Probing of the coupling site of the beta-adrenergic receptor. Competition between different forms of the guanyl nucleotide binding protein for interaction with the receptor.

The interaction of the beta-adrenergic receptor (R) with different forms of the regulatory protein (G) was studied. For this purpose, the reconstituted system formed from separate soluble preparations of R and G was employed (Citri, Y., and Schramm, M. (1980) Nature (Lond.) 287, 297-300). Soluble preparations of the native nonactive G, to which GDP is bound (GGDP), and the persistently active G, to which guanyl-5'-yl-imidophosphate (Gpp(NH)p) is bound GGPP(MH)P), were prepared. Reconstituted systems made of GGDP, GGPP(NH)P, and R were used to test whether each of the two forms of G can affect the other's interaction with R. GGPP(NH)P was found to compete with GGDP for the interaction with R. However, GGDP was unable to interfere with the interaction of R with GGPP(NH)P. Similar experiments were carried out with another persistently active G (GGTP gamma S). In sharp contrast to GGPP(NH)P, GGTP gamma S was found incapable of competing with GGDP for R. The above experiments suggest that GGDP and GGPP(NH)P interact with the same coupling site on R. However, the degree of recognition of G by R depends strongly on the guanyl nucleotide which is bound to G. The relative order of recognition being GGPP(NH)P greater than GGDP greater than GGTP gamma S approximately 0. These findings may also explain the known irreversible effects of GTP gamma S in the adenylate cyclase system.