Bovines have evolved a subset of antibodies with ultra-long CDRH3 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.
Structural datasets presented in this study have been made publicly available in the Protein Data Bank (PDB) and Small Angle Scattering Biological Data Bank (SASBDB)
Crystal structure C5-K8 complexProtein Data Bank, 7AD7.
Crystal structure of C5-K92 complexProtein Data Bank, 7AD6.
SAXS data and models of C5-bovine knob domain peptidesSmall Angle Scattering Biological Data Bank, SASDJA6.
No specific external funding was received for this work.
- John Kuriyan, University of California, Berkeley, United States
© 2021, Macpherson et al.
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