G beta(5)gamma(2) is a highly selective activator of phospholipid-dependent enzymes

In this study, G beta specificity in the regulation of G beta gamma-sensiti ve phosphoinositide 3-kinases (PI3Ks) and phospholipase C beta (PLC beta) i sozymes was examined. Recombinant mammalian G beta(1-3)gamma(2) complexes p urified from Sf9 membranes stimulated PI3K gamma lipid kinase activity with similar potency (10-30 nM) and efficacy, whereas transducin G beta gamma w as less potent. Functionally active G beta(5)gamma(2) dimers were purified from Sf9 cell membranes following coexpression of G beta(5) and G gamma(2-H is). This preparation as well as G beta(1)gamma(2-His) supported pertussis toxin-mediated ADP-ribosylation of G alpha(i1) G beta(1)gamma(2-His) Stimul ated PI3K gamma lipid and protein kinase activities at nanomolar concentrat ions, whereas G beta(5)gamma(2-His) had no effect. Accordingly, G beta(1)ga mma(2-His), but not G beta(5)gamma(2-His), significantly stimulated the lip id kinase activity of PI3K beta in the presence or absence of tyrosine-phos phorylated peptides derived from the p85-binding domain of the platelet der ived-growth factor receptor. Conversely, both preparations were able to sti mulate PLC beta(2) and PLC beta(1). However, G beta(1)gamma(2-His) but not G beta(5)gamma(2-His), activated PLC beta(3). Experimental evidence suggest s that the mechanism of G beta(5)-dependent effector selectivity may differ between PI3K and PLC beta. In conclusion, these data indicate that G beta subunits are able to discriminate among effecters independently of G alpha due to selective protein-protein interaction.