T2RreCEPTorer

T2R receptorer, or type 2 taste receptors, are a family of G protein-coupled receptors that detect bitter compounds. In humans they are encoded by the TAS2R gene family and are expressed mainly in the taste receptor cells of the circumvallate, foliate, and fungiform papillae on the tongue. The receptors are seven-transmembrane GPCRs, and each receptor can be activated by a range of bitter ligands, contributing to the broad perception of bitterness.

The human genome contains roughly 25 functional TAS2R genes and a number of nonfunctional pseudogenes, with substantial variation between individuals in which receptors are present. This genetic diversity helps explain differences in bitter taste sensitivity, including responsiveness to compounds such as PROP/PTC.

Within taste buds, T2Rs are expressed in type II taste cells. Upon ligand binding, they couple to the G protein gustducin (GNAT3), triggering a signaling cascade via phospholipase Cβ2 (PLCβ2), release of Ca2+ from intracellular stores, activation of the cation channel TRPM5, and subsequent neurotransmitter release to gustatory nerve fibers.

In addition to the tongue, T2Rs have been reported in various extragustatory tissues, including airway and gastrointestinal epithelia, where they are thought to participate in chemosensation and may play roles in innate defense, mucosal signaling, or the regulation of local motility and immune responses. Evolutionarily, T2R genes are highly diverse and rapidly evolving, reflecting adaptation to diverse bitter compounds across species.