The melanocortin-4 receptor (MC4R), a hypothalamic master regulator of energy homeostasis and appetite, is a class A G-protein-coupled receptor and a prime target for the pharmacological treatment of obesity. Here, we present cryo-electron microscopy structures of MC4R–Gs-protein complexes with two drugs recently approved by the FDA, the peptide agonists NDP-α-MSH and setmelanotide, with 2.9 Å and 2.6 Å resolution. Together with signaling data from structure-derived MC4R mutants, the complex structures reveal the agonist-induced origin of transmembrane helix (TM) 6-regulated receptor activation. The ligand-binding modes of NDP-α-MSH, a high-affinity linear variant of the endogenous agonist α-MSH, and setmelanotide, a cyclic anti-obesity drug with biased signaling toward Gq/11, underline the key role of TM3 in ligand-specific interactions and of calcium ion as a ligand-adaptable cofactor. The agonist-specific TM3 interplay subsequently impacts receptor–Gs-protein interfaces at intracellular loop 2, which also regulates the G-protein coupling profile of this promiscuous receptor. Finally, our structures reveal mechanistic details of MC4R activation/inhibition, and provide important insights into the regulation of the receptor signaling profile which will facilitate the development of tailored anti-obesity drugs.

黑皮质素 4 受体 (MC4R) 是下丘脑能量稳态和食欲的主要调节剂，是 A 类 G 蛋白偶联受体，也是肥胖药物治疗的主要靶点。在这里，我们展示了 MC4R-Gs-蛋白复合物与 FDA 最近批准的两种药物的低温电子显微镜结构，肽激动剂 NDP-α-MSH 和 setmelanotide，分辨率分别为 2.9 Å 和 2.6 Å。连同来自结构衍生的 MC4R 突变体的信号数据，复杂的结构揭示了激动剂诱导的跨膜螺旋 (TM) 6 调节受体激活的起源。NDP-α-MSH（一种内源性激动剂 α-MSH 的高亲和力线性变体）和 setmelanotide（一种具有偏向 Gq/11 信号传导的环状抗肥胖药物）的配体结合模式，强调 TM3 在配体特异性相互作用中的关键作用以及钙离子作为配体适应性辅助因子的关键作用。激动剂特异性 TM3 相互作用随后会影响细胞内环 2 的受体-Gs-蛋白界面，这也调节这种混杂受体的 G-蛋白偶联谱。最后，我们的结构揭示了 MC4R 激活/抑制的机制细节，并为受体信号通路的调节提供了重要的见解，这将有助于开发定制的抗肥胖药物。