Oligomerization of G protein-coupled receptors: Still doubted?

Experimental data accumulated during the last 10 years strongly support the existence and functional significance of oligomerization of G protein-coupled receptors (GPCRs). In this essay, we discuss the unique biochemical properties of GPCR oligomers in the frame of "allosterism" and how these properties can be used to identify GPCR oligomers in artificial systems and in native tissues. We also address how the significant advances in biophysical, computational and crystallization techniques have provided significant structural insights about the mechanisms behind allosterism in GPCRs, giving distinct clues about the mechanisms of allosteric interactions in GPCR homomers and heteromers. Finally, we elaborate on the emerging picture of the role of GPCR oligomers as components of pre-coupled macromolecular complexes that include different G proteins and effectors, such as adenylyl cyclase. Allosteric properties of GPCR oligomers can therefore extend to ligand interactions through the different components of the macromolecular complexes.