TAS1R2

Taste receptor type 1 member 2 is a is_associated_with::protein that in humans is encoded by the TAS1R2 is_associated_with::gene.

Structure
The protein encoded by the TAS1R2 gene is a is_associated_with::G protein-coupled receptor with seven trans-membrane domains and is a component of the heterodimeric amino acid taste receptor T1R2+3. This receptor is formed as a dimer of the TAS1R2 and is_associated_with::TAS1R3 proteins. Moreover, the TAS1R2 protein is not functional without formation of the 2+3 heterodimer. Another interesting quality of the TAS1R2 and is_associated_with::TAS1R1 genes is their spontaneous activity in the absence of the extracellular domains and binding ligands. This may mean that the extracellular domain regulates function of the receptor by preventing spontaneous action as well as binding to activating ligands such as is_associated_with::sucrose.

Ligands
The TAS1R2+3 receptor has been shown to respond to natural sugars is_associated_with::sucrose and is_associated_with::fructose, and to the artificial sweetners is_associated_with::saccharin, is_associated_with::acesulfame potassium, is_associated_with::dulcin, and guanidinoacetic acid. Research initially suggested that rat receptors did not respond to many other natural and artificial sugars, such as is_associated_with::glucose and is_associated_with::aspartame, leading to the conclusion that there must be more than one type of sweet taste receptor. Contradictory evidence, however, suggested that cells expressing the human TAS1R2+3 receptor showed sensitivity to both is_associated_with::aspartame and is_associated_with::glucose but cells expressing the rat TAS1R2+3 receptor were only slightly activated by is_associated_with::glucose and showed no is_associated_with::aspartame activation. These results are inconclusive about the existence of another sweet taste receptor, but show that the TAS1R2+3 receptors are responsible for a wide variety of different sweet tastes.

Signal transduction
TAS1R2 and is_associated_with::TAS1R1 receptors have been shown to bind to is_associated_with::G proteins, most often the is_associated_with::gustducin Gα subunit, although a gusducin knock-out has shown small residual activity. TAS1R2 and is_associated_with::TAS1R1 have also been shown to activate Gαo and Gαi protein subunits. This suggests that TAS1R1 and TAS1R2 are is_associated_with::G protein-coupled receptors that inhibit is_associated_with::adenylyl cyclases to decrease is_associated_with::cyclic guanosine monophosphate (cGMP) levels in is_associated_with::taste receptors. Research done by creating knock-outs of common channels activated by sensory G-protein is_associated_with::second messenger systems has also shown a connection between sweet taste perception and the is_associated_with::phosphatidylinositol (PIP2) pathway. The nonselecive cation is_associated_with::Transient Receptor Potential channel TRPM5 has been shown to correlate with both umami and sweet taste. Also, the is_associated_with::phospholipase PLCβ2 was shown to similarly correlate with umami and sweet taste. This suggests that activation of the G-protein pathway and subsequent activation of PLC β2 and the TRPM5 channel in these taste cells functions to activate the cell.

Location and innervation
TAS1R2+3 expressing cells are found in is_associated_with::circumvallate papillae and is_associated_with::foliate papillae near the back of the is_associated_with::tongue and is_associated_with::palate taste receptor cells in the roof of the mouth. These cells are shown to is_associated_with::synapse upon the is_associated_with::chorda tympani and is_associated_with::glossopharyngeal nerves to send their signals to the brain. TAS1R and TAS2R (bitter) channels are not expressed together in is_associated_with::taste buds.