The allosteric modulation of complement C5 by knob domain peptides

Bovines have evolved a subset of antibodies with ultra-long heavy chain complementarity determining regions that harbour cysteine-rich knob domains. To produce high-affinity peptides, we previously isolated autonomous 3-6 kDa knob domains from bovine antibodies. Here, we show that binding of four knob domain peptides elicits a range of effects on the clinically validated drug target complement C5. Allosteric mechanisms predominated, with one peptide selectively inhibiting C5 cleavage by the alternative pathway C5 convertase, revealing a targetable mechanistic difference between the classical and alternative pathway C5 convertases. Taking a hybrid biophysical approach, we present C5-knob domain co-crystal structures and, by solution methods, observed allosteric effects propagating >50 Å from the binding sites. This study expands the therapeutic scope of C5, presents new inhibitors, and introduces knob domains as new, low molecular weight antibody fragments, with therapeutic potential.
Keywords: bovine immunoglobulin; complement C5; human; immunology; inflammation; knob-domain peptides; molecular biophysics; structural biology.

Reference
Macpherson, A., Laabei, M., Ahdash, Z., Graewert, M. A., Birtley, J. R., Schulze, M. S. E., ... & van den Elsen, J. M. (2021). The allosteric modulation of Complement C5 by knob domain peptides. Elife, 10, e63586.

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