1
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Bhatia V, Maghsoudi S, Hinton M, Bhagirath AY, Singh N, Jaggupilli A, Chelikani P, Dakshinamurti S. Characterization of Adenylyl Cyclase Isoform 6 Residues Interacting with Forskolin. BIOLOGY 2023; 12:biology12040572. [PMID: 37106773 PMCID: PMC10135528 DOI: 10.3390/biology12040572] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 02/17/2023] [Revised: 03/26/2023] [Accepted: 04/03/2023] [Indexed: 04/29/2023]
Abstract
BACKGROUND The adenylyl cyclase (AC) pathway, crucial for pulmonary vasodilation, is inhibited by hypoxia. Forskolin (FSK) binds allosterically to AC, stimulating ATP catalysis. As AC6 is the primary AC isoform in the pulmonary artery, selective reactivation of AC6 could provide targeted reinstatement of hypoxic AC activity. This requires elucidation of the FSK binding site in AC6. METHODS HEK293T cells stably overexpressing AC 5, 6, or 7 were incubated in normoxia (21% O2) or hypoxia (10% O2) or exposed to s-nitrosocysteine (CSNO). AC activity was measured using terbium norfloxacin assay; AC6 structure built by homology modeling; ligand docking to examine FSK-interacting amino acids; roles of selected residues determined by site-directed mutagenesis; FSK-dependent cAMP generation measured in wild-type and FSK-site mutants by biosensor-based live cell assay. RESULTS Only AC6 is inhibited by hypoxia and nitrosylation. Homology modeling and docking revealed residues T500, N503, and S1035 interacting with FSK. Mutation of T500, N503, or S1035 decreased FSK-stimulated AC activity. FSK site mutants were not further inhibited by hypoxia or CSNO; however, mutation of any of these residues prevented AC6 activation by FSK following hypoxia or CSNO treatment. CONCLUSIONS FSK-interacting amino acids are not involved in the hypoxic inhibition mechanism. This study provides direction to design FSK derivatives for selective activation of hypoxic AC6.
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Affiliation(s)
- Vikram Bhatia
- Biology of Breathing Theme, Children's Hospital Research Institute of Manitoba, Winnipeg, MB R3E 3P4, Canada
- Department of Oral Biology, University of Manitoba, Winnipeg, MB R3E 0W2, Canada
- Department of Pediatrics and Child Health, University of Manitoba, Winnipeg, MB R3A 1S1, Canada
| | - Saeid Maghsoudi
- Biology of Breathing Theme, Children's Hospital Research Institute of Manitoba, Winnipeg, MB R3E 3P4, Canada
- Department of Physiology and Pathophysiology, University of Manitoba, Winnipeg, MB R3E 0J9, Canada
| | - Martha Hinton
- Biology of Breathing Theme, Children's Hospital Research Institute of Manitoba, Winnipeg, MB R3E 3P4, Canada
- Department of Physiology and Pathophysiology, University of Manitoba, Winnipeg, MB R3E 0J9, Canada
| | - Anjali Y Bhagirath
- Biology of Breathing Theme, Children's Hospital Research Institute of Manitoba, Winnipeg, MB R3E 3P4, Canada
- Department of Oral Biology, University of Manitoba, Winnipeg, MB R3E 0W2, Canada
| | - Nisha Singh
- Department of Oral Biology, University of Manitoba, Winnipeg, MB R3E 0W2, Canada
| | | | - Prashen Chelikani
- Biology of Breathing Theme, Children's Hospital Research Institute of Manitoba, Winnipeg, MB R3E 3P4, Canada
- Department of Oral Biology, University of Manitoba, Winnipeg, MB R3E 0W2, Canada
- Department of Physiology and Pathophysiology, University of Manitoba, Winnipeg, MB R3E 0J9, Canada
- Department of Biochemistry and Medical Genetics, University of Manitoba, Winnipeg, MB R3E 0J9, Canada
| | - Shyamala Dakshinamurti
- Biology of Breathing Theme, Children's Hospital Research Institute of Manitoba, Winnipeg, MB R3E 3P4, Canada
- Department of Pediatrics and Child Health, University of Manitoba, Winnipeg, MB R3A 1S1, Canada
- Department of Physiology and Pathophysiology, University of Manitoba, Winnipeg, MB R3E 0J9, Canada
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Schihada H, Shekhani R, Schulte G. Quantitative assessment of constitutive G protein-coupled receptor activity with BRET-based G protein biosensors. Sci Signal 2021; 14:eabf1653. [PMID: 34516756 DOI: 10.1126/scisignal.abf1653] [Citation(s) in RCA: 36] [Impact Index Per Article: 12.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/03/2023]
Abstract
[Figure: see text].
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Affiliation(s)
- Hannes Schihada
- Section for Receptor Biology and Signaling, Department of Physiology and Pharmacology, Karolinska Institutet, Biomedicum, Solnavägen 9, SE-17165 Stockholm, Sweden
| | - Rawan Shekhani
- Section for Receptor Biology and Signaling, Department of Physiology and Pharmacology, Karolinska Institutet, Biomedicum, Solnavägen 9, SE-17165 Stockholm, Sweden
| | - Gunnar Schulte
- Section for Receptor Biology and Signaling, Department of Physiology and Pharmacology, Karolinska Institutet, Biomedicum, Solnavägen 9, SE-17165 Stockholm, Sweden
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3
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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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4
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Santhosh KT, Sikarwar AS, Hinton M, Chelikani P, Dakshinamurti S. Thromboxane receptor hyper-responsiveness in hypoxic pulmonary hypertension requires serine 324. Br J Pharmacol 2014; 171:676-87. [PMID: 24490858 DOI: 10.1111/bph.12487] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/15/2013] [Revised: 09/21/2013] [Accepted: 10/03/2013] [Indexed: 11/28/2022] Open
Abstract
BACKGROUND AND PURPOSE Dysregulation of the thromboxane A₂ (TP) receptor, resulting in agonist hypersensitivity and hyper-responsiveness, contributes to exaggerated vasoconstriction in the hypoxic pulmonary artery in neonatal persistent pulmonary hypertension. We previously reported that hypoxia inhibits TP receptor phosphorylation, causing desensitization. Hence, we examined the role of PKA-accessible serine residues in determining TP receptor affinity, using site-directed mutational analysis. EXPERIMENTAL APPROACH Vasoconstriction to a thromboxane mimetic and phosphorylation of TP receptor serine was examined in pulmonary arteries from neonatal swine with persistent pulmonary hypertension and controls. Effects of hypoxia were determined in porcine and human TP receptors. Human TPα serines at positions 324, 329 and 331 (C-terminal tail) were mutated to alanine and transiently expressed in HEK293T cells. Saturation binding and displacement kinetics of a TP antagonist and agonist were determined in porcine TP, wild-type human TPα and all TP mutants. Agonist-elicited calcium mobilization was determined for each TP mutant, in the presence of a PKA activator or inhibitor, and in hypoxic and normoxic conditions. KEY RESULTS The Ser324A mutant was insensitive to PKA activation and hypoxia, had a high affinity for agonist and increased agonist-induced calcium mobilization. Ser329A was no different from wild-type TP receptors. Ser331A was insensitive to hypoxia and PKA with a decreased agonist-mediated response. CONCLUSIONS AND IMPLICATIONS In hypoxic pulmonary hypertension, loss of site-specific phosphorylation of the TP receptor causes agonist hyper-responsiveness. Ser324 is the primary residue phosphorylated by PKA, which regulates TP receptor-agonist interactions. Ser331 mutation confers loss of TP receptor-agonist interaction, regardless of PKA activity.
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Affiliation(s)
- K T Santhosh
- Biology of Breathing Group, Manitoba Institute of Child Health, Winnipeg, MB, Canada
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5
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Neveu C, Dulin F, Lefranc B, Galas L, Calbrix C, Bureau R, Rault S, Chuquet J, Boutin JA, Guilhaudis L, Ségalas-Milazzo I, Vaudry D, Vaudry H, Santos JSDO, Leprince J. Molecular basis of agonist docking in a human GPR103 homology model by site-directed mutagenesis and structure-activity relationship studies. Br J Pharmacol 2014; 171:4425-39. [PMID: 24913445 DOI: 10.1111/bph.12808] [Citation(s) in RCA: 11] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/24/2013] [Revised: 04/04/2014] [Accepted: 05/15/2014] [Indexed: 01/07/2023] Open
Abstract
BACKGROUND AND PURPOSE The neuropeptide 26RFa and its cognate receptor GPR103 are involved in the control of food intake and bone mineralization. Here, we have tested, experimentally, the predicted ligand-receptor interactions by site-directed mutagenesis of GPR103 and designed point-substituted 26RFa analogues. EXPERIMENTAL APPROACH Using the X-ray structure of the β2 -adrenoceptor, a 3-D molecular model of GPR103 has been built. The bioactive C-terminal octapeptide 26RFa(19-26) , KGGFSFRF-NH2 , was docked in this GPR103 model and the ligand-receptor complex was submitted to energy minimization. KEY RESULTS In the most stable complex, the Phe-Arg-Phe-NH2 part was oriented inside the receptor cavity, whereas the N-terminal Lys residue remained outside. A strong intermolecular interaction was predicted between the Arg(25) residue of 26RFa and the Gln(125) residue located in the third transmembrane helix of GPR103. To confirm this interaction experimentally, we tested the ability of 26RFa and Arg-modified 26RFa analogues to activate the wild-type and the Q125A mutant receptors transiently expressed in CHO cells. 26RFa (10(-6) M) enhanced [Ca(2+) ]i in wild-type GPR103-transfected cells, but failed to increase [Ca(2+) ]i in Q125A mutant receptor-expressing cells. Moreover, asymmetric dimethylation of the side chain of arginine led to a 26RFa analogue, [ADMA(25) ]26RFa(20-26) , that was unable to activate the wild-type GPR103, but antagonized 26RFa-evoked [Ca(2+) ]i increase. CONCLUSION AND IMPLICATIONS Altogether, these data provide strong evidence for a functional interaction between the Arg(25) residue of 26RFa and the Gln(125) residue of GPR103 upon ligand-receptor activation, which can be exploited for the rational design of potent GPR103 agonists and antagonists.
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Affiliation(s)
- C Neveu
- Inserm U982, Laboratory of Neuronal and Neuroendocrine Cell Differentiation and Communication, Neurotrophic Factors and Neuronal Differentiation Team, Institute for Research and Innovation in Biomedicine (IRIB); Cell Imaging Platform of Normandy (PRIMACEN), IRIB; Normandie Univ, France
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6
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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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7
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Chakraborty R, Bhullar RP, Dakshinamurti S, Hwa J, Chelikani P. Inverse agonism of SQ 29,548 and Ramatroban on Thromboxane A2 receptor. PLoS One 2014; 9:e85937. [PMID: 24465800 PMCID: PMC3900440 DOI: 10.1371/journal.pone.0085937] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/18/2013] [Accepted: 12/03/2013] [Indexed: 12/30/2022] Open
Abstract
G protein-coupled receptors (GPCRs) show some level of basal activity even in the absence of an agonist, a phenomenon referred to as constitutive activity. Such constitutive activity in GPCRs is known to have important pathophysiological roles in human disease. The thromboxane A2 receptor (TP) is a GPCR that promotes thrombosis in response to binding of the prostanoid, thromboxane A2. TP dysfunction is widely implicated in pathophysiological conditions such as bleeding disorders, hypertension and cardiovascular disease. Recently, we reported the characterization of a few constitutively active mutants (CAMs) in TP, including a genetic variant A160T. Using these CAMs as reporters, we now test the inverse agonist properties of known antagonists of TP, SQ 29,548, Ramatroban, L-670596 and Diclofenac, in HEK293T cells. Interestingly, SQ 29,548 reduced the basal activity of both, WT-TP and the CAMs while Ramatroban was able to reduce the basal activity of only the CAMs. Diclofenac and L-670596 showed no statistically significant reduction in basal activity of WT-TP or CAMs. To investigate the role of these compounds on human platelet function, we tested their effects on human megakaryocyte based system for platelet activation. Both SQ 29,548 and Ramatroban reduced the platelet hyperactivity of the A160T genetic variant. Taken together, our results suggest that SQ 29,548 and Ramatroban are inverse agonists for TP, whereas, L-670596 and Diclofenac are neutral antagonists. Our findings have important therapeutic applications in the treatment of TP mediated pathophysiological conditions.
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MESH Headings
- Amino Acid Substitution
- Blood Platelets/drug effects
- Blood Platelets/metabolism
- Bridged Bicyclo Compounds, Heterocyclic
- Calcium Signaling/drug effects
- Carbazoles/pharmacology
- Drug Evaluation, Preclinical
- Fatty Acids, Unsaturated
- HEK293 Cells
- Humans
- Hydrazines/pharmacology
- Inositol 1,4,5-Trisphosphate/metabolism
- Mutagenesis, Site-Directed
- Receptors, Thromboxane A2, Prostaglandin H2/agonists
- Receptors, Thromboxane A2, Prostaglandin H2/genetics
- Receptors, Thromboxane A2, Prostaglandin H2/metabolism
- Sulfonamides/pharmacology
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Affiliation(s)
- Raja Chakraborty
- Department of Oral Biology, University of Manitoba, Winnipeg, Manitoba, Canada
- Biology of Breathing Group- Manitoba Institute of Child Health, Winnipeg, Manitoba, Canada
| | - Rajinder P. Bhullar
- Department of Oral Biology, University of Manitoba, Winnipeg, Manitoba, Canada
| | - Shyamala Dakshinamurti
- Departments of Pediatrics, Physiology, University of Manitoba, Winnipeg, Manitoba, Canada
- Biology of Breathing Group- Manitoba Institute of Child Health, Winnipeg, Manitoba, Canada
| | - John Hwa
- Department of Internal Medicine (Cardiology), Cardiovascular Research Center, Yale University School of Medicine, New Haven, Connecticut, United States of America
| | - Prashen Chelikani
- Department of Oral Biology, University of Manitoba, Winnipeg, Manitoba, Canada
- Departments of Pediatrics, Physiology, University of Manitoba, Winnipeg, Manitoba, Canada
- Biology of Breathing Group- Manitoba Institute of Child Health, Winnipeg, Manitoba, Canada
- * E-mail:
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8
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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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9
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High-level expression, purification and characterization of a constitutively active thromboxane A2 receptor polymorphic variant. PLoS One 2013; 8:e76481. [PMID: 24086743 PMCID: PMC3781061 DOI: 10.1371/journal.pone.0076481] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/19/2012] [Accepted: 08/27/2013] [Indexed: 01/06/2023] Open
Abstract
G protein-coupled receptors (GPCRs) exhibit some level of basal signaling even in the absence of a bound agonist. This basal or constitutive signaling can have important pathophysiological roles. In the past few years, a number of high resolution crystal structures of GPCRs have been reported, including two crystal structures of constitutively active mutants (CAM) of the dim-light receptor, rhodopsin. The structural characterizations of CAMs are impeded by the lack of proper expression systems. The thromboxane A2 receptor (TP) is a GPCR that mediates vasoconstriction and promotes thrombosis in response to the binding of thromboxane. Here, we report on the expression and purification of a genetic variant and CAM in TP, namely A160T, using tetracycline-inducible HEK293S-TetR and HEK293S (GnTI¯)-TetR cell lines. Expression of the TP and the A160T genes in these mammalian cell lines resulted in a 4-fold increase in expression to a level of 15.8 ±0.3 pmol of receptor/mg of membrane protein. The receptors expressed in the HEK293S (GnTI(-))-TetR cell line showed homogeneous glycosylation. The functional yield of the receptors using a single step affinity purification was 45 µg/10⁶ cells. Temperature- dependent secondary structure changes of the purified TP and A160T receptors were characterized using circular dichroism (CD) spectropolarimetry. The CD spectra shows that the loss of activity or thermal sensitivity that was previously observed for the A160T mutant, is not owing to large unfolding of the protein but rather to a more subtle effect. This is the first study to report on the successful high-level expression, purification, and biophysical characterization of a naturally occurring, diffusible ligand activated GPCR CAM.
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10
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Sikarwar AS, Hinton M, Santhosh KT, Chelikani P, Dakshinamurti S. Palmitoylation of Gαq Determines its Association with the Thromboxane Receptor in Hypoxic Pulmonary Hypertension. Am J Respir Cell Mol Biol 2013; 50:135-43. [DOI: 10.1165/rcmb.2013-0085oc] [Citation(s) in RCA: 10] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/24/2022] Open
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11
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Gleim S, Stitham J, Tang WH, Li H, Douville K, Chelikani P, J.Rade J, Martin KA, Hwa J. Human thromboxane A2 receptor genetic variants: in silico, in vitro and "in platelet" analysis. PLoS One 2013; 8:e67314. [PMID: 23840660 PMCID: PMC3696120 DOI: 10.1371/journal.pone.0067314] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/10/2013] [Accepted: 05/16/2013] [Indexed: 11/19/2022] Open
Abstract
Thromboxane and its receptor have emerged as key players in modulating vascular thrombotic events. Thus, a dysfunctional hTP genetic variant may protect against (hypoactivity) or promote (hyperactivity) vascular events, based upon its activity on platelets. After extensive in silico analysis, six hTP-α variants were selected (C68S, V80E, E94V, A160T, V176E, and V217I) for detailed biochemical studies based on structural proximity to key regions involved in receptor function and in silico predictions. Variant biochemical profiles ranged from severe instability (C68S) to normal (V217I), with most variants demonstrating functional alteration in binding, expression or activation (V80E, E94V, A160T, and V176E). In the absence of patient platelet samples, we developed and validated a novel megakaryocyte based system to evaluate human platelet function in the presence of detected dysfunctional genetic variants. Interestingly, variant V80E exhibited reduced platelet activation whereas A160T demonstrated platelet hyperactivity. This report provides the most comprehensive in silico, in vitro and “in platelet” evaluation of hTP variants to date and highlightscurrent inherent problems in evaluating genetic variants, with possible solutions. The study additionally provides clinical relevance to characterized dysfunctional hTP variants.
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MESH Headings
- Amino Acid Sequence
- Amino Acid Substitution
- Aspirin/pharmacology
- Binding Sites
- Binding, Competitive
- Blood Platelets/drug effects
- Blood Platelets/metabolism
- Cell Line
- Cyclooxygenase Inhibitors/pharmacology
- Genetic Association Studies
- Humans
- Models, Molecular
- Molecular Sequence Data
- Phosphoproteins/metabolism
- Platelet Activation/drug effects
- Polymorphism, Single Nucleotide
- Protein Structure, Secondary
- Protein Structure, Tertiary
- Proteome/metabolism
- Receptors, Thromboxane A2, Prostaglandin H2/chemistry
- Receptors, Thromboxane A2, Prostaglandin H2/genetics
- Receptors, Thromboxane A2, Prostaglandin H2/metabolism
- Signal Transduction
- Thromboxanes/physiology
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Affiliation(s)
- Scott Gleim
- Internal Medicine, Cardiovascular Medicine, Yale University School of Medicine, New Haven Connecticut, United States of America
| | - Jeremiah Stitham
- Internal Medicine, Cardiovascular Medicine, Yale University School of Medicine, New Haven Connecticut, United States of America
| | - Wai Ho Tang
- Internal Medicine, Cardiovascular Medicine, Yale University School of Medicine, New Haven Connecticut, United States of America
| | - Hong Li
- Department of Pharmacology and Toxicology, Dartmouth Medical School, Hanover New Hampshire, United States of America
| | - Karen Douville
- Department of Pharmacology and Toxicology, Dartmouth Medical School, Hanover New Hampshire, United States of America
| | - Prashen Chelikani
- Department of Oral Biology, University of Manitoba Faculty of Dentistry, Winnipeg, Manitoba, Canada
| | - Jeffrey J.Rade
- Internal Medicine-Section of Cardiology, UMass School of Medicine and Medical Center, Worcester, Massachusetts, United States of America
| | - Kathleen A. Martin
- Internal Medicine, Cardiovascular Medicine, Yale University School of Medicine, New Haven Connecticut, United States of America
| | - John Hwa
- Internal Medicine, Cardiovascular Medicine, Yale University School of Medicine, New Haven Connecticut, United States of America
- Department of Pharmacology and Toxicology, Dartmouth Medical School, Hanover New Hampshire, United States of America
- * E-mail:
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12
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Francis BR. Evolution of the genetic code by incorporation of amino acids that improved or changed protein function. J Mol Evol 2013; 77:134-58. [PMID: 23743924 DOI: 10.1007/s00239-013-9567-y] [Citation(s) in RCA: 26] [Impact Index Per Article: 2.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/11/2013] [Accepted: 05/25/2013] [Indexed: 12/31/2022]
Abstract
Fifty years have passed since the genetic code was deciphered, but how the genetic code came into being has not been satisfactorily addressed. It is now widely accepted that the earliest genetic code did not encode all 20 amino acids found in the universal genetic code as some amino acids have complex biosynthetic pathways and likely were not available from the environment. Therefore, the genetic code evolved as pathways for synthesis of new amino acids became available. One hypothesis proposes that early in the evolution of the genetic code four amino acids-valine, alanine, aspartic acid, and glycine-were coded by GNC codons (N = any base) with the remaining codons being nonsense codons. The other sixteen amino acids were subsequently added to the genetic code by changing nonsense codons into sense codons for these amino acids. Improvement in protein function is presumed to be the driving force behind the evolution of the code, but how improved function was achieved by adding amino acids has not been examined. Based on an analysis of amino acid function in proteins, an evolutionary mechanism for expansion of the genetic code is described in which individual coded amino acids were replaced by new amino acids that used nonsense codons differing by one base change from the sense codons previously used. The improved or altered protein function afforded by the changes in amino acid function provided the selective advantage underlying the expansion of the genetic code. Analysis of amino acid properties and functions explains why amino acids are found in their respective positions in the genetic code.
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Affiliation(s)
- Brian R Francis
- Department of Molecular Biology, University of Wyoming, Laramie, WY, 82071-3944, USA,
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New insights into structural determinants for prostanoid thromboxane A2 receptor- and prostacyclin receptor-G protein coupling. Mol Cell Biol 2012; 33:184-93. [PMID: 23109431 DOI: 10.1128/mcb.00725-12] [Citation(s) in RCA: 21] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/29/2022] Open
Abstract
G protein-coupled receptors (GPCRs) interact with heterotrimeric G proteins and initiate a wide variety of signaling pathways. The molecular nature of GPCR-G protein interactions in the clinically important thromboxane A2 (TxA(2)) receptor (TP) and prostacyclin (PGI(2)) receptor (IP) is poorly understood. The TP activates its cognate G protein (Gαq) in response to the binding of thromboxane, while the IP signals through Gαs in response to the binding of prostacyclin. Here, we utilized a combination of approaches consisting of chimeric receptors, molecular modeling, and site-directed mutagenesis to precisely study the specificity of G protein coupling. Multiple chimeric receptors were constructed by replacing the TP intracellular loops (ICLs) with the ICL regions of the IP. Our results demonstrate that both the sequences and lengths of ICL2 and ICL3 influenced G protein specificity. Importantly, we identified a precise ICL region on the prostanoid receptors TP and IP that can switch G protein specificities. The validities of the chimeric technique and the derived molecular model were confirmed by introducing clinically relevant naturally occurring mutations (R60L in the TP and R212C in the IP). Our findings provide new molecular insights into prostanoid receptor-G protein interactions, which are of general significance for understanding the structural basis of G protein activation by GPCRs in basic health and cardiovascular disease.
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Pydi SP, Bhullar RP, Chelikani P. Constitutively active mutant gives novel insights into the mechanism of bitter taste receptor activation. J Neurochem 2012; 122:537-44. [DOI: 10.1111/j.1471-4159.2012.07808.x] [Citation(s) in RCA: 29] [Impact Index Per Article: 2.4] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
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