1
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Delgado-Bermúdez A, Yeste M, Bonet S, Pinart E. Physiological role of potassium channels in mammalian germ cell differentiation, maturation, and capacitation. Andrology 2024. [PMID: 38436215 DOI: 10.1111/andr.13606] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/30/2023] [Revised: 01/16/2024] [Accepted: 01/29/2024] [Indexed: 03/05/2024]
Abstract
BACKGROUND Ion channels are essential for differentiation and maturation of germ cells, and even for fertilization in mammals. Different types of potassium channels have been identified, which are grouped into voltage-gated channels (Kv), ligand-gated channels (Kligand ), inwardly rectifying channels (Kir ), and tandem pore domain channels (K2P ). MATERIAL-METHODS The present review includes recent findings on the role of potassium channels in sperm physiology of mammals. RESULTS-DISCUSSION While most studies conducted thus far have been focused on the physiological role of voltage- (Kv1, Kv3, and Kv7) and calcium-gated channels (SLO1 and SLO3) during sperm capacitation, especially in humans and rodents, little data about the types of potassium channels present in the plasma membrane of differentiating germ cells exist. In spite of this, recent evidence suggests that the content and regulation mechanisms of these channels vary throughout spermatogenesis. Potassium channels are also essential for the regulation of sperm cell volume during epididymal maturation and for preventing premature membrane hyperpolarization. It is important to highlight that the nature, biochemical properties, localization, and regulation mechanisms of potassium channels are species-specific. In effect, while SLO3 is the main potassium channel involved in the K+ current during sperm capacitation in rodents, different potassium channels are implicated in the K+ outflow and, thus, plasma membrane hyperpolarization during sperm capacitation in other mammalian species, such as humans and pigs. CONCLUSIONS Potassium conductance is essential for male fertility, not only during sperm capacitation but throughout the spermiogenesis and epididymal maturation.
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Affiliation(s)
- Ariadna Delgado-Bermúdez
- Biotechnology of Animal and Human Reproduction (TechnoSperm), Institute of Food and Agricultural Technology, University of Girona, Girona, Spain
- Department of Biology, Faculty of Sciences, Unit of Cell Biology, University of Girona, Girona, Spain
| | - Marc Yeste
- Biotechnology of Animal and Human Reproduction (TechnoSperm), Institute of Food and Agricultural Technology, University of Girona, Girona, Spain
- Department of Biology, Faculty of Sciences, Unit of Cell Biology, University of Girona, Girona, Spain
- Catalan Institution for Research and Advanced Studies (ICREA), Barcelona, Spain
| | - Sergi Bonet
- Biotechnology of Animal and Human Reproduction (TechnoSperm), Institute of Food and Agricultural Technology, University of Girona, Girona, Spain
- Department of Biology, Faculty of Sciences, Unit of Cell Biology, University of Girona, Girona, Spain
| | - Elisabeth Pinart
- Biotechnology of Animal and Human Reproduction (TechnoSperm), Institute of Food and Agricultural Technology, University of Girona, Girona, Spain
- Department of Biology, Faculty of Sciences, Unit of Cell Biology, University of Girona, Girona, Spain
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2
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Fan C, Flood E, Sukomon N, Agarwal S, Allen TW, Nimigean CM. Calcium-gated potassium channel blockade via membrane-facing fenestrations. Nat Chem Biol 2024; 20:52-61. [PMID: 37653172 PMCID: PMC10847966 DOI: 10.1038/s41589-023-01406-2] [Citation(s) in RCA: 1] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/04/2021] [Accepted: 07/18/2023] [Indexed: 09/02/2023]
Abstract
Quaternary ammonium blockers were previously shown to bind in the pore to block both open and closed conformations of large-conductance calcium-activated potassium (BK and MthK) channels. Because blocker entry was assumed through the intracellular entryway (bundle crossing), closed-pore access suggested that the gate was not at the bundle crossing. Structures of closed MthK, a Methanobacterium thermoautotrophicum homolog of BK channels, revealed a tightly constricted intracellular gate, leading us to investigate the membrane-facing fenestrations as alternative pathways for blocker access directly from the membrane. Atomistic free energy simulations showed that intracellular blockers indeed access the pore through the fenestrations, and a mutant channel with narrower fenestrations displayed no closed-state TPeA block at concentrations that blocked the wild-type channel. Apo BK channels display similar fenestrations, suggesting that blockers may use them as access paths into closed channels. Thus, membrane fenestrations represent a non-canonical pathway for selective targeting of specific channel conformations, opening novel ways to selectively drug BK channels.
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Affiliation(s)
- Chen Fan
- Department of Anesthesiology, Weill Cornell Medicine, New York, NY, USA
- Science for Life Laboratory, Department of Biochemistry and Biophysics, Stockholm University, Solna, Sweden
| | - Emelie Flood
- School of Science, RMIT University, Melbourne, Victoria, Australia
- Schrödinger, Inc., New York, NY, USA
| | - Nattakan Sukomon
- Department of Anesthesiology, Weill Cornell Medicine, New York, NY, USA
| | - Shubhangi Agarwal
- Department of Anesthesiology, Weill Cornell Medicine, New York, NY, USA
| | - Toby W Allen
- School of Science, RMIT University, Melbourne, Victoria, Australia.
| | - Crina M Nimigean
- Department of Anesthesiology, Weill Cornell Medicine, New York, NY, USA.
- Department of Physiology and Biophysics, Weill Cornell Medicine, New York, NY, USA.
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3
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Kallure GS, Pal K, Zhou Y, Lingle CJ, Chowdhury S. High-resolution structures illuminate key principles underlying voltage and LRRC26 regulation of Slo1 channels. BIORXIV : THE PREPRINT SERVER FOR BIOLOGY 2023:2023.12.20.572542. [PMID: 38187713 PMCID: PMC10769243 DOI: 10.1101/2023.12.20.572542] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 01/09/2024]
Abstract
Multi-modal regulation of Slo1 channels by membrane voltage, intracellular calcium, and auxiliary subunits enables its pleiotropic physiological functions. Our understanding of how voltage impacts Slo1 conformational dynamics and the mechanisms by which auxiliary subunits, particularly of the LRRC (Leucine Rich Repeat containing) family of proteins, modulate its voltage gating remain unresolved. Here, we used single particle cryo-electron microscopy to determine structures of human Slo1 mutants which functionally stabilize the closed pore (F315A) or the activated voltage-sensor (R207A). Our structures, obtained under calcium-free conditions, reveal that a key step in voltage-sensing by Slo1 involves a rotameric flip of the voltage-sensing charges (R210 and R213) moving them by ∼6 Å across a hydrophobic gasket. Next we obtained reconstructions of a complex of human Slo1 with the human LRRC26 (γ1) subunit in absence of calcium. Together with extensive biochemical tests, we show that the extracellular domains of γ1 form a ring of interlocked dominos that stabilizes the quaternary assembly of the complex and biases Slo1:γ1 assembly towards high stoichiometric complexes. The transmembrane helix of γ1 is kinked and tightly packed against the Slo1 voltage-sensor. We hypothesize that γ1 subunits exert relatively small effects on early steps in voltage-gating but structurally stabilize non-S4 helices of Slo1 voltage-sensor which energetically facilitate conformational rearrangements that occur late in voltage stimulated transitions.
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4
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Benko F, Urminská D, Ďuračka M, Tvrdá E. Signaling Roleplay between Ion Channels during Mammalian Sperm Capacitation. Biomedicines 2023; 11:2519. [PMID: 37760960 PMCID: PMC10525812 DOI: 10.3390/biomedicines11092519] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/30/2023] [Revised: 08/31/2023] [Accepted: 09/06/2023] [Indexed: 09/29/2023] Open
Abstract
In order to accomplish their primary goal, mammalian spermatozoa must undergo a series of physiological, biochemical, and functional changes crucial for the acquisition of fertilization ability. Spermatozoa are highly polarized cells, which must swiftly respond to ionic changes on their passage through the female reproductive tract, and which are necessary for male gametes to acquire their functional competence. This review summarizes the current knowledge about specific ion channels and transporters located in the mammalian sperm plasma membrane, which are intricately involved in the initiation of changes within the ionic milieu of the sperm cell, leading to variations in the sperm membrane potential, membrane depolarization and hyperpolarization, changes in sperm motility and capacitation to further lead to the acrosome reaction and sperm-egg fusion. We also discuss the functionality of selected ion channels in male reproductive health and/or disease since these may become promising targets for clinical management of infertility in the future.
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Affiliation(s)
- Filip Benko
- Institute of Biotechnology, Faculty of Biotechnology and Food Sciences, Slovak University of Agriculture in Nitra, Tr. A. Hlinku 2, 949 76 Nitra, Slovakia; (D.U.); (E.T.)
| | - Dana Urminská
- Institute of Biotechnology, Faculty of Biotechnology and Food Sciences, Slovak University of Agriculture in Nitra, Tr. A. Hlinku 2, 949 76 Nitra, Slovakia; (D.U.); (E.T.)
| | - Michal Ďuračka
- AgroBioTech Research Centre, Slovak University of Agriculture in Nitra, Tr. A. Hlinku 2, 949 76 Nitra, Slovakia;
| | - Eva Tvrdá
- Institute of Biotechnology, Faculty of Biotechnology and Food Sciences, Slovak University of Agriculture in Nitra, Tr. A. Hlinku 2, 949 76 Nitra, Slovakia; (D.U.); (E.T.)
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5
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Geng Y, Li P, Butler A, Wang B, Salkoff L, Magleby KL. BK channels of five different subunit combinations underlie the de novo KCNMA1 G375R channelopathy. J Gen Physiol 2023; 155:e202213302. [PMID: 36995317 PMCID: PMC10067970 DOI: 10.1085/jgp.202213302] [Citation(s) in RCA: 3] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/22/2022] [Revised: 02/08/2023] [Accepted: 03/14/2023] [Indexed: 03/31/2023] Open
Abstract
The molecular basis of a severe developmental and neurological disorder associated with a de novo G375R variant of the tetrameric BK channel is unknown. Here, we address this question by recording from single BK channels expressed to mimic a G375R mutation heterozygous with a WT allele. Five different types of functional BK channels were expressed: 3% were consistent with WT, 12% with homotetrameric mutant, and 85% with three different types of hybrid (heterotetrameric) channels assembled from both mutant and WT subunits. All channel types except WT showed a marked gain-of-function in voltage activation and a smaller decrease-of-function in single-channel conductance, with both changes in function becoming more pronounced as the number of mutant subunits per tetrameric channel increased. The net cellular response from the five different types of channels comprising the molecular phenotype was a shift of -120 mV in the voltage required to activate half of the maximal current through BK channels, giving a net gain-of-function. The WT and homotetrameric mutant channels in the molecular phenotype were consistent with genetic codominance as each displayed properties of a channel arising from only one of the two alleles. The three types of hybrid channels in the molecular phenotype were consistent with partial dominance as their properties were intermediate between those of mutant and WT channels. A model in which BK channels randomly assemble from mutant and WT subunits, with each subunit contributing increments of activation and conductance, approximated the molecular phenotype of the heterozygous G375R mutation.
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Affiliation(s)
- Yanyan Geng
- Department of Physiology and Biophysics, Miller School of Medicine, University of Miami, Miami, FL, USA
| | - Ping Li
- Department of Neuroscience, Washington University St. Louis, St. Louis, MO, USA
| | - Alice Butler
- Department of Neuroscience, Washington University St. Louis, St. Louis, MO, USA
| | - Bill Wang
- Department of Neuroscience, Washington University St. Louis, St. Louis, MO, USA
| | - Lawrence Salkoff
- Department of Neuroscience, Washington University St. Louis, St. Louis, MO, USA
- Department of Genetics, Washington University St. Louis, St. Louis, MO, USA
| | - Karl L. Magleby
- Department of Physiology and Biophysics, Miller School of Medicine, University of Miami, Miami, FL, USA
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6
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Sun L, Horrigan FT. A gating lever and molecular logic gate that couple voltage and calcium sensor activation to opening in BK potassium channels. SCIENCE ADVANCES 2022; 8:eabq5772. [PMID: 36516264 PMCID: PMC9750137 DOI: 10.1126/sciadv.abq5772] [Citation(s) in RCA: 5] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Abstract] [Grants] [Track Full Text] [Download PDF] [Figures] [Subscribe] [Scholar Register] [Received: 04/18/2022] [Accepted: 11/08/2022] [Indexed: 06/17/2023]
Abstract
BK channels uniquely integrate voltage and calcium signaling in diverse cell types through allosteric activation of their K+-conducting pore by structurally distinct V and Ca2+ sensor domains. Here, we define mechanisms and interaction pathways that link V sensors to the pore by analyzing effects on allosteric coupling of point mutations in the context of Slo1 BK channel structure. A gating lever, mediated by S4/S5 segment interaction within the transmembrane domain, rotates to engage and stabilize the open conformation of the S6 inner pore helix upon V sensor activation. In addition, an indirect pathway, mediated by the carboxyl-terminal cytosolic domain (CTD) and C-linker that connects the CTD to S6, stabilizes the closed conformation when V sensors are at rest. Unexpectedly, this mechanism, which bypasses the covalent connections of C-linker to CTD and pore, also transduces Ca2+-dependent coupling in a manner that is completely nonadditive with voltage, analogous to the function of a digital logic (OR) gate.
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Affiliation(s)
- Liang Sun
- Department of Integrative Physiology, Baylor College of Medicine, Houston, TX 77030, USA
| | - Frank T. Horrigan
- Department of Integrative Physiology, Baylor College of Medicine, Houston, TX 77030, USA
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7
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Zhang G, Xu X, Jia Z, Geng Y, Liang H, Shi J, Marras M, Abella C, Magleby KL, Silva JR, Chen J, Zou X, Cui J. An allosteric modulator activates BK channels by perturbing coupling between Ca 2+ binding and pore opening. Nat Commun 2022; 13:6784. [PMID: 36351900 PMCID: PMC9646747 DOI: 10.1038/s41467-022-34359-6] [Citation(s) in RCA: 7] [Impact Index Per Article: 3.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/25/2022] [Accepted: 10/21/2022] [Indexed: 11/10/2022] Open
Abstract
BK type Ca2+-activated K+ channels activate in response to both voltage and Ca2+. The membrane-spanning voltage sensor domain (VSD) activation and Ca2+ binding to the cytosolic tail domain (CTD) open the pore across the membrane, but the mechanisms that couple VSD activation and Ca2+ binding to pore opening are not clear. Here we show that a compound, BC5, identified from in silico screening, interacts with the CTD-VSD interface and specifically modulates the Ca2+ dependent activation mechanism. BC5 activates the channel in the absence of Ca2+ binding but Ca2+ binding inhibits BC5 effects. Thus, BC5 perturbs a pathway that couples Ca2+ binding to pore opening to allosterically affect both, which is further supported by atomistic simulations and mutagenesis. The results suggest that the CTD-VSD interaction makes a major contribution to the mechanism of Ca2+ dependent activation and is an important site for allosteric agonists to modulate BK channel activation.
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Affiliation(s)
- Guohui Zhang
- Department of Biomedical Engineering, Center for the Investigation of Membrane Excitability Disorders, Cardiac Bioelectricity and Arrhythmia Center, Washington University, St. Louis, MO, USA
| | - Xianjin Xu
- Dalton Cardiovascular Research Center, University of Missouri - Columbia, Columbia, MO, USA.,Department of Physics and Astronomy, University of Missouri - Columbia, Columbia, MO, USA.,Department of Biochemistry, University of Missouri - Columbia, Columbia, MO, USA.,Institute for Data Science and Informatics, University of Missouri - Columbia, Columbia, MO, USA
| | - Zhiguang Jia
- Department of Chemistry, University of Massachusetts, Amherst, MA, USA.,Department of Biochemistry and Molecular Biology, University of Massachusetts, Amherst, MA, USA
| | - Yanyan Geng
- Department of Physiology and Biophysics, University of Miami Miller School of Medicine, Miami, FL, USA
| | - Hongwu Liang
- Department of Biomedical Engineering, Center for the Investigation of Membrane Excitability Disorders, Cardiac Bioelectricity and Arrhythmia Center, Washington University, St. Louis, MO, USA
| | - Jingyi Shi
- Department of Biomedical Engineering, Center for the Investigation of Membrane Excitability Disorders, Cardiac Bioelectricity and Arrhythmia Center, Washington University, St. Louis, MO, USA
| | - Martina Marras
- Department of Biomedical Engineering, Center for the Investigation of Membrane Excitability Disorders, Cardiac Bioelectricity and Arrhythmia Center, Washington University, St. Louis, MO, USA
| | - Carlota Abella
- Department of Biomedical Engineering, Center for the Investigation of Membrane Excitability Disorders, Cardiac Bioelectricity and Arrhythmia Center, Washington University, St. Louis, MO, USA
| | - Karl L Magleby
- Department of Physiology and Biophysics, University of Miami Miller School of Medicine, Miami, FL, USA
| | - Jonathan R Silva
- Department of Biomedical Engineering, Center for the Investigation of Membrane Excitability Disorders, Cardiac Bioelectricity and Arrhythmia Center, Washington University, St. Louis, MO, USA.
| | - Jianhan Chen
- Department of Chemistry, University of Massachusetts, Amherst, MA, USA. .,Department of Biochemistry and Molecular Biology, University of Massachusetts, Amherst, MA, USA.
| | - Xiaoqin Zou
- Dalton Cardiovascular Research Center, University of Missouri - Columbia, Columbia, MO, USA. .,Department of Physics and Astronomy, University of Missouri - Columbia, Columbia, MO, USA. .,Department of Biochemistry, University of Missouri - Columbia, Columbia, MO, USA. .,Institute for Data Science and Informatics, University of Missouri - Columbia, Columbia, MO, USA.
| | - Jianmin Cui
- Department of Biomedical Engineering, Center for the Investigation of Membrane Excitability Disorders, Cardiac Bioelectricity and Arrhythmia Center, Washington University, St. Louis, MO, USA.
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8
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Nowicka-Bauer K, Szymczak-Cendlak M. Structure and Function of Ion Channels Regulating Sperm Motility-An Overview. Int J Mol Sci 2021; 22:ijms22063259. [PMID: 33806823 PMCID: PMC8004680 DOI: 10.3390/ijms22063259] [Citation(s) in RCA: 23] [Impact Index Per Article: 7.7] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/03/2021] [Revised: 03/18/2021] [Accepted: 03/19/2021] [Indexed: 12/18/2022] Open
Abstract
Sperm motility is linked to the activation of signaling pathways that trigger movement. These pathways are mainly dependent on Ca2+, which acts as a secondary messenger. The maintenance of adequate Ca2+ concentrations is possible thanks to proper concentrations of other ions, such as K+ and Na+, among others, that modulate plasma membrane potential and the intracellular pH. Like in every cell, ion homeostasis in spermatozoa is ensured by a vast spectrum of ion channels supported by the work of ion pumps and transporters. To achieve success in fertilization, sperm ion channels have to be sensitive to various external and internal factors. This sensitivity is provided by specific channel structures. In addition, novel sperm-specific channels or isoforms have been found with compositions that increase the chance of fertilization. Notably, the most significant sperm ion channel is the cation channel of sperm (CatSper), which is a sperm-specific Ca2+ channel required for the hyperactivation of sperm motility. The role of other ion channels in the spermatozoa, such as voltage-gated Ca2+ channels (VGCCs), Ca2+-activated Cl-channels (CaCCs), SLO K+ channels or voltage-gated H+ channels (VGHCs), is to ensure the activation and modulation of CatSper. As the activation of sperm motility differs among metazoa, different ion channels may participate; however, knowledge regarding these channels is still scarce. In the present review, the roles and structures of the most important known ion channels are described in regard to regulation of sperm motility in animals.
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Affiliation(s)
- Karolina Nowicka-Bauer
- Department of Chemical Physics, Faculty of Chemistry, Adam Mickiewicz University in Poznań, 61-614 Poznan, Poland
- Correspondence:
| | - Monika Szymczak-Cendlak
- Department of Animal Physiology and Development, Faculty of Biology, Adam Mickiewicz University in Poznań, 61-614 Poznan, Poland;
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9
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Abstract
Potassium channels are present in every living cell and essential to setting up a stable, non-zero transmembrane electrostatic potential which manifests the off-equilibrium livelihood of the cell. They are involved in other cellular activities and regulation, such as the controlled release of hormones, the activation of T-cells for immune response, the firing of action potential in muscle cells and neurons, etc. Pharmacological reagents targeting potassium channels are important for treating various human diseases linked to dysfunction of the channels. High-resolution structures of these channels are very useful tools for delineating the detailed chemical basis underlying channel functions and for structure-based design and optimization of their pharmacological and pharmaceutical agents. Structural studies of potassium channels have revolutionized biophysical understandings of key concepts in the field - ion selectivity, conduction, channel gating, and modulation, making them multi-modality targets of pharmacological regulation. In this chapter, I will select a few high-resolution structures to illustrate key structural insights, proposed allostery behind channel functions, disagreements still open to debate, and channel-lipid interactions and co-evolution. The known structural consensus allows the inference of conserved molecular mechanisms shared among subfamilies of K+ channels and makes it possible to develop channel-specific pharmaceutical agents.
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Affiliation(s)
- Qiu-Xing Jiang
- Laboratory of Molecular Physiology and Biophysics and the Cryo-EM Center, Hauptmann-Woodward Medical Research Institute, Buffalo, NY, USA.
- Department of Medicinal Chemistry, University of Florida, Gainesville, FL, USA.
- Departments of Materials Design and Invention and Physiology and Biophysics, University of Buffalo (SUNY), Buffalo, NY, USA.
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10
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An Additional Ca 2+ Binding Site Allosterically Controls TMEM16A Activation. Cell Rep 2020; 33:108570. [PMID: 33378669 PMCID: PMC7786149 DOI: 10.1016/j.celrep.2020.108570] [Citation(s) in RCA: 22] [Impact Index Per Article: 5.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/27/2020] [Revised: 08/18/2020] [Accepted: 12/08/2020] [Indexed: 12/13/2022] Open
Abstract
Calcium (Ca2+) is the primary stimulus for transmembrane protein 16 (TMEM16) Ca2+-activated chloride channels and phospholipid scramblases, which regulate important physiological processes ranging from smooth muscle contraction to blood coagulation and tumor progression. Binding of intracellular Ca2+ to two highly conserved orthosteric binding sites in transmembrane helices (TMs) 6-8 efficiently opens the permeation pathway formed by TMs 3-7. Recent structures of TMEM16K and TMEM16F scramblases revealed an additional Ca2+ binding site between TM2 and TM10, whose functional relevance remains unknown. Here, we report that Ca2+ binds with high affinity to the equivalent third Ca2+ site in TMEM16A to enhance channel activation. Our cadmium (Cd2+) metal bridging experiments reveal that the third Ca2+ site's conformational states can profoundly influence TMEM16A's opening. Our study thus confirms the existence of a third Ca2+ site in TMEM16A, defines its functional importance in channel gating, and provides insight into a long-range allosteric gating mechanism of TMEM16 channels and scramblases.
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11
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Zhang G, Gibson RA, McDonald M, Liang P, Kang PW, Shi J, Yang H, Cui J, Mikati MA. A Gain-of-Function Mutation in KCNMA1 Causes Dystonia Spells Controlled With Stimulant Therapy. Mov Disord 2020; 35:1868-1873. [PMID: 32633875 DOI: 10.1002/mds.28138] [Citation(s) in RCA: 14] [Impact Index Per Article: 3.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/15/2020] [Revised: 05/08/2020] [Accepted: 05/15/2020] [Indexed: 12/11/2022] Open
Abstract
BACKGROUND The mutations of KCNMA1 BK-type K+ channel have been identified in patients with various movement disorders. The underlying pathophysiology and corresponding therapeutics are lacking. OBJECTIVES To report our clinical and biophysical characterizations of a novel de novo KCNMA1 variant, as well as an effective therapy for the patient's dystonia-atonia spells. METHODS Combination of phenotypic characterization, therapy, and biophysical characterization of the patient and her mutation. RESULTS The patient had >100 dystonia-atonia spells per day with mild cerebellar atrophy. She also had autism spectrum disorder, intellectual disability, and attention deficit hyperactivity disorder. Whole-exome sequencing identified a heterozygous de novo BK N536H mutation. Our biophysical characterization demonstrates that N536H is a gain-of-function mutation with markedly enhanced voltage-dependent activation. Remarkably, administration of dextroamphetamine completely suppressed the dystonia-atonia spells. CONCLUSIONS BK N536H is a gain-of-function that causes dystonia and other neurological symptoms. Our stimulant therapy opens a new avenue to mitigate KCNMA1-linked movement disorders. © 2020 International Parkinson and Movement Disorder Society.
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Affiliation(s)
- Guohui Zhang
- Department of Biomedical Engineering, Washington University in St. Louis, St. Louis, Missouri, USA
| | - Rebecca A Gibson
- Department of Pediatrics, Duke University Medical Center, Durham, North Carolina, USA
| | - Marie McDonald
- Department of Pediatrics, Duke University Medical Center, Durham, North Carolina, USA
| | - Pengfei Liang
- Department of Biochemistry, Duke University Medical Center, Durham, North Carolina, USA
| | - Po Wei Kang
- Department of Biomedical Engineering, Washington University in St. Louis, St. Louis, Missouri, USA
| | - Jingyi Shi
- Department of Biomedical Engineering, Washington University in St. Louis, St. Louis, Missouri, USA
| | - Huanghe Yang
- Department of Biochemistry, Duke University Medical Center, Durham, North Carolina, USA.,Department of Neurobiology, Duke University Medical Center, Durham, North Carolina, USA
| | - Jianmin Cui
- Department of Biomedical Engineering, Washington University in St. Louis, St. Louis, Missouri, USA
| | - Mohamad A Mikati
- Department of Pediatrics, Duke University Medical Center, Durham, North Carolina, USA.,Department of Neurobiology, Duke University Medical Center, Durham, North Carolina, USA
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12
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Yazdani M, Zhang G, Jia Z, Shi J, Cui J, Chen J. Aromatic interactions with membrane modulate human BK channel activation. eLife 2020; 9:55571. [PMID: 32597752 PMCID: PMC7371421 DOI: 10.7554/elife.55571] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/05/2020] [Accepted: 06/28/2020] [Indexed: 12/22/2022] Open
Abstract
Large-conductance potassium (BK) channels are transmembrane (TM) proteins that can be synergistically and independently activated by membrane voltage and intracellular Ca2+. The only covalent connection between the cytosolic Ca2+ sensing domain and the TM pore and voltage sensing domains is a 15-residue ‘C-linker’. To determine the linker’s role in human BK activation, we designed a series of linker sequence scrambling mutants to suppress potential complex interplay of specific interactions with the rest of the protein. The results revealed a surprising sensitivity of BK activation to the linker sequence. Combining atomistic simulations and further mutagenesis experiments, we demonstrated that nonspecific interactions of the linker with membrane alone could directly modulate BK activation. The C-linker thus plays more direct roles in mediating allosteric coupling between BK domains than previously assumed. Our results suggest that covalent linkers could directly modulate TM protein function and should be considered an integral component of the sensing apparatus.
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Affiliation(s)
- Mahdieh Yazdani
- Department of Chemistry, University of Massachusetts, Amherst, United States
| | - Guohui Zhang
- Department of Biomedical Engineering, Center for the Investigation of Membrane Excitability Disorders, Cardiac Bioelectricity and Arrhythmia Center, Washington University, St Louis, United States
| | - Zhiguang Jia
- Department of Chemistry, University of Massachusetts, Amherst, United States
| | - Jingyi Shi
- Department of Biomedical Engineering, Center for the Investigation of Membrane Excitability Disorders, Cardiac Bioelectricity and Arrhythmia Center, Washington University, St Louis, United States
| | - Jianmin Cui
- Department of Biomedical Engineering, Center for the Investigation of Membrane Excitability Disorders, Cardiac Bioelectricity and Arrhythmia Center, Washington University, St Louis, United States
| | - Jianhan Chen
- Department of Chemistry, University of Massachusetts, Amherst, United States.,Department of Biochemistry and Molecular Biology, University of Massachusetts, Amherst, United States
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13
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Coupling of Ca 2+ and voltage activation in BK channels through the αB helix/voltage sensor interface. Proc Natl Acad Sci U S A 2020; 117:14512-14521. [PMID: 32513714 DOI: 10.1073/pnas.1908183117] [Citation(s) in RCA: 12] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/27/2022] Open
Abstract
Large-conductance Ca2+ and voltage-activated K+ (BK) channels control membrane excitability in many cell types. BK channels are tetrameric. Each subunit is composed of a voltage sensor domain (VSD), a central pore-gate domain, and a large cytoplasmic domain (CTD) that contains the Ca2+ sensors. While it is known that BK channels are activated by voltage and Ca2+, and that voltage and Ca2+ activations interact, less is known about the mechanisms involved. We explore here these mechanisms by examining the gating contribution of an interface formed between the VSDs and the αB helices located at the top of the CTDs. Proline mutations in the αB helix greatly decreased voltage activation while having negligible effects on gating currents. Analysis with the Horrigan, Cui, and Aldrich model indicated a decreased coupling between voltage sensors and pore gate. Proline mutations decreased Ca2+ activation for both Ca2+ bowl and RCK1 Ca2+ sites, suggesting that both high-affinity Ca2+ sites transduce their effect, at least in part, through the αB helix. Mg2+ activation also decreased. The crystal structure of the CTD with proline mutation L390P showed a flattening of the first helical turn in the αB helix compared to wild type, without other notable differences in the CTD, indicating that structural changes from the mutation were confined to the αB helix. These findings indicate that an intact αB helix/VSD interface is required for effective coupling of Ca2+ binding and voltage depolarization to pore opening and that shared Ca2+ and voltage transduction pathways involving the αB helix may be involved.
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14
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Abstract
Ca2+- and voltage-gated K+ channels of large conductance (BK channels) are expressed in a diverse variety of both excitable and inexcitable cells, with functional properties presumably uniquely calibrated for the cells in which they are found. Although some diversity in BK channel function, localization, and regulation apparently arises from cell-specific alternative splice variants of the single pore-forming α subunit ( KCa1.1, Kcnma1, Slo1) gene, two families of regulatory subunits, β and γ, define BK channels that span a diverse range of functional properties. We are just beginning to unravel the cell-specific, physiological roles served by BK channels of different subunit composition.
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Affiliation(s)
- Vivian Gonzalez-Perez
- Department of Anesthesiology, Washington University School of Medicine, St. Louis, Missouri 63110, USA;
| | - Christopher J Lingle
- Department of Anesthesiology, Washington University School of Medicine, St. Louis, Missouri 63110, USA;
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15
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Barros F, de la Peña P, Domínguez P, Sierra LM, Pardo LA. The EAG Voltage-Dependent K + Channel Subfamily: Similarities and Differences in Structural Organization and Gating. Front Pharmacol 2020; 11:411. [PMID: 32351384 PMCID: PMC7174612 DOI: 10.3389/fphar.2020.00411] [Citation(s) in RCA: 20] [Impact Index Per Article: 5.0] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/20/2019] [Accepted: 03/18/2020] [Indexed: 12/17/2022] Open
Abstract
EAG (ether-à-go-go or KCNH) are a subfamily of the voltage-gated potassium (Kv) channels. Like for all potassium channels, opening of EAG channels drives the membrane potential toward its equilibrium value for potassium, thus setting the resting potential and repolarizing action potentials. As voltage-dependent channels, they switch between open and closed conformations (gating) when changes in membrane potential are sensed by a voltage sensing domain (VSD) which is functionally coupled to a pore domain (PD) containing the permeation pathway, the potassium selectivity filter, and the channel gate. All Kv channels are tetrameric, with four VSDs formed by the S1-S4 transmembrane segments of each subunit, surrounding a central PD with the four S5-S6 sections arranged in a square-shaped structure. Structural information, mutagenesis, and functional experiments, indicated that in "classical/Shaker-type" Kv channels voltage-triggered VSD reorganizations are transmitted to PD gating via the α-helical S4-S5 sequence that links both modules. Importantly, these Shaker-type channels share a domain-swapped VSD/PD organization, with each VSD contacting the PD of the adjacent subunit. In this case, the S4-S5 linker, acting as a rigid mechanical lever (electromechanical lever coupling), would lead to channel gate opening at the cytoplasmic S6 helices bundle. However, new functional data with EAG channels split between the VSD and PD modules indicate that, in some Kv channels, alternative VSD/PD coupling mechanisms do exist. Noticeably, recent elucidation of the architecture of some EAG channels, and other relatives, showed that their VSDs are non-domain swapped. Despite similarities in primary sequence and predicted structural organization for all EAG channels, they show marked kinetic differences whose molecular basis is not completely understood. Thus, while a common general architecture may establish the gating system used by the EAG channels and the physicochemical coupling of voltage sensing to gating, subtle changes in that common structure, and/or allosteric influences of protein domains relatively distant from the central gating machinery, can crucially influence the gating process. We consider here the latest advances on these issues provided by the elucidation of eag1 and erg1 three-dimensional structures, and by both classical and more recent functional studies with different members of the EAG subfamily.
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Affiliation(s)
- Francisco Barros
- Departamento de Bioquímica y Biología Molecular, Universidad de Oviedo, Edificio Santiago Gascón, Oviedo, Spain
| | - Pilar de la Peña
- Departamento de Bioquímica y Biología Molecular, Universidad de Oviedo, Edificio Santiago Gascón, Oviedo, Spain
| | - Pedro Domínguez
- Departamento de Bioquímica y Biología Molecular, Universidad de Oviedo, Edificio Santiago Gascón, Oviedo, Spain
| | - Luisa Maria Sierra
- Departamento de Biología Funcional (Area de Genética), Instituto Universitario de Oncología del Principado de Asturias (IUOPA), Instituto de Investigación Sanitaria del Principado de Asturias (ISPA), Universidad de Oviedo, Oviedo, Spain
| | - Luis A. Pardo
- Oncophysiology Group, Max Planck Institute of Experimental Medicine, Göttingen, Germany
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16
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Fan C, Sukomon N, Flood E, Rheinberger J, Allen TW, Nimigean CM. Ball-and-chain inactivation in a calcium-gated potassium channel. Nature 2020; 580:288-293. [PMID: 32269335 PMCID: PMC7153497 DOI: 10.1038/s41586-020-2116-0] [Citation(s) in RCA: 36] [Impact Index Per Article: 9.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/02/2019] [Accepted: 01/15/2020] [Indexed: 01/21/2023]
Abstract
Inactivation is the process by which ion channels terminate ion flux through their pores while the opening stimulus is still present1. In neurons, inactivation of both sodium and potassium channels is crucial for the generation of action potentials and regulation of firing frequency1,2. A cytoplasmic domain of either the channel or an accessory subunit is thought to plug the open pore to inactivate the channel via a 'ball-and-chain' mechanism3-7. Here we use cryo-electron microscopy to identify the molecular gating mechanism in calcium-activated potassium channels by obtaining structures of the MthK channel from Methanobacterium thermoautotrophicum-a purely calcium-gated and inactivating channel-in a lipid environment. In the absence of Ca2+, we obtained a single structure in a closed state, which was shown by atomistic simulations to be highly flexible in lipid bilayers at ambient temperature, with large rocking motions of the gating ring and bending of pore-lining helices. In Ca2+-bound conditions, we obtained several structures, including multiple open-inactivated conformations, further indication of a highly dynamic protein. These different channel conformations are distinguished by rocking of the gating rings with respect to the transmembrane region, indicating symmetry breakage across the channel. Furthermore, in all conformations displaying open channel pores, the N terminus of one subunit of the channel tetramer sticks into the pore and plugs it, with free energy simulations showing that this is a strong interaction. Deletion of this N terminus leads to functionally non-inactivating channels and structures of open states without a pore plug, indicating that this previously unresolved N-terminal peptide is responsible for a ball-and-chain inactivation mechanism.
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Affiliation(s)
- Chen Fan
- Department of Anesthesiology, Weill Cornell Medical College, New York, NY, USA
| | - Nattakan Sukomon
- Department of Anesthesiology, Weill Cornell Medical College, New York, NY, USA
| | - Emelie Flood
- School of Science, RMIT University, Melbourne, Victoria, Australia
| | - Jan Rheinberger
- Department of Anesthesiology, Weill Cornell Medical College, New York, NY, USA
- Department of Structural Biology, Groningen Biomolecular Sciences and Biotechnology Institute, University of Groningen, Groningen, The Netherlands
| | - Toby W Allen
- School of Science, RMIT University, Melbourne, Victoria, Australia
| | - Crina M Nimigean
- Department of Anesthesiology, Weill Cornell Medical College, New York, NY, USA.
- Department of Physiology and Biophysics, Weill Cornell Medical College, New York, NY, USA.
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17
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Schrecker M, Wunnicke D, Hänelt I. How RCK domains regulate gating of K+ channels. Biol Chem 2020; 400:1303-1322. [PMID: 31361596 DOI: 10.1515/hsz-2019-0153] [Citation(s) in RCA: 9] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [Key Words] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/10/2019] [Accepted: 07/02/2019] [Indexed: 11/15/2022]
Abstract
Potassium channels play a crucial role in the physiology of all living organisms. They maintain the membrane potential and are involved in electrical signaling, pH homeostasis, cell-cell communication and survival under osmotic stress. Many prokaryotic potassium channels and members of the eukaryotic Slo channels are regulated by tethered cytoplasmic domains or associated soluble proteins, which belong to the family of regulator of potassium conductance (RCK). RCK domains and subunits form octameric rings, which control ion gating. For years, a common regulatory mechanism was suggested: ligand-induced conformational changes in the octameric ring would pull open a gate in the pore via flexible linkers. Consistently, ligand-dependent conformational changes were described for various RCK gating rings. Yet, recent structural and functional data of complete ion channels uncovered that the following signal transduction to the pore domains is divers. The different RCK-regulated ion channels show remarkably heterogeneous mechanisms with neither the connection from the RCK domain to the pore nor the gate being conserved. Some channels even lack the flexible linkers, while in others the gate cannot easily be assigned. In this review we compare available structures of RCK-gated potassium channels, highlight the similarities and differences of channel gating, and delineate existing inconsistencies.
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Affiliation(s)
- Marina Schrecker
- Institute of Biochemistry, Biocenter, Goethe University Frankfurt, Max-von-Laue Str. 9, D-60438 Frankfurt Main, Germany
| | - Dorith Wunnicke
- Institute of Biochemistry, Biocenter, Goethe University Frankfurt, Max-von-Laue Str. 9, D-60438 Frankfurt Main, Germany
| | - Inga Hänelt
- Institute of Biochemistry, Biocenter, Goethe University Frankfurt, Max-von-Laue Str. 9, D-60438 Frankfurt Main, Germany
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18
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Lorenzo-Ceballos Y, Carrasquel-Ursulaez W, Castillo K, Alvarez O, Latorre R. Calcium-driven regulation of voltage-sensing domains in BK channels. eLife 2019; 8:44934. [PMID: 31509109 PMCID: PMC6763263 DOI: 10.7554/elife.44934] [Citation(s) in RCA: 9] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/07/2019] [Accepted: 09/10/2019] [Indexed: 12/17/2022] Open
Abstract
Allosteric interactions between the voltage-sensing domain (VSD), the Ca2+-binding sites, and the pore domain govern the mammalian Ca2+- and voltage-activated K+ (BK) channel opening. However, the functional relevance of the crosstalk between the Ca2+- and voltage-sensing mechanisms on BK channel gating is still debated. We examined the energetic interaction between Ca2+ binding and VSD activation by investigating the effects of internal Ca2+ on BK channel gating currents. Our results indicate that Ca2+ sensor occupancy has a strong impact on VSD activation through a coordinated interaction mechanism in which Ca2+ binding to a single α-subunit affects all VSDs equally. Moreover, the two distinct high-affinity Ca2+-binding sites contained in the C-terminus domains, RCK1 and RCK2, contribute equally to decrease the free energy necessary to activate the VSD. We conclude that voltage-dependent gating and pore opening in BK channels is modulated to a great extent by the interaction between Ca2+ sensors and VSDs.
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Affiliation(s)
- Yenisleidy Lorenzo-Ceballos
- Doctorado en Ciencias Mención Neurociencia, Facultad de Ciencias, Universidad de Valparaíso, Valparaíso, Chile.,Centro Interdisciplinario de Neurociencia de Valparaíso, Facultad de Ciencias, Universidad de Valparaíso, Valparaíso, Chile
| | - Willy Carrasquel-Ursulaez
- Centro Interdisciplinario de Neurociencia de Valparaíso, Facultad de Ciencias, Universidad de Valparaíso, Valparaíso, Chile
| | - Karen Castillo
- Centro Interdisciplinario de Neurociencia de Valparaíso, Facultad de Ciencias, Universidad de Valparaíso, Valparaíso, Chile
| | - Osvaldo Alvarez
- Centro Interdisciplinario de Neurociencia de Valparaíso, Facultad de Ciencias, Universidad de Valparaíso, Valparaíso, Chile.,Departamento de Biología, Facultad de Ciencias, Universidad de Chile, Santiago, Chile
| | - Ramon Latorre
- Centro Interdisciplinario de Neurociencia de Valparaíso, Facultad de Ciencias, Universidad de Valparaíso, Valparaíso, Chile
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19
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Abstract
Ca2+- and voltage-gated K+ channels of large conductance (BK channels) are expressed in a diverse variety of both excitable and inexcitable cells, with functional properties presumably uniquely calibrated for the cells in which they are found. Although some diversity in BK channel function, localization, and regulation apparently arises from cell-specific alternative splice variants of the single pore-forming α subunit ( KCa1.1, Kcnma1, Slo1) gene, two families of regulatory subunits, β and γ, define BK channels that span a diverse range of functional properties. We are just beginning to unravel the cell-specific, physiological roles served by BK channels of different subunit composition.
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Affiliation(s)
- Vivian Gonzalez-Perez
- Department of Anesthesiology, Washington University School of Medicine, St. Louis, Missouri 63110, USA;
| | - Christopher J Lingle
- Department of Anesthesiology, Washington University School of Medicine, St. Louis, Missouri 63110, USA;
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20
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Barros F, Pardo LA, Domínguez P, Sierra LM, de la Peña P. New Structures and Gating of Voltage-Dependent Potassium (Kv) Channels and Their Relatives: A Multi-Domain and Dynamic Question. Int J Mol Sci 2019; 20:ijms20020248. [PMID: 30634573 PMCID: PMC6359393 DOI: 10.3390/ijms20020248] [Citation(s) in RCA: 24] [Impact Index Per Article: 4.8] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/20/2018] [Revised: 12/30/2018] [Accepted: 01/07/2019] [Indexed: 12/15/2022] Open
Abstract
Voltage-dependent potassium channels (Kv channels) are crucial regulators of cell excitability that participate in a range of physiological and pathophysiological processes. These channels are molecular machines that display a mechanism (known as gating) for opening and closing a gate located in a pore domain (PD). In Kv channels, this mechanism is triggered and controlled by changes in the magnitude of the transmembrane voltage sensed by a voltage-sensing domain (VSD). In this review, we consider several aspects of the VSD–PD coupling in Kv channels, and in some relatives, that share a common general structure characterized by a single square-shaped ion conduction pore in the center, surrounded by four VSDs located at the periphery. We compile some recent advances in the knowledge of their architecture, based in cryo-electron microscopy (cryo-EM) data for high-resolution determination of their structure, plus some new functional data obtained with channel variants in which the covalent continuity between the VSD and PD modules has been interrupted. These advances and new data bring about some reconsiderations about the use of exclusively a classical electromechanical lever model of VSD–PD coupling by some Kv channels, and open a view of the Kv-type channels as allosteric machines in which gating may be dynamically influenced by some long-range interactional/allosteric mechanisms.
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Affiliation(s)
- Francisco Barros
- Departamento de Bioquímica y Biología Molecular, Universidad de Oviedo, Edificio Santiago Gascón, Campus de El Cristo, 33006 Oviedo, Asturias, Spain.
| | - Luis A Pardo
- Oncophysiology Group, Max Planck Institute of Experimental Medicine, Hermann-Rein-Strasse 3, 37075 Göttingen, Germany.
| | - Pedro Domínguez
- Departamento de Bioquímica y Biología Molecular, Universidad de Oviedo, Edificio Santiago Gascón, Campus de El Cristo, 33006 Oviedo, Asturias, Spain.
| | - Luisa Maria Sierra
- Departamento de Biología Funcional (Area de Genética), Instituto Universitario de Oncología del Principado de Asturias (IUOPA), Universidad de Oviedo, 33006 Oviedo, Asturias, Spain.
| | - Pilar de la Peña
- Departamento de Bioquímica y Biología Molecular, Universidad de Oviedo, Edificio Santiago Gascón, Campus de El Cristo, 33006 Oviedo, Asturias, Spain.
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21
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Miranda P, Holmgren M, Giraldez T. Voltage-dependent dynamics of the BK channel cytosolic gating ring are coupled to the membrane-embedded voltage sensor. eLife 2018; 7:40664. [PMID: 30526860 PMCID: PMC6301790 DOI: 10.7554/elife.40664] [Citation(s) in RCA: 14] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/31/2018] [Accepted: 12/11/2018] [Indexed: 12/21/2022] Open
Abstract
In humans, large conductance voltage- and calcium-dependent potassium (BK) channels are regulated allosterically by transmembrane voltage and intracellular Ca2+. Divalent cation binding sites reside within the gating ring formed by two Regulator of Conductance of Potassium (RCK) domains per subunit. Using patch-clamp fluorometry, we show that Ca2+ binding to the RCK1 domain triggers gating ring rearrangements that depend on transmembrane voltage. Because the gating ring is outside the electric field, this voltage sensitivity must originate from coupling to the voltage-dependent channel opening, the voltage sensor or both. Here we demonstrate that alterations of the voltage sensor, either by mutagenesis or regulation by auxiliary subunits, are paralleled by changes in the voltage dependence of the gating ring movements, whereas modifications of the relative open probability are not. These results strongly suggest that conformational changes of RCK1 domains are specifically coupled to the voltage sensor function during allosteric modulation of BK channels.
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Affiliation(s)
- Pablo Miranda
- National Institute of Neurological Disorders and Stroke, National Institutes of Health, Bethesda, United States
| | - Miguel Holmgren
- National Institute of Neurological Disorders and Stroke, National Institutes of Health, Bethesda, United States
| | - Teresa Giraldez
- Departamento de Ciencias Medicas Basicas, Universidad de La Laguna, San Cristóbal de La Laguna, Spain.,Instituto de Tecnologias Biomedicas, Universidad de La Laguna, San Cristóbal de La Laguna, Spain
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22
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Pantazis A, Westerberg K, Althoff T, Abramson J, Olcese R. Harnessing photoinduced electron transfer to optically determine protein sub-nanoscale atomic distances. Nat Commun 2018; 9:4738. [PMID: 30413716 PMCID: PMC6226468 DOI: 10.1038/s41467-018-07218-6] [Citation(s) in RCA: 21] [Impact Index Per Article: 3.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/30/2018] [Accepted: 10/16/2018] [Indexed: 11/29/2022] Open
Abstract
Proteins possess a complex and dynamic structure, which is influenced by external signals and may change as they perform their biological functions. We present an optical approach, distance-encoding photoinduced electron transfer (DEPET), capable of the simultaneous study of protein structure and function. An alternative to FRET-based methods, DEPET is based on the quenching of small conjugated fluorophores by photoinduced electron transfer: a reaction that requires contact of the excited fluorophore with a suitable electron donor. This property allows DEPET to exhibit exceptional spatial and temporal resolution capabilities in the range pertinent to protein conformational change. We report the first implementation of DEPET on human large-conductance K+ (BK) channels under voltage clamp. We describe conformational rearrangements underpinning BK channel sensitivity to electrical excitation, in conducting channels expressed in living cells. Finally, we validate DEPET in synthetic peptide length standards, to evaluate its accuracy in measuring sub- and near-nanometer intramolecular distances.
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Affiliation(s)
- Antonios Pantazis
- Division of Molecular Medicine, Department of Anesthesiology & Perioperative Medicine, UCLA, Los Angeles, CA, 90095, USA. .,Division of Neurobiology, Department of Clinical and Experimental Medicine (IKE), Linköping University, Linköping, 581 83, Sweden. .,Wallenberg Center for Molecular Medicine, Linköping University, Linköping, 581 83, Sweden.
| | - Karin Westerberg
- 0000 0001 0657 5612grid.417886.4Amgen, Thousand Oaks, CA 91320 USA
| | - Thorsten Althoff
- 0000 0000 9632 6718grid.19006.3eDepartment of Physiology, UCLA, Los Angeles, CA 90095 USA
| | - Jeff Abramson
- 0000 0000 9632 6718grid.19006.3eDepartment of Physiology, UCLA, Los Angeles, CA 90095 USA
| | - Riccardo Olcese
- Division of Molecular Medicine, Department of Anesthesiology & Perioperative Medicine, UCLA, Los Angeles, CA, 90095, USA. .,Department of Physiology, UCLA, Los Angeles, CA, 90095, USA.
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23
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Abstract
The gating mechanism of transmembrane ion channels is crucial for understanding how these proteins control ion flow across membranes in various physiological processes. Big potassium (BK) channels are particularly interesting with large single-channel conductance and dual regulation by membrane voltage and intracellular Ca2+. Recent atomistic structures of BK channels failed to identify structural features that could physically block the ion flow in the closed state. Here, we show that gating of BK channels does not seem to require a physical gate. Instead, changes in the pore shape and surface hydrophobicity in the Ca2+-free state allow the channel to readily undergo hydrophobic dewetting transitions, giving rise to a large free energy barrier for K+ permeation. Importantly, the dry pore remains physically open and is readily accessible to quaternary ammonium channel blockers. The hydrophobic gating mechanism is also consistent with scanning mutagenesis studies showing that modulation of pore hydrophobicity is correlated with activation properties. BK channels are regulated by membrane voltage and intracellular Ca2+ but the structural features that block the ion flow in the closed state remain unknown. Here authors use molecular dynamics simulation and show that a physical gate is not required; instead ion flow is regulated by hydrophobic dewetting due to changes in pore shape and surface hydrophobicity.
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24
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Abstract
Exome and targeted sequencing have revolutionized clinical diagnosis. This has been particularly striking in epilepsy and neurodevelopmental disorders, for which new genes or new variants of preexisting candidate genes are being continuously identified at increasing rates every year. A surprising finding of these efforts is the recognition that gain of function potassium channel variants are actually associated with certain types of epilepsy, such as malignant migrating partial seizures of infancy or early-onset epileptic encephalopathy. This development has been difficult to understand as traditionally potassium channel loss-of-function, not gain-of-function, has been associated with hyperexcitability disorders. In this article, we describe the current state of the field regarding the gain-of-function potassium channel variants associated with epilepsy (KCNA2, KCNB1, KCND2, KCNH1, KCNH5, KCNJ10, KCNMA1, KCNQ2, KCNQ3, and KCNT1) and speculate on the possible cellular mechanisms behind the development of seizures and epilepsy in these patients. Understanding how potassium channel gain-of-function leads to epilepsy will provide new insights into the inner working of neural circuits and aid in developing new therapies.
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Affiliation(s)
- Zachary Niday
- Dept. of Physiology and Neurobiology, University of Connecticut, Storrs, CT 06269, USA
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25
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Kshatri AS, Gonzalez-Hernandez A, Giraldez T. Physiological Roles and Therapeutic Potential of Ca 2+ Activated Potassium Channels in the Nervous System. Front Mol Neurosci 2018; 11:258. [PMID: 30104956 PMCID: PMC6077210 DOI: 10.3389/fnmol.2018.00258] [Citation(s) in RCA: 63] [Impact Index Per Article: 10.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/04/2018] [Accepted: 07/06/2018] [Indexed: 12/21/2022] Open
Abstract
Within the potassium ion channel family, calcium activated potassium (KCa) channels are unique in their ability to couple intracellular Ca2+ signals to membrane potential variations. KCa channels are diversely distributed throughout the central nervous system and play fundamental roles ranging from regulating neuronal excitability to controlling neurotransmitter release. The physiological versatility of KCa channels is enhanced by alternative splicing and co-assembly with auxiliary subunits, leading to fundamental differences in distribution, subunit composition and pharmacological profiles. Thus, understanding specific KCa channels’ mechanisms in neuronal function is challenging. Based on their single channel conductance, KCa channels are divided into three subtypes: small (SK, 4–14 pS), intermediate (IK, 32–39 pS) and big potassium (BK, 200–300 pS) channels. This review describes the biophysical characteristics of these KCa channels, as well as their physiological roles and pathological implications. In addition, we also discuss the current pharmacological strategies and challenges to target KCa channels for the treatment of various neurological and psychiatric disorders.
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Affiliation(s)
- Aravind S Kshatri
- Department of Basic Medical Sciences, Medical School, Universidad de La Laguna, Tenerife, Spain.,Instituto de Tecnologias Biomedicas, Universidad de La Laguna, Tenerife, Spain
| | - Alberto Gonzalez-Hernandez
- Department of Basic Medical Sciences, Medical School, Universidad de La Laguna, Tenerife, Spain.,Instituto de Tecnologias Biomedicas, Universidad de La Laguna, Tenerife, Spain
| | - Teresa Giraldez
- Department of Basic Medical Sciences, Medical School, Universidad de La Laguna, Tenerife, Spain.,Instituto de Tecnologias Biomedicas, Universidad de La Laguna, Tenerife, Spain
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26
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Lu M, Li JR, Alvarez-Lugo L, Li Y, Yu S, Li X, Shi B, Chai TC. Lipopolysaccharide stimulates BK channel activity in bladder umbrella cells. Am J Physiol Cell Physiol 2018; 314:C643-C653. [PMID: 29466671 DOI: 10.1152/ajpcell.00339.2017] [Citation(s) in RCA: 7] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/08/2023]
Abstract
Bladder urothelium plays an active role in response to bacterial infection. There is little known about the electrophysiological activity in urothelial cells in this process. We used a nonenzymatic method to isolate bladder urothelial tissue and to patch clamp umbrella cells in situ. A 200 pS conductance potassium (K+) channel was detected from female C57BL6 mice. Of 58 total patches, 17.2% patches displayed the 200 pS K+ conductance channel. This K+ conductance channel showed Ca2+ sensitivity and voltage dependence. Specific big-conductance potassium channel (BK) inhibitors (paxilline, iberiotoxin) blocked the 200 pS K+ conductance channel activity. RT-PCR and immunoblot confirmed BK channel pore-forming α-subunit (BK-α) mRNA and protein in urothelium. Immunohistochemistry also showed the BK-α located in urothelium. The above data provided evidence that the 200 pS K+ conductance channel was a BK channel. Lipopolysaccharide (LPS), a component of uropathogenic Escherichia coli, was used to investigate the role of BK channel in the pathogenesis of urinary tract infection. BK channel activity as NPo increased threefold within 30 min of exposure to LPS. mRNAs for LPS receptors (TLR4, CD14, MD-2) were expressed in the urothelium but not in lamina propria or detrusor. Blockade of the receptors by an antagonist (polymyxin B) abrogated LPS's effect on BK channel. The involvement of protein kinase A (PKA) on BK channel activity was demonstrated by applying PKA blockers (H89 and PKI). Both PKA inhibitors abolished the BK channel activity induced by LPS. In conclusion, BK channel was identified in bladder umbrella cells, and its activity was significantly increased by LPS.
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Affiliation(s)
- Ming Lu
- Department of Urology, Yale University School of Medicine , New Haven, Connecticut
| | - Jian-Ri Li
- Department of Urology, Yale University School of Medicine , New Haven, Connecticut
| | - Lery Alvarez-Lugo
- Department of Urology, Yale University School of Medicine , New Haven, Connecticut
| | - Yan Li
- Department of Urology, Qilu Hospital, Shandong University , Jinan , China
| | - Shan Yu
- Department of Urology, Yale University School of Medicine , New Haven, Connecticut
| | - XuanHao Li
- Department of Urology, Yale University School of Medicine , New Haven, Connecticut
| | - Benkang Shi
- Department of Urology, Qilu Hospital, Shandong University , Jinan , China
| | - Toby C Chai
- Department of Urology, Yale University School of Medicine , New Haven, Connecticut
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