title: Substitution of manganese for iron in ribonucleotide reductase from Escherichia coli. Spectroscopic and crystallographic characterization.
abstract: Each polypeptide chain of protein R2, the small subunit of ribonucleotide reductase from Escherichia coli, contains a stable tyrosyl radical and two antiferromagnetically coupled oxo-bridged ferric ions. A refined structure of R2 has been recently obtained. R2 can be converted into apoR2 by chelating out the metal cofactor and scavenging the radical. This study shows that apoR2 has a very strong affinity for four stable Mn2+ ions. The manganese-containing form of R2, named Mn-R2, has been studied by EPR spectroscopy and x-ray crystallography. It contains two binuclear manganese clusters in which the two manganese ions occupy the natural iron-binding sites and are only bridged by carboxylates from glutamates 115 and 238. This in turn explains why the spin-exchange interaction between the two ions is very weak and why Mn-R2 is EPR active. Mn-R2 could provide a model for the native diferrous form of protein R2, and a detailed molecular mechanism for the reduction of the iron center of protein R2 is proposed.
authors.affiliation: Laboratoire d'Etudes Dynamiques et Structurales de la Sélectivité, URA Centre National de la Recherche Scientifique 0332, Université J. Fourier, Grenoble, France.
authors.forename: M
authors.initials: M
authors.lastname: Atta
authors.forename: P
authors.initials: P
authors.lastname: Nordlund
authors.forename: A
authors.initials: A
authors.lastname: Aberg
authors.forename: H
authors.initials: H
authors.lastname: Eklund
authors.forename: M
authors.initials: M
authors.lastname: Fontecave
mesh_terms: D000595:Amino Acid Sequence; D001665:Binding Sites; D004578:Electron Spin Resonance Spectroscopy / Q000379:methods; D004789:Enzyme Activation; D004926:Escherichia coli / Q000201:enzymology*; D007501:Iron / Q000378:metabolism*; D008345:Manganese / Q000378:metabolism*; D008958:Models, Molecular; D011487:Protein Conformation; D012264:Ribonucleotide Reductases / Q000737:chemistry* / Q000378:metabolism; D014961:X-Ray Diffraction / Q000379:methods
chemical_list: D008345:Manganese; D007501:Iron; D012264:Ribonucleotide Reductases