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The allosteric modulation of complement C5 by knob domain peptides.

eLife (2021-02-12)
Alex Macpherson, Maisem Laabei, Zainab Ahdash, Melissa A Graewert, James R Birtley, Monika-Sarah Ed Schulze, Susan Crennell, Sarah A Robinson, Ben Holmes, Vladas Oleinikovas, Per H Nilsson, James Snowden, Victoria Ellis, Tom Eirik Mollnes, Charlotte M Deane, Dmitri Svergun, Alastair Dg Lawson, Jean Mh van den Elsen
ABSTRACT

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.

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Sigma-Aldrich
Anti-Sheep Red Blood Cell Stroma antibody produced in rabbit, fractionated antiserum, lyophilized powder