1101
|
Gomes I, Gupta A, Filipovska J, Szeto HH, Pintar JE, Devi LA. A role for heterodimerization of mu and delta opiate receptors in enhancing morphine analgesia. Proc Natl Acad Sci U S A 2004; 101:5135-9. [PMID: 15044695 PMCID: PMC387386 DOI: 10.1073/pnas.0307601101] [Citation(s) in RCA: 335] [Impact Index Per Article: 16.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/26/2023] Open
Abstract
Opiates such as morphine are the choice analgesic in the treatment of chronic pain. However their long-term use is limited because of the development of tolerance and dependence. Due to its importance in therapy, different strategies have been considered for making opiates such as morphine more effective, while curbing its liability to be abused. One such strategy has been to use a combination of drugs to improve the effectiveness of morphine. In particular, delta opioid receptor ligands have been useful in enhancing morphine's potency. The underlying molecular basis for these observations is not understood. We propose the modulation of receptor function by physical association between mu and delta opioid receptors as a potential mechanism. In support of this hypothesis, we show that mu-delta interacting complexes exist in live cells and native membranes and that the occupancy of delta receptors (by antagonists) is sufficient to enhance mu opioid receptor binding and signaling activity. Furthermore, delta receptor antagonists enhance morphine-mediated intrathecal analgesia. Thus, heterodimeric associations between mu-delta opioid receptors can be used as a model for the development of novel combination therapies for the treatment of chronic pain and other pathologies.
Collapse
Affiliation(s)
- Ivone Gomes
- Department of Pharmacology and Biological Chemistry, Mount Sinai School of Medicine, One Gustave L. Levy Place, New York, NY 10029, USA
| | | | | | | | | | | |
Collapse
|
1102
|
Salbe AD, DelParigi A, Pratley RE, Drewnowski A, Tataranni PA. Taste preferences and body weight changes in an obesity-prone population. Am J Clin Nutr 2004; 79:372-8. [PMID: 14985209 DOI: 10.1093/ajcn/79.3.372] [Citation(s) in RCA: 131] [Impact Index Per Article: 6.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/14/2022] Open
Abstract
BACKGROUND Taste preferences for highly palatable foods rich in sugar and fat may underlie the current epidemic of obesity. OBJECTIVE This study aimed to determine whether the hedonic response to sweet and creamy solutions differs between whites and Pima Indians and whether a preference for these tastes predicts weight gain. DESIGN One hundred twenty-three Pima Indian and 64 white volunteers taste tested solutions of nonfat milk (0.1% fat), whole milk (3.5% fat), half and half (11.3% fat), and cream (37.5% fat) containing 0%, 5%, 10%, or 20% sugar by weight. Solutions were rated for perceived sweetness, creaminess, and pleasantness (hedonic response) on a 100-mm visual analogue scale. Follow-up body weight was measured in 75 Pima Indians 5.5 +/- 3.0 y ( +/- SD) after baseline taste testing. RESULTS The Pima Indians had a significantly (P = 0.006) lower hedonic response than did the whites (repeated-measures analysis of variance). Neither body size (P = 0.56) nor adiposity (P = 0.86) was a significant predictor of the hedonic response. There was a positive correlation (r = 0.28, P = 0.01) between the maximal hedonic response at baseline and subsequent weight gain in the Pima Indians. CONCLUSION Although the Pima Indians liked sweet and creamy solutions less than the whites did, a heightened hedonic response for these solutions among the Pima Indians was associated with weight gain.
Collapse
Affiliation(s)
- Arline D Salbe
- Clinical Diabetes and Nutrition Section, Phoenix Epidemiology and Clinical Research Branch, National Institute of Diabetes and Digestive and Kidney Diseases, National Institutes of Health, Phoenix, AZ 85016, USA
| | | | | | | | | |
Collapse
|
1103
|
Kim MR, Kusakabe Y, Miura H, Shindo Y, Ninomiya Y, Hino A. Regional expression patterns of taste receptors and gustducin in the mouse tongue. Biochem Biophys Res Commun 2004; 312:500-6. [PMID: 14637165 DOI: 10.1016/j.bbrc.2003.10.137] [Citation(s) in RCA: 110] [Impact Index Per Article: 5.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/17/2022]
Abstract
In order to understand differences in taste sensitivities of taste bud cells between the anterior and posterior part of tongue, it is important to analyze the regional expression patterns of genes related to taste signal transduction on the tongue. Here we examined the expression pattern of a taste receptor family, the T1r family, and gustducin in circumvallate and fungiform papillae of the mouse tongue using double-labeled in situ hybridization. Each member of the T1r family was expressed in both circumvallate and fungiform papillae with some differences in their expression patterns. The most striking difference between fungiform and circumvallate papillae was observed in their co-expression patterns of T1r2, T1r3, and gustducin. T1r2-positive cells in fungiform papillae co-expressed T1r3 and gustducin, whereas T1r2 and T1r3 double-positive cells in circumvallate papillae merely expressed gustducin. These results suggested that in fungiform papillae, gustducin might play a role in the sweet taste signal transduction cascade mediated by a sweet receptor based on the T1r2 and T1r3 combination, in fungiform papillae.
Collapse
Affiliation(s)
- Mi-Ryung Kim
- Gustatory Biology Laboratory, National Food Research Institute, 2-1-12 Kannondai, Tsukuba, Ibaraki 305-8642, Japan
| | | | | | | | | | | |
Collapse
|
1104
|
Abstract
Recently, many G-protein-coupled receptors (GPCRs) have been demonstrated to form constitutive dimers consisting of identical or distinct monomeric subunits. The discovery of GPCR dimerization has revealed a new level of molecular cross-talk between signalling molecules and may define a general mechanism that modulates the function of GPCRs under both physiological and pathological conditions. The heterodimerization between distinct GPCRs could be responsible for the generation of pharmacologically defined receptors for which no gene has been identified so far. Elucidating the role of dimerization in the activation processes of GPCRs will lead us to develop novel pharmaceutical agents that allosterically promote activation or inhibition of GPCR signalling.
Collapse
Affiliation(s)
- Mei Bai
- Endocrine-Hypertension Division and Membrane Biology Program, Department of Medicine, Brigham and Women's Hospital and Harvard Medical School, Boston, MA 02115, USA.
| |
Collapse
|
1105
|
|
1106
|
Zhao GQ, Zhang Y, Hoon MA, Chandrashekar J, Erlenbach I, Ryba NJP, Zuker CS. The receptors for mammalian sweet and umami taste. Cell 2004; 115:255-66. [PMID: 14636554 DOI: 10.1016/s0092-8674(03)00844-4] [Citation(s) in RCA: 870] [Impact Index Per Article: 43.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/26/2022]
Abstract
Sweet and umami (the taste of monosodium glutamate) are the main attractive taste modalities in humans. T1Rs are candidate mammalian taste receptors that combine to assemble two heteromeric G-protein-coupled receptor complexes: T1R1+3, an umami sensor, and T1R2+3, a sweet receptor. We now report the behavioral and physiological characterization of T1R1, T1R2, and T1R3 knockout mice. We demonstrate that sweet and umami taste are strictly dependent on T1R-receptors, and show that selective elimination of T1R-subunits differentially abolishes detection and perception of these two taste modalities. To examine the basis of sweet tastant recognition and coding, we engineered animals expressing either the human T1R2-receptor (hT1R2), or a modified opioid-receptor (RASSL) in sweet cells. Expression of hT1R2 in mice generates animals with humanized sweet taste preferences, while expression of RASSL drives strong attraction to a synthetic opiate, demonstrating that sweet cells trigger dedicated behavioral outputs, but their tastant selectivity is determined by the nature of the receptors.
Collapse
Affiliation(s)
- Grace Q Zhao
- Howard Hughes Medical Institute and Departments of Biology and Neurosciences, University of California at San Diego, La Jolla, CA 92093, USA
| | | | | | | | | | | | | |
Collapse
|
1107
|
Hague C, Uberti MA, Chen Z, Hall RA, Minneman KP. Cell surface expression of alpha1D-adrenergic receptors is controlled by heterodimerization with alpha1B-adrenergic receptors. J Biol Chem 2004; 279:15541-9. [PMID: 14736874 DOI: 10.1074/jbc.m314014200] [Citation(s) in RCA: 135] [Impact Index Per Article: 6.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/13/2022] Open
Abstract
alpha(1)-Adrenergic receptors (ARs) belong to the large Class I G protein-coupled receptor superfamily and comprise three subtypes (alpha(1A), alpha(1B), and alpha(1D)). Previous work with heterologously expressed C-terminal green fluorescent protein (GFP)-tagged alpha(1)-ARs showed that alpha(1A)- and alpha(1B)-ARs localize to the plasma membrane, whereas alpha(1D)-ARs accumulate intracellularly. We recently showed that alpha(1D)- and alpha(1B)-ARs form heterodimers, whereas alpha(1D)- and alpha(1A)-ARs do not. Here, we examined the role of heterodimerization in regulating alpha(1D)-AR localization using both confocal imaging of GFP- or CFP-tagged alpha(1)-ARs and a luminometer-based surface expression assay in HEK293 cells. Co-expression with alpha(1B)-ARs caused alpha(1D)-ARs to quantitatively translocate to the cell surface, but co-expression with alpha(1A)-ARs did not. Truncation of the alpha(1B)-AR extracellular N terminus or intracellular C terminus had no effect on surface expression of alpha(1D)-ARs, suggesting primary involvement of the hydrophobic core. Co-transfection with an uncoupled mutant alpha(1B)-AR (Delta12alpha(1B)) increased both alpha(1D)-AR surface expression and coupling to norepinephrine-stimulated Ca(2+) mobilization. Finally, GFP-tagged alpha(1D)-ARs were not detected on the cell surface when expressed in rat aortic smooth muscle cells that express no endogenous ARs, but were almost exclusively localized on the surface when expressed in DDT(1)MF-2 cells, which express endogenous alpha(1B)-ARs. These studies demonstrate that alpha(1B)/alpha(1D)-AR heterodimerization controls surface expression and functional coupling of alpha(1D)-ARs, the N- and C-terminal domains are not involved in this interaction, and that alpha(1B)-AR G protein coupling is not required. These observations may be relevant to many other Class I G protein-coupled receptors, where the functional consequences of heterodimerization are still poorly understood.
Collapse
Affiliation(s)
- Chris Hague
- Department of Pharmacology, Emory University, Atlanta, Georgia 30322, USA
| | | | | | | | | |
Collapse
|
1108
|
Hiroi M, Meunier N, Marion-Poll F, Tanimura T. Two antagonistic gustatory receptor neurons responding to sweet-salty and bitter taste inDrosophila. ACTA ACUST UNITED AC 2004; 61:333-42. [PMID: 15389687 DOI: 10.1002/neu.20063] [Citation(s) in RCA: 123] [Impact Index Per Article: 6.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022]
Abstract
In Drosophila, gustatory receptor neurons (GRNs) occur within hair-like structures called sensilla. Most taste sensilla house four GRNs, which have been named according to their preferred sensitivity to basic stimuli: water (W cell), sugars (S cell), salt at low concentration (L1 cell), and salt at high concentration (L2 cell). Labellar taste sensilla are classified into three types, l-, s-, and i-type, according to their length and location. Of these, l- and s-type labellar sensilla possess these four cells, but most i-type sensilla house only two GRNs. In i-type sensilla, we demonstrate here that the first GRN responds to sugar and to low concentrations of salt (10-50 mM NaCl). The second GRN detects a range of bitter compounds, among which strychnine is the most potent; and also to salt at high concentrations (over 400 mM NaCl). Neither type of GRN responds to water. The detection of feeding stimulants in i-type sensilla appears to be performed by one GRN with the combined properties of S+L1 cells, while the other GRN detects feeding inhibitors in a similar manner to bitter-sensitive L2 cells on the legs. These sensilla thus house two GRNs having an antagonistic effect on behavior, suggesting that the expression of taste receptors is segregated across them accordingly.
Collapse
Affiliation(s)
- Makoto Hiroi
- Department of Biology, Graduate School of Sciences, Kyushu University, Ropponmatsu 4-2-1, Fukuoka 810-8560, Japan
| | | | | | | |
Collapse
|
1109
|
Abstract
Protein-protein interactions are fundamental processes for many biological systems including those involving the superfamily of G-protein coupled receptors (GPCRs). A growing body of biochemical and functional evidence supports the existence of GPCR-GPCR homo- and hetero-oligomers. In particular, hetero-oligomers can display pharmacological and functional properties distinct from those of the homodimer or oligomer thus adding another level of complexity to how GPCRs are activated, signal and traffick in the cell. Dimerization may also play a role in influencing the activity of agonists and antagonists. We are only beginning to unravel how and why such complexes are formed, the functional implications of which will have an enormous impact on GPCR biology. Future research that studies GPCRs as dimeric or oligomeric complexes will enhance not only our understanding of GPCRs in cellular function but will also be critical for novel drug design and improved treatment of the vast array of GPCR-related conditions.
Collapse
Affiliation(s)
- Karen M Kroeger
- Western Australian Institute for Medical Research, Centre for Medical Research, University of Western Australia, Sir Charles Gairdner Hospital, Hospital Avenue, Nedlands, 6009, Perth, WA, Australia
| | | | | |
Collapse
|
1110
|
Hague C, Chen Z, Uberti M, Minneman KP. α1-Adrenergic receptor subtypes: non-identical triplets with different dancing partners? Life Sci 2003; 74:411-8. [PMID: 14609720 DOI: 10.1016/j.lfs.2003.07.008] [Citation(s) in RCA: 31] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/26/2022]
Abstract
Alpha(1)-adrenergic receptors are one of the three subfamilies of G protein coupled receptors activated by epinephrine and norepinephrine to control important functions in many target organs. Three human subtypes (alpha(1A), alpha(1B), alpha(1D)) are derived from separate genes and are highly homologous in their transmembrane domains but not in their amino or carboxyl termini. Recent advances in our understanding of these "non-identical triplets" include development of knockout mice lacking single or multiple subtypes, new insights into subcellular localization and trafficking, identification of allosteric modulators, and increasing evidence for an important role in brain function. Although all three subtypes activate the same G(q/11) signaling pathway, they also appear to interact with different protein binding partners. Recent evidence suggests they may also form dimers, and may initiate independent signals through pathways yet to be clearly elucidated. Thus, this subfamily represents a common phenomenon of a group of similar but non-identical receptor subtypes activated by the same neurotransmitter, whose individual functional roles remain to be clearly established.
Collapse
Affiliation(s)
- Chris Hague
- Department of Pharmacology, Emory University, Atlanta, GA 30322, USA.
| | | | | | | |
Collapse
|
1111
|
Jordan BA, Gomes I, Rios C, Filipovska J, Devi LA. Functional interactions between mu opioid and alpha 2A-adrenergic receptors. Mol Pharmacol 2003; 64:1317-24. [PMID: 14645661 DOI: 10.1124/mol.64.6.1317] [Citation(s) in RCA: 138] [Impact Index Per Article: 6.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022] Open
Abstract
Adrenergic and opioid receptors belong to the rhodopsin family of G-protein coupled receptors, couple to analogous signal transduction pathways, and affect the nociceptive system. Although a number of previous studies have reported functional interactions between these two receptors, the basis for this has not been well explored. We propose that direct receptor-receptor interactions could account, in part, for opioid-adrenergic cross-talk. In this report, we have addressed this using biophysical, biochemical, and pharmacological studies. We show that mu opioid and alpha2A adrenergic receptors reside in close proximity in live cells using the bioluminescence resonance energy transfer assay. These receptors colocalize to proximal dendrites in primary hippocampal neurons. mu-alpha2A Receptor complexes can be isolated from heterologous cells or primary neurons coexpressing these receptors. In these cells, the activation of either mu or alpha2A receptor leads to a significant increase in the level of immunoprecipitable mu-alpha2A complexes, whereas activation of both receptors leads to a significant decrease. The implications of these effects on signaling were examined using the agonist-mediated increase in G-protein activity and mitogen-activated protein kinase activity. We find that activation of either mu or alpha2A receptors leads to an increase in the extent of signaling, whereas activation of both receptors leads to a decrease. The increase in signaling by individual ligands and decrease by a combination of ligands is also seen in primary spinal cord neurons endogenously expressing these receptors. Taken together, these results suggest that physical associations between mu and alpha2A receptors could play a role in the functional interactions between these receptors.
Collapse
MESH Headings
- Adrenergic alpha-2 Receptor Agonists
- Animals
- Cell Line
- Clonidine/metabolism
- Clonidine/pharmacology
- Dogs
- Dose-Response Relationship, Drug
- Humans
- Morphine/metabolism
- Morphine/pharmacology
- Rats
- Rats, Sprague-Dawley
- Receptors, Adrenergic, alpha-2/genetics
- Receptors, Adrenergic, alpha-2/metabolism
- Receptors, Opioid, mu/agonists
- Receptors, Opioid, mu/genetics
- Receptors, Opioid, mu/metabolism
Collapse
Affiliation(s)
- B A Jordan
- Department of Pharmacology and Biological Chemistry, Mount Sinai School of Medicine, 19-84 Annenberg Building, One Gustave L. Levy Place, New York, NY 10029, USA
| | | | | | | | | |
Collapse
|
1112
|
Chyb S, Dahanukar A, Wickens A, Carlson JR. Drosophila Gr5a encodes a taste receptor tuned to trehalose. Proc Natl Acad Sci U S A 2003; 100 Suppl 2:14526-30. [PMID: 14523229 PMCID: PMC304113 DOI: 10.1073/pnas.2135339100] [Citation(s) in RCA: 147] [Impact Index Per Article: 7.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/18/2022] Open
Abstract
Recent studies have suggested that Drosophila taste receptors are encoded by a family of G protein-coupled receptor genes comprising at least 56 members. One of these genes, Gr5a, has been shown by genetic analysis to be required by the fly for behavioral and sensory responses to a sugar, trehalose. Here, we show that Gr5a is expressed in neurons of taste sensilla located on the labellum and legs. Expression is observed in most if not all labellar sensilla and suggests that many taste neurons express more than one receptor. We demonstrate by heterologous expression in a Drosophila S2 cell line that Gr5a encodes a receptor tuned to trehalose. This is the first functional expression of an invertebrate taste receptor.
Collapse
Affiliation(s)
- Sylwester Chyb
- Imperial College London, Wye Campus, Kent TN25 5AH, United Kingdom
| | | | | | | |
Collapse
|
1113
|
Bigiani A, Ghiaroni V, Fieni F. Channels as taste receptors in vertebrates. PROGRESS IN BIOPHYSICS AND MOLECULAR BIOLOGY 2003; 83:193-225. [PMID: 12887980 DOI: 10.1016/s0079-6107(03)00058-0] [Citation(s) in RCA: 23] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 12/14/2022]
Abstract
Taste reception is fundamental for proper selection of food and beverages. Chemicals detected as taste stimuli by vertebrates include a large variety of substances, ranging from inorganic ions (e.g., Na(+), H(+)) to more complex molecules (e.g., sucrose, amino acids, alkaloids). Specialized epithelial cells, called taste receptor cells (TRCs), express specific membrane proteins that function as receptors for taste stimuli. Classical view of the early events in chemical detection was based on the assumption that taste substances bind to membrane receptors in TRCs without permeating the tissue. Although this model is still valid for some chemicals, such as sucrose, it does not hold for small ions, such as Na(+), that actually diffuse inside the taste tissue through ion channels. Electrophysiological, pharmacological, biochemical, and molecular biological studies have provided evidence that indeed TRCs use ion channels to reveal the presence of certain substances in foodstuff. In this review, we focus on the functional and molecular properties of ion channels that serve as receptors in taste transduction.
Collapse
Affiliation(s)
- Albertino Bigiani
- Dipartimento di Scienze Biomediche, Sezione di Fisiologia, Università di Modena e Reggio Emilia, via Campi 287, 41100 Modena, Italy.
| | | | | |
Collapse
|
1114
|
Zubare-Samuelov M, Peri I, Tal M, Tarshish M, Spielman AI, Naim M. Some sweet and bitter tastants stimulate inhibitory pathway of adenylyl cyclase via melatonin and alpha 2-adrenergic receptors in Xenopus laevis melanophores. Am J Physiol Cell Physiol 2003; 285:C1255-62. [PMID: 12839835 DOI: 10.1152/ajpcell.00149.2003] [Citation(s) in RCA: 18] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022]
Abstract
The sweeteners saccharin, D-tryptophan, and neohesperidin dihydrochalcone (NHD) and the bitter tastant cyclo(Leu-Trp) stimulated concentration-dependent pigment aggregation in a Xenopus laevis melanophore cell line similar to melatonin. Like melatonin, these tastants inhibited (by 45-92%) cAMP formation in melanophores; pertussis toxin pretreatment almost completely abolished the tastant-induced cAMP inhibition, suggesting the involvement of the inhibitory pathway (Gi) of adenylyl cyclase. The presence of luzindole (melatonin receptor antagonist) almost completely abolished the inhibition of cAMP formation induced by saccharin, D-tryptophan, and cyclo(Leu-Trp) but only slightly affected the inhibitory effect of NHD. In contrast, the presence of an alpha2-adrenergic receptor antagonist, yohimbine, almost completely abolished the inhibition of cAMP formation induced by NHD but had only a minor effect on that induced by the other tastants. Thus saccharin, D-tryptophan, and cyclo(Leu-Trp) are melatonin receptor agonists whereas NHD is an alpha2-adrenergic receptor agonist, but both pathways lead to the same transduction output and cellular response. Formation of D-myo-inositol 1,4,5-trisphosphate (IP3) in melanophores was reduced (15-58%, no concentration dependence) by saccharin, D-tryptophan, and cyclo(Leu-Trp) stimulation but increased by NHD stimulation. Tastant stimulation did not affect cGMP. Although some of the above tastants were found to be membrane permeant, their direct activation of downstream transduction components in this experimental system is questionable. MT1 and MT2 melatonin receptor mRNAs were identified in rat circumvallate papilla taste buds and nonsensory epithelium, suggesting the occurrence of MT1 and MT2 receptors in these tissues. Melatonin stimulation reduced the cellular content of cAMP in taste cells, which may or may not be related to taste sensation.
Collapse
Affiliation(s)
- Meirav Zubare-Samuelov
- Institute of Biochemistry, Food Science and Nutrition, Faculty of Agricultural, Food and Environmental Quality Sciences, The Hebrew University of Jerusalem, PO Box 12, Rehovot 76-100, Israel
| | | | | | | | | | | |
Collapse
|
1115
|
Offermanns S. G-proteins as transducers in transmembrane signalling. PROGRESS IN BIOPHYSICS AND MOLECULAR BIOLOGY 2003; 83:101-30. [PMID: 12865075 DOI: 10.1016/s0079-6107(03)00052-x] [Citation(s) in RCA: 196] [Impact Index Per Article: 9.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 01/19/2023]
Abstract
The G-protein-mediated signalling system has evolved as one of the most widely used transmembrane signalling mechanisms in mammalian organisms. All mammalian cells express G-protein-coupled receptors as well as several types of heterotrimeric G-proteins and effectors. G-protein-mediated signalling is involved in many physiological and pathological processes. This review summarizes some general aspects of G-protein-mediated signalling and focusses on recent data especially from studies in mutant mice which have elucidated some of the cellular and biological functions of heterotrimeric G-prtoteins.
Collapse
Affiliation(s)
- Stefan Offermanns
- Institute of Pharmacology, University of Heidelberg, Im Neuenheimer Feld 366, 69120 Heidelberg, Germany.
| |
Collapse
|
1116
|
Bray S, Amrein H. A putative Drosophila pheromone receptor expressed in male-specific taste neurons is required for efficient courtship. Neuron 2003; 39:1019-29. [PMID: 12971900 DOI: 10.1016/s0896-6273(03)00542-7] [Citation(s) in RCA: 194] [Impact Index Per Article: 9.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Abstract
Propagation in higher animals requires the efficient and accurate display of innate mating behaviors. In Drosophila melanogaster, male courtship consists of a stereotypic sequence of behaviors involving multiple sensory modalities, such as vision, audition, and chemosensation. For example, taste bristles located in the male forelegs and the labial palps are thought to recognize nonvolatile pheromones secreted by the female. Here, we report the identification of the putative pheromone receptor GR68a, which is expressed in chemosensory neurons of about 20 male-specific gustatory bristles in the forelegs. Gr68a expression is dependent on the sex determination gene doublesex, which controls many aspects of sexual differentiation and is necessary for normal courtship behavior. Tetanus toxin-mediated inactivation of Gr68a-expressing neurons or transgene-mediated RNA interference of Gr68a RNA leads to a significant reduction in male courtship performance, suggesting that GR68a protein is an essential component of pheromone-driven courtship behavior in Drosophila.
Collapse
Affiliation(s)
- Steven Bray
- Duke University Medical Center, Department of Molecular Genetics and Microbiology, 252 CARL Building, Research Drive, Durham, NC 27710, USA
| | | |
Collapse
|
1117
|
Assadi-Porter FM, Abildgaard F, Blad H, Markley JL. Correlation of the sweetness of variants of the protein brazzein with patterns of hydrogen bonds detected by NMR spectroscopy. J Biol Chem 2003; 278:31331-9. [PMID: 12732626 DOI: 10.1074/jbc.m302663200] [Citation(s) in RCA: 27] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
In sequence-function investigations, approaches are needed for rapidly screening protein variants for possible changes in conformation. Recent NMR methods permit direct detection of hydrogen bonds through measurements of scalar couplings that traverse hydrogen bonds (trans-hydrogen bond couplings). We have applied this approach to screen a series of five single site mutants of the sweet protein brazzein with altered sweetness for possible changes in backbone hydrogen bonding with respect to wild-type. Long range, three-dimensional data correlating connectivities among backbone 1HN, 15N, and 13C' atoms were collected from the six brazzein proteins labeled uniformly with carbon-13 and nitrogen-15. In wild-type brazzein, this approach identified 17 backbone hydrogen bonds. In the mutants, altered magnitudes of the couplings identified hydrogen bonds that were strengthened or weakened; missing couplings identified hydrogen bonds that were broken, and new couplings indicated the presence of new hydrogen bonds. Within the series of brazzein mutants investigated, a pattern was observed between sweetness and the integrity of particular hydrogen bonds. All three "sweet" variants exhibited the same pattern of hydrogen bonds, whereas all three "non-sweet" variants lacked one hydrogen bond at the middle of the alpha-helix, where it is kinked, and one hydrogen bond in the middle of beta-strands II and III, where they are twisted. Two of the non-sweet variants lack the hydrogen bond connecting the N and C termini. These variants showed greater mobility in the N- and C-terminal regions than wild-type brazzein.
Collapse
Affiliation(s)
- Fariba M Assadi-Porter
- National Magnetic Resonance Facility at Madison, Department of Biochemistry, University of Wisconsin, Madison, Wisconsin 53706, USA.
| | | | | | | |
Collapse
|
1118
|
Damak S, Rong M, Yasumatsu K, Kokrashvili Z, Varadarajan V, Zou S, Jiang P, Ninomiya Y, Margolskee RF. Detection of sweet and umami taste in the absence of taste receptor T1r3. Science 2003; 301:850-3. [PMID: 12869700 DOI: 10.1126/science.1087155] [Citation(s) in RCA: 441] [Impact Index Per Article: 21.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/02/2022]
Abstract
The tastes of sugars (sweet) and glutamate (umami) are thought to be detected by T1r receptors expressed in taste cells. Molecular genetics and heterologous expression implicate T1r2 plus T1r3 as a sweet-responsive receptor,and T1r1 plus T1r3,as well as a truncated form of the type 4 metabotropic glutamate receptor (taste-mGluR4),as umami-responsive receptors. Here,we show that mice lacking T1r3 showed no preference for artificial sweeteners and had diminished but not abolished behavioral and nerve responses to sugars and umami compounds. These results indicate that T1r3-independent sweet- and umami-responsive receptors and/or pathways exist in taste cells.
Collapse
Affiliation(s)
- Sami Damak
- Department of Biophysics and Physiology, Mount Sinai School of Medicine, Box 1677, 1425 Madison Avenue, New York, NY 10029, USA
| | | | | | | | | | | | | | | | | |
Collapse
|
1119
|
Abstract
Olfactory receptors lead lives of exclusivity and privilege, the monarchs of fiefdoms organized solely to carry out their instructions. Each olfactory sensory neuron expresses one allele of one of approximately 1000 olfactory receptor genes. It is thought that olfactory receptor diversity is critical for the ability of animals to detect many thousands of odorants, but supporting functional evidence has been difficult to obtain because olfactory receptors expressed in heterologous cells are typically retained in the endoplasmic reticulum. The membrane trafficking entitlements enjoyed by olfactory receptors appear to be available only in mature olfactory sensory neurons. Evidence is accumulating that cell-type-specific accessory proteins regulate first the exit of olfactory receptors from the endoplasmic reticulum, and then the trafficking of olfactory receptors from post-Golgi compartments to the plasma membrane of the olfactory cilia where the receptors gain access to odorants. Critical olfactory receptor accessory proteins are known only in the nematode Caenorhabditis elegans, where the absence of a novel protein called ODR-4 or a clathrin adaptor, UNC-101, interferes with proper trafficking. Similar functional specificity also occurs in a parallel chemosensory system, the mammalian vomeronasal organ. Trafficking of the V2R type of vomeronasal receptors is mediated by a vomeronasal-specific family of major histocompatibility complex proteins. Removal of olfactory receptors from the plasma membrane may be regulated in a more conventional fashion because odor stimulation has been linked to receptor phosphorylation, to the function of G-protein coupled receptor kinase 3, and to an increase in vesicles retrieved from the plasma membrane.
Collapse
|
1120
|
Lemon CH, Imoto T, Smith DV. Differential gurmarin suppression of sweet taste responses in rat solitary nucleus neurons. J Neurophysiol 2003; 90:911-23. [PMID: 12702710 DOI: 10.1152/jn.00215.2003] [Citation(s) in RCA: 14] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022] Open
Abstract
We examined the effect of the sweet transduction blocker gurmarin on taste responses recorded from neurons in the rat solitary nucleus (NST) to determine how gurmarin sensitivity is distributed across neuronal type. Initially, responses evoked by washing the anterior tongue and palate with 0.5 M sucrose, 0.1 M NaCl, 0.01 M HCl, and 0.01 M quinine-HCl were recorded from 35 neurons. For some cells, responses to a sucrose concentration series (0.01-1.0 M) or an array of sweet-tasting compounds were also measured. Gurmarin (10 microg/ml, 2-4 ml) was then applied to the tongue and palate. Stimuli were reapplied after 10-15 min. Neurons were segregated into groups based on similarities among their initial response profiles using hierarchical cluster analysis (HCA). Results indicated that sucrose responses recorded from neurons representative of each HCA-defined class were suppressed by gurmarin. However, a disproportionate percentage of cells in each group displayed sucrose responses that were substantially attenuated after gurmarin treatment. Postgurmarin sucrose responses recorded from neurons that composed 57% of class S, 40% of class N, and 33% of class H were suppressed by >or=50% relative to control. On average, attenuation was statistically significant only in class S and N neurons. Although the magnitude of gurmarin-induced response suppression did not differ across sucrose concentration, responses to different sweet-tasting compounds were differentially affected. Responses to NaCl, HCl, or quinine were not suppressed by gurmarin. Results suggest that information from gurmarin-sensitive and -insensitive receptor processes converges onto single NST neurons.
Collapse
Affiliation(s)
- Christian H Lemon
- Department of Anatomy and Neurobiology, University of Tennessee College of Medicine, Memphis, Tennessee 38163, USA.
| | | | | |
Collapse
|
1121
|
Abstract
Heterodimerization enhances the complexity of ligand recognition and diversity of signaling responses of heterotrimeric guanine nucleotide-binding protein-coupled receptors (GPCRs). Many accessory proteins (for ion channels or GPCRs) appear to associate with their partners relatively early in the process whereby proteins are transported to the cell surface; their roles in modulating function may have evolved out of simple proximity to a protein that once upon a time they either facilitated or accompanied through the maturation process. The receptor activity-modifying proteins (RAMPs) are a family of single-transmembrane accessory proteins that heterodimerize with GPCRs and, thereby, allow individual GPCRs to recognize multiple ligands and to activate various signaling pathways in response to ligand binding. The M10 family of major histocompatibility complex (MHC) class 1b proteins has recently been shown to associate with murine vomeronasal V2R receptors, as well as to escort them to the cell surface. The exact role of M10 in modulating V2R function (or vice versa) remains to be determined.
Collapse
Affiliation(s)
- Steven M Foord
- Target Bioinformatics, GlaxoSmithKline Medicine Research Centre, Stevenage, Hertfordshire SG1 2NY, UK.
| |
Collapse
|
1122
|
Foord SM. Matching Accessories. Sci Signal 2003. [DOI: 10.1126/scisignal.1902003pe25] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/02/2022]
|
1123
|
Dulac C, Torello AT. Molecular detection of pheromone signals in mammals: from genes to behaviour. Nat Rev Neurosci 2003; 4:551-62. [PMID: 12838330 DOI: 10.1038/nrn1140] [Citation(s) in RCA: 425] [Impact Index Per Article: 20.2] [Reference Citation Analysis] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/20/2022]
Affiliation(s)
- Catherine Dulac
- Department of Molecular and Cellular Biology, Howard Hughes Medical Institute, Harvard University, Cambridge, Massachusetts 02138, USA.
| | | |
Collapse
|
1124
|
Shimizu Y, Yamazaki M, Nakanishi K, Sakurai M, Sanada A, Takewaki T, Tonosaki K. Enhanced responses of the chorda tympani nerve to sugars in the ventromedial hypothalamic obese rat. J Neurophysiol 2003; 90:128-33. [PMID: 12634283 DOI: 10.1152/jn.01170.2002] [Citation(s) in RCA: 14] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022] Open
Abstract
Sweet taste sensitivity in obese rats with lesions of the ventromedial hypothalamus (VMH) was studied by examining chorda tympani nerve responses to various taste stimuli including sugars. In the early progressive phase of obesity (2 wk after creating VMH lesions), there was no significant difference in the nerve responses to any taste stimulus between sham-operated and VMH-lesioned rats. In contrast, in the late phase of obesity (15-18 wk after VMH lesions), the magnitude of responses to sugars (except for fructose) was prominently greater than that in age-matched controls. High-fat diet-induced obese rats and streptozotocin-diabetic rats also showed greater chorda tympani nerve responses to sugars as was observed in VMH-lesioned obese rats, indicating that VMH lesions might not be specifically related to the enhanced gustatory neural responses to sugars. Although it has been demonstrated that the enhanced responses of the chorda tympani nerve to sugars in genetically diabetic db/db mice is largely attributable to the lack of the direct suppressive effect of leptin on the taste receptor cells, plasma leptin levels were not correlated with the changes in chorda tympani responsiveness to sugars in these models of obesity and diabetes. Accordingly, our results suggest that some chronic factors, including high blood glucose, inefficiency of insulin action, or leptin resistance may be related to the enhancement of chorda tympani nerve responses to sugars.
Collapse
Affiliation(s)
- Yasutake Shimizu
- Department of Veterinary Physiology, Faculty of Agriculture, United Graduate School of Veterinary Sciences, Gifu University, Gifu 501-1193, Japan
| | | | | | | | | | | | | |
Collapse
|
1125
|
Conte C, Ebeling M, Marcuz A, Nef P, Andres-Barquin PJ. Evolutionary relationships of the Tas2r receptor gene families in mouse and human. Physiol Genomics 2003; 14:73-82. [PMID: 12734386 DOI: 10.1152/physiolgenomics.00060.2003] [Citation(s) in RCA: 61] [Impact Index Per Article: 2.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022] Open
Abstract
The early molecular events in the perception of bitter taste start with the binding of specific water-soluble molecules to G protein-coupled receptors (GPCRs) encoded by the Tas2r family of taste receptor genes. The identification of the complete TAS2R receptor family repertoire in mouse and a comparative study of the Tas2r gene families in mouse and human might help to better understand bitter taste perception. We have identified, cloned, and characterized 13 new mouse Tas2r sequences, 9 of which encode putative functional bitter taste receptors. The encoded proteins are between 293 and 333 amino acids long and share between 18% and 54% sequence identity with other mouse TAS2R proteins. Including the 13 sequences identified, the mouse Tas2r family contains approximately 30% more genes and 60% fewer pseudogenes than the human TAS2R family. Sequence and phylogenetic analyses of the proteins encoded by all mouse and human Tas2r genes indicate that TAS2R proteins present a lower degree of sequence conservation in mouse than in human and suggest a classification in five groups that may reflect a specialization in their functional activity to detect bitter compounds. Tas2r genes are organized in clusters in both mouse and human genomes, and an analysis of these clusters and phylogenetic analyses indicates that the five TAS2R protein groups were present prior to the divergence of the primate and rodent lineages. However, differences in subsequent evolutionary processes, including local duplications, interchromosomal duplications, divergence, and deletions, gave rise to species-specific sequences and shaped the diversity of the current TAS2R receptor families during mouse and human evolution.
Collapse
Affiliation(s)
- Caroline Conte
- Neuroscience, Pharma Research, F. Hoffmann-La Roche, Basel 4070, Switzerland
| | | | | | | | | |
Collapse
|
1126
|
|
1127
|
Pin JP, Galvez T, Prézeau L. Evolution, structure, and activation mechanism of family 3/C G-protein-coupled receptors. Pharmacol Ther 2003; 98:325-54. [PMID: 12782243 DOI: 10.1016/s0163-7258(03)00038-x] [Citation(s) in RCA: 452] [Impact Index Per Article: 21.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/12/2022]
Abstract
G-protein-coupled receptors (GPCRs) represent one of the largest gene families in the animal genome. These receptors can be classified into several groups based on the sequence similarity of their common heptahelical domain. The family 3 (or C) GPCRs are receptors for the main neurotransmitters glutamate and gamma-aminobutyric acid, for Ca(2+), for sweet and amino acid taste compounds, and for some pheromone molecules, as well as for odorants in fish. Although none of these family 3 receptors have been found in plants, members have been identified in ancient organisms, such as slime molds (Dictyostelium) and sponges. Like any other GPCRs, family 3 receptors possess a transmembrane heptahelical domain responsible for G-protein activation. However, most of these identified receptors also possess a large extracellular domain that is responsible for ligand recognition, is structurally similar to bacterial periplasmic proteins involved in the transport of small molecules, and is called a Venus Flytrap module. The recent resolution of the structure of this binding domain in one of these receptors, the metabotropic glutamate 1 receptor, together with the recent demonstration that these receptors are dimers, revealed a unique mechanism of activation for these GPCRs. Such data open new possibilities in the development of drugs aimed at modulating these receptors, and raise a number of interesting questions on the activation mechanism of the other GPCRs.
Collapse
Affiliation(s)
- Jean-Philippe Pin
- Department of Molecular Pharmacology, CCIPE, 141 rue de la Cardonille, 34094 Montpellier Cedex 5, France.
| | | | | |
Collapse
|
1128
|
Vanti WB, Nguyen T, Cheng R, Lynch KR, George SR, O'Dowd BF. Novel human G-protein-coupled receptors. Biochem Biophys Res Commun 2003; 305:67-71. [PMID: 12732197 DOI: 10.1016/s0006-291x(03)00709-5] [Citation(s) in RCA: 42] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/27/2022]
Abstract
G-protein-coupled receptors (GPCRs) are important mediators of signal transduction and targets for pharmacological therapeutics. Novel receptor-ligand systems have been discovered through the identification and analysis of orphan GPCRs (oGPCRs). Here we describe the discovery of seven novel human genes encoding oGPCRs. Each novel oGPCR gene was discovered using customized searches of the GenBank genomic databases with previously known GPCR-encoding sequences. The expressed genes can now be used in assays to determine endogenous and pharmacological ligands. GPR133, GPR134, GPR135, GPR136, and GPR137 share identities with a prostate-specific odorant-like GPCR-encoding gene (PSGR). GPR138 and GPR139 share identities with an odorant-like gene derived from human erythroid cells. Transcripts encoding GPR133, GPR134, GPR135, GPR136, and GPR137 were detected in various CNS tissues. The expression of odorant-like genes in non-olfactory tissues requires further clarification, which may be achieved through the search for endogenous cognate ligands for these and other oGPCRs.
Collapse
Affiliation(s)
- William B Vanti
- Department of Pharmacology, Medical Sciences Building, Room 4352, University of Toronto, 1 King's College Circle, Toronto, Ont, Canada M5S 1A8
| | | | | | | | | | | |
Collapse
|
1129
|
Spadaccini R, Trabucco F, Saviano G, Picone D, Crescenzi O, Tancredi T, Temussi PA. The mechanism of interaction of sweet proteins with the T1R2-T1R3 receptor: evidence from the solution structure of G16A-MNEI. J Mol Biol 2003; 328:683-92. [PMID: 12706725 DOI: 10.1016/s0022-2836(03)00346-2] [Citation(s) in RCA: 47] [Impact Index Per Article: 2.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/30/2022]
Abstract
The mechanism by which sweet proteins elicit a response on the T1R2-T1R3 sweet taste receptor is still mostly unknown but has been so far related to the presence of "sweet fingers" on the protein surface able to interact with the same mechanism as that of low molecular mass sweeteners. In the search for the identification of sweet fingers, we have solved the solution structure of G16A MNEI, a structural mutant that shows a reduction of one order of magnitude in sweetness with respect to its parent protein, MNEI, a single-chain monellin. Comparison of the structures of wild-type monellin and its G16A mutant shows that the mutation does not affect the structure of potential glucophores but produces a distortion of the surface owing to the partial relative displacement of elements of secondary structure. These results show conclusively that sweet proteins do not possess a sweet finger and strongly support the hypothesis that the mechanism of interaction of sweet-tasting proteins with the recently identified T1R2-T1R3 GPC receptor is different from that of low molecular mass sweeteners.
Collapse
Affiliation(s)
- Roberta Spadaccini
- Dipartimento di Chimica, Università di Napoli Federico II, Via Cinthia 45, 80126 Naples, Italy
| | | | | | | | | | | | | |
Collapse
|
1130
|
Galvez T, Pin JP. [How do G-protein-coupled receptors work? The case of metabotropic glutamate and GABA receptors]. Med Sci (Paris) 2003; 19:559-65. [PMID: 12836389 DOI: 10.1051/medsci/2003195559] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/14/2022] Open
Abstract
G-protein coupled receptors (GPCRs) represent the largest membrane proteins family in animal genomes. Being the receptors for most hormones and neurotransmitters, these proteins play a central role in intercellular communication. GPCRs can be classified into several groups based on the sequence similarity of their common structural feature: the heptahelical domain. The metabotropic receptors for the main neurotransmitters glutamate and gamma-aminobutyric acid (GABA) belong to the class III of GPCRs, together with others receptors for Ca2+, for sweet and amino acid taste compounds and for some pheromones, as well as for odorants in fish. Besides their transmembrane heptahelical domain responsible for G-protein activation, most of class III receptors possess a large extracellular domain responsible for ligand recognition. The recent resolution of the structure of this binding domain of one of these receptors, the mGlu1 receptor, together with the recent demonstration that these receptors are dimers, revealed an original mechanism of activation for these GPCRs. Such data open new possibilities to develop drugs aimed at modulating these receptors, and raised a number of interesting questions on the activation mechanism of other GPCRs.
Collapse
Affiliation(s)
- Thierry Galvez
- Center for Clinical Sciences Research, Department of Molecular Pharmacology, Stanford University Medical Center, 269, Campus Drive, Room 3230, Stanford, CA 94305, USA.
| | | |
Collapse
|
1131
|
|
1132
|
Liao J, Schultz PG. Three sweet receptor genes are clustered in human chromosome 1. Mamm Genome 2003; 14:291-301. [PMID: 12856281 DOI: 10.1007/s00335-002-2233-0] [Citation(s) in RCA: 44] [Impact Index Per Article: 2.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/29/2002] [Accepted: 12/13/2002] [Indexed: 11/30/2022]
Abstract
A search of the human genome database led us to identify three human candidate taste receptors, hT1R1, hT1R2, and hT1R3, which contain seven transmembrane domains. All three genes map to a small region of Chromosome (Chr) 1. This region is syntenous to the distal end of Chr 4 in mouse, which contains the Sac (saccharin preference) locus that is involved in detecting sweet tastants. A genetic marker, DVL1, which is linked to the Sac locus, is within 1700 bp of human T1R3. Recently, the murine T1Rs and its human ortholog have been independently identified in combination as sweet and umami receptors near the Sac locus. All three hT1Rs genes are expressed selectively in human taste receptor cells in the fungiform papillae, consistent with their role in taste perception.
Collapse
Affiliation(s)
- Jiayu Liao
- Department of Chemistry, Skaggs Institute for Chemical Biology, Scripps Research Institute, 10550 North Torrey Pines Road, La Jolla, California 92037, USA.
| | | |
Collapse
|
1133
|
Pérez CA, Margolskee RF, Kinnamon SC, Ogura T. Making sense with TRP channels: store-operated calcium entry and the ion channel Trpm5 in taste receptor cells. Cell Calcium 2003; 33:541-9. [PMID: 12765699 DOI: 10.1016/s0143-4160(03)00059-9] [Citation(s) in RCA: 68] [Impact Index Per Article: 3.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/27/2022]
Abstract
The sense of taste plays a critical role in the life and nutritional status of organisms. During the last decade, several molecules involved in taste detection and transduction have been identified, providing a better understanding of the molecular physiology of taste receptor cells. However, a comprehensive catalogue of the taste receptor cell signaling machinery is still unavailable. We have recently described the occurrence of calcium signaling mechanisms in taste receptor cells via apparent store-operated channels and identified Trpm5, a novel candidate taste transduction element belonging to the mammalian family of transient receptor potential channels. Trpm5 is expressed in a tissue-restricted manner, with high levels in gustatory tissue. In taste cells, Trpm5 is co-expressed with taste-signaling molecules such as alpha-gustducin, Ggamma(13), phospholipase C beta(2) and inositol 1,4,5-trisphosphate receptor type III. Biophysical studies of Trpm5 heterologously expressed in Xenopus oocytes and mammalian CHO-K1 cells indicate that it functions as a store-operated channel that mediates capacitative calcium entry. The role of store-operated channels and Trpm5 in capacitative calcium entry in taste receptor cells in response to bitter compounds is discussed.
Collapse
Affiliation(s)
- Cristian A Pérez
- Department of Physiology & Biophysics, Howard Hughes Medical Institute, Mount Sinai School of Medicine, New York University, New York, NY 10029, USA.
| | | | | | | |
Collapse
|
1134
|
Xu J, He J, Castleberry AM, Balasubramanian S, Lau AG, Hall RA. Heterodimerization of alpha 2A- and beta 1-adrenergic receptors. J Biol Chem 2003; 278:10770-7. [PMID: 12529373 DOI: 10.1074/jbc.m207968200] [Citation(s) in RCA: 92] [Impact Index Per Article: 4.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
beta- and alpha(2)-adrenergic receptors are known to exhibit substantial cross-talk and mutual regulation in tissues where they are expressed together. We have found that the beta(1)-adrenergic receptor (beta(1)AR) and alpha(2A)-adrenergic receptor (alpha(2A)AR) heterodimerize when coexpressed in cells. Immunoprecipitation studies with differentially tagged beta(1)AR and alpha(2A)AR expressed in HEK-293 cells revealed robust co-immunoprecipitation of the two receptors. Moreover, agonist stimulation of alpha(2A)AR was found to induce substantial internalization of coexpressed beta(1)AR, providing further evidence for a physical association between the two receptors in a cellular environment. Ligand binding assays examining displacement of [(3)H]dihydroalprenolol binding to the beta(1)AR by various ligands revealed that beta(1)AR pharmacological properties were significantly altered when the receptor was coexpressed with alpha(2A)AR. Finally, beta(1)AR/alpha(2A)AR heterodimerization was found to be markedly enhanced by a beta(1)AR point mutation (N15A) that blocks N-linked glycosylation of the beta(1)AR as well as by point mutations (N10A/N14A) that block N-linked glycosylation of the alpha(2A)AR. These data reveal an interaction between beta(1)AR and alpha(2A)AR that is regulated by glycosylation and that may play a key role in cross-talk and mutual regulation between these receptors.
Collapse
Affiliation(s)
- Jianguo Xu
- Department of Pharmacology, Rollins Research Center, Emory University School of Medicine, Atlanta, Georgia 30322, USA
| | | | | | | | | | | |
Collapse
|
1135
|
Danilova V, Hellekant G. Comparison of the responses of the chorda tympani and glossopharyngeal nerves to taste stimuli in C57BL/6J mice. BMC Neurosci 2003; 4:5. [PMID: 12617752 PMCID: PMC153500 DOI: 10.1186/1471-2202-4-5] [Citation(s) in RCA: 73] [Impact Index Per Article: 3.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/15/2002] [Accepted: 03/04/2003] [Indexed: 11/10/2022] Open
Abstract
BACKGROUND Recent progress in discernment of molecular pathways of taste transduction underscores the need for comprehensive phenotypic information for the understanding of the influence of genetic factors in taste. To obtain information that can be used as a base line for assessment of effects of genetic manipulations in mice taste, we have recorded the whole-nerve integrated responses to a wide array of taste stimuli in the chorda tympani (CT) and glossopharyngeal (NG) nerves, the two major taste nerves from the tongue. RESULTS In C57BL/6J mice the responses in the two nerves were not the same. In general sweeteners gave larger responses in the CT than in the NG, while responses to bitter taste in the NG were larger. Thus the CT responses to cyanosuosan, fructose, NC00174, D-phenylalanline and sucrose at all concentrations were significantly larger than in the NG, whereas for acesulfame-K, L-proline, saccharin and SC45647 the differences were not significant. Among bitter compounds amiloride, atropine, cycloheximide, denatonium benzoate, L-phenylalanine, 6-n-propyl-2-thiouracil (PROP) and tetraethyl ammonium chloride (TEA) gave larger responses in the NG, while the responses to brucine, chloroquine, quinacrine, quinine hydrochloride (QHCl), sparteine and strychnine, known to be very bitter to humans, were not significantly larger in the NG than in the CT. CONCLUSION These data provide a comprehensive survey and comparison of the taste sensitivity of the normal C57BL/6J mouse against which the effects of manipulations of its gustatory system can be better assessed.
Collapse
Affiliation(s)
- Vicktoria Danilova
- Department of Animal Health and Biomedical Sciences, University of Wisconsin-Madison, 1656 Linden Dr. Madison, WI 53706, USA
| | - Göran Hellekant
- Department of Animal Health and Biomedical Sciences, University of Wisconsin-Madison, 1656 Linden Dr. Madison, WI 53706, USA
| |
Collapse
|
1136
|
|
1137
|
Abstract
A contentious issue in taste research might have come to a close. Zhang et al., in this issue of Cell, provide broad support for the notion that the recognition of sweet, umami, and bitter tastes use the same signaling molecules. Moreover, they show that individual taste cells are dedicated to the transduction of only one of these three taste qualities.
Collapse
Affiliation(s)
- Hubert Amrein
- Department of Molecular Genetics and Microbiology, Duke University Medical Center, 252 CARL Bldg/Research Drive, Durham, NC 27710, USA
| | | |
Collapse
|
1138
|
Zhang Y, Hoon MA, Chandrashekar J, Mueller KL, Cook B, Wu D, Zuker CS, Ryba NJP. Coding of sweet, bitter, and umami tastes: different receptor cells sharing similar signaling pathways. Cell 2003; 112:293-301. [PMID: 12581520 DOI: 10.1016/s0092-8674(03)00071-0] [Citation(s) in RCA: 895] [Impact Index Per Article: 42.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/26/2022]
Abstract
Mammals can taste a wide repertoire of chemosensory stimuli. Two unrelated families of receptors (T1Rs and T2Rs) mediate responses to sweet, amino acids, and bitter compounds. Here, we demonstrate that knockouts of TRPM5, a taste TRP ion channel, or PLCbeta2, a phospholipase C selectively expressed in taste tissue, abolish sweet, amino acid, and bitter taste reception, but do not impact sour or salty tastes. Therefore, despite relying on different receptors, sweet, amino acid, and bitter transduction converge on common signaling molecules. Using PLCbeta2 taste-blind animals, we then examined a fundamental question in taste perception: how taste modalities are encoded at the cellular level. Mice engineered to rescue PLCbeta2 function exclusively in bitter-receptor expressing cells respond normally to bitter tastants but do not taste sweet or amino acid stimuli. Thus, bitter is encoded independently of sweet and amino acids, and taste receptor cells are not broadly tuned across these modalities.
Collapse
Affiliation(s)
- Yifeng Zhang
- Howard Hughes Medical Institute, Department of Biology, University of California, San Diego, La Jolla, CA 92093, USA
| | | | | | | | | | | | | | | |
Collapse
|
1139
|
Bachmanov AA, Kiefer SW, Molina JC, Tordoff MG, Duffy VB, Bartoshuk LM, Mennella JA. Chemosensory factors influencing alcohol perception, preferences, and consumption. Alcohol Clin Exp Res 2003; 27:220-31. [PMID: 12605071 PMCID: PMC1940064 DOI: 10.1097/01.alc.0000051021.99641.19] [Citation(s) in RCA: 99] [Impact Index Per Article: 4.7] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/27/2023]
Abstract
This article presents the proceedings of a symposium at the 2002 RSA/ISBRA Meeting in San Francisco, California, co-organized by Julie A. Mennella and Alexander A. Bachmanov of the Monell Chemical Senses Center. The goal of this symposium was to review the role that chemosensory factors (taste, smell, and chemical irritation) play in the perception, preference, and consumption of alcohol. The presented research focused on both humans and laboratory animals and used a variety of approaches including genetic, developmental, pharmacological, behavioral, and psychophysical studies. The presentations were as follows: (1) Introduction and overview of the chemical senses (Julie A. Mennella and Alexander A. Bachmanov); (2) Taste reactivity as a measure of alcohol palatability and its relation to alcohol consumption in rats (Stephen W. Kiefer); (3) Early learning about the sensory properties of alcohol in laboratory animals (Juan Carlos Molina); (4) Early learning about the sensory properties of alcohol in humans (Julie A. Mennella); (5) Genetic dissection of the ethanol-sweet taste relationship in mice (Alexander A. Bachmanov and Michael Tordoff); and (6) Human genetic variation in taste: connections with alcohol sensation and intake (Valerie B. Duffy and Linda M. Bartoshuk). The symposium concluded with a general discussion.
Collapse
|
1140
|
Vicogne J, Pin JP, Lardans V, Capron M, Noël C, Dissous C. An unusual receptor tyrosine kinase of Schistosoma mansoni contains a Venus Flytrap module. Mol Biochem Parasitol 2003; 126:51-62. [PMID: 12554084 DOI: 10.1016/s0166-6851(02)00249-9] [Citation(s) in RCA: 72] [Impact Index Per Article: 3.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/24/2022]
Abstract
Previous studies have suggested that successful development of the parasitic helminth Schistosoma mansoni must be dependent on an adaptative molecular dialogue with its hosts and on the existence of receptors for growth factors and hormones. Attempts to identify a homolog of the insulin receptor (IR) have led us to characterize a new receptor tyrosine kinase (RTK) molecule in S. mansoni. SmRTK-1 is an integral membrane protein with a single membrane-spanning sequence separating an extracellular ligand-binding domain and a cytoplasmic TK domain. Structural and phylogenetic analyses of the kinase domain of SmRTK-1 confirmed its similarity to IR catalytic domains. However, sequence analysis of the extracellular domain of SmRTK-1 revealed similarity with various proteins (such as drug receptors) that share a structure known as the Venus Flytrap (VFT) module. Alignment with other VFT modules for which the structure has been solved was used to generate a 3D model of the putative VFT module of SmRTK-1. Phylogenetic analysis indicated that the SmRTK-1 VFT module was closer to that of the GABA(B) receptor. Numerous RTK genes recently discovered in vertebrate and invertebrate species code for large families of modular proteins with diverse structures and ligand-binding specificities. SmRTK-1 probably represents a new class of RTK whose function remains to be determined. RTKs are present in all metazoans and associated with the control of metabolism, growth and development. The preferential localization of SmRTK-1 in sporocyst germinal cells and ovocytes could be in favor of its function in schistosome growth and differentiation.
Collapse
Affiliation(s)
- Jérôme Vicogne
- Unité INSERM 547, Institut Pasteur Lille, 1 rue du Pr. Calmette, France
| | | | | | | | | | | |
Collapse
|
1141
|
Ariyasu T, Matsumoto S, Kyono F, Hanaya T, Arai S, Ikeda M, Kurimoto M. Taste receptor T1R3 is an essential molecule for the cellular recognition of the disaccharide trehalose. In Vitro Cell Dev Biol Anim 2003; 39:80-8. [PMID: 12892531 DOI: 10.1290/1543-706x(2003)039<0080:trtiae>2.0.co;2] [Citation(s) in RCA: 21] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/25/2023]
Abstract
Recently, a sweet taste receptor family, the T1R family, that recognizes some carbohydrates including sucrose was identified. Although the T1R3 molecule is known to participate in heterodimers that are used as sweet- and umami-tasting receptors, there is no evidence that T1R3 alone recognizes similar ligands. We demonstrate for the first time that the candidate sweet taste receptor T1R3 is essential for the recognition and response to the disaccharide trehalose. Our system is a valuable tool not only for understanding the relationship between sweeteners and their receptors but also for exploring the diversities of their receptors, resulting in the design of new high-potency sweeteners.
Collapse
Affiliation(s)
- Toshio Ariyasu
- Fujisaki Institute, Hayashibara Biochemical Laboratories, Inc., 675-1 Fujisaki, Okayama 702-8006, Japan.
| | | | | | | | | | | | | |
Collapse
|
1142
|
Abstract
The olfactory systems of insects and mammals have analogous anatomical features and use similar molecular logic for olfactory coding. The molecular underpinnings of the chemosensory systems that detect taste and pheromone cues have only recently been characterized. Comparison of these systems in Drosophila and mouse uncovers clear differences and a few surprising similarities.
Collapse
Affiliation(s)
- Hiroaki Matsunami
- Department of Molecular Genetics and Microbiology, Duke University Medical Center, Durham, NC 27710, USA
| | - Hubert Amrein
- Department of Molecular Genetics and Microbiology, Duke University Medical Center, Durham, NC 27710, USA
| |
Collapse
|
1143
|
Simon SA. Interactions between salt and acid stimuli: a lesson in gustation from simultaneous epithelial and neural recordings. J Gen Physiol 2002; 120:787-91. [PMID: 12451049 PMCID: PMC2229563 DOI: 10.1085/jgp.20028735] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/23/2022] Open
Affiliation(s)
- S A Simon
- Department of Neurobiology, Duke University Medical Center, Durham, NC 27710, USA
| |
Collapse
|
1144
|
Abstract
Gustatory perception arises not only from intracellular transduction cascades within taste receptor cells but also from cell-to-cell communication among the cells of the taste bud. This study presents novel data demonstrating that the brain-gut peptide cholecystokinin (CCK) is expressed in subsets of taste receptor cells, and that it may play a signaling role unknown previously within the taste bud. Immunocytochemistry revealed positively stained subsets of cells within taste buds throughout the oral cavity. These cells typically displayed round nuclei with full processes, similar to those classified as light cells. Peptide expression was verified using nested PCR on template cDNA derived from mRNA extracted from isolated posterior taste buds. Multiple physiological actions of cholecystokinin on taste receptor cells were observed. An outward potassium current, recorded with the patch-clamp technique, was inhibited by exogenous application of sulfated cholecystokinin octapeptide in a reversible and concentration-dependent manner. Pharmacological analysis suggests that this inhibition is mediated by CCK-A receptors and involves PKC phosphorylation. An inwardly rectifying potassium current, typically invariant to stimulation, was also inhibited by cholecystokinin. Additionally, exogenous cholecystokinin was effective in elevating intracellular calcium as measured by ratiometric techniques with the calcium-sensitive dye fura-2. Pharmacology similarly demonstrated that these calcium elevations were mediated by CCK-A receptors and were dependent on intracellular calcium stores. Collectively, these observations suggest a newly discovered role for peptide neuromodulation in the peripheral processing of taste information.
Collapse
|
1145
|
Jensen AA, Greenwood JR, Bräuner-Osborne H. The dance of the clams: twists and turns in the family C GPCR homodimer. Trends Pharmacol Sci 2002; 23:491-3. [PMID: 12413796 DOI: 10.1016/s0165-6147(02)02107-7] [Citation(s) in RCA: 23] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/27/2022]
|
1146
|
Gilbert AN, Firestein S. Dollars and scents: commercial opportunities in olfaction and taste. Nat Neurosci 2002; 5 Suppl:1043-5. [PMID: 12403982 DOI: 10.1038/nn937] [Citation(s) in RCA: 27] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/02/2002] [Accepted: 09/04/2002] [Indexed: 11/09/2022]
Abstract
Research successes over the past decade have provided a broad outline of the neuroscience of olfaction and taste. Our understanding of these systems now spans the molecular to the psychological. It will soon reach critical mass and begin to generate a variety of practical applications with commercial potential. Given the ubiquity of smell and taste and their importance to health, nutrition and quality of life, these applications could have a major impact on consumer product markets and create entirely new ones. Sensory biotechnology could be the first post-genomic application to break through to the consumer market. We describe odor modulation technologies with implications for food intake, health care and other arenas. Our deeper understanding of olfaction and taste in animal behavior and reproduction provides opportunities in pest control and animal husbandry, where environmentally neutral interventions are much in demand.
Collapse
Affiliation(s)
- Avery N Gilbert
- Sense of Smell Institute, 145 E. 32nd Street, New York, New York 10016-6002, USA
| | | |
Collapse
|
1147
|
Pérez CA, Huang L, Rong M, Kozak JA, Preuss AK, Zhang H, Max M, Margolskee RF. A transient receptor potential channel expressed in taste receptor cells. Nat Neurosci 2002; 5:1169-76. [PMID: 12368808 DOI: 10.1038/nn952] [Citation(s) in RCA: 428] [Impact Index Per Article: 19.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/15/2002] [Accepted: 09/09/2002] [Indexed: 11/09/2022]
Abstract
We used differential screening of cDNAs from individual taste receptor cells to identify candidate taste transduction elements in mice. Among the differentially expressed clones, one encoded Trpm5, a member of the mammalian family of transient receptor potential (TRP) channels. We found Trpm5 to be expressed in a restricted manner, with particularly high levels in taste tissue. In taste cells, Trpm5 was coexpressed with taste-signaling molecules such as alpha-gustducin, Ggamma13, phospholipase C-beta2 (PLC-beta2) and inositol 1,4,5-trisphosphate receptor type III (IP3R3). Our heterologous expression studies of Trpm5 indicate that it functions as a cationic channel that is gated when internal calcium stores are depleted. Trpm5 may be responsible for capacitative calcium entry in taste receptor cells that respond to bitter and/or sweet compounds.
Collapse
Affiliation(s)
- Cristian A Pérez
- Howard Hughes Medical Institute, Mount Sinai School of Medicine, New York University, Box 1677, 1425 Madison Avenue, New York, New York 10029, USA
| | | | | | | | | | | | | | | |
Collapse
|
1148
|
Abstract
Sensory organs are specialized to detect and decode stimuli in terms of intensity and quality. In the gustatory system, the process of identifying and distinguishing taste qualities (e.g. bitter versus sweet) begins in taste buds. A central question in gustatory research is how information about taste quality is extracted by taste receptor cells. For instance, whether and how individual taste cells respond to multiple chemical stimuli is still a matter for debate. A recent study showed that taste cells expressing bitter-responsive taste receptors do not also express sweet-responsive taste receptors and vice versa. These results suggest that the gustatory system may use separate cellular pathways to process bitter and sweet signals independently. Results from electrophysiological studies, however, reveal that individual taste receptor cells respond to stimuli representing multiple taste qualities. Here we used non-invasive Ca(2+) imaging in slices of lingual tissue containing taste buds to address the issue of quality detection in murine taste receptor cells. We recorded calcium transients elicited by chemical stimuli representing different taste qualities (sweet, salty, sour and bitter). Many receptor cells (38 %) responded to multiple taste qualities, with some taste cells responding to both appetitive ("sweet") and aversive ("bitter") stimuli. Thus, there appears to be no strict and separate detection of taste qualities by distinct subpopulations of taste cells in peripheral gustatory sensory organs in mice.
Collapse
Affiliation(s)
- Alejandro Caicedo
- Department of Physiology and Biophysics, University of Miami School of Medicine, 1600 NW 10th Avenue, Miami, FL 33136, USA.
| | | | | |
Collapse
|
1149
|
Abstract
Feeding provides substrate for energy metabolism, which is vital to the survival of every living animal and therefore is subject to intense regulation by brain homeostatic and hedonic systems. Over the last decade, our understanding of the circuits and molecules involved in this process has changed dramatically, in large part due to the availability of animal models with genetic lesions. In this review, we examine the role played in homeostatic regulation of feeding by systemic mediators such as leptin and ghrelin, which act on brain systems utilizing neuropeptide Y, agouti-related peptide, melanocortins, orexins, and melanin concentrating hormone, among other mediators. We also examine the mechanisms for taste and reward systems that provide food with its intrinsically reinforcing properties and explore the links between the homeostatic and hedonic systems that ensure intake of adequate nutrition.
Collapse
Affiliation(s)
- Clifford B Saper
- Department of Neurology, Beth Israel Deaconess Medical Center, Boston, MA 02215, USA.
| | | | | |
Collapse
|
1150
|
Vaidehi N, Floriano WB, Trabanino R, Hall SE, Freddolino P, Choi EJ, Zamanakos G, Goddard WA. Prediction of structure and function of G protein-coupled receptors. Proc Natl Acad Sci U S A 2002; 99:12622-7. [PMID: 12351677 PMCID: PMC130510 DOI: 10.1073/pnas.122357199] [Citation(s) in RCA: 234] [Impact Index Per Article: 10.6] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Accepted: 06/14/2002] [Indexed: 12/22/2022] Open
Abstract
G protein-coupled receptors (GPCRs) mediate our sense of vision, smell, taste, and pain. They are also involved in cell recognition and communication processes, and hence have emerged as a prominent superfamily for drug targets. Unfortunately, the atomic-level structure is available for only one GPCR (bovine rhodopsin), making it difficult to use structure-based methods to design drugs and mutation experiments. We have recently developed first principles methods (MembStruk and HierDock) for predicting structure of GPCRs, and for predicting the ligand binding sites and relative binding affinities. Comparing to the one case with structural data, bovine rhodopsin, we find good accuracy in both the structure of the protein and of the bound ligand. We report here the application of MembStruk and HierDock to beta1-adrenergic receptor, endothelial differential gene 6, mouse and rat I7 olfactory receptors, and human sweet receptor. We find that the predicted structure of beta1-adrenergic receptor leads to a binding site for epinephrine that agrees well with the mutation experiments. Similarly the predicted binding sites and affinities for endothelial differential gene 6, mouse and rat I7 olfactory receptors, and human sweet receptor are consistent with the available experimental data. These predicted structures and binding sites allow the design of mutation experiments to validate and improve the structure and function prediction methods. As these structures are validated they can be used as targets for the design of new receptor-selective antagonists or agonists for GPCRs.
Collapse
Affiliation(s)
- Nagarajan Vaidehi
- Materials and Process Simulation Center, MC 139-74, and Department of Biology, California Institute of Technology, Pasadena, CA 91125, USA
| | | | | | | | | | | | | | | |
Collapse
|