Guanine nucleotide-binding protein G(t) subunit alpha-3 (Gnat3)

Transduction by this alpha subunit involves coupling of specific cell-surface receptors with a cGMP-phosphodiesterase; Activation of phosphodiesterase lowers intracellular levels of cAMP and cGMP which may start a cyclic nucleotide-suppressible cation channel resulting in influx of calcium, ultimately resulting in release of neurotransmitter. Indeed, denatonium and strychnine induce transient decrease in cAMP and cGMP in taste tissue, whereas this decrease is inhibited by GNAT3 antibody.

Gustducin heterotrimer transduces reaction to bitter and sweet compounds via regulation of phosphodiesterase for alpha subunit, in addition to via activation of phospholipase C for beta and gamma subunits, with ultimate increase inositol trisphosphate and increase of intracellular Calcium. GNAT3 can functionally couple to taste receptors to transmit intracellular signal: receptor heterodimer TAS1R2/TAS1R3 senses sweetness and TAS1R1/TAS1R3 transduces umami flavor, whereas the T2R family GPCRs behave as bitter sensors.