title: Characterization and radio-resistant function of manganese superoxide dismutase of Rubrobacter radiotolerans.
abstract: Rubrobacter radiotolerans is the most radio-resistant eubacterium without spore-formation in the life cycle, and its D(37) is 16,000 Gy against gamma-rays. To understand the molecular mechanism of the high radio-resistance, we purified and characterized superoxide dismutase (SOD) of this organism as enzymatic radical scavenger, and then analyzed its genetic information. The purified SOD protein formed homo-tetramerization of 24,000 Da-monomer, while maintaining its enzymatic activity against potassium cyanide and hydrogen peroxide. We obtained a partial amino acid sequence of the protein and cloned the gene from it. Sequence analysis of the cloned gene indicated that the protein showed a similarity to other bacterial manganese SODs (Mn-SODs). Sequencing for adjacent regions of the gene showed that the gene had promoter elements with an open reading frame for putative PAS/PAC sensor protein at the 5'-adjacent region. Introduction of the gene into Escherichia coli cells lacking intrinsic SOD genes restored the cellular enzymatic activity and resistance to methyl viologen, indicating the gene at work. A mutant cell harboring this gene also became resistant against gamma-rays. The present results suggest that the protein in question is the Mn-SOD of R. radiotolerans, a good candidate as a radio-protection factor for this bacterial radio-resistance.
authors.affiliation: Analytical Research Center for Experimental Sciences, Saga University, Saga 849-8501, Japan. terato@cc.saga-u.ac.jp
authors.forename: Hiroaki
authors.initials: H
authors.lastname: Terato
authors.forename: Katsuyuki
authors.initials: K
authors.lastname: Suzuki
authors.forename: Nobuhiro
authors.initials: N
authors.lastname: Nishioka
authors.forename: Atsushi
authors.initials: A
authors.lastname: Okamoto
authors.forename: Yuka
authors.initials: Y
authors.lastname: Shimazaki-Tokuyama
authors.forename: Yuko
authors.initials: Y
authors.lastname: Inoue
authors.forename: Takeshi
authors.initials: T
authors.lastname: Saito
mesh_terms: D039903:Actinobacteria / Q000201:enzymology* / Q000235:genetics / Q000528:radiation effects*; D000595:Amino Acid Sequence; D001426:Bacterial Proteins / Q000737:chemistry / Q000235:genetics / Q000378:metabolism; D001483:Base Sequence; D004269:DNA, Bacterial / Q000235:genetics; D005720:Gamma Rays; D005798:Genes, Bacterial; D008969:Molecular Sequence Data; D020836:Protein Structure, Quaternary; D011836:Radiation Tolerance / Q000235:genetics / Q000502:physiology; D013482:Superoxide Dismutase / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*
chemical_list: D001426:Bacterial Proteins; D004269:DNA, Bacterial; D013482:Superoxide Dismutase