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Chemical Senses 2005 30(Supplement 1):i16; doi:10.1093/chemse/bjh090
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Chemical Senses Vol. 30 No. suppl 1 © Oxford University Press 2005; all rights reserved

Functional Interaction between TAS2R Receptors and G-Protein {alpha} Subunits Expressed in Taste Receptor Cells

Takashi Ueda, Shinya Ugawa and Shoichi Shimada

Department of Molecular Morphology, Graduate School of Medical Sciences, Nagoya City University, 1 Kawasumi, Mizuho-cho, Mizuho-ku, Nagoya, Aichi, Japan

Correspondence to be sent to: Takashi Ueda, e-mail: tueda{at}med.nagoya-cu.ac.jp

Key words: bitter taste, calcium imaging, T2R receptor, G{alpha}, chimera, G protein {alpha}, subunit, gustducin


   Introduction
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 Introduction
Acknowledgements
 References
 
Bitter taste perception is a conserved chemical sense against the ingestion of poisonous substances in mammals. It could be mediated by G protein-coupled receptors that need the appropriate G proteins to transduce the signals. TAS2R receptors and a G protein {alpha} subunit, {alpha}–gustducin are believed to be key molecules for its perception (Margolskee, 2002Go; Montmayeur and Matsunami, 2002Go), but little is known about the molecular basis for its interaction. In the present study, we used a heterologous expression system to determine a specific domain of gustducin necessary to TAS2R coupling. Two chimeric G{alpha}16 proteins harboring 37 and 44 gustducin-specific sequences at their C termini (G16/gust37 and G16/gust44) responded to different TAS2R receptors with known ligands in dose-dependent manner, but G16, G16/gust 23, G16/gust11 and G16/gust5 did not exhibit any responses (Figure 1). The former two chimeras contained a predicted ß6 sheet, an {alpha}5 helix and an extreme C-terminus of gustducin, and all the domains were indispensable to the expression of TAS2R activity. Taste receptor cells express a variety of G{alpha}i subunit, but these functions are not well known. We next expressed G16 protein chimeras with the corresponding domain from other G{alpha}i proteins, cone-transducin (G{alpha}t2), G{alpha}i2 and G{alpha}z (G16/t2, G16/i2 and G16/z). As a result, G16/t2 and G16/i2 produced specific responses of TAS2Rs, but G16/z did not (Figure 1). Since G{alpha}t2 and G{alpha}i2 are expressed in taste receptors cells, these may be also involved in bitter taste perception via TAS2R receptors. The present G{alpha}16-based chimeras could be powerful tools to analyze the functions of many orphan G protein-coupled taste receptors.



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  		Figure 1 Schematic illustrations of chimeric G16/gust proteins with different lengths of C terminal amino acids found in gustducin and G16-based chimeras with C-terminal 44 amino acids of G{alpha}t2, G{alpha}i2 or G{alpha}z and their abilities to couple to TAS2Rs indicated. ‘+’ specifically responded to the ligand in dose dependent manner; ‘–’ did not exhibit any responses even at 1000-fold higher ligand concentration. Putative secondary structure on the basis of the G{alpha}t1 crystal structure is indicated by the bars above the G protein sequences. eCT, extreme C terminus.

 

   Acknowledgements
Top
 Introduction
 Acknowledgements
References
 
This work was supported by research grants from the Japan Society for the Promotion of Science.


   References
Top
 Introduction
 Acknowledgements
 References
 
Margolskee, R.F. (2002) Molecular mechanisms of bitter and sweet taste transduction. J. Biol. Chem., 277, 1–4.[Free Full Text]

Montmayeur, J.-P. and Matsunami, H. (2002) Receptors for bitter and sweet taste. Curr. Opin. Neurobiol., 12, 366–371.[CrossRef][Web of Science][Medline]


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This Article
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