1
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Noonan JD, Beech RN. Two residues determine nicotinic acetylcholine receptor requirement for RIC-3. Protein Sci 2023; 32:e4718. [PMID: 37417463 PMCID: PMC10443321 DOI: 10.1002/pro.4718] [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] [Received: 01/28/2023] [Revised: 06/11/2023] [Accepted: 06/26/2023] [Indexed: 07/08/2023]
Abstract
Nicotinic acetylcholine receptors (N-AChRs) mediate fast synaptic signaling and are members of the pentameric ligand-gated ion channel (pLGIC) family. They rely on a network of accessory proteins in vivo for correct formation and transport to the cell surface. Resistance to cholinesterase 3 (RIC-3) is an endoplasmic reticulum protein that physically interacts with nascent pLGIC subunits and promotes their oligomerization. It is not known why some N-AChRs require RIC-3 in heterologous expression systems, whereas others do not. Previously we reported that the ACR-16 N-AChR from the parasitic nematode Dracunculus medinensis does not require RIC-3 in Xenopus laevis oocytes. This is unusual because all other nematode ACR-16, like the closely related Ascaris suum ACR-16, require RIC-3. Their high sequence similarity limits the number of amino acids that may be responsible, and the goal of this study was to identify them. A series of chimeras and point mutations between A. suum and D. medinensis ACR-16, followed by functional characterization with electrophysiology, identified two residues that account for a majority of the receptor requirement for RIC-3. ACR-16 with R/K159 in the cys-loop and I504 in the C-terminal tail did not require RIC-3 for functional expression. Mutating either of these to R/K159E or I504T, residues found in other nematode ACR-16, conferred a RIC-3 requirement. Our results agree with previous studies showing that these regions interact and are involved in receptor synthesis. Although it is currently unclear what precise mechanism they regulate, these residues may be critical during specific subunit folding and/or assembly cascades that RIC-3 may promote.
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Affiliation(s)
- Jennifer D. Noonan
- Institute of Parasitology, Macdonald Campus, McGill UniversityMontrealQuébecCanada
| | - Robin N. Beech
- Institute of Parasitology, Macdonald Campus, McGill UniversityMontrealQuébecCanada
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2
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Structure and gating mechanism of the α7 nicotinic acetylcholine receptor. Cell 2021; 184:2121-2134.e13. [PMID: 33735609 DOI: 10.1016/j.cell.2021.02.049] [Citation(s) in RCA: 119] [Impact Index Per Article: 39.7] [Reference Citation Analysis] [Abstract] [Key Words] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/13/2020] [Revised: 01/13/2021] [Accepted: 02/22/2021] [Indexed: 12/13/2022]
Abstract
The α7 nicotinic acetylcholine receptor plays critical roles in the central nervous system and in the cholinergic inflammatory pathway. This ligand-gated ion channel assembles as a homopentamer, is exceptionally permeable to Ca2+, and desensitizes faster than any other Cys-loop receptor. The α7 receptor has served as a prototype for the Cys-loop superfamily yet has proven refractory to structural analysis. We present cryo-EM structures of the human α7 nicotinic receptor in a lipidic environment in resting, activated, and desensitized states, illuminating the principal steps in the gating cycle. The structures also reveal elements that contribute to its function, including a C-terminal latch that is permissive for channel opening, and an anionic ring in the extracellular vestibule that contributes to its high conductance and calcium permeability. Comparisons among the α7 structures provide a foundation for mapping the gating cycle and reveal divergence in gating mechanisms in the Cys-loop receptor superfamily.
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3
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Zhang Q, Du Y, Zhang J, Xu X, Xue F, Guo C, Huang Y, Lukas RJ, Chang Y. Functional Impact of 14 Single Nucleotide Polymorphisms Causing Missense Mutations of Human α7 Nicotinic Receptor. PLoS One 2015; 10:e0137588. [PMID: 26340537 PMCID: PMC4560414 DOI: 10.1371/journal.pone.0137588] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/12/2015] [Accepted: 08/18/2015] [Indexed: 01/17/2023] Open
Abstract
The α7nicotinic receptor (nAChR) is a major subtype of the nAChRs in the central nervous system, and the receptor plays an important role in brain function. In the dbSNP database, there are 55 single nucleotide polymorphisms (SNPs) that cause missense mutations of the human α7nAChR in the coding region. In this study, we tested the impact of 14 SNPs that cause missense mutations in the agonist binding site or the coupling region between binding site and channel gate on the receptor function. The wild type or mutant receptors were expressed or co-expressed in Xenopus oocytes, and the agonist-induced currents were tested using two-electrode voltage clamp. Our results demonstrated that 6 mutants were nonfunctional, 4 mutants had reduced current expression, and 1 mutants altered ACh and nicotine efficacy in the opposite direction, and one additional mutant had slightly reduced agonist sensitivity. Interestingly, the function of most of these nonfunctional mutants could be rescued by α7nAChR positive allosteric modulator PNU-120596 and agonist-PAM 4BP-TQS. Finally, when coexpressed with the wild type, the nonfunctional mutants could also influence the receptor function. These changes of the receptor properties by the mutations could potentially have an impact on the physiological function of the α7nAChR-mediated cholinergic synaptic transmission and anti-inflammatory effects in the human SNP carriers. Rescuing the nonfunctional mutants could provide a novel way to treat the related disorders.
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Affiliation(s)
- Qinhui Zhang
- Department of Zoology, College of Life Sciences, Sichuan University, Chengdu, Sichuan Province, 610064, China
- Chengdu institute of Biology, Chinese Academy of Sciences, Chengdu, Sichuan 610041, China
- Division of Neurobiology, Barrow Neurological Institute, St. Joseph’s Hospital and Medical Center, Phoenix, Arizona 85013, United States of America
| | - Yingjie Du
- University of California Los Angeles, Henry Samueli School of Engineering and Applied Science, Los Angeles, California 90095, United States of America
| | - Jianliang Zhang
- Division of Neurobiology, Barrow Neurological Institute, St. Joseph’s Hospital and Medical Center, Phoenix, Arizona 85013, United States of America
- Department of Neurobiology, Beijing Institute of Brain Disorders, Capital Medical University, Key Laboratory for Neurodegenerative Disease of the Ministry of Education, Beijing Center of Neural Regeneration and Repair, Beijing Key Laboratory of Brain Major Disorders; State Key Lab Incubation Base, Beijing Neuroscience Disciplines, Beijing 100069, China
| | - Xiaojun Xu
- Division of Neurobiology, Barrow Neurological Institute, St. Joseph’s Hospital and Medical Center, Phoenix, Arizona 85013, United States of America
| | - Fenqin Xue
- Division of Neurobiology, Barrow Neurological Institute, St. Joseph’s Hospital and Medical Center, Phoenix, Arizona 85013, United States of America
- Core Facilities for Electrophysiology, Core Facilities Center, Capital Medical University, Beijing 100069, China
| | - Cong Guo
- Department of Zoology, College of Life Sciences, Sichuan University, Chengdu, Sichuan Province, 610064, China
- Chengdu institute of Biology, Chinese Academy of Sciences, Chengdu, Sichuan 610041, China
| | - Yao Huang
- Department of Obstetrics and Gynecology, St. Joseph’s Hospital and Medical Center, Phoenix, Arizona 85013, United States of America
| | - Ronald J. Lukas
- Division of Neurobiology, Barrow Neurological Institute, St. Joseph’s Hospital and Medical Center, Phoenix, Arizona 85013, United States of America
| | - Yongchang Chang
- Division of Neurobiology, Barrow Neurological Institute, St. Joseph’s Hospital and Medical Center, Phoenix, Arizona 85013, United States of America
- * E-mail:
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4
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The role of the M4 lipid-sensor in the folding, trafficking, and allosteric modulation of nicotinic acetylcholine receptors. Neuropharmacology 2014; 96:157-68. [PMID: 25433148 DOI: 10.1016/j.neuropharm.2014.11.011] [Citation(s) in RCA: 34] [Impact Index Per Article: 3.4] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/21/2014] [Revised: 10/31/2014] [Accepted: 11/18/2014] [Indexed: 11/24/2022]
Abstract
With the availability of high resolution structural data, increasing attention has focused on the mechanisms by which drugs and endogenous compounds allosterically modulate nicotinic acetylcholine receptor (nAChR) function. Lipids are potent modulators of the nAChR from Torpedo. Membrane lipids influence nAChR function by both conformational selection and kinetic mechanisms, stabilizing varying proportions of pre-existing resting, open, desensitized, and uncoupled conformations, as well as influencing the transitions between these conformational states. Structural and functional data highlight a role for the lipid-exposed M4 transmembrane α-helix of each subunit in lipid sensing, and suggest that lipids influence gating by altering the binding of M4 to the adjacent transmembrane α-helices, M1 and M3. M4 has also been implicated in both the folding and trafficking of nAChRs to the cell surface, as well as in the potentiation of nAChR gating by neurosteroids. Here, we discuss the roles of M4 in the folding, trafficking, and allosteric modulation of nAChRs. We also consider the hypothesis that variable chemistry at the M4-M1/M3 transmembrane α-helical interface in different nAChR subunits governs the capacity for potentiation by activating lipids. This article is part of the Special Issue entitled 'The Nicotinic Acetylcholine Receptor: From Molecular Biology to Cognition'.
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5
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Ballesta JJ, del Pozo C, Castelló-Banyuls J, Faura CC. Selective down-regulation of α4β2 neuronal nicotinic acetylcholine receptors in the brain of uremic rats with cognitive impairment. Exp Neurol 2012; 236:28-33. [PMID: 22510484 DOI: 10.1016/j.expneurol.2012.03.020] [Citation(s) in RCA: 13] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/27/2011] [Revised: 01/31/2012] [Accepted: 03/29/2012] [Indexed: 01/02/2023]
Abstract
Cognitive impairment is common in patients with chronic kidney disease. Brain nicotinic acetylcholine receptors modulate cognitive functions, such as learning and memory. Pharmacological cholinergic enhancement is useful in patients with cognitive dysfunction. The major nicotinic acetylcholine receptor subtypes in the brain are heteromeric α4β2 and homomeric α7 receptors. To study the involvement of neuronal acetylcholine receptors in cognitive impairment in uremic rats, bilateral nephrectomy was performed. 24 weeks after nephrectomy, memory was assessed using the one trial step-down inhibitory avoidance test. Neuronal nicotinic acetylcholine receptors in the brain were studied by radioligand binding, immunoprecipitation, Western blot and sucrose gradient experiments. We demonstrated that rats with severe renal failure show disorders of short term memory. Long term memory was not altered in these rats. The number of functional α4β2 heteromeric neuronal nicotinic receptors was decreased in the brains of rats with severe renal failure. There was a significant correlation between the degree of renal impairment and the number of heteromeric nicotinic acetylcholine receptors in the brain. The down-regulation of functional α4β2 receptors in the brains of rats with severe renal failure was not due to a reduction of α4 or β2 subunit proteins. The number of α7 homomeric neuronal nicotinic acetylcholine receptors was not altered. These findings may have important clinical significance for the management of cognitive impairment in patients with chronic kidney disease.
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Affiliation(s)
- Juan J Ballesta
- Institute of Neurosciences, CSIC-Universidad Miguel Hernández, Avenida Ramon y Cajal, 03550 San Juan de Alicante, Spain.
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6
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Pless SA, Leung AWY, Galpin JD, Ahern CA. Contributions of conserved residues at the gating interface of glycine receptors. J Biol Chem 2011; 286:35129-36. [PMID: 21835920 DOI: 10.1074/jbc.m111.269027] [Citation(s) in RCA: 22] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/21/2023] Open
Abstract
Glycine receptors (GlyRs) are chloride channels that mediate fast inhibitory neurotransmission and are members of the pentameric ligand-gated ion channel (pLGIC) family. The interface between the ligand binding domain and the transmembrane domain of pLGICs has been proposed to be crucial for channel gating and is lined by a number of charged and aromatic side chains that are highly conserved among different pLGICs. However, little is known about specific interactions between these residues that are likely to be important for gating in α1 GlyRs. Here we use the introduction of cysteine pairs and the in vivo nonsense suppression method to incorporate unnatural amino acids to probe the electrostatic and hydrophobic contributions of five highly conserved side chains near the interface, Glu-53, Phe-145, Asp-148, Phe-187, and Arg-218. Our results suggest a salt bridge between Asp-148 in loop 7 and Arg-218 in the pre-M1 domain that is crucial for channel gating. We further propose that Phe-145 and Phe-187 play important roles in stabilizing this interaction by providing a hydrophobic environment. In contrast to the equivalent residues in loop 2 of other pLGICs, the negative charge at Glu-53 α1 GlyRs is not crucial for normal channel function. These findings help decipher the GlyR gating pathway and show that distinct residue interaction patterns exist in different pLGICs. Furthermore, a salt bridge between Asp-148 and Arg-218 would provide a possible mechanistic explanation for the pathophysiologically relevant hyperekplexia, or startle disease, mutant Arg-218 → Gln.
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Affiliation(s)
- Stephan A Pless
- Department of Anesthesiology, University of British Columbia, Vancouver, British Columbia V6T 1Z3, Canada.
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7
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An extracellular RRR motif flanking the M1 transmembrane domain governs the biogenesis of homomeric neuronal nicotinic acetylcholine receptors. FEBS Lett 2011; 585:1169-74. [PMID: 21420959 DOI: 10.1016/j.febslet.2011.03.028] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/14/2011] [Revised: 03/10/2011] [Accepted: 03/12/2011] [Indexed: 11/21/2022]
Abstract
We have previously demonstrated that the highly conserved R209, that flanks the M1 transmembrane segment of nicotinic acetylcholine (ACh) receptors, is required for the transport of assembled homomeric neuronal α7 nicotinic ACh receptors to the cell surface. In the present paper we show that basic residues at positions 208 and 210 are necessary for the assembly of α7 receptors. On the contrary, a basic residue at position 210 of α3 subunit decreases the assembly of heteromeric neuronal α3β4 nicotinic ACh receptors. A basic residue at position 210 of the β4 subunit slightly decreases α3β4 receptor expression. We conclude that a pre-M1 RRR motif is necessary for the biogenesis of homomeric α-bungarotoxin-sensitive neuronal α7 nicotinic ACh receptors.
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8
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Spitzmaul G, Corradi J, Bouzat C. Mechanistic contributions of residues in the M1 transmembrane domain of the nicotinic receptor to channel gating. Mol Membr Biol 2009; 21:39-50. [PMID: 14668137 DOI: 10.1080/09687680310001607341] [Citation(s) in RCA: 11] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/26/2022]
Abstract
The nicotinic receptor (AChR) is a pentamer of homologous subunits with an alpha(2)betaepsilondelta composition in adult muscle. Each subunit contains four transmembrane domains (M1-M4). Position 15' of the M1 domain is phenylalanine in alpha subunits while it is isoleucine in non-alpha subunits. Given this peculiar conservation pattern, we studied its contribution to muscle AChR activation by combining mutagenesis with single-channel kinetic analysis. AChRs containing the mutant alpha subunit (alphaF15'I) as well as those containing the reverse mutations in the non-alpha subunits (betaI15'F, deltaI15'F, and epsilonI15'F) show prolonged lifetimes of the diliganded open channel resulting from a slower closing rate with respect to wild-type AChRs. The kinetic changes are not equivalent among subunits, the beta subunit, being the one that produces the most significant stabilization of the open state. Kinetic analysis of betaI15'F of AChR channels activated by the low-efficacious agonist choline revealed a 10-fold decrease in the closing rate, a 2.5-fold increase in the opening rate, a 28-fold increase in the gating equilibrium constant in the diliganded receptor, and a significant increase opening in the absence of agonist. Mutations at betaI15' showed that the structural bases of its contribution to gating is complex. Rate-equilibrium linear free-energy relationships suggest an approximately 70% closed-state-like environment for the beta15' position at the transition state of gating. The overall results identify position 15' as a subunit-selective determinant of channel gating and add new experimental evidence that gives support to the involvement of the M1 domain in the operation of the channel gating apparatus.
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Affiliation(s)
- Guillermo Spitzmaul
- Instituto de Investigaciones Bioquímicas, UNS-CONICET, Bahía Blanca, Argentina
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9
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Purohit P, Auerbach A. Acetylcholine receptor gating at extracellular transmembrane domain interface: the "pre-M1" linker. ACTA ACUST UNITED AC 2008; 130:559-68. [PMID: 18040058 PMCID: PMC2151659 DOI: 10.1085/jgp.200709857] [Citation(s) in RCA: 47] [Impact Index Per Article: 2.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022]
Abstract
Charged residues in the beta10-M1 linker region ("pre-M1") are important in the expression and function of neuromuscular acetylcholine receptors (AChRs). The perturbation of a salt bridge between pre-M1 residue R209 and loop 2 residue E45 has been proposed as being a principle event in the AChR gating conformational "wave." We examined the effects of mutations to all five residues in pre-M1 (positions M207-P211) plus E45 in loop 2 in the mouse alpha(1)-subunit. M207, Q208, and P211 mutants caused small (approximately threefold) changes in the gating equilibrium constant (K(eq)), but the changes for R209, L210, and E45 were larger. Of 19 different side chain substitutions at R209 on the wild-type background, only Q, K, and H generated functional channels, with the largest change in K(eq) (67-fold) from R209Q. Various R209 mutants were functional on different E45 backgrounds: H, Q, and K (E45A), H, A, N, and Q (E45R), and K, A, and N (E45L). Phi values for R209 (on the E45A background), L210, and E45 were 0.74, 0.35, and 0.80, respectively. Phi values for R209 on the wt and three other backgrounds could not be estimated because of scatter. The average coupling energy between 209/45 side chains (six different pairs) was only -0.33 kcal/mol (for both alpha subunits, combined). Pre-M1 residues are important for expression of functional channels and participate in gating, but the relatively modest changes in closed- vs. open-state energy caused mutations, the weak coupling energy between these residues and the functional activity of several unmatched-charge pairs are not consistent with the perturbation of a salt bridge between R209 and E45 playing the principle role in gating.
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Affiliation(s)
- Prasad Purohit
- Department of Physiology and Biophysics, State University of New York at Buffalo, Buffalo, NY 14214, USA
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10
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Wang J, Lester HA, Dougherty DA. Establishing an ion pair interaction in the homomeric rho1 gamma-aminobutyric acid type A receptor that contributes to the gating pathway. J Biol Chem 2007; 282:26210-6. [PMID: 17606618 DOI: 10.1074/jbc.m702314200] [Citation(s) in RCA: 25] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
gamma-Aminobutyric acid type A (GABA(A)) receptors are members of the Cys-loop superfamily of ligand-gated ion channels. Upon agonist binding, the receptor undergoes a structural transition from the closed to the open state, but the mechanism of gating is not well understood. Here we utilized a combination of conventional mutagenesis and the high precision methodology of unnatural amino acid incorporation to study the gating interface of the human homopentameric rho1 GABA(A) receptor. We have identified an ion pair interaction between two conserved charged residues, Glu(92) in loop 2 of the extracellular domain and Arg(258) in the pre-M1 region. We hypothesize that the salt bridge exists in the closed state by kinetic measurements and free energy analysis. Several other charged residues at the gating interface are not critical to receptor function, supporting previous conclusions that it is the global charge pattern of the gating interface that controls receptor function in the Cys-loop superfamily.
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Affiliation(s)
- Jinti Wang
- Division of Chemistry and Chemical Engineering and Division of Biology, California Institute of Technology, Pasadena, California 91125, USA
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11
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Aldea M, Mulet J, Sala S, Sala F, Criado M. Non-charged amino acids from three different domains contribute to link agonist binding to channel gating in alpha7 nicotinic acetylcholine receptors. J Neurochem 2007; 103:725-35. [PMID: 17635664 DOI: 10.1111/j.1471-4159.2007.04771.x] [Citation(s) in RCA: 9] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Abstract
Binding of agonists to nicotinic acetylcholine receptors results in channel opening. Previously, we have shown that several charged residues at three different domains of the alpha7 nicotinic receptor are involved in coupling binding and gating, probably through a network of electrostatic interactions. This network, however, could also be integrated by other residues. To test this hypothesis, non-charged amino acids were mutated and expression levels and electrophysiological responses of mutant receptors were determined. Mutants at positions Asn47 and Gln48 (loop 2), Ile130, Trp134, and Gln140 (loop 7), and Thr264 (M2-M3 linker) showed poor or null functional responses, despite significant membrane expression. By contrast, mutants F137A and S265A exhibited a gain of function effect. In all cases, changes in dose-response relationships were small, EC(50) values being between threefold smaller and fivefold larger, arguing against large modifications of agonist binding. Peak currents decayed at the same rate in all receptors except two, excluding large effects on desensitization. Thus, the observed changes could be mostly caused by alterations of the gating characteristics. Moreover, analysis of double mutants showed an interconnection between some residues in these domains, especially Gln48 with Ile130, suggesting a potential coupling between agonist binding and channel gating through these amino acids.
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Affiliation(s)
- Marcos Aldea
- Instituto de Neurociencias de Alicante, Universidad Miguel Hernández-CSIC, Sant Joan d'Alacant, Alicante, Spain
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12
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Price KL, Millen KS, Lummis SCR. Transducing agonist binding to channel gating involves different interactions in 5-HT3 and GABAC receptors. J Biol Chem 2007; 282:25623-30. [PMID: 17606617 DOI: 10.1074/jbc.m702524200] [Citation(s) in RCA: 32] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
5-hydroxytryptamine (5-HT)3 and gamma-aminobutyric acid, type C (GABAC) receptors are members of the Cys-loop superfamily of neurotransmitter receptors, which also includes nicotinic acetylcholine, GABAA, and glycine receptors. The details of how agonist binding to these receptors results in channel opening is not fully understood but is known to involve charged residues at the extracellular/transmembrane interface. Here we have examined the roles of such residues in 5-HT3 and GABAC receptors. Charge reversal experiments combined with data from activation by the partial agonist beta-alanine show that in GABAC receptors there is a salt bridge between Glu-92 (in loop 2) and Arg-258 (in the pre-M1 region), which is involved in receptor gating. The equivalent residues in the 5-HT3 receptor are important for receptor expression, but charge reversal experiments do not restore function, indicating that there is not a salt bridge here. There is, however, an interaction between Glu-215 (loop 9) and Arg-246 (pre-M1) in the 5-HT3 receptor, although the coupling energy determined from mutant cycle analysis is lower than might be expected for a salt bridge. Overall the data show that charged residues at the extracellular/transmembrane domain interfaces in 5-HT3 and GABAC receptors are important and that specific, but not equivalent, molecular interactions between them are involved in the gating process. Thus, we propose that the molecular details of interactions in the transduction pathway between the binding site and the pore can differ between different Cys-loop receptors.
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Affiliation(s)
- Kerry L Price
- Department of Biochemistry, University of Cambridge and Neurobiology Division, MRC-LMB, Hills Rd., Cambridge CB2 2QH, United Kingdom
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13
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Roccamo AM, Barrantes FJ. Charged amino acid motifs flanking each extreme of the alphaM4 transmembrane domain are involved in assembly and cell-surface targeting of the muscle nicotinic acetylcholine receptor. J Neurosci Res 2007; 85:285-93. [PMID: 17131427 DOI: 10.1002/jnr.21123] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/09/2022]
Abstract
The alphaM4 transmembrane domain of the nicotinic acetylcholine receptor (AChR) is flanked by two basic amino acids (His(408) and Arg(429)) located at its cytoplasmic- and extracellular-facing extremes, respectively, at the level of the phospholipid polar head regions of the postsynaptic membrane. A series of single and double alphaM4 mutants (His(408)Ala, Arg(429)Ala, Arg(429)Glu, His(408)Ala/Arg(429)Ala, and His(408)Ala/Arg(429)Glu) of the adult muscle-type AChR were produced and coexpressed with wild-type beta, delta, and epsilon subunits as stable clones in a mammalian heterologous expression system (CHO-K1 cells). The mutants were studied by alpha-bungarotoxin ([(125)I]alpha-BTX) binding, fluorescence microscopy, and equilibrium sucrose gradient centrifugation. Cell-surface [(125)I]alpha-BTX binding diminished approximately 40% in His(408)Ala and as much as 95% in the Arg(429)Ala mutant. Reversing the amino acid charge (e.g., Arg(429)Glu) abolished cell-surface expression of AChR. Fluorescence microscopy disclosed that AChR was retained at the endoplasmic reticulum, with an enhanced occurrence of unassembled AChR species in the mutant clones. Centrifugation analysis confirmed the lack of fully assembled AChR pentamers in all mutants with the exception of His(408)Ala. We conclude that His(408) and Arg(429) in alphaM4 are involved in assembly and cell-surface targeting of muscle AChR. Arg(429) plays a more decisive role in these two processes, suggesting an asymmetric weight of the charged motifs at each extreme of the alpha subunit M4 transmembrane segment. (c) 2006 Wiley-Liss, Inc.
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Affiliation(s)
- A M Roccamo
- Instituto de Investigaciones Bioquimicas and UNESCO Chair of Biophysics and Molecular Neurobiology, Bahía Blanca, Argentina
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14
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Mercado J, Czajkowski C. Charged residues in the alpha1 and beta2 pre-M1 regions involved in GABAA receptor activation. J Neurosci 2006; 26:2031-40. [PMID: 16481436 PMCID: PMC6674915 DOI: 10.1523/jneurosci.4555-05.2006] [Citation(s) in RCA: 56] [Impact Index Per Article: 3.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022] Open
Abstract
For Cys-loop ligand-gated ion channels (LGIC), the protein movements that couple neurotransmitter binding to channel gating are not well known. The pre-M1 region, which links the extracellular agonist-binding domain to the channel-containing transmembrane domain, is in an ideal position to transduce binding site movements to gating movements. A cluster of cationic residues in this region is observed in all LGIC subunits, and in particular, an arginine residue is absolutely conserved. We mutated charged pre-M1 residues in the GABAA receptor alpha1 (K219, R220, K221) and beta2 (K213, K215, R216) subunits to cysteine and expressed the mutant subunits with wild-type beta2 or alpha1 in Xenopus oocytes. Cysteine substitution of beta2R216 abolished channel gating by GABA without altering the binding of the GABA agonist [3H]muscimol, indicating that this residue plays a key role in coupling GABA binding to gating. Tethering thiol-reactive methanethiosulfonate (MTS) reagents onto alpha1K219C, beta2K213C, and beta2K215C increased maximal GABA-activated currents, suggesting that structural perturbations of the pre-M1 regions affect channel gating. GABA altered the rates of sulfhydryl modification of alpha1K219C, beta2K213C, and beta2K215C, indicating that the pre-M1 regions move in response to channel activation. A positively charged MTS reagent modified beta2K213C and beta2K215C significantly faster than a negatively charged reagent, and GABA activation eliminated modification of beta2K215C by the negatively charged reagent. Overall, the data indicate that the pre-M1 region is part of the structural machinery coupling GABA binding to gating and that the transduction of binding site movements to channel movements is mediated, in part, by electrostatic interactions.
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15
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Lee WY, Sine SM. Principal pathway coupling agonist binding to channel gating in nicotinic receptors. Nature 2005; 438:243-7. [PMID: 16281039 DOI: 10.1038/nature04156] [Citation(s) in RCA: 228] [Impact Index Per Article: 12.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/06/2005] [Accepted: 08/09/2005] [Indexed: 11/08/2022]
Abstract
Synaptic receptors respond to neurotransmitters by opening an intrinsic ion channel in the final step in synaptic transmission. How binding of the neurotransmitter is conveyed over the long distance to the channel remains a central question in neurobiology. Here we delineate a principal pathway that links neurotransmitter binding to channel gating by using a structural model of the Torpedo acetylcholine receptor at 4-A resolution, recordings of currents through single receptor channels and determinations of energetic coupling between pairs of residues. We show that a pair of invariant arginine and glutamate residues in each receptor alpha-subunit electrostatically links peripheral and inner beta-sheets from the binding domain and positions them to engage with the channel. The key glutamate and flanking valine residues energetically couple to conserved proline and serine residues emerging from the top of the channel-forming alpha-helix, suggesting that this is the point at which the binding domain triggers opening of the channel. The series of interresidue couplings identified here constitutes a primary allosteric pathway that links neurotransmitter binding to channel gating.
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Affiliation(s)
- Won Yong Lee
- Receptor Biology Laboratory, Department of Physiology and Biomedical Engineering, Mayo Clinic College of Medicine, Rochester, Minnesota 55905, USA
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Castillo M, Mulet J, Gutiérrez LM, Ortiz JA, Castelán F, Gerber S, Sala S, Sala F, Criado M. Dual Role of the RIC-3 Protein in Trafficking of Serotonin and Nicotinic Acetylcholine Receptors. J Biol Chem 2005; 280:27062-8. [PMID: 15927954 DOI: 10.1074/jbc.m503746200] [Citation(s) in RCA: 82] [Impact Index Per Article: 4.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
The ric-3 gene is required for maturation of nicotinic acetylcholine receptors in Caenorhabditis elegans. The human homolog of RIC-3, hRIC-3, enhances expression of alpha7 nicotinic receptors in Xenopus laevis oocytes, whereas it totally abolishes expression of alpha4beta2 nicotinic and 5-HT3 serotonergic receptors. Both the N-terminal region of hRIC-3, which contains two transmembrane segments, and the C-terminal region are needed for these differential effects. hRIC-3 inhibits receptor expression by hindering export of mature receptors to the cell membrane. By using chimeric proteins made of alpha7 and 5-HT3 receptors, we have shown that the presence of an extracellular isoleucine close to the first transmembrane receptor fragment is responsible for the transport arrest induced by hRIC-3. Enhancement of alpha7 receptor expression occurs, at least, at two levels: by increasing the number of mature receptors and facilitating its transport to the membrane. Certain amino acids of a putative amphipathic helix present at the large cytoplasmic region of the alpha7 subunit are required for these actions. Therefore, hRIC-3 can act as a specific regulator of receptor expression at different levels.
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Affiliation(s)
- Mar Castillo
- Instituto de Neurociencias de Alicante, Universidad Miguel Hernández-Consejo Superior de Investigaciones Científicas, Apartado 18, 03550 Sant Joan d'Alacant, Alicante, Spain
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Craig PJ, Bose S, Zwart R, Beattie RE, Folly EA, Johnson LR, Bell E, Evans NM, Benedetti G, Pearson KH, McPhie GI, Volsen SG, Millar NS, Sher E, Broad LM. Stable expression and characterisation of a human alpha 7 nicotinic subunit chimera: a tool for functional high-throughput screening. Eur J Pharmacol 2005; 502:31-40. [PMID: 15464087 DOI: 10.1016/j.ejphar.2004.08.042] [Citation(s) in RCA: 23] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/29/2004] [Revised: 08/09/2004] [Accepted: 08/19/2004] [Indexed: 11/23/2022]
Abstract
A chimera comprising the N-terminal region of the human alpha7 nicotinic acetylcholine receptor, fused to the transmembrane/C-terminal domains of the mouse serotonin 5-HT3 receptor, was constructed. Injection of the chimera cDNA into Xenopus oocytes, or transient transfection in human embryonic kidney (HEK-293) cells, resulted in the expression of functional channels that were sensitive to nicotinic acetylcholine, but not serotonin receptor ligands. In both systems, the responses obtained from chimeric receptors inactivated more slowly than those recorded following activation of wild-type alpha7 receptors. A stable HEK-293 cell line expressing the human alpha7/mouse 5-HT3 chimera was established, which showed that the chimera displayed a similar pharmacological profile to wild-type alpha7 receptors. Use of this chimera in high-throughput screening may enable the identification of novel pharmacological agents that will help to define further the role of alpha7 nicotinic receptors in physiology and disease.
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Affiliation(s)
- Peter J Craig
- Eli Lilly and Company Ltd., Lilly Research Centre, Erl Wood Manor, Windlesham, Surrey GU20 6PH, UK.
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Metzler DE, Metzler CM, Sauke DJ. Chemical Communication Between Cells. Biochemistry 2001. [DOI: 10.1016/b978-012492543-4/50033-7] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/23/2022]
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