G-PROTEIN BETA-GAMMA-SUBUNITS - SIMPLIFIED PURIFICATION AND PROPERTIES OF NOVEL ISOFORMS

The beta and gamma subunits of heterotrimeric guanine nucleotide-bindi ng regulatory proteins (G proteins) form tightly associated complexes. To examine functional differences among the large number of possible combinations of unique beta and gamma subunits, we have synthesized an d characterized beta gamma complexes containing gamma(5) and gamma(7), two widely distributed gamma subunits. When either gamma(5) or gamma( 7) is expressed concurrently with beta 1 or beta(2) subunits in a bacu lovirus/Sf9 cell system, all four subunit complexes support pertussis toxin-catalyzed ADP-ribosylation of rG(i alpha 1) (where ''r'' indicat es recombinant), indicating formation of functional complexes. Each of the complexes was purified by subunit exchange chromatography, using the G203A mutant of rG(i alpha 1) as the immobilized ligand. The purif ied preparations were compared with other recombinant beta gamma subun its, including beta(1) gamma(1) and beta(1) gamma(2), for their abilit y to modulate type I and II adenylyl cyclase activities; stimulate pho sphoinositide-specific phospholipase C beta; support pertussis toxin-c atalyzed ADP-ribosylation of rG(i alpha 1) and G(o alpha); and inhibit steady-state GTP hydrolysis catalyzed by G(s alpha), G(o alpha), and myristoylated rG(i alpha 2) The results emphasize the unique propertie s of beta(1) gamma(1). The properties of the complexes containing gamm a(5) or gamma(7) were similar to each other and to those of beta(1) ga mma(2).