title: The activating component of the anaerobic ribonucleotide reductase from Escherichia coli. An iron-sulfur center with only three cysteines.
abstract: Class III anaerobic ribonucleotide reductase small component, named protein beta, contains a (4Fe-4S) center. Its function is to mediate electron transfer from reduced flavodoxin to S-adenosylmethionine, required for the introduction of a glycyl radical in the large component, named protein alpha, which then becomes active for the reduction of ribonucleotides. By site-directed mutagenesis we demonstrate that the three cysteines of the conserved CXXXCXXC sequence are involved in iron chelation. Such a sequence is also present in the activase of the pyruvate formate-lyase and in the biotin synthase, both carrying an iron-sulfur center involved in reductive activation of S-adenosylmethionine. Even though they are able to bind iron in the (4Fe-4S) form, as shown by Mössbauer spectroscopy, the corresponding Cys to Ala mutants are catalytically inactive. Mutation of the two other cysteines of the protein did not result in inactivation. We thus conclude that the (4Fe-4S) cluster has, in the wild type protein, only three cysteine ligands and a fourth still unidentified ligand.
authors.affiliation: Laboratoire de Chimie et Biochimie des Centres Rédox Biologiques, Commissariat à l'Energie Atomique/Département de Biologie Moléculaire et Structurale, EP 1087 CNRS, Université Joseph Fourier, 17, rue des Martyrs, 38054 Grenoble, France.
authors.forename: J
authors.initials: J
authors.lastname: Tamarit
authors.forename: C
authors.initials: C
authors.lastname: Gerez
authors.forename: C
authors.initials: C
authors.lastname: Meier
authors.forename: E
authors.initials: E
authors.lastname: Mulliez
authors.forename: A
authors.initials: A
authors.lastname: Trautwein
authors.forename: M
authors.initials: M
authors.lastname: Fontecave
mesh_terms: D000595:Amino Acid Sequence; D000693:Anaerobiosis; D001426:Bacterial Proteins / Q000737:chemistry* / Q000235:genetics; D001665:Binding Sites; D003545:Cysteine / Q000737:chemistry / Q000235:genetics; D004578:Electron Spin Resonance Spectroscopy; D004789:Enzyme Activation; D004795:Enzyme Stability; D004926:Escherichia coli / Q000201:enzymology*; D007506:Iron-Sulfur Proteins / Q000737:chemistry* / Q000235:genetics; D008969:Molecular Sequence Data; D016297:Mutagenesis, Site-Directed; D012264:Ribonucleotide Reductases / Q000737:chemistry* / Q000235:genetics; D017386:Sequence Homology, Amino Acid; D013053:Spectrophotometry; D015204:Spectroscopy, Mossbauer
chemical_list: D001426:Bacterial Proteins; D007506:Iron-Sulfur Proteins; D012264:Ribonucleotide Reductases; D003545:Cysteine