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Characterization of a covalent polysulfane bridge in copper-zinc superoxide dismutase .

ABSTRACT: In the course of studies on human copper-zinc superoxide dismutase (SOD1), we observed a modified form of the protein whose mass was increased by 158 mass units. The covalent modification was characterized, and we established that it is a novel heptasulfane bridge connecting the two Cys111 residues in the SOD1 homodimer. The heptasulfane bridge was visualized directly in the crystal structure of a recombinant human mutant SOD1, H46R/H48Q, produced in yeast. The modification is reversible, with the bridge being cleaved by thiols, by cyanide, and by unfolding of the protein to expose the polysulfane. The polysulfane bridge can be introduced in vitro by incubation of purified SOD1 with elemental sulfur, even under anaerobic conditions and in the presence of a metal chelator. Because polysulfanes and polysulfides can catalyze the generation of reactive oxygen and sulfur species, the modification may endow SOD1 with a toxic gain of function.

SUBMITTER: You Z

PROVIDER: S-EPMC2819567 | biostudies-literature | 2010 Feb

REPOSITORIES: biostudies-literature

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Characterization of a covalent polysulfane bridge in copper-zinc superoxide dismutase .

You Zheng Z Cao Xiaohang X Taylor Alexander B AB Hart P John PJ Levine Rodney L RL

Biochemistry 20100201 6

In the course of studies on human copper-zinc superoxide dismutase (SOD1), we observed a modified form of the protein whose mass was increased by 158 mass units. The covalent modification was characterized, and we established that it is a novel heptasulfane bridge connecting the two Cys111 residues in the SOD1 homodimer. The heptasulfane bridge was visualized directly in the crystal structure of a recombinant human mutant SOD1, H46R/H48Q, produced in yeast. The modification is reversible, with t ...[more]

PMID: 20052996

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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

Characterization of a covalent polysulfane bridge in copper-zinc superoxide dismutase .

Publications

Characterization of a covalent polysulfane bridge in copper-zinc superoxide dismutase .

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