A point mutation in Gαo and Gαi1 blocks interaction with regulator of G protein signaling proteins

Regulator of G protein-signaling (RGS) proteins accelerate GTP hydrolysis by G alpha subunits and are thought to be responsible for rapid deactivation of enzymes and ion channels controlled by G proteins, We wanted to identify and characterize G(i)-family alpha subunits that were insensitive to RGS action. Based on a glycine to serine mutation in the yeast G alpha subunit Gpa1(sst) that prevents deactivation by Sst2 (DiBello, P, R,, Garrison, T, R,, Apanovitch, D, M., Hoffman, G,, Shuey, D, J,, Mason, R,, Cockett, M. I., and Dohlman, II, G, (1998) J. Biol Chem. 273, 5780-5784), site-directed mutagenesis of alpha(o) and alpha(i1) was done. G184S alpha(o) and G183S alpha(i1) show kinetics of GDP release and GTP hydrolysis similar to wild type. In contrast, GTP hydrolysis by the G --> S mutant proteins is not stimulated by RGS4 or by a truncated RGS7, Quantitative flow cytometry binding studies show IC50 values of 30 and 96 nM, respectively, for aluminum fluoride-activated wild type alpha(o) and alpha(i1) to compete with fluorescein isothiocyanate-alpha(o) binding to glutathione S-transferase-RGS4, The G --> S mutant proteins showed a greater than 30-100-fold lower affinity for RGS4. Thus, we have defined the mechanism of a point mutation in alpha(o) and alpha(i1) that prevents RGS binding and GTPase activating activity, These mutant subunits should be useful in biochemical or expression studies to evaluate the role of endogenous RGS proteins in G(i) function.