GUST27 and closely related G-protein-coupled receptors are localized in taste buds together with Gi-protein α-subunit

Gustatory, like olfactory signalling is probably mediated by seven-transmembrane receptors and coupling GTP-binding proteins (G proteins). We investigated the expression of a subset of these receptors and the Gi protein α-subunit by using their specific antibodies. Based on our previous finding that the mRNA for GUST27, one of these receptors, is expressed in rat lingual epithelia, we first prepared an antibody to the synthetic nonapeptide, H·Ser-Tyr-Ser-Gln-Ile-Ala-Ser-Ser-Leu·OH which corresponds to the third intracellular domain of GUST27 and also to those of a subset of related receptors whose occurrence can be predicted by PCR. Immunohistochemical studies with rat circumvallate papillae indicated that the anti-GUST27 antibody reacted with many of the taste buds examined, with strong signals appearing in particular taste cells. We then carried out a similar immunohistochemical experiment with an antibody to the Gi protein α-subunit and found that this subunit is also expressed in taste buds as demonstrated in the case of gustducin and transducin. Taken together, these results strongly suggest that GUST27 and closely related receptors, as well as Giα proteins, are involved in intracellular taste signal transduction.