G-protein βγ dimers: Membrane targeting requires subunit coexpression and intact γ C-A-A-X domain

Attachment of heterotrimeric G-proteins to the inner face of the plasma membrane is fundamental to their role as signal transducers by allowing interaction with both receptors and effectors. Certain G-protein α subunits are anchored to the membrane by covalent myristoylation. The βγ complex is required for G-protein interaction with receptors and is independently membrane associated through an unknown mechanism. A series of carboxyl-terminal modifications including isoprenylation which may contribute to membrane attachment has been identified recently in G-protein γ subunits. Expression and membrane targeting of β and γ subunits were examined in COS cells. The expression of either subunit was found to require cotransfection with both β and γ cDNAs. Mutation of the carboxyl-terminal cysteine residue of γ shown to undergo isoprenylation and carboxymethyl-esterification preserved βγ expression but blocked isoprenylation and membrane attachment. These results implicate the carboxyl-terminal processing of G-protein γ subunits and β coexpression as necessary and sufficient for membrane targeting of the βγ complex.