trace amine-associated receptors 2, 3, 4, and similar receptors, member of the class A family of seven-transmembrane G protein-coupled receptors
TAAR2, TAAR3, and TAAR4 are among the 15 identified trace amine-associated receptor subtypes, which form a distinct subfamily within the class A G protein-coupled receptor family. Trace amines are endogenous amines of unknown function that have strong structural and metabolic similarity to classical monoamine neurotransmitters (serotonin, noradrenaline, adrenaline, dopamine, and histamine), which play critical roles in human and animal physiological activities such as cognition, consciousness, mood, motivation, perception, and autonomic responses. However, trace amines are found in the mammalian brain at very low concentrations compared to classical monoamines. Trace amines, including p-tyramine, beta-phenylethylamine, and tryptamine, are also thought to act as chemical messengers to exert their biological effects in vertebrates. All GPCRs have a common structural architecture comprising of seven-transmembrane (TM) alpha-helices interconnected by three extracellular and three intracellular loops. A general feature of GPCR signaling is agonist-induced conformational changes in the receptors, leading to activation of the heterotrimeric G proteins, which consist of the guanine nucleotide-binding G-alpha subunit and the dimeric G-beta-gamma subunits. The activated G proteins then bind to and activate numerous downstream effector proteins, which generate second messengers that mediate a broad range of cellular and physiological processes.