Protein involved in taste signal transduction. Human perceives five basic taste qualities: bitter, salty, sour, sweet, and umami, the taste of glutamate. Taste perception begins when a taste-eliciting molecule, or tastant, interacts with specialized receptors in the membrane of taste receptor cells. Taste responses to bitter, sweet, and umami compounds are initiated by G-protein-coupled receptors and transduced via G-protein signaling cascades. Salty and sour tastes are transduced by ion channels.

Receptors which transduce extracellular signals across the cell membrane. At the external side they receive a ligand (a photon in case of opsins), and at the cytosolic side they activate a guanine nucleotide-binding (G) protein. These receptors are hydrophobic proteins that cross the membrane seven times.

Protein which binds to, or responds to, a ligand with high specificity.

Protein which converts an input signal into an output signal of a different form.

A reference proteome is a set of protein sequences derived from a complete proteome which constitutes a defined standard for a particular user community. Reference proteomes are manually defined according to a number of criteria. They cover the proteomes of well- studied model organisms and other proteomes of interest for biomedical and biotechnological research. Reference proteomes have been selected to provide broad coverage of the tree of life, and constitute a representative cross-section of the taxonomic diversity to be found within UniProtKB.