(μ-OH)FeIII species. This final intermediate precedes formation of the MnIII/FeIII resting state and is suggested to be relevant to understanding the endogenous reactivity of R2lox.
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Affiliation(s)
- Effie C Kisgeropoulos
- The Ohio State Biochemistry Program, The Ohio State University, 100 W 18th Avenue, Columbus, Ohio 43210, United States
| | - Yunqiao J Gan
- Department of Chemistry and Biochemistry, The Ohio State University, 100 W 18th Avenue, Columbus, Ohio 43210, United States
| | - Samuel M Greer
- National High Magnetic Field Laboratory, Florida State University, Tallahassee, Florida 32310, United States.,Department of Chemistry and Biochemistry, Florida State University, Tallahassee, Florida 32306, United States
| | - Joseph M Hazel
- Department of Chemistry and Biochemistry, The Ohio State University, 100 W 18th Avenue, Columbus, Ohio 43210, United States
| | - Hannah S Shafaat
- The Ohio State Biochemistry Program, The Ohio State University, 100 W 18th Avenue, Columbus, Ohio 43210, United States.,Department of Chemistry and Biochemistry, The Ohio State University, 100 W 18th Avenue, Columbus, Ohio 43210, United States
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10
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Brown AC, Thompson NB, Suess DLM. Evidence for Low-Valent Electronic Configurations in Iron-Sulfur Clusters. J Am Chem Soc 2022; 144:9066-9073. [PMID: 35575703 DOI: 10.1021/jacs.2c01872] [Citation(s) in RCA: 11] [Impact Index Per Article: 5.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/24/2023]
Abstract
Although biological iron-sulfur (Fe-S) clusters perform some of the most difficult redox reactions in nature, they are thought to be composed exclusively of Fe2+ and Fe3+ ions, as well as mixed-valent pairs with average oxidation states of Fe2.5+. We herein show that Fe-S clusters formally composed of these valences can access a wider range of electronic configurations─in particular, those featuring low-valent Fe1+ centers. We demonstrate that CO binding to a synthetic [Fe4S4]0 cluster supported by N-heterocyclic carbene ligands induces the generation of Fe1+ centers via intracluster electron transfer, wherein a neighboring pair of Fe2+ sites reduces the CO-bound site to a low-valent Fe1+ state. Similarly, CO binding to an [Fe4S4]+ cluster induces electron delocalization with a neighboring Fe site to form a mixed-valent Fe1.5+Fe2.5+ pair in which the CO-bound site adopts partial low-valent character. These low-valent configurations engender remarkable C-O bond activation without having to traverse highly negative and physiologically inaccessible [Fe4S4]0/[Fe4S4]- redox couples.
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Affiliation(s)
- Alexandra C Brown
- Department of Chemistry, Massachusetts Institute of Technology, Cambridge, Massachusetts 02139, United States
| | - Niklas B Thompson
- Department of Chemistry, Massachusetts Institute of Technology, Cambridge, Massachusetts 02139, United States
| | - Daniel L M Suess
- Department of Chemistry, Massachusetts Institute of Technology, Cambridge, Massachusetts 02139, United States
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11
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Gee LB, Scott AD, Dapper CH, Newton WE, Cramer SP. Carbon monoxide binding to α-R277H Mo-nitrogenase – Evidence for multiple pH-dependent species from IR-monitored photolysis. J Inorg Biochem 2022; 232:111806. [DOI: 10.1016/j.jinorgbio.2022.111806] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/30/2021] [Revised: 02/28/2022] [Accepted: 03/21/2022] [Indexed: 10/18/2022]
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