title: Radical SAM-dependent carbon insertion into the nitrogenase M-cluster.
abstract: The active site of nitrogenase, the M-cluster, is a metal-sulfur cluster containing a carbide at its core. Using radiolabeling experiments, we show that this carbide originates from the methyl group of S-adenosylmethionine (SAM) and that it is inserted into the M-cluster by the assembly protein NifB. Our SAM cleavage and deuterium substitution analyses suggest a similarity between the mechanism of carbon insertion by NifB and the proposed mechanism of RNA methylation by the radical SAM enzymes RlmN and Cfr, which involves methyl transfer from one SAM equivalent, followed by hydrogen atom abstraction from the methyl group by a 5'-deoxyadenosyl radical generated from a second SAM equivalent. This work is an initial step toward unraveling the importance of the interstitial carbide and providing insights into the nitrogenase mechanism.
authors.affiliation: Department of Molecular Biology & Biochemistry, University of California, Irvine 92697-3900.
authors.forename: Jared A
authors.initials: JA
authors.lastname: Wiig
authors.affiliation: Department of Molecular Biology & Biochemistry, University of California, Irvine 92697-3900.
authors.forename: Yilin
authors.initials: Y
authors.lastname: Hu
authors.affiliation: Department of Molecular Biology & Biochemistry, University of California, Irvine 92697-3900.
authors.forename: Chi
authors.initials: C
authors.lastname: Chung Lee
authors.affiliation: Department of Molecular Biology & Biochemistry, University of California, Irvine 92697-3900.
authors.forename: Markus W
authors.initials: MW
authors.lastname: Ribbe
mesh_terms: D001426:Bacterial Proteins / Q000737:chemistry*; D002244:Carbon / Q000737:chemistry*; D020134:Catalytic Domain; D041961:Deuterium Exchange Measurement; D008745:Methylation; D008780:Methyltransferases / Q000737:chemistry; D009591:Nitrogenase / Q000737:chemistry*; D012313:RNA / Q000737:chemistry*; D012436:S-Adenosylmethionine / Q000737:chemistry*
chemical_list: D001426:Bacterial Proteins; C092498:NifB protein, Bacteria; D012313:RNA; D002244:Carbon; D012436:S-Adenosylmethionine; D009591:Nitrogenase; D008780:Methyltransferases