T2RFamilien

The T2R family, also known as TAS2Rs in humans, comprises bitter taste receptor proteins that belong to the family of G protein-coupled receptors. They are predominantly expressed in type II taste receptor cells within taste buds on the tongue and in other oral epithelia, where they detect a wide range of bitter compounds, including plant alkaloids and microbial metabolites. The activity of these receptors contributes to the perception of bitterness and helps identify potentially toxic substances.

Structure and genes

Each T2R is a seven-transmembrane GPCR encoded by a single gene. The human genome contains roughly two dozen functional TAS2R genes, along with several pseudogenes; the exact count and repertoire vary among individuals and across species. The T2R gene family is highly diverse, reflecting adaptation to a broad spectrum of bitter ligands in different ecological niches. In non-human species, the number and diversity of TAS2R genes can be substantially greater.

Signaling and mechanism

Upon ligand binding, T2Rs activate heterotrimeric G proteins, typically gustducin (GNAT3), which stimulates phospholipase Cβ2 (PLCβ2). This triggers IP3-mediated Ca2+ release, opening of the TRPM5 channel, and depolarization of the taste receptor cell. The resulting signal is transmitted to gustatory nerves, in part through ATP release via CALHM1/3 channels.

Extraoral roles and variation

Beyond taste, T2Rs are expressed in various tissues, including the gut and upper airway epithelia, where they may participate in innate immune responses and modulate tissue physiology. Genetic variation in TAS2R genes, most notably TAS2R38, influences bitter taste sensitivity to compounds such as PTC and PROP and can correlate with dietary preferences and, in some contexts, susceptibility to certain infections or respiratory conditions.

Evolution and research

The T2R family shows rapid evolution and substantial species-specific diversification. Ongoing research aims to deorphanize receptors, map ligand repertoires, and understand their physiological roles and clinical implications.