Recent perspectives on the molecular structure and regulation of the beta 2-adrenoceptor

The recent cloning of the beta 2-AR and other members of the adrenergic receptor family and related molecules has generated a flood of new information about the structure of this ubiquitous class of receptor molecules, and the ways in which their unique structures determine their function. Agonists interact with the receptor-binding pocket and somehow trigger conformational changes in the cytoplasmic portions of the receptor. These intracellular changes are then transmitted to the G-protein alpha-subunit. Phosphorylation of the receptor by several protein kinases and subsequent binding of additional cytosolic factors appear to be a major step in the control of receptor function. Changes in receptor gene expression which regulate receptor number and responsiveness provide another means to regulate transmembrance signalling. The realization that G-protein-coupled receptors are transcriptionally regulated by their own second messengers indicates that the parallels among the various members of this receptor family extend beyond their structural homologies, of 7 transmembrane segments and G-protein coupling, to include the genetic aspects of their regulation.