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Wang S, Liu H, Roberts JB, Wiley AP, Marayati BF, Adams KL, Luessen DJ, Eldeeb K, Sun H, Zhang K, Chen R. Prolonged ethanol exposure modulates constitutive internalization and recycling of 5-HT1A receptors. J Neurochem 2022; 160:469-481. [PMID: 34928513 PMCID: PMC8828711 DOI: 10.1111/jnc.15564] [Citation(s) in RCA: 2] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/04/2021] [Revised: 11/24/2021] [Accepted: 12/13/2021] [Indexed: 02/03/2023]
Abstract
Alcohol exposure alters the signaling of the serotoninergic system, which is involved in alcohol consumption, reward, and dependence. In particular, dysregulation of serotonin receptor type 1A (5-HT1AR) is associated with alcohol intake and withdrawal-induced anxiety-like behavior in rodents. However, how ethanol regulates 5-HT1AR activity and cell surface availability remains elusive. Using neuroblastoma 2a cells stably expressing human 5-HT1ARs tagged with hemagglutinin at the N-terminus, we found that prolonged ethanol exposure (18 h) reduced the basal surface levels of 5-HT1ARs in a concentration-dependent manner. This reduction is attributed to both enhanced receptor internalization and attenuated receptor recycling. Moreover, constitutive 5-HT1AR internalization in ethanol naïve cells was blocked by concanavalin A (ConA) but not nystatin, suggesting clathrin-dependent 5-HT1AR internalization. In contrast, constitutive 5-HT1AR internalization in ethanol-treated cells was blocked by nystatin but not by ConA, indicating that constitutive 5-HT1AR internalization switched from a clathrin- to a caveolin-dependent pathway. Dynasore, an inhibitor of dynamin, blocked 5-HT1AR internalization in both vehicle- and ethanol-treated cells. Furthermore, ethanol exposure enhanced the activity of dynamin I via dephosphorylation and reduced myosin Va levels, which may contribute to increased internalization and reduced recycling of 5-HT1ARs, respectively. Our findings suggest that prolonged ethanol exposure not only alters the endocytic trafficking of 5-HT1ARs but also the mechanism by which constitutive 5-HT1AR internalization occurs.
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Affiliation(s)
- Shiyu Wang
- Department of Physiology & Pharmacology, Wake Forest School of Medicine, Winston Salem, NC 27157
| | - Haoran Liu
- Department of Biology, Wake Forest University, Winston Salem, NC 27106
| | - Jonté B. Roberts
- Department of Physiology & Pharmacology, Wake Forest School of Medicine, Winston Salem, NC 27157
| | - Aidan P. Wiley
- Department of Physiology & Pharmacology, Wake Forest School of Medicine, Winston Salem, NC 27157
| | | | - Kristen L. Adams
- Department of Physiology & Pharmacology, Wake Forest School of Medicine, Winston Salem, NC 27157
| | - Deborah J. Luessen
- Department of Physiology & Pharmacology, Wake Forest School of Medicine, Winston Salem, NC 27157
| | - Khalil Eldeeb
- Department of Physiology & Pharmacology, Wake Forest School of Medicine, Winston Salem, NC 27157
- Campbell University School of Osteopathic Medicine, Lillington, NC 27546
| | - Haiguo Sun
- Department of Physiology & Pharmacology, Wake Forest School of Medicine, Winston Salem, NC 27157
| | - Ke Zhang
- Department of Biology, Wake Forest University, Winston Salem, NC 27106
- Center for Molecular Signaling, Wake Forest University, Winston Salem, NC 27106
| | - Rong Chen
- Department of Physiology & Pharmacology, Wake Forest School of Medicine, Winston Salem, NC 27157
- Center for Molecular Signaling, Wake Forest University, Winston Salem, NC 27106
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Kalipatnapu S, Chattopadhyay A. Membrane Organization and Function of the Serotonin1A Receptor. Cell Mol Neurobiol 2007; 27:1097-116. [PMID: 17710529 DOI: 10.1007/s10571-007-9189-2] [Citation(s) in RCA: 55] [Impact Index Per Article: 3.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/10/2007] [Accepted: 07/27/2007] [Indexed: 01/02/2023]
Abstract
(1) The serotonin(1A) receptor is a G-protein coupled receptor involved in several cognitive, behavioral, and developmental functions. It binds the neurotransmitter serotonin and signals across the membrane through its interactions with heterotrimeric G-proteins. (2) Lipid-protein interactions in membranes play an important role in the assembly, stability, and function of membrane proteins. The role of membrane environment in serotonin(1A) receptor function is beginning to be addressed by exploring the consequences of lipid manipulations on the ligand binding and G-protein coupling of serotonin(1A) receptors, the ability to functionally solubilize the serotonin(1A) receptor, and the factors influencing the membrane organization of the serotonin(1A) receptor. (3) Recent developments involving the application of detergent-based and detergent-free approaches to understand the membrane organization of the serotonin(1A) receptor under conditions of ligand activation and modulation of membrane lipid content, with an emphasis on membrane cholesterol, are described.
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Affiliation(s)
- Shanti Kalipatnapu
- Divisionof Biological Sciences, University of California, San Diego, La Jolla, CA 92093-0377, USA
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3
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Pucadyil TJ, Chattopadhyay A. Role of cholesterol in the function and organization of G-protein coupled receptors. Prog Lipid Res 2006; 45:295-333. [PMID: 16616960 DOI: 10.1016/j.plipres.2006.02.002] [Citation(s) in RCA: 225] [Impact Index Per Article: 12.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/26/2022]
Abstract
Cholesterol is an essential component of eukaryotic membranes and plays a crucial role in membrane organization, dynamics and function. The modulatory role of cholesterol in the function of a number of membrane proteins is well established. This effect has been proposed to occur either due to a specific molecular interaction between cholesterol and membrane proteins or due to alterations in the membrane physical properties induced by the presence of cholesterol. The contemporary view regarding heterogeneity in cholesterol distribution in membrane domains that sequester certain types of membrane proteins while excluding others has further contributed to its significance in membrane protein function. The seven transmembrane domain G-protein coupled receptors (GPCRs) are among the largest protein families in mammals and represent approximately 2% of the total proteins coded by the human genome. Signal transduction events mediated by this class of proteins are the primary means by which cells communicate with and respond to their external environment. GPCRs therefore represent major targets for the development of novel drug candidates in all clinical areas. In view of their importance in cellular signaling, the interaction of cholesterol with such receptors represents an important determinant in functional studies of such receptors. This review focuses on the effect of cholesterol on the membrane organization and function of GPCRs from a variety of sources, with an emphasis on the more contemporary role of cholesterol in maintaining a domain-like organization of such receptors on the cell surface. Importantly, the recently reported role of cholesterol in the function and organization of the neuronal serotonin(1A) receptor, a representative of the GPCR family which is present endogenously in the hippocampal region of the brain, will be highlighted.
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Affiliation(s)
- Thomas J Pucadyil
- Centre for Cellular and Molecular Biology, Uppal Road, Hyderabad 500007, India
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Pucadyil TJ, Kalipatnapu S, Chattopadhyay A. The serotonin1A receptor: a representative member of the serotonin receptor family. Cell Mol Neurobiol 2005; 25:553-80. [PMID: 16075379 DOI: 10.1007/s10571-005-3969-3] [Citation(s) in RCA: 189] [Impact Index Per Article: 9.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/10/2004] [Accepted: 08/03/2004] [Indexed: 12/14/2022]
Abstract
1. Serotonin is an intrinsically fluorescent biogenic amine that acts as a neurotransmitter and is found in a wide variety of sites in the central and peripheral nervous system. Serotonergic signaling appears to play a key role in the generation and modulation of various cognitive and behavioral functions. 2. Serotonin exerts its diverse actions by binding to distinct cell surface receptors which have been classified into many groups. The serotonin1A (5-HT1A) receptor is the most extensively studied of the serotonin receptors and belongs to the large family of seven transmembrane domain G-protein coupled receptors. 3. The tissue and sub-cellular distribution, structural characteristics, signaling of the serotonin1A receptor and its interaction with G-proteins are discussed. 4. The pharmacology of serotonin1A receptors is reviewed in terms of binding of agonists and antagonists and sensitivity of their binding to guanine nucleotides. 5. Membrane biology of 5-HT1A receptors is presented using the bovine hippocampal serotonin1A receptor as a model system. The ligand binding activity and G-protein coupling of the receptor is modulated by membrane cholesterol thereby indicating the requirement of cholesterol in maintaining the receptor organization and function. This, along with the reported detergent resistance characteristics of the receptor, raises important questions on the role of membrane lipids and domains in the function of this receptor.
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Affiliation(s)
- Thomas J Pucadyil
- Centre for Cellular and Molecular Biology, Uppal Road, Hyderabad, 500 007, India
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5
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Javadekar-Subhedar V, Chattopadhyay A. Temperature-dependent interaction of the bovine hippocampal serotonin(1A) receptor with G-proteins. Mol Membr Biol 2004; 21:119-23. [PMID: 15204441 DOI: 10.1080/09687680310001058335] [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: 10/26/2022]
Abstract
The ligand binding and G-protein coupling of the bovine hippocampal 5-HT1A receptor as a function of temperature was monitored. There is an almost complete and irreversible loss in agonist binding at 50 degrees C. However, the antagonist binding is reduced only by 50%, and this could be reversed if the temperature is lowered to 25 degrees C. Interestingly, the agonist binding of the 5-HT1A receptor in membranes exposed to 50 degrees C is inhibited to a much lesser extent by GTP-gamma-S, a non-hydrolysable analogue of GTP, indicating uncoupling of the 5-HT1A receptor to G-proteins at 50 degrees C. We propose that high temperature selectively and irreversibly inactivates G-proteins thereby affecting G-protein-receptor interaction and agonist binding of the 5-HT1A receptor.
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Pucadyil TJ, Chattopadhyay A. Cholesterol modulates ligand binding and G-protein coupling to serotonin(1A) receptors from bovine hippocampus. BIOCHIMICA ET BIOPHYSICA ACTA-BIOMEMBRANES 2004; 1663:188-200. [PMID: 15157621 DOI: 10.1016/j.bbamem.2004.03.010] [Citation(s) in RCA: 189] [Impact Index Per Article: 9.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 01/12/2004] [Revised: 03/08/2004] [Accepted: 03/19/2004] [Indexed: 10/26/2022]
Abstract
The serotonin(1A) (5-HT(1A)) receptor is an important member of the superfamily of seven-transmembrane domain G-protein-coupled receptors. We have examined the modulatory role of cholesterol on the ligand binding activity and G-protein coupling of the bovine hippocampal 5-HT(1A) receptor by depleting cholesterol from native membranes using methyl-beta-cyclodextrin (MbetaCD). Removal of cholesterol from bovine hippocampal membranes using varying concentrations of MbetaCD results in a concentration-dependent reduction in specific binding of the agonist 8-OH-DPAT to 5-HT(1A) receptors. This is accompanied by alterations in binding affinity and sites obtained from analysis of binding data. Importantly, cholesterol depletion affected G-protein-coupling of the receptor as monitored by the GTP-gamma-S assay. The concomitant changes in membrane order were reported by changes in fluorescence polarization of membrane probes such as DPH and TMA-DPH, which are incorporated at different locations (depths) in the membrane. Replenishment of membranes with cholesterol led to recovery of ligand binding activity as well as membrane order to a considerable extent. Our results provide evidence, for the first time, that cholesterol is necessary for ligand binding and G-protein coupling of this important neurotransmitter receptor. These results could have significant implications in understanding the influence of the membrane lipid environment on the activity and signal transduction of other G-protein-coupled transmembrane receptors.
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Affiliation(s)
- Thomas J Pucadyil
- Centre for Cellular and Molecular Biology, Uppal Road, Hyderabad 500 007, India
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Pucadyil TJ, Shrivastava S, Chattopadhyay A. The sterol-binding antibiotic nystatin differentially modulates ligand binding of the bovine hippocampal serotonin1A receptor. Biochem Biophys Res Commun 2004; 320:557-62. [PMID: 15219865 DOI: 10.1016/j.bbrc.2004.06.004] [Citation(s) in RCA: 29] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/30/2004] [Indexed: 01/24/2023]
Abstract
We have monitored the ligand binding of the bovine hippocampal 5-HT1A receptor following treatment with the sterol-binding antifungal antibiotic nystatin. Nystatin considerably inhibits the specific binding of the antagonist to 5-HT1A receptors in a concentration-dependent manner. However, the specific agonist binding does not show significant changes. Fluorescence polarization measurements of membrane probes incorporated at different locations in the membrane revealed a substantial decrease in the membrane order in the interior of the bilayer. Experiments with cholesterol-depleted membranes indicate that the action of nystatin is mediated through membrane cholesterol. These results represent the first report on the effect of a cholesterol-perturbing agent on the ligand-binding activity of this important neurotransmitter receptor.
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Affiliation(s)
- Thomas J Pucadyil
- Centre for Cellular and Molecular Biology, Uppal Road, Hyderabad 500 007, India
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8
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Pucadyil TJ, Chattopadhyay A. Exploring detergent insolubility in bovine hippocampal membranes: a critical assessment of the requirement for cholesterol. BIOCHIMICA ET BIOPHYSICA ACTA-BIOMEMBRANES 2004; 1661:9-17. [PMID: 14967470 DOI: 10.1016/j.bbamem.2003.11.013] [Citation(s) in RCA: 25] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 04/24/2003] [Revised: 09/10/2003] [Accepted: 11/19/2003] [Indexed: 11/18/2022]
Abstract
The phenomenon of detergent insolubility of bovine hippocampal membranes in Triton X-100 was monitored by estimating the presence of phospholipids in the insoluble pellet. This represents a convenient and unambiguous assay and reports the dependence of the extent of phospholipid solubilization on detergent concentration. The advantage of this approach is its ability to accurately determine the extent of detergent insolubility in natural membranes. Importantly, our results show that when suboptimal concentrations of Triton X-100 are used for solubilization, interpretations of the mechanism and extent of detergent insolubility should be made with adequate caution. At concentrations of Triton X-100 that leads to no further solubilization, approximately 44% of phospholipids are left insoluble at 4 degrees C in bovine hippocampal membranes. Cholesterol depletion using methyl-beta-cyclodextrin enhanced phospholipid solubilization at low detergent concentrations but produced no significant change in the amount of insoluble phospholipids at saturating detergent concentration. Progressive solubilization by the detergent resulted in insoluble membranes that contained lipids with higher fatty acyl chain order as reported by fluorescence polarization studies using 1,6-diphenyl-1,3,5-hexatriene (DPH). These results suggest that it is the presence of such lipids rather than their association with cholesterol that determines detergent insolubility in membranes.
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Affiliation(s)
- Thomas J Pucadyil
- Centre for Cellular and Molecular Biology, Uppal Road, Hyderabad 500 007, India
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Sánchez-Moreno C, Paniagua M, Madrid A, Martín A. Protective effect of vitamin C against the ethanol mediated toxic effects on human brain glial cells. J Nutr Biochem 2003; 14:606-13. [PMID: 14559112 DOI: 10.1016/j.jnutbio.2003.07.003] [Citation(s) in RCA: 39] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/17/2022]
Abstract
It is now known that chronic consumption of excessive amounts of alcohol is a major source of social and medical problems. Ethanol-mediated glial cell activation may lead to neuron damage in many ways, including the formation of free radicals and production of pro-inflammatory molecules. Vitamin C (vit-C) is an essential dietary nutrient required as a co-factor for many enzymes and a very efficient antioxidant, protecting cells against free radical-mediated damage. The objective of this study was to evaluate the protective effects of vit-C on glial cell activation and viability against ethanol-mediated toxicity. Human brain astrocyte cells (HA) were exposed to ethanol (0, 50, and 350 mmol/L) for 24 h. We found that glial cells incubated with different concentrations of vit-C increase their vit-C in a dose-dependent manner. HA incubated with 0, 50 or 350 mmol/L of ethanol for up to 24 h showed toxic effects that were proportional to the levels of ethanol in the medium, HA showed increased levels of heat shock protein (Hsp70). However, cells enriched with vit-C before being exposed to ethanol, were better protected against the alcohol-mediated toxicity than non-supplemented cells, and showed significantly lower concentrations of Hsp70. Ethanol also caused increased expression of cyclooxygenase-2 (COX-2) and synthesis of prostaglandin E2 (PGE2), which were reduced by vit-C. In summary, HA supplemented with vit-C were significantly more resistant to the ethanol-mediated toxic effects.
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Affiliation(s)
- Concepción Sánchez-Moreno
- Nutrition and Neurocognitive Laboratory, Jean Mayer USDA-Human Nutrition Research Center on Aging at Tufts University, Boston, MA, USA
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10
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Fischer W, Wirkner K, Weber M, Eberts C, Köles L, Reinhardt R, Franke H, Allgaier C, Gillen C, Illes P. Characterization of P2X3, P2Y1 and P2Y4 receptors in cultured HEK293-hP2X3 cells and their inhibition by ethanol and trichloroethanol. J Neurochem 2003; 85:779-90. [PMID: 12694404 DOI: 10.1046/j.1471-4159.2003.01716.x] [Citation(s) in RCA: 48] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022]
Abstract
Membrane currents and changes in the intracellular Ca2+ concentration ([Ca2+]i) were measured in HEK293 cells transfected with the human P2X3 receptor (HEK293-hP2X3). RT-PCR and immunocytochemistry indicated the additional presence of endogenous P2Y1 and to some extent P2Y4 receptors. P2 receptor agonists induced inward currents in HEK293-hP2X3 cells with the rank order of potency alpha,beta-meATP approximately ATP > ADP-beta-S > UTP. A comparable rise in [Ca2+]i was observed after the slow superfusion of ATP, ADP-beta-S and UTP; alpha,beta-meATP was ineffective. These data, in conjunction with results obtained by using the P2 receptor antagonists TNP-ATP, PPADS and MRS2179 indicate that the current response to alpha,beta-meATP is due to P2X3 receptor activation, while the ATP-induced rise in [Ca2+]i is evoked by P2Y1 and P2Y4 receptor activation. TCE depressed the alpha,beta-meATP current in a manner compatible with a non-competitive antagonism. The ATP-induced increase of [Ca2+]i was much less sensitive to the inhibitory effect of TCE than the current response to alpha,beta-meATP. The present study indicates that in HEK293-hP2X3 cells, TCE, but not ethanol, potently inhibits ligand-gated P2X3 receptors and, in addition, moderately interferes with G protein-coupled P2Y1 and P2Y4 receptors. Such an effect may be relevant for the interruption of pain transmission in dorsal root ganglion neurons following ingestion of chloral hydrate or trichloroethylene.
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Affiliation(s)
- Wolfgang Fischer
- Rudolf-Boehm-Department of Pharmacology and Toxicology, Department of Forensic Medicine, University of Leipzig, Leipzig, Germany
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11
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Rebecchi MJ, Pentyala SN. Anaesthetic actions on other targets: protein kinase C and guanine nucleotide-binding proteins. Br J Anaesth 2002; 89:62-78. [PMID: 12173242 DOI: 10.1093/bja/aef160] [Citation(s) in RCA: 32] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/25/2023] Open
Affiliation(s)
- M J Rebecchi
- Departments of Anesthesiology and Physiology & Biophysics, School of Medicine, State University of New York, Stony Brook, NY 11794-8480, USA
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12
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Harikumar KG, Chattopadhyay A. Modulation of antagonist binding to serotonin1A receptors from bovine hippocampus by metal ions. Cell Mol Neurobiol 2001; 21:453-64. [PMID: 11860184 DOI: 10.1023/a:1013811221577] [Citation(s) in RCA: 12] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/12/2022]
Abstract
1. The serotonin1A (5-HT1A) receptors are members of a superfamily of seven transmembrane domain receptors that couple to G-proteins. They appear to be involved in various behavioral and cognitive functions. Although specific 5-HT1A agonists have been discovered more than a decade back, the development of selective 5-HT1A antagonists has been achieved only recently. 2. We have examined the modulation of the specific antagonist [3H]p-MPPF binding to 5-HT1A receptors from bovine hippocampal membranes by monovalent and divalent metal ions. Our results show that the antagonist binding to 5-HT1A receptors is inhibited by both monovalent and divalent cations in a concentration-dependent manner. This is accompanied by a concomitant reduction in binding affinity. 3. Our results also show that the specific antagonist p-MPPF binds to all available receptors in the bovine hippocampal membrane irrespective of their state of G-protein coupling and other serotonergic ligands such as 5-HT and OH-DPAT effectively compete with the specific antagonist [3H]p-MPPF. 4. These results are relevant to ongoing analyses of the overall modulation of ligand binding in G-protein-coupled seven transmembrane domain receptors.
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Affiliation(s)
- K G Harikumar
- Centre for Cellular and Molecular Biology, Hyderabad, India
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13
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Li W, Zheng T, Altura BT, Altura BM. Antioxidants prevent depletion of [Mg2+]i induced by alcohol in cultured canine cerebral vascular smooth muscle cells: possible relationship to alcohol-induced stroke. Brain Res Bull 2001; 55:475-8. [PMID: 11543947 DOI: 10.1016/s0361-9230(01)00547-0] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/18/2022]
Abstract
Low serum concentrations of Mg(2+) ions have been reported, recently, in patients with coronary disease, atherosclerosis, and stroke as well as in patients with cerebral hemorrhage. The aim of the present study was to determine whether potent antioxidants [alpha-tocopherol and pyrrolidine dithiocarbamate (PDTC)] can prevent or ameliorate intracellular Mg(2+) ([Mg(2+)](i)) depletion associated with cerebral vascular injury induced by alcohol. Exposure of cultured canine cerebral vascular smooth muscle cells to alcohol (10-100 mM) for 24 h induced marked depletion in [Mg(2+)](i) (i.e., approximately 30-65%, depending upon alcohol concentration). Treatment of the cultured cells with either PDTC (0.1 microM) or alpha-tocopherol (15 microM) for 24 h, alone, failed to interfere with basal [Mg(2+)](i) levels. However, preincubation of the cells with either alpha-tocopherol or PDTC for 24 h completely inhibited the depletion of [Mg(2+)](i) induced by exposure to 10-100 mM ethanol. These results indicate that alpha-tocopherol and PDTC prevent decreases in [Mg(2+)](i) produced by ethanol. Moreover, these new results suggest that such protective effects of alpha-tocopherol and PDTC on cerebral vascular cells might be useful therapeutic tools in prevention and amelioration of cerebral vascular injury and stroke in alcoholics.
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Affiliation(s)
- W Li
- Department of Physiology and Pharmacology, State University of New York, Health Science Centre at Brooklyn, Brooklyn, NY 11203, USA
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Harikumar KG, John PT, Chattopadhyay A. Role of disulfides and sulfhydryl groups in agonist and antagonist binding in serotonin1A receptors from bovine hippocampus. Cell Mol Neurobiol 2000; 20:665-81. [PMID: 11100975 DOI: 10.1023/a:1007046707845] [Citation(s) in RCA: 14] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/12/2022]
Abstract
I. The serotonin1A (5-HT1A) receptors are members of a superfamily of seven-transmembrane-domain receptors that couple to G-proteins. They appear to be involved in various behavioral and cognitive functions. Mutagenesis and modeling studies point out that the ligand-binding sites in serotonin receptors are located in the transmembrane domain. However, these binding sites are not very well characterized. Since disulfide bonds and sulfhydryl groups have been shown to play vital roles in the assembly, organization, and function of various G-protein-coupled receptors, we report here the effect of disulfide and sulfhydryl group modifications on the agonist and antagonist binding activity of 5-HT1A receptors from bovine hippocampus. 2. DTT or NEM treatment caused a concentration-dependent reduction in specific binding of the agonist and antagonist in 5-HT1A receptors from bovine hippocampal native and solubilized membranes. This is supported by a concomitant reduction in binding affinity. 3. Pretreatment of the receptor with unlabeled ligands prior to chemical modifications indicate that the majority of disulfides or sulfhydryl groups that undergo modification giving rise to inhibition in binding activity could be at the vicinity of the ligand-binding sites. 4. In addition, ligand-binding studies in presence of GTP-gamma-S, a nonhydrolyzable analogue of GTP, indicate that sulfhydryl groups (and disulfide bonds to a lesser extent) are vital for efficient coupling between the 5-HT1A receptor and the G-protein. 5. Our results point out that disulfide bonds and sulfhydryl groups could play an important role in ligand binding in 5-HT1A receptors.
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Affiliation(s)
- K G Harikumar
- Centre for Cellular & Molecular Biology, Hyderabad, India
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