Sci. STKE, 19 March 2002
Taste Perception A Savory Story
Specific G protein-coupled receptors (GPCRs) are activated during the sensation of light, smell, and taste. Nelson et al. used a transfected cell assay to show that the heterodimeric GPCR, comprised of TL1R1 and TL1R3, is a taste receptor activated by L-amino acids, but not sweet D-amino acids. Furthermore, this TL1R1-TL1R3 dimer also exhibited three properties consistent with its being involved in the detection of the taste of umami. Namely, monosodium glutamate (MSG) and the glutamate receptor agonist L-AP4 activate TL1R1-TL1R3, and its responsiveness is potentiated by purine nucleotides. Umami is the taste associated with foods containing MSG, such as Chinese foods. The TL1R3 GPCR is also part of a heterodimeric GPCR that responds to sweet substances. Thus, changing one subunit of the GPCR dimer confers completely different ligand specificity. In mice, the Sac gene encodes the TL1R3 receptor and "nontaster" Sac mice have a mutation in TL1R3 and do not respond to sweet taste, however, they respond normally to amino acids. One proposal was that the mutation in nontaster TL1R3 prevented the assembly of the sweet receptor dimer without affecting the amino acid receptor dimer. However, Nelson et al. showed that nontaster TL1R3 coprecipitated with TL1R1 and TL1R2, yet sweet substances did not activate the nontaster-containing receptor dimer. Mice and humans respond differently to various taste substances, and these differences can be explained by differences in the primary sequences of the TL1 receptors, because substituting the TL1 receptors from mouse or human in the transfected cell assay produced altered sensitivities to different taste stimuli.
G. Nelson, J. Chandrashekar, M. A. Hoon, L. Feng, G. Zhao, N. J. P. Ryba, C. S. Zuker, An amino-acid taste receptor. Nature 416, 199-202 (2002). [Online Journal]
Citation: A Savory Story. Sci. STKE 2002, tw109 (2002).
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