title: Structure of the large subunit of class Ib ribonucleotide reductase from Salmonella typhimurium and its complexes with allosteric effectors.
abstract: The three-dimensional structure of the large subunit of the first member of a class Ib ribonucleotide reductase, R1E of Salmonella typhimurium, has been determined in its native form and together with three allosteric effectors. The enzyme contains the characteristic ten-stranded alpha/beta-barrel with catalytic residues at a finger loop in its center and with redox-active cysteine residues at two adjacent barrel strands. Structures where the redox-active cysteine residues are in reduced thiol form and in oxidized disulfide form have been determined revealing local structural changes. The R1E enzyme differs from the class Ia enzyme, Escherichia coli R1, by not having an overall allosteric regulation. This is explained from the structure by differences in the N-terminal domain, which is about 50 residues shorter and lacks the overall allosteric binding site. R1E has an allosteric substrate specificity regulation site and the binding site for the nucleotide effectors is located at the dimer interface similarly as for the class Ia enzymes. We have determined the structures of R1E in the absence of effectors and with dTTP, dATP and dCTP bound. The low affinity for ATP at the specificity site is explained by a tyrosine, which hinders nucleotides containing a 2'-OH group to bind.
authors.affiliation: Department of Molecular Biosciences section of Structure Biology, Uppsala Biomedical Center, Swedish University of Agricultural Sciences, Box 590, Sweden.
authors.forename: Malin
authors.initials: M
authors.lastname: Uppsten
authors.forename: Mathias
authors.initials: M
authors.lastname: Färnegårdh
authors.forename: Albert
authors.initials: A
authors.lastname: Jordan
authors.forename: Rolf
authors.initials: R
authors.lastname: Eliasson
authors.forename: Hans
authors.initials: H
authors.lastname: Eklund
authors.forename: Ulla
authors.initials: U
authors.lastname: Uhlin
mesh_terms: D000494:Allosteric Regulation / Q000502:physiology; D000495:Allosteric Site; D000595:Amino Acid Sequence; D001665:Binding Sites; D018360:Crystallography, X-Ray; D003545:Cysteine / Q000737:chemistry / Q000378:metabolism; D003838:Deoxyadenine Nucleotides / Q000737:chemistry / Q000378:metabolism; D003845:Deoxycytosine Nucleotides / Q000737:chemistry / Q000378:metabolism; D019281:Dimerization; D004926:Escherichia coli / Q000201:enzymology; D046911:Macromolecular Substances; D008958:Models, Molecular; D008969:Molecular Sequence Data; D010084:Oxidation-Reduction; D011487:Protein Conformation; D021122:Protein Subunits / Q000737:chemistry / Q000378:metabolism; D012264:Ribonucleotide Reductases / Q000737:chemistry* / Q000378:metabolism*; D012486:Salmonella typhimurium / Q000201:enzymology*; D017386:Sequence Homology, Amino Acid; D013942:Thymine Nucleotides / Q000737:chemistry / Q000378:metabolism
chemical_list: D003838:Deoxyadenine Nucleotides; D003845:Deoxycytosine Nucleotides; D046911:Macromolecular Substances; D021122:Protein Subunits; D013942:Thymine Nucleotides; C024107:2'-deoxycytidine 5'-triphosphate; D012264:Ribonucleotide Reductases; C108427:ribonucleotide reductase R2 subunit; D003545:Cysteine; C026600:2'-deoxyadenosine triphosphate; C024157:thymidine 5'-triphosphate