Gβ5γ2 Is a Highly Selective Activator of Phospholipid-dependent Enzymes

In this study, Gβ specificity in the regulation of Gβγ-sensitive phosphoinositide 3-kinases (PI3Ks) and phospholipase Cβ (PLCβ) isozymes was examined. Recombinant mammalian Gβ 1–3 γ 2 complexes purified from Sf9 membranes stimulated PI3Kγ lipid kinase activity with similar potency (10–30 n m ) and efficacy, whereas transducin Gβγ was less potent. Functionally active Gβ 5 γ 2 dimers were purified from Sf9 cell membranes following coexpression of Gβ 5 and Gγ 2-His . This preparation as well as Gβ 1 γ 2-His supported pertussis toxin-mediated ADP-ribosylation of Gα i1 . Gβ 1 γ 2-His stimulated PI3Kγ lipid and protein kinase activities at nanomolar concentrations, whereas Gβ 5 γ 2-His had no effect. Accordingly, Gβ 1 γ 2-His , but not Gβ 5 γ 2-His , significantly stimulated the lipid kinase activity of PI3Kβ in the presence or absence of tyrosine-phosphorylated peptides derived from the p85-binding domain of the platelet derived-growth factor receptor. Conversely, both preparations were able to stimulate PLCβ 2 and PLCβ 1 . However, Gβ 1 γ 2-His , but not Gβ 5 γ 2-His , activated PLCβ 3 . Experimental evidence suggests that the mechanism of Gβ 5 -dependent effector selectivity may differ between PI3K and PLCβ. In conclusion, these data indicate that Gβ subunits are able to discriminate among effectors independently of Gα due to selective protein-protein interaction.