Properties of the beta 1- and beta 2-adrenergic receptor subtypes revealed by molecular cloning

The beta 1- and beta 2-adrenergic receptor subtypes are biochemically and functionally similar, because both receptors mediate the catecholamine-dependent activation of adenylate cyclase through the GTP-binding protein, Gs. Pharmacologically, the two receptors can be distinguished on the basis of their relative affinities for the agonists epinephrine and norepinephrine as well as their affinities for several selective antagonists. The primary structures of the human beta 1- and beta 2-adrenergic receptors have recently been deduced from the cloning of their genes and (or) cDNAs, revealing high sequence homology and a membrane topography of seven putative transmembrane regions similar to that of rhodopsin. Chimeric beta 1/beta 2-adrenergic receptor cDNAs have been constructed by site-directed mutagenesis and the chimeric RNA transcripts expressed in Xenopus laevis oocytes. The pharmacological properties of the expressed chimeric receptor proteins were assessed by radioligand binding utilizing subtype-selective agonists and antagonists. Apparently, several of the putative transmembrane regions contribute significantly to the determination of subtype selectivity, presumably by formation of a ligand-binding pocket, with determinants for agonist and antagonist binding being distinguishable.