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Modulation of sweet taste by umami compounds via sweet taste receptor subunit hT1R2.

Shim J, Son HJ, Kim Y, Kim KH, Kim JT, Moon H, Kim MJ, Misaka T, Rhyu MR - PLoS ONE (2015)

Bottom Line: The sensitivity of sucrose to hT1R2/hT1R3 was significantly attenuated by MSG and umami active peptides but not by umami active nucleotides.Application of umami compounds with lactisole, inhibitory drugs that target T1R3, exerted a more severe inhibitory effect.These results suggest that umami peptides affect sweet taste receptors and this interaction prevents sweet receptor agonists from binding to the T1R2 ECD in an allosteric manner, not to the T1R3.

View Article: PubMed Central - PubMed

Affiliation: Division of Creative Food Science for Health, Korea Food Research Institute, Bundang-gu, Sungnam-si, Gyeonggi-do, Republic of Korea.

ABSTRACT
Although the five basic taste qualities-sweet, sour, bitter, salty and umami-can be recognized by the respective gustatory system, interactions between these taste qualities are often experienced when food is consumed. Specifically, the umami taste has been investigated in terms of whether it enhances or reduces the other taste modalities. These studies, however, are based on individual perception and not on a molecular level. In this study we investigated umami-sweet taste interactions using umami compounds including monosodium glutamate (MSG), 5'-mononucleotides and glutamyl-dipeptides, glutamate-glutamate (Glu-Glu) and glutamate-aspartic acid (Glu-Asp), in human sweet taste receptor hT1R2/hT1R3-expressing cells. The sensitivity of sucrose to hT1R2/hT1R3 was significantly attenuated by MSG and umami active peptides but not by umami active nucleotides. Inhibition of sweet receptor activation by MSG and glutamyl peptides is obvious when sweet receptors are activated by sweeteners that target the extracellular domain (ECD) of T1R2, such as sucrose and acesulfame K, but not by cyclamate, which interact with the T1R3 transmembrane domain (TMD). Application of umami compounds with lactisole, inhibitory drugs that target T1R3, exerted a more severe inhibitory effect. The inhibition was also observed with F778A sweet receptor mutant, which have the defect in function of T1R3 TMD. These results suggest that umami peptides affect sweet taste receptors and this interaction prevents sweet receptor agonists from binding to the T1R2 ECD in an allosteric manner, not to the T1R3. This is the first report to define the interaction between umami and sweet taste receptors.

No MeSH data available.


Inhibition of sucrose-induced calcium responses in hT1R2/hT1R3-expressing cells by MSG (A), Glu-Glu (B), Glu-Asp (C), Gly-Gly (E), IMP (F), and GMP (G).Glu-Glu and Glu-Asp are umami peptides and Gly-Gly is tasteless peptide. Inhibitory effect of umami compounds evaluated using the Flex system. Co-application of MSG or glutamyl dipeptides with sucrose inhibited the response of sweet receptor cells to sucrose. However, co-application of the 5’-ribonucleotides IMP and GMP with sucrose did not inhibit the response of sweet receptor cells to sucrose. (D) Osmolarity effects in hT1R2/hT1R3-expressing cells. (H) Sucrose response with dipeptides adjusted to pH 7.4. The value of y-axis means the ratio which the value with agonists and/or compounds normalized by the value without agonist. Asterisk *, **, *** stands for p<0.05, p<0.01, p<0.001, respectively. (I) Ca2+ cell images using fluo-4 dye is captured at 30 seconds later after co-applied sucrose and/or umami-compounds. Responded cell emitted the green fluorescence signals. Similar to the results of the Flex system, the response of sweet receptor cells to sucrose was attenuated by the co-application of Glu-Glu, Glu-Asp or MSG. (J) The ratio of responding cells to total cells.
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pone.0124030.g001: Inhibition of sucrose-induced calcium responses in hT1R2/hT1R3-expressing cells by MSG (A), Glu-Glu (B), Glu-Asp (C), Gly-Gly (E), IMP (F), and GMP (G).Glu-Glu and Glu-Asp are umami peptides and Gly-Gly is tasteless peptide. Inhibitory effect of umami compounds evaluated using the Flex system. Co-application of MSG or glutamyl dipeptides with sucrose inhibited the response of sweet receptor cells to sucrose. However, co-application of the 5’-ribonucleotides IMP and GMP with sucrose did not inhibit the response of sweet receptor cells to sucrose. (D) Osmolarity effects in hT1R2/hT1R3-expressing cells. (H) Sucrose response with dipeptides adjusted to pH 7.4. The value of y-axis means the ratio which the value with agonists and/or compounds normalized by the value without agonist. Asterisk *, **, *** stands for p<0.05, p<0.01, p<0.001, respectively. (I) Ca2+ cell images using fluo-4 dye is captured at 30 seconds later after co-applied sucrose and/or umami-compounds. Responded cell emitted the green fluorescence signals. Similar to the results of the Flex system, the response of sweet receptor cells to sucrose was attenuated by the co-application of Glu-Glu, Glu-Asp or MSG. (J) The ratio of responding cells to total cells.

Mentions: To examine interaction between sweet and umami taste signaling at the receptor level, we evaluated the response of sweet receptor cells after treatment with various combinations of umami compounds and sucrose. The response of sweet receptor cells was monitored using the Flex system with the Ca4 dye. When MSG was co-applied with sucrose, the induced response of sweet receptor cells by sucrose was attenuated (Fig 1A). Other umami compounds; i.e., glutamate-glutamate (Glu-Glu) dipeptide, and glutamate-aspartate (Glu-Asp) dipeptide, also reduced significantly the response of sweet receptor cells (Fig 1B and 1C). To investigate whether all dipeptides might affect sweet receptor activity, we tested the sweet response with glycine-glycine (Gly-Gly) dipeptide which is well known as the taste-less dipeptides. Gly-Gly did not show inhibitory effect as induction of sweet receptor by sucrose (Fig 1E). Attenuated effect by MSG or umami dipeptides got clear as strong induction by treatment of high concentration of sucrose. Since treatment of sucrose in higher concentration than 150 mM had the effect on only Flp-In 293 cells without expressing sweet receptors, we did not perform the experiments with higher than 150 mM sucrose. The inhibitory effect of MSG and dipeptides showed dose-dependency (Fig 1A–1C). Because high osmolarity with MSG might cause inhibitory effect of sucrose response, we performed the control experiment using high concentration of Mannitol to mimic high osmolarity [22]. 50 mM of Mannitol causes the inhibited sucrose response. However, it seems to be ignorable because the inhibitory rate by Mannitol is much less than that by MSG (Fig 1D). In addition, low pH with acidic dipeptides might cause inhibited sucrose response. To remove the pH effect, we checked the response of sucrose with dipeptides revised to pH 7.4 using NaOH [23]. They are still highly effective in the inhibited sucrose response as much as unrevised dipeptides are (Fig 1H). Sweet receptor signaling finally increases cellular Ca2+ level via cAMP or IP3 production [24]. Although the change of cellular Ca2+ level was detected by Flex system, this phenomenon was more convinced by visualization of cellular Ca2+ level using imaging system with the Fluo-4 dye (Fig 1I and 1J). Visualized images using Fluo-4 dye also showed the inhibited sucrose response by MSG or dipeptides. These results were quantified by measuring the ratio of fluorescent cells by total cells in the Fig 1J. To investigate whether all umami compounds could inhibit sweet receptor activity, we tested the response of sweet receptor cells after treatment with 5’-ribonucleotide umami agonists such as IMP and GMP (Fig 1F and 1G). However, the 5’-ribonucleotide umami compounds did not reduce the response of sweet receptor cells to sucrose. Since 5’-ribonucleotide affects the T1R1 receptor, a component of the umami receptor complex, understandably the agonists had no effect on the T1R2/T1R3 sweet receptor complex.


Modulation of sweet taste by umami compounds via sweet taste receptor subunit hT1R2.

Shim J, Son HJ, Kim Y, Kim KH, Kim JT, Moon H, Kim MJ, Misaka T, Rhyu MR - PLoS ONE (2015)

Inhibition of sucrose-induced calcium responses in hT1R2/hT1R3-expressing cells by MSG (A), Glu-Glu (B), Glu-Asp (C), Gly-Gly (E), IMP (F), and GMP (G).Glu-Glu and Glu-Asp are umami peptides and Gly-Gly is tasteless peptide. Inhibitory effect of umami compounds evaluated using the Flex system. Co-application of MSG or glutamyl dipeptides with sucrose inhibited the response of sweet receptor cells to sucrose. However, co-application of the 5’-ribonucleotides IMP and GMP with sucrose did not inhibit the response of sweet receptor cells to sucrose. (D) Osmolarity effects in hT1R2/hT1R3-expressing cells. (H) Sucrose response with dipeptides adjusted to pH 7.4. The value of y-axis means the ratio which the value with agonists and/or compounds normalized by the value without agonist. Asterisk *, **, *** stands for p<0.05, p<0.01, p<0.001, respectively. (I) Ca2+ cell images using fluo-4 dye is captured at 30 seconds later after co-applied sucrose and/or umami-compounds. Responded cell emitted the green fluorescence signals. Similar to the results of the Flex system, the response of sweet receptor cells to sucrose was attenuated by the co-application of Glu-Glu, Glu-Asp or MSG. (J) The ratio of responding cells to total cells.
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pone.0124030.g001: Inhibition of sucrose-induced calcium responses in hT1R2/hT1R3-expressing cells by MSG (A), Glu-Glu (B), Glu-Asp (C), Gly-Gly (E), IMP (F), and GMP (G).Glu-Glu and Glu-Asp are umami peptides and Gly-Gly is tasteless peptide. Inhibitory effect of umami compounds evaluated using the Flex system. Co-application of MSG or glutamyl dipeptides with sucrose inhibited the response of sweet receptor cells to sucrose. However, co-application of the 5’-ribonucleotides IMP and GMP with sucrose did not inhibit the response of sweet receptor cells to sucrose. (D) Osmolarity effects in hT1R2/hT1R3-expressing cells. (H) Sucrose response with dipeptides adjusted to pH 7.4. The value of y-axis means the ratio which the value with agonists and/or compounds normalized by the value without agonist. Asterisk *, **, *** stands for p<0.05, p<0.01, p<0.001, respectively. (I) Ca2+ cell images using fluo-4 dye is captured at 30 seconds later after co-applied sucrose and/or umami-compounds. Responded cell emitted the green fluorescence signals. Similar to the results of the Flex system, the response of sweet receptor cells to sucrose was attenuated by the co-application of Glu-Glu, Glu-Asp or MSG. (J) The ratio of responding cells to total cells.
Mentions: To examine interaction between sweet and umami taste signaling at the receptor level, we evaluated the response of sweet receptor cells after treatment with various combinations of umami compounds and sucrose. The response of sweet receptor cells was monitored using the Flex system with the Ca4 dye. When MSG was co-applied with sucrose, the induced response of sweet receptor cells by sucrose was attenuated (Fig 1A). Other umami compounds; i.e., glutamate-glutamate (Glu-Glu) dipeptide, and glutamate-aspartate (Glu-Asp) dipeptide, also reduced significantly the response of sweet receptor cells (Fig 1B and 1C). To investigate whether all dipeptides might affect sweet receptor activity, we tested the sweet response with glycine-glycine (Gly-Gly) dipeptide which is well known as the taste-less dipeptides. Gly-Gly did not show inhibitory effect as induction of sweet receptor by sucrose (Fig 1E). Attenuated effect by MSG or umami dipeptides got clear as strong induction by treatment of high concentration of sucrose. Since treatment of sucrose in higher concentration than 150 mM had the effect on only Flp-In 293 cells without expressing sweet receptors, we did not perform the experiments with higher than 150 mM sucrose. The inhibitory effect of MSG and dipeptides showed dose-dependency (Fig 1A–1C). Because high osmolarity with MSG might cause inhibitory effect of sucrose response, we performed the control experiment using high concentration of Mannitol to mimic high osmolarity [22]. 50 mM of Mannitol causes the inhibited sucrose response. However, it seems to be ignorable because the inhibitory rate by Mannitol is much less than that by MSG (Fig 1D). In addition, low pH with acidic dipeptides might cause inhibited sucrose response. To remove the pH effect, we checked the response of sucrose with dipeptides revised to pH 7.4 using NaOH [23]. They are still highly effective in the inhibited sucrose response as much as unrevised dipeptides are (Fig 1H). Sweet receptor signaling finally increases cellular Ca2+ level via cAMP or IP3 production [24]. Although the change of cellular Ca2+ level was detected by Flex system, this phenomenon was more convinced by visualization of cellular Ca2+ level using imaging system with the Fluo-4 dye (Fig 1I and 1J). Visualized images using Fluo-4 dye also showed the inhibited sucrose response by MSG or dipeptides. These results were quantified by measuring the ratio of fluorescent cells by total cells in the Fig 1J. To investigate whether all umami compounds could inhibit sweet receptor activity, we tested the response of sweet receptor cells after treatment with 5’-ribonucleotide umami agonists such as IMP and GMP (Fig 1F and 1G). However, the 5’-ribonucleotide umami compounds did not reduce the response of sweet receptor cells to sucrose. Since 5’-ribonucleotide affects the T1R1 receptor, a component of the umami receptor complex, understandably the agonists had no effect on the T1R2/T1R3 sweet receptor complex.

Bottom Line: The sensitivity of sucrose to hT1R2/hT1R3 was significantly attenuated by MSG and umami active peptides but not by umami active nucleotides.Application of umami compounds with lactisole, inhibitory drugs that target T1R3, exerted a more severe inhibitory effect.These results suggest that umami peptides affect sweet taste receptors and this interaction prevents sweet receptor agonists from binding to the T1R2 ECD in an allosteric manner, not to the T1R3.

View Article: PubMed Central - PubMed

Affiliation: Division of Creative Food Science for Health, Korea Food Research Institute, Bundang-gu, Sungnam-si, Gyeonggi-do, Republic of Korea.

ABSTRACT
Although the five basic taste qualities-sweet, sour, bitter, salty and umami-can be recognized by the respective gustatory system, interactions between these taste qualities are often experienced when food is consumed. Specifically, the umami taste has been investigated in terms of whether it enhances or reduces the other taste modalities. These studies, however, are based on individual perception and not on a molecular level. In this study we investigated umami-sweet taste interactions using umami compounds including monosodium glutamate (MSG), 5'-mononucleotides and glutamyl-dipeptides, glutamate-glutamate (Glu-Glu) and glutamate-aspartic acid (Glu-Asp), in human sweet taste receptor hT1R2/hT1R3-expressing cells. The sensitivity of sucrose to hT1R2/hT1R3 was significantly attenuated by MSG and umami active peptides but not by umami active nucleotides. Inhibition of sweet receptor activation by MSG and glutamyl peptides is obvious when sweet receptors are activated by sweeteners that target the extracellular domain (ECD) of T1R2, such as sucrose and acesulfame K, but not by cyclamate, which interact with the T1R3 transmembrane domain (TMD). Application of umami compounds with lactisole, inhibitory drugs that target T1R3, exerted a more severe inhibitory effect. The inhibition was also observed with F778A sweet receptor mutant, which have the defect in function of T1R3 TMD. These results suggest that umami peptides affect sweet taste receptors and this interaction prevents sweet receptor agonists from binding to the T1R2 ECD in an allosteric manner, not to the T1R3. This is the first report to define the interaction between umami and sweet taste receptors.

No MeSH data available.