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Electron Paramagnetic Resonance Characterization of Three Iron–Sulfur Clusters Present in the Nitrogenase Cofactor Maturase NifB from Methanocaldococcus infernus

Wilcoxen, Jarett, Arragain, Simon, Scandurra, Alessandro A., Jimenez-Vicente, Emilio, Echavarri-Erasun, Carlos, Pollmann, Stephan, Britt, R. David, Rubio, Luis M.
Journal of the American Chemical Society 2016 v.138 no.24 pp. 7468-7471
Methanocaldococcus, dissociation, electron paramagnetic resonance spectroscopy, methanogens, methionine, nitrogen, nitrogenase
NifB utilizes two equivalents of S-adenosyl methionine (SAM) to insert a carbide atom and fuse two substrate [Fe–S] clusters forming the NifB cofactor (NifB-co), which is then passed to NifEN for further modification to form the iron–molybdenum cofactor (FeMo-co) of nitrogenase. Here, we demonstrate that NifB from the methanogen Methanocaldococcus infernus is a radical SAM enzyme able to reductively cleave SAM to 5′-deoxyadenosine radical and is competent in FeMo-co maturation. Using electron paramagnetic resonance spectroscopy we have characterized three [4Fe–4S] clusters, one SAM binding cluster, and two auxiliary clusters probably acting as substrates for NifB-co formation. Nitrogen coordination to one or more of the auxiliary clusters in NifB was observed, and its mechanistic implications for NifB-co dissociation from the maturase are discussed.