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Title: Structural characterization of the P 1+ intermediate state of the P-cluster of nitrogenase

Nitrogenase is the enzyme that reduces atmospheric dinitrogen (N 2) to ammonia (NH 3) 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 N 2 is reduced to NH 3. 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 (P N) state to the two-electron oxidized P 2+ 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 (P 2+, P 1+, and P N) 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 P 1+ state retains the serine hydroxyl coordination but lacks the backbone amide coordination observed in the Pmore » 2+ states. Lastly, these results provide a complete picture of the redox-dependent ligand rearrangements of the three P-cluster redox states.« less
Authors:
 [1] ;  [2] ;  [3] ;  [4] ;  [5] ;  [5] ;  [1] ;  [1] ;  [1] ;  [6] ;  [7] ;  [8]
  1. Montana State Univ., Bozeman, MT (United States)
  2. Washington State Univ., Pullman, WA (United States)
  3. Pacific Northwest National Lab. (PNNL), Richland, WA (United States); Univ. of Washington, Seattle, WA (United States)
  4. Pacific Northwest National Lab. (PNNL), Richland, WA (United States)
  5. Utah State Univ., Logan, UT (United States)
  6. Washington State Univ., Pullman, WA (United States); Pacific Northwest National Lab. (PNNL), Richland, WA (United States)
  7. Pacific Northwest National Lab. (PNNL), Richland, WA (United States); Utah State Univ., Logan, UT (United States)
  8. Montana State Univ., Bozeman, MT (United States); Washington State Univ., Pullman, WA (United States); Pacific Northwest National Lab. (PNNL), Richland, WA (United States)
Publication Date:
Grant/Contract Number:
MCB-1330807; AC05-76RL01830
Type:
Accepted Manuscript
Journal Name:
Journal of Biological Chemistry
Additional Journal Information:
Journal Volume: 293; Journal Issue: 25; Journal ID: ISSN 0021-9258
Publisher:
American Society for Biochemistry and Molecular Biology
Research Org:
Pacific Northwest National Lab. (PNNL), Richland, WA (United States)
Sponsoring Org:
USDOE
Country of Publication:
United States
Language:
English
Subject:
36 MATERIALS SCIENCE; oxidation-reduction (redox); metalloprotein; nitrogenase; enzyme structure; computational biology; nitrogen fixation; nitrogen reduction; P-cluster of MoFe protein; poised states; redox mediators; redox-dependent ligand exchange; [8Fe-7S] cluster
OSTI Identifier:
1461545