After activation by an agonist, G-protein-coupled receptors (GPCRs) recruit β-arrestin, which desensitizes heterotrimeric G-protein signalling and promotes receptor endocytosis¹. Additionally, β-arrestin directly regulates many cell signalling pathways that can induce cellular responses distinct from that of G proteins². In contrast to G proteins, for which there are many high-resolution structures in complex with GPCRs, the molecular mechanisms underlying the interaction of β-arrestin with GPCRs are much less understood. Here we present a cryo-electron microscopy structure of β-arrestin 1 (βarr1) in complex with M2 muscarinic receptor (M2R) reconstituted in lipid nanodiscs. The M2R–βarr1 complex displays a multimodal network of flexible interactions, including binding of the N domain of βarr1 to phosphorylated receptor residues and insertion of the finger loop of βarr1 into the M2R seven-transmembrane bundle, which adopts a conformation similar to that in the M2R–heterotrimeric G_o protein complex³. Moreover, the cryo-electron microscopy map reveals that the C-edge of βarr1 engages the lipid bilayer. Through atomistic simulations and biophysical, biochemical and cellular assays, we show that the C-edge is critical for stable complex formation, βarr1 recruitment, receptor internalization, and desensitization of G-protein activation. Taken together, these data suggest that the cooperative interactions of β-arrestin with both the receptor and the phospholipid bilayer contribute to its functional versatility.

在被激动剂激活后，G 蛋白偶联受体 (GPCRs) 募集 β-arrestin，从而使异源三聚体 G 蛋白信号转导脱敏并促进受体内吞作用¹。此外，β-arrestin 直接调节许多细胞信号通路，这些信号通路可以诱导不同于 G 蛋白的细胞反应². 与 G 蛋白相比，G 蛋白有许多与 GPCRs 复合的高分辨率结构，β-arrestin 与 GPCRs 相互作用的分子机制知之甚少。在这里，我们展示了 β-arrestin 1 (βarr1) 与在脂质纳米盘中重组的 M2 毒蕈碱受体 (M2R) 复合的低温电子显微镜结构。M2R-βarr1 复合物显示出灵活相互作用的多模式网络，包括 βarr1 的 N 结构域与磷酸化受体残基的结合以及 βarr1 的指环插入 M2R 七跨膜束，其构象类似于M2R-异三聚体 G _o蛋白复合物³. 此外，低温电子显微镜图显示 βarr1 的 C 边缘与脂质双层结合。通过原子模拟和生物物理、生化和细胞分析，我们表明 C 边缘对于稳定的复合物形成、βarr1 募集、受体内化和 G 蛋白激活的脱敏至关重要。总之，这些数据表明 β-arrestin 与受体和磷脂双层的协同相互作用有助于其功能的多功能性。