Cryo-EM structures of MC4R-Gq complex illuminate biased signaling, driving renewed efforts for selective metabolic therapies.

The melanocortin-4 receptor (MC4R) is a crucial G-protein-coupled receptor (GPCR) in the hypothalamus, regulating energy balance and appetite. Early drug discovery efforts targeting MC4R were hindered by an incomplete understanding of its complex signal transduction mechanisms and the broad activation of Gs pathways, leading to off-target effects. A key gap was identifying specific signaling pathways responsible for therapeutic effects versus adverse ones. This paper addresses this by highlighting the central role of Gq/11 signaling in specific neuronal populations for appetite suppression, providing a clearer path for targeted drug design.

This review synthesizes recent advances in MC4R signal transduction, highlighting the critical role of Gq/11 pathways in appetite suppression within paraventricular nucleus (PVN) neurons. The authors also present novel high-resolution cryo-electron microscopy (cryo-EM) structures of the setmelanotide-MC4R-Gq complex. These structures provide detailed molecular insights into ligand binding and receptor activation mechanisms. The work further discusses the potential of combination therapies involving MC4R modulators and GLP-1 mimetics, alongside their implications for melanocortin signaling dysfunction.

Early MC4R drug discovery was hampered by an incomplete understanding of its signal transduction and broad activation of Gs pathways. Recent findings reveal that MC4R elicits multiple intracellular responses, with Gq/11 signaling in PVN neurons playing a central role in appetite suppression. This biased signaling mechanism is critical for therapeutic efficacy.

High-resolution cryo-electron microscopy (cryo-EM) structures of the setmelanotide-MC4R-Gq complex offer critical insights into ligand binding, receptor activation, and the specific molecular determinants of biased signaling. These structural details enable the rational design of more selective MC4R agonists with improved safety profiles by targeting specific Gq/11 activation. Furthermore, combination therapies, such as MC4R modulators with GLP-1 mimetics and other metabolic agents, have shown promise to enhance weight loss outcomes.