G Protein–Coupled Receptor Multimers: A Question Still Open Despite the Use of Novel Approaches

Abstract

Heteromerization of G protein-coupled receptors (GPCRs) can significantly change the functional properties of involved receptors. Various biochemical and biophysical methodologies have been developed in the last two decades to identify and functionally evaluate GPCR heteromers in heterologous cells, with recent approaches focusing on GPCR complex stoichiometry and stability. Yet validation of these observations in native tissues is still lagging behind for the majority of GPCR heteromers. Remarkably, recent studies, particularly some involving advanced fluorescence microscopy techniques, are contributing to our current knowledge of aspects that were not well known until now, such as GPCR complex stoichiometry and stability. In parallel, a growing effort is being applied to move the field forward into native systems. This short review will highlight recent developments to study the stoichiometry and stability of GPCR complexes and methodologies to detect native GPCR dimers.

Structural Analysis of Chemokine Receptor–Ligand Interactions

“…Although the CXCR4 crystal structure may represent a possible conformation of a chemokine receptor homodimer, 248 several other GPCR oligomerization models have been proposed, 249 and more information is needed to identify and validate chemokine receptors oligomerization models that are pharmacologically relevant. 250 The recently solved allosteric antagonist bound CCR9 crystal structure and CCR2 chemokine receptor crystal structure simultaneously targeted by orthosteric and allosteric antagonists provide high resolution structural templates to investigate structural interactions with distinct ligand binding pockets in chemokine receptors and will increase our understanding of the interplay between orthosteric and allosteric ligand binding. The accumulated information on the extracellular and intracellular binding sites of chemokine receptors, as well as so far unexploited extrahelical binding sites identified in other GPCRs 197,251 can open up new possibilities for the computer-aided discovery and design of novel chemokine receptor ligands with complementary modes of action.…”

Mechanism of Assembly and Cooperativity of Homomeric and Heteromeric Metabotropic Glutamate Receptors

“…Despite the interest in GPCR oligomerization, complexes have been difficult to observe and analyze structurally or biophysically within the class A and B families of GPCRs (Vischer et al, 2015). However, class C GPCRs, which are characterized by a large extracellular ligand binding domain (LBD), have been shown to assemble into stable dimers or higher order oligomers both in crystal structures of isolated LBDs (Geng et al, 2013; Kunishima et al, 2000) and biochemical or spectroscopic analyses of full length proteins (Romano et al, 1996; Doumazane et al, 2011; Maurel et al, 2008; Comps-Agrar et al, 2011).…”

Membrane-Mediated Oligomerization of G Protein Coupled Receptors and Its Implications for GPCR Function

“…In addition to the growing number of structures, more and more computational methods were employed to unveil the dynamics of GPCR multimerization (Meng et al, 2014; Kaczor et al, 2015). The functionality of GPCR dimers was further validated by advanced fluorescence methods such as Förster resonance energy transfer (FRET), bioluminescence resonance energy transfer (BRET), or fluorescence correlation spectroscopy (FCS) experiments, which allow to measure signaling and aggregation of GPCRs simultaneously (Goddard and Watts, 2012a; Kasai and Kusumi, 2014; Vischer et al, 2015). …”