title: The structure of rabbit extracellular superoxide dismutase differs from the human protein.
abstract: The cDNA sequence encoding rabbit, mouse, and rat extracellular superoxide dismutase (EC-SOD) predicts that the protein contains five cysteine residues. Human EC-SOD contains an additional cysteine residue and folds into two forms with distinct disulfide bridge patterns. One form is enzymatically active (aEC-SOD), while the other is inactive (iEC-SOD). Due to the lack of the additional cysteine residue rabbit, mouse, and rat EC-SOD are unable to generate an inactive fold identical to human iEC-SOD. The amino acid sequences predict the formation of aEC-SOD only, but other folding variants cannot be ruled out based on the heterogeneity observed for human EC-SOD. To test this, we purified EC-SOD from rabbit plasma and determined the disulfide bridge pattern. The results revealed that the disulfide bridges are homogeneous and identical to human aEC-SOD. Four cysteine residues are involved in two intra-disulfide bonds while the C-terminal cysteine residue forms an intersubunit disulfide bond. No evidence for other folding variants was detected. These findings show that rabbit EC-SOD exists as an enzymatically active form only. The absence of iEC-SOD in rabbits suggests that the structure and aspects of the physiological function of EC-SOD differs significantly between rabbit and humans. This is an important notion to take when using these animals as model systems for oxidative stress.
authors.affiliation: Department of Molecular Biology, University of Aarhus, DK-8000 Aarhus, Denmark.
authors.forename: Steen V
authors.initials: SV
authors.lastname: Petersen
authors.forename: Anne V
authors.initials: AV
authors.lastname: Due
authors.forename: Zuzana
authors.initials: Z
authors.lastname: Valnickova
authors.forename: Tim D
authors.initials: TD
authors.lastname: Oury
authors.forename: James D
authors.initials: JD
authors.lastname: Crapo
authors.forename: Jan J
authors.initials: JJ
authors.lastname: Enghild
mesh_terms: D000595:Amino Acid Sequence; D000818:Animals; D003545:Cysteine / Q000378:metabolism; D019281:Dimerization; D004220:Disulfides / Q000378:metabolism; D004789:Enzyme Activation; D005109:Extracellular Matrix / Q000201:enzymology*; D006801:Humans; D051379:Mice; D008969:Molecular Sequence Data; D010446:Peptide Fragments / Q000378:metabolism; D011817:Rabbits; D051381:Rats; D019032:Spectrometry, Mass, Matrix-Assisted Laser Desorption-Ionization; D013482:Superoxide Dismutase / Q000097:blood / Q000737:chemistry* / Q000378:metabolism; D014357:Trypsin / Q000378:metabolism
chemical_list: D004220:Disulfides; D010446:Peptide Fragments; C441642:SOD3 protein, human; C499090:Sod3 protein, mouse; C499089:Sod3 protein, rat; D013482:Superoxide Dismutase; D014357:Trypsin; D003545:Cysteine