Structure of the Large Subunit of Class Ib Ribonucleotide Reductase from Salmonella typhimurium and its Complexes with Allosteric Effectors

• Published in: Journal of molecular biology 2003-06, Vol.330 (1), p.87-97
• Main Authors: Uppsten, Malin, Färnegårdh, Mathias, Jordan, Albert, Eliasson, Rolf, Eklund, Hans, Uhlin, Ulla
• Format: Article
• Language: English
• Subjects: active site cysteine residues; allosteric effectors; Allosteric Regulation - physiology; Allosteric Site; Amino Acid Sequence; Binding Sites; catalytic subunit; Crystallography, X-Ray; Cysteine - chemistry; Cysteine - metabolism; Deoxyadenine Nucleotides - chemistry; Deoxyadenine Nucleotides - metabolism; Deoxycytosine Nucleotides - chemistry; Deoxycytosine Nucleotides - metabolism; Dimerization; Escherichia coli - enzymology; Macromolecular Substances; Medicin och hälsovetenskap; Models, Molecular; Molecular Sequence Data; Oxidation-Reduction; Protein Conformation; Protein Subunits - chemistry; Protein Subunits - metabolism; ribonucleotide reductase; Ribonucleotide Reductases - chemistry; Ribonucleotide Reductases - metabolism; Salmonella typhimurium - enzymology; Sequence Homology, Amino Acid; Thymine Nucleotides - chemistry; Thymine Nucleotides - metabolism
• ISSN: 0022-2836; 1089-8638
• DOI: 10.1016/S0022-2836(03)00538-2

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 α/β-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.