T1R3

T1R3, or taste receptor type 1 member 3, is a subunit of the T1R family of taste receptors and is encoded by the TAS1R3 gene. It is a class C G protein-coupled receptor with a large extracellular venus flytrap domain and a seven-transmembrane region. T1R3 functions as part of heterodimers that detect sweet and umami stimuli.

In tasting, T1R3 pairs with T1R2 to form the sweet receptor (T1R2/T1R3) and with T1R1 to form the umami receptor (T1R1/T1R3). These receptors respond to a range of ligands: the sweet receptor is activated by sugars and many artificial sweeteners, while the umami receptor is activated by L-glutamate and certain nucleotides. Upon ligand binding, the receptor signals through heterotrimeric G proteins such as gustducin (Gαgust) and Gβγ, triggering the PLCβ2 pathway, IP3 production, and Ca2+ influx, ultimately leading to neurotransmitter release from taste cells and the perception of sweetness or savoriness. The signaling cascade often involves the TRPM5 ion channel, which contributes to the electrical responses of taste receptor cells.

T1R3 is expressed primarily in taste buds on the tongue, including various papillae. It is also found in extraoral tissues, such as enteroendocrine cells of the gut, pancreatic islets, and airway epithelia, where it participates in nutrient sensing and hormonal regulation. Genetic variation in TAS1R3 can influence sweet taste sensitivity and preference.

Overall, T1R3 is a central component of the mammalian chemosensory system for sweet and umami tastes, with additional roles in metabolic regulation that extend beyond the oral cavity.