title: Oxygen reactivity of mammalian sulfite oxidase provides a concept for the treatment of sulfite oxidase deficiency.
abstract: Mammalian sulfite oxidase (SO) is a dimeric enzyme consisting of a molybdenum cofactor- (Moco) and haem-containing domain and catalyses the oxidation of toxic sulfite to sulfate. Following sulfite oxidation, electrons are passed from Moco via the haem cofactor to cytochrome c, the terminal electron acceptor. In contrast, plant SO (PSO) lacks the haem domain and electrons shuttle from Moco to molecular oxygen. Given the high similarity between plant and mammalian SO Moco domains, factors that determine the reactivity of PSO towards oxygen, remained unknown. In the present study, we generated mammalian haem-deficient and truncated SO variants and demonstrated their oxygen reactivity by hydrogen peroxide formation and oxygen-consumption studies. We found that intramolecular electron transfer between Moco and haem showed an inverse correlation to SO oxygen reactivity. Haem-deficient SO variants exhibited oxygen-dependent sulfite oxidation similar to PSO, which was confirmed further using haem-deficient human SO in a cell-based assay. This finding suggests the possibility to use oxygen-reactive SO variants in sulfite detoxification, as the loss of SO activity is causing severe neurodegeneration. Therefore we evaluated the potential use of PEG attachment (PEGylation) as a modification method for future enzyme substitution therapies using oxygen-reactive SO variants, which might use blood-dissolved oxygen as the electron acceptor. PEGylation has been shown to increase the half-life of other therapeutic proteins. PEGylation resulted in the modification of up to eight surface-exposed lysine residues of SO, an increased conformational stability and similar kinetic properties compared with wild-type SO.
authors.affiliation: Institute of Biochemistry, Department of Chemistry, Center for Molecular Medicine Cologne (CMMC) and Cologne Excellence Cluster on Cellular Stress Responses in Ageing-Associated Diseases (CECAD), University of Cologne, Zuelpicher Straße 47, 50674 Cologne, Germany.
authors.forename: Abdel A
authors.initials: AA
authors.lastname: Belaidi
authors.affiliation: Institute of Biochemistry, Department of Chemistry, Center for Molecular Medicine Cologne (CMMC) and Cologne Excellence Cluster on Cellular Stress Responses in Ageing-Associated Diseases (CECAD), University of Cologne, Zuelpicher Straße 47, 50674 Cologne, Germany.
authors.forename: Juliane
authors.initials: J
authors.lastname: Röper
authors.affiliation: Institute of Biochemistry, Department of Chemistry, Center for Molecular Medicine Cologne (CMMC) and Cologne Excellence Cluster on Cellular Stress Responses in Ageing-Associated Diseases (CECAD), University of Cologne, Zuelpicher Straße 47, 50674 Cologne, Germany.
authors.forename: Sita
authors.initials: S
authors.lastname: Arjune
authors.affiliation: Institute of Biochemistry, Department of Chemistry, Center for Molecular Medicine Cologne (CMMC) and Cologne Excellence Cluster on Cellular Stress Responses in Ageing-Associated Diseases (CECAD), University of Cologne, Zuelpicher Straße 47, 50674 Cologne, Germany.
authors.forename: Sabina
authors.initials: S
authors.lastname: Krizowski
authors.affiliation: CECAD Research Center, University of Cologne, Joseph-Stelzmann-Straße 26, 50931 Cologne, Germany.
authors.forename: Aleksandra
authors.initials: A
authors.lastname: Trifunovic
authors.affiliation: Institute of Biochemistry, Department of Chemistry, Center for Molecular Medicine Cologne (CMMC) and Cologne Excellence Cluster on Cellular Stress Responses in Ageing-Associated Diseases (CECAD), University of Cologne, Zuelpicher Straße 47, 50674 Cologne, Germany gschwarz@uni-koeln.de.
authors.forename: Guenter
authors.initials: G
authors.lastname: Schwarz
mesh_terms: D000592:Amino Acid Metabolism, Inborn Errors / Q000188:drug therapy* / Q000235:genetics / Q000378:metabolism; D000818:Animals; D056947:Enzyme Replacement Therapy; D004795:Enzyme Stability / Q000235:genetics; D057809:HEK293 Cells; D006418:Heme / Q000737:chemistry / Q000235:genetics / Q000378:metabolism; D006801:Humans; D006861:Hydrogen Peroxide; D051379:Mice; D050862:Oxidoreductases Acting on Sulfur Group Donors / Q000737:chemistry / Q000235:genetics / Q000378:metabolism / Q000627:therapeutic use; D010100:Oxygen / Q000737:chemistry / Q000378:metabolism; D010101:Oxygen Consumption / Q000187:drug effects; D011092:Polyethylene Glycols / Q000737:chemistry; D050876:Sulfite Oxidase / Q000172:deficiency* / Q000235:genetics / Q000378:metabolism
chemical_list: D011092:Polyethylene Glycols; D006418:Heme; D006861:Hydrogen Peroxide; D050862:Oxidoreductases Acting on Sulfur Group Donors; C503599:SUOX protein, human; D050876:Sulfite Oxidase; D010100:Oxygen
keywords: PEGylation; hydrogen peroxide; intramolecular electron transfer; molybdenum cofactor deficiency; oxygen reactivity; sulfite oxidase