G protein βγ subunits. Simplified purification and properties of novel isoforms

The β and γ subunits of heterotrimeric guanine nucleotide-binding regulatory proteins (G proteins) form tightly associated complexes. To examine functional differences among the large number of possible combinations of unique β and γ subunits, we have synthesized and characterized βγ complexes containing γ₅ and γ₇, two widely distributed γ subunits. When either γ₅ or γ₇ is expressed concurrently with β₁ or β₂ subunits in a baculovirus/Sf9 cell system, all four subunit complexes support pertussis toxin-catalyzed ADP-ribosylation of rG(iα1) (where 'r' indicates recombinant), indicating formation of functional complexes. Each of the complexes was purified by subunit exchange chromatography, using the G203A mutant of rG(iα1) as the immobilized ligand. The purified preparations were compared with other recombinant βγ subunits, including β₁γ₁ and β₁γ₂, for their ability to modulate type I and II adenylyl cyclase activities; stimulate phosphoinositide-specific phospholipase Cβ; support pertussis toxin-catalyzed ADP-ribosylation of rG(iα1) and G(oα); and inhibit steady-state GTP hydrolysis catalyzed by G(sα), G(oα), and myristoylated rG(iα2). The results emphasize the unique properties of β₁γ₁. The properties of the complexes containing γ₅ or γ₇ were similar to each other and to those of β₁γ₂.