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

Journal Article · · Proceedings of the National Academy of Sciences of the United States of America
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Mo-dependent nitrogenase catalyzes the biological reduction of atmospheric dinitrogen (N2) to two ammonia (NH3) 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 and 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.

Research Organization:
Pacific Northwest National Laboratory (PNNL), Richland, WA (United States); Energy Frontier Research Centers (EFRC) (United States). Center for Biological Electron Transfer and Catalysis (BETCy)
Sponsoring Organization:
USDOE Office of Science (SC), Basic Energy Sciences (BES)
Grant/Contract Number:
SC0012518; AC05-76RL01830
OSTI ID:
1328477
Alternate ID(s):
OSTI ID: 1340770; OSTI ID: 1388830
Report Number(s):
PNNL-SA-111505
Journal Information:
Proceedings of the National Academy of Sciences of the United States of America, Journal Name: Proceedings of the National Academy of Sciences of the United States of America Vol. 113 Journal Issue: 40; ISSN 0027-8424
Publisher:
National Academy of Sciences, Washington, DC (United States)Copyright Statement
Country of Publication:
United States
Language:
English
Citation Metrics:
Cited by: 30 works
Citation information provided by
Web of Science

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Related Subjects

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CHEMISTRY
59 BASIC BIOLOGICAL SCIENCES
ATP hydrolysis
conformational control
allosteric control
half-sites reactivity