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Coonen L, Martinez-Morales E, Van De Sande DV, Snyders DJ, Cortes DM, Cuello LG, Labro AJ. The nonconducting W434F mutant adopts upon membrane depolarization an inactivated-like state that differs from wild-type Shaker-IR potassium channels. Sci Adv 2022; 8:eabn1731. [PMID: 36112676 PMCID: PMC9481120 DOI: 10.1126/sciadv.abn1731] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Grants] [Track Full Text] [Download PDF] [Figures] [Subscribe] [Scholar Register] [Received: 11/08/2021] [Accepted: 08/01/2022] [Indexed: 06/15/2023]
Abstract
Voltage-gated K+ (Kv) channels mediate the flow of K+ across the cell membrane by regulating the conductive state of their activation gate (AG). Several Kv channels display slow C-type inactivation, a process whereby their selectivity filter (SF) becomes less or nonconductive. It has been proposed that, in the fast inactivation-removed Shaker-IR channel, the W434F mutation epitomizes the C-type inactivated state because it functionally accelerates this process. By introducing another pore mutation that prevents AG closure, P475D, we found a way to record ionic currents of the Shaker-IR-W434F-P475D mutant at hyperpolarized membrane potentials as the W434F-mutant SF recovers from its inactivated state. This W434F conductive state lost its high K+ over Na+ selectivity, and even NMDG+ can permeate, features not observed in a wild-type SF. This indicates that, at least during recovery from inactivation, the W434F-mutant SF transitions to a widened and noncationic specific conformation.
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Affiliation(s)
- Laura Coonen
- Department of Biomedical Sciences, Faculty of Pharmaceutical, Biomedical and Veterinary Sciences, University of Antwerp, 2610 Antwerp, Belgium
| | - Evelyn Martinez-Morales
- Department of Biomedical Sciences, Faculty of Pharmaceutical, Biomedical and Veterinary Sciences, University of Antwerp, 2610 Antwerp, Belgium
| | - Dieter V. Van De Sande
- Department of Biomedical Sciences, Faculty of Pharmaceutical, Biomedical and Veterinary Sciences, University of Antwerp, 2610 Antwerp, Belgium
| | - Dirk J. Snyders
- Department of Biomedical Sciences, Faculty of Pharmaceutical, Biomedical and Veterinary Sciences, University of Antwerp, 2610 Antwerp, Belgium
| | - D. Marien Cortes
- Cell Physiology and Molecular Biophysics, Center for Membrane Protein Research, Texas Tech University Health Sciences Center, Lubbock, TX 79430, USA
| | - Luis G. Cuello
- Cell Physiology and Molecular Biophysics, Center for Membrane Protein Research, Texas Tech University Health Sciences Center, Lubbock, TX 79430, USA
| | - Alain J. Labro
- Department of Biomedical Sciences, Faculty of Pharmaceutical, Biomedical and Veterinary Sciences, University of Antwerp, 2610 Antwerp, Belgium
- Department of Basic and Applied Medical Sciences, Faculty of Medicine, Ghent University, 9000 Ghent, Belgium
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2
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Van Theemsche KM, Heymans JG, Popovic NZ, Martinez-Morales E, Snyders DJ, Labro AJ. Offsetting Voltage-Dependent Kv1.5 Channel Opening Through Charged Residue Substitutions on Top of the First Transmembrane Segment. Bioelectricity 2022. [DOI: 10.1089/bioe.2022.0005] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/13/2022] Open
Affiliation(s)
- Kenny M. Van Theemsche
- Department of Basic and Applied Medical Sciences, Faculty of Medicine, Ghent University, Ghent, Belgium
- Department of Biomedical Sciences, University of Antwerp, Antwerp, Belgium
| | - Joni G. Heymans
- Department of Basic and Applied Medical Sciences, Faculty of Medicine, Ghent University, Ghent, Belgium
| | - Nikola Z. Popovic
- Department of Basic and Applied Medical Sciences, Faculty of Medicine, Ghent University, Ghent, Belgium
| | | | - Dirk J. Snyders
- Department of Biomedical Sciences, University of Antwerp, Antwerp, Belgium
| | - Alain J. Labro
- Department of Basic and Applied Medical Sciences, Faculty of Medicine, Ghent University, Ghent, Belgium
- Department of Biomedical Sciences, University of Antwerp, Antwerp, Belgium
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3
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Coonen L, Martinez-Morales E, Cuello LG, Snyders DJ, Labro AJ. The recovery from the C-type inactivated state differs between Shaker and Shaker-W434F K+channels. Biophys J 2022. [DOI: 10.1016/j.bpj.2021.11.274] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/02/2022] Open
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4
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Arora R, Van Theemsche KM, Van Remoortel S, Snyders DJ, Labro AJ, Timmermans JP. Constitutive, Basal, and β-Alanine-Mediated Activation of the Human Mas-Related G Protein-Coupled Receptor D Induces Release of the Inflammatory Cytokine IL-6 and Is Dependent on NF-κB Signaling. Int J Mol Sci 2021; 22:ijms222413254. [PMID: 34948051 PMCID: PMC8703779 DOI: 10.3390/ijms222413254] [Citation(s) in RCA: 8] [Impact Index Per Article: 2.7] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/04/2020] [Revised: 12/03/2021] [Accepted: 12/04/2021] [Indexed: 12/14/2022] Open
Abstract
G protein-coupled receptors (GPCRs) have emerged as key players in regulating (patho)physiological processes, including inflammation. Members of the Mas-related G protein coupled receptors (MRGPRs), a subfamily of GPCRs, are largely expressed by sensory neurons and known to modulate itch and pain. Several members of MRGPRs are also expressed in mast cells, macrophages, and in cardiovascular tissue, linking them to pseudo-allergic drug reactions and suggesting a pivotal role in the cardiovascular system. However, involvement of the human Mas-related G-protein coupled receptor D (MRGPRD) in the regulation of the inflammatory mediator interleukin 6 (IL-6) has not been demonstrated to date. By stimulating human MRGPRD-expressing HeLa cells with the agonist β-alanine, we observed a release of IL-6. β-alanine-induced signaling through MRGPRD was investigated further by probing downstream signaling effectors along the Gαq/Phospholipase C (PLC) pathway, which results in an IkB kinases (IKK)-mediated canonical activation of nuclear factor kappa-B (NF-κB) and stimulation of IL-6 release. This IL-6 release could be blocked by a Gαq inhibitor (YM-254890), an IKK complex inhibitor (IKK-16), and partly by a PLC inhibitor (U-73122). Additionally, we investigated the constitutive (ligand-independent) and basal activity of MRGPRD and concluded that the observed basal activity of MRGPRD is dependent on the presence of fetal bovine serum (FBS) in the culture medium. Consequently, the dynamic range for IL-6 detection as an assay for β-alanine-mediated activation of MRGPRD is substantially increased by culturing the cells in FBS free medium before treatment. Overall, the observation that MRGPRD mediates the release of IL-6 in an in vitro system, hints at a role as an inflammatory mediator and supports the notion that IL-6 can be used as a marker for MRGPRD activation in an in vitro drug screening assay.
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Affiliation(s)
- Rohit Arora
- Laboratory of Cell Biology and Histology, Department of Veterinary Sciences, University of Antwerp, 2610 Wilrijk, Belgium; (R.A.); (S.V.R.)
- Laboratory for Molecular, Cellular and Network Excitability, Department of Biomedical Sciences, University of Antwerp, 2610 Wilrijk, Belgium; (K.M.V.T.); (D.J.S.)
| | - Kenny M. Van Theemsche
- Laboratory for Molecular, Cellular and Network Excitability, Department of Biomedical Sciences, University of Antwerp, 2610 Wilrijk, Belgium; (K.M.V.T.); (D.J.S.)
| | - Samuel Van Remoortel
- Laboratory of Cell Biology and Histology, Department of Veterinary Sciences, University of Antwerp, 2610 Wilrijk, Belgium; (R.A.); (S.V.R.)
| | - Dirk J. Snyders
- Laboratory for Molecular, Cellular and Network Excitability, Department of Biomedical Sciences, University of Antwerp, 2610 Wilrijk, Belgium; (K.M.V.T.); (D.J.S.)
| | - Alain J. Labro
- Laboratory for Molecular, Cellular and Network Excitability, Department of Biomedical Sciences, University of Antwerp, 2610 Wilrijk, Belgium; (K.M.V.T.); (D.J.S.)
- Department of Basic and Applied Medical Sciences, Ghent University, 9000 Ghent, Belgium
- Correspondence: (A.J.L.); (J.-P.T.); Tel.: +32-9-3320034 (A.J.L.); +32-3-2653327 (J.-P.T.)
| | - Jean-Pierre Timmermans
- Laboratory of Cell Biology and Histology, Department of Veterinary Sciences, University of Antwerp, 2610 Wilrijk, Belgium; (R.A.); (S.V.R.)
- Correspondence: (A.J.L.); (J.-P.T.); Tel.: +32-9-3320034 (A.J.L.); +32-3-2653327 (J.-P.T.)
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Van de Sande DV, Kopljar I, Maaike A, Teisman A, Gallacher DJ, Bart L, Snyders DJ, Leybaert L, Lu HR, Labro AJ. The resting membrane potential of hSC-CM in a syncytium is more hyperpolarised than that of isolated cells. Channels (Austin) 2021; 15:239-252. [PMID: 33465001 PMCID: PMC7817136 DOI: 10.1080/19336950.2021.1871815] [Citation(s) in RCA: 3] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/20/2020] [Revised: 11/20/2020] [Accepted: 12/31/2020] [Indexed: 01/11/2023] Open
Abstract
Human-induced pluripotent stem cell (hiPSC) and stem cell (hSC) derived cardiomyocytes (CM) are gaining popularity as in vitro model for cardiology and pharmacology studies. A remaining flaw of these cells, as shown by single-cell electrophysiological characterization, is a more depolarized resting membrane potential (RMP) compared to native CM. Most reports attribute this to a lower expression of the Kir2.1 potassium channel that generates the IK1 current. However, most RMP recordings are obtained from isolated hSC/hiPSC-CMs whereas in a more native setting these cells are interconnected with neighboring cells by connexin-based gap junctions, forming a syncytium. Hereby, these cells are electrically connected and the total pool of IK1 increases. Therefore, the input resistance (Ri) of interconnected cells is lower than that of isolated cells. During patch clamp experiments pipettes need to be well attached or sealed to the cell, which is reflected in the seal resistance (Rs), because a nonspecific ionic current can leak through this pipette-cell contact or seal and balance out small currents within the cell such as IK1. By recording the action potential of isolated hSC-CMs and that of hSC-CMs cultured in small monolayers, we show that the RMP of hSC-CMs in monolayer is approximately -20 mV more hyperpolarized compared to isolated cells. Accordingly, adding carbenoxolone, a connexin channel blocker, isolates the cell that is patch clamped from its neighboring cells of the monolayer and depolarizes the RMP. The presented data show that the recorded RMP of hSC-CMs in a syncytium is more negative than that determined from isolated hSC/hiPSC-CMs, most likely because the active pool of Kir2.1 channels increased.
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Affiliation(s)
| | - Ivan Kopljar
- Global Safety Pharmacology, Non-Clinical Safety, Janssen R&D, Beerse, Belgium
| | - Alaerts Maaike
- Centre of Medical Genetics, University of Antwerp, Antwerp, Belgium
| | - Ard Teisman
- Global Safety Pharmacology, Non-Clinical Safety, Janssen R&D, Beerse, Belgium
| | - David J. Gallacher
- Global Safety Pharmacology, Non-Clinical Safety, Janssen R&D, Beerse, Belgium
| | - Loeys Bart
- Centre of Medical Genetics, University of Antwerp, Antwerp, Belgium
| | - Dirk J. Snyders
- Department of Biomedical Sciences, University of Antwerp, Antwerp, Belgium
| | - Luc Leybaert
- Department of Basic and Applied Medical Sciences, Ghent University, Ghent, Belgium
| | - Hua Rong Lu
- Global Safety Pharmacology, Non-Clinical Safety, Janssen R&D, Beerse, Belgium
| | - Alain J. Labro
- Department of Biomedical Sciences, University of Antwerp, Antwerp, Belgium
- Department of Basic and Applied Medical Sciences, Ghent University, Ghent, Belgium
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6
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Van Theemsche KM, Van de Sande DV, Snyders DJ, Labro AJ. Hydrophobic Drug/Toxin Binding Sites in Voltage-Dependent K + and Na + Channels. Front Pharmacol 2020; 11:735. [PMID: 32499709 PMCID: PMC7243439 DOI: 10.3389/fphar.2020.00735] [Citation(s) in RCA: 6] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/31/2020] [Accepted: 05/04/2020] [Indexed: 12/26/2022] Open
Abstract
In the Nav channel family the lipophilic drugs/toxins binding sites and the presence of fenestrations in the channel pore wall are well defined and categorized. No such classification exists in the much larger Kv channel family, although certain lipophilic compounds seem to deviate from binding to well-known hydrophilic binding sites. By mapping different compound binding sites onto 3D structures of Kv channels, there appear to be three distinct lipid-exposed binding sites preserved in Kv channels: the front and back side of the pore domain, and S2-S3/S3-S4 clefts. One or a combination of these sites is most likely the orthologous equivalent of neurotoxin site 5 in Nav channels. This review describes the different lipophilic binding sites and location of pore wall fenestrations within the Kv channel family and compares it to the knowledge of Nav channels.
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Affiliation(s)
- Kenny M Van Theemsche
- Laboratory of Molecular, Cellular, and Network Excitability, University of Antwerp, Antwerp, Belgium
| | - Dieter V Van de Sande
- Laboratory of Molecular, Cellular, and Network Excitability, University of Antwerp, Antwerp, Belgium
| | - Dirk J Snyders
- Laboratory of Molecular, Cellular, and Network Excitability, University of Antwerp, Antwerp, Belgium
| | - Alain J Labro
- Laboratory of Molecular, Cellular, and Network Excitability, University of Antwerp, Antwerp, Belgium
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7
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Moeller L, Labro AJ, Snyders DJ, Blunck R. Choosing the Correct Stoichiometry from Single Subunit Counting Data. Biophys J 2020. [DOI: 10.1016/j.bpj.2019.11.1518] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/25/2022] Open
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8
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Van de Sande DV, Kopljar I, Teisman A, Gallacher DJ, Snyders DJ, Lu HR, Labro AJ. Pharmacological Profile of the Sodium Current in Human Stem Cell-Derived Cardiomyocytes Compares to Heterologous Nav1.5+β1 Model. Front Pharmacol 2019; 10:1374. [PMID: 31920633 PMCID: PMC6917651 DOI: 10.3389/fphar.2019.01374] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/27/2019] [Accepted: 10/29/2019] [Indexed: 12/20/2022] Open
Abstract
The cardiac Nav1.5 mediated sodium current (INa) generates the upstroke of the action potential in atrial and ventricular myocytes. Drugs that modulate this current can therefore be antiarrhythmic or proarrhythmic, which requires preclinical evaluation of their potential drug-induced inhibition or modulation of Nav1.5. Since Nav1.5 assembles with, and is modulated by, the auxiliary β1-subunit, this subunit can also affect the channel’s pharmacological response. To investigate this, the effect of known Nav1.5 inhibitors was compared between COS-7 cells expressing Nav1.5 or Nav1.5+β1 using whole-cell voltage clamp experiments. For the open state class Ia blockers ajmaline and quinidine, and class Ic drug flecainide, the affinity did not differ between both models. For class Ib drugs phenytoin and lidocaine, which are inactivated state blockers, the affinity decreased more than a twofold when β1 was present. Thus, β1 did not influence the affinity for the class Ia and Ic compounds but it did so for the class Ib drugs. Human stem cell-derived cardiomyocytes (hSC-CMs) are a promising translational cell source for in vitro models that express a representative repertoire of channels and auxiliary proteins, including β1. Therefore, we subsequently evaluated the same drugs for their response on the INa in hSC-CMs. Consequently, it was expected and confirmed that the drug response of INa in hSC-CMs compares best to INa expressed by Nav1.5+β1.
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Affiliation(s)
- Dieter V Van de Sande
- Laboratory of Molecular, Cellular, and Network Excitability, University of Antwerp, Antwerp, Belgium
| | - Ivan Kopljar
- Laboratory of Molecular, Cellular, and Network Excitability, University of Antwerp, Antwerp, Belgium.,Global Safety Pharmacology, Non-Clinical Safety, Janssen R&D, Beerse, Belgium
| | - Ard Teisman
- Global Safety Pharmacology, Non-Clinical Safety, Janssen R&D, Beerse, Belgium
| | - David J Gallacher
- Global Safety Pharmacology, Non-Clinical Safety, Janssen R&D, Beerse, Belgium
| | - Dirk J Snyders
- Laboratory of Molecular, Cellular, and Network Excitability, University of Antwerp, Antwerp, Belgium
| | - Hua Rong Lu
- Global Safety Pharmacology, Non-Clinical Safety, Janssen R&D, Beerse, Belgium
| | - Alain J Labro
- Laboratory of Molecular, Cellular, and Network Excitability, University of Antwerp, Antwerp, Belgium
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9
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Arora R, Van Remoortel S, Van Raemdonck G, Baggerman G, Buckinx R, Snyders DJ, Labro AJ, Timmermans J. Activation of Human Mas‐related G Protein‐coupled Receptor F (MRGPRF) by the Cysteine Protease Cathepsin S: Implication in Neuro‐Immune Communication Within the Gut. FASEB J 2019. [DOI: 10.1096/fasebj.2019.33.1_supplement.585.1] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/11/2022]
Affiliation(s)
- Rohit Arora
- Veterinary Sciences, Lab Cell Biology & HistologyUniversity of AntwerpWilrijkAntwerpBelgium
| | - Samuel Van Remoortel
- Veterinary Sciences, Lab Cell Biology & HistologyUniversity of AntwerpWilrijkAntwerpBelgium
| | | | | | - Roeland Buckinx
- Veterinary Sciences, Lab Cell Biology & HistologyUniversity of AntwerpWilrijkAntwerpBelgium
| | - Dirk J Snyders
- Biomedical Sciences, Lab Molecular, Cellular and Network ExcitabilityUniversity of AntwerpWilrijkAntwerpBelgium
| | - Alain J Labro
- Biomedical Sciences, Lab Molecular, Cellular and Network ExcitabilityUniversity of AntwerpWilrijkAntwerpBelgium
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Bocksteins E, Snyders DJ, Holmgren M. Independent movement of the voltage sensors in K V2.1/K V6.4 heterotetramers. Sci Rep 2017; 7:41646. [PMID: 28139741 PMCID: PMC5282584 DOI: 10.1038/srep41646] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/28/2016] [Accepted: 12/20/2016] [Indexed: 01/11/2023] Open
Abstract
Heterotetramer voltage-gated K+ (KV) channels KV2.1/KV6.4 display a gating charge-voltage (QV) distribution composed by two separate components. We use state dependent chemical accessibility to cysteines substituted in either KV2.1 or KV6.4 to assess the voltage sensor movements of each subunit. By comparing the voltage dependences of chemical modification and gating charge displacement, here we show that each gating charge component corresponds to a specific subunit forming the heterotetramer. The voltage sensors from KV6.4 subunits move at more negative potentials than the voltage sensors belonging to KV2.1 subunits. These results indicate that the voltage sensors from the tetrameric channels move independently. In addition, our data shows that 75% of the total charge is attributed to KV2.1, while 25% to KV6.4. Thus, the most parsimonious model for KV2.1/KV6.4 channels’ stoichiometry is 3:1.
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Affiliation(s)
- Elke Bocksteins
- Laboratory for Molecular Biophysics, Physiology and Pharmacology, Department for Biomedical Sciences, University of Antwerp, Antwerp, Belgium.,Molecular Neurophysiology Section, Porter Neuroscience Research Center, National Institute of Neurological Disorders and Stroke, National Institutes of Health, Bethesda, Maryland, USA
| | - Dirk J Snyders
- Laboratory for Molecular Biophysics, Physiology and Pharmacology, Department for Biomedical Sciences, University of Antwerp, Antwerp, Belgium
| | - Miguel Holmgren
- Molecular Neurophysiology Section, Porter Neuroscience Research Center, National Institute of Neurological Disorders and Stroke, National Institutes of Health, Bethesda, Maryland, USA
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11
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Regnier G, Bocksteins E, Marei WF, Pintelon I, Timmermans JP, Leroy JLMR, Snyders DJ. Targeted deletion of the Kv6.4 subunit causes male sterility due to disturbed spermiogenesis. Reprod Fertil Dev 2017; 29:1567-1575. [DOI: 10.1071/rd16075] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [What about the content of this article? (0)] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/12/2016] [Accepted: 07/16/2016] [Indexed: 12/18/2022] Open
Abstract
Electrically silent voltage-gated potassium (KvS) channel subunits (i.e. Kv5–Kv6 and Kv8–Kv9) do not form functional homotetrameric Kv channels, but co-assemble with Kv2 subunits, generating functional heterotetrameric Kv2–KvS channel complexes in which the KvS subunits modulate the Kv2 channel properties. Several KvS subunits are expressed in testis tissue but knowledge about their contribution to testis physiology is lacking. Here, we report that the targeted deletion of Kv6.4 in a transgenic mouse model (Kcng4–/–) causes male sterility as offspring from homozygous females were only obtained after mating with wild-type (WT) or heterozygous males. Semen quality analysis revealed that the sterility of the homozygous males was caused by a severe reduction in total sperm-cell count and the absence of motile spermatozoa in the semen. Furthermore, spermatozoa of homozygous mice showed an abnormal morphology characterised by a smaller head and a shorter tail compared with WT spermatozoa. Comparison of WT and Kcng4–/– testicular tissue indicated that this inability to produce (normal) spermatozoa was due to disturbed spermiogenesis. These results suggest that Kv6.4 subunits are involved in the regulation of the late stages of spermatogenesis, which makes them a potentially interesting pharmacological target for the development of non-hormonal male contraceptives.
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12
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Stas JI, Bocksteins E, Jensen CS, Schmitt N, Snyders DJ. The anticonvulsant retigabine suppresses neuronal K V2-mediated currents. Sci Rep 2016; 6:35080. [PMID: 27734968 PMCID: PMC5062084 DOI: 10.1038/srep35080] [Citation(s) in RCA: 20] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/15/2016] [Accepted: 09/20/2016] [Indexed: 11/09/2022] Open
Abstract
Enhancement of neuronal M-currents, generated through KV7.2-KV7.5 channels, has gained much interest for its potential in developing treatments for hyperexcitability-related disorders such as epilepsy. Retigabine, a KV7 channel opener, has proven to be an effective anticonvulsant and has recently also gained attention due to its neuroprotective properties. In the present study, we found that the auxiliary KCNE2 subunit reduced the KV7.2-KV7.3 retigabine sensitivity approximately 5-fold. In addition, using both mammalian expression systems and cultured hippocampal neurons we determined that low μM retigabine concentrations had ‘off-target’ effects on KV2.1 channels which have recently been implicated in apoptosis. Clinical retigabine concentrations (0.3–3 μM) inhibited KV2.1 channel function upon prolonged exposure. The suppression of the KV2.1 conductance was only partially reversible. Our results identified KV2.1 as a new molecular target for retigabine, thus giving a potential explanation for retigabine’s neuroprotective properties.
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Affiliation(s)
- Jeroen I Stas
- Laboratory for Molecular Biophysics, Physiology and Pharmacology, Department of Biomedical Sciences, University of Antwerp, CDE, Universiteitsplein 1, 2610 Antwerp, Belgium.,Ion Channel Group, Department of Biomedical Sciences, University of Copenhagen, Blegdamsvej 3, DK-2200 Copenhagen N, Denmark
| | - Elke Bocksteins
- Laboratory for Molecular Biophysics, Physiology and Pharmacology, Department of Biomedical Sciences, University of Antwerp, CDE, Universiteitsplein 1, 2610 Antwerp, Belgium
| | - Camilla S Jensen
- Ion Channel Group, Department of Biomedical Sciences, University of Copenhagen, Blegdamsvej 3, DK-2200 Copenhagen N, Denmark
| | - Nicole Schmitt
- Ion Channel Group, Department of Biomedical Sciences, University of Copenhagen, Blegdamsvej 3, DK-2200 Copenhagen N, Denmark
| | - Dirk J Snyders
- Laboratory for Molecular Biophysics, Physiology and Pharmacology, Department of Biomedical Sciences, University of Antwerp, CDE, Universiteitsplein 1, 2610 Antwerp, Belgium
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13
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Regnier G, Bocksteins E, Van de Vijver G, Snyders DJ, van Bogaert PP. The contribution of Kv2.2-mediated currents decreases during the postnatal development of mouse dorsal root ganglion neurons. Physiol Rep 2016; 4:4/6/e12731. [PMID: 27033450 PMCID: PMC4814888 DOI: 10.14814/phy2.12731] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/11/2016] [Accepted: 02/12/2016] [Indexed: 11/24/2022] Open
Abstract
Delayed rectifier voltage-gated K(+)(Kv) channels play an important role in the regulation of the electrophysiological properties of neurons. In mouse dorsal root ganglion (DRG) neurons, a large fraction of the delayed rectifier current is carried by both homotetrameric Kv2 channels and heterotetrameric channels consisting of Kv2 and silent Kv (KvS) subunits (i.e., Kv5-Kv6 and Kv8-Kv9). However, little is known about the contribution of Kv2-mediated currents during the postnatal development ofDRGneurons. Here, we report that the Stromatoxin-1 (ScTx)-sensitive fraction of the total outward K(+)current (IK) from mouseDRGneurons gradually decreased (~13%,P < 0.05) during the first month of postnatal development. Because ScTx inhibits both Kv2.1- and Kv2.2-mediated currents, this gradual decrease may reflect a decrease in currents containing either subunit. However, the fraction of Kv2.1 antibody-sensitive current that only reflects the Kv2.1-mediated currents remained constant during that same period. These results suggested that the fractional contribution of Kv2.2-mediated currents relative toIKdecreased with postnatal age. SemiquantitativeRT-PCRanalysis indicated that this decrease can be attributed to developmental changes in Kv2.2 expression as themRNAlevels of the Kv2.2 subunit decreased gradually between 1 and 4 weeks of age. In addition, we observed age-dependent fluctuations in themRNAlevels of the Kv6.3, Kv8.1, Kv9.1, and Kv9.3 subunits. These results support an important role of both Kv2 and KvS subunits in the postnatal maturation ofDRGneurons.
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Affiliation(s)
- Glenn Regnier
- Laboratory for Molecular Biophysics, Physiology and Pharmacology, Department of Biomedical Sciences, University of Antwerp, CDE, Antwerpen, Belgium
| | - Elke Bocksteins
- Laboratory for Molecular Biophysics, Physiology and Pharmacology, Department of Biomedical Sciences, University of Antwerp, CDE, Antwerpen, Belgium
| | - Gerda Van de Vijver
- Laboratory for Cardiovascular Research, Institute Born-Bunge University of Antwerp, CDE, Antwerpen, Belgium
| | - Dirk J Snyders
- Laboratory for Molecular Biophysics, Physiology and Pharmacology, Department of Biomedical Sciences, University of Antwerp, CDE, Antwerpen, Belgium
| | - Pierre-Paul van Bogaert
- Laboratory for Cardiovascular Research, Institute Born-Bunge University of Antwerp, CDE, Antwerpen, Belgium
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Kopljar I, Grottesi A, de Block T, Rainier JD, Tytgat J, Labro AJ, Snyders DJ. Voltage-sensor conformation shapes the intra-membrane drug binding site that determines gambierol affinity in Kv channels. Neuropharmacology 2016; 107:160-167. [PMID: 26956727 DOI: 10.1016/j.neuropharm.2016.03.010] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/21/2015] [Revised: 02/13/2016] [Accepted: 03/04/2016] [Indexed: 01/02/2023]
Abstract
Marine ladder-shaped polyether toxins are implicated in neurological symptoms of fish-borne food poisonings. The toxin gambierol, produced by the marine dinoflagellate Gambierdiscus toxicus, belongs to the group of ladder-shaped polyether toxins and inhibits Kv3.1 channels with nanomolar affinity through a mechanism of gating modification. Binding determinants for gambierol localize at the lipid-exposed interface of the pore forming S5 and S6 segments, suggesting that gambierol binds outside of the permeation pathway. To explore a possible involvement of the voltage-sensing domain (VSD), we made different chimeric channels between Kv3.1 and Kv2.1, exchanging distinct parts of the gating machinery. Our results showed that neither the electro-mechanical coupling nor the S1-S3a region of the VSD affect gambierol sensitivity. In contrast, the S3b-S4 part of the VSD (paddle motif) decreased gambierol sensitivity in Kv3.1 more than 100-fold. Structure determination by homology modeling indicated that the position of the S3b-S4 paddle and its primary structure defines the shape and∖or the accessibility of the binding site for gambierol, explaining the observed differences in gambierol affinity between the channel chimeras. Furthermore, these findings explain the observed difference in gambierol affinity for the closed and open channel configurations of Kv3.1, opening new possibilities for exploring the VSDs as selectivity determinants in drug design.
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Affiliation(s)
- Ivan Kopljar
- Laboratory for Molecular Biophysics, Physiology and Pharmacology, University of Antwerp, 2610, Antwerp, Belgium
| | | | - Tessa de Block
- Laboratory for Molecular Biophysics, Physiology and Pharmacology, University of Antwerp, 2610, Antwerp, Belgium
| | - Jon D Rainier
- Department of Chemistry, University of Utah, Salt Lake City, UT, 84112-0850, USA
| | - Jan Tytgat
- Toxicology and Pharmacology, University of Leuven Campus Gasthuisberg, 3000, Leuven, Belgium
| | - Alain J Labro
- Laboratory for Molecular Biophysics, Physiology and Pharmacology, University of Antwerp, 2610, Antwerp, Belgium
| | - Dirk J Snyders
- Laboratory for Molecular Biophysics, Physiology and Pharmacology, University of Antwerp, 2610, Antwerp, Belgium.
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15
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Stas JI, Bocksteins E, Snyders DJ. Suppression of Kv2-Mediated Currents by the Anticonvulsant Retigabine. Biophys J 2016. [DOI: 10.1016/j.bpj.2015.11.2408] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/26/2022] Open
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16
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Stas JI, Bocksteins E, Labro AJ, Snyders DJ. Modulation of Closed-State Inactivation in Kv2.1/Kv6.4 Heterotetramers as Mechanism for 4-AP Induced Potentiation. PLoS One 2015; 10:e0141349. [PMID: 26505474 PMCID: PMC4623978 DOI: 10.1371/journal.pone.0141349] [Citation(s) in RCA: 12] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/23/2015] [Accepted: 10/06/2015] [Indexed: 12/26/2022] Open
Abstract
The voltage-gated K+ (Kv) channel subunits Kv2.1 and Kv2.2 are expressed in almost every tissue. The diversity of Kv2 current is increased by interacting with the electrically silent Kv (KvS) subunits Kv5-Kv6 and Kv8-Kv9, into functional heterotetrameric Kv2/KvS channels. These Kv2/KvS channels possess unique biophysical properties and display a more tissue-specific expression pattern, making them more desirable pharmacological and therapeutic targets. However, little is known about the pharmacological properties of these heterotetrameric complexes. We demonstrate that Kv5.1, Kv8.1 and Kv9.3 currents were inhibited differently by the channel blocker 4-aminopyridine (4-AP) compared to Kv2.1 homotetramers. In contrast, Kv6.4 currents were potentiated by 4-AP while displaying moderately increased affinities for the channel pore blockers quinidine and flecainide. We found that the 4-AP induced potentiation of Kv6.4 currents was caused by modulation of the Kv6.4-mediated closed-state inactivation: suppression by 4-AP of the Kv2.1/Kv6.4 closed-state inactivation recovered a population of Kv2.1/Kv6.4 channels that was inactivated at resting conditions, i.e. at a holding potential of -80 mV. This modulation also resulted in a slower initiation and faster recovery from closed-state inactivation. Using chimeric substitutions between Kv6.4 and Kv9.3 subunits, we demonstrated that the lower half of the S6 domain (S6c) plays a crucial role in the 4-AP induced potentiation. These results demonstrate that KvS subunits modify the pharmacological response of Kv2 subunits when assembled in heterotetramers and illustrate the potential of KvS subunits to provide unique pharmacological properties to the heterotetramers, as is the case for 4-AP on Kv2.1/Kv6.4 channels.
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Affiliation(s)
- Jeroen I. Stas
- Laboratory for Molecular Biophysics, Physiology and Pharmacology, Department of Biomedical Sciences, University of Antwerp, CDE, Universiteitsplein 1, Antwerp, Belgium
| | - Elke Bocksteins
- Laboratory for Molecular Biophysics, Physiology and Pharmacology, Department of Biomedical Sciences, University of Antwerp, CDE, Universiteitsplein 1, Antwerp, Belgium
| | - Alain J. Labro
- Laboratory for Molecular Biophysics, Physiology and Pharmacology, Department of Biomedical Sciences, University of Antwerp, CDE, Universiteitsplein 1, Antwerp, Belgium
| | - Dirk J. Snyders
- Laboratory for Molecular Biophysics, Physiology and Pharmacology, Department of Biomedical Sciences, University of Antwerp, CDE, Universiteitsplein 1, Antwerp, Belgium
- * E-mail:
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17
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Bocksteins E, Snyders DJ, Holmgren M. Movements of the Kv2.1 and Kv6.4 S4 Segments in Heterotetrameric Kv2.1/Kv6.4 Channels. Biophys J 2015. [DOI: 10.1016/j.bpj.2014.11.656] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/24/2022] Open
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18
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Martinez-Morales E, Snyders DJ, Labro AJ. Mutations in the S6 gate isolate a late step in the activation pathway and reduce 4-AP sensitivity in shaker K(v) channel. Biophys J 2014; 106:134-44. [PMID: 24411245 DOI: 10.1016/j.bpj.2013.11.025] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/08/2013] [Revised: 10/28/2013] [Accepted: 11/12/2013] [Indexed: 01/12/2023] Open
Abstract
Kv channels detect changes in the membrane potential via their voltage-sensing domains (VSDs) that control the status of the S6 bundle crossing (BC) gate. The movement of the VSDs results in a transfer of the S4 gating charges across the cell membrane but only the last 10-20% of the total gating charge movement is associated with BC gate opening, which involves cooperative transition(s) in the subunits. Substituting the proline residue P475 in the S6 of the Shaker channel by a glycine or alanine causes a considerable shift in the voltage-dependence of the cooperative transition(s) of BC gate opening, effectively isolating the late gating charge component from the other gating charge that originates from earlier VSD movements. Interestingly, both mutations also abolished Shaker's sensitivity to 4-aminopyridine, which is a pharmacological tool to isolate the late gating charge component. The alanine substitution (that would promote a α-helical configuration compared to proline) resulted in the largest separation of both gating charge components; therefore, BC gate flexibility appears to be important for enabling the late cooperative step of channel opening.
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Affiliation(s)
- Evelyn Martinez-Morales
- Laboratory for Molecular Biophysics, Physiology and Pharmacology, University of Antwerp, Antwerp, Belgium
| | - Dirk J Snyders
- Laboratory for Molecular Biophysics, Physiology and Pharmacology, University of Antwerp, Antwerp, Belgium
| | - Alain J Labro
- Laboratory for Molecular Biophysics, Physiology and Pharmacology, University of Antwerp, Antwerp, Belgium.
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Bocksteins E, Mayeur E, Van Tilborg A, Regnier G, Timmermans JP, Snyders DJ. The subfamily-specific interaction between Kv2.1 and Kv6.4 subunits is determined by interactions between the N- and C-termini. PLoS One 2014; 9:e98960. [PMID: 24901643 PMCID: PMC4047056 DOI: 10.1371/journal.pone.0098960] [Citation(s) in RCA: 15] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/14/2014] [Accepted: 05/08/2014] [Indexed: 12/14/2022] Open
Abstract
The "silent" voltage-gated potassium (KvS) channel subunit Kv6.4 does not form electrically functional homotetramers at the plasma membrane but assembles with Kv2.1 subunits, generating functional Kv2.1/Kv6.4 heterotetramers. The N-terminal T1 domain determines the subfamily-specific assembly of Kv1-4 subunits by preventing interactions between subunits that belong to different subfamilies. For Kv6.4, yeast-two-hybrid experiments showed an interaction of the Kv6.4 N-terminus with the Kv2.1 N-terminus, but unexpectedly also with the Kv3.1 N-terminus. We confirmed this interaction by Fluorescence Resonance Energy Transfer (FRET) and co-immunoprecipitation (co-IP) using N-terminal Kv3.1 and Kv6.4 fragments. However, full-length Kv3.1 and Kv6.4 subunits do not form heterotetramers at the plasma membrane. Therefore, additional interactions between the Kv6.4 and Kv2.1 subunits should be important in the Kv2.1/Kv6.4 subfamily-specificity. Using FRET and co-IP approaches with N- and C-terminal fragments we observed that the Kv6.4 C-terminus physically interacts with the Kv2.1 N-terminus but not with the Kv3.1 N-terminus. The N-terminal amino acid sequence CDD which is conserved between Kv2 and KvS subunits appeared to be a key determinant since charge reversals with arginine substitutions abolished the interaction between the N-terminus of Kv2.1 and the C-terminus of both Kv2.1 and Kv6.4. In addition, the Kv6.4(CKv3.1) chimera in which the C-terminus of Kv6.4 was replaced by the corresponding domain of Kv3.1, disrupted the assembly with Kv2.1. These results indicate that the subfamily-specific Kv2.1/Kv6.4 heterotetramerization is determined by interactions between Kv2.1 and Kv6.4 that involve both the N- and C-termini in which the conserved N-terminal CDD sequence plays a key role.
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Affiliation(s)
- Elke Bocksteins
- Laboratory for Molecular Biophysics, Physiology and Pharmacology, Department of Biomedical Sciences, University of Antwerp, Antwerp, Belgium
| | - Evy Mayeur
- Laboratory for Molecular Biophysics, Physiology and Pharmacology, Department of Biomedical Sciences, University of Antwerp, Antwerp, Belgium
| | - Abbi Van Tilborg
- Laboratory for Molecular Biophysics, Physiology and Pharmacology, Department of Biomedical Sciences, University of Antwerp, Antwerp, Belgium
| | - Glenn Regnier
- Laboratory for Molecular Biophysics, Physiology and Pharmacology, Department of Biomedical Sciences, University of Antwerp, Antwerp, Belgium
| | - Jean-Pierre Timmermans
- Laboratory of Cell Biology and Histology, Department of Veterinary Sciences, University of Antwerp, Antwerp, Belgium
| | - Dirk J. Snyders
- Laboratory for Molecular Biophysics, Physiology and Pharmacology, Department of Biomedical Sciences, University of Antwerp, Antwerp, Belgium
- * E-mail:
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Stas JI, Bocksteins E, Labro AJ, Snyders DJ. Diversity in the Pharmacological Profile of Heterotetrameric KV2/KVS Channels for Channel Blockers. Biophys J 2014. [DOI: 10.1016/j.bpj.2013.11.3024] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/23/2022] Open
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21
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Martinez-Morales E, Labro AJ, Snyders DJ. Offsetting the Electric Field Sensed by KV Channels through Residue Substitutions on Top of S1. Biophys J 2014. [DOI: 10.1016/j.bpj.2013.11.2993] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/23/2022] Open
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22
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Bocksteins E, Trimmer JS, Snyders DJ. Modulation of KV2.1 and KV2.1/KV6.4 Channels by Auxiliary KCNE Subunits. Biophys J 2014. [DOI: 10.1016/j.bpj.2013.11.819] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/23/2022] Open
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23
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Kopljar I, Labro AJ, de Block T, Rainier JD, Tytgat J, Snyders DJ. The ladder-shaped polyether toxin gambierol anchors the gating machinery of Kv3.1 channels in the resting state. ACTA ACUST UNITED AC 2013; 141:359-69. [PMID: 23401573 PMCID: PMC3581691 DOI: 10.1085/jgp.201210890] [Citation(s) in RCA: 22] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/17/2022]
Abstract
Voltage-gated potassium (Kv) and sodium (Nav) channels are key determinants of cellular excitability and serve as targets of neurotoxins. Most marine ciguatoxins potentiate Nav channels and cause ciguatera seafood poisoning. Several ciguatoxins have also been shown to affect Kv channels, and we showed previously that the ladder-shaped polyether toxin gambierol is a potent Kv channel inhibitor. Most likely, gambierol acts via a lipid-exposed binding site, located outside the K+ permeation pathway. However, the mechanism by which gambierol inhibits Kv channels remained unknown. Using gating and ionic current analysis to investigate how gambierol affected S6 gate opening and voltage-sensing domain (VSD) movements, we show that the resting (closed) channel conformation forms the high-affinity state for gambierol. The voltage dependence of activation was shifted by >120 mV in the depolarizing direction, precluding channel opening in the physiological voltage range. The (early) transitions between the resting and the open state were monitored with gating currents, and provided evidence that strong depolarizations allowed VSD movement up to the activated-not-open state. However, for transition to the fully open (ion-conducting) state, the toxin first needed to dissociate. These dissociation kinetics were markedly accelerated in the activated-not-open state, presumably because this state displayed a much lower affinity for gambierol. A tetrameric concatemer with only one high-affinity binding site still displayed high toxin sensitivity, suggesting that interaction with a single binding site prevented the concerted step required for channel opening. We propose a mechanism whereby gambierol anchors the channel’s gating machinery in the resting state, requiring more work from the VSD to open the channel. This mechanism is quite different from the action of classical gating modifier peptides (e.g., hanatoxin). Therefore, polyether toxins open new opportunities in structure–function relationship studies in Kv channels and in drug design to modulate channel function.
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Affiliation(s)
- Ivan Kopljar
- Laboratory for Molecular Biophysics, Physiology and Pharmacology, University of Antwerp, 2610 Antwerp, Belgium
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24
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Regnier G, Bocksteins E, Snyders DJ. Stoichiometric Analysis of Heterotetrameric Kv2.1/Kv6.4 Channels. Biophys J 2013. [DOI: 10.1016/j.bpj.2012.11.722] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/27/2022] Open
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25
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Martinez-Morales E, Kopljar I, Labro AJ, Snyders DJ. 1-Butanol and Gambierol:Low and High Affinity Compounds that Immobilize Charge Movement in Shaker and Kv3.1 Potassium Channels. Biophys J 2013. [DOI: 10.1016/j.bpj.2012.11.721] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/01/2022] Open
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26
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Stas J, Kopljar I, Labro A, Peigneur S, Zaharenko AJ, Tytgat J, Snyders DJ. A Gating Modulator Peptide Toxin for Shaker-Type KV1 Channels Derived from the Sea Anemone Bunodosoma cangicum. Biophys J 2013. [DOI: 10.1016/j.bpj.2012.11.720] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022] Open
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27
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Abderemane-Ali F, Es-Salah-Lamoureux Z, Delemotte L, Kasimova MA, Labro AJ, Snyders DJ, Fedida D, Tarek M, Baró I, Loussouarn G. Dual Effect of PIP2 on Shaker K+ Channels. Biophys J 2013. [DOI: 10.1016/j.bpj.2012.11.2567] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/26/2022] Open
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Labro AJ, Lacroix JJ, Villalba-Galea CA, Snyders DJ, Bezanilla F. Molecular mechanism for depolarization-induced modulation of Kv channel closure. ACTA ACUST UNITED AC 2012; 140:481-93. [PMID: 23071266 PMCID: PMC3483114 DOI: 10.1085/jgp.201210817] [Citation(s) in RCA: 36] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022]
Abstract
Voltage-dependent potassium (Kv) channels provide the repolarizing power that shapes the action potential duration and helps control the firing frequency of neurons. The K+ permeation through the channel pore is controlled by an intracellularly located bundle-crossing (BC) gate that communicates with the voltage-sensing domains (VSDs). During prolonged membrane depolarizations, most Kv channels display C-type inactivation that halts K+ conduction through constriction of the K+ selectivity filter. Besides triggering C-type inactivation, we show that in Shaker and Kv1.2 channels (expressed in Xenopus laevis oocytes), prolonged membrane depolarizations also slow down the kinetics of VSD deactivation and BC gate closure during the subsequent membrane repolarization. Measurements of deactivating gating currents (reporting VSD movement) and ionic currents (BC gate status) showed that the kinetics of both slowed down in two distinct phases with increasing duration of the depolarizing prepulse. The biphasic slowing in VSD deactivation and BC gate closure was strongly correlated in time and magnitude. Simultaneous recordings of ionic currents and fluorescence from a probe tracking VSD movement in Shaker directly demonstrated that both processes were synchronized. Whereas the first slowing originates from a stabilization imposed by BC gate opening, the subsequent slowing reflects the rearrangement of the VSD toward its relaxed state (relaxation). The VSD relaxation was observed in the Ciona intestinalis voltage-sensitive phosphatase and in its isolated VSD. Collectively, our results show that the VSD relaxation is not kinetically related to C-type inactivation and is an intrinsic property of the VSD. We propose VSD relaxation as a general mechanism for depolarization-induced slowing of BC gate closure that may enable Kv1.2 channels to modulate the firing frequency of neurons based on the depolarization history.
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Affiliation(s)
- Alain J Labro
- Department of Biochemistry and Molecular Biology, University of Chicago, Chicago, IL 60637, USA
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Abstract
Kv channels form voltage-dependent potassium selective pores in the outer cell membrane and are composed out of four α-subunits, each having six membrane-spanning α-helices (S1–S6). The α-subunits tetramerize such that the S5–S6 pore domains co-assemble into a centrally located K+ pore which is surrounded by four operational voltage-sensing domains (VSD) that are each formed by the S1–S4 segments. Consequently, each subunit is capable of responding to changes in membrane potential and dictates whether the pore should be conductive or not. K+ permeation through the pore can be sealed off by two separate gates in series: (a) at the inner S6 bundle crossing (BC gate) and (b) at the level of the selectivity filter (SF gate) located at the extracellular entrance of the pore. Within the last years a general consensus emerged that a direct communication between the S4S5-linker and the bottom part of S6 (S6c) constitutes the coupling with the VSD thus making the BC gate the main voltage-controllable activation gate. While the BC gate listens to the VSD, the SF changes its conformation depending on the status of the BC gate. Through the eyes of an entering K+ ion, the operation of the BC gate apparatus can be compared with the iris-like motion of the diaphragm from a camera whereby its diameter widens. Two main gating motions have been proposed to create this BC gate widening: (1) tilting of the helix whereby the S6 converts from a straight α-helix to a tilted one or (2) swiveling of the S6c whereby the S6 remains bent. Such motions require a flexible hinge that decouples the pre- and post-hinge segment. Roughly at the middle of the S6 there exists a highly conserved glycine residue and a tandem proline motif that seem to fulfill the role of a gating hinge which allows for tilting/swiveling/rotations of the post-hinge S6 segment. In this review we delineate our current view on the operation of the BC gate for controlling K+ permeation in Kv channels.
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Affiliation(s)
- Alain J Labro
- Department of Biomedical Sciences, University of Antwerp Antwerp, Belgium
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30
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Abderemane-Ali F, Es-Salah-Lamoureux Z, Delemotte L, Kasimova MA, Labro AJ, Snyders DJ, Fedida D, Tarek M, Baró I, Loussouarn G. Dual effect of phosphatidylinositol (4,5)-bisphosphate PIP(2) on Shaker K(+) [corrected] channels. J Biol Chem 2012; 287:36158-67. [PMID: 22932893 DOI: 10.1074/jbc.m112.382085] [Citation(s) in RCA: 37] [Impact Index Per Article: 3.1] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
Phosphatidylinositol (4,5)-bisphosphate (PIP(2)) is a phospholipid of the plasma membrane that has been shown to be a key regulator of several ion channels. Functional studies and more recently structural studies of Kir channels have revealed the major impact of PIP(2) on the open state stabilization. A similar effect of PIP(2) on the delayed rectifiers Kv7.1 and Kv11.1, two voltage-gated K(+) channels, has been suggested, but the molecular mechanism remains elusive and nothing is known on PIP(2) effect on other Kv such as those of the Shaker family. By combining giant-patch ionic and gating current recordings in COS-7 cells, and voltage-clamp fluorimetry in Xenopus oocytes, both heterologously expressing the voltage-dependent Shaker channel, we show that PIP(2) exerts 1) a gain-of-function effect on the maximal current amplitude, consistent with a stabilization of the open state and 2) a loss-of-function effect by positive-shifting the activation voltage dependence, most likely through a direct effect on the voltage sensor movement, as illustrated by molecular dynamics simulations.
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Kopljar I, Labro AJ, Rainier JD, Tytgat J, Snyders DJ. 110. Voltage Sensor Trapping in Voltage-Gated K-Channels by the Marine Neurotoxin Gambierol. Toxicon 2012. [DOI: 10.1016/j.toxicon.2012.04.111] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [What about the content of this article? (0)] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/28/2022]
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32
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Bocksteins E, Van de Vijver G, Van Bogaert PP, Snyders DJ. Kv3 channels contribute to the delayed rectifier current in small cultured mouse dorsal root ganglion neurons. Am J Physiol Cell Physiol 2012; 303:C406-15. [PMID: 22673617 DOI: 10.1152/ajpcell.00343.2011] [Citation(s) in RCA: 12] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022]
Abstract
Delayed rectifier voltage-gated K(+) (K(V)) channels are important determinants of neuronal excitability. However, the large number of K(V) subunits poses a major challenge to establish the molecular composition of the native neuronal K(+) currents. A large part (∼60%) of the delayed rectifier current (I(K)) in small mouse dorsal root ganglion (DRG) neurons has been shown to be carried by both homotetrameric K(V)2.1 and heterotetrameric channels of K(V)2 subunits with silent K(V) subunits (K(V)S), while a contribution of K(V)1 channels has also been demonstrated. Because K(V)3 subunits also generate delayed rectifier currents, we investigated the contribution of K(V)3 subunits to I(K) in small mouse DRG neurons. After stromatoxin (ScTx) pretreatment to block the K(V)2-containing component, application of 1 mM TEA caused significant additional block, indicating that the ScTx-insensitive part of I(K) could include K(V)1, K(V)3, and/or M-current channels (KCNQ2/3). Combining ScTx and dendrotoxin confirmed a relevant contribution of K(V)2 and K(V)2/K(V)S, and K(V)1 subunits to I(K) in small mouse DRG neurons. After application of these toxins, a significant TEA-sensitive current (∼19% of total I(K)) remained with biophysical properties that corresponded to those of K(V)3 currents obtained in expression systems. Using RT-PCR, we detected K(V)3.1-3 mRNA in DRG neurons. Furthermore, Western blot and immunocytochemistry using K(V)3.1-specific antibodies confirmed the presence of K(V)3.1 in cultured DRG neurons. These biophysical, pharmacological, and molecular results demonstrate a relevant contribution (∼19%) of K(V)3-containing channels to I(K) in small mouse DRG neurons, supporting a substantial role for K(V)3 subunits in these neurons.
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Affiliation(s)
- Elke Bocksteins
- Laboratory for Molecular Biophysics, Physiology and Pharmacology, Department of Biomedical Sciences, University of Antwerp, Campus Drie Eiken, Belgium
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Bocksteins E, Labro AJ, Snyders DJ, Mohapatra DP. The electrically silent Kv6.4 subunit confers hyperpolarized gating charge movement in Kv2.1/Kv6.4 heterotetrameric channels. PLoS One 2012; 7:e37143. [PMID: 22615922 PMCID: PMC3355112 DOI: 10.1371/journal.pone.0037143] [Citation(s) in RCA: 14] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/06/2012] [Accepted: 04/18/2012] [Indexed: 12/20/2022] Open
Abstract
The voltage-gated K(+) (Kv) channel subunit Kv6.4 does not form functional homotetrameric channels but co-assembles with Kv2.1 to form functional Kv2.1/Kv6.4 heterotetrameric channels. Compared to Kv2.1 homotetramers, Kv6.4 exerts a ~40 mV hyperpolarizing shift in the voltage-dependence of Kv2.1/Kv6.4 channel inactivation, without a significant effect on activation gating. However, the underlying mechanism of this Kv6.4-induced modulation of Kv2.1 channel inactivation, and whether the Kv6.4 subunit participates in the voltage-dependent gating of heterotetrameric channels is not well understood. Here we report distinct gating charge movement of Kv2.1/Kv6.4 heterotetrameric channels, compared to Kv2.1 homotetramers, as revealed by gating current recordings from mammalian cells expressing these channels. The gating charge movement of Kv2.1/Kv6.4 heterotetrameric channels displayed an extra component around the physiological K(+) equilibrium potential, characterized by a second sigmoidal relationship of the voltage-dependence of gating charge movement. This distinct gating charge displacement reflects movement of the Kv6.4 voltage-sensing domain and has a voltage-dependency that matches the hyperpolarizing shift in Kv2.1/Kv6.4 channel inactivation. These results provide a mechanistic basis for the modulation of Kv2.1 channel inactivation gating kinetics by silent Kv6.4 subunits.
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Affiliation(s)
- Elke Bocksteins
- Laboratory for Molecular Biophysics, Physiology and Pharmacology, Department of Biomedical Sciences, University of Antwerp, CDE, Universiteitsplein 1, Antwerpen, Belgium
- Department of Pharmacology, The University of Iowa Roy J. and Lucile A. Carver College of Medicine, Iowa City, Iowa, United States of America
| | - Alain J. Labro
- Laboratory for Molecular Biophysics, Physiology and Pharmacology, Department of Biomedical Sciences, University of Antwerp, CDE, Universiteitsplein 1, Antwerpen, Belgium
| | - Dirk J. Snyders
- Laboratory for Molecular Biophysics, Physiology and Pharmacology, Department of Biomedical Sciences, University of Antwerp, CDE, Universiteitsplein 1, Antwerpen, Belgium
- * E-mail: (DPM); (DJS)
| | - Durga P. Mohapatra
- Department of Pharmacology, The University of Iowa Roy J. and Lucile A. Carver College of Medicine, Iowa City, Iowa, United States of America
- * E-mail: (DPM); (DJS)
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Abstract
Electrically silent voltage-gated potassium (KvS) α-subunits do not form homotetramers but heterotetramerize with Kv2 subunits, generating functional Kv2/KvS channel complexes in which the KvS subunits modulate the Kv2 current. This poses intriguing questions into the molecular mechanisms by which these KvS subunits cannot form functional homotetramers, why they only interact with Kv2 subunits, and how they modulate the Kv2 current.
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Affiliation(s)
- Elke Bocksteins
- Department of Biomedical Sciences, Laboratory for Molecular Biophysics, Physiology and Pharmacology, University of Antwerp, Antwerpen, Belgium
| | - Dirk J. Snyders
- Department of Biomedical Sciences, Laboratory for Molecular Biophysics, Physiology and Pharmacology, University of Antwerp, Antwerpen, Belgium
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Bocksteins E, Labro AJ, Snyders DJ, Mohapatra DP. The Silent K+ Channel Subunit, KV6.4. Influences the Gating Charge Movement of KV2.1 in a Heterotetrameric Channel Complex. Biophys J 2012. [DOI: 10.1016/j.bpj.2011.11.2907] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/15/2022] Open
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36
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Veys K, Labro AJ, Snyders DJ. Electrophysiological and Gene Expression Profiling at Single Cell Level through an Improved Whole Cell Patch Clamp Quantitative Real-Time PCR Technique. Biophys J 2012. [DOI: 10.1016/j.bpj.2011.11.755] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/25/2022] Open
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37
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Labro AJ, Cortes DM, Gagnon DG, Snyders DJ, Cuello LG. The Role of the 2nd Threonine Within the TTVGYGD Sequence of Kv-Channels in C-Type Inactivation Gating, Ion Selectivity and Permeation. Biophys J 2012. [DOI: 10.1016/j.bpj.2011.11.094] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/14/2022] Open
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38
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Bocksteins E, Mayeur E, Bruyns T, Snyders DJ. The T1 Domain is not the Only Determinant of the Obligatory KV2.1/KV6.4 Heterotetramerization. Biophys J 2011. [DOI: 10.1016/j.bpj.2010.12.2098] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022] Open
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39
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Labro AJ, Boulet IR, Choveau FS, Mayeur E, Bruyns T, Loussouarn G, Raes AL, Snyders DJ. The S4-S5 linker of KCNQ1 channels forms a structural scaffold with the S6 segment controlling gate closure. J Biol Chem 2010; 286:717-25. [PMID: 21059661 DOI: 10.1074/jbc.m110.146977] [Citation(s) in RCA: 49] [Impact Index Per Article: 3.5] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/21/2022] Open
Abstract
In vivo, KCNQ1 α-subunits associate with the β-subunit KCNE1 to generate the slowly activating cardiac potassium current (I(Ks)). Structurally, they share their topology with other Kv channels and consist out of six transmembrane helices (S1-S6) with the S1-S4 segments forming the voltage-sensing domain (VSD). The opening or closure of the intracellular channel gate, which localizes at the bottom of the S6 segment, is directly controlled by the movement of the VSD via an electromechanical coupling. In other Kv channels, this electromechanical coupling is realized by an interaction between the S4-S5 linker (S4S5(L)) and the C-terminal end of S6 (S6(T)). Previously we reported that substitutions for Leu(353) in S6(T) resulted in channels that failed to close completely. Closure could be incomplete because Leu(353) itself is the pore-occluding residue of the channel gate or because of a distorted electromechanical coupling. To resolve this and to address the role of S4S5(L) in KCNQ1 channel gating, we performed an alanine/tryptophan substitution scan of S4S5(L). The residues with a "high impact" on channel gating (when mutated) clustered on one side of the S4S5(L) α-helix. Hence, this side of S4S5(L) most likely contributes to the electromechanical coupling and finds its residue counterparts in S6(T). Accordingly, substitutions for Val(254) resulted in channels that were partially constitutively open and the ability to close completely was rescued by combination with substitutions for Leu(353) in S6(T). Double mutant cycle analysis supported this cross-talk indicating that both residues come in close contact and stabilize the closed state of the channel.
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Affiliation(s)
- Alain J Labro
- Laboratory for Molecular Biophysics, Physiology and Pharmacology, Department of Biomedical Sciences, University of Antwerp, CDE, Universiteitsplein 1, 2610 Antwerp, Belgium
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40
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Choveau FS, Rodriguez N, Abderemane Ali F, Labro AJ, Rose T, Dahimène S, Boudin H, Le Hénaff C, Escande D, Snyders DJ, Charpentier F, Mérot J, Baró I, Loussouarn G. KCNQ1 channels voltage dependence through a voltage-dependent binding of the S4-S5 linker to the pore domain. J Biol Chem 2010; 286:707-16. [PMID: 20940310 DOI: 10.1074/jbc.m110.146324] [Citation(s) in RCA: 47] [Impact Index Per Article: 3.4] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/29/2022] Open
Abstract
Voltage-dependent potassium (Kv) channels are tetramers of six transmembrane domain (S1-S6) proteins. Crystallographic data demonstrate that the tetrameric pore (S5-S6) is surrounded by four voltage sensor domains (S1-S4). One key question remains: how do voltage sensors (S4) regulate pore gating? Previous mutagenesis data obtained on the Kv channel KCNQ1 highlighted the critical role of specific residues in both the S4-S5 linker (S4S5(L)) and S6 C terminus (S6(T)). From these data, we hypothesized that S4S5(L) behaves like a ligand specifically interacting with S6(T) and stabilizing the closed state. To test this hypothesis, we designed plasmid-encoded peptides corresponding to portions of S4S5(L) and S6(T) of the voltage-gated potassium channel KCNQ1 and evaluated their effects on the channel activity in the presence and absence of the ancillary subunit KCNE1. We showed that S4S5(L) peptides inhibit KCNQ1, in a reversible and state-dependent manner. S4S5(L) peptides also inhibited a voltage-independent KCNQ1 mutant. This inhibition was competitively prevented by a peptide mimicking S6(T), consistent with S4S5(L) binding to S6(T). Val(254) in S4S5(L) is known to contact Leu(353) in S6(T) when the channel is closed, and mutations of these residues alter the coupling between the two regions. The same mutations introduced in peptides altered their effects, further confirming S4S5(L) binding to S6(T). Our results suggest a mechanistic model in which S4S5(L) acts as a voltage-dependent ligand bound to its receptor on S6 at rest. This interaction locks the channel in a closed state. Upon plasma membrane depolarization, S4 pulls S4S5(L) away from S6(T), allowing channel opening.
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Bocksteins E, Van Vijver G, Bruyns T, Van Bogaert PP, Snyders DJ. Identification of Kv Subunits Underlying the Delayed Rectifier K+ Current (Ik) in Small Cultured DRG Neurons. Biophys J 2010. [DOI: 10.1016/j.bpj.2009.12.2908] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/19/2022] Open
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42
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Labro AJ, Boulet IR, Raes AL, Snyders DJ. Substitution Scan of the S4-S5 Linker Region in KCNQ1 Channel: Structural Scaffold for Critical Protein Interactions. Biophys J 2010. [DOI: 10.1016/j.bpj.2009.12.657] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/16/2022] Open
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43
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Labro AJ, Boulet IR, Timmermans JP, Ottschytsch N, Snyders DJ. The rate-dependent biophysical properties of the LQT1 H258R mutant are counteracted by a dominant negative effect on channel trafficking. J Mol Cell Cardiol 2009; 48:1096-104. [PMID: 19913547 DOI: 10.1016/j.yjmcc.2009.10.027] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 09/07/2009] [Revised: 10/28/2009] [Accepted: 10/28/2009] [Indexed: 01/17/2023]
Abstract
The long QT syndrome (LQTS) is a cardiac disorder caused by a prolonged ventricular repolarization. The co-assembly of the pore-forming human KCNQ1 alpha-subunits with the modulating hKCNE1 beta-subunits generates I(Ks)in vivo, explaining why mutations in the hKCNQ1 gene underlie the LQT1 form of congenital LQT. Here we describe the functional defects of the LQT1 mutation H258R located in the S4-S5 linker, a segment important for channel gating. Mutant subunits with this arginine substitution generated no or barely detectable currents in a homotetrameric condition, but did generate I(Ks)-like currents in association with hKCNE1. Compared to the WT hKCNQ1/hKCNE1 complex, the H258R/hKCNE1 complex displayed accelerated activation kinetics, slowed channel closure and a hyperpolarizing shift of the voltage-dependence of activation, thus predicting an increased K(+) current. However, current density analysis combined with subcellular localization indicated that the H258R subunit exerted a dominant negative effect on channel trafficking to the plasma membrane. The co-expression hKCNQ1/H258R/hKCNE1, mimicking the heterozygous state of a patient, displayed similar properties. During repetitive stimulation the mutant yielded more current compared to WT at 1 Hz but this effect was counteracted by the trafficking defect at faster frequencies. These rate-dependent effects may be relevant given the larger contribution of I(Ks) to the "repolarization reserve" at higher action potential rates. The combination of complex kinetics that counteract the trafficking problem represents a particular mechanism underlying LQT1.
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Affiliation(s)
- Alain J Labro
- Laboratory for Molecular Biophysics, Physiology and Pharmacology, Department of Biomedical Sciences, University of Antwerp (UA), Universiteitsplein 1, 2610 Antwerp, Belgium
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44
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Bocksteins E, Labro AJ, Mayeur E, Bruyns T, Timmermans JP, Adriaensen D, Snyders DJ. Conserved negative charges in the N-terminal tetramerization domain mediate efficient assembly of Kv2.1 and Kv2.1/Kv6.4 channels. J Biol Chem 2009; 284:31625-34. [PMID: 19717558 DOI: 10.1074/jbc.m109.039479] [Citation(s) in RCA: 17] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
Voltage-gated potassium (Kv) channels are transmembrane tetramers of individual alpha-subunits. Eight different Shaker-related Kv subfamilies have been identified in which the tetramerization domain T1, located on the intracellular N terminus, facilitates and controls the assembly of both homo- and heterotetrameric channels. Only the Kv2 alpha-subunits are able to form heterotetramers with members of the silent Kv subfamilies (Kv5, Kv6, Kv8, and Kv9). The T1 domain contains two subdomains, A and B box, which presumably determine subfamily specificity by preventing incompatible subunits to assemble. In contrast, little is known about the involvement of the A/B linker sequence. Both Kv2 and silent Kv subfamilies contain a fully conserved and negatively charged sequence (CDD) in this linker that is lacking in the other subfamilies. Neutralizing these aspartates in Kv2.1 by mutating them to alanines did not affect the gating properties, but reduced the current density moderately. However, charge reversal arginine substitutions strongly reduced the current density of these homotetrameric mutant Kv2.1 channels and immunocytochemistry confirmed the reduced expression at the plasma membrane. Förster resonance energy transfer measurements using confocal microscopy showed that the latter was not due to impaired trafficking, but to a failure to assemble the tetramer. This was further confirmed with co-immunoprecipitation experiments. The corresponding arginine substitution in Kv6.4 prevented its heterotetrameric interaction with Kv2.1. These results indicate that these aspartates (especially the first one) in the A/B box linker of the T1 domain are required for efficient assembly of both homotetrameric Kv2.1 and heterotetrameric Kv2.1/silent Kv6.4 channels.
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Affiliation(s)
- Elke Bocksteins
- Department of Biomedical Sciences, Laboratory for Molecular Biophysics, Physiology and Pharmacology, University of Antwerp, CDE, Universiteitsplein 1, 2610 Antwerp, Belgium
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45
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Bocksteins E, Raes AL, Van de Vijver G, Bruyns T, Van Bogaert PP, Snyders DJ. Kv2.1 and silent Kv subunits underlie the delayed rectifier K+ current in cultured small mouse DRG neurons. Am J Physiol Cell Physiol 2009; 296:C1271-8. [PMID: 19357235 DOI: 10.1152/ajpcell.00088.2009] [Citation(s) in RCA: 50] [Impact Index Per Article: 3.3] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/08/2023]
Abstract
Silent voltage-gated K(+) (K(v)) subunits interact with K(v)2 subunits and primarily modulate the voltage dependence of inactivation of these heterotetrameric channels. Both K(v)2 and silent K(v) subunits are expressed in the mammalian nervous system, but little is known about their expression and function in sensory neurons. This study reports the presence of K(v)2.1, K(v)2.2, and silent subunit K(v)6.1, K(v)8.1, K(v)9.1, K(v)9.2, and K(v)9.3 mRNA in mouse dorsal root ganglia (DRG). Immunocytochemistry confirmed the protein expression of K(v)2.x and K(v)9.x subunits in cultured small DRG neurons. To investigate if K(v)2 and silent K(v) subunits are underlying the delayed rectifier K(+) current (I(K)) in these neurons, K(v)2-mediated currents were isolated by the extracellular application of rStromatoxin-1 (ScTx) or by the intracellular application of K(v)2 antibodies. Both ScTx- and anti-K(v)2.1-sensitive currents displayed two components in their voltage dependence of inactivation. Together, both components accounted for approximately two-thirds of I(K). A comparison with results obtained in heterologous expression systems suggests that one component reflects homotetrameric K(v)2.1 channels, whereas the other component represents heterotetrameric K(v)2.1/silent K(v) channels. These observations support a physiological role for silent K(v) subunits in small DRG neurons.
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Affiliation(s)
- Elke Bocksteins
- Laboratory for Molecular Biophysics, Physiology and Pharmacology, Department of Biomedical Sciences, University of Antwerp, Antwerpen 2610, Belgium
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46
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Labro AJ, Raes AL, Grottesi A, Van Hoorick D, Sansom MSP, Snyders DJ. Kv channel gating requires a compatible S4-S5 linker and bottom part of S6, constrained by non-interacting residues. ACTA ACUST UNITED AC 2009; 132:667-80. [PMID: 19029374 PMCID: PMC2585865 DOI: 10.1085/jgp.200810048] [Citation(s) in RCA: 64] [Impact Index Per Article: 4.3] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/01/2022]
Abstract
Voltage-dependent K+ channels transfer the voltage sensor movement into gate opening or closure through an electromechanical coupling. To test functionally whether an interaction between the S4-S5 linker (L45) and the cytoplasmic end of S6 (S6T) constitutes this coupling, the L45 in hKv1.5 was replaced by corresponding hKv2.1 sequence. This exchange was not tolerated but could be rescued by also swapping S6T. Exchanging both L45 and S6T transferred hKv2.1 kinetics to an hKv1.5 background while preserving the voltage dependence. A one-by-one residue substitution scan of L45 and S6T in hKv1.5 further shows that S6T needs to be α-helical and forms a “crevice” in which residues I422 and T426 of L45 reside. These residues transfer the mechanical energy onto the S6T crevice, whereas other residues in S6T and L45 that are not involved in the interaction maintain the correct structure of the coupling.
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Affiliation(s)
- Alain J Labro
- Laboratory for Molecular Biophysics, Physiology, and Pharmacology, Department of Biomedical Sciences, University of Antwerp, 2610 Antwerp, Belgium
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47
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Labro AJ, Grottesi A, Sansom MSP, Raes AL, Snyders DJ. A Kv channel with an altered activation gate sequence displays both “fast” and “slow” activation kinetics. Am J Physiol Cell Physiol 2008; 294:C1476-84. [DOI: 10.1152/ajpcell.00479.2007] [Citation(s) in RCA: 10] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [What about the content of this article? (0)] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022]
Abstract
The Kv1–4 families of K+ channels contain a tandem proline motif (P XP) in the S6 helix that is crucial for channel gating. In human Kv1.5, replacing the first proline by an alanine resulted in a nonfunctional channel. This mutant was rescued by introducing another proline at a nearby position, changing the sequence into AVPP. This resulted in a channel that activated quickly (ms range) upon the first depolarization. However, thereafter, the channel became trapped in another gating mode that was characterized by slow activation kinetics (s range) with a shallow voltage dependence. The switch in gating mode was observed even with very short depolarization steps, but recovery to the initial “fast” mode was extremely slow. Computational modeling suggested that switching occurred during channel deactivation. To test the effect of the altered P XP sequence on the mobility of the S6 helix, we used molecular dynamics simulations of the isolated S6 domain of wild type (WT) and mutants starting from either a closed or open conformation. The WT S6 helix displayed movements around the P XP region with simulations starting from either state. However, the S6 with a AVPP sequence displayed flexibility only when started from the closed conformation and was rigid when started from the open state. These results indicate that the region around the P XP motif may serve as a “hinge” and that changing the sequence to AVPP results in channels that deactivate to a state with an alternate configuration that renders them “reluctant” to open subsequently.
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48
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Cuypers E, Abdel-Mottaleb Y, Kopljar I, Rainier JD, Raes AL, Snyders DJ, Tytgat J. Gambierol, a toxin produced by the dinoflagellate Gambierdiscus toxicus, is a potent blocker of voltage-gated potassium channels. Toxicon 2008; 51:974-83. [PMID: 18313714 DOI: 10.1016/j.toxicon.2008.01.004] [Citation(s) in RCA: 57] [Impact Index Per Article: 3.6] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/02/2007] [Revised: 12/20/2007] [Accepted: 01/09/2008] [Indexed: 10/22/2022]
Abstract
In this study, we pharmacologically characterized gambierol, a marine polycyclic ether toxin which is produced by the dinoflagellate Gambierdiscus toxicus. Besides several other polycyclic ether toxins like ciguatoxins, this scarcely studied toxin is one of the compounds that may be responsible for ciguatera fish poisoning (CFP). Unfortunately, the biological target(s) that underlies CFP is still partly unknown. Today, ciguatoxins are described to specifically activate voltage-gated sodium channels by interacting with their receptor site 5. But some dispute about the role of gambierol in the CFP story shows up: some describe voltage-gated sodium channels as the target, while others pinpoint voltage-gated potassium channels as targets. Since gambierol was never tested on isolated ion channels before, it was subjected in this work to extensive screening on a panel of 17 ion channels: nine cloned voltage-gated ion channels (mammalian Na(v)1.1-Na(v)1.8 and insect Para) and eight cloned voltage-gated potassium channels (mammalian K(v)1.1-K(v)1.6, hERG and insect ShakerIR) expressed in Xenopus laevis oocytes using two-electrode voltage-clamp technique. All tested sodium channel subtypes are insensitive to gambierol concentrations up to 10 microM. In contrast, K(v)1.2 is the most sensitive voltage-gated potassium channel subtype with almost full block (>97%) and an half maximal inhibitory concentration (IC(50)) of 34.5 nM. To the best of our knowledge, this is the first study where the selectivity of gambierol is tested on isolated voltage-gated ion channels. Therefore, these results lead to a better understanding of gambierol and its possible role in CFP and they may also be useful in the development of more effective treatments.
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Affiliation(s)
- Eva Cuypers
- Laboratorium voor Toxicologie, Campus Gasthuisberg, Onderwijs en Navorsing 2, Herestraat 49, Bus 922, KULeuven B-3000, Belgium
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49
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Abstract
Co-assembly of KCNQ1 alpha-subunits with KCNE1 beta-subunits results in the channel complex underlying the cardiac IKs current in vivo. Like other voltage-gated K+ channels, KCNQ1 has a tetrameric configuration. The S6 segment of each subunit lines the ion channel pore with the lower part forming the activation gate. To determine residues involved in protein-protein interactions in the C-terminal part of S6 (S6T), alanine and tryptophan perturbation scans were performed from residue 348-362 in the KCNQ1 channel. Several residues were identified to be relevant in channel gating, as substitutions affected the activation and/or deactivation process. Some mutations (F351A and V355W) drastically altered the gating characteristics of the resultant KCNQ1 channel, to the point of mimicking the IKs current. Furthermore, mutagenesis of residue L353 to an alanine or a charged residue impaired normal channel closure upon hyperpolarization, generating a constitutively open phenotype. This indicates that the L353 residue is essential for stabilizing the closed conformation of the channel gate. These findings together with the identification of several LQT1 mutations in the S6 C-terminus of KCNQ1 underscore the relevance of this region in KCNQ1 and IKs channel gating.
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Affiliation(s)
- Inge R Boulet
- Laboratory for Molecular Biophysics, Pharmacology and Physiology, University of Antwerp, Department of Biomedical Sciences, Antwerp, Belgium
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50
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Abstract
The KChIP1b splice variant has been shown to induce slow recovery from inactivation for Kv4.2 whereas KChIP1a enhanced the recovery. Both splice variants differ only by the insertion of the exon1b, rich in aromatic residues (5/11). We analysed in detail the modifications of Kv4.2 gating induced by the KChIP1b splice variant and the role for the aromatic cluster in KChIP1b in inducing these changes. By substituting alanine for the aromatic residues individually or in combination, we could convert the KChIP1b recovery behaviour into that of KChIP1a. The replacement of one or two aromatic residues resulted in a partial restitution of the KChIP1a recovery behaviour. When three aromatic residues were replaced in the exon1b, the recovery from inactivation was fast with time constants that were similar to those obtained with KChIP1a. Moreover, similar findings were observed for closed state inactivation and for the voltage dependence of inactivation. Thus, reduction of the side chain bulkiness in exon1b resulted in the conversion of the KChIP1b phenotype into the KChIP1a phenotype. These results indicate that the aromatic cluster in exon1b modulates the transitions towards and from the closed inactivated states and the steady state distribution over the respective states.
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Affiliation(s)
- D Van Hoorick
- Laboratory for Molecular Biophysics, Physiology and Pharmacology, Department of Biomedical Sciences, University of Antwerp, Universiteitsplein 1, 2610 Antwerp, Belgium
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