Key words Superoxide dismutase
Springer Online Journal Archives 1860-2000
Chemistry and Pharmacology
Abstract The three-dimensional structure of the manganese-dependent superoxide dismutase (MnSOD) from Escherichia coli has been determined by X-ray crystallography at 2.1 Å resolution. The protein crystallizes with two homodimers in the asymmetric unit, and a model comprising 6528 protein atoms (residues 1–205 of all four monomers), four manganese ions and 415 water molecules has been refined to an R factor of 0.188 (R free 0.218). The structure shows a high degree of similarity with other MnSOD and FeSOD enzymes. The Mn centres are 5-coordinate, trigonal bipyramidal, with His26 and a solvent molecule, probably a hydroxide ion, as apical ligands, and His81, Asp167 and His171 as equatorial ligands. The coordinated solvent molecule is linked to a network of hydrogen bonds involving the non-coordinated carboxylate oxygen of Asp167 and a conserved glutamine residue, Gln146. The MnSOD dimer is notable for the way in which the two active sites are interconnected and a "bridge" comprising His171 of one monomer and Glu170 of the other offers a route for inter-site communication. Comparison of E. coli MnSOD and FeSOD (a) reveals some differences in the dimer interface, (b) yields no obvious explanation for their metal specificities, and (c) provides a structural basis for differences in DNA binding, where for MnSOD the groove formed by dimerization is complementary in charge and surface contour to B-DNA.
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