Structural basis for high-affinity HER2 receptor binding by an engineered protein
Structural basis for high-affinity HER2 receptor binding by an engineered protein
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DOI：
10.1073/pnas.1005025107
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发表时间：
2010-08-24
影响因子：
11.1
通讯作者：
Hard, Torleif
中科院分区：
文献类型：
--
作者：
Eigenbrot, Charles;Ultsch, Mark;Hard, Torleif
人类表皮生长因子受体2(HER2)在几种癌症的肿瘤中特异地过度表达，包括一种侵袭性乳腺癌。因此，它是癌症诊断和治疗的目标。58个氨基酸残基的ZHER2亲和体分子此前被设计为HER2的高亲和力结合蛋白。在这里，我们测定了ZHER2在溶液中的结构，以及ZHER2与HER2胞外区形成的络合物的晶体结构。ZHER2与HER2上的构象表位结合，而该表位与治疗抗体曲妥珠单抗和pertuzumab识别的表位相去甚远。它的小体积和缺乏干扰可能为ZHER2在诊断方面提供优势，甚至在曲妥珠单抗或pertuzumab已经使用的情况下为HER2表达的肿瘤提供治疗药物。生物物理表征表明，ZHER2在折叠状态下热力学稳定，但在亚毫秒级的时间尺度上发生构象转换。数据表明，HER2结合的构象是在结合之前瞬时形成的。尽管如此，结合很强，解离常数K(D)=22 pM，因此，工程结合蛋白不一定需要完美的构象均一性。将原始的Z结构域支架与自由和结合的ZHER2结构进行比较，揭示了高亲和力结合是如何在选择和亲和成熟过程中进化的，并暗示了如何在结合表面优化与非结合状态的稳定性和动力学之间达成妥协。
The human epidermal growth factor receptor 2 (HER2) is specifically overexpressed in tumors of several cancers, including an aggressive form of breast cancer. It is therefore a target for both cancer diagnostics and therapy. The 58 amino acid residue ZHER2 affibody molecule was previously engineered as a high-affinity binder of HER2. Here we determined the structure of ZHER2 in solution and the crystal structure of ZHER2 in complex with the HER2 extracellular domain. ZHER2 binds to a conformational epitope on HER2 that is distant from those recognized by the therapeutic antibodies trastuzumab and pertuzumab. Its small size and lack of interference may provide ZHER2 with advantages for diagnostic use or even for delivery of therapeutic agents to HER2-expressing tumors when trastuzumab or pertuzumab are already employed. Biophysical characterization shows that ZHER2 is thermodynamically stable in the folded state yet undergoing conformational interconversion on a submillisecond time scale. The data suggest that it is the HER2-binding conformation that is formed transiently prior to binding. Still, binding is very strong with a dissociation constant K(D) = 22 pM, and perfect conformational homogeneity is therefore not necessarily required in engineered binding proteins. A comparison of the original Z domain scaffold to free and bound ZHER2 structures reveals how high-affinity binding has evolved during selection and affinity maturation and suggests how a compromise between binding surface optimization and stability and dynamics of the unbound state has been reached.