Arrestins have pivotal roles in regulating G protein-coupled receptor (GPCR) signalling by desensitizing G protein activation and mediating receptor internalization^1,2. It has been proposed that the arrestin binds to the receptor in two different conformations, ‘tail’ and ‘core’, which were suggested to govern distinct processes of receptor signalling and trafficking^3,4. However, little structural information is available for the tail engagement of the arrestins. Here we report two structures of the glucagon receptor (GCGR) bound to β-arrestin 1 (βarr1) in glucagon-bound and ligand-free states. These structures reveal a receptor tail-engaged binding mode of βarr1 with many unique features, to our knowledge, not previously observed. Helix VIII, instead of the receptor core, has a major role in accommodating βarr1 by forming extensive interactions with the central crest of βarr1. The tail-binding pose is further defined by a close proximity between the βarr1 C-edge and the receptor helical bundle, and stabilized by a phosphoinositide derivative that bridges βarr1 with helices I and VIII of GCGR. Lacking any contact with the arrestin, the receptor core is in an inactive state and loosely binds to glucagon. Further functional studies suggest that the tail conformation of GCGR–βarr governs βarr recruitment at the plasma membrane and endocytosis of GCGR, and provides a molecular basis for the receptor forming a super-complex simultaneously with G protein and βarr to promote sustained signalling within endosomes. These findings extend our knowledge about the arrestin-mediated modulation of GPCR functionalities.

抑制蛋白通过使 G 蛋白激活脱敏并介导受体内化，在调节 G 蛋白偶联受体 (GPCR) 信号传导方面发挥关键作用^1,2。有人提出，视紫红质抑制蛋白以两种不同的构象“尾部”和“核心”与受体结合，这被认为控制着受体信号传导和运输的不同过程^3,4。然而，关于抑制蛋白尾部接合的结构信息很少。在这里，我们报告了在胰高血糖素结合和无配体状态下与 β-arrestin 1 (βarr1) 结合的胰高血糖素受体 (GCGR) 的两种结构。据我们所知，这些结构揭示了 βarr1 的受体尾部接合结合模式，具有许多以前未观察到的独特特征。螺旋 VIII 代替受体核心，通过与 βarr1 的中央嵴形成广泛的相互作用，在调节 βarr1 方面发挥着重要作用。尾部结合姿势由 βarr1 C 边缘和受体螺旋束之间的紧密接近进一步定义，并通过桥接 βarr1 与 GCGR 螺旋 I 和 VIII 的磷酸肌醇衍生物来稳定。由于与抑制蛋白没有任何接触，受体核心处于非活性状态并与胰高血糖素松散结合。进一步的功能研究表明，GCGR-βarr的尾部构象控制着βarr在质膜上的募集和GCGR的内吞作用，并为受体与G蛋白和βarr同时形成超级复合物以促进内涵体内的持续信号传导提供了分子基础。这些发现扩展了我们对抑制蛋白介导的 GPCR 功能调节的认识。