title: Crystal structure of manganese superoxide dismutase from Bacillus stearothermophilus at 2.4 A resolution.
abstract: The crystal structure of manganese superoxide dismutase (MnSOD) from Bacillus stearothermophilus has been solved at 2.4 A resolution by a combination of multiple isomorphous replacement and molecular replacement (1 A = 0.1 nm). The structure has been refined to a conventional R-factor for all 16,560 unique reflections at 2.4 A of 0.26, and the 2Fo-Fc density maps show features more consistent with the known amino acid sequence of MnSOD from B. stearothermophilus than with the starting model, the MnSOD from Thermus thermophilus. The molecule is a dimer of identical subunits, each with 203 amino acid residues. The polypeptide chain of the monomer is organized into two domains, one of which has an "all-alpha" structure and the other an "alpha/beta" structure, with the manganese ion bound between them. The ion is co-ordinated by three histidine residues, 26, 81 and 167, and one aspartic acid residue, 173, in a tetrahedral arrangement strongly distorted towards trigonal pyramidal. We anticipate that Tyr34, whose hydroxyl group is only 5 A from the metal, is involved in the catalytic reaction. The active site is particularly rich in aromatic amino acid residues. As in the Cu/ZnSOD there are indications that MnSOD provides electrostatic guidance to the substrate entering the active site.
authors.affiliation: Laboratory of Molecular Biophysics, University of Oxford, England.
authors.forename: M W
authors.initials: MW
authors.lastname: Parker
authors.forename: C C
authors.initials: CC
authors.lastname: Blake
mesh_terms: D000595:Amino Acid Sequence; D001665:Binding Sites; D001411:Geobacillus stearothermophilus / Q000201:enzymology*; D046911:Macromolecular Substances; D008345:Manganese; D008969:Molecular Sequence Data; D011487:Protein Conformation; D013482:Superoxide Dismutase; D014961:X-Ray Diffraction
chemical_list: D046911:Macromolecular Substances; D008345:Manganese; D013482:Superoxide Dismutase