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Title: Exploring Electron/Proton Transfer and Conformational Changes in the Nitrogenase MoFe Protein and FeMo-cofactor Through Cryoreduction/EPR Measurements

Here, we combine cryoreduction/annealing/EPR measurements of nitrogenase MoFe protein with results of earlier investigations to provide a detailed view of the electron/proton transfer events and conformational changes that occur during early stages of [e -/H +] accumulation by the MoFe protein. This includes reduction of (i) the non-catalytic state of the iron-molybdenum cofactor (FeMo-co) active site that is generated by chemical oxidation of the resting-state cofactor (S = 3/2)) within resting MoFe (E 0), and (ii) the catalytic state that has accumulated n =1 [e -/H +] above the resting-state level, denoted E 1(1H) (S ≥ 1) in the Lowe-Thorneley kinetic scheme. FeMo-co does not undergo a major change of conformation during reduction of oxidized FeMo-co. In contrast, FeMo-co undergoes substantial conformational changes during the reduction of E 0 to E 1(1H), and of E 1(1H) to E 2(2H) (n = 2; S = 3/2). The experimental results further suggest that the E 1(1H) → E 2(2H) step involves coupled delivery of a proton and electron (PCET) to FeMo-co of E 1(H) to generate a non-equilibrium S = ½ form E 2(2H)*. This subsequently undergoes conformational relaxation and attendant change in FeMo-co spin state, to generate the equilibrium E 2(2H)more » (S = 3/2) state. Unexpectedly, these experiments also reveal conformational coupling between FeMo-co and P-cluster, and between Fe protein binding and FeMo-co, which might play a role in gated ET from reduced Fe protein to FeMo-co.« less
Authors:
 [1] ;  [2] ;  [2] ;  [2] ;  [1] ;  [3] ;  [2] ;  [1]
  1. Northwestern Univ., Evanston, IL (United States). Dept. of Chemistry
  2. Utah State Univ., Logan, UT (United States). Dept. of Chemistry and Biochemistry
  3. Virginia Polytechnic Inst. and State Univ. (Virginia Tech), Blacksburg, VA (United States). Dept. of Biochemistry
Publication Date:
Grant/Contract Number:
SC0010687; GM 111097; SC0010834
Type:
Accepted Manuscript
Journal Name:
Israel Journal of Chemistry
Additional Journal Information:
Journal Volume: 56; Journal Issue: 9-10; Journal ID: ISSN 0021-2148
Publisher:
Wiley
Research Org:
Utah State Univ., Logan, UT (United States)
Sponsoring Org:
USDOE Office of Science (SC), Basic Energy Sciences (BES) (SC-22); National Institutes of Health (NIH)
Country of Publication:
United States
Language:
English
Subject:
37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CHEMISTRY; 59 BASIC BIOLOGICAL SCIENCES; conformation analysis; electron transfer; enzyme catalysis; EPR spectroscopy; proton transfer
OSTI Identifier:
1463083
Alternate Identifier(s):
OSTI ID: 1401224