European Molecular Biology Laboratory, Hamburg Unit, Hamburg, Germany
James R Birtley
UCB, Slough, United Kingdom
Monika-Sarah ED Schulze
UCB, Slough, United Kingdom
Susan Crennell
Department of Biology and Biochemistry, University of Bath, Bath, United Kingdom
Sarah A Robinson
Department of Statistics, University of Oxford, Oxford, United Kingdom
Ben Holmes
UCB, Slough, United Kingdom
Vladas Oleinikovas
UCB, Slough, United Kingdom
Per H Nilsson
UCB, Slough, United Kingdom; Department of Chemistry and Biomedicine, Linnaeus University, Kalmar, Sweden; Department of Immunology, Oslo University Hospital, University of Oslo, Oslo, Norway
Department of Immunology, Oslo University Hospital, University of Oslo, Oslo, Norway; Research Laboratory, Bodø Hospital, K.G. Jebsen TREC, University of Tromsø, Tromsø, Norway; Centre of Molecular Inflammation Research, Norwegian University of Science and Technology, Trondheim, Norway
Charlotte M Deane
Department of Statistics, University of Oxford, Oxford, United Kingdom
Dmitri Svergun
European Molecular Biology Laboratory, Hamburg Unit, Hamburg, Germany
Department of Biology and Biochemistry, University of Bath, Bath, United Kingdom; Centre for Therapeutic Innovation, University of Bath, Bath, United Kingdom
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.
