T2R

T2R refers to the taste receptor type 2 family, a group of G protein-coupled receptors that detect bitter compounds. These receptors are primarily expressed in type II taste receptor cells within taste buds on the tongue and other parts of the oral cavity, where they contribute to the sensation of bitterness and help animals avoid potentially toxic substances. The T2R family is encoded by the TAS2R gene family, which consists of multiple genes. In humans, the TAS2R complement includes many genes, most of which are functional, though some pseudogenes exist, and the exact roster varies among individuals and species.

Biochemically, T2Rs are seven-transmembrane GPCRs. Upon binding a bitter ligand, they activate a G protein signaling cascade that involves gustducin, phospholipase C β2 (PLCβ2), inositol triphosphate (IP3), and an increase in intracellular calcium. This calcium signal opens the TRPM5 channel, leading to depolarization of the taste cell and the release of neurotransmitters to afferent gustatory nerves, ultimately producing a bitter taste perception. Many T2Rs are broadly tuned and can respond to a range of structurally diverse bitter compounds, contributing to a combinatorial code for bitterness.

Genetic variation in TAS2R genes underpins substantial individual differences in bitter taste sensitivity. For example, variations in specific TAS2R genes influence how strongly people perceive certain bitter substances such as 6-n-propylthiouracil (PROP). Beyond taste, T2Rs are also found in extraoral tissues, including the airway and gastrointestinal tract, where they may participate in innate defense and chemosensation.

Evolutionarily, the T2R gene family is widespread among vertebrates, showing species-specific expansion and variation that reflect ecological and dietary differences.