A gain-of-function polymorphism in a G-protein coupling domain of the human beta(1)-adrenergic receptor

The beta(1)-adrenergic receptor (beta(1)AR) is a key cell surface signaling protein expressed in the heart and other organs that mediates the actions of catecholamines of the sympathetic nervous system. A polymorphism in the intracellular cytoplasmic tail near the seventh transmembrane-spanning segm ent of the human beta(1)AR has been identified in a cohort of normal indivi duals. At amino acid position 389, Gly or Arg can be found (allele frequenc ies 0.26 and 0.74, respectively), the former previously considered as the h uman wild-type beta(1)AR. Using site-directed mutagenesis to mimic the two variants, CHW-1102 cells were permanently transfected to express the Gly-38 9 and Arg-389 receptors, In functional studies with matched expression, the Arg-389 receptors had slightly higher basal levels of adenylyl cyclase act ivities (10.7 +/- 1.2 versus 6.1 +/- 0.4 pmol/min/mg), However, maximal iso proterenol-stimulated levels were markedly higher for the Arg-389 as compar ed to the Gly-389 receptor (63.3 +/- 6.1 versus 20.9 +/- 2.0 pmol/min/mg), Agonist-promoted [S-35]guanosine 5'-O-(thiotriphosphate) binding was also i ncreased with the Arg-389 receptor consistent with enhanced coupling to G(s ) and increased adenylyl cyclase activation. In agonist competition studies carried out in the absence of guanosine 5'-(beta,gamma-imido)triphosphate, high affinity binding could not be resolved with the Gly-389 receptor, whe reas Arg-389 displayed an accumulation of the agonist high affinity recepto r complex (R-H = 26%). Taken together, these data indicate that this polymo rphic variation of the human beta(1)AR results in alterations of receptor-G (s) interaction with functional signal transduction consequences, consisten t with its localization in a putative G-protein binding domain. The genetic variation of beta(1)AR at this locus may be the basis of interindividual d ifferences in pathophysiologic characteristics or in the response to therap eutic beta AR agonists and antagonists in cardiovascular and other diseases .