Ga subunit dissociation

Heterotrimeric G proteins are composed of a, P, and y polypeptide chains. Usually, the a and y chains are anchored to the inner leaflet of the plasma membrane by Upid anchors that consist of a fatty acid that is linked to a cysteine side chain by a thioester bond. As shown schematically in Fig. 6-13, the binding of a signaling ligand leads to exchange of a molecule of GDP for a molecule of GTP, bound to the Ga subunit. Concurrently, the Ga subunit dissociates from the GpGy subunit. This allows both the Ga and the GPGy subunits to interact with other signaling molecules. 

---