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 alpha subunit of gustducin (alpha-gustducin) is critical for transduction of responses to bitter or sweet compounds. We identified a G-protein gamma subunit (G gamma 13) that colocalized with alpha-gustducin in taste receptor cells. Of 19 alpha-gustducin/Gy13-positive taste receptor cells profiled, all expressed the G protein beta 3 subunit (G beta 3); similar to 80% also expressed G beta 1. Gustducin heterotrimers (alpha-gustducin/G beta 1/G gamma 13) were activated by taste cell membranes plus bitter denatonium. Antibodies against G gamma 13 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 alpha-gustducin's regulation of phosphodiesterase (PDE) and G beta gamma's activation of phospholipase C (PLC).