Human Bitter Taste Receptors hTAS2R8 and hTAS2R39 with Differential Functions to Recognize Bitter Peptides

The strong bitter peptide, Phe-Phe-Pro-Arg, activated cultured cells expressing either of the known human bitter taste receptors, hTAS2R8 and hTAS2R39. The partial structure of Pro-Arg activated hTAS2R39, but did not activate hTAS2R8. These receptors may not indiscriminately recognize bitter peptides, but have a differential function in their recognition.     

苦味受体与甜味、鲜味受体具有不同的进化途径

通过生物信息学和系统发育学分析,研究了苦味受体和甜味／鲜味受体的进化途径。结果显示,苦味受体和甜味／鲜味受体在进化上具有远相关,并且具有不同的进化途径,提示这可能是导致这些受体具有不同功能,传导不同味觉的原因。     

A New World Monkey Resembles Human in Bitter Taste Receptor Evolution and Function via a Single Parallel Amino Acid Substitution

Bitter taste receptors serve as a vital component in the defense system against toxin intake by animals, and the family of genes encoding these receptors has been demonstrated, usually by family size variance, to correlate with dietary preference. However, few systematic studies of specific Tas2R to unveil their functional evolution have been conducted. Here, we surveyed Tas2R16 across all major clades of primates and reported a rare case of a convergent change to increase sensitivity to β-glucopyranosides in human and a New World monkey, the white-faced saki. Combining analyses at multiple levels, we demonstrate that a parallel amino acid substitution (K172N) shared by these two species is responsible for this functional convergence of Tas2R16. Considering the specialized feeding preference of the white-faced saki, the K172N change likely played an important adaptive role in its early evolution to avoid potentially toxic cyanogenic glycosides, as suggested for the human TAS2R16 gene.     

Local Adaptation of Bitter Taste and Ecological Speciation in a Wild Mammal

Sensory systems are attractive evolutionary models to address how organisms adapt to local environments that can cause ecological speciation. However, tests of these evolutionary models have focused on visual, auditory, and olfactory senses. Here, we show local adaptation of bitter taste receptor genes in two neighboring populations of a wild mammal—the blind mole rat Spalax galili—that show ecological speciation in divergent soil environments. We found that basalt-type bitter receptors showed higher response intensity and sensitivity compared with chalk-type ones using both genetic and cell-based functional analyses. Such functional changes could help animals adapted to basalt soil select plants with less bitterness from diverse local foods, whereas a weaker reception to bitter taste may allow consumption of a greater range of plants for animals inhabiting chalk soil with a scarcity of food supply. Our study shows divergent selection on food resources through local adaptation of bitter receptors, and suggests that taste plays an important yet underappreciated role in speciation.     

Top-Down Control of Sweet and Bitter Taste in the Mammalian Brain

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黄芩苷通过苦味受体促进哮喘小鼠呼吸道炎性细胞凋亡

全球哮喘患者有3亿多人。目前,约有一半患者的病情不能较好地用现有药物来控制。因此,寻找新的更有效的治疗哮喘病的药物是非常必要的。最近的研究发现,苦味受体(bitter taste receptors,Tas2rs)在呼吸系统中表达,且苦味剂对哮喘有治疗潜力,苦味受体可能成为哮喘治疗的新靶点。为此,本文研究了苦味化合物黄芩苷(baicalin,BA)对哮喘的干预作用,分析黄芩苷对哮喘小鼠呼吸道炎性细胞凋亡的干预作用及其与苦味信号转导的关系。选雄性BALB/c小鼠,随机分为对照组(CK组)、腹腔注射致敏加雾化吸入卵清蛋白(ovalbumin,OVA)激发制成的哮喘模型组(OVA组)和黄芩苷灌胃干预哮喘组(OVA+BA组)。结果发现,OVA组小鼠肺泡灌洗液中白细胞总数和分类细胞计数显著增加,黄芩苷干预组白细胞数量显著减少;HE染色后,OVA组小鼠肺组织中可见炎性细胞浸润、肺泡隔增厚和肺泡囊缩小,上述症状在OVA+BA组小鼠肺部明显减轻;实时荧光定量RT-PCR检测发现,肺组织中黏蛋白Muc5ac表达水平在OVA组明显增高(P <0.05),黄芩苷干预组显著低于OVA组(P <0.05)。OVA致敏哮喘小鼠呼吸道中Tas2r108、Tas2r126、Tas2r135和Tas2r143及其下游信号转导分子α-gust和Trpm5下调表达(P <0.05),促凋亡因子P53、Bax和胱天蛋白酶(caspase,Casp)Casp3转录抑制,凋亡抑制基因Bcl2上调表达,胱天蛋白酶3活性显著降低(P <0.05);黄芩苷干预组4个Tas2rs及苦味信号转导分子转录上调(P <0.05),促凋亡基因P53、Bax和Casp3转录上调,Bcl2转录抑制,胱天蛋白酶3活性显著高于OVA组(P <0.05)。结果表明,黄芩苷干预可激活哮喘鼠呼吸道苦味信号转导通路,并使呼吸道炎性细胞减少、黏蛋白分泌减少。即苦味物质黄芩苷可能作为一种苦味受体激动剂,通过激活苦味信号转导系统促进呼吸道炎性细胞凋亡,减轻肺部炎症和损伤,缓解哮喘发作。     

呼吸道苦味信号转导抑制与小鼠哮喘相关

鉴于哮喘病患病人数众多,约有一半的病人病情得不到较好的控制,急需新的治疗方法和药物.最近研究发现,苦味受体(bitter taste receptors,T2 Rs)在多个组织中表达,且苦味剂对哮喘有治疗潜力,T2Rs有可能成为哮喘治疗的新靶点.本文选C57BL/6小鼠随机分为对照组、二氧化硫(sulfur dioxi...     

Synergism,Bifunctionality, and the Evolution of a Gradual Sensory Trade-off in Hummingbird Taste Receptors

Sensory receptor evolution can imply trade-offs between ligands, but the extent to which such trade-offs occur and the underlying processes shaping their evolution is not well understood. For example, hummingbirds have repurposed their ancestral savory receptor (T1R1–T1R3) to detect sugars, but the impact of this sensory shift on amino acid perception is unclear. Here, we use functional and behavioral approaches to show that the hummingbird T1R1–T1R3 acts as a bifunctional receptor responsive to both sugars and amino acids. Our comparative analyses reveal substantial functional diversity across the hummingbird radiation and suggest an evolutionary timeline for T1R1–T1R3 retuning. Finally, we identify a novel form of synergism between sugars and amino acids in vertebrate taste receptors. This work uncovers an unexplored axis of sensory diversity, suggesting new ways in which nectar chemistry and pollinator preferences can coevolve.     

Functional Diversity and Evolution of Bitter Taste Receptors in Egg-Laying Mammals

Egg-laying mammals (monotremes) are a sister clade of therians (placental mammals and marsupials) and a key clade to understand mammalian evolution. They are classified into platypus and echidna, which exhibit distinct ecological features such as habitats and diet. Chemosensory genes, which encode sensory receptors for taste and smell, are believed to adapt to the individual habitats and diet of each mammal. In this study, we focused on the molecular evolution of bitter taste receptors (TAS2Rs) in monotremes. The sense of bitter taste is important to detect potentially harmful substances. We comprehensively surveyed agonists of all TAS2Rs in platypus (Ornithorhynchus anatinus) and short-beaked echidna (Tachyglossus aculeatus) and compared their functions with orthologous TAS2Rs of marsupial and placental mammals (i.e., therians). As results, the agonist screening revealed that the deorphanized monotreme receptors were functionally diversified. Platypus TAS2Rs had broader receptive ranges of agonists than those of echidna TAS2Rs. While platypus consumes a variety of aquatic invertebrates, echidna mainly consumes subterranean social insects (ants and termites) as well as other invertebrates. This result indicates that receptive ranges of TAS2Rs could be associated with feeding habits in monotremes. Furthermore, some orthologous receptors in monotremes and therians responded to β-glucosides, which are feeding deterrents in plants and insects. These results suggest that the ability to detect β-glucosides and other substances might be shared and ancestral among mammals.     

Evaluation of the Suppressive Effect on Bitter Taste of Gluconate

Improved conditions for the production and characterization of 1-arylpropane-1, 2-diols and related compounds were developed. Experimental conditions providing highly enhanced activity of pyruvate decarboxylase in bakers’ yeast in the presence of pyruvate, thiamine pyrophosphate, and magnesium(II) salt were applied to the preparation of (R)-1-hydroxy-1-phenyl-2-propanone from benzaldehyde. Subsequent reduction with bakers’ yeast efficiently afforded 1-phenyl-1, 2-propanediol (35%). The composition of its stereoisomers was precisely determined, and the major (1R, 2S)-isomer (89% of the total mixture) could be isolated by recrystallizing the corresponding benzoate. The analytical method for identifying the stereoisomeric composition was also effective for the determination of 5-phenyl-4-pentene-2, 3-diol, the biotransformation product from cinnamaldehyde, the vinylogous substrate of benzaldehyde. Furthermore, the structural characterization of 1-(2-furyl)propane-1, 2-diol, which was obtained from furfural (28%) by the action of brewers’ yeast Saccharomyces cerevisiae (carlsbergensis), is described. The major (1S, 2S)-isomer could be isolated by recrystallizing the crude product.     

Computational Studies of Ligand-Receptor Interactions in Bitter Taste Receptors

Phenylthiocarbamide tastes intensely bitter to some individuals, but others find it completely tasteless. Recently, it was suggested that phenylthiocarbamide elicits bitter taste by interacting with a human G protein-coupled receptor (hTAS2R38) encoded by the PTC gene. The phenylthiocarbamide nontaster trait was linked to three single nucleotide polymorphisms occurring in the PTC gene. Using the crystal structure of bovine rhodopsin as template, we generated the 3D structure of hTAS2R38 bitter taste receptor. We were able to map on the receptor structure the amino acids affected by the genetic polymorphisms and to propose molecular functions for two of them that explained the emergence of the nontaster trait. We used molecular docking simulations to find that phenylthiocarbamide exhibited a higher affinity for the target receptor than the structurally similar molecule 6-n-propylthiouracil, in line with recent experimental studies. A 3D model was constructed for the hTAS2R16 bitter taste receptor as well, by applying the same protocol. We found that the recently published experimental ligand binding affinity data for this receptor correlated well with the binding scores obtained from our molecular docking calculations.     

Evolution of bitter taste receptors in humans and apes

Bitter taste perception is crucial for the survival of organismsbecause it enables them to avoid the ingestion of potentiallyharmful substances. Bitter taste receptors are encoded by agene family that in humans has been shown to contain 25 putativelyfunctional genes and 8 pseudogenes and in mouse 33 putativelyfunctional genes and 3 pseudogenes. Lineage-specific expansionsof bitter taste receptors have taken place in both mouse andhuman, but very little is known about the evolution of thesereceptors in primates. We report the analysis of the almostcomplete repertoires of bitter taste receptor genes in human,great apes, and two Old World monkeys. As a group, these genesseem to be under little selective constraint compared with olfactoryreceptors and other genes in the studied species. However, incontrast to the olfactory receptor gene repertoire, where humanshave a higher proportion of pseudogenes than apes, there isno evidence that the rate of loss of bitter taste receptor genesvaries among humans and apes.     

Bitter taste thresholds, numbers and diameters of circumvallate papillae and their relation with age in a Turkish population

Objectives: This study analyses the relationship between the sense of bitter taste and age. The relationships between these and the numbers and diameters of Circumvallate Papillae (CP) are also analysed. Subjects: Twenty-four elderly subjects (from 65 to 85 years) and 30 young subjects (from 17 to 25 years) were studied. Method: Bitter taste thresholds were determined by the three drop method with an ascending series of concentrations. The numbers and diameters of CP were observed by direct naked eye observation using a wooden tongue depressor, a gauge and a light source. Results: The bitter taste acuity was significantly poorer in the older sample. There was no relationship between the bitter taste acuity and number of papillae but an inverse relationship was observed between the bitter taste acuity and diameters of papillae, thus lower acuity was associated with larger papillae. It was also observed that the diameters of papillae were inversely related to the numbers of CP. The distribution of numbers and diameters of CP were not significantly different between these samples with age.     

Evolution of sex-peptide in Drosophila

The Drosophila sex-peptide (SP) has been identified as a seminal fluid component that induces post-mating responses (PMRs) in the inseminated females, such as inhibition of remating and stimulation of egg-laying. SP has been thought to play a central role in sexual conflict and sexually antagonistic co-evolution. Most of the sequenced Drosophila genomes contain SP orthologs, but their functions have been poorly characterized. Recently, we have investigated cross-species activity of D. melanogaster SP by means of injection into virgin females of other species. Among 11 species examined, SP response was observed in 6 species belonging to the D. melanogaster species group only. These species females express SP receptor (SPR) in their oviducts at relatively high levels, which was visualized by using a GFP-tagged SP. Furthermore, females of this species group responded to their own SP orthologs. However, females of the species outside the group did not respond to their own SP orthologs, even though all of them were potent inducers of SP-response in D. melanogaster. Our results suggested that the SP/SPR-mediated PMR was established in the lineage of the D. melanogaster species group.     

Temperature and Sweet Taste Integration in Drosophila

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羚牛苦味受体3(Tas2R3)基因的克隆及生物信息学分析

Tas2R3是苦味受体基因家族中一个重要的成员,为了进一步了解和研究羚牛(Budorcas taxicolor)苦味受体基因的结构和功能,本研究对羚牛苦味受体3 (Tas2R3)基因进行了克隆和生物信息学分析(GenBank登录号:MG650195)。结果显示,羚牛Tas2R3基因编码区(coding sequence, CDS)序列全长951 bp,共编码316个氨基酸,以亮氨酸含量最高,谷氨酰胺含量最低。其蛋白质等电点为9.68,分子量为51.96 kD。高级结构功能预测显示,二级结构以α-螺旋为主,蛋白质为碱性、稳定的亲水性蛋白,由4个胞外区、7个跨膜区和4个胞内区组成。预测到2种类型共8个糖基化功能位点和4种类型共15个磷酸化功能位点。通过比较Tas2R3基因种间相似性发现,在偶蹄目中具有很高的同源性,羚牛与绵羊(Ovis aries)的相似性最高(0.98),与褐家鼠(Rattus norvegicus)最低(0.52)。用羚牛、绵羊等12个物种的Tas2R3基因CDS序列构建的NJ树与ME树结构一致,表明Tas2R3基因适合用于构建不同物种间的系统进化树。     

The human bitter taste receptor hTAS2R39 is the primary receptor for the bitterness of theaflavins

We purified several hundred mgs of four major theaflavins (theaflavin, theaflavin-3-O-gallate, theaflavin-3′-O-gallate, and theaflavin-3,3′-O-digallate). Among the 25 hTAS2Rs expressed in HEK293T cells, hTAS2R39 and hTAS2R14 were activated by theaflavins. Both hTAS2R39 and hTAS2R14 responded to theaflavin-3′-O-gallate. In addition, hTAS2R39 was activated by theaflavin and theaflavin-3,3′-O-gallate, but not by theaflavin-3-O-gallate. In contrast, hTAS2R14 responded to theaflavin-3-O-gallate.