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Updated: Aug 26, 2025

Sequence-specific Labeling of Nucleic Acids and Proteins with Methyltransferases and Cofactor Analogues
Published on: November 22, 2014
Evidence of substrate binding and product release via belt-sulfur mobilization of the nitrogenase cofactor
Chi Chung Lee1, Wonchull Kang1,2, Andrew J Jasniewski1
1Department of Molecular Biology and Biochemistry, University of California, Irvine, CA 92697-3900.
Abstract:
The Mo-nitrogenase catalyses the ambient reduction of N2 to NH3 at the M-cluster, a complex cofactor that comprises two metal-sulphur partial cubanes ligated by an interstitial carbide and three belt-sulphurs. A recent crystallographic study suggests binding of N2 via displacement of the belt-sulphur(s) of the M-cluster upon turnover. However, the direct proof of N2 binding and belt-sulphur mobilization during catalysis remains elusive. Here we show that N2 is captured on the M-cluster via electron- and sulphur-depletion, and that the N2-captured state is catalytically competent in generating NH3. Moreover, we demonstrate that product release only occurs when sulphite is supplied along with a reductant, that sulphite is inserted as sulphide into the belt-sulphur displaced positions, and that there is a dynamic in-and-out of the belt-sulphurs during catalysis. Together, these results establish the mobilization of the cofactor belt-sulphurs as a crucial, yet overlooked, mechanistic element of the nitrogenase reaction.
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