Modulation of Receptor Pharmacology by G Protein-Coupled Receptor Dimerization

Although it was classically believed that G protein-coupled receptors (GPCRs) acted as monomeric entities, it is now well-established that they exist and function as dimers (or oligomers) in the plasma membrane. In addition to forming homodimers, GPCRs can associate with closely or distantly related members of the GPCR superfamily to form heterodimers. Dissection of the functional relevance of these associations is currently an area of enormous interest. Additionally, there is mounting evidence that heterodimerization can generate receptors with novel characteristics, leading to altered pharmacological properties. This could at least partially account for pharmacologically defined receptor subtypes for which no gene has been identified. This chapter reviews recent reports of GPCR dimerization and its effect on ligand pharmacology and function. Because current techniques do not readily allow the distinction between the functional effects of GPCR dimers and oligomers, the receptor complexes resulting from GPCR interactions are referred to as “dimers” and the phenomenon as “dimerization.” Additionally, interactions between identical proteins are referred to as “homodimers,” and interactions between nonidentical proteins are referred to as “heterodimers.”