Family A receptors make up the largest group of GPCRs, are involved in almost every aspect of human physiology, and are activated by a diverse variety of ligands (e.g.-. hormones, neurotransmitters, light).
Family B GPCRs are peptide binding receptors comprised of two sub-families: the secretin-like receptors that primarily bind peptide hormones and adhesion receptors that are characterized by large extracellular domains.
Family C GPCRs function as obligate dimers with large extracellular domains, termed the Venus flytrap (VFT). Unlike other classes of GPCRs orthosteric ligand binding occurs at the VFTs which are distal to the transmembrane region.
G protein-coupled inward rectifying potassium channels (GIRKs) are downstream effectors of Gβγ signaling. Activation of GIRK results in an opening of the channel to allow efflux of K+ ions.
G protein responsive phosphodiesterase (PDE) is found in the visual system. Activation of PDE6 by G protein transducin results in the degradation of cGMP.
Resistence to Inhibitors of Cholinesterase-8 (Ric-8) proteins are necesary and specific chaperones for the proper biosynthesis of the G alpha subunit of the G protein heterotrimer.