The α2 and β2 adrenergic receptors, both of which are activated by epinephrine, but which can be differentiated by selective drugs, have opposite effects (inhibitory and stimulatory) on die adenylyl cyclase system. The two receptors are homologous with each other, rhodopsin, and other receptors coupled to guanine nucleotide regulatory proteins and they contain seven hydrophobic domains, which may represent transmembrane spanning segments. The function of specific structural domains of these receptors was determined after construction and expression of a series of chimeric α2-,β2-adrenergic receptor genes. The specificity for coupling to die stimulatory guanine nucleotide regulatory protein lies within a region extending from the amino terminus of the fifth hydrophobic domain to the carboxyl terminus of the sixth. Major determinants of α2- and β2-adrenergic receptor agonist and antagonist ligand binding specificity are contained within the seventh membrane spanning domain. Chimeric receptors should prove useful for elucidating the structural basis of receptor function.
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