Molecular organization and dynamics of the melatonin MT1 receptor/RGS20/Gi protein complex reveal asymmetry of receptor dimers for RGS and Gi coupling

Abstract

Functional asymmetry of G-protein-coupled receptor (GPCR) dimers has been reported for an increasing number of cases, but the molecular architecture of signalling units associated to these dimers remains unclear. Here, we characterized the molecular complex of the melatonin MT 1 receptor, which directly and constitutively couples to G i proteins and the regulator of G-protein signalling (RGS) 20. The molecular organization of the ternary MT 1 /G i /RGS20 complex was monitored in its basal and activated state by bioluminescence resonance energy transfer between probes inserted at multiple sites of the complex. On the basis of the reported crystal structures of G i and the RGS domain, we propose a model wherein one G i and one RGS20 protein bind to separate protomers of MT 1 dimers in a pre-associated complex that rearranges upon agonist activation. This model was further validated with MT 1 /MT 2 heterodimers. Collectively, our data extend the concept of asymmetry within GPCR dimers, reinforce the notion of receptor specificity for RGS proteins and highlight the advantage of GPCRs organized as dimers in which each protomer fulfils its specific task by binding to different GPCR-interacting proteins.

G Protein–Coupled Receptor Oligomerization Revisited: Functional and Pharmacological Perspectives

“…GPCR oligomerization potentially provides a larger platform to accommodate the different GPCR interacting proteins necessary for receptor function (reviewed in Maurice et al, 2011). This is demonstrated in the complex of melatonin MT 1 receptor dimers, G i protein and RGS20 (a protein that regulates the speed of G protein signal transduction), which both bind directly to helix 8 of the receptor (Maurice et al, 2010). In this complex, protomer 1 binds the ligand and the G protein and protomer 2 binds RGS20.…”

“…In this complex, protomer 1 binds the ligand and the G protein and protomer 2 binds RGS20. In this case, RGS20, by slowing down the decay time of G protein inactivation, thus participates in prolonged signal transduction (Maurice et al, 2010).…”

Distinct roles of metabotropic glutamate receptor dimerization in agonist activation and G-protein coupling

“…In such dimeric complexes, even if a single 7TM is responsible for G-protein activation, the associated 7TMs can be involved in other functions, which may include coupling efficacy (39,44), controlling G-protein-independent signaling pathways (47), or recruiting any number of intracellular associated proteins to be part of the larger signaling complexes (48,49). Although dimers are likely important for GPCR biology (50,51), our study also indicates that understanding and studying structural changes that occur in the context of individual 7TM monomers could be relevant and useful for the development of class C allosteric modulators as new therapeutic tools.…”

Asymmetric perturbations of signalling oligomers

“…This was observed for melatonin MT 1 receptor homodimers coupled to G i proteins and to a regulator of G protein signalling via radioligand binding and BRET measurements (Maurice et al, 2010). Arrestin, a mediator of GPCR desensitization, binds to phosphorylated opsin and induces asymmetric binding of the agonist trans-retinal to these class A GPCR subunits in 1:2:1 ratio (Sommer et al, 2012).…”

“…In an illustrative example, bioluminescence resonance energy transfer (BRET) and electrophysiology have been used to characterize the complex of melatonin MT1 receptor, RGS20, and G i proteins in its basal and agonist-activated state to reveal functional asymmetry of RGS20 and G i coupling to MT1 (Maurice, 2010).…”