A C-TERMINAL MUTANT OF THE G-PROTEIN BETA-SUBUNIT DEFICIENT IN THE ACTIVATION OF PHOSPHOLIPASE C-BETA

The molecular mechanism by which the G protein py complex modulates mu ltiple mammalian effector pathways is unknown. Homolog-scanning mutage nesis of the G protein beta subunit was employed to identify residues critical for the activation of phospholipase C-beta(2) (PLC-beta(2)). A series of chimeras was made by introducing small segments of the Dic tyostelium beta subunit into a background of mammalian beta(1) and tes ted in COS cell cotransfection assays for their ability ito activate P LC-beta(2), and assemble with mammalian gamma(2). A chimera that conta ined four Dictyostelium beta substitutions within the C-terminal 14 re sidues was unable to activate PLC beta(2), when cotransfected with gam ma, despite its demonstrable expression in a gamma-dependent manner. C otransfection of the mutant blocked m2 muscarinic receptor activation of PLC by a pertussis toxin-sensitive pathway. This C-terminal mutant retained the ability, however, to stimulate the mitogen-activated prot ein kinase pathway. These results imply that activation of different b eta gamma-responsive effectors is mediated by distinct domains.