T1R1T1R3

T1R1T1R3 refers to the heterodimer formed by the type 1 taste receptor subunits T1R1 and T1R3, which together function as the mammalian umami taste receptor. It is a class C G protein-coupled receptor (GPCR) that detects savory amino acids, with L-glutamate being the primary ligand in humans and many other mammals.

The two subunits are encoded by the TAS1R1 and TAS1R3 genes. Each subunit has a large extracellular Venus flytrap domain responsible for ligand binding, followed by seven transmembrane helices characteristic of GPCRs. Dimerization of T1R1 with T1R3 is essential for proper surface expression and signaling of the receptor.

Activation of the T1R1T1R3 complex occurs in taste receptor cells of taste buds, particularly in the circumvallate, foliate, and fungiform papillae. Upon ligand binding, the receptor couples to the G protein gustducin, triggering a phospholipase Cβ2–IP3/DAG signaling cascade. This leads to an increase in intracellular calcium and the release of ATP as a neurotransmitter to gustatory neurons, conveying the umami taste signal to the brain.

Ligands for the receptor include L-glutamate and other amino acids, with taste perception enhanced by 5′-ribonucleotides such as inosine monophosphate (IMP) or guanosine monophosphate (GMP), which act as positive allosteric modulators. Evolutionarily, the T1R family is conserved across vertebrates, and genetic variation in TAS1R1 or TAS1R3 can influence individual sensitivity to umami.