Activating Mutations of the Luteinizing Hormone Receptor Gene in Familial Testotoxicosis

Heptahelical, membrane-spanning cell-surface receptors utilize he-terotrimeric guanine nucleotide binding proteins (G proteins) to transmit extracellular signals to cellular effectors (1–4). Diverse stimuli, including photons, hormones, neurotransmitters, odorants, proteases, and ions, trigger conformational changes in the receptor transmembrane helices that are relayed to the cytoplasmic surface, leading to G protein activation (Fig. 20.1A).