G protein-coupled receptors (GPCRs) generally accommodate specific ligands in the orthosteric-binding pockets. Ligand binding triggers a receptor allosteric conformational change that leads to the activation of intracellular transducers, G proteins and β-arrestins. Because these signals often induce adverse effects, the selective activation mechanism for each transducer must be elucidated. Thus, many orthosteric-biased agonists have been developed, and intracellular-biased agonists have recently attracted broad interest. These agonists bind within the receptor intracellular cavity and preferentially tune the specific signalling pathway over other signalling pathways, without allosteric rearrangement of the receptor from the extracellular side^1,2,3. However, only antagonist-bound structures are currently available^1,4,5,6, and there is no evidence to support that biased agonist binding occurs within the intracellular cavity. This limits the comprehension of intracellular-biased agonism and potential drug development. Here we report the cryogenic electron microscopy structure of a complex of G_s and the human parathyroid hormone type 1 receptor (PTH1R) bound to a PTH1R agonist, PCO371. PCO371 binds within an intracellular pocket of PTH1R and directly interacts with G_s. The PCO371-binding mode rearranges the intracellular region towards the active conformation without extracellularly induced allosteric signal propagation. PCO371 stabilizes the significantly outward-bent conformation of transmembrane helix 6, which facilitates binding to G proteins rather than β-arrestins. Furthermore, PCO371 binds within the highly conserved intracellular pocket, activating 7 out of the 15 class B1 GPCRs. Our study identifies a new and conserved intracellular agonist-binding pocket and provides evidence of a biased signalling mechanism that targets the receptor–transducer interface.

G 蛋白偶联受体 (GPCR) 通常在正构结合袋中容纳特定配体。配体结合触发受体变构构象变化，从而激活细胞内转导器、G 蛋白和 β-抑制蛋白。由于这些信号通常会引起不利影响，因此必须阐明每个传感器的选择性激活机制。因此，已经开发了许多正位偏向激动剂，并且细胞内偏向激动剂最近引起了广泛的兴趣。这些激动剂在受体细胞内腔内结合，并优先调节特定信号传导途径而不是其他信号传导途径，而不会从细胞外侧对受体进行变构重排^1,2,3 。然而，目前只有拮抗剂结合结构可用^1,4,5,6 ，并且没有证据支持偏向激动剂结合发生在细胞内腔内。这限制了对细胞内偏向激动和潜在药物开发的理解。在这里，我们报道了 G _s和人甲状旁腺激素 1 型受体 (PTH1R) 与 PTH1R 激动剂 PCO371 结合的复合物的低温电子显微镜结构。 PCO371 结合在 PTH1R 的细胞内口袋内并直接与_G相互作用。 PCO371 结合模式将细胞内区域重新排列为活性构象，而无需细胞外诱导的变构信号传播。 PCO371 稳定了跨膜螺旋 6 显着向外弯曲的构象，这有利于与 G 蛋白而不是 β-抑制蛋白的结合。此外，PCO371 结合在高度保守的细胞内口袋内，激活 15 个 B1 类 GPCR 中的 7 个。 我们的研究发现了一个新的、保守的细胞内激动剂结合袋，并提供了针对受体-传感器界面的偏向信号传导机制的证据。