title: The Zn center of the anaerobic ribonucleotide reductase from E. coli.
abstract: Strict and facultative anaerobes depend on a class III ribonucleotide reductase for their growth. These enzymes are the sole cellular catalysts for de novo biosynthesis of the deoxyribonucleotides needed for DNA chain elongation and repair. In its active form, the class III ribonucleotide reductase from Escherichia coli contains a free radical located on the G681 residue which is essential for the activation of the ribonucleotide substrate toward its reduction. The 3D structure of the homologous enzyme from bacteriophage T4 has revealed the presence of a metal center bound to four conserved cysteine residues. In this report we identify the metal of the E. coli enzyme as Zn. We show that the presence of Zn in this site protects the protein from proteolysis and prevents the formation of disulfide bridges within it. Finally, we show with the fully Zn-loaded reductase that thioredoxin or small thiols are dispensable for the formation of the glycyl radical. However, they are necessary for obtaining high turnover numbers, suggesting that they intervene in radical transfer steps subsequent to the formation of the glycyl radical.
authors.affiliation: LCBM, Groupe de Biocatalyse, CEA-Grenoble, Institut de Recherches en Technologies et Sciences pour le Vivant (iRTSV), Grenoble, France.
authors.forename: Florence
authors.initials: F
authors.lastname: Luttringer
authors.forename: Etienne
authors.initials: E
authors.lastname: Mulliez
authors.forename: Bernard
authors.initials: B
authors.lastname: Dublet
authors.forename: David
authors.initials: D
authors.lastname: Lemaire
authors.forename: Marc
authors.initials: M
authors.lastname: Fontecave
mesh_terms: D000693:Anaerobiosis; D001665:Binding Sites; D004220:Disulfides / Q000737:chemistry / Q000378:metabolism; D004795:Enzyme Stability; D004926:Escherichia coli / Q000201:enzymology*; D005609:Free Radicals / Q000378:metabolism; D020035:Holoenzymes / Q000378:metabolism; D012264:Ribonucleotide Reductases / Q000737:chemistry* / Q000378:metabolism*; D013379:Substrate Specificity; D013438:Sulfhydryl Compounds / Q000378:metabolism; D015032:Zinc
chemical_list: D004220:Disulfides; D005609:Free Radicals; D020035:Holoenzymes; D013438:Sulfhydryl Compounds; D012264:Ribonucleotide Reductases; D015032:Zinc