Similarities and differences in the coupling of human β1- and β2-adrenoceptors to Gsα splice variants

The human beta(1)-adrenoceptor (beta(1)AR) and beta(2)-adrenoceptor (beta(2)AR) couple to G(s)-proteins to activate adenylyl cyclase (AC). There are differences in desensitization between the beta(2)AR and the originally cloned Gly389-beta(1)AR, but with respect to ternary complex formation, constitutive activity, and AC activation the picture is unclear. To learn more about the similarities and differences between the beta(1)AR and beta(2)AR, we analyzed coupling of the Gly389-beta(1)AR to the G(salpha) splice variants G(salphaL) and G(salphaS) using beta(1)AR-G(salpha) fusion proteins expressed in Sf9 cells and compared the data with previously published data on beta(2)AR-G(salphaS), fusion proteins (Seifert et al., J Biol Chem 1998;273:5109-16). Fusion ensures defined receptor/G-protein stoichiometry and efficient coupling. The agonist (-)-isoproterenol stabilized the ternary complex at beta(1)AR-G(salphaL), beta(1)AR-G(salphaL), beta(2)AR-G(salphaS), and beta(2)AR-G(salphaL) with similar efficiency. beta(1)AR-G(salphaL) but not beta(1)AR-G(salphaS) showed the hallmarks of constitutive activity as assessed by increased potencies and efficacies of partial agonists and AC activation by the agonist-free receptor. Similar differences were observed previously for beta(2)AR-G(salphaS) and beta(2)AR-G(salphaL). beta(1)AR-G(salphaS) and beta(2)AR-G(salphaS) were similarly efficient at activating AC, but beta(1)AR-G(salphaL) was similar to4-fold more efficient at activating AC than beta(2)AR-G(salphaL). Our data show that (i) the beta(1)AR and beta(2)AR are similarly efficient at stabilizing the ternary complex with G(salpha) splice variants, (ii) G(salphaL) confers constitutive activity to the beta(1)AR and beta(2)AR, and (iii) the beta(1)AR coupled to G(salphaL) is more efficient at activating AC than the beta(2)AR coupled to G(salphaL). These data help us understand some of the discrepancies regarding similarities and differences between the beta(1)AR and beta(2)AR. (C) 2002 Elsevier Science Inc. All rights reserved.