Chemokines are unusual class-A GPCR agonists because of their large size (~10 kDa) and binding at two distinct receptor sites: N-terminal domain (Site-I, unique to chemokines) and a groove defined by extracellular loop/transmembrane helices (Site-II, shared with all small molecule class-A ligands). Whereas binding at Site-II triggers receptor activation, the role of Site-I is not known. Structures and sequence analysis reveal that the receptor N-terminal domains (N-domains) are flexible and contain intrinsic disorder. Using a hybrid NMR-MD approach, we characterized the role of Site-I interactions for the CXCL8-CXCR1 pair. NMR data indicate that the CXCR1 N-domain becomes structured on binding and that the binding interface is extensive with 30% of CXCL8 residues participating in this initial interaction. MD simulations indicate that CXCL8 bound at Site-I undergoes extensive reorganization on engaging Site-II with several residues initially engaged at Site-I also engaging Site-II. We conclude that structural plasticity of Site-I interactions plays an active role in driving ligand recognition by a chemokine receptor.

中文翻译：

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远距离运动是趋化因子受体识别配体的基础

趋化因子是不寻常的A类GPCR激动剂，因为它们的大小大（〜10 kDa）并在两个不同的受体位点结合：N末端结构域（Site-I，趋化因子特有的）和由细胞外环/跨膜螺旋限定的凹槽（位点II，与所有小分子A类配体共享）。尽管在Site-II处的结合会触发受体激活，但Site-I的作用尚不清楚。结构和序列分析表明，受体N末端域（N域）具有柔韧性并包含内在的紊乱。使用混合NMR-MD方法，我们表征了CXCL8-CXCR1对的Site-I相互作用的作用。NMR数据表明CXCR1 N结构域在结合时结构化，并且结合界面广泛，有30％的CXCL8残基参与此初始相互作用。MD模拟表明，结合于Site-II的CXCL8在与Site-II结合时经历了广泛的重组，最初与Site-I结合的多个残基也与Site-II结合。我们得出结论，Site-I相互作用的结构可塑性在趋化因子受体驱动配体识别中起积极作用。