NifB-dependent in vitro synthesis of the iron-molybdenum cofactor of nitrogenase.

Biological nitrogen fixation, an essential process of the biogeochemical nitrogen cycle that supports life on Earth, is catalyzed by the nitrogenase enzyme. The nitrogenase active site contains an iron and molybdenum cofactor (FeMo-co) composed of 7Fe-9S-Mo-homocitrate and one not-yet-identified atom, which probably is the most complex [Fe-S] cluster in nature. Here, we show the in vitro synthesis of FeMo-co from its simple constituents, Fe, S, Mo, and homocitrate. The in vitro FeMo-co synthesis requires purified NifB and depends on S-adenosylmethionine, indicating that radical chemistry is required during FeMo-co assembly.