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Brockmöller S, Molitor LM, Seeger T, Worek F, Rothmiller S. N-Glycosylation Deficiency in Transgene α7 nAChR and RIC3 Expressing CHO Cells Without NACHO. J Membr Biol 2024; 257:245-256. [PMID: 38967800 DOI: 10.1007/s00232-024-00317-0] [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: 04/17/2024] [Accepted: 06/25/2024] [Indexed: 07/06/2024]
Abstract
The human neuronal nicotinic acetylcholine receptor α7 (nAChR) is an important target implicated in diseases like Alzheimer's or Parkinson's, as well as a validated target for drug discovery. For α7 nAChR model systems, correct folding and ion influx functions are essential. Two chaperones, resistance to inhibitors of cholinesterase 3 (RIC3) and novel nAChR regulator (NACHO), enhance the assembly and function of α7 nAChR. This study investigates the consequence of NACHO absence on α7 nAChR expression and function. Therefore, the sequences of human α7 nAChR and human RIC3 were transduced in Chinese hamster ovary (CHO) cells. Protein expression and function of α7 nAChR were confirmed by Western blot and voltage clamp, respectively. Cellular viability was assessed by cell proliferation and lactate dehydrogenase assays. Intracellular and extracellular expression were determined by in/on-cell Western, compared with another nAChR subtype by novel cluster fluorescence-linked immunosorbent assay, and N-glycosylation efficiency was assessed by glycosylation digest. The transgene CHO cell line showed expected protein expression and function for α7 nAChR and cell viability was barely influenced by overexpression. While intracellular levels of α7 nAChR were as anticipated, plasma membrane insertion was low. The glycosylation digest revealed no appreciable N-glycosylation product. This study demonstrates a stable and functional cell line expressing α7 nAChR, whose protein expression, function, and viability are not affected by the absence of NACHO. The reduced plasma membrane insertion of α7 nAChR, combined with incorrect matured N-glycosylation at the Golgi apparatus, suggests a loss of recognition signal for lectin sorting.
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Affiliation(s)
| | | | - Thomas Seeger
- Bundeswehr Institute of Pharmacology and Toxicology, Munich, Germany
| | - Franz Worek
- Bundeswehr Institute of Pharmacology and Toxicology, Munich, Germany
| | - Simone Rothmiller
- Bundeswehr Institute of Pharmacology and Toxicology, Munich, Germany
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2
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Brockmöller S, Worek F, Rothmiller S. Protein networking: nicotinic acetylcholine receptors and their protein-protein-associations. Mol Cell Biochem 2024; 479:1627-1642. [PMID: 38771378 DOI: 10.1007/s11010-024-05032-x] [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: 01/22/2024] [Accepted: 05/04/2024] [Indexed: 05/22/2024]
Abstract
Nicotinic acetylcholine receptors (nAChR) are complex transmembrane proteins involved in neurotransmission in the nervous system and at the neuromuscular junction. nAChR disorders may lead to severe, potentially fatal pathophysiological states. To date, the receptor has been the focus of basic and applied research to provide novel therapeutic interventions. Since most studies have investigated only the nAChR itself, it is necessary to consider the receptor as part of its protein network to understand or elucidate-specific pathways. On its way through the secretory pathway, the receptor interacts with several chaperones and proteins. This review takes a closer look at these molecular interactions and focuses especially on endoplasmic reticulum biogenesis, secretory pathway sorting, Golgi maturation, plasma membrane presentation, retrograde internalization, and recycling. Additional knowledge regarding the nAChR protein network may lead to a more detailed comprehension of the fundamental pathomechanisms of diseases or may lead to the discovery of novel therapeutic drug targets.
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Affiliation(s)
- Sabrina Brockmöller
- Bundeswehr Institute of Pharmacology and Toxicology, Munich, Bavaria, Germany.
| | - Franz Worek
- Bundeswehr Institute of Pharmacology and Toxicology, Munich, Bavaria, Germany
| | - Simone Rothmiller
- Bundeswehr Institute of Pharmacology and Toxicology, Munich, Bavaria, Germany
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3
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Pradhan A, Mounford H, Peixinho J, Rea E, Epeslidou E, Scott JS, Cull J, Maxwell S, Webster R, Beeson D, Dong YY, Prekovic S, Bermudez I, Newbury DF. Unraveling the molecular interactions between α7 nicotinic receptor and a RIC3 variant associated with backward speech. Cell Mol Life Sci 2024; 81:129. [PMID: 38472514 DOI: 10.1007/s00018-024-05149-8] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/10/2023] [Revised: 01/28/2024] [Accepted: 01/30/2024] [Indexed: 03/14/2024]
Abstract
Recent work putatively linked a rare genetic variant of the chaperone Resistant to Inhibitors of acetylcholinesterase (RIC3) (NM_024557.4:c.262G > A, NP_078833.3:p.G88R) to a unique ability to speak backwards, a language skill that is associated with exceptional working memory capacity. RIC3 is important for the folding, maturation, and functional expression of α7 nicotinic acetylcholine receptors (nAChR). We compared and contrasted the effects of RIC3G88R on assembly, cell surface expression, and function of human α7 receptors using fluorescent protein tagged α7 nAChR and Förster resonance energy transfer (FRET) microscopy imaging in combination with functional assays and 125I-α-bungarotoxin binding. As expected, the wild-type RIC3 protein was found to increase both cell surface and functional expression of α7 receptors. In contrast, the variant form of RIC3 decreased both. FRET analysis showed that RICG88R increased the interactions between RIC3 and α7 protein in the endoplasmic reticulum. These results provide interesting and novel data to show that a RIC3 variant alters the interaction of RIC3 and α7, which translates to decreased cell surface and functional expression of α7 nAChR.
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Affiliation(s)
- Aditi Pradhan
- Department of Biological and Molecular Sciences, Faculty of Health and Life Sciences, Oxford Brookes University, Oxford, OX3 0BP, England
| | - Hayley Mounford
- Department of Biological and Molecular Sciences, Faculty of Health and Life Sciences, Oxford Brookes University, Oxford, OX3 0BP, England
| | - Jessica Peixinho
- Department of Biological and Molecular Sciences, Faculty of Health and Life Sciences, Oxford Brookes University, Oxford, OX3 0BP, England
| | - Edward Rea
- Department of Biological and Molecular Sciences, Faculty of Health and Life Sciences, Oxford Brookes University, Oxford, OX3 0BP, England
- Oxford Brookes Centre for Bioimaging, Oxford Brookes University, Oxford, OX3 0BP, England
| | - Emmanouela Epeslidou
- Center for Molecular Medicine, University Medical Center Utrecht, Utrecht, The Netherlands
| | - Julia S Scott
- Center for Molecular Medicine, University Medical Center Utrecht, Utrecht, The Netherlands
| | - Joanna Cull
- Department of Biological and Molecular Sciences, Faculty of Health and Life Sciences, Oxford Brookes University, Oxford, OX3 0BP, England
| | - Susan Maxwell
- Neurosciences Group, Weatherall Institute of Molecular Medicine, John Radcliffe Hospital, Oxford, OX3 9DS, England
| | - Richard Webster
- Neurosciences Group, Weatherall Institute of Molecular Medicine, John Radcliffe Hospital, Oxford, OX3 9DS, England
| | - David Beeson
- Neurosciences Group, Weatherall Institute of Molecular Medicine, John Radcliffe Hospital, Oxford, OX3 9DS, England
| | - Yin Yao Dong
- Nuffield Department of Clinical Neurosciences, University of Oxford, Oxford, OX3 9DS, England
| | - Stefan Prekovic
- Center for Molecular Medicine, University Medical Center Utrecht, Utrecht, The Netherlands
| | - Isabel Bermudez
- Department of Biological and Molecular Sciences, Faculty of Health and Life Sciences, Oxford Brookes University, Oxford, OX3 0BP, England
| | - Dianne F Newbury
- Department of Biological and Molecular Sciences, Faculty of Health and Life Sciences, Oxford Brookes University, Oxford, OX3 0BP, England.
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4
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Chrestia JF, Turani O, Araujo NR, Hernando G, Esandi MDC, Bouzat C. Regulation of nicotinic acetylcholine receptors by post-translational modifications. Pharmacol Res 2023; 190:106712. [PMID: 36863428 DOI: 10.1016/j.phrs.2023.106712] [Citation(s) in RCA: 8] [Impact Index Per Article: 8.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 01/12/2023] [Revised: 02/21/2023] [Accepted: 02/24/2023] [Indexed: 03/04/2023]
Abstract
Nicotinic acetylcholine receptors (nAChRs) comprise a family of pentameric ligand-gated ion channels widely distributed in the central and peripheric nervous system and in non-neuronal cells. nAChRs are involved in chemical synapses and are key actors in vital physiological processes throughout the animal kingdom. They mediate skeletal muscle contraction, autonomic responses, contribute to cognitive processes, and regulate behaviors. Dysregulation of nAChRs is associated with neurological, neurodegenerative, inflammatory and motor disorders. In spite of the great advances in the elucidation of nAChR structure and function, our knowledge about the impact of post-translational modifications (PTMs) on nAChR functional activity and cholinergic signaling has lagged behind. PTMs occur at different steps of protein life cycle, modulating in time and space protein folding, localization, function, and protein-protein interactions, and allow fine-tuned responses to changes in the environment. A large body of evidence demonstrates that PTMs regulate all levels of nAChR life cycle, with key roles in receptor expression, membrane stability and function. However, our knowledge is still limited, restricted to a few PTMs, and many important aspects remain largely unknown. There is thus a long way to go to decipher the association of aberrant PTMs with disorders of cholinergic signaling and to target PTM regulation for novel therapeutic interventions. In this review we provide a comprehensive overview of what is known about how different PTMs regulate nAChR.
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Affiliation(s)
- Juan Facundo Chrestia
- Instituto de Investigaciones Bioquímicas de Bahía Blanca, Departamento de Biología, Bioquímica y Farmacia, Universidad Nacional del Sur-Consejo Nacional de Investigaciones Científicas y Técnicas (CONICET), Bahía Blanca 8000, Argentina
| | - Ornella Turani
- Instituto de Investigaciones Bioquímicas de Bahía Blanca, Departamento de Biología, Bioquímica y Farmacia, Universidad Nacional del Sur-Consejo Nacional de Investigaciones Científicas y Técnicas (CONICET), Bahía Blanca 8000, Argentina
| | - Noelia Rodriguez Araujo
- Instituto de Investigaciones Bioquímicas de Bahía Blanca, Departamento de Biología, Bioquímica y Farmacia, Universidad Nacional del Sur-Consejo Nacional de Investigaciones Científicas y Técnicas (CONICET), Bahía Blanca 8000, Argentina
| | - Guillermina Hernando
- Instituto de Investigaciones Bioquímicas de Bahía Blanca, Departamento de Biología, Bioquímica y Farmacia, Universidad Nacional del Sur-Consejo Nacional de Investigaciones Científicas y Técnicas (CONICET), Bahía Blanca 8000, Argentina
| | - María Del Carmen Esandi
- Instituto de Investigaciones Bioquímicas de Bahía Blanca, Departamento de Biología, Bioquímica y Farmacia, Universidad Nacional del Sur-Consejo Nacional de Investigaciones Científicas y Técnicas (CONICET), Bahía Blanca 8000, Argentina
| | - Cecilia Bouzat
- Instituto de Investigaciones Bioquímicas de Bahía Blanca, Departamento de Biología, Bioquímica y Farmacia, Universidad Nacional del Sur-Consejo Nacional de Investigaciones Científicas y Técnicas (CONICET), Bahía Blanca 8000, Argentina.
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Mocatta J, Mesoy SM, Dougherty DA, Lummis SCR. 5-HT 3 Receptor MX Helix Contributes to Receptor Function. ACS Chem Neurosci 2022; 13:2338-2345. [PMID: 35867037 PMCID: PMC9354082 DOI: 10.1021/acschemneuro.2c00339] [Citation(s) in RCA: 2] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022] Open
Abstract
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5-HT3 receptors are members of the family
of pentameric
ligand-gated ion channels. Each subunit has an extracellular, transmembrane,
and intracellular domain. Only part of the intracellular domain structure
has been solved, revealing it contains two α-helical segments;
one, the MA helix, is an extension of M4, while the other, the MX
helix, is formed from residues located close to the end of M3. This
MX helix is in distinct locations in open and closed receptor structures,
suggesting it may play a role in function. Here, we explore this hypothesis
using functional responses of Ala-substituted mutant receptors expressed
in HEK293 cells. The data show altering many of the MX residues results
in a small decrease in EC50 (up to 5-fold), although in
one (H232A) this is increased. Radiolabeled ligand binding on selected
mutants showed no change in binding affinity, indicating an effect
on gating and not binding. In addition, five mutations (P316A, V317A,
P318A, D319A, and H323A) initially resulted in nonfunctional receptors,
but the function could be rescued by coexpression with a chaperone
protein, suggesting a likely role in assembly or folding. Examination
of previously obtained MD simulation data shows that the extent of
MX encompassed by membrane lipids differs considerably in the open
and closed structures, suggesting that lipid–protein interactions
in this region could have a major effect on channel opening propensity.
We conclude that the MX helix can modulate the function of the receptor
and propose that its interactions with membrane lipids play a major
role in this.
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Affiliation(s)
- James Mocatta
- Department of Biochemistry, University of Cambridge, Tennis Court Road, Cambridge CB2 1GA, United Kingdom
| | - Susanne M Mesoy
- Department of Biochemistry, University of Cambridge, Tennis Court Road, Cambridge CB2 1GA, United Kingdom
| | - Dennis A Dougherty
- Division of Chemistry and Chemical Engineering, California Institute of Technology, Pasadena, California 91125, United States
| | - Sarah C R Lummis
- Department of Biochemistry, University of Cambridge, Tennis Court Road, Cambridge CB2 1GA, United Kingdom
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Speculation on How RIC-3 and Other Chaperones Facilitate α7 Nicotinic Receptor Folding and Assembly. MOLECULES (BASEL, SWITZERLAND) 2022; 27:molecules27144527. [PMID: 35889400 PMCID: PMC9318448 DOI: 10.3390/molecules27144527] [Citation(s) in RCA: 4] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Subscribe] [Scholar Register] [Received: 06/22/2022] [Revised: 07/07/2022] [Accepted: 07/09/2022] [Indexed: 11/17/2022]
Abstract
The process of how multimeric transmembrane proteins fold and assemble in the endoplasmic reticulum is not well understood. The alpha7 nicotinic receptor (α7 nAChR) is a good model for multimeric protein assembly since it has at least two independent and specialized chaperones: Resistance to Inhibitors of Cholinesterase 3 (RIC-3) and Nicotinic Acetylcholine Receptor Regulator (NACHO). Recent cryo-EM and NMR data revealed structural features of α7 nAChRs. A ser-ala-pro (SAP) motif precedes a structurally important but unique "latch" helix in α7 nAChRs. A sampling of α7 sequences suggests the SAP motif is conserved from C. elegans to humans, but the latch sequence is only conserved in vertebrates. How RIC-3 and NACHO facilitate receptor subunits folding into their final pentameric configuration is not known. The artificial intelligence program AlphaFold2 recently predicted structures for NACHO and RIC-3. NACHO is highly conserved in sequence and structure across species, but RIC-3 is not. This review ponders how different intrinsically disordered RIC-3 isoforms from C. elegans to humans interact with α7 nAChR subunits despite having little sequence homology across RIC-3 species. Two models from the literature about how RIC-3 assists α7 nAChR assembly are evaluated considering recent structural information about the receptor and its chaperones.
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7
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Thompson MJ, Domville JA, Edrington CH, Venes A, Giguère PM, Baenziger JE. Distinct functional roles for the M4 α-helix from each homologous subunit in the hetero-pentameric ligand-gated ion channel nAChR. J Biol Chem 2022; 298:102104. [PMID: 35679899 PMCID: PMC9260303 DOI: 10.1016/j.jbc.2022.102104] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/04/2021] [Revised: 05/30/2022] [Accepted: 06/03/2022] [Indexed: 11/04/2022] Open
Abstract
The outermost lipid-exposed α-helix (M4) in each of the homologous α, β, δ, and γ/ε subunits of the muscle nicotinic acetylcholine receptor (nAChR) has previously been proposed to act as a lipid sensor. However, the mechanism by which this sensor would function is not clear. To explore how the M4 α-helix from each subunit in human adult muscle nAChR influences function, and thus explore its putative role in lipid sensing, we functionally characterized alanine mutations at every residue in αM4, βM4, δM4, and εM4, along with both alanine and deletion mutations in the post-M4 region of each subunit. Although no critical interactions involving residues on M4 or in post-M4 were identified, we found that numerous mutations at the M4–M1/M3 interface altered the agonist-induced response. In addition, homologous mutations in M4 in different subunits were found to have different effects on channel function. The functional effects of multiple mutations either along M4 in one subunit or at homologous positions of M4 in different subunits were also found to be additive. Finally, when characterized in both Xenopus oocytes and human embryonic kidney 293T cells, select αM4 mutations displayed cell-specific phenotypes, possibly because of the different membrane lipid environments. Collectively, our data suggest different functional roles for the M4 α-helix in each heteromeric nAChR subunit and predict that lipid sensing involving M4 occurs primarily through the cumulative interactions at the M4–M1/M3 interface, as opposed to the alteration of specific interactions that are critical to channel function.
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Pursuing High-Resolution Structures of Nicotinic Acetylcholine Receptors: Lessons Learned from Five Decades. Molecules 2021; 26:molecules26195753. [PMID: 34641297 PMCID: PMC8510392 DOI: 10.3390/molecules26195753] [Citation(s) in RCA: 9] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/28/2021] [Revised: 09/19/2021] [Accepted: 09/20/2021] [Indexed: 01/04/2023] Open
Abstract
Since their discovery, nicotinic acetylcholine receptors (nAChRs) have been extensively studied to understand their function, as well as the consequence of alterations leading to disease states. Importantly, these receptors represent pharmacological targets to treat a number of neurological and neurodegenerative disorders. Nevertheless, their therapeutic value has been limited by the absence of high-resolution structures that allow for the design of more specific and effective drugs. This article offers a comprehensive review of five decades of research pursuing high-resolution structures of nAChRs. We provide a historical perspective, from initial structural studies to the most recent X-ray and cryogenic electron microscopy (Cryo-EM) nAChR structures. We also discuss the most relevant structural features that emerged from these studies, as well as perspectives in the field.
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