Induction of the manganese-containing superoxide dismutase in Escherichia coli by nalidixic acid and by iron chelators (original) (raw)
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Fems Microbiology Reviews, 1994
Abstract: 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, O−2; 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 O−2 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 ironchelation 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 respiratkm control) system. The potential Fur-, Fnr- and AreA-binding sites in the sodA promoter region have bcen identified by using different cis-acting regulatory mutations that caused anaerobic derepression of the gene. An updated model is presented to accommodate these findings and explain the biological significance of regulation by multi-regulatory elements in response to multi-environmental effectors.
Archives of Biochemistry and Biophysics, 2002
Escherichia coli, lacking cytoplasmic superoxide dismutases, exhibits a variety of oxygen-dependent phenotypic deficits. Enrichment of the growth medium with Mn(II) relieved those deficits. Extracts of cells grown on Mn(II)-rich medium exhibited superoxide dismutase-like activity that was due partially to low-molecular-weight and partially to high-molecular-weight complexes. The high-molecular-weight activity was sensitive to proteolysis. Hence this activity is likely associated with low-affinity binding of Mn to proteins.
Journal of Biological Chemistry, 1998
Enrichment of the growth medium with iron partially relieves the phenotypic deficits imposed on Escherichia coli by lack of both manganese and iron superoxide dismutases. Thus iron supplementation increased the aerobic growth rate, decreased the leakage of sulfite, and diminished sensitivity toward paraquat. Iron supplementation increased the activities of several [4Fe-4S]-containing dehydratases, and this was seen even in the presence of 50 g/ml of rifampicin, an amount which completely inhibited growth. Assessing the O 2. scavenging activity by means of lucigenin luminescence indicated that the iron-enriched sodAsodB cells had gained some means of eliminating O 2. , which was not detectable as superoxide dismutase activity in cell extracts. It is noteworthy that iron-enriched cells were not more sensitive toward the lethality of H 2 O 2 despite having the usual amount of catalase activity. This indicates that iron taken into the cells from the medium is not available for Fenton chemistry, but is available for reconstitution of iron-sulfur clusters. We suppose that oxidation of the [4Fe-4S] clusters of dehydratases by O 2. and their subsequent reductive reconstitution provides a mechanism for scavenging O 2. and that speeding this reductive reconstitution by iron enrichment both spared other targets from O 2. attack and maintained adequate levels of these enzymes to meet the metabolic needs of the cells. Among the targets susceptible to direct oxidation by O 2. are those dehydratases that contain [4Fe-4S] clusters. These enzymes, which include dihydroxy acid dehydratase (1-3), aconitase (4, 5), 6-phosphogluconate dehydratase (6-7), and fumarases A and B (8, 9), react with O 2. with rate constants of ϳ10 7 M Ϫ1 s Ϫ1. Univalent oxidation of the [4Fe-4S] clusters by O 2 .
Transcriptional activation of Mn-superoxide dismutase gene (sodA) of Escherichia coli by MnCl2
Biochimica et Biophysica Acta (BBA) - Gene Structure and Expression, 1993
Transcription of the manganese-superoxide dismutase gene (sodA) in Escherichia coli was shown to be activated by manganese. Addition of MnCI z increased the expression of/3-galactosidase from a sodA::lacZ protein fusion and increased the concentration of mRNA transcribed from sodA + and sodA::lacZ constructs. The stimulatory affect of manganese on the expression of sodA::lacZ was greatly reduced (i.e., > 90%) in a strain harboring a fur mutation. We also found that manganese was capable of altering DNA topology. These results show that Mn z+ causes activation of soda transcription.
European Journal of Biochemistry, 2002
The structurally homologous mononuclear iron and manganese superoxide dismutases (FeSOD and MnSOD, respectively) contain a highly conserved glutamine residue in the active site which projects toward the active-site metal centre and participates in an extensive hydrogen bonding network. The position of this residue is different for each SOD isoenzyme (Q69 in FeSOD and Q146 in MnSOD of Escherichia coli). Although site-directed mutant enzymes lacking this glutamine residue (FeSOD[Q69G] and MnSOD[Q146A]) demonstrated a higher degree of selectivity for their respective metal, they showed little or no activity compared with wild types. FeSOD double mutants (FeSOD[Q69G/A141Q]), which mimic the glutamine position in MnSOD, elicited 25% the activity of wild-type FeSOD while the activity of the corresponding MnSOD double mutant (MnSOD[G77Q/Q146A]) increased to 150% (relative to wild-type MnSOD). Both double mutants showed reduced selectivity toward their metal. Differences exhibited in the thermostability of SOD activity was most obvious in the mutants that contained two glutamine residues (FeSOD[A141Q] and MnSOD[G77Q]), where the MnSOD mutant was thermostable and the FeSOD mutant was thermolabile. Significantly, the MnSOD double mutant exhibited a thermal-inactivation profile similar to that of wild-type FeSOD while that of the FeSOD double mutant was similar to wild-type MnSOD. We conclude therefore that the position of this glutamine residue contributes to metal selectivity and is responsible for some of the different physicochemical properties of these SODs, and in particular their characteristic thermostability.
Proceedings of The National Academy of Sciences, 1992
Transcriptional regulation of the sodA gene, encoding the manganese superoxide dismutase (superoxide: superoxide oxidoreductase, EC 1.15.1.1) of Escherchia coli, was studied by monitoring expression of sodA-lacZ in different genetic backgrounds and under different growth conditions. Mutations in the fnr gene were found to affect aerobic and anaerobic expression of sodA-wacZ. Potential Fnr-binding sites were identified in the promoter region of sodA. Strains harboring simultaneous mutations in arcAiB and fur expressed sodA-lacZ under anaerobic growth conditions but were still inducible by iron chelators. However, in the triple mutants (fnr fur arcAiB) sodA-lacZ was fully expressed under anaerobiosis and was not further induced by the presence of 2,2'-dipyridyl, nitrate, or oxidants. On the other hand, aerobic expression of sodA-lacZ from a Fur-strain was -3.8-fold higher than that
The manganese and iron superoxide dismutases protect Escherichia coli from heavy metal toxicity
Research in Microbiology, 2001
Superoxide dismutases (SODs) are vital components that defend against oxidative stress through decomposition of superoxide radical. Escherichia coli contains two highly homologous SODs, a manganese-and an iron-containing enzyme (Mn-SOD and Fe-SOD, respectively). In contrast, a single Mn-SOD is present in Bacillus subtilis. In E. coli, the absence of SODs was found to be associated with an increased sensitivity to cadmium, nickel and cobalt ions. Mutants lacking either sodA or sodB exhibited metal resistance to levels comparable to that of the wild-type strain. Although soddeficient mutant cells were more resistant to zinc than their wild-type counterpart, no differences between the strains were observed in the presence of copper. In B. subtilis, the sodA mutation had no effect on cadmium and copper resistance. These results suggest that intracellular generation of superoxide by cadmium, nickel and cobalt is toxic in E. coli. They support the participation of sod genes in its protection against metal stress. 2001 Éditions scientifiques et médicales Elsevier SAS Escherichia coli / Bacillus subtilis / superoxide dismutase / oxidative stress / heavy metal resistance