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

Journal Article · · Israel Journal of Chemistry
 [1];  [2];  [2];  [2];  [3];  [4];  [2];  [3]
  1. Northwestern Univ., Evanston, IL (United States). Dept. of Chemistry; OSTI
  2. Utah State Univ., Logan, UT (United States). Dept. of Chemistry and Biochemistry
  3. Northwestern Univ., Evanston, IL (United States). Dept. of Chemistry
  4. Virginia Polytechnic Inst. and State Univ. (Virginia Tech), Blacksburg, VA (United States). Dept. of Biochemistry
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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 (E0), and (ii) the catalytic state that has accumulated n =1 [e-/H+] above the resting-state level, denoted E1(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 E0 to E1(1H), and of E1(1H) to E2(2H) (n = 2; S = 3/2). The experimental results further suggest that the E1(1H) → E2(2H) step involves coupled delivery of a proton and electron (PCET) to FeMo-co of E1(H) to generate a non-equilibrium S = ½ form E2(2H)*. This subsequently undergoes conformational relaxation and attendant change in FeMo-co spin state, to generate the equilibrium E2(2H) (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.
Research Organization:
Utah State Univ., Logan, UT (United States)
Sponsoring Organization:
National Inst. of Health (NIH); USDOE Office of Science (SC), Basic Energy Sciences (BES) (SC-22)
Grant/Contract Number:
SC0010687; SC0010834
OSTI ID:
1463083
Alternate ID(s):
OSTI ID: 1401224
Journal Information:
Israel Journal of Chemistry, Journal Name: Israel Journal of Chemistry Journal Issue: 9-10 Vol. 56; ISSN 0021-2148
Publisher:
WileyCopyright Statement
Country of Publication:
United States
Language:
English

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Cited By (2)

X‐ray Magnetic Circular Dichroism Spectroscopy Applied to Nitrogenase and Related Models: Experimental Evidence for a Spin‐Coupled Molybdenum(III) Center journal June 2019
X-ray Magnetic Circular Dichroism Spectroscopy Applied to Nitrogenase and Related Models: Experimental Evidence for a Spin-Coupled Molybdenum(III) Center journal June 2019

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Related Subjects

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CHEMISTRY
59 BASIC BIOLOGICAL SCIENCES
EPR spectroscopy
conformation analysis
electron transfer
enzyme catalysis
proton transfer