Many types of cell surface as well as intracellular DNA-binding receptors exist and function as dimers; formation of homodimers or heterodimers appears to not only provide molecular mechanisms for agonist-induced activation but also increase specificity of ligand recognition and versatility of downstream signaling. G-protein-coupled receptors (GPCRs) were long thought to be an exception, but in recent years a lot of evidence has accumulated that GPCRs also can form dimers, even though it is far from certain when and where they actually do so under physiological conditions. Dimerization of GPCRs does not generally seem to be required for ligand recognition or signaling. However, dimerization may serve to affect receptor mobility at the cell surface and in intracellular trafficking, and may be involved in and affect their signaling functions.
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