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

Zwarthoff, S. A.; Widmer, K.; Kuipers, A.; Strasser, J.; Ruyken, M.; Aerts, P.; de Haas, C. J. C.; Ugurlar, D.; Vidarsson, G.; van Strijp, J.; Gros, P.; Parren, P.; van Kessel, K. P. M.; Preiner, J.; Beurskens, F. J.; Schuurman, J.; Ricklin, D.; Rooijakkers, S. H. M.

doi:10.1101/2021.02.08.430229

bioRxiv · 10.1101/2021.02.08.430229

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

Zwarthoff, S. A.·Widmer, K.·Kuipers, A.·Strasser, J.·Ruyken, M.·Aerts, P.·de Haas, C. J. C.·Ugurlar, D.·Vidarsson, G.·van Strijp, J.·Gros, P.·Parren, P.·van Kessel, K. P. M.·Preiner, J.·Beurskens, F. J.·Schuurman, J.·Ricklin, D.·Rooijakkers, S. H. M.

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Abstract

Complement is an important effector mechanism for antibody-mediated clearance of infections and tumor cells. Upon binding to target cells, the antibodys 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-Fcs 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 DNP-coated surfaces and pathogenic Staphylococcus aureus). The extent to which C1r2s2 contribute 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 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.

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Zwarthoff, S. A., Widmer, K., Kuipers, A., Strasser, J., Ruyken, M., Aerts, P., de Haas, C. J. C., Ugurlar, D., Vidarsson, G., van Strijp, J., Gros, P., Parren, P., van Kessel, K. P. M., Preiner, J., Beurskens, F. J., Schuurman, J., Ricklin, D., Rooijakkers, S. H. M.. 2021-02-10. C1q binding to surface-bound IgG is stabilized by C1r2s2 proteases. https://doi.org/10.1101/2021.02.08.430229

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