Adrenergic receptors are representative of a large group of plasma membrane bound receptors that functionally interact with GTP binding proteins (G- proteins) in the process of signal transduction. The adrenergic receptors play a major role in the neural and humoral control of the cardiovascular system and are also important in the humoral regulation of carbohydrates and fatty acid metabolism. Much has been learned about the primary structure of these receptors from the genomic and cDNA clones encoding these proteins. However, very little is known about the tertiary structure of these receptors, how the receptors interact with the plasma membrane, or how they interact with G-proteins. Furthermore, nothing is known about the mechanism by which the hormone activates the receptor. Biochemical characterization of the structure of these receptors has been particularly challenging due to the inherent difficulties in studying integral membrane proteins. To facilitate biochemical studies of the beta-2 adrenergic receptor, a cell free expression system has been developed and characterized. Using this system it is possible to express beta-2 adrenergic receptors which are labeled to a high specific activity with radioactive amino acids and inserted undirectionally into lipid vesicles. Receptor made using this expression system will be used in biochemical studies designed to: (1) learn about the tertiary structure of the receptor using intramolecular crosslinking; (2) determine the sites of membrane insertion by isolating and sequencing the protease resistant membrane bound peptides; (3) study the sites of interaction between the receptor and its G-protein using intermolecular crosslinking; (4) study the dynamic changes in receptor structure by labeling the receptor with fluorescent probes and following changes in the distance between the probes during a cycle of signal transduction by monitoring fluorescent energy transfer.
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