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1.
Cell Rep ; 27(6): 1650-1656.e4, 2019 May 07.
Artigo em Inglês | MEDLINE | ID: mdl-31067452

RESUMO

The gustatory system plays an important role in sensing appetitive and aversive tastes for evaluating food quality. In mice, taste signals are relayed by multiple brain regions, including the parabrachial nucleus (PBN) of the pons, before reaching the gustatory cortex via the gustatory thalamus. Recent studies show that taste information at the periphery is encoded in a labeled-line manner, such that each taste modality has its own receptors and neuronal pathway. In contrast, the molecular identity of gustatory neurons in the CNS remains unknown. Here, we show that SatB2-expressing neurons in the PBN play a pivotal role in sweet taste transduction. With cell ablation, in vivo calcium imaging, and optogenetics, we reveal that SatB2PBN neurons encode positive valance and selectively transmit sweet taste signals to the gustatory thalamus.

2.
PLoS One ; 14(3): e0213552, 2019.
Artigo em Inglês | MEDLINE | ID: mdl-30883570

RESUMO

Lactisole, an inhibitor of the human sweet taste receptor, has a 2-phenoxypropionic acid skeleton and has been shown to interact with the transmembrane domain of the T1R3 subunit (T1R3-TMD) of the receptor. Another inhibitor, 2,4-DP, which shares the same molecular skeleton as lactisole, was confirmed to be approximately 10-fold more potent in its inhibitory activity than lactisole; however the structural basis of their inhibitory mechanisms against the receptor remains to be elucidated. Crystal structures of the TMD of metabotropic glutamate receptors, which along with T1Rs are categorized as class C G-protein coupled receptors, have recently been reported and made it possible to create an accurate structural model for T1R3-TMD. In this study, the detailed structural mechanism underlying sweet taste inhibition was characterized by comparing the action of lactisole on T1R3-TMD with that of 2,4-DP. We first performed a series of experiments using cultured cells expressing the sweet taste receptor with mutations and examined the interactions with these inhibitors. Based on the results, we next performed docking simulations and then applied molecular dynamics-based energy minimization. Our analyses clearly revealed that the (S)-isomers of both lactisole and 2,4-DP, interacted with the same seven residues in T1R3-TMD and that the inhibitory potencies of those inhibitors were mainly due to stabilizing interactions mediated via their carboxyl groups in the vertical dimension of the ligand pocket of T1R3-TMD. In addition, 2,4-DP engaged in a hydrophobic interaction mediated by its o-Cl group, and this interaction may be chiefly responsible for the higher inhibitory potency of 2,4-DP.

3.
Acta Histochem ; 2018 Nov 22.
Artigo em Inglês | MEDLINE | ID: mdl-30473241

RESUMO

Nasal obstruction causes mouth breathing, and affects the growth and development of craniofacial structures, muscle function in the stomatognathic system, and the taste perceptive system. However, the detailed mechanism underlying the effects of nasal obstruction on taste perception has not been fully elucidated. In this study, we investigated this mechanism using the two-bottle taste preference test, immunohistological analysis, and quantification of the mRNA expression of taste-related molecules in the circumvallate papillae. Neonatal male Wistar rats were divided randomly into control and experimental groups. Rats in the experimental group underwent unilateral nasal obstruction by cauterization of the external nostril at the age of 8 days. Arterial oxygen saturation (SpO2) was recorded in awake rats using collar clip sensors. Taste preference for five basic taste solutions was evaluated. Immunohistochemical analysis and quantitative real-time polymerase chain reaction (RT-PCR) were conducted to evaluate the expressions of taste-related molecules in the taste cells of the circumvallate papillae. Body weights were similar between the two groups throughout the experimental period. The SpO2 in the 7- to 12-week-old rats in the experimental group was significantly lower than that in the age-matched rats in the control group. In the two-bottle taste preference test, the sensitivities to sweet taste decreased in the experimental group. The mRNA expression of T1R2, T1R3, α-gustducin, and PLCß2 was significantly lower in the experimental group than in the control group as determined by quantitative RT-PCR, and the immunohistochemical staining for α-gustducin and PLCß2 was less prominent. These findings suggest that nasal obstruction may affect sweet taste perception via the reduced expression of taste-related molecules in the taste cells in rat circumvallate papillae.

4.
Biosci Biotechnol Biochem ; : 1-8, 2018 Oct 21.
Artigo em Inglês | MEDLINE | ID: mdl-30343635

RESUMO

The epithelial sodium channel (ENaC) plays a pivotal role in sodium homeostasis, and the development of drugs that modulate ENaC activity is of great potential therapeutic relevance. We screened 6100 chemicals for their ability to activate sodium permeability of ENaC. We used a two-step strategy: a high throughput cell-based assay and an electrophysiological assay. Five compounds were identified showing common structural features including an indole or benzothiophene ring. ENaC consists of three subunits: α, ß, and γ. Changing the heteromeric combination of human and mouse ENaC αßγ subunits, we found that all five compounds activated the human ß subunit but not the mouse subunit. However, four of them exhibited lower activity when the human γ subunit was substituted by the mouse γ subunit. Our findings provide a structural basis for designing human ENaC activity modulators. Abbreviations: ENaC: Epithelial sodium channel; ΔRFU: delta relative fluorescence units; EC50: Half-maximal effective concentration; Emax: maximum effect value.

5.
Exp Gerontol ; 113: 64-73, 2018 Nov.
Artigo em Inglês | MEDLINE | ID: mdl-30243894

RESUMO

To investigate aging-dependent changes in taste sensitivities, we performed behavioral tests regarding taste sensitivity among young and old SAMP1 mice. In this senescence-accelerated mice model, dramatic changes in taste sensitivities were observed at least 70 weeks old. As for in a brief access test, old mice showed significantly increased taste sensitivity to bitter, salty, sweet, and umami tastes. On the other hand, in a two-bottle test, avoidance of bitter and salty tastes increased, while preference for umami decreased with aging. To investigate the participation of peripheral taste detection systems in the observed changes, we analyzed both the expression of representative taste-related molecules and also turnover rates of taste bud cells. The mRNA expressions of the bitter taste receptor Tas2r105 and its coupled G protein gustducin were significantly decreased with aging. However, the majority of molecules tested did not show significant expression changes. In addition, no significant differences in the turnover rates of taste bud cells were observed between the two age groups. These results suggest that the changes in taste sensitivity of SAMP1 mice due to aging are caused by factors other than the deterioration of taste detection systems in the oral cavity.

6.
Sci Rep ; 8(1): 11796, 2018 Aug 07.
Artigo em Inglês | MEDLINE | ID: mdl-30087430

RESUMO

Taste is a vital sensation for vertebrates, enabling the detection of nutritionally important substances or potential toxins. A heteromeric complex of two class C GPCRs, T1R1 and T1R3, was identified as the umami (savory) taste receptor. Amino acids and 5'-ribonucleotides are well known to be natural ligands for human T1R1/T1R3. In this study, we reveal that methional, which is a familiar flavor component in foods, is an allosteric modulator of T1R1/T1R3. Receptor expression experiments showed that methional served as a positive allosteric modulator (PAM) of human T1R1/T1R3 and functioned as a negative allosteric modulator (NAM) of mouse T1R1/T1R3. Although amino acids and 5'-ribonucleotides bound to the extracellular domain of T1R1, the use of interspecies chimeric receptors demonstrated that methional interacted with the transmembrane domain of T1R1. Site-directed mutagenesis and molecular modeling showed that methional could potentially bind at two distinct sites in the transmembrane domain of T1R1 and that the amino acid residues in the bottom of the allosteric pocket engendered the switch between the PAM and NAM modes, which could contribute to switching the binding position of methional. These results may be applicable for elucidating the molecular mechanisms underlying ligand recognition by other class C GPCRs.

7.
Biochem Biophys Res Commun ; 503(4): 2301-2305, 2018 Sep 18.
Artigo em Inglês | MEDLINE | ID: mdl-29964016

RESUMO

We attempted to identify mouse bitter taste receptors, Tas2rs, that respond to tea catechins. Among representative tea catechins, avoidance behavior of mice to (-)-epicatechin gallate (ECg) was the strongest, followed by (-)-epigallocatechin gallate (EGCg). Therefore, we measured ECg response using Tas2rs-expressing cells. Among the 35 members of Tas2r family, Tas2r108, 110, 113, 125, and 144 responded to ECg. Among these receptors, Tas2r113 and 125 also responded to EGCg. Because the response profiles of Tas2r125 were consistent with the results of the behavior assays, it was considered that Tas2r125 functions as the main receptor for detecting bitterness of tea catechins in the oral cavity. To determine the involvement of Tas2rs in the physiological action of catechins, mRNA expression of 5 Tas2rs was investigated in various tissues. Because mRNA expression of Tas2r108 was observed in some tissues including the gastrointestinal tract, it may be envisaged that Tas2r108 plays a part in exerting the physiological action of ECg. Tas2r125 expression was not observed in any of the tested tissues except the circumvallate papillae. Therefore, Tas2r125 was considered to mainly function in the events of catechin reception in the oral cavity.

8.
Biosci Biotechnol Biochem ; 82(4): 573-583, 2018 Apr.
Artigo em Inglês | MEDLINE | ID: mdl-29316856

RESUMO

In Japan, where a super-aging society is realized, we are most concerned about healthy longevity, which would ascertain the wellness of people by improving their quality of life (QOL). In 2014, the Cabinet Office proposed a strategic innovation promotion programme, launching a national project for the development of the agricultural-forestry-fisheries food products with new functionalities for the next generation. In addition to focusing on a conventional prevention of lifestyle-associated metabolic syndromes, the project targets the scientific evidence of the activation of brain cognitive ability and the improvement of bodily locomotive function. The project also involves the analysis of the foods-sports interrelation of chronic importance, and the development of devices for the verification of QOL-associated maintenance of homeostasis. In this review, we provide an overview of these studies, with special reference to cognition as a case of the gut-brain axis which the author is particularly interested in.


Assuntos
Cognição/fisiologia , Alimento Funcional , Locomoção/fisiologia , Envelhecimento , Animais , Encéfalo/fisiologia , Metabolismo Energético , Exercício , Homeostase , Humanos , Intestinos/fisiologia , Japão , Estilo de Vida , Doenças Metabólicas/fisiopatologia , Doenças Metabólicas/prevenção & controle , Camundongos , Desenvolvimento de Programas , Qualidade de Vida
9.
Neuroscience ; 358: 249-260, 2017 09 01.
Artigo em Inglês | MEDLINE | ID: mdl-28687314

RESUMO

Previous studies have shown that aging modifies taste sensitivity. However, the factors affecting the changes in taste sensitivity remain unclear. To investigate the cause of the age-related changes in taste sensitivity, we compared the peripheral taste detection systems in young and old mice. First, we examined whether taste sensitivity varied according to age using behavioral assays. We confirmed that the taste sensitivities to salty and bitter tastes decreased with aging. In other assays, the gustatory nerve responses to salty and sweet tastes increased significantly with aging, while those to bitter taste did not change. Thus, the profile of the gustatory nerve responses was inconsistent with the profile of the behavioral responses. Next, we evaluated the expressions of taste-related molecules in the taste buds. Although no apparent differences in the expressions of representative taste receptors were observed between the two age groups, the mRNA expressions of signaling effectors were slightly, but significantly, decreased in old mice. No significant differences in the turnover rates of taste bud cells were observed between the two age groups. Thus, we did not observe any large decreases in the expressions of taste-related molecules and turnover rates of taste bud cells with aging. Based on these findings, we conclude that changes in taste sensitivity with aging were not caused by aging-related degradation of peripheral taste organs. Meanwhile, the concentrations of several serum components that modify taste responses changed with age. Thus, taste signal-modifying factors such as serum components may have a contributing role in aging-related changes in taste sensitivity.


Assuntos
Vias Aferentes/fisiologia , Envelhecimento/fisiologia , Papilas Gustativas/fisiologia , Percepção Gustatória/fisiologia , Paladar/fisiologia , Animais , Animais Recém-Nascidos , Canais de Cálcio/genética , Canais de Cálcio/metabolismo , Nervo da Corda do Tímpano/fisiologia , Relação Dose-Resposta a Droga , Regulação da Expressão Gênica no Desenvolvimento , Canal de Potássio KCNQ1/genética , Canal de Potássio KCNQ1/metabolismo , Masculino , Camundongos , Motivação , Fosfolipase C beta/genética , Fosfolipase C beta/metabolismo , Receptores de Superfície Celular/genética , Receptores de Superfície Celular/metabolismo , Receptores Acoplados a Proteínas-G/genética , Receptores Acoplados a Proteínas-G/metabolismo , Transdução de Sinais/efeitos dos fármacos , Transdução de Sinais/genética , Estimulação Química , Transducina/genética , Transducina/metabolismo
10.
Neurosci Lett ; 648: 53-58, 2017 05 01.
Artigo em Inglês | MEDLINE | ID: mdl-28359935

RESUMO

The connections between taste receptor cells (TRCs) and innervating gustatory neurons are formed in a mutually dependent manner during development. To investigate whether a change in the ratio of cell types that compose taste buds influences the number of innervating gustatory neurons, we analyzed the proportion of gustatory neurons that transmit sour taste signals in adult Skn-1a-/- mice in which the number of sour TRCs is greatly increased. We generated polycystic kidney disease 1 like 3-wheat germ agglutinin (pkd1l3-WGA)/Skn-1a+/+ and pkd1l3-WGA/Skn-1a-/- mice by crossing Skn-1a-/- mice and pkd1l3-WGA transgenic mice, in which neural pathways of sour taste signals can be visualized. The number of WGA-positive cells in the circumvallate papillae is 3-fold higher in taste buds of pkd1l3-WGA/Skn-1a-/- mice relative to pkd1l3-WGA/Skn-1a+/+ mice. Intriguingly, the ratio of WGA-positive neurons to P2X2-expressing gustatory neurons in nodose/petrosal ganglia was similar between pkd1l3-WGA/Skn-1a+/+ and pkd1l3-WGA/Skn-1a-/- mice. In conclusion, an alteration in the ratio of cell types that compose taste buds does not influence the number of gustatory neurons that transmit sour taste signals.


Assuntos
Neurônios/citologia , Fatores de Transcrição de Octâmero/fisiologia , Papilas Gustativas/citologia , Paladar , Animais , Camundongos , Camundongos Knockout , Neurônios/metabolismo , Fatores de Transcrição de Octâmero/genética , Transdução de Sinais , Papilas Gustativas/metabolismo , Aglutininas do Germe de Trigo/metabolismo
11.
Biophys Physicobiol ; 13: 165-171, 2016.
Artigo em Inglês | MEDLINE | ID: mdl-27924271

RESUMO

In mammals, bitter taste is mediated by TAS2Rs, which belong to the family of seven transmembrane G protein-coupled receptors. Since TAS2Rs are directly involved in the interaction between mammals and their dietary sources, it is likely that these genes evolved to reflect species-specific diets during mammalian evolution. Here, we analyzed the amino acids responsible for the difference in sensitivities of TAS2R16s of various primates using a cultured cell expression system. We found that the sensitivity of TAS2R16 varied due to several amino acid residues. Mutation of amino acid residues at E86T, L247M, and V260F in human and langur TAS2R16 for mimicking the macaque TAS2R16 decreased the sensitivity of the receptor in an additive manner, which suggests its contribution to the potency of salicin, possibly via direct interaction. However, mutation of amino acid residues 125 and 133 in human TAS2R16, which are situated in helix 4, to the macaque sequence increased the sensitivity of the receptor. These results suggest the possibility that bitter taste sensitivities evolved independently by replacing specific amino acid residues of TAS2Rs in different primate species to adapt to species-specific food.

12.
BMC Evol Biol ; 16(1): 208, 2016 Oct 12.
Artigo em Inglês | MEDLINE | ID: mdl-27733116

RESUMO

BACKGROUND: New World monkeys (NWMs) are unique in that they exhibit remarkable interspecific variation in color vision and feeding behavior, making them an excellent model for studying sensory ecology. However, it is largely unknown whether non-visual senses co-vary with feeding ecology, especially gustation, which is expected to be indispensable in food selection. Bitter taste, which is mediated by bitter taste receptors (TAS2Rs) in the tongue, helps organisms avoid ingesting potentially toxic substances in food. In this study, we compared the ligand sensitivities of the TAS2Rs of five species of NWMs by heterologous expression in HEK293T cells and calcium imaging. RESULTS: We found that TAS2R1 and TAS2R4 orthologs differ in sensitivity among the NWM species for colchicine and camphor, respectively. We then reconstructed the ancestral receptors of NWM TAS2R1 and TAS2R4, measured the evolutionary shift in ligand sensitivity, and identified the amino acid replacement at residue 62 as responsible for the high sensitivity of marmoset TAS2R4 to colchicine. CONCLUSIONS: Our results provide a basis for understanding the differences in feeding ecology among NWMs with respect to bitter taste.


Assuntos
Platirrinos/fisiologia , Receptores Acoplados a Proteínas-G/fisiologia , Paladar , Animais , Evolução Molecular , Células HEK293 , Humanos , Filogenia , Platirrinos/classificação , Polimorfismo de Nucleotídeo Único , Receptores Acoplados a Proteínas-G/química , Especificidade da Espécie
13.
Neurosci Lett ; 617: 46-51, 2016 Mar 23.
Artigo em Inglês | MEDLINE | ID: mdl-26854841

RESUMO

Taste cells release neurotransmitters to gustatory neurons to transmit chemical information they received. Sweet, umami, and bitter taste cells use ATP as a neurotransmitter. However, ATP release from sour taste cells has not been observed so far. Instead, they release serotonin when they are activated by sour/acid stimuli. Thus it is still controversial whether sour taste cells use ATP, serotonin, or both. By reverse transcription-polymerase chain reaction and subsequent in situ hybridization (ISH) analyses, we revealed that of 14 serotonin receptor genes only 5-HT3A and 5-HT3B showed significant/clear signals in a subset of neurons of cranial sensory ganglia in which gustatory neurons reside. Double-fluorescent labeling analyses of ISH for serotonin receptor genes with wheat germ agglutinin (WGA) in cranial sensory ganglia of pkd1l3-WGA mice whose sour neural pathway is visualized by the distribution of WGA originating from sour taste cells in the posterior region of the tongue revealed that WGA-positive cranial sensory neurons rarely express either of serotonin receptor gene. These results suggest that serotonin receptors expressed in cranial sensory neurons do not play any role as neurotransmitter receptor from sour taste cells.


Assuntos
Gânglios Sensitivos/metabolismo , Receptores de Serotonina/metabolismo , Crânio/inervação , Animais , Expressão Gênica , Masculino , Camundongos Endogâmicos C57BL , Camundongos Transgênicos , Receptores Purinérgicos P2X2/genética , Receptores Purinérgicos P2X2/metabolismo , Receptores de Serotonina/genética , Receptores 5-HT3 de Serotonina/genética , Receptores 5-HT3 de Serotonina/metabolismo , Células Receptoras Sensoriais/metabolismo , Paladar
14.
J Histochem Cytochem ; 64(3): 205-15, 2016 03.
Artigo em Inglês | MEDLINE | ID: mdl-26718243

RESUMO

Taste signals are received by taste buds. To better understand the taste reception system, expression patterns of taste-related molecules are determined by in situ hybridization (ISH) analyses at the histological level. Nevertheless, even though ISH is essential for determining mRNA expression, few taste bud markers can be applied together with ISH. Ulex europaeus agglutinin-1 (UEA-1) appears to be a reliable murine taste bud marker based on immunohistochemistry (IHC) analyses. However, there is no evidence as to whether UEA-1 can be used for ISH. Thus, the present study evaluated UEA-1 using various histochemical methods, especially ISH. When lectin staining was performed after ISH procedures, UEA-1 clearly labeled taste cellular membranes and distinctly indicated boundaries between taste buds and the surrounding epithelial cells. Additionally, UEA-1 was determined as a taste bud marker not only when used in single-colored ISH but also when employed with double-labeled ISH or during simultaneous detection using IHC and ISH methods. These results suggest that UEA-1 is a useful marker when conducting analyses based on ISH methods. To clarify UEA-1 staining details, multi-fluorescent IHC (together with UEA-1 staining) was examined, resulting in more than 99% of cells being labeled by UEA-1 and overlapping with KCNQ1-expressing cells.


Assuntos
Hibridização In Situ , Lectinas de Plantas/análise , Papilas Gustativas/química , Animais , Biomarcadores/análise , Imuno-Histoquímica , Masculino , Camundongos , Camundongos Endogâmicos C57BL , Papilas Gustativas/citologia
15.
Sci Rep ; 5: 12947, 2015 Aug 11.
Artigo em Inglês | MEDLINE | ID: mdl-26263392

RESUMO

Neoculin (NCL) is a heterodimeric protein isolated from the edible fruit of Curculigo latifolia. It exerts a taste-modifying activity by converting sourness to sweetness. We previously demonstrated that NCL changes its action on the human sweet receptor hT1R2-hT1R3 from antagonism to agonism as the pH changes from neutral to acidic values, and that the histidine residues of NCL molecule play critical roles in this pH-dependent functional change. Here, we comprehensively screened key amino acid residues of NCL using nuclear magnetic resonance (NMR) spectroscopy and alanine scanning mutagenesis. We found that the mutations of Arg48, Tyr65, Val72 and Phe94 of NCL basic subunit increased or decreased both the antagonist and agonist activities. The mutations had only a slight effect on the pH-dependent functional change. These residues should determine the affinity of NCL for the receptor regardless of pH. Their locations were separated from the histidine residues responsible for the pH-dependent functional change in the tertiary structure. From these results, we concluded that NCL interacts with hT1R2-hT1R3 through a pH-independent affinity interface including the four residues and a pH-dependent activation interface including the histidine residues. Thus, the receptor activation is induced by local structural changes in the pH-dependent interface.


Assuntos
Proteínas de Plantas/metabolismo , Receptores Acoplados a Proteínas-G/metabolismo , Células HEK293 , Humanos , Concentração de Íons de Hidrogênio , Modelos Moleculares , Mutagênese , Ressonância Magnética Nuclear Biomolecular , Proteínas de Plantas/química , Proteínas de Plantas/genética , Ligação Proteica
16.
PLoS One ; 10(7): e0132016, 2015.
Artigo em Inglês | MEDLINE | ID: mdl-26201026

RESUMO

Bitter taste receptors (TAS2R proteins) allow mammals to detect and avoid ingestion of toxins in food. Thus, TAS2Rs play an important role in food choice and are subject to complex natural selection pressures. In our previous study, we examined nucleotide variation in TAS2R38, a gene expressing bitter taste receptor for phenylthiocarbamide (PTC), in 333 Japanese macaques (Macaca fuscata) from 9 local populations in Japan. We identified a PTC "non-taster" TAS2R38 allele in Japanese macaques that was caused by a loss of the start codon. This PTC non-taster allele was only found in a limited local population (the Kii area), at a frequency of 29%. In this study, we confirmed that this allele was present in only the Kii population by analyzing an additional 264 individuals from eight new populations. Using cellular and behavioral experiments, we found that this allele lost its receptor function for perceiving PTC. The nucleotide sequences of the allele including flanking regions (of about 10 kb) from 23 chromosomes were identical, suggesting that a non-taster allele arose and expanded in the Kii population during the last 13,000 years. Genetic analyses of non-coding regions in Kii individuals and neighboring populations indicated that the high allele frequency in the Kii population could not be explained by demographic history, suggesting that positive selection resulted in a rapid increase in PTC non-tasters in the Kii population. The loss-of-function that occurred at the TAS2R38 locus presumably provided a fitness advantage to Japanese macaques in the Kii population. Because TAS2R38 ligands are often found in plants, this functional change in fitness is perhaps related to feeding habit specificity. These findings should provide valuable insights for elucidating adaptive evolutionary changes with respect to various environments in wild mammals.


Assuntos
Códon de Iniciação , Macaca/genética , Polimorfismo de Nucleotídeo Único , Receptores Acoplados a Proteínas-G/genética , Paladar/genética , Animais , Cromossomos de Mamíferos , Evolução Molecular , Variação Genética , Japão , Macaca/metabolismo , Feniltioureia/farmacologia , Seleção Genética , Paladar/efeitos dos fármacos
17.
PLoS One ; 10(4): e0124030, 2015.
Artigo em Inglês | MEDLINE | ID: mdl-25853419

RESUMO

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.


Assuntos
Receptores Acoplados a Proteínas-G/metabolismo , Sacarose/farmacologia , Percepção Gustatória/fisiologia , Regulação Alostérica , Derivados de Benzeno/farmacologia , Ciclamatos/farmacologia , Dipeptídeos/farmacologia , Interações de Medicamentos , Células HEK293 , Humanos , Ligação Proteica , Isoformas de Proteínas/agonistas , Isoformas de Proteínas/antagonistas & inibidores , Isoformas de Proteínas/metabolismo , Receptores Acoplados a Proteínas-G/agonistas , Receptores Acoplados a Proteínas-G/antagonistas & inibidores , Glutamato de Sódio/farmacologia , Sacarose/agonistas , Sacarose/antagonistas & inibidores , Edulcorantes/farmacologia , Paladar/fisiologia , Tiazinas/farmacologia
18.
J Neurochem ; 133(6): 806-14, 2015 Jun.
Artigo em Inglês | MEDLINE | ID: mdl-25692331

RESUMO

Taste information from type III taste cells to gustatory neurons is thought to be transmitted via synapses. However, the molecular mechanisms underlying taste transduction through this pathway have not been fully elucidated. In this study, to identify molecules that participate in synaptic taste transduction, we investigated whether complexins (Cplxs), which play roles in regulating membrane fusion in synaptic vesicle exocytosis, were expressed in taste bud cells. Among four Cplx isoforms, strong expression of Cplx2 mRNA was detected in type III taste cells. To investigate the function of CPLX2 in taste transduction, we observed taste responses in CPLX2-knockout mice. When assessed with electrophysiological and behavioral assays, taste responses to some sour stimuli in CPLX2-knockout mice were significantly lower than those in wild-type mice. These results suggested that CPLX2 participated in synaptic taste transduction from type III taste cells to gustatory neurons. A part of taste information is thought to be transmitted via synapses. However, the molecular mechanisms have not been fully elucidated. To identify molecules that participate in synaptic taste transduction, we investigated complexins (Cplxs) expression in taste bud cells. Strong expression of Cplx2 mRNA was detected in taste bud cells. Furthermore, taste responses to some sour stimuli in CPLX2- knockout mice were significantly lower than those in wild-type mice. These suggested that CPLX2 participated in synaptic taste transduction.


Assuntos
Proteínas Adaptadoras de Transporte Vesicular/metabolismo , Proteínas do Tecido Nervoso/metabolismo , Papilas Gustativas/metabolismo , Paladar/fisiologia , Animais , Exocitose/fisiologia , Hibridização In Situ , Mecanotransdução Celular , Camundongos , Camundongos Endogâmicos C57BL , Camundongos Knockout , Reação em Cadeia da Polimerase Via Transcriptase Reversa , Sinapses/metabolismo
19.
Biochem Biophys Res Commun ; 456(2): 586-90, 2015 Jan 09.
Artigo em Inglês | MEDLINE | ID: mdl-25490385

RESUMO

Taste-taste interactions often showed in human psychophysical studies. Considering that each tastant in foodstuffs individually stimulates its responsible gustatory systems to elicit relevant taste modalities, taste-taste interaction should be performed in taste receptor cell-based assay. While umami substances have been proposed to suppress the bitterness of various chemicals in human sensory evaluation, the bitter-umami interaction has not been explored in bitter taste receptors, TAS2Rs. We investigated umami-bitter taste interactions by presenting umami peptides with bitter substance (salicin) on Ca(2+)-flux signaling assay using hTAS2R16-expressing cells. Five representative umami peptides (Glu-Asp, Glu-Glu, Glu-Ser, Asp-Glu-Ser, and Glu-Gly-Ser) derived from soybean markedly attenuated the salicin-induced intracellular calcium influx in a time-dependent manner, respectively, while Gly-Gly, a tasteless peptide did not. The efficacies of Glu-Glu suppressing salicin-induced activation of hTAS2R16 were higher than that of probenecid, a specific antagonist of hTAS2R16. According to Ca(2+)-flux signaling assay using the mixtures of salicin and umami peptides, all five umami peptides suppressed salicin-induced intracellular calcium influx in a noncompetitive manner. These results may provide evidence that umami peptides suppress bitter taste via bitter taste receptor(s). This is the first report which defines the interaction between bitter and umami taste in taste receptor level.


Assuntos
Oligopeptídeos/farmacologia , Receptores Acoplados a Proteínas-G/antagonistas & inibidores , Paladar/efeitos dos fármacos , Álcoois Benzílicos/farmacologia , Cálcio/farmacologia , Linhagem Celular , Dipeptídeos/farmacologia , Glucosídeos/farmacologia , Humanos , Receptores Acoplados a Proteínas-G/metabolismo
20.
Science ; 345(6199): 929-33, 2014 Aug 22.
Artigo em Inglês | MEDLINE | ID: mdl-25146290

RESUMO

Sensory systems define an animal's capacity for perception and can evolve to promote survival in new environmental niches. We have uncovered a noncanonical mechanism for sweet taste perception that evolved in hummingbirds since their divergence from insectivorous swifts, their closest relatives. We observed the widespread absence in birds of an essential subunit (T1R2) of the only known vertebrate sweet receptor, raising questions about how specialized nectar feeders such as hummingbirds sense sugars. Receptor expression studies revealed that the ancestral umami receptor (the T1R1-T1R3 heterodimer) was repurposed in hummingbirds to function as a carbohydrate receptor. Furthermore, the molecular recognition properties of T1R1-T1R3 guided taste behavior in captive and wild hummingbirds. We propose that changing taste receptor function enabled hummingbirds to perceive and use nectar, facilitating the massive radiation of hummingbird species.


Assuntos
Evolução Molecular , Receptores Acoplados a Proteínas-G/genética , Percepção Gustatória/fisiologia , Paladar/fisiologia , Sequência de Aminoácidos , Animais , Camundongos , Dados de Sequência Molecular , Néctar de Plantas , Estrutura Terciária de Proteína , Receptores Acoplados a Proteínas-G/química , Receptores Acoplados a Proteínas-G/classificação , Percepção Gustatória/genética
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