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Indurthi DC. The effect of unliganded gating on agonist response in nicotinic receptors. Eur J Pharmacol 2024; 980:176830. [PMID: 39032761 DOI: 10.1016/j.ejphar.2024.176830] [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: 01/31/2024] [Revised: 07/02/2024] [Accepted: 07/18/2024] [Indexed: 07/23/2024]
Abstract
Understanding the agonist concentration-response curve (CRC) is the cornerstone in pharmacology. While CRC parameters, agonist potency (EC50) and efficacy (maximum response, Imax) are well-studied, the role of unliganded gating (minimum response, Imin) on CRC is often overlooked. This study explores the effect of unliganded gating on agonist response in muscle-type acetylcholine (ACh) receptors, focusing on the underexplored role of Imin in modulating EC50 and Imax. Three Gain-of-Function (GOF) mutations that increase, and two Loss-of-Function (LOF) mutations that decrease the unliganded gating equilibrium constant (L0) were studied using automated patch-clamp electrophysiology. GOF mutations enhanced agonist potency, whereas LOF mutations reduced it. The calculated CRC aligned well with empirical results, indicating that agonist CRC can be estimated from knowledge of L0. Reduction in agonist efficacy due to LOF mutations was calculated and subsequently validated using single-channel patch-clamp electrophysiology, a factor often obscured in normalized CRC. The study also evaluated the combined impact of mutations (L0) on CRC, confirming the predictive model. Further, no significant energetic coupling between distant residues (>15 Å) was found, indicating that the mutations' effects are localized and do not alter overall agonist affinity. These findings substantiate the role of unliganded gating in modulating agonist responses and establishes a predictive model for estimating CRC parameters from known changes in L0. The study highlights the importance of intrinsic activity in receptor theory.
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Affiliation(s)
- Dinesh C Indurthi
- Department of Physiology and Biophysics, University at Buffalo, State University of New York, Buffalo, United States.
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2
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Li H, Teng J, Hibbs RE. Structural switch in acetylcholine receptors in developing muscle. Nature 2024; 632:1174-1180. [PMID: 39085615 DOI: 10.1038/s41586-024-07774-6] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/08/2024] [Accepted: 07/02/2024] [Indexed: 08/02/2024]
Abstract
During development, motor neurons originating in the brainstem and spinal cord form elaborate synapses with skeletal muscle fibres1. These neurons release acetylcholine (ACh), which binds to nicotinic ACh receptors (AChRs) on the muscle, initiating contraction. Two types of AChR are present in developing muscle cells, and their differential expression serves as a hallmark of neuromuscular synapse maturation2-4. The structural principles underlying the switch from fetal to adult muscle receptors are unknown. Here, we present high-resolution structures of both fetal and adult muscle nicotinic AChRs, isolated from bovine skeletal muscle in developmental transition. These structures, obtained in the absence and presence of ACh, provide a structural context for understanding how fetal versus adult receptor isoforms are tuned for synapse development versus the all-or-none signalling required for high-fidelity skeletal muscle contraction. We find that ACh affinity differences are driven by binding site access, channel conductance is tuned by widespread surface electrostatics and open duration changes result from intrasubunit interactions and structural flexibility. The structures further reveal pathogenic mechanisms underlying congenital myasthenic syndromes.
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Affiliation(s)
- Huanhuan Li
- Department of Neurobiology, University of California San Diego, La Jolla, CA, USA
| | - Jinfeng Teng
- Department of Neurobiology, University of California San Diego, La Jolla, CA, USA
| | - Ryan E Hibbs
- Department of Neurobiology, University of California San Diego, La Jolla, CA, USA.
- Department of Pharmacology, University of California San Diego, La Jolla, CA, USA.
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Kumari M, Khatoon N, Sharma R, Adusumilli S, Auerbach A, Kashyap HK, Nayak TK. Mechanism of hydrophobic gating in the acetylcholine receptor channel pore. J Gen Physiol 2024; 156:e202213189. [PMID: 38153395 PMCID: PMC10757554 DOI: 10.1085/jgp.202213189] [Citation(s) in RCA: 1] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/10/2022] [Revised: 06/16/2023] [Accepted: 12/06/2023] [Indexed: 12/29/2023] Open
Abstract
Neuromuscular acetylcholine receptors (AChRs) are hetero-pentameric, ligand-gated ion channels. The binding of the neurotransmitter acetylcholine (ACh) to two target sites promotes a global conformational change of the receptor that opens the channel and allows ion conduction through the channel pore. Here, by measuring free-energy changes from single-channel current recordings and using molecular dynamics simulations, we elucidate how a constricted hydrophobic region acts as a "gate" to regulate the channel opening in the pore of AChRs. Mutations of gate residues, including those implicated in congenital myasthenia syndrome, lower the permeation barrier of the channel substantially and increase the unliganded gating equilibrium constant (constitutive channel openings). Correlations between hydrophobicity and the observed free-energy changes, supported by calculations of water densities in the wild-type versus mutant channel pores, provide evidence for hydrophobic wetting-dewetting transition at the gate. The analysis of a coupled interaction network provides insight into the molecular mechanism of closed- versus open-state conformational changes at the gate. Studies of the transition state by "phi"(φ)-value analysis indicate that agonist binding serves to stabilize both the transition and the open state. Intersubunit interaction energy measurements and molecular dynamics simulations suggest that channel opening involves tilting of the pore-lining M2 helices, asymmetric outward rotation of amino acid side chains, and wetting transition of the gate region that lowers the barrier to ion permeation and stabilizes the channel open conformation. Our work provides new insight into the hydrophobic gate opening and shows why the gate mutations result in constitutive AChR channel activity.
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Affiliation(s)
- Monika Kumari
- Department of Chemistry, Indian Institute of Technology Delhi, Hauz Khas, New Delhi, India
| | - Nadira Khatoon
- Kusuma School of Biological Sciences, Indian Institute of Technology Delhi, Hauz Khas, New Delhi, India
| | - Rachita Sharma
- Kusuma School of Biological Sciences, Indian Institute of Technology Delhi, Hauz Khas, New Delhi, India
| | - Sushanth Adusumilli
- Kusuma School of Biological Sciences, Indian Institute of Technology Delhi, Hauz Khas, New Delhi, India
| | - Anthony Auerbach
- Jacobs School of Medicine and Biomedical Sciences, University at Buffalo, Buffalo, NY, USA
| | - Hemant K. Kashyap
- Department of Chemistry, Indian Institute of Technology Delhi, Hauz Khas, New Delhi, India
| | - Tapan K. Nayak
- Kusuma School of Biological Sciences, Indian Institute of Technology Delhi, Hauz Khas, New Delhi, India
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Lee JY, Seo KH. Can previously injected botulinum toxin cause paradoxical masseter muscle rigidity after administration of a nondepolarizing neuromuscular blocking agent? Can J Anaesth 2024; 71:294-295. [PMID: 37853281 DOI: 10.1007/s12630-023-02629-6] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/22/2023] [Revised: 09/25/2023] [Accepted: 09/26/2023] [Indexed: 10/20/2023] Open
Affiliation(s)
- Ji Yung Lee
- Department of Anesthesiology and Pain Medicine, Yeouido St. Mary's Hospital, College of Medicine, The Catholic University of Korea, Seoul, South Korea
| | - Kwon Hui Seo
- Department of Anesthesiology and Pain Medicine, Yeouido St. Mary's Hospital, College of Medicine, The Catholic University of Korea, Seoul, South Korea.
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Brooks SV, Guzman SD, Ruiz LP. Skeletal muscle structure, physiology, and function. HANDBOOK OF CLINICAL NEUROLOGY 2023; 195:3-16. [PMID: 37562874 DOI: 10.1016/b978-0-323-98818-6.00013-3] [Citation(s) in RCA: 2] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 08/12/2023]
Abstract
Contractions of skeletal muscles provide the stability and power for all body movements. Consequently, any impairment in skeletal muscle function results in some degree of instability or immobility. Factors that influence skeletal muscle structure and function are therefore of great interest scientifically and clinically. Injury, neuromuscular disease, and old age are among the factors that commonly contribute to impairments in skeletal muscle function. The goal of this chapter is to summarize the fundamentals of skeletal muscle structure and function to provide foundational knowledge for this Handbook volume. We examine the molecular interactions that provide the basis for the generation of force and movement, discuss mechanisms of the regulation of contraction at the level of myofibers, and introduce concepts of the activation and control of muscle function in vivo. Where appropriate, the chapter updates the emerging science that will increase understanding of muscle function.
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Affiliation(s)
- Susan V Brooks
- Department of Molecular & Integrative Physiology, University of Michigan, Ann Arbor, MI, United States; Department of Biomedical Engineering, University of Michigan, Ann Arbor, MI, United States.
| | - Steve D Guzman
- Department of Molecular & Integrative Physiology, University of Michigan, Ann Arbor, MI, United States
| | - Lloyd P Ruiz
- Department of Molecular & Integrative Physiology, University of Michigan, Ann Arbor, MI, United States
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Khatoon N, Adusumilli S, Dey P, Sharma R, Kampani P, Shandilya J, Nayak TK. Protein engineering and design in ion channels and receptors. Methods Cell Biol 2022; 169:143-168. [DOI: 10.1016/bs.mcb.2021.12.031] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/19/2022]
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Cetin H, Beeson D, Vincent A, Webster R. The Structure, Function, and Physiology of the Fetal and Adult Acetylcholine Receptor in Muscle. Front Mol Neurosci 2020; 13:581097. [PMID: 33013323 PMCID: PMC7506097 DOI: 10.3389/fnmol.2020.581097] [Citation(s) in RCA: 41] [Impact Index Per Article: 10.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/07/2020] [Accepted: 08/13/2020] [Indexed: 12/31/2022] Open
Abstract
The neuromuscular junction (NMJ) is a highly developed synapse linking motor neuron activity with muscle contraction. A complex of molecular cascades together with the specialized NMJ architecture ensures that each action potential arriving at the motor nerve terminal is translated into an action potential in the muscle fiber. The muscle-type nicotinic acetylcholine receptor (AChR) is a key molecular component located at the postsynaptic muscle membrane responsible for the generation of the endplate potential (EPP), which usually exceeds the threshold potential necessary to activate voltage-gated sodium channels and triggers a muscle action potential. Two AChR isoforms are found in mammalian muscle. The fetal isoform is present in prenatal stages and is involved in the development of the neuromuscular system whereas the adult isoform prevails thereafter, except after denervation when the fetal form is re-expressed throughout the muscle. This review will summarize the structural and functional differences between the two isoforms and outline congenital and autoimmune myasthenic syndromes that involve the isoform specific AChR subunits.
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Affiliation(s)
- Hakan Cetin
- Department of Neurology, Medical University of Vienna, Vienna, Austria.,Nuffield Department of Clinical Neurosciences, University of Oxford, Oxford, United Kingdom
| | - David Beeson
- Nuffield Department of Clinical Neurosciences, University of Oxford, Oxford, United Kingdom
| | - Angela Vincent
- Nuffield Department of Clinical Neurosciences, University of Oxford, Oxford, United Kingdom
| | - Richard Webster
- Nuffield Department of Clinical Neurosciences, University of Oxford, Oxford, United Kingdom
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Tripathy S, Zheng W, Auerbach A. A single molecular distance predicts agonist binding energy in nicotinic receptors. J Gen Physiol 2019; 151:452-464. [PMID: 30635370 PMCID: PMC6445573 DOI: 10.1085/jgp.201812212] [Citation(s) in RCA: 10] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/17/2018] [Revised: 11/07/2018] [Accepted: 12/11/2018] [Indexed: 11/20/2022] Open
Abstract
Agonists turn on receptors because they bind more strongly to active (R*) versus resting (R) conformations of their target sites. Here, to explore how agonists activate neuromuscular acetylcholine receptors, we built homology models of R and R* neurotransmitter binding sites, docked ligands to those sites, ran molecular dynamics simulations to relax ("equilibrate") the structures, measured binding site structural parameters, and correlated them with experimental agonist binding energies. Each binding pocket is a pyramid formed by five aromatic amino acids and covered partially by loop C. We found that in R* versus R, loop C is displaced outward, the pocket is smaller and skewed, the agonist orientation is reversed, and a key nitrogen atom in the agonist is closer to the pocket center (distance dx) and a tryptophan pair but farther from αY190. Of these differences, the change in dx shows the largest correlation with experimental binding energy and provides a good estimate of agonist affinity, efficacy, and efficiency. Indeed, concentration-response curves can be calculated from just dx values. The contraction and twist of the binding pocket upon activation resemble gating rearrangements of the extracellular domain of related receptors at a smaller scale.
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Affiliation(s)
- Sushree Tripathy
- Department of Physics, State University of New York, Buffalo, Buffalo, NY
| | - Wenjun Zheng
- Department of Physics, State University of New York, Buffalo, Buffalo, NY
| | - Anthony Auerbach
- Department of Physiology and Biophysics, State University of New York, Buffalo, Buffalo, NY
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Bouzat C, Mukhtasimova N. The nicotinic acetylcholine receptor as a molecular machine for neuromuscular transmission. CURRENT OPINION IN PHYSIOLOGY 2018. [DOI: 10.1016/j.cophys.2018.04.008] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/16/2022]
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Jin Y, Huang X, Papke RL, Jutkiewicz EM, Showalter HD, Zhan CG. Design, synthesis, and biological activity of 5'-phenyl-1,2,5,6-tetrahydro-3,3'-bipyridine analogues as potential antagonists of nicotinic acetylcholine receptors. Bioorg Med Chem Lett 2017; 27:4350-4353. [PMID: 28838693 DOI: 10.1016/j.bmcl.2017.08.025] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/30/2017] [Accepted: 08/12/2017] [Indexed: 10/19/2022]
Abstract
Starting from a known non-specific agonist (1) of nicotinic acetylcholine receptors (nAChRs), rationally guided structural-based design resulted in the discovery of a small series of 5'-phenyl-1,2,5,6-tetrahydro-3,3'-bipyridines (3a-3e) incorporating a phenyl ring off the pyridine core of 1. The compounds were synthesized via successive Suzuki couplings on a suitably functionalized pyridine starting monomer 4 to append phenyl and pyridyl substituents off the 3- and 5-positions, respectively, and then subsequent modifications were made on the flanking pyridyl ring to provide target compounds. Compound 3a is a novel antagonist, which is highly selective for α3β4 nAChR (Ki=123nM) over the α4β2 and α7 receptors.
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Affiliation(s)
- Yafei Jin
- Department of Medicinal Chemistry and Vahlteich Medicinal Chemistry Core, University of Michigan, Ann Arbor, MI 48109, United States
| | - Xiaoqin Huang
- Department of Pharmaceutical Sciences and Molecular Modeling and Biopharmaceutical Center, College of Pharmacy, University of Kentucky, 789 South Limestone Street, Lexington, KY 40536, United States
| | - Roger L Papke
- Department of Pharmacology and Therapeutics, University of Florida, Gainesville, FL 32610, United States
| | - Emily M Jutkiewicz
- Department of Pharmacology, University of Michigan Medical School, Ann Arbor, MI 48109, United States
| | - Hollis D Showalter
- Department of Medicinal Chemistry and Vahlteich Medicinal Chemistry Core, University of Michigan, Ann Arbor, MI 48109, United States.
| | - Chang-Guo Zhan
- Department of Pharmaceutical Sciences and Molecular Modeling and Biopharmaceutical Center, College of Pharmacy, University of Kentucky, 789 South Limestone Street, Lexington, KY 40536, United States.
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Affiliation(s)
- Alasdair J Gibb
- Department of Neuroscience, Physiology and Pharmacology, University College London, London, WC1E 6BT, UK
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Bruhova I, Auerbach A. Molecular recognition at cholinergic synapses: acetylcholine versus choline. J Physiol 2016; 595:1253-1261. [PMID: 27779761 DOI: 10.1113/jp273291] [Citation(s) in RCA: 10] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/13/2016] [Accepted: 10/12/2016] [Indexed: 11/08/2022] Open
Abstract
KEY POINTS Neuromuscular acetylcholine (ACh) receptors have a high affinity for the neurotransmitter ACh and a low affinity for its metabolic product choline. At each transmitter binding site three aromatic groups determine affinity, and together provide ∼50% more binding energy for ACh than for choline. Deprotonation of αY190 by a nearby lysine strengthens the interaction between this aromatic ring and both ACh and choline. H-bonds position ACh and choline differently in the aromatic cage to generate the different affinities. ABSTRACT Acetylcholine (ACh) released at the vertebrate nerve-muscle synapse is hydrolysed rapidly to choline (Cho), so endplate receptors (AChRs) are exposed to high concentrations of both of these structurally related ligands. To understand how these receptors distinguish ACh and Cho, we used single-channel electrophysiology to measure resting affinities (binding free energies) of these and other agonists in adult-type mouse AChRs having a mutation(s) at the transmitter-binding sites. The aromatic rings of αY190, αW149 and αY198 each provide ∼50% less binding energy for Cho compared to ACh. At αY198 a phenylalanine substitution had no effect, but at αY190 this substitution caused a large, agonist-independent loss in binding energy that depended on the presence of αK145. The results suggest that (1) αY190 is deprotonated by αK145 to strengthen the interaction between this benzene ring and the agonist's quaternary ammonium (QA) and (2) AChRs respond strongly to ACh because an H-bond positions the QA to interact optimally with the rings, and weakly to Cho because a different H-bond tethers the ligand to misalign the QA and form weaker interactions with the aromatic groups. The results suggest that the difference in ACh versus Cho binding energies is determined by different ligand positions within a fixed protein structure.
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Affiliation(s)
- Iva Bruhova
- Department of Physiology and Biophysics, SUNY at Buffalo, Buffalo, NY, 14214, USA
| | - Anthony Auerbach
- Department of Physiology and Biophysics, SUNY at Buffalo, Buffalo, NY, 14214, USA
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Gupta S, Chakraborty S, Vij R, Auerbach A. A mechanism for acetylcholine receptor gating based on structure, coupling, phi, and flip. J Gen Physiol 2016; 149:85-103. [PMID: 27932572 PMCID: PMC5217088 DOI: 10.1085/jgp.201611673] [Citation(s) in RCA: 36] [Impact Index Per Article: 4.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/21/2016] [Revised: 09/20/2016] [Accepted: 11/10/2016] [Indexed: 01/29/2023] Open
Abstract
Gupta et al. use single-channel electrophysiology to investigate the gating mechanism of acetylcholine receptor ion channels. They propose that channel opening starts at the M2–M3 linker and ligand-binding sites and proceeds through four brief intermediate conformations before ending with the collapse of a gate bubble. Nicotinic acetylcholine receptors are allosteric proteins that generate membrane currents by isomerizing (“gating”) between resting and active conformations under the influence of neurotransmitters. Here, to explore the mechanisms that link the transmitter-binding sites (TBSs) with the distant gate, we use mutant cycle analyses to measure coupling between residue pairs, phi value analyses to sequence domain rearrangements, and current simulations to reproduce a microsecond shut component (“flip”) apparent in single-channel recordings. Significant interactions between amino acids separated by >15 Å are rare; an exception is between the αM2–M3 linkers and the TBSs that are ∼30 Å apart. Linker residues also make significant, local interactions within and between subunits. Phi value analyses indicate that without agonists, the linker is the first region in the protein to reach the gating transition state. Together, the phi pattern and flip component suggest that a complete, resting↔active allosteric transition involves passage through four brief intermediate states, with brief shut events arising from sojourns in all or a subset. We derive energy landscapes for gating with and without agonists, and propose a structure-based model in which resting→active starts with spontaneous rearrangements of the M2–M3 linkers and TBSs. These conformational changes stabilize a twisted extracellular domain to promote transmembrane helix tilting, gate dilation, and the formation of a “bubble” that collapses to initiate ion conduction. The energy landscapes suggest that twisting is the most energetically unfavorable step in the resting→active conformational change and that the rate-limiting step in the reverse process is bubble formation.
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Affiliation(s)
- Shaweta Gupta
- Department of Physiology and Biophysics, State University of New York at Buffalo, Buffalo, NY 14214
| | - Srirupa Chakraborty
- Department of Physiology and Biophysics, State University of New York at Buffalo, Buffalo, NY 14214
| | - Ridhima Vij
- Department of Physiology and Biophysics, State University of New York at Buffalo, Buffalo, NY 14214
| | - Anthony Auerbach
- Department of Physiology and Biophysics, State University of New York at Buffalo, Buffalo, NY 14214
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