Detection of G protein-coupled receptor (GPCR) dimerization by coimmunoprecipitation.

With 356 members in the human genome, G protein-coupled receptors (GPCRs) constitute the largest family of proteins involved in signal transduction across biological membranes. GPCRs are integral membrane proteins featuring a conserved structural topology with seven transmembrane domains. By recognizing a large diversity of hormones and neurotransmitters, GPCRs mediate signal transduction pathways through their interactions with both extracellular small-molecule ligands and intracellular G proteins to initiate appropriate cellular signaling cascades. As there is a clear link between GPCRs and several disorders, GPCRs currently constitute the largest family of proteins targeted by marketed pharmaceuticals. Therefore, a detailed understanding of the biogenesis of these receptors and of GPCR-protein complex assembly can help to answer some important questions. In this chapter, we will discuss several methods to isolate GPCRs and to study, via coimmunoprecipitation, protein-protein interactions. Special attention will be given to GPCR dimerization, which often starts already in the endoplasmic reticulum and influences the maturation of the receptor. Next, we will also explain an elegant tool to study GPCR biogenesis based on the glycosylation pattern of the receptor of interest.