Primary structure and cell-type specific expression of a gustatory G protein-coupled receptor related to olfactory receptors

We have reported on the partial structures of a multigene family encoding GTP-binding protein (G protein)-coupled, seven-transmembrane receptors expressed in the tongue (Abe, K., Kusakabe, Y., Tanemura, K., Emori, Y., and Arai, S. (1993) FEBS Lett. 316, 253-256). Here we describe a full-length cDNA clone encoding a tongue cell-type specific receptor. The encoded protein consists of 312 amino acid residues. In overall structure, the protein is similar to known G protein-coupled, seven-transmembrane receptors such as an olfactory receptor (56% identity) but is significantly different in part, particularly in NH₂-terminal extracellular and COOH-terminal cytoplasmic domain structures. Northern analysis showed that the mRNA for this protein is expressed only in the epithelium of the tongue, not in other organs. In situ hybridization experiments clearly indicated that the mRNA is expressed exclusively on the tongue apical surface, not on the reverse side of the tongue nor in its muscle layer. Expression was also detected in the taste buds and surrounding cellular tissues of the fungiform and circumvallate papillae. It is suggested that this gustatory receptor structurally related to olfactory receptors may be a candidate for a taste receptor.