Date Published: August 21, 2009
Publisher: Public Library of Science
Author(s): Noriatsu Shigemura, Shinya Shirosaki, Keisuke Sanematsu, Ryusuke Yoshida, Yuzo Ninomiya, Hiroaki Matsunami. http://doi.org/10.1371/journal.pone.0006717
Abstract: Umami taste (corresponds to savory in English) is elicited by L-glutamate, typically as its Na salt (monosodium glutamate: MSG), and is one of five basic taste qualities that plays a key role in intake of amino acids. A particular property of umami is the synergistic potentiation of glutamate by purine nucleotide monophosphates (IMP, GMP). A heterodimer of a G protein coupled receptor, TAS1R1 and TAS1R3, is proposed to function as its receptor. However, little is known about genetic variation of TAS1R1 and TAS1R3 and its potential links with individual differences in umami sensitivity. Here we investigated the association between recognition thresholds for umami substances and genetic variations in human TAS1R1 and TAS1R3, and the functions of TAS1R1/TAS1R3 variants using a heterologous expression system. Our study demonstrated that the TAS1R1-372T creates a more sensitive umami receptor than -372A, while TAS1R3-757C creates a less sensitive one than -757R for MSG and MSG plus IMP, and showed a strong correlation between the recognition thresholds and in vitro dose – response relationships. These results in human studies support the propositions that a TAS1R1/TAS1R3 heterodimer acts as an umami receptor, and that genetic variation in this heterodimer directly affects umami taste sensitivity.
Partial Text: Taste is the sensory system devoted to the evaluation of the quality of potential foods and to the determination of whether they should be ingested or rejected. The sense of taste is widely believed to be composed of a small number of primary qualities, in particular sweet, sour, bitter, salty and umami (a Japanese word that roughly translates into delicious and corresponds in many ways to savory in English). Of these five taste qualities or modalities, umami is elicited by L-glutamate, typically as its Na salt (monosodium glutamate: MSG), some amino acids and purine nucleotides (such as IMP and GMP). A salient feature of umami taste in rodents and humans is their impressive potentiation by purine nucleotides , . Many protein (amino acid) rich foods, including meat, milk and seafood taste delicious (umami) to humans, and are attractive to rodents and other animals, suggesting that umami perception plays a particularly key role in ingestion of amino acids (especially L-glutamate) which act as biosynthetic precursors of various molecules, metabolic fuels and neurotransmitters.
Distributions of MSG, IMP and M+I thresholds showed that individual subjects exhibited very different levels of sensitivity. Hence, large variations in recognition threshold sensitivity to umami substances were demonstrated. The distribution of MSG and M+I (Figure 1) may be made up of combinations of the varying underlying distributions of the TAS1R1-372 and TAS1R3-757 haplotypes, because we found only 2 SNPs (associated with differences in taste recognition thresholds) with high minor allele frequencies in human TAS1R1 and TAS1R3. Distributions of the 3 groups divided according to TAS1R1-A372T and TAS1R3-R757C haplotypes showed 3 types of curves with about 2∼3-fold different mean values in MSG and M+I recognition thresholds (Figure 2). The mean values were TR