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Pellows LM, Vansuch GE, Chica B, Yang ZY, Ruzicka JL, Willis MA, Clinger A, Brown KA, Seefeldt LC, Peters JW, Dukovic G, Mulder DW, King PW. Low-temperature trapping of N2 reduction reaction intermediates in nitrogenase MoFe protein-CdS quantum dot complexes. J Chem Phys 2023; 159:235102. [PMID: 38117020 DOI: 10.1063/5.0170405] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/02/2023] [Accepted: 11/24/2023] [Indexed: 12/21/2023] Open
Abstract
The biological reduction of N2 to ammonia requires the ATP-dependent, sequential delivery of electrons from the Fe protein to the MoFe protein of nitrogenase. It has been demonstrated that CdS nanocrystals can replace the Fe protein to deliver photoexcited electrons to the MoFe protein. Herein, light-activated electron delivery within the CdS:MoFe protein complex was achieved in the frozen state, revealing that all the electron paramagnetic resonance (EPR) active E-state intermediates in the catalytic cycle can be trapped and characterized by EPR spectroscopy. Prior to illumination, the CdS:MoFe protein complex EPR spectrum was composed of a S = 3/2 rhombic signal (g = 4.33, 3.63, and 2.01) consistent with the FeMo-cofactor in the resting state, E0. Illumination for sequential 1-h periods at 233 K under 1 atm of N2 led to a cumulative attenuation of E0 by 75%. This coincided with the appearance of S = 3/2 and S = 1/2 signals assigned to two-electron (E2) and four-electron (E4) reduced states of the FeMo-cofactor, together with additional S = 1/2 signals consistent with the formation of E6 and E8 states. Simulations of EPR spectra allowed quantification of the different E-state populations, along with mapping of these populations onto the Lowe-Thorneley kinetic scheme. The outcome of this work demonstrates that the photochemical delivery of electrons to the MoFe protein can be used to populate all of the EPR active E-state intermediates of the nitrogenase MoFe protein cycle.
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Affiliation(s)
- Lauren M Pellows
- Department of Chemistry, University of Colorado Boulder, Boulder, Colorado 80309, USA
| | - Gregory E Vansuch
- Biosciences Center, National Renewable Energy Laboratory, Golden, Colorado 80401, USA
| | - Bryant Chica
- Biosciences Center, National Renewable Energy Laboratory, Golden, Colorado 80401, USA
| | - Zhi-Yong Yang
- Department of Chemistry and Biochemistry, Utah State University, Logan, Utah 84322, USA
| | - Jesse L Ruzicka
- Department of Chemistry, University of Colorado Boulder, Boulder, Colorado 80309, USA
| | - Mark A Willis
- Institute of Biological Chemistry, Washington State University, Pullman, Washington 99163, USA
| | - Andrew Clinger
- Department of Chemistry and Biochemistry, Utah State University, Logan, Utah 84322, USA
| | - Katherine A Brown
- Biosciences Center, National Renewable Energy Laboratory, Golden, Colorado 80401, USA
| | - Lance C Seefeldt
- Department of Chemistry and Biochemistry, Utah State University, Logan, Utah 84322, USA
| | - John W Peters
- Institute of Biological Chemistry, Washington State University, Pullman, Washington 99163, USA
- Department of Chemistry and Biochemistry, University of Oklahoma, Norman, Oklahoma 73019, USA
| | - Gordana Dukovic
- Department of Chemistry, University of Colorado Boulder, Boulder, Colorado 80309, USA
- Materials Science and Engineering, University of Colorado Boulder, Boulder, Colorado 80303, USA
- Renewable and Sustainable Energy Institute (RASEI), University of Colorado Boulder, Boulder, Colorado 80303, USA
| | - David W Mulder
- Biosciences Center, National Renewable Energy Laboratory, Golden, Colorado 80401, USA
| | - Paul W King
- Biosciences Center, National Renewable Energy Laboratory, Golden, Colorado 80401, USA
- Renewable and Sustainable Energy Institute (RASEI), University of Colorado Boulder, Boulder, Colorado 80303, USA
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Vansuch G, Mulder DW, Chica B, Ruzicka JL, Yang ZY, Pellows LM, Willis MA, Brown KA, Seefeldt LC, Peters JW, Dukovic G, King PW. Cryo-annealing of Photoreduced CdS Quantum Dot-Nitrogenase MoFe Protein Complexes Reveals the Kinetic Stability of the E 4(2N2H) Intermediate. J Am Chem Soc 2023; 145:21165-21169. [PMID: 37729189 PMCID: PMC10557137 DOI: 10.1021/jacs.3c06832] [Citation(s) in RCA: 2] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/28/2023] [Indexed: 09/22/2023]
Abstract
A critical step in the mechanism of N2 reduction to 2NH3 catalyzed by the enzyme nitrogenase is the reaction of the four-electron/four-proton reduced intermediate state of the active-site FeMo-cofactor (E4(4H)). This state is a junction in the catalytic mechanism, either relaxing by the reaction of a metal bound Fe-hydride with a proton forming H2 or going forward with N2 binding coupled to the reductive elimination (re) of two Fe-hydrides as H2 to form the E4(2N2H) state. E4(2N2H) can relax to E4(4H) by the oxidative addition (oa) of H2 and release of N2 or can be further reduced in a series of catalytic steps to release 2NH3. If the H2 re/oa mechanism is correct, it requires that oa of H2 be associative with E4(2N2H). In this report, we have taken advantage of CdS quantum dots in complex with MoFe protein to achieve photodriven electron delivery in the frozen state, with cryo-annealing in the dark, to reveal details of the E-state species and to test the stability of E4(2N2H). Illumination of frozen CdS:MoFe protein complexes led to formation of a population of reduced intermediates. Electron paramagnetic resonance spectroscopy identified E-state signals including E2 and E4(2N2H), as well as signals suggesting the formation of E6 or E8. It is shown that in the frozen state when pN2 is much greater than pH2, the E4(2N2H) state is kinetically stable, with very limited forward or reverse reaction rates. These results establish that the oa of H2 to the E4(2N2H) state follows an associative reaction mechanism.
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Affiliation(s)
- Gregory
E. Vansuch
- Biosciences
Center, National Renewable Energy Laboratory, Golden, Colorado 80401, United States
| | - David W. Mulder
- Biosciences
Center, National Renewable Energy Laboratory, Golden, Colorado 80401, United States
| | - Bryant Chica
- Biosciences
Center, National Renewable Energy Laboratory, Golden, Colorado 80401, United States
| | - Jesse L. Ruzicka
- Department
of Chemistry, University of Colorado Boulder, Boulder, Colorado 80309, United States
| | - Zhi-Yong Yang
- Department
of Chemistry and Biochemistry, Utah State
University, Logan, Utah 84322, United States
| | - Lauren M. Pellows
- Department
of Chemistry, University of Colorado Boulder, Boulder, Colorado 80309, United States
| | - Mark A. Willis
- Institute
of Biological Chemistry, Washington State
University, Pullman, Washington 99163, United States
| | - Katherine A. Brown
- Biosciences
Center, National Renewable Energy Laboratory, Golden, Colorado 80401, United States
| | - Lance C. Seefeldt
- Department
of Chemistry and Biochemistry, Utah State
University, Logan, Utah 84322, United States
| | - John W. Peters
- Institute
of Biological Chemistry, Washington State
University, Pullman, Washington 99163, United States
- Department
of Chemistry and Biochemistry, University
of Oklahoma, Norman, Oklahoma 73019, United States
| | - Gordana Dukovic
- Department
of Chemistry, University of Colorado Boulder, Boulder, Colorado 80309, United States
- Materials
Science and Engineering, University of Colorado
Boulder, Boulder, Colorado 80303, United States
- Renewable
and Sustainable Energy Institute, University
of Colorado Boulder, Boulder, Colorado 80303, United States
| | - Paul W. King
- Biosciences
Center, National Renewable Energy Laboratory, Golden, Colorado 80401, United States
- Renewable
and Sustainable Energy Institute, University
of Colorado Boulder, Boulder, Colorado 80303, United States
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Reis DM, Nunes GG, Sá EL, Friedermann GR, Mangrich AS, Evans DJ, Hitchcock PB, Leigh GJ, Soares JF. Iron(iii) and titanium(iv) oxoalkoxide chemistry: synthetic, structural, magnetochemical and spectroscopic studies of [Ti3(μ3-OPri)2(μ-OPri)3(OPri)6][FeCl4] and [Fe5(μ5-O)(μ-OPri)8Cl5]. NEW J CHEM 2004. [DOI: 10.1039/b403899a] [Citation(s) in RCA: 14] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022]
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