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Title: Negative cooperativity in the nitrogenase Fe protein electron delivery cycle

Mo-dependent nitrogenase catalyzes the biological reduction of atmospheric dinitrogen (N 2) to two ammonia (NH 3) molecules, through the action of two component proteins, the MoFe protein and the Fe protein. The catalytic MoFe protein is a symmetric dimer of αβ units, each of which contains one active site FeMo-co (FeMo-co; [7Fe-9S-Mo-C-homocitrate]) and an electron-carrier P cluster. Each half of the nitrogenase ternary complex, in which one Fe protein with two bound ATP molecules has bound to each MoFe protein αβ unit, undergoes an electron transfer (ET) cycle with ET from a Fe protein [4Fe-4S] cluster into its αβ unit followed by the hydrolysis of the two ATP to two ADP and two Pi. The prevailing model holds that each αβ unit of the MoFe protein functions independently. We now report that the ET cycle exhibits negative cooperativity, with ET and ATP hydrolysis in one half of the ternary nitrogenase complex suppressing these processes in the other half. The observed ET, ATP hydrolysis, and Pi release behavior is captured in a global fit to a two-branch negative-cooperativity kinetic model. A possible mechanism for communication between the two halves of MoFe protein is suggested by normal mode analysis showing correlated andmore » anti-correlated motions between the two nitrogenase αβ halves. EPR spectra furthermore show small differences between those of resting-state and singly-reduced MoFe protein that can be attributed to an intra-complex allosteric perturbation of the resting-state FeMo-co in one αβ unit by reduction of FeMo-co in the other. This work is supported as a part of the Biological and Electron Transfer and Catalysis (EFRC) program, an Energy Frontiers Research Center funded by the US Department of Energy (DOE), Office of Science (DE-SC0012518) to LCS, by National Institutes of Health (NIH) grants HL 63203 and GM 111097to BMH, and R15GM110671 to EA, and by the Division of Chemical Sciences, Geosciences, and Bio-Sciences, DOE to SR. The protein production, ATP hydrolysis, and stopped flow electron transfer studies were supported by the EFRC program, phosphate release and pulse chase by the NIH, calculations by the DOE, and rapid freeze quench and data fitting by the NIH.« less
Authors:
 [1] ;  [1] ;  [2] ;  [1] ;  [2] ;  [2] ;  [2] ;  [3] ;  [4] ;  [2] ;  [1] ;  [5]
  1. Utah State Univ., Logan, UT (United States)
  2. Northwestern Univ., Evanston, IL (United States)
  3. Virginia Polytechnic Inst. and State Univ. (Virginia Tech), Blacksburg, VA (United States)
  4. Pacific Northwest National Lab. (PNNL), Richland, WA (United States)
  5. Marquette Univ., Milwaukee, WI (United States)
Publication Date:
Report Number(s):
PNNL-SA-111505
Journal ID: ISSN 0027-8424; KC0304020
Grant/Contract Number:
AC05-76RL01830; SC0012518
Type:
Published Article
Journal Name:
Proceedings of the National Academy of Sciences of the United States of America
Additional Journal Information:
Journal Volume: 113; Journal Issue: 40; Journal ID: ISSN 0027-8424
Publisher:
National Academy of Sciences, Washington, DC (United States)
Research Org:
Pacific Northwest National Lab. (PNNL), Richland, WA (United States)
Sponsoring Org:
USDOE
Country of Publication:
United States
Language:
English
Subject:
37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CHEMISTRY; 59 BASIC BIOLOGICAL SCIENCES; ATP hydrolysis; conformational control; allosteric control; half-sites reactivity
OSTI Identifier:
1328477
Alternate Identifier(s):
OSTI ID: 1340770