title: A prokaryotic superoxide dismutase paralog lacking two Cu ligands: from largely unstructured in solution to ordered in the crystal.
abstract: Little is known about prokaryotic homologs of Cu,Zn superoxide dismutase (SOD), an enzyme highly conserved among eukaryotic species. In 138 Archaea and Bacteria genomes, 57 of these putative homologs were found, 11 of which lack at least one of the metal ligands. Both the solution and the crystal structures of the SOD-like protein from Bacillus subtilis, lacking two Cu ligands and found to be enzymatically inactive, were determined. In solution, the protein is monomeric. The available nuclear Overhauser effects, together with chemical-shift index values, allowed us to define and to recognize the typical Cu,Zn SOD Greek beta-barrel but with largely unstructured loops (which, therefore, sample a wide range of conformations). On the contrary, in the crystal structure (obtained in the presence of slight excess of Zn), the protein is well structured and organized in covalent dimers held by a symmetric bridge consisting of a Zn ion bound to an Asp-His dyad in a tetrahedral geometry. Couples of dimers held by hydrophobic interactions and H bonds are further organized in long chains. The order/disorder transition is discussed in terms of metal binding and physical state.
authors.affiliation: Department of Chemistry, University of Florence, Via Luigi Sacconi 6, 50019 Sesto, Florence, Italy.
authors.forename: Lucia
authors.initials: L
authors.lastname: Banci
authors.forename: Ivano
authors.initials: I
authors.lastname: Bertini
authors.forename: Vito
authors.initials: V
authors.lastname: Calderone
authors.forename: Fiorenza
authors.initials: F
authors.lastname: Cramaro
authors.forename: Rebecca
authors.initials: R
authors.lastname: Del Conte
authors.forename: Adele
authors.initials: A
authors.lastname: Fantoni
authors.forename: Stefano
authors.initials: S
authors.lastname: Mangani
authors.forename: Alessandro
authors.initials: A
authors.lastname: Quattrone
authors.forename: Maria Silvia
authors.initials: MS
authors.lastname: Viezzoli
mesh_terms: D000595:Amino Acid Sequence; D001412:Bacillus subtilis / Q000235:genetics / Q000378:metabolism*; D019295:Computational Biology; D018360:Crystallography, X-Ray; D019281:Dimerization; D020745:Genome, Archaeal; D016680:Genome, Bacterial; D023281:Genomics; D008024:Ligands; D009682:Magnetic Resonance Spectroscopy; D008958:Models, Molecular; D008969:Molecular Sequence Data; D010802:Phylogeny; D017434:Protein Structure, Tertiary; D016415:Sequence Alignment; D013482:Superoxide Dismutase / Q000235:genetics / Q000378:metabolism / Q000648:ultrastructure*
chemical_list: D008024:Ligands; D013482:Superoxide Dismutase