| Co-Investigator(Kenkyū-buntansha) |
UEDA Takashi Nagoya City University, Graduate School of Medical Sciences, Research Associate, 大学院・医学研究科, 助手 (90244540)
SHIMADA Shoichi Nagoya City University, Graduate School of Medical Sciences, Professor, 大学院・医学研究科, 教授 (20216063)
FUJIMORI Osamu Nagoya City University, Graduate School of Medical Sciences, Associate Professor, 大学院・医学研究科, 助教授 (30128350)
UGAWA Shinya Nagoya City University, Graduate School of Medical Sciences, Assistant Professor, 大学院・医学研究科, 講師 (20326135)
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| Research Abstract |
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 a subunit (Gα), gustducin, are believed to be key molecules for its perception, but little is known about the molecular basis for its interaction. We have used a heterologous expression system to determine a specific domain of gustducin necessary for T2R coupling. Two chimeric Gα16 proteins harboring 37 and 44 guatducin-specific sequences at their C termini (G16/gust37 and G16/gust44) responded to different T2R receptors with known ligands, but G16/gust23, G16/gust11 and G16/gust5 did not. The former two chimeras contained a predicted β6 sheet, an α5 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 G_i proteins, cone-transducin (Gαt2), Gαi2, and Gαz (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 Gαt2 and Gαi2 are expressed in the taste receptor cells, these G-protein αi subunits may also be involved in bitter taste perception via T2R receptors. We have also found the tissue expressions and coding single -nucleotide polymorphisms (cSNPs) in human T2R genes (hT2R3, hT2R4, and hT2R5) on chromosome 7q31. We identified six cSNPs within the T2R receptor genes. The hT2R4 and hT2R5 contained four and on cSNPs that cause missense mutations, respectively, while hT2R3 included one silent nucleotide mutation. However, we could not find any nonsense mutations that resulted in a frame shift or a premature stop codon within the open reading flames.
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