Functional interaction between T2R taste receptors and G-protein alpha subunits expressed in taste receptor cells.
Bitter taste perception is a conserved chemical sense against the ingestion of poisonous substances in mammals. A multigene family of G-protein-coupled receptors, T2R (so-called TAS2R or TRB) receptors and a G-protein alpha subunit (Galpha), gustducin, are believed to be key molecules for its perception, but little is known about the molecular basis for its interaction. Here, we use a heterologous expression system to determine a specific domain of gustducin necessary for T2R coupling. Two chimeric Galpha16 proteins harboring 37 and 44 gustducin-specific sequences at their C termini (G16/gust37 and G16/gust44) responded to different T2R receptors with known ligands, but G16/gust 23, G16/gust11, and G16/gust5 did not. The former two chimeras contained a predicted beta6 sheet, an alpha5 helix, and an extreme C terminus of gustducin, and all the domains were indispensable to the expression of T2R activity. We also expressed G16 protein chimeras with the corresponding domain from other Galpha(i) proteins, cone-transducin (Galpha(t2)), Galpha(i2), and Galpha(z) (G16/t2, G16/i2, and G16/z). As a result, G16/t2 and G16/i2 produced specific responses of T2Rs, but G16/z did not. Because Galpha(t2) and Galpha(i2) are expressed in the taste receptor cells, these G-protein alpha(i) subunits may also be involved in bitter taste perception via T2R receptors. The present Galpha16-based chimeras could be useful tools to analyze the functions of many orphan G-protein-coupled taste receptors.
Ueda
Takashi
T
Department of Molecular Morphology, Graduate School of Medical Sciences, Nagoya City University, Nagoya 467-8601, Japan. tueda@med.nagoya-cu.ac.jp
Ugawa
Shinya
S
Yamamura
Hisao
H
Imaizumi
Yuji
Y
Shimada
Shoichi
S
D000595:Amino Acid Sequence; D000818:Animals; D002118:Calcium / Q000378:metabolism; D002460:Cell Line; D018922:HL-60 Cells; D020962:Heterotrimeric GTP-Binding Proteins / Q000737:chemistry / Q000378:metabolism*; D006801:Humans; D008024:Ligands; D008969:Molecular Sequence Data; D017434:Protein Structure, Tertiary; D051381:Rats; D011956:Receptors, Cell Surface / Q000378:metabolism*; D043562:Receptors, G-Protein-Coupled; D011993:Recombinant Fusion Proteins / Q000737:chemistry / Q000378:metabolism; D011984:Sensory Receptor Cells / Q000378:metabolism; D016415:Sequence Alignment; D015293:Transducin / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*; D000098706:Taste Receptors, Type 2
D008024:Ligands; D011956:Receptors, Cell Surface; D043562:Receptors, G-Protein-Coupled; D011993:Recombinant Fusion Proteins; D000098706:Taste Receptors, Type 2; C075192:gustducin; D020962:Heterotrimeric GTP-Binding Proteins; D015293:Transducin; D002118:Calcium