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Science. 2012 Sep 28;337(6102):1672-5. doi: 10.1126/science.1224603.

Radical SAM-dependent carbon insertion into the nitrogenase M-cluster.

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1
Department of Molecular Biology & Biochemistry, University of California, Irvine 92697-3900.
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Contributed equally

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.

PMID:
23019652
PMCID:
PMC3836454
DOI:
10.1126/science.1224603
[Indexed for MEDLINE]
Free PMC Article
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