Carbamylation of immunoglobulin abrogates activation of the classical complement pathway

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  • Catalin Koro, Broegelmann Research Laboratory, Department of Clinical Science, University of Bergen, Bergen, Norway., Ukendt
  • Ewa Bielecka, Department of Microbiology, Faculty of Biochemistry, Biophysics and Biotechnology, Jagiellonian University, Krakow, Poland, Polen
  • Anders Dahl-Knudsen, Ukendt
  • Jan Johannes Enghild
  • Carsten Scavenius
  • Johan G Brun, Department of Rheumatology, Haukeland University Hospital and Department of Clinical Science, University of Bergen, Bergen, Norway, Norge
  • Veronika Binder, Broegelmann Research Laboratory, Department of Clinical Science, University of Bergen, Bergen, Norway., Norge
  • Annelie Hellvard, Broegelmann Research Laboratory, Department of Clinical Science, University of Bergen, Bergen, Norway., Norge
  • Brith Bergum, Broegelmann Research Laboratory, Department of Clinical Science, University of Bergen, Bergen, Norway., Norge
  • Roland Jonsson, Broegelmann Research Laboratory, Department of Clinical Science, University of Bergen, Bergen, Norway., Centre for Oral Health and Systemic Diseases, University of Louisville School of Dentistry, Louisville, KY, USA, Norge
  • Jan Potempa, Department of Microbiology, Faculty of Biochemistry, Biophysics and Biotechnology, Jagiellonian University, Krakow, Poland, Polen
  • Anna M Blom, Department of Laboratory Medicine Malmö, Lund University, Malmö, Sweden, Sverige
  • Piotr Mydel, Broegelmann Research Laboratory, Department of Clinical Science, University of Bergen, Bergen, Norway., Norge

Post-translational modifications of proteins significantly affect their structure and function. The carbamylation of positively charged lysine residues to form neutral homocitrulline occurs primarily under inflammatory conditions through myeloperoxidase-dependent cyanate (CNO(-) ) formation. We analysed the pattern of human IgG1 carbamylation under inflammatory conditions and the effects that this modification has on the ability of antibodies to trigger complement activation via the classical pathway. We found that the lysine residues of IgG1 are rapidly modified after brief exposure to CNO(-) . Interestingly, modifications were not random, but instead limited to only few lysines within the hinge area and the N-terminal fragment of the CH2 domain. A complement activation assay combined with mass spectrometry analysis revealed a highly significant inverse correlation between carbamylation of several key lysine residues within the hinge region and N-terminus of the CH2 domain and the proper binding of C1q to human IgG1 followed by subsequent complement activation. This severely hindered complement-dependent cytotoxicity of therapeutic IgG1 . The reaction can apparently occur in vivo, as we found carbamylated antibodies in synovial fluid from rheumatoid arthritis patients. Taken together, our data suggest that carbamylation has a profound impact on the complement-activating ability of IgG1 and reveals a pivotal role for previously uncharacterised lysine residues in that process. This article is protected by copyright. All rights reserved.

OriginalsprogEngelsk
TidsskriftEuropean Journal of Immunology
Vol/bind44
Nummer11
Sider (fra-til)3403-3412
Antal sider10
ISSN0014-2980
DOI
StatusUdgivet - nov. 2014

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