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Cloning and analysis of sodC, encoding the copper-zinc superoxide dismutase of Escherichia coli.

ABSTRACT: Benov and Fridovich recently reported the existence of a copper- and zinc-containing superoxide dismutase (CuZnSOD) in Escherichia coli (L. T. Benov and I. Fridovich, J. Biol. Chem. 269:25310-25314,1994). We have used the N-terminal protein sequence to isolate the gene encoding this enzyme. The gene, denoted sodC, is located at 37.1 min on the chromosome, adjacent to lhr and sodB. A monocistronic transcript of sodC accumulates only in stationary phase. The presence of a conventional leader sequence is consistent with physical data indicating that the E. coli enzyme, like other bacterial CuZnSODs, is secreted into the periplasm. Because superoxide cannot cross membranes, this localization indicates that the enzyme has evolved to defend periplasmic biomolecules against an extracytoplasmic superoxide source. Neither the source nor the target of the superoxide is known. Although once considered an exclusively eukaryotic enzyme, CuZnSOD has now been found in species that span three subdivisions of the purple bacteria. The bacterial CuZnSODs are more homologous to one another than to the eukaryotic enzymes, but active-site residues and structural motifs are clearly shared by both families of enzymes. The use of copper and an invariant disulfide bond suggest that the ancestral gene of present-day CuZnSODs evolved in an aerobic environment, long after the evolutionary split between the eukaryotes and the eubacteria. If so, a CuZnSOD gene must have been transferred laterally between members of these domains. The eukaryotic SODs most closely resemble that of Caulobacter crescentus, a relatively close descendant of the mitochondrial ancestor, suggesting that sodC may have entered the eukaryotes during the establishment of mitochondria.

SUBMITTER: Imlay KR

PROVIDER: S-EPMC177980 | biostudies-other | 1996 May

REPOSITORIES: biostudies-other

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Cloning and analysis of sodC, encoding the copper-zinc superoxide dismutase of Escherichia coli.

Imlay K R KR Imlay J A JA

Journal of bacteriology 19960501 9

Benov and Fridovich recently reported the existence of a copper- and zinc-containing superoxide dismutase (CuZnSOD) in Escherichia coli (L. T. Benov and I. Fridovich, J. Biol. Chem. 269:25310-25314,1994). We have used the N-terminal protein sequence to isolate the gene encoding this enzyme. The gene, denoted sodC, is located at 37.1 min on the chromosome, adjacent to lhr and sodB. A monocistronic transcript of sodC accumulates only in stationary phase. The presence of a conventional leader seque ...[more]

PMID: 8626323

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Project description:UnlabelledSuperoxide dismutases (SODs) are metalloproteins that protect organisms from toxic reactive oxygen species by catalyzing the conversion of superoxide anion to hydrogen peroxide and molecular oxygen. Chlorovirus PBCV-1 encodes a 187-amino-acid protein that resembles a Cu-Zn SOD with all of the conserved amino acid residues for binding copper and zinc (named cvSOD). cvSOD has an internal Met that results in a 165-amino-acid protein (named tcvSOD). Both cvSOD and tcvSOD recombinant proteins inhibited nitroblue tetrazolium reduction of superoxide anion generated in a xanthine-xanthine oxidase system in solution. tcvSOD was chosen for further characterization because it was easier to produce. Recombinant tcvSOD also inhibited a riboflavin photochemical reduction system in a polyacrylamide gel assay, which was blocked by the Cu-Zn SOD inhibitor cyanide but not by azide, which inhibits Fe and Mn SODs. A k(cat)/K(m) value for cvSOD was determined by stop-flow spectrophotometry as 1.28 × 10(8) M(-1) s(-1), suggesting that cvSOD-catalyzed O2 (-) dismutation was not a diffusion controlled encounter. The cvsod gene was expressed as a late gene, and cvSOD activity was detected in purified virions. Superoxide accumulated rapidly during virus infection, and circumstantial evidence indicates that cvSOD aids its decomposition to benefit virus replication. Cu-Zn SOD homologs have been described to occur in 3 other families of large DNA viruses, poxviruses, baculoviruses, and mimiviruses, which group as a clade. Interestingly, cvSOD does not group in the same clade as the other virus SODs but instead groups in an expanded clade that includes Cu-Zn SODs from many cellular organisms.ImportanceVirus infection often leads to an increase in toxic reactive oxygen species in the host, which can be detrimental to virus replication. Viruses have developed various ways to overcome this barrier. As reported in this article, the chloroviruses often encode and package a functional Cu-Zn superoxide dismutase in the virion that presumably lowers the concentration of reactive oxygen induced early during virus infection.

Dataset Information

Cloning and analysis of sodC, encoding the copper-zinc superoxide dismutase of Escherichia coli.

Publications

Cloning and analysis of sodC, encoding the copper-zinc superoxide dismutase of Escherichia coli.

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