title: The radical site in chlamydial ribonucleotide reductase defines a new R2 subclass.
abstract: Ribonucleotide reductase (RNR) synthesizes the deoxyribonucleotides for DNA synthesis. The R2 protein of normal class I ribonucleotide reductases contains a diiron site that produces a stable tyrosyl free radical, essential for enzymatic activity. Structural and electron paramagnetic resonance studies of R2 from Chlamydia trachomatis reveal a protein lacking a tyrosyl radical site. Instead, the protein yields an iron-coupled radical upon reconstitution. The coordinating structure of the diiron site is similar to that of diiron oxidases/monoxygenases and supports a role for this radical in the RNR mechanism. The specific ligand pattern in the C. trachomatis R2 metal site characterizes a new group of R2 proteins that so far has been found in eight organisms, three of which are human pathogens.
authors.affiliation: Department of Biochemistry and Biophysics, Stockholm University, Roslagstullsbacken 15, Albanova University Center, SE-10691 Stockholm, Sweden.
authors.forename: Martin
authors.initials: M
authors.lastname: Högbom
authors.forename: Pål
authors.initials: P
authors.lastname: Stenmark
authors.forename: Nina
authors.initials: N
authors.lastname: Voevodskaya
authors.forename: Grant
authors.initials: G
authors.lastname: McClarty
authors.forename: Astrid
authors.initials: A
authors.lastname: Gräslund
authors.forename: Pär
authors.initials: P
authors.lastname: Nordlund
mesh_terms: D000595:Amino Acid Sequence; D002692:Chlamydia trachomatis / Q000201:enzymology*; D018360:Crystallography, X-Ray; D004578:Electron Spin Resonance Spectroscopy; D005609:Free Radicals; D006860:Hydrogen Bonding; D007501:Iron / Q000032:analysis; D008024:Ligands; D008958:Models, Molecular; D008969:Molecular Sequence Data; D010084:Oxidation-Reduction; D010100:Oxygen / Q000378:metabolism; D017510:Protein Folding; D017433:Protein Structure, Secondary; D012264:Ribonucleotide Reductases / Q000737:chemistry* / Q000145:classification / Q000378:metabolism; D014443:Tyrosine / Q000032:analysis
chemical_list: D005609:Free Radicals; D008024:Ligands; D014443:Tyrosine; D007501:Iron; D012264:Ribonucleotide Reductases; C108427:ribonucleotide reductase R2 subunit; D010100:Oxygen