title: Chlorovirus PBCV-1 encodes an active copper-zinc superoxide dismutase.
abstract: Superoxide 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.
  
  
  OBJECTIVE
  Virus 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.
authors.affiliation: Nebraska Center for Virology, University of Nebraska-Lincoln, Lincoln, Nebraska, USA Department of Plant Pathology, University of Nebraska-Lincoln, Lincoln, Nebraska, USA.
authors.forename: Ming
authors.initials: M
authors.lastname: Kang
authors.affiliation: Department of Biology, Nebraska Wesleyan University, Lincoln, Nebraska, USA.
authors.forename: Garry A
authors.initials: GA
authors.lastname: Duncan
authors.affiliation: Nebraska Center for Virology, University of Nebraska-Lincoln, Lincoln, Nebraska, USA Department of Pathology and Microbiology, University of Nebraska Medical Center, Omaha, Nebraska, USA.
authors.forename: Charles
authors.initials: C
authors.lastname: Kuszynski
authors.affiliation: Department of Chemical and Biomolecular Engineering, Johns Hopkins University, Baltimore, Maryland, USA Synaptic Research, LLC, Baltimore, Maryland, USA.
authors.forename: George
authors.initials: G
authors.lastname: Oyler
authors.affiliation: Department of Pharmacology and Therapeutics, University of Florida, Gainesville, Florida, USA.
authors.forename: Jiayin
authors.initials: J
authors.lastname: Zheng
authors.affiliation: Department of Biochemistry and Redox Biology Center, University of Nebraska-Lincoln, Lincoln, Nebraska, USA.
authors.forename: Donald F
authors.initials: DF
authors.lastname: Becker
authors.affiliation: Department of Plant Pathology, University of Nebraska-Lincoln, Lincoln, Nebraska, USA Nebraska Center for Virology, University of Nebraska-Lincoln, Lincoln, Nebraska, USA jvanetten1@unl.edu.
authors.forename: James L
authors.initials: JL
authors.lastname: Van Etten
mesh_terms: D000595:Amino Acid Sequence; D016000:Cluster Analysis; D020869:Gene Expression Profiling; D015967:Gene Expression Regulation, Viral; D007700:Kinetics; D008969:Molecular Sequence Data; D009580:Nitroblue Tetrazolium / Q000378:metabolism; D010084:Oxidation-Reduction; D017862:Phycodnaviridae / Q000201:enzymology* / Q000235:genetics*; D010802:Phylogeny; D012256:Riboflavin / Q000378:metabolism; D016415:Sequence Alignment; D017386:Sequence Homology, Amino Acid; D013482:Superoxide Dismutase / Q000235:genetics* / Q000378:metabolism*; D014771:Virion / Q000201:enzymology
chemical_list: D009580:Nitroblue Tetrazolium; D013482:Superoxide Dismutase; D012256:Riboflavin