title: The C-terminal proteolytic processing of extracellular superoxide dismutase is redox regulated.
abstract: The antioxidant protein extracellular superoxide dismutase (EC-SOD) encompasses a C-terminal region that mediates interactions with a number of ligands in the extracellular matrix (ECM). This ECM-binding region can be removed by limited proteolysis before secretion, thus supporting the formation of EC-SOD tetramers with variable binding capacity. The ECM-binding region contains a cysteine residue (Cys219) that is known to be involved in an intersubunit disulfide bridge. We have determined the redox potential of this disulfide bridge and show that both EC-SOD dimers and EC-SOD monomers are present within the intracellular space. The proteolytic processing of the ECM-binding region in vitro was modulated by the redox status of Cys219, allowing cleavage under reducing conditions only. When wild-type EC-SOD or the monomeric variant Cys219Ser was expressed in mammalian cells proteolysis did not occur. However, when cells were exposed to oxidative stress conditions, proteolytic processing was observed for wild-type EC-SOD but not for the Cys219Ser variant. Although the cellular response to oxidative stress is complex, our data suggest that proteolytic removal of the ECM-binding region is regulated by the intracellular generation of an EC-SOD monomer and that Cys219 plays an important role as a redox switch allowing the cellular machinery to secrete cleaved EC-SOD.
authors: Department of Biomedicine, Aarhus University, Aarhus, Denmark.
authors: Randi H
authors: RH
authors: Gottfredsen
authors: Sophie My-Hang
authors: SM
authors: Tran
authors: Ulrike G
authors: UG
authors: Larsen
authors: Peder
authors: P
authors: Madsen
authors: Morten S
authors: MS
authors: Nielsen
authors: Jan J
authors: JJ
authors: Enghild
authors: Steen V
authors: SV
authors: Petersen
mesh_terms: D000595:Amino Acid Sequence; D001011:Aorta / Q000166:cytology / Q000201:enzymology*; D001665:Binding Sites; D002846:Chromatography, Affinity; D003545:Cysteine / Q000378:metabolism*; D019281:Dimerization; D004220:Disulfides / Q000378:metabolism; D005109:Extracellular Matrix / Q000378:metabolism; D005110:Extracellular Space / Q000378:metabolism; D057809:HEK293 Cells; D006801:Humans; D008969:Molecular Sequence Data; D010084:Oxidation-Reduction; D018384:Oxidative Stress; D011485:Protein Binding; D021122:Protein Subunits / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*; D059748:Proteolysis; D013482:Superoxide Dismutase / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*
chemical_list: D004220:Disulfides; D021122:Protein Subunits; D013482:Superoxide Dismutase; D003545:Cysteine