Metastable GPCR dimers trigger the basal signal by recruiting G-proteins

Abstract

G-protein-coupled receptors (GPCRs) constitute the largest family of integral membrane proteins in the human genome and are responsible for various important signaling pathways for vision, olfaction, gustation, emotion, cell migration, etc. A distinct feature of the GPCR-family proteins is that many GPCRs, including the prototypical GPCR, {beta}2-adrenergic receptor ({beta}2AR), elicit low levels of basal constitutive signals without agonist stimulation, which function in normal development and various diseases1-3. However, how the basal signals are induced is hardly known. Another general distinctive feature of GPCRs is to form metastable homo-dimers, with lifetimes on the order of 0.1 s, even in the resting state. Here, our single-molecule-based quantification4 determined the dissociation constant of {beta}2AR homo-dimers in the PM (1.6 {+/-} 0.29 copies/m2) and their lifetimes (83.2 {+/-} 6.4 ms), and furthermore found that, in the resting state, trimeric G-proteins were recruited to both {beta}2AR monomers and homo-dimers. Importantly, inverse agonists, which suppress the GPCRs basal constitutive activity, specifically blocked the G-protein recruitment to GPCR homo-dimers, without affecting that to monomers. These results indicate that the G-proteins recruited to transient GPCR homo-dimers are responsible for inducing their basic constitutive signals. These results suggest novel drug development strategies to enhance or suppress GPCR homo-dimer formation.