T1R2T1R3

T1R2T1R3 refers to the heterodimer formed by the two taste receptor type 1 subunits, T1R2 and T1R3. This receptor pair is the primary sweet receptor in vertebrates and is part of the class C G protein-coupled receptor family. The heterodimer functions as a single receptor unit, with T1R2 and T1R3 contributing to ligand binding and signal transduction; T1R2 alone is generally nonfunctional for sweet sensing.

Structure and mechanism are characteristic of class C GPCRs. Both subunits possess large extracellular ligand-binding domains, including Venus flytrap–like modules, that come together to form the binding pocket for sweet compounds. T1R2T1R3 assembles in the plasma membrane of taste receptor cells within the taste buds, enabling detection of a wide range of sweetener molecules.

Activation of the receptor initiates a canonical taste signaling pathway. G proteins, often gustducin (Gαgust) or related subunits, are activated, leading to phospholipase Cβ2 stimulation, production of IP3, and release of Ca2+ from internal stores. The rise in intracellular calcium opens the TRPM5 channel, causing cell depolarization and the release of ATP as a neurotransmitter to gustatory nerve fibers, which ultimately conveys the sensation of sweetness to the brain.

Ligands detected by T1R2T1R3 include natural sugars such as glucose, sucrose, and fructose, as well as a variety of artificial sweeteners like aspartame, saccharin, and acesulfame potassium. The receptor exhibits varying sensitivities to different sweeteners and contributes to individual differences in sweet taste perception.

In humans and many other mammals, TAS1R2 and TAS1R3 encode the subunits, and genetic variation can influence sweetness sensitivity. The receptor is also expressed in some extraoral tissues, suggesting roles beyond taste perception.

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