Journal
PROCEEDINGS OF THE NATIONAL ACADEMY OF SCIENCES OF THE UNITED STATES OF AMERICA
Volume 104, Issue 45, Pages 17626-17631Publisher
NATL ACAD SCIENCES
DOI: 10.1073/pnas.0703050104
Keywords
FeMo-co; nitrogen fixation; nif; Fe-S proteins
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Funding
- NIGMS NIH HHS [R37 GM035332, GM-35332] Funding Source: Medline
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Biological nitrogen fixation, the conversion of atmospheric N-2 to NH3r is an essential process in the global biogeochemical cycle of nitrogen that supports life on Earth. Most of the biological nitrogen fixation is catalyzed by the molybdenum nitrogenase, which contains at its active site one of the most complex metal cofactors known to date, the iron-molybdenum cofactor (FeMo-co). FeMo-co is composed of 7Fe, 9S, Mo, R-homocitrate, and one unidentified light atom. Here we demonstrate the complete in vitro synthesis of FeMo-co from Fe2+, S2-, MoO42-, and R-homocitrate using only purified Nif proteins. This synthesis provides direct biochemical support to the current model of FeMo-co biosynthesis. A minimal in vitro system, containing NifB, WEN, and NifH proteins, together with Fe2+, S2-, MoO42-, R-homocitrate, S-adenosyl methionine, and Mg-ATP, is sufficient for the synthesis of FeMo-co and the activation of apo-dinitrogenase under anaerobic-reducing conditions. This in vitro system also provides a biochemical approach to further study the function of accessory proteins involved in nitrogenase maturation (as shown here for NifX and NafY). The significance of these findings in the understanding of the complete FeMo-co biosynthetic pathway and in the study of other complex Fe-S cluster biosyntheses is discussed.
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