Journal
PROCEEDINGS OF THE NATIONAL ACADEMY OF SCIENCES OF THE UNITED STATES OF AMERICA
Volume 103, Issue 5, Pages 1238-1243Publisher
NATL ACAD SCIENCES
DOI: 10.1073/pnas.0507853103
Keywords
biosynthesis; extended x-ray absorption fine structure; nitrogenase; x-ray absorption spectroscopy
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Funding
- NCRR NIH HHS [RR 01209, P41 RR001209] Funding Source: Medline
- NIGMS NIH HHS [R01 GM067626, GM 67626] Funding Source: Medline
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The iron-molybdenum cofactor (FeMoco) of the nitrogenase MoFe protein is a highly complex metallocluster that provides the catalytically essential site for biological nitrogen fixation. FeMoco is assembled outside the MoFe protein in a stepwise process requiring several components, including NifB-co, an iron- and sulfur-containing FeMoco precursor, and NifEN1, an intermediary assembly protein on which NifB-co is presumably converted to FeMoco. Through the comparison of Azotobacter vinelandii strains expressing the NifEN protein in the presence or absence of the nifB gene, the structure of a NifEN-bound FeMoco precursor has been analyzed by x-ray absorption spectroscopy. The results provide physical evidence to support a mechanism for FeMoco biosynthesis. The NifEN-bound precursor is found to be a molybdenum-free analog of FeMoco and not one of the more commonly suggested cluster types based on a standard [4Fe-4S] architecture. A facile scheme by which FeMoco and alternative, non-molybdenum-containing nitrogenase cofactors are constructed from this common precursor is presented that has important implications for the biosynthesis and biomimetic chemical synthesis of FeMoco.
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