olfactory receptors, member of the class A family of seven-transmembrane G protein-coupled receptors
Olfactory receptors (ORs) play a central role in olfaction, the sense of smell. ORs belong to the class A rhodopsin-like family of G protein-coupled receptors and constitute the largest multigene family in mammals of approximately 1,000 genes. More than 60% of human ORs are non-functional pseudogenes compared to only 20% in mouse. Each OR can recognize structurally similar odorants, and a single odorant can be detected by several ORs. Binding of an odorant to the olfactory receptor induces a conformational change that leads to the activation of the olfactory-specific G protein (Golf). The G protein (Golf and/or Gs) in turn stimulates adenylate cyclase to make cAMP. The cAMP opens cyclic nucleotide-gated ion channels, which allow the influx of calcium and sodium ions, resulting in depolarization of the olfactory receptor neuron and triggering an action potential which transmits this information to the brain. A consensus nomenclature system based on evolutionary divergence is used here to classify the olfactory receptor family. The nomenclature begins with the root name OR, followed by an integer representing a family, a letter denoting a subfamily, and an integer representing the individual gene within the subfamily.