title: The first structure of a cold-adapted superoxide dismutase (SOD): biochemical and structural characterization of iron SOD from Aliivibrio salmonicida.
abstract: Superoxide dismutases (SODs) are metalloenzymes that catalyse the dismutation of the superoxide radical anion into O(2) and H(2)O(2) in a two-step reaction. The crystal structure of the iron superoxide dismutase from the cold-adapted and fish-pathogenic bacterium Aliivibrio salmonicida (asFeSOD) has been determined and refined to 1.7 A resolution. The protein has been characterized and compared with the closely related homologous iron superoxide dismutase from the mesophilic Escherichia coli (ecFeSOD) in an attempt to rationalize its environmental adaptation. ecFeSOD shares 75% identity with asFeSOD. Compared with the mesophilic FeSOD, the psychrophilic FeSOD has distinct temperature differences in residual activity and thermostability that do not seem to be related to structural differences such as intramolecular or intermolecular ion bonds, hydrogen bonds or cavity sizes. However, an increased net negative charge on the surface of asFeSOD may explain its lower thermostability compared with ecFeSOD. Activity measurements and differential scanning calorimetry measurements revealed that the psychrophilic asFeSOD had a thermostability that was significantly higher than the optimal growth temperature of the host organism.
authors.affiliation: Department of Molecular Biotechnology, Institute of Medical Biology, University of Tromsø, N-9037 Tromsø, Norway.
authors.forename: Hege Lynum
authors.initials: HL
authors.lastname: Pedersen
authors.forename: Nils Peder
authors.initials: NP
authors.lastname: Willassen
authors.forename: Ingar
authors.initials: I
authors.lastname: Leiros
mesh_terms: D000222:Adaptation, Physiological; D044165:Aliivibrio salmonicida / Q000201:enzymology*; D000595:Amino Acid Sequence; D000818:Animals; D001426:Bacterial Proteins / Q000737:chemistry* / Q000302:isolation & purification; D003080:Cold Temperature; D018360:Crystallography, X-Ray; D004795:Enzyme Stability / Q000502:physiology; D004926:Escherichia coli / Q000201:enzymology; D048388:Gadiformes; D007501:Iron / Q000737:chemistry*; D008969:Molecular Sequence Data; D017386:Sequence Homology, Amino Acid; D013482:Superoxide Dismutase / Q000737:chemistry* / Q000302:isolation & purification; D013816:Thermodynamics
chemical_list: D001426:Bacterial Proteins; D007501:Iron; D013482:Superoxide Dismutase