Gγ13 colocalizes with gustducin in taste receptor cells and mediates IP₃ responses to bitter denatonium

Gustducin is a transducin-like G protein selectively expressed in taste receptor cells. The α subunit of gustducin (α-gustducin) is critical for transduction of responses to bitter or sweet compounds. We identified a G- protein γ subunit (Gγ13) that colocalized with α-gustducin in taste receptor cells. Of 19 α-gustducin/Gγ13-positive taste receptor cells profiled, all expressed the G protein β3 subunit (Gβ3); ~80% also expressed Gβ1. Gustducin heterotrimers (α-gustducin/Gβ1/Gγ13) were activated by taste cell membranes plus bitter denatonium. Antibodies against Gγ13 blocked the denatonium-induced increase of inositol trisphosphate (IP₃) in taste tissue. We conclude that gustducin heterotrimers transduce responses to bitter and sweet compounds via α-gustducin's regulation of phosphodiesterase (PDE) and Gβγ's activation of phospholipase C (PLC).