Structures of active melanocortin-4 receptor–Gs-protein complexes with NDP-α-MSH and setmelanotide

Nicolas A. Heyder, Gunnar Kleinau, David Speck, Andrea Schmidt, Sarah Paisdzior, Michal Szczepek, Brian Bauer, Anja Koch, Monique Gallandi, Dennis Kwiatkowski, Jörg Bürger, Thorsten Mielke, Annette G. Beck-Sickinger, Peter W. Hildebrand, Christian M. T. Spahn, Daniel Hilger, Magdalena Schacherl, Heike Biebermann, Tarek Hilal, Peter Kühnen, Brian K. Kobilka, Patrick Scheerer

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.