TAS1R1TAS1R3

TAS1R1TAS1R3 refers to the heterodimeric type 1 taste receptor formed by the TAS1R1 and TAS1R3 subunits. It constitutes the vertebrate umami taste receptor and is part of the class C GPCR family. The receptor is expressed in taste receptor cells of the tongue and palate and requires the assembly of both subunits for full activity.

Structure and function: Each subunit contributes to a large extracellular Venus flytrap domain and a seven-transmembrane domain; dimerization of TAS1R1 and TAS1R3 is essential for function. Ligand binding primarily involves the Venus flytrap domain, and signaling proceeds through the receptor’s transmembrane region to intracellular pathways.

Ligands and signaling: The primary ligand is L-glutamate, the amino acid responsible for umami flavor. In humans, the response is enhanced by 5′-ribonucleotides such as inosine monophosphate (IMP) and guanosine monophosphate (GMP), which act as synergists. Upon activation, the receptor couples to G proteins, typically gustducin (GNAT3), triggering phospholipase Cβ2 (PLCβ2) activity, increasing IP3 and intracellular Ca2+, and opening the TRPM5 channel to depolarize the cell and promote neurotransmitter release to gustatory nerve fibers.

Expression and role: TAS1R1/TAS1R3 is primarily associated with the perception of umami taste, enabling detection of amino acids in dietary proteins. It is conserved across mammals and other vertebrates. In addition to oral tissues, components of the TAS1R family have been reported in some extraoral tissues, but the functional significance there remains under study.

Genetics and research: Genetic variation in TAS1R1 can influence umami sensitivity among individuals. The TAS1R1/TAS1R3 receptor is distinct from the sweet receptor TAS1R2/TAS1R3; both are class C GPCR heterodimers with different ligand profiles.