title: Structural insights into a protein-bound iron-molybdenum cofactor precursor.
abstract: 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 NifEN, 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.
authors.affiliation: Department of Chemistry, Stanford University, Stanford, CA 94305.
authors.forename: Mary C
authors.initials: MC
authors.lastname: Corbett
authors.forename: Yilin
authors.initials: Y
authors.lastname: Hu
authors.forename: Aaron W
authors.initials: AW
authors.lastname: Fay
authors.forename: Markus W
authors.initials: MW
authors.lastname: Ribbe
authors.forename: Britt
authors.initials: B
authors.lastname: Hedman
authors.forename: Keith O
authors.initials: KO
authors.lastname: Hodgson
mesh_terms: D016948:Azotobacter vinelandii / Q000378:metabolism; D001426:Bacterial Proteins / Q000737:chemistry / Q000378:metabolism; D018360:Crystallography, X-Ray; D007501:Iron / Q000737:chemistry*; D007700:Kinetics; D008958:Models, Molecular; D008982:Molybdenum / Q000737:chemistry*; D009584:Nitrogen / Q000737:chemistry; D009591:Nitrogenase / Q000737:chemistry; D016011:Normal Distribution; D011498:Protein Precursors / Q000737:chemistry; D011506:Proteins / Q000737:chemistry; D013052:Spectrometry, X-Ray Emission
chemical_list: D001426:Bacterial Proteins; C092498:NifB protein, Bacteria; D011498:Protein Precursors; D011506:Proteins; D008982:Molybdenum; D007501:Iron; D009591:Nitrogenase; D009584:Nitrogen