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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.


The target site of the umami peptide in sweet receptors was distinct from that of lactisole(A) The synergistically reduced response of sweet receptor cells upon application of sucrose. Co-application of 1 mM Glu-Glu with indicated concentration of lactisole (Lac) synergistically inhibited the sweet response. Asterisk *, **, *** stands for p<0.05, p<0.01, p<0.001, respectively. (B) The response of F778A mutant to cyclamate and sucrose. F778A means a point mutation at residue 778 of hT1R3 resulting in substitution of phenylalanine for alanine. (C) The response to the co-application of sucrose and Glu-Glu in cells expressing F778A mutant human sweet-taste receptors. (D) Imaging of co-application of 100 mM sucrose with 1 mM Glu-Glu or 50 mM MSG in cells with the F778A mutant receptor. (E) The ratio of responding cells to total cells.
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pone.0124030.g003: The target site of the umami peptide in sweet receptors was distinct from that of lactisole(A) The synergistically reduced response of sweet receptor cells upon application of sucrose. Co-application of 1 mM Glu-Glu with indicated concentration of lactisole (Lac) synergistically inhibited the sweet response. Asterisk *, **, *** stands for p<0.05, p<0.01, p<0.001, respectively. (B) The response of F778A mutant to cyclamate and sucrose. F778A means a point mutation at residue 778 of hT1R3 resulting in substitution of phenylalanine for alanine. (C) The response to the co-application of sucrose and Glu-Glu in cells expressing F778A mutant human sweet-taste receptors. (D) Imaging of co-application of 100 mM sucrose with 1 mM Glu-Glu or 50 mM MSG in cells with the F778A mutant receptor. (E) The ratio of responding cells to total cells.

Mentions: Lactisole is the well-known antagonist by affecting the TMD of T1R3 [25]. To evaluate whether umami compounds works on the TMD of T1R3 for inhibition of sweet receptors, we performed a combination treatment of Glu-Glu and/or lactisole with sucrose. If umami compounds and lactisole share a common interacting surface in the TMD of T1R3, their inhibitory effect might be competitive. If umami compounds works on another site, the inhibitor effects would be additive or synergistic. Since no inhibitory effect of Glu-Glu on cyclamate (which also affects T1R3 TMD) was observed (Fig 2C), we hypothesized that the inhibitory mechanism of Glu-Glu might be different from that of lactisole. As expected, combination treatment of Glu-Glu and lactisole showed a reduced response to sucrose compared to that of each compound alone (Fig 3A). Additionally, we evaluated the inhibitory effect of the response of sweet receptor cells containing a F778A point mutation in T1R3. As a previous report [26], sweet receptor cells containing this point mutation showed defective cyclamate induction, whereas it did not show defective sucrose induction (Fig 3B). Combination treatment with Glu-Glu and sucrose in cells with this mutant receptor still showed the inhibitory effect of Glu-Glu (Fig 3C). These results indicate that the effect of Glu-Glu is not mediated via F778 on T1R3 TMD. Even though the results from Flex system were consistent and convincing, confirmation by the other system such as imaging system using the Fluo-4 dye would make our results stronger. This phenomenon was confirmed using an imaging system that could detect Ca2+ influx caused by receptor activity (Fig 3D). These results were quantified by measuring the ratio of fluorescent cells by total cells (Fig 3E).


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)

The target site of the umami peptide in sweet receptors was distinct from that of lactisole(A) The synergistically reduced response of sweet receptor cells upon application of sucrose. Co-application of 1 mM Glu-Glu with indicated concentration of lactisole (Lac) synergistically inhibited the sweet response. Asterisk *, **, *** stands for p<0.05, p<0.01, p<0.001, respectively. (B) The response of F778A mutant to cyclamate and sucrose. F778A means a point mutation at residue 778 of hT1R3 resulting in substitution of phenylalanine for alanine. (C) The response to the co-application of sucrose and Glu-Glu in cells expressing F778A mutant human sweet-taste receptors. (D) Imaging of co-application of 100 mM sucrose with 1 mM Glu-Glu or 50 mM MSG in cells with the F778A mutant receptor. (E) The ratio of responding cells to total cells.
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Related In: Results  -  Collection

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getmorefigures.php?uid=PMC4390298&req=5

pone.0124030.g003: The target site of the umami peptide in sweet receptors was distinct from that of lactisole(A) The synergistically reduced response of sweet receptor cells upon application of sucrose. Co-application of 1 mM Glu-Glu with indicated concentration of lactisole (Lac) synergistically inhibited the sweet response. Asterisk *, **, *** stands for p<0.05, p<0.01, p<0.001, respectively. (B) The response of F778A mutant to cyclamate and sucrose. F778A means a point mutation at residue 778 of hT1R3 resulting in substitution of phenylalanine for alanine. (C) The response to the co-application of sucrose and Glu-Glu in cells expressing F778A mutant human sweet-taste receptors. (D) Imaging of co-application of 100 mM sucrose with 1 mM Glu-Glu or 50 mM MSG in cells with the F778A mutant receptor. (E) The ratio of responding cells to total cells.
Mentions: Lactisole is the well-known antagonist by affecting the TMD of T1R3 [25]. To evaluate whether umami compounds works on the TMD of T1R3 for inhibition of sweet receptors, we performed a combination treatment of Glu-Glu and/or lactisole with sucrose. If umami compounds and lactisole share a common interacting surface in the TMD of T1R3, their inhibitory effect might be competitive. If umami compounds works on another site, the inhibitor effects would be additive or synergistic. Since no inhibitory effect of Glu-Glu on cyclamate (which also affects T1R3 TMD) was observed (Fig 2C), we hypothesized that the inhibitory mechanism of Glu-Glu might be different from that of lactisole. As expected, combination treatment of Glu-Glu and lactisole showed a reduced response to sucrose compared to that of each compound alone (Fig 3A). Additionally, we evaluated the inhibitory effect of the response of sweet receptor cells containing a F778A point mutation in T1R3. As a previous report [26], sweet receptor cells containing this point mutation showed defective cyclamate induction, whereas it did not show defective sucrose induction (Fig 3B). Combination treatment with Glu-Glu and sucrose in cells with this mutant receptor still showed the inhibitory effect of Glu-Glu (Fig 3C). These results indicate that the effect of Glu-Glu is not mediated via F778 on T1R3 TMD. Even though the results from Flex system were consistent and convincing, confirmation by the other system such as imaging system using the Fluo-4 dye would make our results stronger. This phenomenon was confirmed using an imaging system that could detect Ca2+ influx caused by receptor activity (Fig 3D). These results were quantified by measuring the ratio of fluorescent cells by total cells (Fig 3E).

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.