C1q binding to surface-bound IgG is stabilized by C1r2s2 proteases

  • Proc Natl Acad Sci U S A. 2021 Jun 29;118(26):e2102787118. doi: 10.1073/pnas.2102787118.
Seline A Zwarthoff  1 ,  Kevin Widmer  2 ,  Annemarie Kuipers  1 ,  Jürgen Strasser  3 ,  Maartje Ruyken  1 ,  Piet C Aerts  1 ,  Carla J C de Haas  1 ,  Deniz Ugurlar  4 ,  Maurits A den Boer  5  6 ,  Gestur Vidarsson  7 ,  Jos A G van Strijp  1 ,  Piet Gros  4 ,  Paul W H I Parren  8  9 ,  Kok P M van Kessel  1 ,  Johannes Preiner  3 ,  Frank J Beurskens  10 ,  Janine Schuurman  10 ,  Daniel Ricklin  2 ,  Suzan H M Rooijakkers  11
Affiliations
  • 1. Medical Microbiology, University Medical Center Utrecht, Utrecht University, 3584 CX Utrecht, The Netherlands.
  • 2. Pharmaceutical Sciences, University of Basel, 4001 Basel, Switzerland.
  • 3. Nano Structuring and Bio-Analytics Group, TIMed Center, of Applied Sciences Upper Austria, 4020 Linz, Austria.
  • 4. Structural Biochemistry, Bijvoet Center for Biomolecular Research, Utrecht University, 3584 CH Utrecht, The Netherlands.
  • 5. Biomolecular Mass Spectrometry & Proteomics, Bijvoet Center for Biomolecular Research and Utrecht Institute for Pharmaceutical Sciences, Utrecht University, 3584 CH Utrecht, The Netherlands.
  • 6. Netherlands Proteomics Center, 3584 CH, Utrecht, The Netherlands.
  • 7. Experimental Immunohematology, Sanquin Research, 1066 CX Amsterdam, The Netherlands.
  • 8. Immunohematology and Blood Transfusion, Leiden University Medical Center, 2333 ZA Leiden, The Netherlands.
  • 9. Lava Therapeutics, 3584 CM Utrecht, The Netherlands.
  • 10. Genmab, 3584 CT Utrecht, The Netherlands.
  • 11. Medical Microbiology, University Medical Center Utrecht, Utrecht University, 3584 CX Utrecht, The Netherlands; [email protected].
PMID: 34155115 DOI: 10.1073/pnas.2102787118
Abstract

Complement is an important effector mechanism for antibody-mediated clearance of infections and tumor cells. Upon binding to target cells, the antibody's constant (Fc) domain recruits complement component C1 to initiate a proteolytic cascade that generates lytic pores and stimulates phagocytosis. The C1 complex (C1qr2s2) consists of the large recognition protein C1q and a heterotetramer of proteases C1r and C1s (C1r2s2). While interactions between C1 and IgG-Fc are believed to be mediated by the globular heads of C1q, we here find that C1r2s2 proteases affect the capacity of C1q to form an avid complex with surface-bound IgG molecules (on various 2,4-dinitrophenol [DNP]-coated surfaces and pathogenic Staphylococcus aureus). The extent to which C1r2s2 contributes to C1q-IgG stability strongly differs between human IgG subclasses. Using antibody engineering of monoclonal IgG, we reveal that hexamer-enhancing mutations improve C1q-IgG stability, both in the absence and presence of C1r2s2 In addition, hexamer-enhanced IgGs targeting S. aureus mediate improved complement-dependent phagocytosis by human neutrophils. Altogether, these molecular insights into complement binding to surface-bound IgGs could be important for optimal design of antibody therapies.

Keywords
C1; IgG hexamerization; IgG subclasses; Staphylococcus aureus; complement.