T1R1

T1R1, also known as taste receptor type 1 member 1, is a G protein-coupled receptor that plays a key role in the perception of umami taste. It is encoded by the TAS1R1 gene and belongs to the class C taste receptor family. The protein is expressed in taste receptor cells of taste buds on the tongue and functions as part of a heterodimer with T1R3 to form the canonical umami receptor, T1R1/T1R3.

The receptor's structure features a large extracellular Venus flytrap domain typical of class C GPCRs, a cysteine-rich domain, and a seven-transmembrane region. Ligand binding to the Venus flytrap domain triggers conformational changes that activate associated G proteins, most notably gustducin (Gαgust), leading to a signaling cascade involving phospholipase Cβ2, inositol trisphosphate, and intracellular calcium release. This Ca2+ signal opens TRPM5 channels, resulting in depolarization of the taste cells and the release of ATP as a neurotransmitter to activate gustatory neurons.

Ligands and selectivity: the primary umami ligand is L-glutamate, with other amino acids contributing to the umami sensation. Inosine monophosphate (IMP) and guanosine monophosphate (GMP) can act as positive allosteric modulators, enhancing responses to amino acids.

Genetics and significance: TAS1R1 is part of the TAS1R gene family, which also includes TAS1R2 and TAS1R3. Genetic variation in TAS1R1 can influence individual sensitivity to umami. Research, including animal knockout studies, supports a central role for T1R1 in umami detection and related feeding behaviors.