Probing the coordination and function of Fe4S4 modules in nitrogenase assembly protein NifB

Lee A. Rettberg, Jarett Wilcoxen, Chi Chung Lee, Martin T. Stiebritz, Kazuki Tanifuji, R. David Britt () and Yilin Hu ()
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Lee A. Rettberg: University of California
Jarett Wilcoxen: University of California
Chi Chung Lee: University of California
Martin T. Stiebritz: University of California
Kazuki Tanifuji: University of California
R. David Britt: University of California
Yilin Hu: University of California

Nature Communications, 2018, vol. 9, issue 1, 1-8

Abstract: Abstract NifB is an essential radical S-adenosylmethionine (SAM) enzyme for nitrogenase cofactor assembly. Previous studies show that NifB couples a putative pair of [Fe4S4] modules (designated K1 and K2) into an [Fe8S9C] cofactor precursor concomitant with radical SAM-dependent carbide insertion through the action of its SAM-binding [Fe4S4] module. However, the coordination and function of the NifB cluster modules remain unknown. Here, we use continuous wave and pulse electron paramagnetic resonance spectroscopy to show that K1- and K2-modules are 3-cysteine-coordinated [Fe4S4] clusters, with a histidine-derived nitrogen serving as the fourth ligand to K1 that is lost upon K1/K2-coupling. Further, we demonstrate that coexistence of SAM/K2-modules is a prerequisite for methyltransfer to K2 and hydrogen abstraction from the K2-associated methyl by a 5′-deoxyadenosyl radical. These results establish an important framework for mechanistic explorations of NifB while highlighting the utility of a synthetic-cluster-based reconstitution approach employed herein in functional analyses of iron–sulfur (FeS) enzymes.

Date: 2018
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DOI: 10.1038/s41467-018-05272-8

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