MRAP2 potentiates GPCR signaling by conserved mechanisms that are disrupted by obesity-associated genetic variants

The melanocortin-2 receptor accessory protein (MRAP) family interacts with and regulates signaling of diverse G protein-coupled receptors (GPCRs). MRAP2 modifies signaling of three distinct GPCRs, melanocortin-4 receptor (MC4R), MC3R and ghrelin receptor (GHSR), all essential for appetite regulation. The nature of MRAP2/GPCR complexes and whether there are shared mechanisms for complex assembly, critical structural regions or consistent effects on receptor signaling remains unknown. Here we showed all three GPCRs preferentially interact with MRAP2 as 1:1 complexes and MRAP2 binding disrupts GPCR homodimerization. MRAP2 interacts with shared receptor transmembrane regions to promote GPCR signaling and impairs β-arrestin-2 recruitment to prolong signaling and delay internalization. Deletion of the MRAP2 cytoplasmic region impairs GPCR signaling by modulating constitutive activity. Human MRAP2 variants associated with overweight/obesity modulate constitutive activity of all three GPCRs. Thus, MRAP2 regulates GPCR function using shared molecular mechanisms and we provide further evidence for the importance of GHSR constitutive activity.