Regulation of signal transfer from beta1-adrenoceptor to adenylate cyclase by betagamma subunits in a reconstituted system

Abstract

The .beta..gamma. subunits of guanine nucleotide binding proteins from bovine brain and bovine rod outer segments have different structural and immunochemical properties. In spite of these structural differences, .beta..gamma. subunits from these sources have been found to be fully interchangeable in terms of their interaction with .alpha. subunits of pertussis-toxin-sensitive G proteins. In contrast, however, there are striking differences between these .beta..gamma. subunits with regard to their ability to deactivate fluoride-stimulated Gs. These profound differences were also observed when the interaction of the purified components of the adenylate cyclase system was studied after reconstitution into phospholipid vesicles. Addition of .beta..gamma. subunits purified from bovine brain to vesicles containing .beta.-receptor and Gs results in a biphasic effect on receptor-stimulated GTPase activity, whereas addition of transducin .beta..gamma. was virtually without any effect. Likewise, .beta..gamma. from bovine brain, but not transducin .beta..gamma., affected adenylate cyclase activity of a reconstituted system consisting of three purified components (R, Gs, C). Thus, the .alpha. subunit of Gs, but not the .alpha. subunits of pertussis-toxin-sensitive G proteins discriminate between structurally different .beta..gamma. subunits.