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Wolfgang Meyerhof - One of the best experts on this subject based on the ideXlab platform.
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Amino acid sensing in hypothalamic tanycytes via umami taste receptors
Molecular metabolism, 2017Co-Authors: Greta Lazutkaite, Wolfgang Meyerhof, Kristina Lossow, Alice Soldà, Nicholas DaleAbstract:Abstract Objective Hypothalamic tanycytes are glial cells that line the wall of the third ventricle and contact the cerebrospinal fluid (CSF). While they are known to detect glucose in the CSF we now show that tanycytes also detect amino acids, important nutrients that signal satiety. Methods Ca 2+ imaging and ATP biosensing were used to detect tanycyte responses to l -amino acids. The downstream pathway of the responses was determined using ATP receptor antagonists and channel blockers. The receptors were characterized using mice lacking the TAS1R1 gene, as well as an mGluR4 receptor antagonist. Results Amino acids such as Arg, Lys, and Ala evoke Ca 2+ signals in tanycytes and evoke the release of ATP via pannexin 1 and CalHM1, which amplifies the signal via a P2 receptor dependent mechanism. Tanycytes from mice lacking the TAS1R1 gene had diminished responses to lysine and arginine but not alanine. Antagonists of mGluR4 greatly reduced the responses to alanine and lysine. Conclusion Two receptors previously implicated in taste cells, the TAS1R1/Tas1r3 heterodimer and mGluR4, contribute to the detection of a range of amino acids by tanycytes in CSF.
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A sweet taste receptor-dependent mechanism of glucosensing in hypothalamic tanycytes.
Glia, 2017Co-Authors: Heather Elizabeth Benford, Matei Bolborea, Wolfgang Meyerhof, Sergey Kasparov, Eric Pollatzek, Kristina Lossow, Irm Hermans-borgmeyer, Beihui Liu, Nicholas DaleAbstract:Hypothalamic tanycytes are glial-like glucosensitive cells that contact the cerebrospinal fluid of the third ventricle, and send processes into the hypothalamic nuclei that control food intake and body weight. The mechanism of tanycyte glucosensing remains undetermined. While tanycytes express the components associated with the glucosensing of the pancreatic β cell, they respond to nonmetabolisable glucose analogues via an ATP receptor-dependent mechanism. Here, we show that tanycytes in rodents respond to non-nutritive sweeteners known to be ligands of the sweet taste (Tas1r2/Tas1r3) receptor. The initial sweet tastant-evoked response, which requires the presence of extracellular Ca2+, leads to release of ATP and a larger propagating Ca2+ response mediated by P2Y1 receptors. In Tas1r2 null mice the proportion of glucose nonresponsive tanycytes was greatly increased in these mice, but a subset of tanycytes retained an undiminished sensitivity to glucose. Our data demonstrate that the sweet taste receptor mediates glucosensing in about 60% of glucosensitive tanycytes while the remaining 40% of glucosensitive tanycytes use some other, as yet unknown mechanism.
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Rubemamine and Rubescenamine, Two Naturally Occurring N-Cinnamoyl Phenethylamines with Umami-Taste-Modulating Properties.
Journal of Agricultural and Food Chemistry, 2015Co-Authors: Michael Backes, Wolfgang Meyerhof, Katja Obst, Juliane Bojahr, Anika Thorhauer, Natacha Roudnitzky, Susanne Paetz, Katharina Reichelt, Gerhard Krammer, Jakob LeyAbstract:Sensory screening of a series of naturally occurring N-cinnamoyl derivatives of substituted phenethylamines revealed that rubemamine (9, from Chenopodium album) and rubescenamine (10, from Zanthoxylum rubsecens) elicit strong intrinsic umami taste in water at 50 and 10 ppm, respectively. Sensory tests in glutamate- and nucleotide-containing bases showed that the compounds influence the whole flavor profile of savory formulations. Both rubemamine (9) and rubescenamine (10) at 10–100 ppm dose-dependently positively modulated the umami taste of MSG (0.17–0.22%) up to threefold. Among the investigated amides, only rubemamine (9) and rubescenamine (10) are able to directly activate the TAS1R1-TAS1R3 umami taste receptor. Moreover, both compounds also synergistically modulated the activation of TAS1R1-TAS1R3 by MSG. Most remarkably, rubemamine (9) was able to further positively modulate the IMP-enhanced TAS1R1-TAS1R3 response to MSG ∼1.8-fold. Finally, armatamide (11), zanthosinamide (13), and dioxamine (14), w...
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Oligomerization of Sweet and Bitter Taste Receptors
Methods in cell biology, 2013Co-Authors: Christian Kuhn, Wolfgang MeyerhofAbstract:The superfamily of G protein-coupled receptors (GPCRs) mediates numerous physiological processes, including neurotransmission, cell differentiation and metabolism, and sensory perception. In recent years, it became evident that these receptors might function not only as monomeric receptors but also as homo- or heteromeric receptor complexes. The family of TAS1R taste receptors are prominent examples of GPCR dimerization as they act as obligate functional heteromers: TAS1R1 and TAS1R3 combine to form an umami taste receptor, while the combination of TAS1R2 and TAS1R3 is a sweet taste receptor. So far, TAS2Rs, a second family of ~25 taste receptors in humans that mediates responses to bitter compounds, have been shown to function on their own, but if they do so as receptor monomers or as homomeric receptors still remains unknown. Using two different experimental approaches, we have recently shown that TAS2Rs can indeed form both homomeric and heteromeric receptor complexes. The employed techniques, coimmunoprecipitations and bioluminescence resonance energy transfer (BRET), are based on different principles and complement each other well and therefore provided compelling evidences for TAS2R oligomerization. Furthermore, we have adapted the protocols to include a number of controls and for higher throughput to accommodate the investigation of a large number of receptors and receptor combinations. Here, we present the protocols in detail.
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Genetic Labeling of TAS1R1 and Tas2r131 Taste Receptor Cells in Mice
Chemical senses, 2012Co-Authors: Anja Voigt, Kristina Lossow, Irm Hermans-borgmeyer, Ulrich Boehm, Sandra Hübner, Wolfgang MeyerhofAbstract:Characterization of the peripheral taste system relies on the identification and visualization of the different taste bud cell types. So far, genetic strategies to label taste receptor cells are limited to sweet, sour, and salty detecting cells. To visualize TAS1R1 umami and Tas2r131 bitter sensing cells, we generated animals in which the TAS1R1 and Tas2r131 open reading frames are replaced by expression cassettes containing the fluorescent proteins mCherry or hrGFP, respectively. These animals enabled us to visualize and quantify the entire oral TAS1R1 and Tas2r131 cell populations. TAS1R1-mCherry cells were predominantly detected in fungiform papillae, whereas Tas2r131-hrGFP cells, which are ~4-fold more abundant, were mainly present in foliate and vallate papillae. In the palate, both cell types were similarly distributed. Mice carrying both recombinant alleles demonstrated completely segregated TAS1R1 and Tas2r131 cell populations. Only ~50% of the entire bitter cell population expressed hrGFP, indicating that bitter taste receptor cells express a subset of the bitter receptor repertoire. In extragustatory tissues, mCherry fluorescence was observed in testis and hrGFP fluorescence in testis, thymus, vomeronasal organ, and respiratory epithelium, suggesting that only few extraoral sites express Tas2r131 and TAS1R1 receptors at levels comparable to taste tissue.
Eugeni Roura - One of the best experts on this subject based on the ideXlab platform.
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TAS1R1 and TAS1R3 Polymorphisms Relate to Energy and Protein-Rich Food Choices from a Buffet Meal Respectively.
Nutrients, 2018Co-Authors: Pengfei Han, Russell Keast, Eugeni RouraAbstract:Eating behaviour in humans is a complex trait that involves sensory perception. Genetic variation in sensory systems is one of the factors influencing perception of foods. However, the extent that these genetic variations may determine food choices in a real meal scenario warrants further research. This study investigated how genetic variants of the umami taste receptor (TAS1R1/TAS1R3) related to consumption of umami-tasting foods. Thirty normal-weight adult subjects were offered “ad libitum” access to a variety of foods covering the full range of main taste-types for 40 min using a buffet meal arrangement. Buccal cell samples were collected and analysed for six single nucleotide polymorphisms (SNPs) reported previously related to the TAS1R1/TAS1R3 genes. Participants identified with the CC alleles of the TAS1R3 rs307355 and rs35744813 consumed significantly more protein from the buffet than T carriers. In addition, participants with GG genotype of the TAS1R1 SNP rs34160967 consumed more fat and calories as compared to the genotype group having the A alleles. In summary, these findings revealed a link between the SNPs variations of umami taster receptor gene and fat and protein intake from a buffet meal.
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Salivary leptin and TAS1R2/TAS1R3 polymorphisms are related to sweet taste sensitivity and carbohydrate intake from a buffet meal in healthy young adults.
The British journal of nutrition, 2017Co-Authors: Pengfei Han, Russell Keast, Eugeni RouraAbstract:The influence of sweet taste sensitivity on food intake is not well understood. We investigated the involvement of salivary leptin and SNP of the sweet taste receptor genes (TAS1R2/TAS1R3) on sweet taste sensitivity, sensory-specific satiety (SSS) and macronutrient intake in healthy human adults. In all, nineteen high sweet sensitivity (HS) and eleven low sweet sensitivity (LS) subjects were classified based on the sweetness perception of one solution (9 mm sucrose) forced-choice triangle test. All participants completed a randomised crossover design experiment where they consumed one of three iso-energetic soup preloads differing in primary taste quality (sweet, non-sweet taste-control or no-taste energy-control). A period of 1 h after the preload, participants were offered a buffet meal consisting of foods varying in taste (sweet or non-sweet) and fat content. Subjective measures included hunger/fullness and SSS for sweetness. Saliva and buccal cells were collected to measure leptin level and to study the TAS1R2/TAS1R3 specific SNP, respectively. Salivary leptin concentrations were significantly higher in LS than HS participants (P 05). In addition, HS showed stronger sweet SSS compared with LH participants (P 05), and consumed less carbohydrate (% energy) and more non-sweet foods than LS (P 01 and P 05, respectively). Alleles from each TAS1R2 locus (GG compared with AA alleles of rs12033832, and CT/CC compared with TT alleles of rs35874116) were related to higher consumption of carbohydrates (% energy) and higher amount of sweet foods, respectively (P 05). In contrast, no associations were found for the TAS1R3 alleles. These results contribute to understand the links between taste sensitivity, macronutrient appetite and food consumption.
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Salivary leptin and TAS1R2/TAS1R3 polymorphisms are related to sweet taste sensitivity and carbohydrate intake from a buffet meal in healthy young adults.
The British journal of nutrition, 2017Co-Authors: Pengfei Han, Russell Keast, Eugeni RouraAbstract:The influence of sweet taste sensitivity on food intake is not well understood. We investigated the involvement of salivary leptin and SNP of the sweet taste receptor genes (TAS1R2/TAS1R3) on sweet taste sensitivity, sensory-specific satiety (SSS) and macronutrient intake in healthy human adults. In all, nineteen high sweet sensitivity (HS) and eleven low sweet sensitivity (LS) subjects were classified based on the sweetness perception of one solution (9 mm sucrose) forced-choice triangle test. All participants completed a randomised crossover design experiment where they consumed one of three iso-energetic soup preloads differing in primary taste quality (sweet, non-sweet taste-control or no-taste energy-control). A period of 1 h after the preload, participants were offered a buffet meal consisting of foods varying in taste (sweet or non-sweet) and fat content. Subjective measures included hunger/fullness and SSS for sweetness. Saliva and buccal cells were collected to measure leptin level and to study the TAS1R2/TAS1R3 specific SNP, respectively. Salivary leptin concentrations were significantly higher in LS than HS participants (P
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salivary leptin and tas1r2 tas1r3 polymorphisms are related to sweet taste sensitivity and carbohydrate intake from a buffet meal in healthy young adults
British Journal of Nutrition, 2017Co-Authors: Pengfei Han, Russell Keast, Eugeni RouraAbstract:The influence of sweet taste sensitivity on food intake is not well understood. We investigated the involvement of salivary leptin and SNP of the sweet taste receptor genes (TAS1R2/TAS1R3) on sweet taste sensitivity, sensory-specific satiety (SSS) and macronutrient intake in healthy human adults. In all, nineteen high sweet sensitivity (HS) and eleven low sweet sensitivity (LS) subjects were classified based on the sweetness perception of one solution (9 mm sucrose) forced-choice triangle test. All participants completed a randomised crossover design experiment where they consumed one of three iso-energetic soup preloads differing in primary taste quality (sweet, non-sweet taste-control or no-taste energy-control). A period of 1 h after the preload, participants were offered a buffet meal consisting of foods varying in taste (sweet or non-sweet) and fat content. Subjective measures included hunger/fullness and SSS for sweetness. Saliva and buccal cells were collected to measure leptin level and to study the TAS1R2/TAS1R3 specific SNP, respectively. Salivary leptin concentrations were significantly higher in LS than HS participants (P 05). In addition, HS showed stronger sweet SSS compared with LH participants (P 05), and consumed less carbohydrate (% energy) and more non-sweet foods than LS (P 01 and P 05, respectively). Alleles from each TAS1R2 locus (GG compared with AA alleles of rs12033832, and CT/CC compared with TT alleles of rs35874116) were related to higher consumption of carbohydrates (% energy) and higher amount of sweet foods, respectively (P 05). In contrast, no associations were found for the TAS1R3 alleles. These results contribute to understand the links between taste sensitivity, macronutrient appetite and food consumption.
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A regulatory gene network related to the porcine umami taste receptor (TAS1R1/TAS1R3).
Animal genetics, 2015Co-Authors: J. M. Kim, D. Ren, Antonio Reverter, Eugeni RouraAbstract:Taste perception plays an important role in the mediation of food choices in mammals. The first porcine taste receptor genes identified, sequenced and characterized, TAS1R1 and TAS1R3, were related to the dimeric receptor for umami taste. However, little is known about their regulatory network. The objective of this study was to unfold the genetic network involved in porcine umami taste perception. We performed a meta-analysis of 20 gene expression studies spanning 480 porcine microarray chips and screened 328 taste-related genes by selective mining steps among the available 12,320 genes. A porcine umami taste-specific regulatory network was constructed based on the normalized coexpression data of the 328 genes across 27 tissues. From the network, we revealed the 'taste module' and identified a coexpression cluster for the umami taste according to the first connector with the TAS1R1/TAS1R3 genes. Our findings identify several taste-related regulatory genes and extend previous genetic background of porcine umami taste.
Paul A. S. Breslin - One of the best experts on this subject based on the ideXlab platform.
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perceptual variation in umami taste and polymorphisms in tas1r taste receptor genes
The American Journal of Clinical Nutrition, 2009Co-Authors: Qingying Chen, Suzanne Alarcon, Anilet Tharp, Osama M Ahmed, Nelsa L Estrella, Tiffani A Greene, Joseph Rucker, Paul A. S. BreslinAbstract:Background: The TAS1R1 and TAS1R3 G protein–coupled receptors are believed to function in combination as a heteromeric glutamate taste receptor in humans. Objective: We hypothesized that variations in the umami perception of glutamate would correlate with variations in the sequence of these 2 genes, if they contribute directly to umami taste. Design: In this study, we first characterized the general sensitivity to glutamate in a sample population of 242 subjects. We performed these experiments by sequencing the coding regions of the genomic TAS1R1 and TAS1R3 genes in a separate set of 87 individuals who were tested repeatedly with monopotassium glutamate (MPG) solutions. Last, we tested the role of the candidate umami taste receptor hTAS1R1-hTAS1R3 in a functional expression assay. Results: A subset of subjects displays extremes of sensitivity, and a battery of different psychophysical tests validated this observation. Statistical analysis showed that the rare T allele of single nucleotide polymorphism (SNP) R757C in TAS1R3 led to a doubling of umami ratings of 25 mmol MPG/L. Other suggestive SNPs of TAS1R3 include the A allele of A5T and the A allele of R247H, which both resulted in an approximate doubling of umami ratings of 200 mmol MPG/L. We confirmed the potential role of the human TAS1R1-TAS1R3 heteromer receptor in umami taste by recording responses, specifically to l-glutamate and inosine 5′-monophosphate (IMP) mixtures in a heterologous expression assay in HEK (human embryonic kidney) T cells. Conclusions: There is a reliable and valid variation in human umami taste of l-glutamate. Variations in perception of umami taste correlated with variations in the human TAS1R3 gene. The putative human taste receptor TAS1R1-TAS1R3 responds specifically to l-glutamate mixed with the ribonucleotide IMP. Thus, this receptor likely contributes to human umami taste perception.
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Perceptual variation in umami taste and polymorphisms in TAS1R taste receptor genes.
The American journal of clinical nutrition, 2009Co-Authors: Qingying Chen, Suzanne Alarcon, Anilet Tharp, Osama M Ahmed, Nelsa L Estrella, Tiffani A Greene, Joseph Rucker, Paul A. S. BreslinAbstract:The TAS1R1 and TAS1R3 G protein-coupled receptors are believed to function in combination as a heteromeric glutamate taste receptor in humans. We hypothesized that variations in the umami perception of glutamate would correlate with variations in the sequence of these 2 genes, if they contribute directly to umami taste. In this study, we first characterized the general sensitivity to glutamate in a sample population of 242 subjects. We performed these experiments by sequencing the coding regions of the genomic TAS1R1 and TAS1R3 genes in a separate set of 87 individuals who were tested repeatedly with monopotassium glutamate (MPG) solutions. Last, we tested the role of the candidate umami taste receptor hTAS1R1-hTAS1R3 in a functional expression assay. A subset of subjects displays extremes of sensitivity, and a battery of different psychophysical tests validated this observation. Statistical analysis showed that the rare T allele of single nucleotide polymorphism (SNP) R757C in TAS1R3 led to a doubling of umami ratings of 25 mmol MPG/L. Other suggestive SNPs of TAS1R3 include the A allele of A5T and the A allele of R247H, which both resulted in an approximate doubling of umami ratings of 200 mmol MPG/L. We confirmed the potential role of the human TAS1R1-TAS1R3 heteromer receptor in umami taste by recording responses, specifically to l-glutamate and inosine 5'-monophosphate (IMP) mixtures in a heterologous expression assay in HEK (human embryonic kidney) T cells. There is a reliable and valid variation in human umami taste of l-glutamate. Variations in perception of umami taste correlated with variations in the human TAS1R3 gene. The putative human taste receptor TAS1R1-TAS1R3 responds specifically to l-glutamate mixed with the ribonucleotide IMP. Thus, this receptor likely contributes to human umami taste perception.
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A TAS1R receptor-based explanation of sweet ‘water-taste’
Nature, 2006Co-Authors: Veronica Galindo-cuspinera, Marcel Winnig, Bernd Bufe, Wolfgang Meyerhof, Paul A. S. BreslinAbstract:Paradoxically, artificial sweeteners such as sodium saccharin and acesulfame-K taken in high concentrations are not sweet: they can even seem bitter. And if the mouth is then rinsed out with water, it takes on a sweet taste. These observations have led to new insights into the action of the TAS1R taste receptor. As well as causing the ‘sweet water’ aftertaste, saccharin at high concentrations masks the effect of other sweeteners tasted at the same time. What emerges at the molecular level is a two-site system. Saccharin and acesulfame-K elicit a perception of sweetness when they bind to a high-affinity binding site; at high concentrations they bind to a second low-affinity inhibitory site. When the sweet taste inhibitors are washed away, the sweet receptor re-activates and the perception of sweetness returns. Sweet inhibitors are used in the food industry to offset the high sweetness that results from replacing fats with sweet carbohydrates in some reduced-fat products: the sweet water taste may be a useful predictor for sweet inhibitor activity. ‘Water-tastes’ are gustatory after-impressions elicited by water following the removal of a chemical solution from the mouth, akin to colour after-images appearing on ‘white’ paper after fixation on coloured images. Unlike colour after-images, gustatory after-effects are poorly understood1. One theory posits that ‘water-tastes’ are adaptation phenomena, in which adaptation to one taste solution causes the water presented subsequently to act as a taste stimulus2,3. An alternative hypothesis is that removal of the stimulus upon rinsing generates a receptor-based, positive, off-response in taste-receptor cells, ultimately inducing a gustatory perception4. Here we show that a sweet ‘water-taste’ is elicited when sweet-taste inhibitors are rinsed away. Responses of cultured cells expressing the human sweetener receptor directly parallel the psychophysical responses—water rinses remove the inhibitor from the heteromeric sweetener receptor TAS1R2–TAS1R3, which activates cells and results in the perception of strong sweetness from pure water. This ‘rebound’ activity occurs when equilibrium forces on the two-state allosteric sweet receptors result in their coordinated shift to the activated state upon being released from inhibition by rinsing5,6,7.
Noriatsu Shigemura - One of the best experts on this subject based on the ideXlab platform.
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Binding properties between human sweet receptor and sweet-inhibitor, gymnemic acids
Journal of Oral Biosciences, 2017Co-Authors: Keisuke Sanematsu, Noriatsu ShigemuraAbstract:Abstract Background Gymnemic acids, triterpene glycosides, are known to act as human-specific sweet inhibitors. The long-lasting effect of gymnemic acids is diminished by γ-cyclodextrin. Here, we focus on the molecular mechanisms underlying the interaction between gymnemic acids and sweet taste receptor and/or γ-cyclodextrin by a sweet taste receptor assay in transiently transfected HEK293 cells. Highlight Application of gymnemic acids inhibited intracellular calcium responses to sweet compounds in HEK293 cells expressing human TAS1R2+TAS1R3 but not in those expressing the mouse sweet receptor Tas1r2+Tas1r3 after application of gymnemic acids. The effect of gymnemic acids was reduced after rinsing cells with γ-cyclodextrin. Based on species-specific sensitivities to gymnemic acids, we showed that the transmembrane domain of hTAS1R3 is involved in the sensitivity to gymnemic acids. Point mutation analysis in the transmembrane domain of hTAS1R3 revealed that gymnemic acids shared the same binding pocket with another sweet inhibitor, lactisole. Sensitivity to sweet compounds was also reduced by mixtures of glucuronic acid, a common gymnemic acid. In our molecular models, gymnemic acids interacted with a binding site formed in the transmembrane domain of hTAS1R3. Conclusion Gymnemic acids inhibit sweet responses in humans through an interaction between the glucuronosyl group of gymnemic acids and the transmembrane domain of hTAS1R3. Our molecular model provides a foundation for the development of taste modifiers.
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taste cell expressed α glucosidase enzymes contribute to gustatory responses to disaccharides
Proceedings of the National Academy of Sciences of the United States of America, 2016Co-Authors: Salil Kalarikkal Sukumaran, Ramana Kotha, Sankar Mohan, Shusuke Iwata, Mario B Pinto, Roberto Quezadacalvillo, Buford L Nichols, Noriatsu ShigemuraAbstract:The primary sweet sensor in mammalian taste cells for sugars and noncaloric sweeteners is the heteromeric combination of type 1 taste receptors 2 and 3 (T1R2+T1R3, encoded by Tas1r2 and Tas1r3 genes). However, in the absence of T1R2+T1R3 (e.g., in Tas1r3 KO mice), animals still respond to sugars, arguing for the presence of T1R-independent detection mechanism(s). Our previous findings that several glucose transporters (GLUTs), sodium glucose cotransporter 1 (SGLT1), and the ATP-gated K+ (KATP) metabolic sensor are preferentially expressed in the same taste cells with T1R3 provides a potential explanation for the T1R-independent detection of sugars: sweet-responsive taste cells that respond to sugars and sweeteners may contain a T1R-dependent (T1R2+T1R3) sweet-sensing pathway for detecting sugars and noncaloric sweeteners, as well as a T1R-independent (GLUTs, SGLT1, KATP) pathway for detecting monosaccharides. However, the T1R-independent pathway would not explain responses to disaccharide and oligomeric sugars, such as sucrose, maltose, and maltotriose, which are not substrates for GLUTs or SGLT1. Using RT-PCR, quantitative PCR, in situ hybridization, and immunohistochemistry, we found that taste cells express multiple α-glycosidases (e.g., amylase and neutral α glucosidase C) and so-called intestinal “brush border” disaccharide-hydrolyzing enzymes (e.g., maltase-glucoamylase and sucrase-isomaltase). Treating the tongue with inhibitors of disaccharidases specifically decreased gustatory nerve responses to disaccharides, but not to monosaccharides or noncaloric sweeteners, indicating that lingual disaccharidases are functional. These taste cell-expressed enzymes may locally break down dietary disaccharides and starch hydrolysis products into monosaccharides that could serve as substrates for the T1R-independent sugar sensing pathways.
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Intracellular acidification is required for full activation of the sweet taste receptor by miraculin.
Scientific reports, 2016Co-Authors: Keisuke Sanematsu, Noriatsu Shigemura, Ryusuke Yoshida, Masayuki Kitagawa, Satoru Nirasawa, Yuzo NinomiyaAbstract:Acidification of the glycoprotein, miraculin (MCL), induces sweet taste in humans, but not in mice. The sweet taste induced by MCL is more intense when acidification occurs with weak acids as opposed to strong acids. MCL interacts with the human sweet receptor subunit hTAS1R2, but the mechanisms by which the acidification of MCL activates the sweet taste receptor remain largely unexplored. The work reported here speaks directly to this activation by utilizing a sweet receptor TAS1R2 + TAS1R3 assay. In accordance with previous data, MCL-applied cells displayed a pH dependence with citric acid (weak acid) being right shifted to that with hydrochloric acid (strong acid). When histidine residues in both the intracellular and extracellular region of hTAS1R2 were exchanged for alanine, taste-modifying effect of MCL was reduced or abolished. Stronger intracellular acidification of HEK293 cells was induced by citric acid than by HCl and taste-modifying effect of MCL was proportional to intracellular pH regardless of types of acids. These results suggest that intracellular acidity is required for full activation of the sweet taste receptor by MCL.
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Structure, Function, and Signaling of Taste G-Protein-Coupled Receptors
Current Pharmaceutical Biotechnology, 2014Co-Authors: Keisuke Sanematsu, Ryusuke Yoshida, Noriatsu ShigemuraAbstract:Detection of tastes is critical for animals. Sweet, umami and bitter taste are mediated by G-protein-coupled receptors that are expressed in the taste receptor cells. TAS1Rs which belong to class C G-protein-coupled receptors form heterodimeric complexes to function as sweet (TAS1R2 + TAS1R3) or umami (TAS1R1 + TAS1R3) taste receptors. Umami taste is also considered to be mediated by mGluRs. TAS2Rs belong to class A G-protein-coupled receptors and are responsible for bitter taste. After activation of these receptors, their second messenger pathways lead to depolarization and intracellular calcium increase in taste receptor cells. Then, transmitter is released from taste receptor cells leading to activation of taste nerve fibers and taste information is sent to the central nervous system. Recent studies on heterologous expression system and molecular modeling lead to better understanding of binding site of TAS1Rs and TAS2Rs and molecular mechanisms for interaction between taste substances and these receptors. TAS1Rs and TAS2Rs have multiple and single binding sites for structurally diverse ligands, respectively. Sensitivities of these receptors are known to differ among individuals, strains, and species. In addition, some species abolish these receptors and signaling molecules. Here we focus on structure, function, signaling, polymorphism, and molecular evolution of the taste G-protein-coupled receptors.
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Genetic and molecular basis of individual differences in human umami taste perception.
PloS one, 2009Co-Authors: Noriatsu Shigemura, Keisuke Sanematsu, Ryusuke Yoshida, Shinya Shirosaki, Yuzo NinomiyaAbstract: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.
Marcel Winnig - One of the best experts on this subject based on the ideXlab platform.
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sweet taste receptor interacting protein cib1 is a general inhibitor of insp3 dependent ca2 release in vivo
Journal of Neurochemistry, 2008Co-Authors: Jan K Hennigs, Nicole Burhenne, Frauke Stähler, Marcel Winnig, Bettina Walter, Wolfgang Meyerhof, Hartwig SchmaleAbstract:In a search for sweet taste receptor interacting proteins, we have identified the calcium- and integrin-binding protein 1 (CIB1) as specific binding partner of the intracellular carboxyterminal domain of the rat sweet taste receptor subunit Tas1r2. In heterologous human embryonic kidney 293 (HEK293) cells, the G protein chimeras Gα16gust44 and Gα15i3 link the sweet taste receptor dimer TAS1R2/TAS1R3 to an inositol 1,4,5-trisphosphate (InsP3)-dependent Ca2+ release pathway. To demonstrate the influence of CIB1 on the cytosolic Ca2+ concentration, we used sweet and umami compounds as well as other InsP3-generating ligands in FURA-2-based Ca2+ assays in wild-type HEK293 cells and HEK293 cells expressing functional human sweet and umami taste receptor dimers. Stable and transient depletion of CIB1 by short-hairpin RNA increased the Ca2+ response of HEK293 cells to the InsP3-generating ligands ATP, UTP and carbachol. Over-expression of CIB1 had the opposite effect as shown for the sweet ligand saccharin, the umami receptor ligand monosodium glutamate and UTP. The CIB1 effect was dependent on the thapsigargin-sensitive Ca2+ store of the endoplasmic reticulum (ER) and independent of extracellular Ca2+. The function of CIB1 on InsP3-evoked Ca2+ release from the ER is most likely mediated by its interaction with the InsP3 receptor. Thus, CIB1 seems to be an inhibitor of InsP3-dependent Ca2+ release in vivo.
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sweet taste receptor interacting protein cib1 is a general inhibitor of insp3 dependent ca2 release in vivo
Journal of Neurochemistry, 2008Co-Authors: Jan K Hennigs, Nicole Burhenne, Frauke Stähler, Marcel Winnig, Bettina Walter, Wolfgang Meyerhof, Hartwig SchmaleAbstract:In a search for sweet taste receptor interacting proteins, we have identified the calcium- and integrin-binding protein 1 (CIB1) as specific binding partner of the intracellular carboxyterminal domain of the rat sweet taste receptor subunit Tas1r2. In heterologous human embryonic kidney 293 (HEK293) cells, the G protein chimeras Gα16gust44 and Gα15i3 link the sweet taste receptor dimer TAS1R2/TAS1R3 to an inositol 1,4,5-trisphosphate (InsP3)-dependent Ca2+ release pathway. To demonstrate the influence of CIB1 on the cytosolic Ca2+ concentration, we used sweet and umami compounds as well as other InsP3-generating ligands in FURA-2-based Ca2+ assays in wild-type HEK293 cells and HEK293 cells expressing functional human sweet and umami taste receptor dimers. Stable and transient depletion of CIB1 by short-hairpin RNA increased the Ca2+ response of HEK293 cells to the InsP3-generating ligands ATP, UTP and carbachol. Over-expression of CIB1 had the opposite effect as shown for the sweet ligand saccharin, the umami receptor ligand monosodium glutamate and UTP. The CIB1 effect was dependent on the thapsigargin-sensitive Ca2+ store of the endoplasmic reticulum (ER) and independent of extracellular Ca2+. The function of CIB1 on InsP3-evoked Ca2+ release from the ER is most likely mediated by its interaction with the InsP3 receptor. Thus, CIB1 seems to be an inhibitor of InsP3-dependent Ca2+ release in vivo.
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the binding site for neohesperidin dihydrochalcone at the human sweet taste receptor
BMC Structural Biology, 2007Co-Authors: Marcel Winnig, Bernd Bufe, Jay Patrick Slack, Nicole A Kratochwil, Wolfgang MeyerhofAbstract:Background Differences in sweet taste perception among species depend on structural variations of the sweet taste receptor. The commercially used isovanillyl sweetener neohesperidin dihydrochalcone activates the human but not the rat sweet receptor TAS1R2+TAS1R3. Analysis of interspecies combinations and chimeras of rat and human TAS1R2+TAS1R3 suggested that the heptahelical domain of human TAS1R3 is crucial for the activation of the sweet receptor by neohesperidin dihydrochalcone.
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The binding site for neohesperidin dihydrochalcone at the human sweet taste receptor
BMC Structural Biology, 2007Co-Authors: Marcel Winnig, Bernd Bufe, Jay Patrick Slack, Nicole A Kratochwil, Wolfgang MeyerhofAbstract:Background Differences in sweet taste perception among species depend on structural variations of the sweet taste receptor. The commercially used isovanillyl sweetener neohesperidin dihydrochalcone activates the human but not the rat sweet receptor TAS1R2+TAS1R3. Analysis of interspecies combinations and chimeras of rat and human TAS1R2+TAS1R3 suggested that the heptahelical domain of human TAS1R3 is crucial for the activation of the sweet receptor by neohesperidin dihydrochalcone. Results By mutational analysis combined with functional studies and molecular modeling we identified a set of different amino acid residues within the heptahelical domain of human TAS1R3 that forms the neohesperidin dihydrochalcone binding pocket. Sixteen amino acid residues in the transmembrane domains 2 to 7 and one in the extracellular loop 2 of hTAS1R3 influenced the receptor's response to neohesperidin dihydrochalcone. Some of these seventeen residues are also part of the binding sites for the sweetener cyclamate or the sweet taste inhibitor lactisole. In line with this observation, lactisole inhibited activation of the sweet receptor by neohesperidin dihydrochalcone and cyclamate competitively, whereas receptor activation by aspartame, a sweetener known to bind to the N-terminal domain of TAS1R2, was allosterically inhibited. Seven of the amino acid positions crucial for activation of hTAS1R2+hTAS1R3 by neohesperidin dihydrochalcone are thought to play a role in the binding of allosteric modulators of other class C GPCRs, further supporting our model of the neohesperidin dihydrochalcone pharmacophore. Conclusion From our data we conclude that we identified the neohesperidin dihydrochalcone binding site at the human sweet taste receptor, which overlaps with those for the sweetener cyclamate and the sweet taste inhibitor lactisole. This readily delivers a molecular explanation of our finding that lactisole is a competitive inhibitor of the receptor activation by neohesperidin dihydrochalcone and cyclamate. Some of the amino acid positions crucial for activation of hTAS1R2+hTAS1R3 by neohesperidin dihydrochalcone are involved in the binding of allosteric modulators in other class C GPCRs, suggesting a general role of these amino acid positions in allosterism and pointing to a common architecture of the heptahelical domains of class C GPCRs.
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A TAS1R receptor-based explanation of sweet ‘water-taste’
Nature, 2006Co-Authors: Veronica Galindo-cuspinera, Marcel Winnig, Bernd Bufe, Wolfgang Meyerhof, Paul A. S. BreslinAbstract:Paradoxically, artificial sweeteners such as sodium saccharin and acesulfame-K taken in high concentrations are not sweet: they can even seem bitter. And if the mouth is then rinsed out with water, it takes on a sweet taste. These observations have led to new insights into the action of the TAS1R taste receptor. As well as causing the ‘sweet water’ aftertaste, saccharin at high concentrations masks the effect of other sweeteners tasted at the same time. What emerges at the molecular level is a two-site system. Saccharin and acesulfame-K elicit a perception of sweetness when they bind to a high-affinity binding site; at high concentrations they bind to a second low-affinity inhibitory site. When the sweet taste inhibitors are washed away, the sweet receptor re-activates and the perception of sweetness returns. Sweet inhibitors are used in the food industry to offset the high sweetness that results from replacing fats with sweet carbohydrates in some reduced-fat products: the sweet water taste may be a useful predictor for sweet inhibitor activity. ‘Water-tastes’ are gustatory after-impressions elicited by water following the removal of a chemical solution from the mouth, akin to colour after-images appearing on ‘white’ paper after fixation on coloured images. Unlike colour after-images, gustatory after-effects are poorly understood1. One theory posits that ‘water-tastes’ are adaptation phenomena, in which adaptation to one taste solution causes the water presented subsequently to act as a taste stimulus2,3. An alternative hypothesis is that removal of the stimulus upon rinsing generates a receptor-based, positive, off-response in taste-receptor cells, ultimately inducing a gustatory perception4. Here we show that a sweet ‘water-taste’ is elicited when sweet-taste inhibitors are rinsed away. Responses of cultured cells expressing the human sweetener receptor directly parallel the psychophysical responses—water rinses remove the inhibitor from the heteromeric sweetener receptor TAS1R2–TAS1R3, which activates cells and results in the perception of strong sweetness from pure water. This ‘rebound’ activity occurs when equilibrium forces on the two-state allosteric sweet receptors result in their coordinated shift to the activated state upon being released from inhibition by rinsing5,6,7.
