title: Structure of Salmonella typhimurium nrdF ribonucleotide reductase in its oxidized and reduced forms.
abstract: The first class Ib ribonucleotide reductase R2 structure, from Salmonella typhimurium, has been determined at 2.0 A resolution. The overall structure is similar to the Escherichia coli class Ia enzyme despite only 23% sequence identity. The most spectacular difference is the absence of the pleated sheet and adjacent parts present in the E. coli R2 structure; the heart-shaped structure loses its tip. From sequence comparisons, it appears that this feature is shared with all other class Ib enzymes and, in this respect, is more like the mammalian class Ia enzymes. Both the oxidized and reduced iron forms have been investigated. In the ferric iron center, both iron ions are octahedrally coordinated and bridged by one carboxylate and one oxide ion. The ferrous form has lost the bridging oxide ion but is bridged by two carboxylates. Accompanying the change in redox state, helix E changes its conformation from one covering the metal center in the oxidized form to a more open reduced form. A narrow channel is opened which may permit easier access of oxygen to the ferrous iron site and to efficiently generate the tyrosyl radical.
authors.affiliation: Department of Molecular Biology, Swedish University of Agricultural Sciences, Uppsala Biomedical Center.
authors.forename: M
authors.initials: M
authors.lastname: Eriksson
authors.forename: A
authors.initials: A
authors.lastname: Jordan
authors.forename: H
authors.initials: H
authors.lastname: Eklund
mesh_terms: D000595:Amino Acid Sequence; D001426:Bacterial Proteins; D001665:Binding Sites; D003460:Crystallization; D018360:Crystallography, X-Ray; D019281:Dimerization; D004926:Escherichia coli / Q000235:genetics; D005290:Ferric Compounds / Q000737:chemistry / Q000378:metabolism; D005609:Free Radicals; D007501:Iron / Q000737:chemistry / Q000378:metabolism; D008958:Models, Molecular; D008969:Molecular Sequence Data; D010084:Oxidation-Reduction; D017433:Protein Structure, Secondary; D011994:Recombinant Proteins / Q000096:biosynthesis / Q000737:chemistry / Q000302:isolation & purification; D012264:Ribonucleotide Reductases / Q000737:chemistry* / Q000235:genetics / Q000378:metabolism; D012486:Salmonella typhimurium / Q000201:enzymology*; D017386:Sequence Homology, Amino Acid; D017356:Synchrotrons; D014443:Tyrosine / Q000031:analogs & derivatives / Q000737:chemistry
chemical_list: D001426:Bacterial Proteins; D005290:Ferric Compounds; D005609:Free Radicals; D011994:Recombinant Proteins; C066447:tyrosyl radical Y(D); D014443:Tyrosine; D007501:Iron; C114872:NrdF protein, bacteria; D012264:Ribonucleotide Reductases