title: Biochemical characterization of psychrophilic Mn-superoxide dismutase from newly isolated Exiguobacterium sp. OS-77.
abstract: Many types of superoxide dismutases have been purified and characterized from various bacteria, however, a psychrophilic Mn-superoxide dismutase (MnSOD) has not yet been reported. Here, we describe the purification and the biochemical characterization of the psychrophilic MnSOD from Exiguobacterium sp. strain OS-77 (EgMnSOD). According to 16S rRNA sequence analysis, a newly isolated bacterium strain OS-77 belongs to the genus Exiguobacterium. The optimum growth temperature of the strain OS-77 is 20 °C. The EgMnSOD is a homodimer of 23.5 kDa polypeptides determined by SDS-PAGE and gel filtration analysis. UV-Vis spectrum and ICP-MS analysis clearly indicated that the homogeneously purified enzyme contains only a Mn ion as a metal cofactor. The optimal reaction pH and temperature of the enzyme were pH 9.0 and 5 °C, respectively. Notably, the purified EgMnSOD was thermostable up to 45 °C and retained 50% activity after 21.2 min at 60 °C. The differential scanning calorimetry also indicated that the EgMnSOD is thermostable, exhibiting two protein denaturation peaks at 65 and 84 °C. The statistical analysis of amino acid sequence and composition of the EgMnSOD suggests that the enzyme retains psychrophilic characteristics.
authors.affiliation: International Institute for Carbon-Neutral Energy Research (WPI-I2CNER), Kyushu University, 744 Moto-oka, Nishi-ku, Fukuoka, 819-0395, Japan.
authors.forename: Kyoshiro
authors.initials: K
authors.lastname: Nonaka
authors.forename: Ki-Seok
authors.initials: KS
authors.lastname: Yoon
authors.forename: Seiji
authors.initials: S
authors.lastname: Ogo
mesh_terms: D000595:Amino Acid Sequence; D056449:Bacillales / Q000201:enzymology* / Q000235:genetics / Q000302:isolation & purification; D001426:Bacterial Proteins / Q000737:chemistry / Q000378:metabolism*; D004795:Enzyme Stability; D006358:Hot Temperature; D006863:Hydrogen-Ion Concentration; D008969:Molecular Sequence Data; D010802:Phylogeny; D012336:RNA, Ribosomal, 16S / Q000235:genetics; D013482:Superoxide Dismutase / Q000737:chemistry / Q000378:metabolism*
chemical_list: D001426:Bacterial Proteins; D012336:RNA, Ribosomal, 16S; D013482:Superoxide Dismutase