Crystal Structures of the Iron Protein and Molybdenum-Iron Protein of Nitrogenase

Three-dimensional structures of the nitrogenase iron protein and molybdenum-iron protein from Azotobacter vinelandii have been determined by x-ray crystallography. The iron protein contains a single 4Fe:4S cluster symmetrically liganded by two identical subunits. The molybdenum-iron protein is an α2?2 tetramer, where the homologous α and ? subunits surround two different types of metal centers: the FeMo-cofactor and the P-cluster pair. Both centers are constructed from two bridged clusters; the FeMo-cofactor has 4Fe:3S and 1Mo:3Fe:3S cluster bridged by three non-protein ligands, while the P-cluster pair contains two 4Fe:4S clusters bridged by two cysteine ligands located at the α? subunit interface. Docking studies between the iron protein and molybdenum iron protein suggest a possible interaction mode between these two proteins.