Selectivity in Signal Transduction Determined by γ Subunits of Heterotrimeric G Proteins

Abstract

Various heterotrimeric guanine nucleotide-binding proteins have been identified on the basis of the individual subtypes of their α subunits. The βγ complexes, composed of β and γ subunits, remain tightly associated under physiological conditions and have been assumed to constitute a common pool shared among various guanosine triphosphate (GTP)-binding (G) protein heterotrimers. Particular α and β subunit subtypes participate in the signal transduction processes between somatostatin or muscarinic receptors and the voltage-sensitive L-type calcium channel in rat pituitary GH 3 cells. Among γ subunits the γ 3 subtype was found to be required for coupling of the somatostatin receptor to voltage-sensitive calcium channels, whereas the γ 4 subtype was found to be required for coupling of the muscarinic receptor to those channels.