The allosteric modulation of Complement C5 by knob domain peptides

Alex Macpherson, Maisem Laabei, Zainab Ahdash, Melissa Graewert, James Birtley, Monika-Sarah Schulze, Susan Crennell, Sarah Robinson, Ben Holmes, Vladas Oleinikovas, Per Nilsson, James Snowdon, Victoria Ellis, Tom Eirik Mollnes, Charlotte Deane, Dmitri Svergun, Alastair Lawson, Jean Van Den Elsen

Research output: Contribution to journalArticlepeer-review

18 Citations (SciVal)


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 cocrystal 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.
Original languageEnglish
Article numbere63586
Pages (from-to)1-49
Number of pages49
Publication statusPublished - 11 Feb 2021

Bibliographical note

Funding Information:
This work was performed by A.M. as partial fulfilment of the requirements for a PhD from the University of Bath and was funded by UCB. A.M., S.S., V.O., J.S., B.H., V.E., Z.A. and A.D.G.L are present or past employees of UCB and may hold shares and/or stock options. T.E.M is a Board member of Ra Pharmaceuticals, Inc. All other authors declare no competing interests.

Data availability
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).
The following datasets were generated:
Author(s) Year Dataset title Dataset URL
Database and
Macpherson A,
Elsen JM
2021 Crystal structure C5-K8 complex
RCSB Protein Data
Bank, 7AD7
Macpherson A,
Elsen JM
2021 Crystal structure of C5-K92
RCSB Protein Data
Bank, 7AD6
Macpherson A,
Elsen JM, Graewert
MA, Svergun D
2020 SAXS data and models of C5-
bovine knob domain peptides
Small Angle
Scattering Biological
Data Bank, SASDJA6


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