Opioid receptors and their interacting proteins.

The opioid receptors are among the most highly studied members of the family of G protein-coupled receptors. As for many other members of this family, recent studies have indicated that they do not exist in isolation but are able to interact with a substantial range of other polypeptides. Such interactions can alter the effectiveness of agonist-mediated cell signalling, determine the signals generated, alter the intracellular trafficking routes of the receptors and potentially determine cellular localization by providing a scaffold to link the receptors to the cytoskeletal network. Although virtually all studies on these interactions to date have employed expression into simple heterologous cell lines, the availability of knock-out mouse lines and the capacity to knock-down levels of opioid receptor-interacting proteins using techniques such as siRNA suggest that information on the functional consequences of such protein-protein interactions in a physiological setting will soon be forthcoming.