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Structural Insights into the Role of β3 nAChR Subunit in the Activation of Nicotinic Receptors. Molecules 2022; 27:molecules27144642. [PMID: 35889515 PMCID: PMC9319688 DOI: 10.3390/molecules27144642] [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: 06/17/2022] [Revised: 07/19/2022] [Accepted: 07/20/2022] [Indexed: 02/06/2023] Open
Abstract
The β3 subunit of nicotinic acetylcholine receptors (nAChRs) participates in heteropentameric assemblies with some α and other β neuronal subunits forming a plethora of various subtypes, differing in their electrophysiological and pharmacological properties. While β3 has for several years been considered an accessory subunit without direct participation in the formation of functional binding sites, recent electrophysiology data have disputed this notion and indicated the presence of a functional (+) side on the extracellular domain (ECD) of β3. In this study, we present the 2.4 Å resolution crystal structure of the monomeric β3 ECD, which revealed rather distinctive loop C features as compared to those of α nAChR subunits, leading to intramolecular stereochemical hindrance of the binding site cavity. Vigorous molecular dynamics simulations in the context of full length pentameric β3-containing nAChRs, while not excluding the possibility of a β3 (+) binding site, demonstrate that this site cannot efficiently accommodate the agonist nicotine. From the structural perspective, our results endorse the accessory rather than functional role of the β3 nAChR subunit, in accordance with earlier functional studies on β3-containing nAChRs.
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2
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Liao VWY, Chebib M, Ahring PK. Efficient expression of concatenated α1β2δ and α1β3δ GABA A receptors, their pharmacology and stoichiometry. Br J Pharmacol 2021; 178:1556-1573. [PMID: 33491192 DOI: 10.1111/bph.15380] [Citation(s) in RCA: 6] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/14/2020] [Revised: 12/28/2020] [Accepted: 01/11/2021] [Indexed: 11/28/2022] Open
Abstract
BACKGROUND AND PURPOSE GABAA receptors containing δ-subunits are notorious for being difficult to study in vitro due to heterogeneity of expressed receptor populations and low GABA-evoked current amplitudes. Thus, there are some published misconceptions and contradictory conclusions made regarding the pharmacology and stoichiometry of δ-containing receptors. The aim of this study was to obtain robust homogenous expression of α1βδ receptors for in-depth investigation. EXPERIMENTAL APPROACH Novel δ-containing pentameric concatenated constructs were designed. The resulting α1β2δ and α1β3δ GABAA receptor concatemers were investigated by two-electrode voltage-clamp electrophysiology using Xenopus laevis oocytes. KEY RESULTS First, while homogenous α1βδ GABAA receptor pools could not be obtained by manipulating the ratio of injected cRNAs of free α1, β2/3, and δ subunits, concatenated pentameric α1β2δ and α1β3δ constructs resulted in robust expression levels of concatemers. Second, by using optimised constructs that give unidirectional assembly of concatemers, we found that the δ subunit cannot directly participate in GABA binding and receptor activation. Hence, functional δ-containing receptors are likely to all have a conventional 2α:2β:1δ stoichiometry arranged as βαβαδ when viewed counterclockwise from the extracellular side. Third, α1β2/3δ receptors were found to express efficiently in X. laevis oocytes but have a low estimated open probability of ~0.5% upon GABA activation. Because of this, these receptors are uniquely susceptible to positive allosteric modulation by, for example, neurosteroids. CONCLUSION AND IMPLICATIONS Our data answer important outstanding questions regarding the pharmacology and stoichiometry of α1δ-containing GABAA receptors and pave the way for future analysis and drug discovery efforts.
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Affiliation(s)
- Vivian Wan Yu Liao
- Brain and Mind Centre, Sydney Pharmacy School, Faculty of Medicine and Health, The University of Sydney, Sydney, New South Wales, Australia
| | - Mary Chebib
- Brain and Mind Centre, Sydney Pharmacy School, Faculty of Medicine and Health, The University of Sydney, Sydney, New South Wales, Australia
| | - Philip Kiaer Ahring
- Brain and Mind Centre, Sydney Pharmacy School, Faculty of Medicine and Health, The University of Sydney, Sydney, New South Wales, Australia
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3
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Prevost MS, Bouchenaki H, Barilone N, Gielen M, Corringer PJ. Concatemers to re-investigate the role of α5 in α4β2 nicotinic receptors. Cell Mol Life Sci 2021; 78:1051-1064. [PMID: 32472188 PMCID: PMC11071962 DOI: 10.1007/s00018-020-03558-z] [Citation(s) in RCA: 4] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/22/2019] [Revised: 05/15/2020] [Accepted: 05/22/2020] [Indexed: 01/08/2023]
Abstract
Nicotinic acetylcholine receptors (nAChRs) are pentameric ion channels expressed in the central nervous systems. nAChRs containing the α4, β2 and α5 subunits are specifically involved in addictive processes, but their functional architecture is poorly understood due to the intricacy of assembly of these subunits. Here we constrained the subunit assembly by designing fully concatenated human α4β2 and α4β2α5 receptors and characterized their properties by two-electrodes voltage-clamp electrophysiology in Xenopus oocytes. We found that α5-containing nAChRs are irreversibly blocked by methanethiosulfonate (MTS) reagents through a covalent reaction with a cysteine present only in α5. MTS-block experiments establish that the concatemers are expressed in intact form at the oocyte surface, but that reconstitution of nAChRs from loose subunits show inefficient and highly variable assembly of α5 with α4 and β2. Mutational analysis shows that the concatemers assemble both in clockwise and anticlockwise orientations, and that α5 does not contribute to ACh binding from its principal (+) site. Reinvestigation of suspected α5-ligands such as galantamine show no specific effect on α5-containing concatemers. Analysis of the α5-D398N mutation that is linked to smoking and lung cancer shows no significant effect on the electrophysiological function, suggesting that its effect might arise from alteration of other cellular processes. The concatemeric strategy provides a well-characterized platform for mechanistic analysis and screening of human α5-specific ligands.
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Affiliation(s)
- Marie S Prevost
- Unité Récepteurs-Canaux, Institut Pasteur, UMR 3571, CNRS, 75015, Paris, France
| | - Hichem Bouchenaki
- Unité Récepteurs-Canaux, Institut Pasteur, UMR 3571, CNRS, 75015, Paris, France
| | - Nathalie Barilone
- Unité Récepteurs-Canaux, Institut Pasteur, UMR 3571, CNRS, 75015, Paris, France
| | - Marc Gielen
- Unité Récepteurs-Canaux, Institut Pasteur, UMR 3571, CNRS, 75015, Paris, France.
- Sorbonne Université, 21, rue de l'école de médecine, 75006, Paris, France.
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Richter G, Liao VWY, Ahring PK, Chebib M. The Z-Drugs Zolpidem, Zaleplon, and Eszopiclone Have Varying Actions on Human GABA A Receptors Containing γ1, γ2, and γ3 Subunits. Front Neurosci 2020; 14:599812. [PMID: 33328871 PMCID: PMC7710685 DOI: 10.3389/fnins.2020.599812] [Citation(s) in RCA: 7] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/28/2020] [Accepted: 10/26/2020] [Indexed: 11/13/2022] Open
Abstract
γ-Aminobutyric-acid type A (GABA A ) receptors expressing the γ1 or γ3 subunit are only found within a few regions of the brain, some of which are involved in sleep. No known compounds have been reported to selectively target γ1- or γ3-containing GABA A receptors. Pharmacological assessments of this are conflicting, possibly due to differences in experimental models, conditions, and exact protocols when reporting efficacies and potencies. In this study, we evaluated the modulatory properties of five non-benzodiazepine Z-drugs (zaleplon, indiplon, eszopiclone, zolpidem, and alpidem) used in sleep management and the benzodiazepine, diazepam on human α1β2γ receptors using all three γ subtypes. This was accomplished using concatenated GABA A pentamers expressed in Xenopus laevis oocytes and measured via two-electrode voltage clamp. This approach removes the potential for single subunits to form erroneous receptors that could contribute to the pharmacological assessment of these compounds. No compound tested had significant effects on γ1-containing receptors below 10 μM. Interestingly, zaleplon and indiplon were found to modulate γ3-containing receptors equally as efficacious as γ2-containing receptors. Furthermore, zaleplon had a higher potency for γ3- than for γ2-containing receptors, indicating certain therapeutic effects could occur via these γ3-containing receptors. Eszopiclone modulated γ3-containing receptors with reduced efficacy but no reduction in potency. These data demonstrate that the imidazopyridines zaleplon and indiplon are well suited to further investigate potential γ3 effects on sleep in vivo.
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Affiliation(s)
- Grant Richter
- Brain and Mind Centre, Sydney Pharmacy School, The University of Sydney, Sydney, NSW, Australia
| | - Vivian W Y Liao
- Brain and Mind Centre, Sydney Pharmacy School, The University of Sydney, Sydney, NSW, Australia
| | - Philip K Ahring
- Brain and Mind Centre, Sydney Pharmacy School, The University of Sydney, Sydney, NSW, Australia
| | - Mary Chebib
- Brain and Mind Centre, Sydney Pharmacy School, The University of Sydney, Sydney, NSW, Australia
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Liao VWY, Kusay AS, Balle T, Ahring PK. Heterologous expression of concatenated nicotinic ACh receptors: Pros and cons of subunit concatenation and recommendations for construct designs. Br J Pharmacol 2020; 177:4275-4295. [PMID: 32627170 DOI: 10.1111/bph.15188] [Citation(s) in RCA: 4] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/13/2020] [Revised: 06/15/2020] [Accepted: 06/26/2020] [Indexed: 11/27/2022] Open
Abstract
BACKGROUND AND PURPOSE Concatenation of Cys-loop receptor subunits is a commonly used technique to ensure experimental control of receptor assembly. However, we recently demonstrated that widely used constructs did not lead to the expression of uniform pools of ternary and more complex receptors. The aim was therefore to identify viable strategies for designing concatenated constructs that would allow strict control of resultant receptor pools. EXPERIMENTAL APPROACH Concatenated dimeric, tetrameric, and pentameric α4β2-containing nicotinic ACh (nACh) receptor constructs were designed with successively shorter linker lengths and expressed in Xenopus laevis oocytes. Resulting receptor stoichiometries were investigated by functional analysis in two-electrode voltage-clamp experiments. Molecular dynamics simulations were performed to investigate potential effects of linkers on the 3D structure of concatemers. KEY RESULTS Dimeric constructs were found to be unreliable and should be avoided for expression of ternary receptors. By introducing two short linkers, we obtained efficient expression of uniform receptor pools with tetrameric and pentameric constructs. However, linkers should not be excessively short as that introduces strain on the 3D structure of concatemers. CONCLUSION AND IMPLICATIONS The data demonstrate that design of concatenated Cys-loop receptors requires a compromise between the desire for control of assembly and avoiding introduction of strain on the resulting protein. The overall best strategy was found to be pentameric constructs with carefully optimised linker lengths. Our findings will advance studies of ternary or more complex Cys-loop receptors as well as enabling detailed analysis of how pharmacological agents interact with stoichiometry-specific binding sites.
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Affiliation(s)
- Vivian Wan Yu Liao
- Brain and Mind Centre, The University of Sydney, 94 Mallett Street, Camperdown, NSW, 2050, Australia.,Sydney Pharmacy School, Faculty of Medicine and Health, The University of Sydney, NSW, 2006, Australia
| | - Ali Saad Kusay
- Brain and Mind Centre, The University of Sydney, 94 Mallett Street, Camperdown, NSW, 2050, Australia.,Sydney Pharmacy School, Faculty of Medicine and Health, The University of Sydney, NSW, 2006, Australia
| | - Thomas Balle
- Brain and Mind Centre, The University of Sydney, 94 Mallett Street, Camperdown, NSW, 2050, Australia.,Sydney Pharmacy School, Faculty of Medicine and Health, The University of Sydney, NSW, 2006, Australia
| | - Philip Kiaer Ahring
- Brain and Mind Centre, The University of Sydney, 94 Mallett Street, Camperdown, NSW, 2050, Australia.,Sydney Pharmacy School, Faculty of Medicine and Health, The University of Sydney, NSW, 2006, Australia
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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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Schadzek P, Stahl Y, Preller M, Ngezahayo A. Analysis of the dominant mutation N188T of human connexin46 (hCx46) using concatenation and molecular dynamics simulation. FEBS Open Bio 2019; 9:840-850. [PMID: 31034164 PMCID: PMC6487695 DOI: 10.1002/2211-5463.12624] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/15/2018] [Revised: 02/06/2019] [Accepted: 02/26/2019] [Indexed: 11/27/2022] Open
Abstract
Connexins (Cx) are proteins that form cell-to-cell gap junction channels. A mutation at position 188 in the second extracellular loop (E2) domain of hCx46 has been linked to an autosomal dominant zonular pulverulent cataract. As it is dominantly inherited, it is possible that the mutant variant affects the co-expressed wild-type Cx and/or its interaction with other cellular components. Here, we proposed to use concatenated hCx46wt-hCx46N188T and hCx46N188T-hCx46wt to analyze how hCx46N188T affected co-expressed hCx46wt to achieve a dominant inheritance. Heterodimer hCx46wt-hCx46N188T formed fewer gap junction plaques compared to homodimer hCx46wt-hCx46wt, while the hCx46N188T-hCx46N188T homodimer formed almost no gap junction plaques. Dye uptake experiments showed that hemichannels of concatenated variants were similar to hemichannels of monomers. Molecular dynamics simulations revealed that for docking, the N188 of a protomer was engaged in hydrogen bonds (HBs) with R180, N189, and D191 of the counterpart protomer of the adjacent hemichannel. T188 suppressed the formation of HBs between protomers. Molecular dynamics simulations of an equimolar hCx46wt/hCx46N188T gap junction channel revealed a reduced number of HBs between protomers, suggesting reduction of gap junction channels between lens fibers co-expressing the variants.
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Affiliation(s)
- Patrik Schadzek
- Institute of Cell Biology and BiophysicsDepartment of Cell Physiology and BiophysicsLeibniz University HannoverGermany
| | - Yannick Stahl
- Institute of Cell Biology and BiophysicsDepartment of Cell Physiology and BiophysicsLeibniz University HannoverGermany
| | - Matthias Preller
- Institute for Biophysical ChemistryHannover Medical School (MHH)Germany
- Centre for Structural Systems Biology, DESY‐CampusHamburgGermany
| | - Anaclet Ngezahayo
- Institute of Cell Biology and BiophysicsDepartment of Cell Physiology and BiophysicsLeibniz University HannoverGermany
- Center for System Neurosciences (ZSN)HannoverGermany
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Liao VWY, Chua HC, Kowal NM, Chebib M, Balle T, Ahring PK. Concatenated γ-aminobutyric acid type A receptors revisited: Finding order in chaos. J Gen Physiol 2019; 151:798-819. [PMID: 30988061 PMCID: PMC6572006 DOI: 10.1085/jgp.201812133] [Citation(s) in RCA: 12] [Impact Index Per Article: 2.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/25/2018] [Accepted: 03/20/2019] [Indexed: 12/19/2022] Open
Abstract
Subunit concatenation is a powerful technique used to control the assembly of structurally diverse heteromeric receptors such as GABAARs. Liao et al. find that existing GABAAR concatemers do not assemble as expected and describe refinements that allow expression of uniform receptor populations. γ-aminobutyric acid type A receptors (GABAARs), the major inhibitory neurotransmitter receptors in the mammalian central nervous system, are arguably the most challenging member of the pentameric Cys-loop receptors to study due to their heteromeric structure. When two or more subunits are expressed together in heterologous systems, receptors of variable subunit type, ratio, and orientation can form, precluding accurate interpretation of data from functional studies. Subunit concatenation is a technique that involves the linking of individual subunits and in theory allows the precise control of the uniformity of expressed receptors. In reality, the resulting concatemers from widely used constructs are flexible in their orientation and may therefore assemble with themselves or free GABAAR subunits in unexpected ways. In this study, we examine functional responses of receptors from existing concatenated constructs and describe refinements necessary to allow expression of uniform receptor populations. We find that dimers from two commonly used concatenated constructs, β-23-α and α-10-β, assemble readily in both the clockwise and the counterclockwise orientations when coexpressed with free subunits. Furthermore, we show that concatemers formed from new tetrameric α-10-β-α-β and α-10-β-α-γ constructs also assemble in both orientations with free subunits to give canonical αβγ receptors. To restrict linker flexibility, we systematically shorten linker lengths of dimeric and pentameric constructs and find optimized constructs that direct the assembly of GABAARs only in one orientation, thus eliminating the ambiguity associated with previously described concatemers. Based on our data, we revisit some noncanonical GABAAR configurations proposed in recent years and explain how the use of some concatenated constructs may have led to wrong conclusions. Our results help clarify current contradictions in the literature regarding GABAAR subunit stoichiometry and arrangement. The lessons learned from this study may guide future efforts in understanding other related heteromeric receptors.
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Affiliation(s)
- Vivian Wan Yu Liao
- The University of Sydney, Brain and Mind Centre, School of Pharmacy, Faculty of Medicine and Health, Camperdown, New South Wales, Australia
| | - Han Chow Chua
- The University of Sydney, Brain and Mind Centre, School of Pharmacy, Faculty of Medicine and Health, Camperdown, New South Wales, Australia
| | - Natalia Magdalena Kowal
- The University of Sydney, Brain and Mind Centre, School of Pharmacy, Faculty of Medicine and Health, Camperdown, New South Wales, Australia.,Faculty of Pharmaceutical Sciences, School of Health Sciences, University of Iceland, Reykjavik, Iceland
| | - Mary Chebib
- The University of Sydney, Brain and Mind Centre, School of Pharmacy, Faculty of Medicine and Health, Camperdown, New South Wales, Australia
| | - Thomas Balle
- The University of Sydney, Brain and Mind Centre, School of Pharmacy, Faculty of Medicine and Health, Camperdown, New South Wales, Australia
| | - Philip Kiær Ahring
- The University of Sydney, Brain and Mind Centre, School of Pharmacy, Faculty of Medicine and Health, Camperdown, New South Wales, Australia
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Weltzin MM, George AA, Lukas RJ, Whiteaker P. Distinctive single-channel properties of α4β2-nicotinic acetylcholine receptor isoforms. PLoS One 2019; 14:e0213143. [PMID: 30845161 PMCID: PMC6405073 DOI: 10.1371/journal.pone.0213143] [Citation(s) in RCA: 6] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/14/2018] [Accepted: 02/17/2019] [Indexed: 11/19/2022] Open
Abstract
Central nervous system nicotinic acetylcholine receptors (nAChR) are predominantly of the α4β2 subtype. Two isoforms exist, with high or low agonist sensitivity (HS-(α4β2)2β2- and LS-(α4β2)2α4-nAChR). Both isoforms exhibit similar macroscopic potency and efficacy values at low acetylcholine (ACh) concentrations, mediated by a common pair of high-affinity α4(+)/(-)β2 subunit binding interfaces. However LS-(α4β2)2α4-nAChR also respond to higher concentrations of ACh, acting at a third α4(+)/(-)α4 subunit interface. To probe isoform functional differences further, HS- and LS-α4β2-nAChR were expressed in Xenopus laevis oocytes and single-channel responses were assessed using cell-attached patch-clamp. In the presence of a low ACh concentration, both isoforms produce low-bursting function. HS-(α4β2)2β2-nAChR exhibit a single conductance state, whereas LS-(α4β2)2α4-nAChR display two distinctive conductance states. A higher ACh concentration did not preferentially recruit either conductance state, but did result in increased LS-(α4β2)2α4-nAChR bursting and reduced closed times. Introduction of an α4(+)/(-)α4-interface loss-of-function α4W182A mutation abolished these changes, confirming this site's role in mediating LS-(α4β2)2α4-nAChR responses. Small or large amplitude openings are highly-correlated within individual LS-(α4β2)2α4-nAChR bursts, suggesting that they arise from distinct intermediate states, each of which is stabilized by α4(+)/(-)α4 site ACh binding. These findings are consistent with α4(+)/(-)α4 subunit interface occupation resulting in allosteric potentiation of agonist actions at α4(+)/(-)β2 subunit interfaces, rather than independent induction of high conductance channel openings.
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Affiliation(s)
- Maegan M. Weltzin
- Division of Neurobiology, Barrow Neurological Institute, Phoenix, Arizona, United States of America
- * E-mail:
| | - Andrew A. George
- Division of Neurobiology, Barrow Neurological Institute, Phoenix, Arizona, United States of America
| | - Ronald J. Lukas
- Division of Neurobiology, Barrow Neurological Institute, Phoenix, Arizona, United States of America
| | - Paul Whiteaker
- Division of Neurobiology, Barrow Neurological Institute, Phoenix, Arizona, United States of America
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Mazzaferro S, Bermudez I, Sine SM. Potentiation of a neuronal nicotinic receptor via pseudo-agonist site. Cell Mol Life Sci 2019; 76:1151-1167. [PMID: 30600358 PMCID: PMC8022356 DOI: 10.1007/s00018-018-2993-7] [Citation(s) in RCA: 16] [Impact Index Per Article: 3.2] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/09/2018] [Revised: 11/28/2018] [Accepted: 12/10/2018] [Indexed: 11/26/2022]
Abstract
Neuronal nicotinic receptors containing α4 and β2 subunits assemble in two pentameric stoichiometries, (α4)3(β2)2 and (α4)2(β2)3, each with distinct pharmacological signatures; (α4)3(β2)2 receptors are strongly potentiated by the drug NS9283, whereas (α4)2(β2)3 receptors are unaffected. Despite this stoichiometry-selective pharmacology, the molecular identity of the target for NS9283 remains elusive. Here, studying (α4)3(β2)2 receptors, we show that mutations at either the principal face of the β2 subunit or the complementary face of the α4 subunit prevent NS9283 potentiation of ACh-elicited single-channel currents, suggesting the drug targets the β2-α4 pseudo-agonist sites, the α4-α4 agonist site, or both sites. To distinguish among these possibilities, we generated concatemeric receptors with mutations at specified subunit interfaces, and monitored the ability of NS9283 to potentiate ACh-elicited single-channel currents. We find that a mutation at the principal face of the β2 subunit at either β2-α4 pseudo-agonist site suppresses potentiation, whereas mutation at the complementary face of the α4 subunit at the α4-α4 agonist site allows a significant potentiation. Thus, monitoring potentiation of single concatemeric receptor channels reveals that the β2-α4 pseudo-agonist sites are required for stoichiometry-selective drug action. Together with the recently determined structure of the (α4)3(β2)2 receptor, the findings have implications for structure-guided drug design.
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Affiliation(s)
- Simone Mazzaferro
- Receptor Biology Laboratory, Department of Physiology and Biomedical Engineering, Mayo Clinic College of Medicine, Rochester, MN, 55905, USA
| | - Isabel Bermudez
- School of Life Sciences, Oxford Brookes University, Oxford, OX3 OBP, UK
| | - Steven M Sine
- Receptor Biology Laboratory, Department of Physiology and Biomedical Engineering, Mayo Clinic College of Medicine, Rochester, MN, 55905, USA.
- Department of Neurology, Mayo Clinic College of Medicine, Rochester, MN, 55905, USA.
- Department of Molecular Pharmacology and Experimental Therapeutics, Mayo Clinic College of Medicine, Rochester, MN, 55905, USA.
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11
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Absalom NL, Ahring PK, Liao VW, Balle T, Jiang T, Anderson LL, Arnold JC, McGregor IS, Bowen MT, Chebib M. Functional genomics of epilepsy-associated mutations in the GABA A receptor subunits reveal that one mutation impairs function and two are catastrophic. J Biol Chem 2019; 294:6157-6171. [PMID: 30728247 DOI: 10.1074/jbc.ra118.005697] [Citation(s) in RCA: 18] [Impact Index Per Article: 3.6] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/03/2018] [Revised: 01/30/2019] [Indexed: 12/29/2022] Open
Abstract
A number of epilepsy-causing mutations have recently been identified in the genes of the α1, β3, and γ2 subunits comprising the γ-aminobutyric acid type A (GABAA) receptor. These mutations are typically dominant, and in certain cases, such as the α1 and β3 subunits, they may lead to a mix of receptors at the cell surface that contain no mutant subunits, a single mutated subunit, or two mutated subunits. To determine the effects of mutations in a single subunit or in two subunits on receptor activation, we created a concatenated protein assembly that links all five subunits of the α1β3γ2 receptor and expresses them in the correct orientation. We created nine separate receptor variants with a single-mutant subunit and four receptors containing two subunits of the γ2R323Q, β3D120N, β3T157M, β3Y302C, and β3S254F epilepsy-causing mutations. We found that the singly mutated γ2R323Q subunit impairs GABA activation of the receptor by reducing GABA potency. A single β3D120N, β3T157M, or β3Y302C mutation also substantially impaired receptor activation, and two copies of these mutants within a receptor were catastrophic. Of note, an effect of the β3S254F mutation on GABA potency depended on the location of this mutant subunit within the receptor, possibly because of the membrane environment surrounding the transmembrane region of the receptor. Our results highlight that precise functional genomic analyses of GABAA receptor mutations using concatenated constructs can identify receptors with an intermediate phenotype that contribute to epileptic phenotypes and that are potential drug targets for precision medicine approaches.
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Affiliation(s)
- Nathan L Absalom
- From the Brain and Mind Centre, University of Sydney, 94 Mallett Street, Camperdown, New South Wales 2050, Australia; School of Pharmacy, University of Sydney, Camperdown, New South Wales 2006, Australia
| | - Philip K Ahring
- From the Brain and Mind Centre, University of Sydney, 94 Mallett Street, Camperdown, New South Wales 2050, Australia; School of Pharmacy, University of Sydney, Camperdown, New South Wales 2006, Australia
| | - Vivian W Liao
- From the Brain and Mind Centre, University of Sydney, 94 Mallett Street, Camperdown, New South Wales 2050, Australia; School of Pharmacy, University of Sydney, Camperdown, New South Wales 2006, Australia
| | - Thomas Balle
- From the Brain and Mind Centre, University of Sydney, 94 Mallett Street, Camperdown, New South Wales 2050, Australia; School of Pharmacy, University of Sydney, Camperdown, New South Wales 2006, Australia
| | - Tian Jiang
- From the Brain and Mind Centre, University of Sydney, 94 Mallett Street, Camperdown, New South Wales 2050, Australia; School of Pharmacy, University of Sydney, Camperdown, New South Wales 2006, Australia
| | - Lyndsey L Anderson
- From the Brain and Mind Centre, University of Sydney, 94 Mallett Street, Camperdown, New South Wales 2050, Australia; Discipline of Pharmacology, Faculty of Medicine and Health, University of Sydney, Camperdown, New South Wales 2006, Australia; Lambert Initiative for Cannabinoid Therapeutics, University of Sydney, 94 Mallett Street, Camperdown, New South Wales 2050, Australia
| | - Jonathon C Arnold
- From the Brain and Mind Centre, University of Sydney, 94 Mallett Street, Camperdown, New South Wales 2050, Australia; Discipline of Pharmacology, Faculty of Medicine and Health, University of Sydney, Camperdown, New South Wales 2006, Australia; Lambert Initiative for Cannabinoid Therapeutics, University of Sydney, 94 Mallett Street, Camperdown, New South Wales 2050, Australia
| | - Iain S McGregor
- From the Brain and Mind Centre, University of Sydney, 94 Mallett Street, Camperdown, New South Wales 2050, Australia; Lambert Initiative for Cannabinoid Therapeutics, University of Sydney, 94 Mallett Street, Camperdown, New South Wales 2050, Australia; the School of Psychology, Faculty of Science, University of Sydney, Camperdown, New South Wales 2006, Australia
| | - Michael T Bowen
- From the Brain and Mind Centre, University of Sydney, 94 Mallett Street, Camperdown, New South Wales 2050, Australia; Lambert Initiative for Cannabinoid Therapeutics, University of Sydney, 94 Mallett Street, Camperdown, New South Wales 2050, Australia; the School of Psychology, Faculty of Science, University of Sydney, Camperdown, New South Wales 2006, Australia
| | - Mary Chebib
- From the Brain and Mind Centre, University of Sydney, 94 Mallett Street, Camperdown, New South Wales 2050, Australia; School of Pharmacy, University of Sydney, Camperdown, New South Wales 2006, Australia.
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Activation Stoichiometry and Pore Architecture of TRPA1 Probed with Channel Concatemers. Sci Rep 2018; 8:17104. [PMID: 30459425 PMCID: PMC6244152 DOI: 10.1038/s41598-018-35435-y] [Citation(s) in RCA: 10] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/27/2018] [Accepted: 11/02/2018] [Indexed: 01/17/2023] Open
Abstract
The nociceptor ion channel TRPA1 detects a wide range of hazardous chemicals, including reactive electrophiles such as cinnamaldehyde, which gate the channel allowing Na+ and Ca2+ entry. TRPA1 assembles as a tetramer, with a central pore within which an aspartate residue (D918) determines Ca2+ permeability. Here, we report that introduction of histidine at this position, D918H, makes TRPA1 channels sensitive to block by nanomolar concentration of Zn2+ and can be used to functionally tag subunits in concatemers. Concatemers with increasing numbers of D918H subunits display increasing sensitivity to Zn2+ inhibition, indicating that the four side chains at position 918 of the tetramer directly coordinate Zn2+ and other permeating divalent cations. In the published structure of TRPA1, this requires a rearrangement of the pore region which may represent the true open state of the channel. Concatemeric channels containing subunits mutated to be insensitive to reactive electrophiles (C622S) could be activated by cinnamaldehyde when as few as two subunits contained intact ligand binding sites. Activation upon liganding of just two of the four possible subunits may represent an optimal strategy to rapidly and reliably detect noxious chemicals.
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Schadzek P, Hermes D, Stahl Y, Dilger N, Ngezahayo A. Concatenation of Human Connexin26 (hCx26) and Human Connexin46 (hCx46) for the Analysis of Heteromeric Gap Junction Hemichannels and Heterotypic Gap Junction Channels. Int J Mol Sci 2018; 19:E2742. [PMID: 30217016 PMCID: PMC6163895 DOI: 10.3390/ijms19092742] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/20/2018] [Revised: 09/10/2018] [Accepted: 09/11/2018] [Indexed: 12/16/2022] Open
Abstract
Gap junction channels and hemichannels formed by concatenated connexins were analyzed. Monomeric (hCx26, hCx46), homodimeric (hCx46-hCx46, hCx26-hCx26), and heterodimeric (hCx26-hCx46, hCx46-hCx26) constructs, coupled to GFP, were expressed in HeLa cells. Confocal microscopy showed that the tandems formed gap junction plaques with a reduced plaque area compared to monomeric hCx26 or hCx46. Dye transfer experiments showed that concatenation allows metabolic transfer. Expressed in Xenopus oocytes, the inside-out patch-clamp configuration showed single channels with a conductance of about 46 pS and 39 pS for hemichannels composed of hCx46 and hCx26 monomers, respectively, when chloride was replaced by gluconate on both membrane sides. The conductance was reduced for hCx46-hCx46 and hCx26-hCx26 homodimers, probably due to the concatenation. Heteromerized hemichannels, depending on the connexin-order, were characterized by substates at 26 pS and 16 pS for hCx46-hCx26 and 31 pS and 20 pS for hCx26-hCx46. Because of the linker between the connexins, the properties of the formed hemichannels and gap junction channels (e.g., single channel conductance) may not represent the properties of hetero-oligomerized channels. However, should the removal of the linker be successful, this method could be used to analyze the electrical and metabolic selectivity of such channels and the physiological consequences for a tissue.
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Affiliation(s)
- Patrik Schadzek
- Institut für Biophysik, Leibniz Universität Hannover, Herrenhäuser Straße 2, 30419 Hannover, Germany.
| | - Doris Hermes
- Institut für Biophysik, Leibniz Universität Hannover, Herrenhäuser Straße 2, 30419 Hannover, Germany.
- Department of Clinical Neurophysiology, University of Göttingen, Robert-Koch Str. 40, D-37075 Göttingen, Germany.
| | - Yannick Stahl
- Institut für Biophysik, Leibniz Universität Hannover, Herrenhäuser Straße 2, 30419 Hannover, Germany.
| | - Nadine Dilger
- Institut für Biophysik, Leibniz Universität Hannover, Herrenhäuser Straße 2, 30419 Hannover, Germany.
| | - Anaclet Ngezahayo
- Institut für Biophysik, Leibniz Universität Hannover, Herrenhäuser Straße 2, 30419 Hannover, Germany.
- Zentrum für Systemische Neurowissenschaften Stiftung Tierärztliche Hochschule Hannover, Bünteweg 2, 30559 Hannover, Germany.
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Gaitán-Peñas H, Pusch M, Estévez R. Expression of LRRC8/VRAC Currents in Xenopus Oocytes: Advantages and Caveats. Int J Mol Sci 2018; 19:ijms19030719. [PMID: 29498698 PMCID: PMC5877580 DOI: 10.3390/ijms19030719] [Citation(s) in RCA: 10] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/10/2018] [Revised: 02/25/2018] [Accepted: 02/28/2018] [Indexed: 12/26/2022] Open
Abstract
Volume-regulated anion channels (VRACs) play a role in controlling cell volume by opening upon cell swelling. Apart from controlling cell volume, their function is important in many other physiological processes, such as transport of metabolites or drugs, and extracellular signal transduction. VRACs are formed by heteromers of the pannexin homologous protein LRRC8A (also named Swell1) with other LRRC8 members (B, C, D, and E). LRRC8 proteins are difficult to study, since they are expressed in all cells of our body, and the channel stoichiometry can be changed by overexpression, resulting in non-functional heteromers. Two different strategies have been developed to overcome this issue: complementation by transient transfection of LRRC8 genome-edited cell lines, and reconstitution in lipid bilayers. Alternatively, we have used Xenopus oocytes as a simple system to study LRRC8 proteins. Here, we have reviewed all previous experiments that have been performed with VRAC and LRRC8 proteins in Xenopus oocytes. We also discuss future strategies that may be used to perform structure-function analysis of the VRAC in oocytes and other systems, in order to understand its role in controlling multiple physiological functions.
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Affiliation(s)
- Héctor Gaitán-Peñas
- Facultat de Medicina, Departament de Ciències Fisiològiques, Universitat de Barcelona-IDIBELL, C/Feixa Llarga s/n, L'Hospitalet de Llobregat, 08907 Barcelona, Spain.
- Centro de Investigación en red de Enfermedades Raras (CIBERER), Instituto de Salud Carlos III (ISCIII), 08907 Barcelona, Spain.
| | - Michael Pusch
- Istituto di Biofisica, Consiglio Nazionale delle Ricerche (CNR), I-16149 Genova, Italy.
| | - Raúl Estévez
- Facultat de Medicina, Departament de Ciències Fisiològiques, Universitat de Barcelona-IDIBELL, C/Feixa Llarga s/n, L'Hospitalet de Llobregat, 08907 Barcelona, Spain.
- Centro de Investigación en red de Enfermedades Raras (CIBERER), Instituto de Salud Carlos III (ISCIII), 08907 Barcelona, Spain.
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