Novel intra- and inter-molecular sulfinamide bonds in S100A8 produced by hypochlorite oxidation.
Hypochlorite is a major oxidant generated when neutrophils and macrophages are activated at inflammatory sites, such as in atherosclerotic lesions. Murine S100A8 (A8) is a major cytoplasmic protein in neutrophils and is secreted by macrophages in response to inflammatory stimuli. After incubation with reagent HOCl for 10 min, approximately 85% of A8 was converted to 4 oxidation products, with electrospay ionization mass spectrometry masses of m/z 10354, 10388, 10354 +/- 1, and 20707 +/- 3. All were resistant to reduction by dithiothreitol. Initial formation of a reactive Cys sulfenic acid intermediate was demonstrated by the rapid conjugation of 5,5-dimethyl-1,3-cyclohexanedione (dimedone) to HOCl-treated A8 to form stable adducts. Matrix-assisted laser desorption-reflectron time of flight peptide mass fingerprinting of isolated oxidation products confirmed the mass additions observed in the full-length proteins. Both Met(36/73) were converted to Met(36/73) sulfoxides. An additional product with an unusual mass addition of m/z 14 (+/-0.2) was identified and corresponded to the addition of oxygen to Cys(41), conjugation to various epsilon-amines of Lys(6), Lys(34/35), or Lys(87) with loss of dihydrogen and formation of stable intra- or inter-molecular sulfinamide cross-links. Specific fragmentations identified in matrix-assisted laser desorption-post source decay spectra and low energy collisional-induced dissociation tandem mass spectroscopy spectra of sulfinamide-containing digest peptides confirmed Lys(34/35) to Cys(41) sulfinamide bonds. HOCl oxidation of mutants lacking Cys(41) (Ala(41)S100A8) or specific Lys residues (e.g. Lys(34/35), Ala(34/35)S100A8) did not form sulfinamide cross-links. HOCl generated by myeloperoxidase and H(2)O(2) and by phorbol 12-myristate 13-acetate-activated neutrophils also formed these products(.) In contrast to the disulfide-linked dimer, oxidized monomer retained normal chemotactic activity for neutrophils. Sulfinamide bond formation represents a novel oxidative cross-linking process between thiols and amines and may be a general consequence of HOCl protein oxidation in inflammation not identified previously. Similar modifications in other proteins could potentially regulate normal and pathological processes during aging, atherogenesis, fibrosis, and neurogenerative diseases.
Raftery
M J
MJ
Cytokine Research Unit, School of Pathology, University of New South Wales, Kensington, New South Wales 2052, Australia. m.raferty@unsw.edu.au
Yang
Z
Z
Valenzuela
S M
SM
Geczy
C L
CL
D000595:Amino Acid Sequence; D000943:Antigens, Differentiation / Q000737:chemistry*; D001224:Aspartic Acid / Q000737:chemistry; D001665:Binding Sites; D002135:Calcium-Binding Proteins / Q000737:chemistry*; D040501:Calgranulin A; D002851:Chromatography, High Pressure Liquid; D003512:Cyclohexanones / Q000494:pharmacology; D003545:Cysteine / Q000737:chemistry; D019281:Dimerization; D004220:Disulfides; D004229:Dithiothreitol / Q000494:pharmacology; D004305:Dose-Response Relationship, Drug; D006861:Hydrogen Peroxide / Q000494:pharmacology; D006997:Hypochlorous Acid / Q000378:metabolism*; D008239:Lysine / Q000737:chemistry; D008956:Models, Chemical; D008969:Molecular Sequence Data; D016297:Mutagenesis, Site-Directed; D009154:Mutation; D009504:Neutrophils / Q000378:metabolism; D010100:Oxygen / Q000378:metabolism*; D010455:Peptides / Q000737:chemistry; D009195:Peroxidase / Q000494:pharmacology; D021241:Spectrometry, Mass, Electrospray Ionization; D019032:Spectrometry, Mass, Matrix-Assisted Laser Desorption-Ionization; D013434:Sulfenic Acids / Q000737:chemistry; D013455:Sulfur / Q000737:chemistry* / Q000378:metabolism*; D013755:Tetradecanoylphorbol Acetate / Q000494:pharmacology; D013997:Time Factors
D000943:Antigens, Differentiation; D002135:Calcium-Binding Proteins; D040501:Calgranulin A; D003512:Cyclohexanones; D004220:Disulfides; D010455:Peptides; D013434:Sulfenic Acids; D001224:Aspartic Acid; D013455:Sulfur; D006997:Hypochlorous Acid; C004774:dimedone; D006861:Hydrogen Peroxide; D009195:Peroxidase; D008239:Lysine; D003545:Cysteine; D013755:Tetradecanoylphorbol Acetate; D010100:Oxygen; D004229:Dithiothreitol