The G‐protein coupling properties of the human sweet and amino acid taste receptors

The human T1R taste receptors are family C G‐protein‐coupled receptors (GPCRs) that act as heterodimers to mediate sweet (hT1R2 + hT1R3) and umami (hT1R1 + hT1R3) taste modalities. Each T1R has a large extracellular ligand‐binding domain linked to a seven transmembrane‐spanning core domain (7TMD). We demonstrate that the 7TMDs of hT1R1 and hT1R2 display robust ligand‐independent constitutive activity, efficiently catalyzing the exchange of GDP for GTP on Gα subunits. In contrast, relative to the 7TMDs of hT1R1 and hT1R2, the 7TMD of hT1R3 couples poorly to G‐proteins, suggesting that in vivo signaling may proceed primarily through hT1R1 and hT1R2. In addition, we provide direct evidence that the hT1Rs selectively signal through Gαi/o pathways, coupling to multiple Gαi/o subunits as well as the taste cell specific Gβ1γ13 dimer. © 2007 Wiley Periodicals, Inc. Develop Neurobiol, 2007.