title: Nitrogenase FeMoco investigated by spatially resolved anomalous dispersion refinement.
abstract: The [Mo:7Fe:9S:C] iron-molybdenum cofactor (FeMoco) of nitrogenase is the largest known metal cluster and catalyses the 6-electron reduction of dinitrogen to ammonium in biological nitrogen fixation. Only recently its atomic structure was clarified, while its reactivity and electronic structure remain under debate. Here we show that for its resting S=3/2 state the common iron oxidation state assignments must be reconsidered. By a spatially resolved refinement of the anomalous scattering contributions of the 7 Fe atoms of FeMoco, we conclude that three irons (Fe1/3/7) are more reduced than the other four (Fe2/4/5/6). Our data are in agreement with the recently revised oxidation state assignment for the molybdenum ion, providing the first spatially resolved picture of the resting-state electron distribution within FeMoco. This might provide the long-sought experimental basis for a generally accepted theoretical description of the cluster that is in line with available spectroscopic and functional data.
authors.affiliation: Institute for Biochemistry, Albert-Ludwigs-Universität Freiburg, Albertstrasse 21, 79104 Freiburg, Germany.|Howard Hughes Medical Institute, Division of Chemistry and Chemical Engineering, California Institute of Technology, Pasadena, California 91125, USA.
authors.forename: Thomas
authors.initials: T
authors.lastname: Spatzal
authors.affiliation: Institute for Biochemistry, Albert-Ludwigs-Universität Freiburg, Albertstrasse 21, 79104 Freiburg, Germany.
authors.forename: Julia
authors.initials: J
authors.lastname: Schlesier
authors.affiliation: Institute for Biochemistry, Albert-Ludwigs-Universität Freiburg, Albertstrasse 21, 79104 Freiburg, Germany.
authors.forename: Eva-Maria
authors.initials: EM
authors.lastname: Burger
authors.affiliation: Institute for Biochemistry, Albert-Ludwigs-Universität Freiburg, Albertstrasse 21, 79104 Freiburg, Germany.
authors.forename: Daniel
authors.initials: D
authors.lastname: Sippel
authors.affiliation: Division of Chemistry and Chemical Engineering, California Institute of Technology, Pasadena, California 91125, USA.
authors.forename: Limei
authors.initials: L
authors.lastname: Zhang
authors.affiliation: Institute for Biochemistry, Albert-Ludwigs-Universität Freiburg, Albertstrasse 21, 79104 Freiburg, Germany.|BIOSS Centre for Biological Signalling Studies, Albert-Ludwigs-Universität Freiburg, Hebelstrasse 25, 79104 Freiburg, Germany.
authors.forename: Susana L A
authors.initials: SL
authors.lastname: Andrade
authors.affiliation: Howard Hughes Medical Institute, Division of Chemistry and Chemical Engineering, California Institute of Technology, Pasadena, California 91125, USA.
authors.forename: Douglas C
authors.initials: DC
authors.lastname: Rees
authors.affiliation: Institute for Biochemistry, Albert-Ludwigs-Universität Freiburg, Albertstrasse 21, 79104 Freiburg, Germany.|BIOSS Centre for Biological Signalling Studies, Albert-Ludwigs-Universität Freiburg, Hebelstrasse 25, 79104 Freiburg, Germany.
authors.forename: Oliver
authors.initials: O
authors.lastname: Einsle
mesh_terms: D016948:Azotobacter vinelandii; D003460:Crystallization; D018360:Crystallography, X-Ray; D004583:Electrons; D008983:Molybdoferredoxin / Q000737:chemistry / Q000378:metabolism*; D009591:Nitrogenase / Q000737:chemistry / Q000378:metabolism*; D011487:Protein Conformation
chemical_list: D008983:Molybdoferredoxin; D009591:Nitrogenase