Persistent membrane association of activated and depalmitoylated G protein a subunits (signal transductionythioesteraseylocalizationyimmunof luorescence)

Heterotrimeric signal-transducing G pro- teins are organized at the inner surface of the plasma mem- brane, where they are positioned to interact with membrane- spanning receptors and appropriate effectors. G proteins are activated when they bind GTP and inactivated when they hydrolyze the nucleotide to GDP. However, the topological fate of activated G protein a subunits is disputed. One model declares that depalmitoylation of a, which accompanies acti- vation by a receptor, promotes release of the protein into the cytoplasm. Our data suggest that activation of G protein a subunits causes them to concentrate in subdomains of the plasma membrane but not to be released from the membrane. Furthermore, a subunits remained bound to the membrane when they were activated with guanosine 5*-(3-O-thio)triphos- phate and depalmitoylated with an acyl protein thioesterase. Limitation of a subunits to the plasma membrane obviously restricts their mobility and may contribute to the efficiency and specificity of signaling.