UCB, Slough, United Kingdom.
Department of Biology and Biochemistry, University of Bath, Bath, United Kingdom.
Elife. 2021 Feb 11;10:e63586. doi: 10.7554/eLife.63586.
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.
牛已经进化出一组具有超长长重链互补决定区的抗体，这些抗体含有富含半胱氨酸的 knob 结构域。为了产生高亲和力的肽，我们之前从牛抗体中分离出了自主的 3-6 kDa knob 结构域。在这里，我们表明，四个 knob 结构域肽的结合会引起一系列对临床验证的药物靶标补体 C5 的影响。变构机制占主导地位，一种肽选择性抑制替代途径 C5 转化酶对 C5 的切割，揭示了经典途径和替代途径 C5 转化酶之间可靶向的机制差异。通过混合生物物理方法，我们展示了 C5-knob 结构域共晶结构，并通过溶液方法观察到变构效应从结合位点传播超过 50 Å。这项研究扩展了 C5 的治疗范围，提出了新的抑制剂，并将 knob 结构域作为具有治疗潜力的新型低分子量抗体片段。
