title: Ovotransferrin possesses SOD-like superoxide anion scavenging activity that is promoted by copper and manganese binding.
abstract: The embryo of oviparous species is confronted by a highly oxidative stress generating as it grows and must rely on effective antioxidant system for protection. Proteins of avian egg albumin have been suggested to play the major redox-modulatory role during embryo development. Recently, we found that ovotransferrin (OTf) undergoes distinct thiol-linked self-cleavage in a redox-dependent process. In this study, we explore that OTf is SOD mimic protein with a potent superoxide anion (O(2)(-)) scavenging activity. The O(2)(-) scavenging activity was investigated using the natural xanthine/xanthine oxidase (X/XOD) coupling system. OTf exhibited O(2)(-) scavenging activity in a dose-dependent manner and showed remarkably higher scavenging activity than the known antioxidants, ascorbate or serum albumin. The isolated half-molecules of OTf exhibited higher scavenging activity than the intact molecule, whereas the N-lobe showed much greater activity. OTf dramatically quenched the O(2)(-) flux but had no effect on the urate production in the X/XOD system, indicating its unique specificity to scavenge O(2)(-) but not oxidase inhibition. Strikingly, metal-bound OTf exhibited greater O(2)(-) dismutation capacity than the apo-protein, ranging from moderate (Zn(2+)-OTf and Fe(2+)-OTf) to high (Mn(2+)-OTf and Cu(2+)-OTf) activity with the Cu(2+)-OTf being the most potent scavenger. In a highly sensitive fluorogenic assay, the metal-bound OTf exhibited significant increase in the rate of H(2)O(2) production in the X/XOD reaction than the apo-OTf, providing evidence that Zn(2+)-, Mn(2+)- and Cu(2+)-OTf possess SOD mimic activity. This finding is the first to describe that OTf is an O(2)(-) scavenging molecule, providing insight into its novel SOD-like biological function, and heralding a fascinating opportunity for its potential candidacy as antioxidant drug.
authors.affiliation: Department of Biochemistry and Biotechnology, Faculty of Agriculture, Kagoshima University, Kagoshima 890-0065, Japan. hishamri@chem.agri.kagoshima-u.ac.jp
authors.forename: Hisham R
authors.initials: HR
authors.lastname: Ibrahim
authors.forename: Md Imranul
authors.initials: MI
authors.lastname: Hoq
authors.forename: Takayoshi
authors.initials: T
authors.lastname: Aoki
mesh_terms: D003207:Conalbumin / Q000187:drug effects / Q000378:metabolism*; D003300:Copper / Q000494:pharmacology*; D016166:Free Radical Scavengers / Q000032:analysis*; D007700:Kinetics; D008345:Manganese / Q000494:pharmacology*; D013482:Superoxide Dismutase / Q000187:drug effects / Q000378:metabolism*; D013481:Superoxides / Q000378:metabolism*; D014969:Xanthine Oxidase / Q000378:metabolism
chemical_list: D016166:Free Radical Scavengers; D013481:Superoxides; D003207:Conalbumin; D008345:Manganese; D003300:Copper; D013482:Superoxide Dismutase; D014969:Xanthine Oxidase