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Construction of a bioluminescence-based assay for bitter taste receptors (TAS2Rs). Sci Rep 2022; 12:17658. [PMID: 36271274 PMCID: PMC9587021 DOI: 10.1038/s41598-022-21678-3] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/30/2022] [Accepted: 09/30/2022] [Indexed: 01/18/2023] Open
Abstract
In humans, a family of 25 bitter taste receptors (TAS2Rs) mediates bitter taste perception. A common approach to characterize bitter causative agents involves expressing TAS2Rs and the appropriate signal transducers in heterologous cell systems, and monitoring changes in the intracellular free calcium levels upon ligand exposure using a fluorescence-based modality, which typically suffers from a low signal window, and is susceptible to interference by autofluorescence, therefore prohibiting its application to screening of plant or food extracts, which are likely to contain autofluorescent compounds. The aim of this study is to develop and validate a bioluminescence-based intracellular calcium release assay for TAS2Rs that has a better assay performance than a fluorescence-based assay. Furthermore, the bioluminescence-based assay enabled the evaluation of TAS2R agonists within an autofluorescent matrix, highlighting its potential utility in the assessment of the bitterness-inducing properties of plant or food fractions by the food industry. Additionally, improvement to the bioluminescence-based assay for some TAS2Rs was achieved by altering their N-terminal signal sequences, leading to signal window enhancement. Altogether, the bioluminescence-based TAS2R assay can be used to perform functional studies of TAS2Rs, evaluate TAS2R-modulating properties of autofluorescent samples, and facilitate the discovery of compounds that can function as promising bitter taste modulators.
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Medapati MR, Bhagirath AY, Singh N, Chelikani P. Pharmacology of T2R Mediated Host-Microbe Interactions. Handb Exp Pharmacol 2021; 275:177-202. [PMID: 33580389 DOI: 10.1007/164_2021_435] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/12/2022]
Abstract
Bitter taste receptors (T2Rs) belong to the G protein-coupled receptor superfamily. Humans express 25 T2Rs that are known to detect several bitter compounds including bacterial quorum sensing molecules (QSM). Primarily found to be key receptors for bitter sensation T2Rs are known to play an important role in mediating innate immune responses in oral and extraoral tissues. Several studies have led to identification of Gram-negative and Gram-positive bacterial QSMs as agonists for T2Rs in airway epithelial cells and immune cells. However, the pharmacological characterization for many of the QSM-T2R interactions remains poorly defined. In this chapter, we discuss the extraoral roles including localization of T2Rs in extracellular vesicles, molecular pharmacology of QSM-T2R interactions, role of T2Rs in mediating innate immune responses, and some of the challenges in understanding T2R pharmacology.
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Affiliation(s)
- Manoj Reddy Medapati
- Manitoba Chemosensory Biology Research Group, Department of Oral Biology, Dr. Gerald Niznick College of Dentistry, University of Manitoba, Winnipeg, MB, Canada
- Children's Hospital Research Institute of Manitoba, Winnipeg, MB, Canada
| | - Anjali Y Bhagirath
- Manitoba Chemosensory Biology Research Group, Department of Oral Biology, Dr. Gerald Niznick College of Dentistry, University of Manitoba, Winnipeg, MB, Canada
- Children's Hospital Research Institute of Manitoba, Winnipeg, MB, Canada
| | - Nisha Singh
- Manitoba Chemosensory Biology Research Group, Department of Oral Biology, Dr. Gerald Niznick College of Dentistry, University of Manitoba, Winnipeg, MB, Canada
- Children's Hospital Research Institute of Manitoba, Winnipeg, MB, Canada
| | - Prashen Chelikani
- Manitoba Chemosensory Biology Research Group, Department of Oral Biology, Dr. Gerald Niznick College of Dentistry, University of Manitoba, Winnipeg, MB, Canada.
- Children's Hospital Research Institute of Manitoba, Winnipeg, MB, Canada.
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Uddin MS, Naider F, Becker JM. Dynamic roles for the N-terminus of the yeast G protein-coupled receptor Ste2p. BIOCHIMICA ET BIOPHYSICA ACTA-BIOMEMBRANES 2017; 1859:2058-2067. [PMID: 28754538 DOI: 10.1016/j.bbamem.2017.07.014] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 03/27/2017] [Revised: 07/13/2017] [Accepted: 07/24/2017] [Indexed: 12/11/2022]
Abstract
The Saccharomyces cerevisiae α-factor receptor Ste2p has been used extensively as a model to understand the molecular mechanism of signal transduction by G protein-coupled receptors (GPCRs). Single and double cysteine mutants of Ste2p were created and served as surrogates to detect intramolecular interactions and dimerization of Ste2p using disulfide cross-linking methodology. When a mutation was introduced into the phylogenetically conserved tyrosine residue at position 26 (Y26C) in the N-terminus of Ste2p, dimerization was increased greatly. The amount of dimer formed by this Y26C mutant was greatly reduced by ligand binding even though the ligand binding site is far removed from the N-terminus; the lowering of the dimer formation was consistent with a conformational change in the N-terminus of the receptor upon activation. Dimerization was decreased by double mutations Y26C/V109C or Y26C/T114C indicating that Y26 is in close proximity to V109 and T114 of extracellular loop 1 in native Ste2p. Combined with earlier studies, these results indicate previously unrecognized roles for the N-terminus of Ste2p, and perhaps of GPCRs in general, and reveal a specific N-terminus residue or region, that is involved in GPCR signaling, intrareceptor interactions, and receptor dimerization.
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Affiliation(s)
- M Seraj Uddin
- Department of Microbiology, University of Tennessee, Knoxville, Tennessee 37996, United States
| | - Fred Naider
- Department of Chemistry and Macromolecular Assemblies Institute, College of Staten Island, CUNY, New York, New York 10314, United States; Ph.D. Programs in Biochemistry and Chemistry, The Graduate Center of the City University of New York, New York, NY 10016, United States
| | - Jeffrey M Becker
- Department of Microbiology, University of Tennessee, Knoxville, Tennessee 37996, United States.
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Upadhyaya JD, Chakraborty R, Shaik FA, Jaggupilli A, Bhullar RP, Chelikani P. The Pharmacochaperone Activity of Quinine on Bitter Taste Receptors. PLoS One 2016; 11:e0156347. [PMID: 27223611 PMCID: PMC4880206 DOI: 10.1371/journal.pone.0156347] [Citation(s) in RCA: 29] [Impact Index Per Article: 3.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/01/2015] [Accepted: 05/12/2016] [Indexed: 11/19/2022] Open
Abstract
Bitter taste is one of the five basic taste sensations which is mediated by 25 bitter taste receptors (T2Rs) in humans. The mechanism of bitter taste signal transduction is not yet elucidated. The cellular processes underlying T2R desensitization including receptor internalization, trafficking and degradation are yet to be studied. Here, using a combination of molecular and pharmacological techniques we show that T2R4 is not internalized upon agonist treatment. Pretreatment with bitter agonist quinine led to a reduction in subsequent quinine-mediated calcium responses to 35 ± 5% compared to the control untreated cells. Interestingly, treatment with different bitter agonists did not cause internalization of T2R4. Instead, quinine treatment led to a 2-fold increase in T2R4 cell surface expression which was sensitive to Brefeldin A, suggesting a novel pharmacochaperone activity of quinine. This phenomenon of chaperone activity of quinine was also observed for T2R7, T2R10, T2R39 and T2R46. Our results suggest that the observed action of quinine for these T2Rs is independent of its agonist activity. This study provides novel insights into the pharmacochaperone activity of quinine and possible mechanism of T2R desensitization, which is of fundamental importance in understanding the mechanism of bitter taste signal transduction.
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Affiliation(s)
- Jasbir D. Upadhyaya
- Department of Oral Biology, and Manitoba Chemosensory Biology (MCSB) Research group, University of Manitoba, Winnipeg, MB, R3E 0W2, Canada
- Children’s Hospital Research Institute of Manitoba, Winnipeg, MB, R3E 3P4, Canada
| | - Raja Chakraborty
- Department of Oral Biology, and Manitoba Chemosensory Biology (MCSB) Research group, University of Manitoba, Winnipeg, MB, R3E 0W2, Canada
- Children’s Hospital Research Institute of Manitoba, Winnipeg, MB, R3E 3P4, Canada
| | - Feroz A. Shaik
- Department of Oral Biology, and Manitoba Chemosensory Biology (MCSB) Research group, University of Manitoba, Winnipeg, MB, R3E 0W2, Canada
- Children’s Hospital Research Institute of Manitoba, Winnipeg, MB, R3E 3P4, Canada
| | - Appalaraju Jaggupilli
- Department of Oral Biology, and Manitoba Chemosensory Biology (MCSB) Research group, University of Manitoba, Winnipeg, MB, R3E 0W2, Canada
- Children’s Hospital Research Institute of Manitoba, Winnipeg, MB, R3E 3P4, Canada
| | - Rajinder P. Bhullar
- Department of Oral Biology, and Manitoba Chemosensory Biology (MCSB) Research group, University of Manitoba, Winnipeg, MB, R3E 0W2, Canada
| | - Prashen Chelikani
- Department of Oral Biology, and Manitoba Chemosensory Biology (MCSB) Research group, University of Manitoba, Winnipeg, MB, R3E 0W2, Canada
- Children’s Hospital Research Institute of Manitoba, Winnipeg, MB, R3E 3P4, Canada
- * E-mail:
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Pydi SP, Sobotkiewicz T, Billakanti R, Bhullar RP, Loewen MC, Chelikani P. Amino acid derivatives as bitter taste receptor (T2R) blockers. J Biol Chem 2014; 289:25054-66. [PMID: 25059668 DOI: 10.1074/jbc.m114.576975] [Citation(s) in RCA: 65] [Impact Index Per Article: 6.5] [Reference Citation Analysis] [Abstract] [Key Words] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/20/2022] Open
Abstract
In humans, the 25 bitter taste receptors (T2Rs) are activated by hundreds of structurally diverse bitter compounds. However, only five antagonists or bitter blockers are known. In this study, using molecular modeling guided site-directed mutagenesis, we elucidated the ligand-binding pocket of T2R4. We found seven amino acids located in the extracellular side of transmembrane 3 (TM3), TM4, extracellular loop 2 (ECL2), and ECL3 to be involved in T2R4 binding to its agonist quinine. ECL2 residues Asn-173 and Thr-174 are essential for quinine binding. Guided by a molecular model of T2R4, a number of amino acid derivatives were screened for their ability to bind to T2R4. These predictions were tested by calcium imaging assays that led to identification of γ-aminobutryic acid (GABA) and Nα,Nα-bis(carboxymethyl)-L-lysine (BCML) as competitive inhibitors of quinine-activated T2R4 with an IC50 of 3.2 ± 0.3 μM and 59 ± 18 nM, respectively. Interestingly, pharmacological characterization using a constitutively active mutant of T2R4 reveals that GABA acts as an antagonist, whereas BCML acts as an inverse agonist on T2R4. Site-directed mutagenesis confirms that the two novel bitter blockers share the same orthosteric site as the agonist quinine. The signature residues Ala-90 and Lys-270 play important roles in interacting with BCML and GABA, respectively. This is the first report to characterize a T2R endogenous antagonist and an inverse agonist. The novel bitter blockers will facilitate physiological studies focused on understanding the roles of T2Rs in extraoral tissues.
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Affiliation(s)
- Sai P Pydi
- From the Department of Oral Biology, University of Manitoba, Winnipeg, Manitoba R3E 0W4, the Manitoba Institute of Child Health, Winnipeg, Manitoba R3E 0W4, and
| | - Tyler Sobotkiewicz
- From the Department of Oral Biology, University of Manitoba, Winnipeg, Manitoba R3E 0W4
| | - Rohini Billakanti
- From the Department of Oral Biology, University of Manitoba, Winnipeg, Manitoba R3E 0W4, the Manitoba Institute of Child Health, Winnipeg, Manitoba R3E 0W4, and
| | - Rajinder P Bhullar
- From the Department of Oral Biology, University of Manitoba, Winnipeg, Manitoba R3E 0W4
| | - Michele C Loewen
- the National Research Council of Canada, Saskatoon, Saskatchewan S7N 0W9, Canada
| | - Prashen Chelikani
- From the Department of Oral Biology, University of Manitoba, Winnipeg, Manitoba R3E 0W4, the Manitoba Institute of Child Health, Winnipeg, Manitoba R3E 0W4, and
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Pydi SP, Bhullar RP, Chelikani P. Constitutive Activity of Bitter Taste Receptors (T2Rs). ADVANCES IN PHARMACOLOGY 2014; 70:303-26. [DOI: 10.1016/b978-0-12-417197-8.00010-9] [Citation(s) in RCA: 18] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 12/12/2022]
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Prasad Pydi S, Singh N, Upadhyaya J, Pal Bhullar R, Chelikani P. The third intracellular loop plays a critical role in bitter taste receptor activation. BIOCHIMICA ET BIOPHYSICA ACTA-BIOMEMBRANES 2014; 1838:231-6. [DOI: 10.1016/j.bbamem.2013.08.009] [Citation(s) in RCA: 22] [Impact Index Per Article: 2.2] [Reference Citation Analysis] [Track Full Text] [Subscribe] [Scholar Register] [Received: 03/18/2013] [Revised: 08/12/2013] [Accepted: 08/14/2013] [Indexed: 10/26/2022]
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