1
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Gotti C, Clementi F, Zoli M. Auxiliary protein and chaperone regulation of neuronal nicotinic receptor subtype expression and function. Pharmacol Res 2024; 200:107067. [PMID: 38218358 DOI: 10.1016/j.phrs.2024.107067] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 12/16/2023] [Revised: 01/06/2024] [Accepted: 01/08/2024] [Indexed: 01/15/2024]
Abstract
Neuronal nicotinic acetylcholine receptors (nAChRs) are a family of pentameric, ligand-gated ion channels that are located on the surface of neurons and non-neuronal cells and have multiple physiological and pathophysiological functions. In order to reach the cell surface, many nAChR subtypes require the help of chaperone and/or auxiliary/accessory proteins for their assembly, trafficking, pharmacological modulation, and normal functioning in vivo. The use of powerful genome-wide cDNA screening has led to the identification and characterisation of the molecules and mechanisms that participate in the assembly and trafficking of receptor subtypes, including chaperone and auxiliary or accessory proteins. The aim of this review is to describe the latest findings concerning nAChR chaperones and auxiliary proteins and pharmacological chaperones, and how some of them control receptor biogenesis or regulate channel activation and pharmacology. Some auxiliary proteins are subtype selective, some regulate various subtypes, and some not only modulate nAChRs but also target other receptors and signalling pathways. We also discuss how changes in auxiliary proteins may be involved in nAChR dysfunctions.
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Affiliation(s)
- Cecilia Gotti
- CNR, Institute of Neuroscience, Milan, Italy; NeuroMi Milan Center for Neuroscience, University of Milano-Bicocca, Italy.
| | - Francesco Clementi
- CNR, Institute of Neuroscience, Milan, Italy; Department of Medical Biotechnology and Translational Medicine, Università degli Studi di Milano, Milan, Italy
| | - Michele Zoli
- Department of Biomedical, Metabolic and Neural Sciences, Center for Neuroscience and Neurotechnology (CfNN), University of Modena and Reggio Emilia, Modena, Italy
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2
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Nagori K, Pradhan M, Sharma M, Ajazuddin, Badwaik HR, Nakhate KT. Current Progress on Central Cholinergic Receptors as Therapeutic Targets for Alzheimer's Disease. Curr Alzheimer Res 2024; 21:50-68. [PMID: 38529600 DOI: 10.2174/0115672050306008240321034006] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/23/2024] [Revised: 02/22/2024] [Accepted: 02/26/2024] [Indexed: 03/27/2024]
Abstract
Acetylcholine (ACh) is ubiquitously present in the nervous system and has been involved in the regulation of various brain functions. By modulating synaptic transmission and promoting synaptic plasticity, particularly in the hippocampus and cortex, ACh plays a pivotal role in the regulation of learning and memory. These procognitive actions of ACh are mediated by the neuronal muscarinic and nicotinic cholinergic receptors. The impairment of cholinergic transmission leads to cognitive decline associated with aging and dementia. Therefore, the cholinergic system has been of prime focus when concerned with Alzheimer's disease (AD), the most common cause of dementia. In AD, the extensive destruction of cholinergic neurons occurs by amyloid-β plaques and tau protein-rich neurofibrillary tangles. Amyloid-β also blocks cholinergic receptors and obstructs neuronal signaling. This makes the central cholinergic system an important target for the development of drugs for AD. In fact, centrally acting cholinesterase inhibitors like donepezil and rivastigmine are approved for the treatment of AD, although the outcome is not satisfactory. Therefore, identification of specific subtypes of cholinergic receptors involved in the pathogenesis of AD is essential to develop future drugs. Also, the identification of endogenous rescue mechanisms to the cholinergic system can pave the way for new drug development. In this article, we discussed the neuroanatomy of the central cholinergic system. Further, various subtypes of muscarinic and nicotinic receptors involved in the cognition and pathophysiology of AD are described in detail. The article also reviewed primary neurotransmitters that regulate cognitive processes by modulating basal forebrain cholinergic projection neurons.
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Affiliation(s)
- Kushagra Nagori
- Department of Pharmaceutical Chemistry, Rungta College of Pharmaceutical Sciences and Research, Kurud Road, Kohka, Bhilai 490024, Chhattisgarh, India
| | - Madhulika Pradhan
- Department of Pharmaceutical Technology, Gracious College of Pharmacy, Abhanpur 493661, Chhattisgarh, India
| | - Mukesh Sharma
- Department of Pharmacognosy, Rungta College of Pharmaceutical Sciences and Research, Kurud Road, Kohka, Bhilai 490024, Chhattisgarh, India
| | - Ajazuddin
- Department of Pharmaceutics, Rungta College of Pharmaceutical Sciences and Research, Kurud Road, Kohka, Bhilai 490024, Chhattisgarh, India
| | - Hemant R Badwaik
- Department of Pharmaceutical Chemistry, Shri Shankaracharya Institute of Pharmaceutical Sciences and Research, Junwani, Bhilai 490020, Chhattisgarh, India
| | - Kartik T Nakhate
- Department of Pharmacology, Shri Vile Parle Kelavani Mandal's Institute of Pharmacy, Dhule 424001, Maharashtra, India
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3
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Pei S, Xu C, Tan Y, Wang M, Yu J, Zhangsun D, Zhu X, Luo S. Synthesis, Activity, and Application of Fluorescent Analogs of [D1G, Δ14Q]LvIC Targeting α6β4 Nicotinic Acetylcholine Receptor. Bioconjug Chem 2023; 34:2194-2204. [PMID: 37748043 DOI: 10.1021/acs.bioconjchem.3c00283] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 09/27/2023]
Abstract
α6β4* nicotinic acetylcholine receptor (nAChR) (* represents the possible presence of additional subunits) is mainly distributed in the central and peripheral nervous system and is associated with neurological diseases, such as neuropathic pain; however, the ability to explore its function and distribution is limited due to the lack of pharmacological tools. As one of the analogs of α-conotoxin (α-CTx) LvIC from Conus lividus, [D1G, Δ14Q]LvIC (Lv) selectively and potently blocks α6/α3β4 nAChR (α6/α3 represents a chimera). Here, we synthesized three fluorescent analogs of Lv by connecting fluorescent molecules 6-carboxytetramethylrhodamine succinimidyl ester (6-TAMRA-SE, R), Cy3 NHS ester (Cy3, C) and BODIPY-FL NHS ester (BDP, B) to the N-terminus of the peptide and obtained Lv-R, Lv-C, and Lv-B, respectively. The potency and selectivity of three fluorescent peptides were evaluated using two-electrode voltage-clamp recording on nAChR subtypes expressed in Xenopus laevis oocytes, and the potency and selectivity of Lv-B were almost maintained with the half-maximal inhibition (IC50) of 64 nM. Then, we explored the stability of Lv-B in artificial cerebrospinal fluid and stained rat brain slices with Lv-B. The results indicated that the stability of Lv-B was slightly improved compared to that of native Lv. Additionally, we detected the distribution of the α6β4* nAChR subtype in the cerebral cortex using green fluorescently labeled peptide and fluorescence microscopy. Our findings not only provide a visualized pharmacological tool for exploring the distribution of the α6β4* nAChR subtype in various situ tissues and organs but also extend the application of α-CTx [D1G, Δ14Q]LvIC to demonstrate the involvement of α6β4 nAChR function in pathophysiology and pharmacology.
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Affiliation(s)
- Shengrong Pei
- Guangxi Key Laboratory of Special Biomedicine; School of Medicine, Guangxi University, Nanning 530004, China
| | - Chenxing Xu
- Guangxi Key Laboratory of Special Biomedicine; School of Medicine, Guangxi University, Nanning 530004, China
| | - Yao Tan
- Guangxi Key Laboratory of Special Biomedicine; School of Medicine, Guangxi University, Nanning 530004, China
| | - Meiting Wang
- Guangxi Key Laboratory of Special Biomedicine; School of Medicine, Guangxi University, Nanning 530004, China
| | - Jinpeng Yu
- Guangxi Key Laboratory of Special Biomedicine; School of Medicine, Guangxi University, Nanning 530004, China
| | - Dongting Zhangsun
- Guangxi Key Laboratory of Special Biomedicine; School of Medicine, Guangxi University, Nanning 530004, China
- Key Laboratory of Tropical Biological Resources of Ministry of Education, Hainan University, Haikou 570228, China
| | - Xiaopeng Zhu
- Guangxi Key Laboratory of Special Biomedicine; School of Medicine, Guangxi University, Nanning 530004, China
| | - Sulan Luo
- Guangxi Key Laboratory of Special Biomedicine; School of Medicine, Guangxi University, Nanning 530004, China
- Key Laboratory of Tropical Biological Resources of Ministry of Education, Hainan University, Haikou 570228, China
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Nakayama M, Nishimura O, Nishimura Y, Kitaichi M, Kuraku S, Sone M, Hama C. Control of Synaptic Levels of Nicotinic Acetylcholine Receptor by the Sequestering Subunit Dα5 and Secreted Scaffold Protein Hig. J Neurosci 2023; 43:3989-4004. [PMID: 37117011 PMCID: PMC10255049 DOI: 10.1523/jneurosci.2243-21.2023] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/12/2021] [Revised: 04/05/2023] [Accepted: 04/10/2023] [Indexed: 04/30/2023] Open
Abstract
The presentation of nicotinic acetylcholine receptors (nAChRs) on synaptic membranes is crucial for generating cholinergic circuits, some of which are associated with memory function and neurodegenerative disorders. Although the physiology and structure of nAChR, a cation channel comprising five subunits, have been extensively studied, little is known about how the receptor levels in interneuronal synapses are determined and which nAChR subunits participate in the regulatory process in cooperation with synaptic cleft matrices and intracellular proteins. By a genetic screen of Drosophila, we identified mutations in the nAChR subunit Dα5 gene as suppressors that restored the mutant phenotypes of hig, which encodes a secretory matrix protein localized to cholinergic synaptic clefts in the brain. Only the loss of function of Dα5 among the 10 nAChR subunits suppressed hig mutant phenotypes in both male and female flies. Dα5 behaved as a lethal factor when Hig was defective; loss of Dα5 in hig mutants rescued lethality, upregulating Dα6 synaptic levels. By contrast, levels of Dα5, Dα6, and Dα7 subunits were all reduced in hig mutants. These three subunits have distinct properties for interaction with Hig or trafficking, as confirmed by chimeric subunit experiments. Notably, the chimeric Dα5 protein, which has the extracellular sequences that display no positive interaction with Hig, exhibited abnormal distribution and lethality even in the presence of Hig. We propose that the sequestering subunit Dα5 functions by reducing synaptic levels of nAChR through internalization, and this process is blocked by Hig, which tethers Dα5 to the synaptic cleft matrix.SIGNIFICANCE STATEMENT Because the cholinergic synapse is one of the major synapses that generate various brain functions, numerous studies have sought to reveal the physiology and structure of the nicotinic acetylcholine receptor (nAChR). However, little is known about how synaptic levels of nAChR are controlled and which nAChR subunits participate in the regulatory process in cooperation with synaptic cleft matrices. By a genetic screen of Drosophila, we identified mutations in the nAChR subunit Dα5 gene as suppressors that restored the mutant phenotypes of hig, which encodes a secretory matrix protein localized to cholinergic synaptic clefts. Our data indicate that Dα5 functions in reducing synaptic levels of nAChR, and this process is blocked by Hig, which tethers Dα5 to the synaptic cleft matrix.
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Affiliation(s)
- Minoru Nakayama
- Faculty of Life Sciences, Kyoto Sangyo University, Kyoto 603-8555, Japan
- Faculty of Science, Toho University, Funabashi 274-8510, Japan
| | - Osamu Nishimura
- Laboratory for Phyloinformatics, RIKEN Center for Biosystems Dynamics Research, RIKEN, Kobe 650-0047, Japan
| | - Yuhi Nishimura
- Faculty of Life Sciences, Kyoto Sangyo University, Kyoto 603-8555, Japan
| | - Miwa Kitaichi
- Faculty of Life Sciences, Kyoto Sangyo University, Kyoto 603-8555, Japan
| | - Shigehiro Kuraku
- Laboratory for Phyloinformatics, RIKEN Center for Biosystems Dynamics Research, RIKEN, Kobe 650-0047, Japan
| | - Masaki Sone
- Faculty of Science, Toho University, Funabashi 274-8510, Japan
| | - Chihiro Hama
- Faculty of Life Sciences, Kyoto Sangyo University, Kyoto 603-8555, Japan
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Xie T, Qin Y, Zhao J, Dong J, Qi P, Zhang P, Zhangsun D, Zhu X, Yu J, Luo S. Molecular Determinants of Species Specificity of α-Conotoxin TxIB towards Rat and Human α6/α3β4 Nicotinic Acetylcholine Receptors. Int J Mol Sci 2023; 24:ijms24108618. [PMID: 37239959 DOI: 10.3390/ijms24108618] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/11/2023] [Revised: 05/05/2023] [Accepted: 05/10/2023] [Indexed: 05/28/2023] Open
Abstract
Conotoxins are widely distributed and important for studying ligand-gated ion channels. TxIB, a conotoxin consisting of 16 amino acids derived from Conus textile, is a unique selective ligand that blocks rat α6/α3β2β3 nAChR (IC50 = 28 nM) without affecting other rat subtypes. However, when the activity of TxIB against human nAChRs was examined, it was unexpectedly found that TxIB had a significant blocking effect on not only human α6/α3β2β3 nAChR but also human α6/α3β4 nAChR, with an IC50 of 537 nM. To investigate the molecular mechanism of this species specificity and to establish a theoretical basis for drug development studies of TxIB and its analogs, different amino acid residues between human and rat α6/α3 and β4 nAChR subunits were identified. Each residue of the human species was then substituted with the corresponding residue of the rat species via PCR-directed mutagenesis. The potencies of TxIB towards the native α6/α3β4 nAChRs and their mutants were evaluated through electrophysiological experiments. The results showed that the IC50 of TxIB against h[α6V32L, K61R/α3]β4L107V, V115I was 22.5 μM, a 42-fold decrease in potency compared to the native hα6/α3β4 nAChR. Val-32 and Lys-61 in the human α6/α3 subunit and Leu-107 and Val-115 in the human β4 subunit, together, were found to determine the species differences in the α6/α3β4 nAChR. These results also demonstrate that the effects of species differences between humans and rats should be fully considered when evaluating the efficacy of drug candidates targeting nAChRs in rodent models.
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Affiliation(s)
- Ting Xie
- School of Medicine, Guangxi University, Nanning 530004, China
| | - Yuan Qin
- School of Medicine, Guangxi University, Nanning 530004, China
| | - Jinyuan Zhao
- School of Medicine, Guangxi University, Nanning 530004, China
| | - Jianying Dong
- School of Medicine, Guangxi University, Nanning 530004, China
| | - Panpan Qi
- School of Medicine, Guangxi University, Nanning 530004, China
| | - Panpan Zhang
- School of Medicine, Guangxi University, Nanning 530004, China
| | - Dongting Zhangsun
- Key Laboratory of Tropical Biological Resources, Ministry of Education, Key Laboratory for Marine Drugs of Haikou, Hainan University, Haikou 570228, China
| | - Xiaopeng Zhu
- School of Medicine, Guangxi University, Nanning 530004, China
| | - Jinpeng Yu
- School of Medicine, Guangxi University, Nanning 530004, China
| | - Sulan Luo
- School of Medicine, Guangxi University, Nanning 530004, China
- Key Laboratory of Tropical Biological Resources, Ministry of Education, Key Laboratory for Marine Drugs of Haikou, Hainan University, Haikou 570228, China
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Brunello L, Ménard C, Rousset M, Vignes M, Charnet P, Cens T. Different efficiency of auxiliary/chaperone proteins to promote the functional reconstitution of honeybee glutamate and acetylcholine receptors in Xenopus laevis oocytes. INSECT MOLECULAR BIOLOGY 2022; 31:620-633. [PMID: 35587772 PMCID: PMC9546428 DOI: 10.1111/imb.12791] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Subscribe] [Scholar Register] [Received: 03/01/2022] [Accepted: 05/12/2022] [Indexed: 06/15/2023]
Abstract
Heterologous expression systems (e.g., Xenopus laevis oocytes) are useful to study the biophysical properties and pharmacology of ionotropic receptors such as ionotropic glutamate (iGLuRs) and nicotinic acetylcholine (nAChRs) receptors. However, insect receptors often require the co-expression of chaperone proteins to be functional. Only few iGluRs and nAChRs have been successfully expressed in such systems. Here, we compared the efficiency of chaperone proteins to promote the functional expression of one Apis mellifera iGluR and several nAChR subunit combinations (α1α8β1, α7, α2α8β1 and α2α7α8β1) in Xenopus oocytes. To this end, we cloned a new iGluR (GluR-1) and potential chaperone proteins (e.g., SOL-1, Neto, NACHO) and tested more than 40 combinations of human, nematode and honeybee proteins. We obtained robust expression of GluR-1 and α1α8β1 when co-expressed with honeybee chaperone proteins and found that nAChR expression critically depended on the α1 subunit N-terminal sequence. We recorded small ACh-gated currents in few oocytes when the α7 subunit was co-expressed with Caenorhabditis elegans RIC-3, but none of the chaperone proteins allowed efficient expression of α2α8β1 or α2α7α8β1. Our results show that only some protein combinations can reconstitute functional receptors in Xenopus oocytes and that protein combination efficient in one species is not always efficient in another species.
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Affiliation(s)
- Lorène Brunello
- Intitut des Biomolécules Max Mousseron, Université de Montpellier, CNRS, ENSCMMontpellierFrance
| | - Claudine Ménard
- Intitut des Biomolécules Max Mousseron, Université de Montpellier, CNRS, ENSCMMontpellierFrance
| | - Matthieu Rousset
- Intitut des Biomolécules Max Mousseron, Université de Montpellier, CNRS, ENSCMMontpellierFrance
| | - Michel Vignes
- Intitut des Biomolécules Max Mousseron, Université de Montpellier, CNRS, ENSCMMontpellierFrance
| | - Pierre Charnet
- Intitut des Biomolécules Max Mousseron, Université de Montpellier, CNRS, ENSCMMontpellierFrance
| | - Thierry Cens
- Intitut des Biomolécules Max Mousseron, Université de Montpellier, CNRS, ENSCMMontpellierFrance
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Hone AJ, McIntosh JM. Alkaloid ligands enable function of homomeric human α10 nicotinic acetylcholine receptors. Front Pharmacol 2022; 13:981760. [PMID: 36188578 PMCID: PMC9523446 DOI: 10.3389/fphar.2022.981760] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/29/2022] [Accepted: 08/23/2022] [Indexed: 01/29/2023] Open
Abstract
In the nervous system, nicotinic acetylcholine receptors (nAChRs) rapidly transduce a chemical signal into one that is electrical via ligand-gated ion flux through the central channel of the receptor. However, some nAChR subunits are expressed by non-excitable cells where signal transduction apparently occurs through non-ionic mechanisms. One such nAChR subunit, α10, is present in a discreet subset of immune cells and has been implicated in pathologies including cancer, neuropathic pain, and chronic inflammation. Longstanding convention holds that human α10 subunits require co-assembly with α9 subunits for function. Here we assessed whether cholinergic ligands can enable or uncover ionic functions from homomeric α10 nAChRs. Xenopus laevis oocytes expressing human α10 subunits were exposed to a panel of ligands and examined for receptor activation using voltage-clamp electrophysiology. Functional expression of human α10 nAChRs was achieved by exposing the oocytes to the alkaloids strychnine, brucine, or methyllycaconitine. Furthermore, acute exposure to the alkaloid ligands significantly enhanced ionic responses. Acetylcholine-gated currents mediated by α10 nAChRs were potently inhibited by the snake toxins α-bungarotoxin and α-cobratoxin but not by α-conotoxins that target α9 and α9α10 nAChRs. Our findings indicate that human α10 homomers are expressed in oocytes and exposure to certain ligands can enable ionic functions. To our knowledge, this is the first demonstration that human α10 subunits can assemble as functional homomeric nAChRs. These findings have potential implications for receptor regulatory-mechanisms and will enable structural, functional, and further pharmacological characterization of human α10 nAChRs.
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Affiliation(s)
- Arik J. Hone
- School of Biological Sciences, University of Utah, Salt Lake City, UT, United States
- MIRECC, George E. Whalen Veterans Affairs Medical Center, Salt Lake City, UT, United States
| | - J. Michael McIntosh
- School of Biological Sciences, University of Utah, Salt Lake City, UT, United States
- Department of Psychiatry, University of Utah, Salt Lake City, UT, United States
- George E. Whalen Veterans Affairs Medical Center, Salt Lake City, UT, United States
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Hobson BD, Choi SJ, Mosharov EV, Soni RK, Sulzer D, Sims P. Subcellular proteomics of dopamine neurons in the mouse brain. eLife 2022; 11:70921. [PMID: 35098924 PMCID: PMC8860448 DOI: 10.7554/elife.70921] [Citation(s) in RCA: 22] [Impact Index Per Article: 11.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/02/2021] [Accepted: 01/30/2022] [Indexed: 11/13/2022] Open
Abstract
Dopaminergic neurons modulate neural circuits and behaviors via dopamine (DA) release from expansive, long range axonal projections. The elaborate cytoarchitecture of these neurons is embedded within complex brain tissue, making it difficult to access the neuronal proteome using conventional methods. Here, we demonstrate APEX2 proximity labeling within genetically targeted neurons in the mouse brain, enabling subcellular proteomics with cell-type specificity. By combining APEX2 biotinylation with mass spectrometry, we mapped the somatodendritic and axonal proteomes of midbrain dopaminergic neurons. Our dataset reveals the proteomic architecture underlying proteostasis, axonal metabolism, and neurotransmission in these neurons. We find that most proteins encoded by DA neuron-enriched genes are localized within striatal dopaminergic axons, including ion channels with previously undescribed axonal localization. These proteomic datasets provide a resource for neuronal cell biology, and this approach can be readily adapted for study of other neural cell types.
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Affiliation(s)
- Benjamin D Hobson
- Depart of Systems Biology, Columbia University Medical Center, New York, United States
| | - Se Joon Choi
- New York State Psychiatric Institute, Columbia University Medical Center, New York, United States
| | - Eugene V Mosharov
- New York State Psychiatric Institute, Columbia University Medical Center, New York, United States
| | - Rajesh K Soni
- Herbert Irving Comprehensive Cancer Center, Columbia University Medical Center, New York, United States
| | - David Sulzer
- Department of Psychiatry, Columbia University Medical Center, New York, United States
| | - Peter Sims
- Department of Systems Biology, Columbia University Medical Center, New York, United States
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Wills L, Ables JL, Braunscheidel KM, Caligiuri SPB, Elayouby KS, Fillinger C, Ishikawa M, Moen JK, Kenny PJ. Neurobiological Mechanisms of Nicotine Reward and Aversion. Pharmacol Rev 2022; 74:271-310. [PMID: 35017179 PMCID: PMC11060337 DOI: 10.1124/pharmrev.121.000299] [Citation(s) in RCA: 33] [Impact Index Per Article: 16.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/12/2021] [Accepted: 08/24/2021] [Indexed: 12/27/2022] Open
Abstract
Neuronal nicotinic acetylcholine receptors (nAChRs) regulate the rewarding actions of nicotine contained in tobacco that establish and maintain the smoking habit. nAChRs also regulate the aversive properties of nicotine, sensitivity to which decreases tobacco use and protects against tobacco use disorder. These opposing behavioral actions of nicotine reflect nAChR expression in brain reward and aversion circuits. nAChRs containing α4 and β2 subunits are responsible for the high-affinity nicotine binding sites in the brain and are densely expressed by reward-relevant neurons, most notably dopaminergic, GABAergic, and glutamatergic neurons in the ventral tegmental area. High-affinity nAChRs can incorporate additional subunits, including β3, α6, or α5 subunits, with the resulting nAChR subtypes playing discrete and dissociable roles in the stimulatory actions of nicotine on brain dopamine transmission. nAChRs in brain dopamine circuits also participate in aversive reactions to nicotine and the negative affective state experienced during nicotine withdrawal. nAChRs containing α3 and β4 subunits are responsible for the low-affinity nicotine binding sites in the brain and are enriched in brain sites involved in aversion, including the medial habenula, interpeduncular nucleus, and nucleus of the solitary tract, brain sites in which α5 nAChR subunits are also expressed. These aversion-related brain sites regulate nicotine avoidance behaviors, and genetic variation that modifies the function of nAChRs in these sites increases vulnerability to tobacco dependence and smoking-related diseases. Here, we review the molecular, cellular, and circuit-level mechanisms through which nicotine elicits reward and aversion and the adaptations in these processes that drive the development of nicotine dependence. SIGNIFICANCE STATEMENT: Tobacco use disorder in the form of habitual cigarette smoking or regular use of other tobacco-related products is a major cause of death and disease worldwide. This article reviews the actions of nicotine in the brain that contribute to tobacco use disorder.
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Affiliation(s)
- Lauren Wills
- Nash Family Department of Neuroscience, Icahn School of Medicine at Mount Sinai, One Gustave L. Levy Place, New York, New York
| | - Jessica L Ables
- Nash Family Department of Neuroscience, Icahn School of Medicine at Mount Sinai, One Gustave L. Levy Place, New York, New York
| | - Kevin M Braunscheidel
- Nash Family Department of Neuroscience, Icahn School of Medicine at Mount Sinai, One Gustave L. Levy Place, New York, New York
| | - Stephanie P B Caligiuri
- Nash Family Department of Neuroscience, Icahn School of Medicine at Mount Sinai, One Gustave L. Levy Place, New York, New York
| | - Karim S Elayouby
- Nash Family Department of Neuroscience, Icahn School of Medicine at Mount Sinai, One Gustave L. Levy Place, New York, New York
| | - Clementine Fillinger
- Nash Family Department of Neuroscience, Icahn School of Medicine at Mount Sinai, One Gustave L. Levy Place, New York, New York
| | - Masago Ishikawa
- Nash Family Department of Neuroscience, Icahn School of Medicine at Mount Sinai, One Gustave L. Levy Place, New York, New York
| | - Janna K Moen
- Nash Family Department of Neuroscience, Icahn School of Medicine at Mount Sinai, One Gustave L. Levy Place, New York, New York
| | - Paul J Kenny
- Nash Family Department of Neuroscience, Icahn School of Medicine at Mount Sinai, One Gustave L. Levy Place, New York, New York
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10
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Lipovsek M, Marcovich I, Elgoyhen AB. The Hair Cell α9α10 Nicotinic Acetylcholine Receptor: Odd Cousin in an Old Family. Front Cell Neurosci 2021; 15:785265. [PMID: 34867208 PMCID: PMC8634148 DOI: 10.3389/fncel.2021.785265] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/28/2021] [Accepted: 10/25/2021] [Indexed: 11/13/2022] Open
Abstract
Nicotinic acetylcholine receptors (nAChRs) are a subfamily of pentameric ligand-gated ion channels with members identified in most eumetazoan clades. In vertebrates, they are divided into three subgroups, according to their main tissue of expression: neuronal, muscle and hair cell nAChRs. Each receptor subtype is composed of different subunits, encoded by paralogous genes. The latest to be identified are the α9 and α10 subunits, expressed in the mechanosensory hair cells of the inner ear and the lateral line, where they mediate efferent modulation. α9α10 nAChRs are the most divergent amongst all nicotinic receptors, showing marked differences in their degree of sequence conservation, their expression pattern, their subunit co-assembly rules and, most importantly, their functional properties. Here, we review recent advances in the understanding of the structure and evolution of nAChRs. We discuss the functional consequences of sequence divergence and conservation, with special emphasis on the hair cell α9α10 receptor, a seemingly distant cousin of neuronal and muscle nicotinic receptors. Finally, we highlight potential links between the evolution of the octavolateral system and the extreme divergence of vertebrate α9α10 receptors.
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Affiliation(s)
- Marcela Lipovsek
- Ear Institute, Faculty of Brain Sciences, University College London, London, United Kingdom
| | - Irina Marcovich
- Departments of Otolaryngology & Neurology, Boston Children's Hospital, Harvard Medical School, Boston, MA, United States
| | - Ana Belén Elgoyhen
- Instituto de Investigaciones en Ingeniería Genética y Biología Molecular "Dr. Héctor N. Torres" (INGEBI), Consejo Nacional de Investigaciones Científicas y Técnicas (CONICET), Buenos Aires, Argentina
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Matta JA, Gu S, Davini WB, Bredt DS. Nicotinic acetylcholine receptor redux: Discovery of accessories opens therapeutic vistas. Science 2021; 373:373/6556/eabg6539. [PMID: 34385370 DOI: 10.1126/science.abg6539] [Citation(s) in RCA: 38] [Impact Index Per Article: 12.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/24/2022]
Abstract
The neurotransmitter acetylcholine (ACh) acts in part through a family of nicotinic ACh receptors (nAChRs), which mediate diverse physiological processes including muscle contraction, neurotransmission, and sensory transduction. Pharmacologically, nAChRs are responsible for tobacco addiction and are targeted by medicines for hypertension and dementia. Nicotinic AChRs were the first ion channels to be isolated. Recent studies have identified molecules that control nAChR biogenesis, trafficking, and function. These nAChR accessories include protein and chemical chaperones as well as auxiliary subunits. Whereas some factors act on many nAChRs, others are receptor specific. Discovery of these regulatory mechanisms is transforming nAChR research in cells and tissues ranging from central neurons to spinal ganglia to cochlear hair cells. Nicotinic AChR-specific accessories also enable drug discovery on high-confidence targets for psychiatric, neurological, and auditory disorders.
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Affiliation(s)
| | | | - Weston B Davini
- Neuroscience Discovery, Janssen Pharmaceutical Companies of Johnson & Johnson, San Diego, CA 92121, USA
| | - David S Bredt
- Neuroscience Discovery, Janssen Pharmaceutical Companies of Johnson & Johnson, San Diego, CA 92121, USA.
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12
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Salm EJ, Dunn PJ, Shan L, Yamasaki M, Malewicz NM, Miyazaki T, Park J, Sumioka A, Hamer RRL, He WW, Morimoto-Tomita M, LaMotte RH, Tomita S. TMEM163 Regulates ATP-Gated P2X Receptor and Behavior. Cell Rep 2021; 31:107704. [PMID: 32492420 DOI: 10.1016/j.celrep.2020.107704] [Citation(s) in RCA: 5] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [Key Words] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/30/2019] [Revised: 04/14/2020] [Accepted: 05/06/2020] [Indexed: 12/18/2022] Open
Abstract
Fast purinergic signaling is mediated by ATP and ATP-gated ionotropic P2X receptors (P2XRs), and it is implicated in pain-related behaviors. The properties exhibited by P2XRs vary between those expressed in heterologous cells and in vivo. Several modulators of ligand-gated ion channels have recently been identified, suggesting that there are P2XR functional modulators in vivo. Here, we establish a genome-wide open reading frame (ORF) collection and perform functional screening to identify modulators of P2XR activity. We identify TMEM163, which specifically modulates the channel properties and pharmacology of P2XRs. We also find that TMEM163 is required for full function of the neuronal P2XR and a pain-related ATP-evoked behavior. These results establish TMEM163 as a critical modulator of P2XRs in vivo and a potential target for the discovery of drugs for treating pain.
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Affiliation(s)
- Elizabeth J Salm
- Department of Cellular and Molecular Physiology, Department of Neuroscience, Program in Cellular Neuroscience, Neurodegeneration and Repair, The Yale Kavli Institute, Yale University School of Medicine, New Haven, CT 06520, USA; Interdepartmental Neuroscience Program, Yale University School of Medicine, New Haven, CT 06520, USA
| | - Patrick J Dunn
- Department of Cellular and Molecular Physiology, Department of Neuroscience, Program in Cellular Neuroscience, Neurodegeneration and Repair, The Yale Kavli Institute, Yale University School of Medicine, New Haven, CT 06520, USA
| | - Lili Shan
- Department of Cellular and Molecular Physiology, Department of Neuroscience, Program in Cellular Neuroscience, Neurodegeneration and Repair, The Yale Kavli Institute, Yale University School of Medicine, New Haven, CT 06520, USA
| | - Miwako Yamasaki
- Department of Cellular and Molecular Physiology, Department of Neuroscience, Program in Cellular Neuroscience, Neurodegeneration and Repair, The Yale Kavli Institute, Yale University School of Medicine, New Haven, CT 06520, USA; Department of Anatomy, Faculty of Medicine, Hokkaido University, Sapporo, Japan
| | - Nathalie M Malewicz
- Department of Anesthesiology, Yale University School of Medicine, New Haven, CT 06520, USA
| | - Taisuke Miyazaki
- Department of Cellular and Molecular Physiology, Department of Neuroscience, Program in Cellular Neuroscience, Neurodegeneration and Repair, The Yale Kavli Institute, Yale University School of Medicine, New Haven, CT 06520, USA; Department of Anatomy, Faculty of Medicine, Hokkaido University, Sapporo, Japan
| | - Joongkyu Park
- Department of Cellular and Molecular Physiology, Department of Neuroscience, Program in Cellular Neuroscience, Neurodegeneration and Repair, The Yale Kavli Institute, Yale University School of Medicine, New Haven, CT 06520, USA
| | - Akio Sumioka
- Department of Cellular and Molecular Physiology, Department of Neuroscience, Program in Cellular Neuroscience, Neurodegeneration and Repair, The Yale Kavli Institute, Yale University School of Medicine, New Haven, CT 06520, USA
| | | | - Wei-Wu He
- OriGene Technologies, Inc., Rockville, MD 20850, USA
| | - Megumi Morimoto-Tomita
- Department of Cellular and Molecular Physiology, Department of Neuroscience, Program in Cellular Neuroscience, Neurodegeneration and Repair, The Yale Kavli Institute, Yale University School of Medicine, New Haven, CT 06520, USA
| | - Robert H LaMotte
- Department of Anesthesiology, Yale University School of Medicine, New Haven, CT 06520, USA
| | - Susumu Tomita
- Department of Cellular and Molecular Physiology, Department of Neuroscience, Program in Cellular Neuroscience, Neurodegeneration and Repair, The Yale Kavli Institute, Yale University School of Medicine, New Haven, CT 06520, USA; Interdepartmental Neuroscience Program, Yale University School of Medicine, New Haven, CT 06520, USA.
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13
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Marcovich I, Moglie MJ, Carpaneto Freixas AE, Trigila AP, Franchini LF, Plazas PV, Lipovsek M, Elgoyhen AB. Distinct Evolutionary Trajectories of Neuronal and Hair Cell Nicotinic Acetylcholine Receptors. Mol Biol Evol 2021; 37:1070-1089. [PMID: 31821508 PMCID: PMC7086180 DOI: 10.1093/molbev/msz290] [Citation(s) in RCA: 19] [Impact Index Per Article: 6.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/19/2022] Open
Abstract
The expansion and pruning of ion channel families has played a crucial role in the evolution of nervous systems. Nicotinic acetylcholine receptors (nAChRs) are ligand-gated ion channels with distinct roles in synaptic transmission at the neuromuscular junction, the central and peripheral nervous system, and the inner ear. Remarkably, the complement of nAChR subunits has been highly conserved along vertebrate phylogeny. To ask whether the different subtypes of receptors underwent different evolutionary trajectories, we performed a comprehensive analysis of vertebrate nAChRs coding sequences, mouse single-cell expression patterns, and comparative functional properties of receptors from three representative tetrapod species. We found significant differences between hair cell and neuronal receptors that were most likely shaped by the differences in coexpression patterns and coassembly rules of component subunits. Thus, neuronal nAChRs showed high degree of coding sequence conservation, coupled to greater coexpression variance and conservation of functional properties across tetrapod clades. In contrast, hair cell α9α10 nAChRs exhibited greater sequence divergence, narrow coexpression pattern, and great variability of functional properties across species. These results point to differential substrates for random change within the family of gene paralogs that relate to the segregated roles of nAChRs in synaptic transmission.
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Affiliation(s)
- Irina Marcovich
- Instituto de Investigaciones en Ingeniería Genética y Biología Molecular "Dr. Héctor N. Torres" (INGEBI), Consejo Nacional de Investigaciones Científicas y Técnicas (CONICET), Buenos Aires, Argentina
| | - Marcelo J Moglie
- Instituto de Investigaciones en Ingeniería Genética y Biología Molecular "Dr. Héctor N. Torres" (INGEBI), Consejo Nacional de Investigaciones Científicas y Técnicas (CONICET), Buenos Aires, Argentina
| | - Agustín E Carpaneto Freixas
- Instituto de Investigaciones en Ingeniería Genética y Biología Molecular "Dr. Héctor N. Torres" (INGEBI), Consejo Nacional de Investigaciones Científicas y Técnicas (CONICET), Buenos Aires, Argentina
| | - Anabella P Trigila
- Instituto de Investigaciones en Ingeniería Genética y Biología Molecular "Dr. Héctor N. Torres" (INGEBI), Consejo Nacional de Investigaciones Científicas y Técnicas (CONICET), Buenos Aires, Argentina
| | - Lucia F Franchini
- Instituto de Investigaciones en Ingeniería Genética y Biología Molecular "Dr. Héctor N. Torres" (INGEBI), Consejo Nacional de Investigaciones Científicas y Técnicas (CONICET), Buenos Aires, Argentina
| | - Paola V Plazas
- Instituto de Farmacología, Facultad de Medicina, Universidad de Buenos Aires, Buenos Aires, Argentina
| | - Marcela Lipovsek
- Instituto de Investigaciones en Ingeniería Genética y Biología Molecular "Dr. Héctor N. Torres" (INGEBI), Consejo Nacional de Investigaciones Científicas y Técnicas (CONICET), Buenos Aires, Argentina.,Centre for Developmental Neurobiology, King's College London, Institute of Psychiatry, Psychology and Neuroscience, Guy's Campus, London, United Kingdom
| | - Ana Belén Elgoyhen
- Instituto de Investigaciones en Ingeniería Genética y Biología Molecular "Dr. Héctor N. Torres" (INGEBI), Consejo Nacional de Investigaciones Científicas y Técnicas (CONICET), Buenos Aires, Argentina.,Instituto de Farmacología, Facultad de Medicina, Universidad de Buenos Aires, Buenos Aires, Argentina
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14
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Knowland D, Gu S, Eckert WA, Dawe GB, Matta JA, Limberis J, Wickenden AD, Bhattacharya A, Bredt DS. Functional α6β4 acetylcholine receptor expression enables pharmacological testing of nicotinic agonists with analgesic properties. J Clin Invest 2021; 130:6158-6170. [PMID: 33074244 DOI: 10.1172/jci140311] [Citation(s) in RCA: 8] [Impact Index Per Article: 2.7] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/15/2020] [Accepted: 08/06/2020] [Indexed: 01/25/2023] Open
Abstract
The α6β4 nicotinic acetylcholine receptor (nAChR) is enriched in dorsal root ganglia neurons and is an attractive non-opioid therapeutic target for pain. However, difficulty expressing human α6β4 receptors in recombinant systems has precluded drug discovery. Here, genome-wide screening identified accessory proteins that enable reconstitution of human α6β4 nAChRs. BARP, an auxiliary subunit of voltage-dependent calcium channels, promoted α6β4 surface expression while IRE1α, an unfolded protein response sensor, enhanced α6β4 receptor assembly. Effects on α6β4 involve BARP's N-terminal region and IRE1α's splicing of XBP1 mRNA. Furthermore, clinical efficacy of nicotinic agents in relieving neuropathic pain best correlated with their activity on α6β4. Finally, BARP-knockout, but not NACHO-knockout mice lacked nicotine-induced antiallodynia, highlighting the functional importance of α6β4 in pain. These results identify roles for IRE1α and BARP in neurotransmitter receptor assembly and unlock drug discovery for the previously elusive α6β4 receptor.
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15
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Grant S, Lester HA. Proteins for increased surface expression of the α6β4 nicotinic acetylcholine receptor: nothing but good news? J Clin Invest 2021; 130:5685-5687. [PMID: 33074245 DOI: 10.1172/jci143197] [Citation(s) in RCA: 7] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/21/2022] Open
Abstract
Useful animal models of disease in neuroscience can make accurate predictions about a therapeutic outcome, a feature known as predictive validity. In this issue of the JCI, Knowland et al. provide an improved model to assess nicotinic acetylcholine receptor (nAChR) ligands for treating chronic pain. The authors identify two proteins, the voltage-dependent calcium channel auxiliary subunit BARP and the unfolded protein response sensor IRE1α, that are required for robust heterologous expression of α6β4, an nAChR subtype in dorsal root ganglia (DRG). This nAChR is a candidate for the analgesic effects of nicotine as well as the frog toxin epibatidine. Now researchers can efficiently screen for α6β4 nAChR-selective agonists using heterologous expression systems. Candidates that emerge will enable researchers to test the predictive validity of mouse models for chronic pain in the nAChR context. If all these steps work, one can envision a class of non-opioid nAChR-targeted analgesics for chronic pain.
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Affiliation(s)
| | - Henry A Lester
- Division of Biology and Biological Engineering, California Institute of Technology, Pasadena, California, USA
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16
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Hair cell α9α10 nicotinic acetylcholine receptor functional expression regulated by ligand binding and deafness gene products. Proc Natl Acad Sci U S A 2020; 117:24534-24544. [PMID: 32929005 DOI: 10.1073/pnas.2013762117] [Citation(s) in RCA: 16] [Impact Index Per Article: 4.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/12/2022] Open
Abstract
Auditory hair cells receive olivocochlear efferent innervation, which refines tonotopic mapping, improves sound discrimination, and mitigates acoustic trauma. The olivocochlear synapse involves α9α10 nicotinic acetylcholine receptors (nAChRs), which assemble in hair cells only coincident with cholinergic innervation and do not express in recombinant mammalian cell lines. Here, genome-wide screening determined that assembly and surface expression of α9α10 require ligand binding. Ion channel function additionally demands an auxiliary subunit, which can be transmembrane inner ear (TMIE) or TMEM132e. Both of these single-pass transmembrane proteins are enriched in hair cells and underlie nonsyndromic human deafness. Inner hair cells from TMIE mutant mice show altered postsynaptic α9α10 function and retain α9α10-mediated transmission beyond the second postnatal week associated with abnormally persistent cholinergic innervation. Collectively, this study provides a mechanism to link cholinergic input with α9α10 assembly, identifies unexpected functions for human deafness genes TMIE/TMEM132e, and enables drug discovery for this elusive nAChR implicated in prevalent auditory disorders.
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17
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Dhara M, Matta JA, Lei M, Knowland D, Yu H, Gu S, Bredt DS. Polyamine regulation of ion channel assembly and implications for nicotinic acetylcholine receptor pharmacology. Nat Commun 2020; 11:2799. [PMID: 32493979 PMCID: PMC7271128 DOI: 10.1038/s41467-020-16629-3] [Citation(s) in RCA: 19] [Impact Index Per Article: 4.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/31/2020] [Accepted: 05/15/2020] [Indexed: 01/31/2023] Open
Abstract
Small molecule polyamines are abundant in all life forms and participate in diverse aspects of cell growth and differentiation. Spermidine/spermine acetyltransferase (SAT1) is the rate-limiting enzyme in polyamine catabolism and a primary genetic risk factor for suicidality. Here, using genome-wide screening, we find that SAT1 selectively controls nicotinic acetylcholine receptor (nAChR) biogenesis. SAT1 specifically augments assembly of nAChRs containing α7 or α4β2, but not α6 subunits. Polyamines are classically studied as regulators of ion channel gating that engage the nAChR channel pore. In contrast, we find polyamine effects on assembly involve the nAChR cytosolic loop. Neurological studies link brain polyamines with neurodegenerative conditions. Our pharmacological and transgenic animal studies find that reducing polyamines enhances cortical neuron nAChR expression and augments nicotine-mediated neuroprotection. Taken together, we describe a most unexpected role for polyamines in regulating ion channel assembly, which provides a new avenue for nAChR neuropharmacology. Small molecule polyamines participate in diverse aspects of cell growth and differentiation and are known to regulate ion channel gating. Here authors reveal that cellular polyamines control nicotinic acetylcholine receptor (nAChR) biogenesis, and either catabolic degradation or inhibition of polyamine production augments nAChR assembly.
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Affiliation(s)
- Madhurima Dhara
- Neuroscience Discovery, Janssen Pharmaceutical Companies of Johnson and Johnson, 3210 Merryfield Row, San Diego, CA, 92121, USA
| | - Jose A Matta
- Neuroscience Discovery, Janssen Pharmaceutical Companies of Johnson and Johnson, 3210 Merryfield Row, San Diego, CA, 92121, USA
| | - Min Lei
- Neuroscience Discovery, Janssen Pharmaceutical Companies of Johnson and Johnson, 3210 Merryfield Row, San Diego, CA, 92121, USA
| | - Daniel Knowland
- Neuroscience Discovery, Janssen Pharmaceutical Companies of Johnson and Johnson, 3210 Merryfield Row, San Diego, CA, 92121, USA
| | - Hong Yu
- Neuroscience Discovery, Janssen Pharmaceutical Companies of Johnson and Johnson, 3210 Merryfield Row, San Diego, CA, 92121, USA
| | - Shenyan Gu
- Neuroscience Discovery, Janssen Pharmaceutical Companies of Johnson and Johnson, 3210 Merryfield Row, San Diego, CA, 92121, USA
| | - David S Bredt
- Neuroscience Discovery, Janssen Pharmaceutical Companies of Johnson and Johnson, 3210 Merryfield Row, San Diego, CA, 92121, USA.
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18
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Characterization of AN317, a novel selective agonist of α6β2-containing nicotinic acetylcholine receptors. Biochem Pharmacol 2020; 174:113786. [DOI: 10.1016/j.bcp.2019.113786] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/06/2019] [Accepted: 12/23/2019] [Indexed: 11/23/2022]
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19
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Structural basis for α-bungarotoxin insensitivity of neuronal nicotinic acetylcholine receptors. Neuropharmacology 2019; 160:107660. [PMID: 31163179 DOI: 10.1016/j.neuropharm.2019.05.037] [Citation(s) in RCA: 6] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/11/2019] [Revised: 04/25/2019] [Accepted: 05/30/2019] [Indexed: 01/22/2023]
Abstract
The ten types of nicotinic acetylcholine receptor α-subunits show substantial sequence homology, yet some types confer high affinity for α-bungarotoxin, whereas others confer negligible affinity. Combining sequence alignments with structural data reveals three residues unique to α-toxin-refractory α-subunits that coalesce within the 3D structure of the α4β2 receptor and are predicted to fit between loops I and II of α-bungarotoxin. Mutating any one of these residues, Lys189, Ile196 or Lys153, to the α-toxin-permissive counterpart fails to confer α-bungarotoxin binding. However, mutating both Lys189 and Ile196 affords α-bungarotoxin binding with an apparent dissociation constant of 104 nM, while combining mutation of Lys153 reduces the dissociation constant to 22 nM. Analogous residue substitutions also confer high affinity α-bungarotoxin binding upon α-toxin-refractory α2 and α3 subunits. α4β2 receptors engineered to bind α-bungarotoxin exhibit slow rates of α-toxin association and dissociation, and competition by cholinergic ligands typical of muscle nicotinic receptors. Receptors engineered to bind α-bungarotoxin co-sediment with muscle nicotinic receptors on sucrose gradients, and mirror single channel signatures of their α-toxin-refractory counterparts. Thus the inability of α-bungarotoxin to bind to neuronal nicotinic receptors arises from three unique and interdependent residues that coalesce within the receptor's 3D structure.
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