Structural Basis for Eculizumab-Mediated Inhibition of the Complement Terminal Pathway
Structural Basis for Eculizumab-Mediated Inhibition of the Complement Terminal Pathway
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DOI：
10.4049/jimmunol.1600280
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发表时间：
2016-07-01
影响因子：
4.4
通讯作者：
Andersen, Gregers Rom
中科院分区：
文献类型：
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作者：
Schatz-Jakobsen, Janus Asbjorn;Zhang, Yuchun;Andersen, Gregers Rom
依库珠单抗是一种人源化mAb，获批用于治疗阵发性睡眠性血红蛋白尿和非典型溶血性尿毒综合征患者。依库珠单抗结合补体成分C5并阻止其被C5转化酶裂解，抑制促炎代谢物C5 a的释放和通过C5 b形成膜攻击复合物。在这项研究中，我们以4.2埃的分辨率呈现了C5和与依库珠单抗具有相同序列的Fab片段之间的复合物的晶体结构。五个CDR接触C5巨球蛋白7结构域，其包含整个表位。66个CDR残基的完整突变扫描鉴定出28个残基对于C5-依库珠单抗相互作用是重要的，并且复合物的结构提供了对这些突变体Ab观察到的C5结合降低的解释。此外，相互作用的结构观察结果得到了这些突变Ab的子集抑制膜攻击复合物形成的能力降低的支持，如在溶血测定中所测试的。我们的研究结果表明，依库珠单抗通过空间阻止C5与转化酶结合发挥作用，并解释了依库珠单抗对人C5的精确选择性，以及C5多态性如何导致少数阵发性睡眠性血红蛋白尿症患者对依库珠单抗耐药。
Eculizumab is a humanized mAb approved for treatment of patients with paroxysmal nocturnal hemoglobinuria and atypical hemolytic uremic syndrome. Eculizumab binds complement component C5 and prevents its cleavage by C5 convertases, inhibiting release of both the proinflammatory metabolite C5a and formation of the membrane attack complex via C5b. In this study, we present the crystal structure of the complex between C5 and a Fab fragment with the same sequence as eculizumab at a resolution of 4.2 angstrom. Five CDRs contact the C5 macroglobulin 7 domain, which contains the entire epitope. A complete mutational scan of the 66 CDR residues identified 28 residues as important for the C5-eculizumab interaction, and the structure of the complex offered an explanation for the reduced C5 binding observed for these mutant Abs. Furthermore, the structural observations of the interaction are supported by the reduced ability of a subset of these mutated Abs to inhibit membrane attack complex formation as tested in a hemolysis assay. Our results suggest that eculizumab functions by sterically preventing C5 from binding to convertases and explain the exquisite selectivity of eculizumab for human C5 and how polymorphisms in C5 cause eculizumab-resistance in a small number of patients with paroxysmal nocturnal hemoglobinuria.