GPCR dimers fall apart

G protein-coupled receptors (GPCRs), also known as seven-transmembrane receptors (7TMRs), transduce various sensory and nonsensory signals. It is now widely accepted that these receptors associate with each other as homomeric or heteromeric dimers or as higher-order oligomers. This realization raises a number of questions regarding the quaternary structure of GPCRs and the function of GPCR oligomers: How does ligand binding in one protomer affect an associated protomer? What is the functional unit that activates downstream signaling molecules? What parts of the receptor form the interfaces between protomers? Where along the pathway from synthesis to degradation do oligomers form? Do they ever dissociate? Until recently, this last question has attracted little attention, and GPCR dimers and oligomers have generally been considered to be stable structures. However, biophysical studies have now begun to address this question, and the answer that is emerging will require a reassessment of the stable dimer model.