Roles of manganese and iron in the regulation of the biosynthesis of manganese-superoxide dismutase in Escherichia coli.
Aerobic life-style offers both benefits and risks to living cells. The major risk comes from the formation of reactive oxygen intermediates (i.e. superoxide radical, O2-; hydrogen peroxide, H2O2; and hydroxyl radical, OH.) during normal oxygen metabolism. However, living cells are able to cope with oxygen toxicity by virtue of a unique set of antioxidant enzymes that scavenge O2- and H2O2, and prevent the formation OH.. Superoxide dismutases (SODs; EC 1.15.1.1) are metalloenzymes essential for aerobic survival. Escherichia coli contains two forms of this enzyme: an iron-containing enzyme (FeSOD) and a manganese-containing enzyme (MnSOD). In E. coli, MnSOD biosynthesis is under rigorous control. The enzyme is induced in response to a variety of environmental stress conditions including exposure to oxygen, redox cycling compounds such as paraquat which exacerbate the level of intracellular superoxide radicals, iron chelation (i.e. iron deprivation), and oxidants. A model for the regulation of the MnSOD has been proposed in which the MnSOD gene (sodA) is negatively regulated at the level of transcription by an iron-containing redox-sensitive repressor protein. The effect of iron-chelation most probably results in removal of the iron necessary for repressor activity. Recent studies have shown that sodA expression is regulated by three iron-dependent regulatory proteins, Fur (ferric uptake regulation), Fnr (fumarate nitrate regulation) and SoxR (superoxide regulon), and by the ArcA/ArcB (aerobic respiration control) system. The potential Fur-, Fnr- and ArcA-binding sites in the sodA promoter region have been identified by using different cis-acting regulatory mutations that caused anaerobic derepression of the gene.(ABSTRACT TRUNCATED AT 250 WORDS)
Hassan
H M
HM
Department of Microbiology, North Carolina State University, Raleigh 27695-7615.
Schrum
L W
LW
D000595:Amino Acid Sequence; D001426:Bacterial Proteins / Q000502:physiology; D001483:Base Sequence; D004926:Escherichia coli / Q000201:enzymology*; D029968:Escherichia coli Proteins; D007501:Iron / Q000494:pharmacology*; D007506:Iron-Sulfur Proteins; D008345:Manganese / Q000494:pharmacology*; D008969:Molecular Sequence Data; D012097:Repressor Proteins / Q000502:physiology; D013482:Superoxide Dismutase / Q000096:biosynthesis*
D001426:Bacterial Proteins; D029968:Escherichia coli Proteins; C060704:FNR protein, E coli; D007506:Iron-Sulfur Proteins; D012097:Repressor Proteins; C068477:ferric uptake regulating proteins, bacterial; D008345:Manganese; D007501:Iron; D013482:Superoxide Dismutase