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Beverley KM, Barbera N, Levitan I. Dual pattern of cholesterol-induced decoupling of residue-residue interactions of Kir2.2. J Struct Biol 2024; 216:108091. [PMID: 38641256 DOI: 10.1016/j.jsb.2024.108091] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/13/2023] [Revised: 03/28/2024] [Accepted: 04/09/2024] [Indexed: 04/21/2024]
Abstract
Cholesterol is a negative regulator of a variety of ion channels. We have previously shown that cholesterol suppresses Kir2.2 channels via residue-residue uncoupling on the inter-subunit interfaces within the close state of the channels (3JYC). In this study, we extend this analysis to the other known structure of Kir2.2 that is closer to the open state of Kir2.2 channels (3SPI) and provide additional analysis of the residue distances between the uncoupled residues and cholesterol binding domains in the two conformation states of the channels. We found that the general phenomenon of cholesterol binding leading to uncoupling between specific residues is conserved in both channel states but the specific pattern of the uncoupling residues is distinct between the two states and implies different mechanisms. Specifically, we found that cholesterol binding in the 3SPI state results in an uncoupling of residues in three distinct regions; the transmembrane domain, membrane-cytosolic interface, and the cytosolic domain, with the first two regions forming an envelope around PI(4,5)P2 and cholesterol binding sites and the distal region overlapping with the subunit-subunit interface characterized in our previous study of the disengaged state. We also found that this uncoupling is dependent upon the number of cholesterol molecules bound to the channel. We further generated a mutant channel Kir2.2P187V with a single point mutation in a residue proximal to the PI(4,5)P2 binding site, which is predicted to be uncoupled from other residues in its vicinity upon cholesterol binding and found that this mutation abrogates the sensitivity of Kir2.2 to cholesterol changes in the membrane. These findings suggest that cholesterol binding to this conformation state of Kir2.2 channels may destabilize the PI(4,5)P2 interactions with the channels while in the disengaged state the destabilization occurs where the subunits interact. These findings give insight into the structural mechanistic basis for the functional effects of cholesterol binding to the Kir2.2 channel.
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Affiliation(s)
- Katie M Beverley
- Division of Pulmonary and Critical Care Medicine, Department of Medicine, University of Illinois at Chicago, Chicago, IL 60612, USA.
| | - Nicolas Barbera
- Division of Pulmonary and Critical Care Medicine, Department of Medicine, University of Illinois at Chicago, Chicago, IL 60612, USA; Center for Public Health Genomics, Department of Biomedical Engineering, School of Engineering &Applied Science, University of Virginia, Charlottesville, VA 22904, USA
| | - Irena Levitan
- Division of Pulmonary and Critical Care Medicine, Department of Medicine, University of Illinois at Chicago, Chicago, IL 60612, USA.
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2
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Sourisseau F, Chahine C, Pouliot V, Cens T, Charnet P, Chahine M. Cloning, functional expression, and pharmacological characterization of inwardly rectifying potassium channels (Kir) from Apis mellifera. Sci Rep 2024; 14:7834. [PMID: 38570597 PMCID: PMC10991380 DOI: 10.1038/s41598-024-58234-0] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/01/2023] [Accepted: 03/26/2024] [Indexed: 04/05/2024] Open
Abstract
Potassium channels belong to the super family of ion channels and play a fundamental role in cell excitability. Kir channels are potassium channels with an inwardly rectifying property. They play a role in setting the resting membrane potential of many excitable cells including neurons. Although putative Kir channel family genes can be found in the Apis mellifera genome, their functional expression, biophysical properties, and sensitivity to small molecules with insecticidal activity remain to be investigated. We cloned six Kir channel isoforms from Apis mellifera that derive from two Kir genes, AmKir1 and AmKir2, which are present in the Apis mellifera genome. We studied the tissue distribution, the electrophysiological and pharmacological characteristics of three isoforms that expressed functional currents (AmKir1.1, AmKir2.2, and AmKir2.3). AmKir1.1, AmKir2.2, and AmKir2.3 isoforms exhibited distinct characteristics when expressed in Xenopus oocytes. AmKir1.1 exhibited the largest potassium currents and was impermeable to cesium whereas AmKir2.2 and AmKir2.3 exhibited smaller currents but allowed cesium to permeate. AmKir1 exhibited faster opening kinetics than AmKir2. Pharmacological experiments revealed that both AmKir1.1 and AmKir2.2 are blocked by the divalent ion barium, with IC50 values of 10-5 and 10-6 M, respectively. The concentrations of VU041, a small molecule with insecticidal properties required to achieve a 50% current blockade for all three channels were higher than those needed to block Kir channels in other arthropods, such as the aphid Aphis gossypii and the mosquito Aedes aegypti. From this, we conclude that Apis mellifera AmKir channels exhibit lower sensitivity to VU041.
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Affiliation(s)
- Fabien Sourisseau
- CERVO Brain Research Centre, 2601, chemin de la Canardière, Quebec City, QC, G1J 2G3, Canada
| | - Chaimaa Chahine
- CERVO Brain Research Centre, 2601, chemin de la Canardière, Quebec City, QC, G1J 2G3, Canada
| | - Valérie Pouliot
- CERVO Brain Research Centre, 2601, chemin de la Canardière, Quebec City, QC, G1J 2G3, Canada
| | - Thierry Cens
- Institut des Biomolécules Max Mousseron (IBMM), CNRS UMR 5247, 1919 Route de Mende, Montpellier, France
| | - Pierre Charnet
- Institut des Biomolécules Max Mousseron (IBMM), CNRS UMR 5247, 1919 Route de Mende, Montpellier, France
| | - Mohamed Chahine
- CERVO Brain Research Centre, 2601, chemin de la Canardière, Quebec City, QC, G1J 2G3, Canada.
- Department of Medicine, Faculty of Medicine, Université Laval, Quebec City, QC, Canada.
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3
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Rohacs T. Phosphoinositide Regulation of TRP Channels: A Functional Overview in the Structural Era. Annu Rev Physiol 2024; 86:329-355. [PMID: 37871124 DOI: 10.1146/annurev-physiol-042022-013956] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/25/2023]
Abstract
Transient receptor potential (TRP) ion channels have diverse activation mechanisms including physical stimuli, such as high or low temperatures, and a variety of intracellular signaling molecules. Regulation by phosphoinositides and their derivatives is their only known common regulatory feature. For most TRP channels, phosphatidylinositol 4,5-bisphosphate [PI(4,5)P2] serves as a cofactor required for activity. Such dependence on PI(4,5)P2 has been demonstrated for members of the TRPM subfamily and for the epithelial TRPV5 and TRPV6 channels. Intracellular TRPML channels show specific activation by PI(3,5)P2. Structural studies uncovered the PI(4,5)P2 and PI(3,5)P2 binding sites for these channels and shed light on the mechanism of channel opening. PI(4,5)P2 regulation of TRPV1-4 as well as some TRPC channels is more complex, involving both positive and negative effects. This review discusses the functional roles of phosphoinositides in TRP channel regulation and molecular insights gained from recent cryo-electron microscopy structures.
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Affiliation(s)
- Tibor Rohacs
- Department of Pharmacology, Physiology and Neuroscience, Rutgers New Jersey Medical School, Newark, New Jersey;
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4
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Bukiya AN, Rosenhouse-Dantsker A. From Crosstalk to Synergism: The Combined Effect of Cholesterol and PI(4,5)P 2 on Inwardly Rectifying Potassium Channels. ADVANCES IN EXPERIMENTAL MEDICINE AND BIOLOGY 2023; 1422:169-191. [PMID: 36988881 DOI: 10.1007/978-3-031-21547-6_6] [Citation(s) in RCA: 1] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 03/30/2023]
Abstract
Inwardly rectifying potassium (Kir) channels are integral membrane proteins that control the flux of potassium ions across cell membranes and regulate membrane permeability. All eukaryotic Kir channels require the membrane phospholipid phosphatidylinositol 4,5-bisphosphate (PI(4,5)P2) for activation. In recent years, it has become evident that the function of many members of this family of channels is also mediated by another essential lipid-cholesterol. Here, we focus on members of the Kir2 and Kir3 subfamilies and their modulation by these two key lipids. We discuss how PI(4,5)P2 and cholesterol bind to Kir2 and Kir3 channels and how they affect channel activity. We also discuss the accumulating evidence indicating that there is interplay between PI(4,5)P2 and cholesterol in the modulation of Kir2 and Kir3 channels. In particular, we review the crosstalk between PI(4,5)P2 and cholesterol in the modulation of the ubiquitously expressed Kir2.1 channel and the synergy between these two lipids in the modulation of the Kir3.4 channel, which is primarily expressed in the heart. Additionally, we demonstrate that there is also synergy in the modulation of Kir3.2 channels, which are expressed in the brain. These observations suggest that alterations in the relative levels PI(4,5)P2 and cholesterol may fine-tune Kir channel activity.
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Affiliation(s)
- Anna N Bukiya
- Department of Pharmacology, Addiction Science and Toxicology, College of Medicine, The University of Tennessee Health Science Center, Memphis, TN, USA
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5
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Rosenhouse-Dantsker A, Gazgalis D, Logothetis DE. PI(4,5)P 2 and Cholesterol: Synthesis, Regulation, and Functions. ADVANCES IN EXPERIMENTAL MEDICINE AND BIOLOGY 2023; 1422:3-59. [PMID: 36988876 DOI: 10.1007/978-3-031-21547-6_1] [Citation(s) in RCA: 3] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [Key Words] [Subscribe] [Scholar Register] [Indexed: 03/30/2023]
Abstract
Phosphatidylinositol 4,5-bisphosphate (PI(4,5)P2) is the most abundant membrane phosphoinositide and cholesterol is an essential component of the plasma membrane (PM). Both lipids play key roles in a variety of cellular functions including as signaling molecules and major regulators of protein function. This chapter provides an overview of these two important lipids. Starting from a brief description of their structure, synthesis, and regulation, the chapter continues to describe the primary functions and signaling processes in which PI(4,5)P2 and cholesterol are involved. While PI(4,5)P2 and cholesterol can act independently, they often act in concert or affect each other's impact. The chapters in this volume on "Cholesterol and PI(4,5)P2 in Vital Biological Functions: From Coexistence to Crosstalk" focus on the emerging relationship between cholesterol and PI(4,5)P2 in a variety of biological systems and processes. In this chapter, the next section provides examples from the ion channel field demonstrating that PI(4,5)P2 and cholesterol can act via common mechanisms. The chapter ends with a discussion of future directions.
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Affiliation(s)
| | - Dimitris Gazgalis
- Department of Pharmaceutical Sciences, School of Pharmacy and Pharmaceutical Sciences, Bouvé College of Health Sciences, Northeastern University, Boston, MA, USA
| | - Diomedes E Logothetis
- Department of Pharmaceutical Sciences, School of Pharmacy and Pharmaceutical Sciences, Bouvé College of Health Sciences, Northeastern University, Boston, MA, USA
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6
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Riel EB, Jürs BC, Cordeiro S, Musinszki M, Schewe M, Baukrowitz T. The versatile regulation of K2P channels by polyanionic lipids of the phosphoinositide and fatty acid metabolism. J Gen Physiol 2022; 154:212926. [PMID: 34928298 PMCID: PMC8693234 DOI: 10.1085/jgp.202112989] [Citation(s) in RCA: 2] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/02/2021] [Accepted: 12/01/2021] [Indexed: 12/29/2022] Open
Abstract
Work over the past three decades has greatly advanced our understanding of the regulation of Kir K+ channels by polyanionic lipids of the phosphoinositide (e.g., PIP2) and fatty acid metabolism (e.g., oleoyl-CoA). However, comparatively little is known regarding the regulation of the K2P channel family by phosphoinositides and by long-chain fatty acid–CoA esters, such as oleoyl-CoA. We screened 12 mammalian K2P channels and report effects of polyanionic lipids on all tested channels. We observed activation of members of the TREK, TALK, and THIK subfamilies, with the strongest activation by PIP2 for TRAAK and the strongest activation by oleoyl-CoA for TALK-2. By contrast, we observed inhibition for members of the TASK and TRESK subfamilies. Our results reveal that TASK-2 channels have both activatory and inhibitory PIP2 sites with different affinities. Finally, we provided evidence that PIP2 inhibition of TASK-1 and TASK-3 channels is mediated by closure of the recently identified lower X-gate as critical mutations within the gate (i.e., L244A, R245A) prevent PIP2-induced inhibition. Our findings establish that K+ channels of the K2P family are highly sensitive to polyanionic lipids, extending our knowledge of the mechanisms of lipid regulation and implicating the metabolism of these lipids as possible effector pathways to regulate K2P channel activity.
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Affiliation(s)
- Elena B Riel
- Institute of Physiology, Kiel University, Kiel, Germany
| | - Björn C Jürs
- Institute of Physiology, Kiel University, Kiel, Germany.,Medical School Hamburg, University of Applied Sciences and Medical University, Hamburg, Germany
| | | | | | - Marcus Schewe
- Institute of Physiology, Kiel University, Kiel, Germany
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7
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Stieger B, Steiger J, Locher KP. Membrane lipids and transporter function. Biochim Biophys Acta Mol Basis Dis 2021; 1867:166079. [PMID: 33476785 DOI: 10.1016/j.bbadis.2021.166079] [Citation(s) in RCA: 21] [Impact Index Per Article: 7.0] [Reference Citation Analysis] [Abstract] [Key Words] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/15/2020] [Revised: 12/12/2020] [Accepted: 01/07/2021] [Indexed: 02/07/2023]
Abstract
Transport proteins are essential for cells in allowing the exchange of substances between cells and their environment across the lipid bilayer forming a tight barrier. Membrane lipids modulate the function of transmembrane proteins such as transporters in two ways: Lipids are tightly and specifically bound to transport proteins and in addition they modulate from the bulk of the lipid bilayer the function of transport proteins. This overview summarizes currently available information at the ultrastructural level on lipids tightly bound to transport proteins and the impact of altered bulk membrane lipid composition. Human diseases leading to altered lipid homeostasis will lead to altered membrane lipid composition, which in turn affect the function of transporter proteins.
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Affiliation(s)
- Bruno Stieger
- Department of Clinical Pharmacology and Toxicology, University Hospital Zurich, University of Zurich, 8091 Zurich, Switzerland.
| | - Julia Steiger
- Department of Clinical Pharmacology and Toxicology, University Hospital Zurich, University of Zurich, 8091 Zurich, Switzerland
| | - Kaspar P Locher
- Department of Biology, Institute of Molecular Biology and Biophysics, ETH Zurich, 8093 Zurich, Switzerland
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Clinical Importance of the Human Umbilical Artery Potassium Channels. Cells 2020; 9:cells9091956. [PMID: 32854241 PMCID: PMC7565333 DOI: 10.3390/cells9091956] [Citation(s) in RCA: 16] [Impact Index Per Article: 4.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/15/2020] [Revised: 08/21/2020] [Accepted: 08/24/2020] [Indexed: 02/06/2023] Open
Abstract
Potassium (K+) channels are usually predominant in the membranes of vascular smooth muscle cells (SMCs). These channels play an important role in regulating the membrane potential and vessel contractility-a role that depends on the vascular bed. Thus, the activity of K+ channels represents one of the main mechanisms regulating the vascular tone in physiological and pathophysiological conditions. Briefly, the activation of K+ channels in SMC leads to hyperpolarization and vasorelaxation, while its inhibition induces depolarization and consequent vascular contraction. Currently, there are four different types of K+ channels described in SMCs: voltage-dependent K+ (KV) channels, calcium-activated K+ (KCa) channels, inward rectifier K+ (Kir) channels, and 2-pore domain K+ (K2P) channels. Due to the fundamental role of K+ channels in excitable cells, these channels are promising therapeutic targets in clinical practice. Therefore, this review discusses the basic properties of the various types of K+ channels, including structure, cellular mechanisms that regulate their activity, and new advances in the development of activators and blockers of these channels. The vascular functions of these channels will be discussed with a focus on vascular SMCs of the human umbilical artery. Then, the clinical importance of K+ channels in the treatment and prevention of cardiovascular diseases during pregnancy, such as gestational hypertension and preeclampsia, will be explored.
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9
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The intriguing effect of ethanol and nicotine on acetylcholine-sensitive potassium current IKAch: Insight from a quantitative model. PLoS One 2019; 14:e0223448. [PMID: 31600261 PMCID: PMC6786802 DOI: 10.1371/journal.pone.0223448] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/04/2019] [Accepted: 09/20/2019] [Indexed: 02/01/2023] Open
Abstract
Recent experimental work has revealed unusual features of the effect of certain drugs on cardiac inwardly rectifying potassium currents, including the constitutively active and acetylcholine-induced components of acetylcholine-sensitive current (IKAch). These unusual features have included alternating susceptibility of the current components to activation and inhibition induced by ethanol or nicotine applied at various concentrations, and significant correlation between the drug effect and the current magnitude measured under drug-free conditions. To explain these complex drug effects, we have developed a new type of quantitative model to offer a possible interpretation of the effect of ethanol and nicotine on the IKAch channels. The model is based on a description of IKAch as a sum of particular currents related to the populations of channels formed by identical assemblies of different α-subunits. Assuming two different channel populations in agreement with the two reported functional IKAch-channels (GIRK1/4 and GIRK4), the model was able to simulate all the above-mentioned characteristic features of drug-channel interactions and also the dispersion of the current measured in different cells. The formulation of our model equations allows the model to be incorporated easily into the existing integrative models of electrical activity of cardiac cells involving quantitative description of IKAch. We suppose that the model could also help make sense of certain observations related to the channels that do not show inward rectification. This new ionic channel model, based on a concept we call population type, may allow for the interpretation of complex interactions of drugs with ionic channels of various types, which cannot be done using the ionic channel models available so far.
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10
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Sarmiento BE, Santos Menezes LF, Schwartz EF. Insulin Release Mechanism Modulated by Toxins Isolated from Animal Venoms: From Basic Research to Drug Development Prospects. Molecules 2019; 24:E1846. [PMID: 31091684 PMCID: PMC6571724 DOI: 10.3390/molecules24101846] [Citation(s) in RCA: 5] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/01/2019] [Revised: 04/23/2019] [Accepted: 05/09/2019] [Indexed: 12/12/2022] Open
Abstract
Venom from mammals, amphibians, snakes, arachnids, sea anemones and insects provides diverse sources of peptides with different potential medical applications. Several of these peptides have already been converted into drugs and some are still in the clinical phase. Diabetes type 2 is one of the diseases with the highest mortality rate worldwide, requiring specific attention. Diverse drugs are available (e.g., Sulfonylureas) for effective treatment, but with several adverse secondary effects, most of them related to the low specificity of these compounds to the target. In this context, the search for specific and high-affinity compounds for the management of this metabolic disease is growing. Toxins isolated from animal venom have high specificity and affinity for different molecular targets, of which the most important are ion channels. This review will present an overview about the electrical activity of the ion channels present in pancreatic β cells that are involved in the insulin secretion process, in addition to the diversity of peptides that can interact and modulate the electrical activity of pancreatic β cells. The importance of prospecting bioactive peptides for therapeutic use is also reinforced.
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Affiliation(s)
- Beatriz Elena Sarmiento
- Departamento de Ciências Fisiológicas, Instituto de Ciências Biológicas, Universidade de Brasília, Brasília, DF 70910-900, Brazil.
| | - Luis Felipe Santos Menezes
- Departamento de Ciências Fisiológicas, Instituto de Ciências Biológicas, Universidade de Brasília, Brasília, DF 70910-900, Brazil.
| | - Elisabeth F Schwartz
- Departamento de Ciências Fisiológicas, Instituto de Ciências Biológicas, Universidade de Brasília, Brasília, DF 70910-900, Brazil.
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11
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Rosenhouse-Dantsker A. Cholesterol Binding Sites in Inwardly Rectifying Potassium Channels. ADVANCES IN EXPERIMENTAL MEDICINE AND BIOLOGY 2019; 1135:119-138. [DOI: 10.1007/978-3-030-14265-0_7] [Citation(s) in RCA: 10] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 12/02/2022]
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12
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Meng XY, Kang SG, Zhou R. Molecular mechanism of phosphoinositides' specificity for the inwardly rectifying potassium channel Kir2.2. Chem Sci 2018; 9:8352-8362. [PMID: 30542582 PMCID: PMC6247517 DOI: 10.1039/c8sc01284a] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/19/2018] [Accepted: 09/04/2018] [Indexed: 12/04/2022] Open
Abstract
We investigated the binding mechanism of PI(4,5)P2 and variants on the inwardly rectifying potassium channel, Kir2.2. Our results not only demonstrated the molecular origin for their binding specificity, but also revealed the major driving forces.
Phosphoinositides are essential signaling lipids that play a critical role in regulating ion channels, and their dysregulation often results in fatal diseases including cardiac arrhythmia and paralysis. Despite decades of intensive research, the underlying molecular mechanism of lipid agonism and specificity remains largely unknown. Here, we present a systematic study of the binding mechanism and specificity of a native agonist, phosphatidylinositol 4,5-bisphosphate (PI(4,5)P2) and two of its variants, PI(3,4)P2 and PI(3,4,5)P3, on inwardly rectifying potassium channel Kir2.2, using molecular dynamics simulations and free energy perturbations (FEPs). Our results demonstrate that the major driving force for the PI(4,5)P2 specificity on Kir2.2 comes from the highly organized salt-bridge network formed between the charged inositol head and phosphodiester linker of PI(4,5)P2. The unsaturated arachidonic chain is also shown to contribute to the stable binding through hydrophobic interactions with nearby Kir2.2 hydrophobic residues. Consistent with previous experimental findings, our FEP results confirmed that non-native ligands, PI(3,4)P2 and PI(3,4,5)P3, show significant loss in binding affinity as a result of the substantial shift from the native binding mode and unfavorable local solvation environment. However, surprisingly, the underlying molecular pictures for the unfavorable binding of both ligands are quite distinctive: for PI(3,4)P2, it is due to a direct destabilization in the bound state, whereas for PI(3,4,5)P3, it is due to a relative stabilization in its free state. Our findings not only provide a theoretical basis for the ligand specificity, but also generate new insights into the allosteric modulation of ligand-gated ion channels.
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Affiliation(s)
- Xuan-Yu Meng
- State Key Laboratory of Radiation Medicine and Protection , School for Radiological and Interdisciplinary Sciences (RAD-X) , Collaborative Innovation Centre of Radiation Medicine of Jiangsu Higher Education Institutions , Soochow University , Suzhou 215123 , China
| | - Seung-Gu Kang
- IBM Thomas J. Watson Research Center , Yorktown Heights , NY 10598 , USA .
| | - Ruhong Zhou
- State Key Laboratory of Radiation Medicine and Protection , School for Radiological and Interdisciplinary Sciences (RAD-X) , Collaborative Innovation Centre of Radiation Medicine of Jiangsu Higher Education Institutions , Soochow University , Suzhou 215123 , China.,IBM Thomas J. Watson Research Center , Yorktown Heights , NY 10598 , USA . .,Department of Chemistry , Columbia University , New York , NY 10027 , USA
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13
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Choveau FS, De la Rosa V, Bierbower SM, Hernandez CC, Shapiro MS. Phosphatidylinositol 4,5-bisphosphate (PIP 2) regulates KCNQ3 K + channels by interacting with four cytoplasmic channel domains. J Biol Chem 2018; 293:19411-19428. [PMID: 30348901 DOI: 10.1074/jbc.ra118.005401] [Citation(s) in RCA: 29] [Impact Index Per Article: 4.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/15/2018] [Revised: 10/12/2018] [Indexed: 01/11/2023] Open
Abstract
Phosphatidylinositol 4,5-bisphosphate (PIP2) in the plasma membrane regulates the function of many ion channels, including M-type (potassium voltage-gated channel subfamily Q member (KCNQ), Kv7) K+ channels; however, the molecular mechanisms involved remain unclear. To this end, we here focused on the KCNQ3 subtype that has the highest apparent affinity for PIP2 and performed extensive mutagenesis in regions suggested to be involved in PIP2 interactions among the KCNQ family. Using perforated patch-clamp recordings of heterologously transfected tissue culture cells, total internal reflection fluorescence microscopy, and the zebrafish (Danio rerio) voltage-sensitive phosphatase to deplete PIP2 as a probe, we found that PIP2 regulates KCNQ3 channels through four different domains: 1) the A-B helix linker that we previously identified as important for both KCNQ2 and KCNQ3, 2) the junction between S6 and the A helix, 3) the S2-S3 linker, and 4) the S4-S5 linker. We also found that the apparent strength of PIP2 interactions within any of these domains was not coupled to the voltage dependence of channel activation. Extensive homology modeling and docking simulations with the WT or mutant KCNQ3 channels and PIP2 were consistent with the experimental data. Our results indicate that PIP2 modulates KCNQ3 channel function by interacting synergistically with a minimum of four cytoplasmic domains.
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Affiliation(s)
- Frank S Choveau
- From the Department of Cell and Integrative Physiology, University of Texas Health San Antonio, San Antonio, Texas 78229
| | - Victor De la Rosa
- From the Department of Cell and Integrative Physiology, University of Texas Health San Antonio, San Antonio, Texas 78229
| | - Sonya M Bierbower
- From the Department of Cell and Integrative Physiology, University of Texas Health San Antonio, San Antonio, Texas 78229
| | - Ciria C Hernandez
- the Department of Neurology, Vanderbilt University Medical Center, Nashville, Tennessee 37232, and .,the Life Sciences Institute, University of Michigan, Ann Arbor, Michigan 48109
| | - Mark S Shapiro
- From the Department of Cell and Integrative Physiology, University of Texas Health San Antonio, San Antonio, Texas 78229,
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York N, Halbach P, Chiu MA, Bird IM, Pillers DAM, Pattnaik BR. Oxytocin (OXT)-stimulated inhibition of Kir7.1 activity is through PIP 2-dependent Ca 2+ response of the oxytocin receptor in the retinal pigment epithelium in vitro. Cell Signal 2017; 37:93-102. [PMID: 28603013 DOI: 10.1016/j.cellsig.2017.06.005] [Citation(s) in RCA: 22] [Impact Index Per Article: 3.1] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/20/2017] [Revised: 05/28/2017] [Accepted: 06/05/2017] [Indexed: 01/26/2023]
Abstract
Oxytocin (OXT) is a neuropeptide that activates the oxytocin receptor (OXTR), a rhodopsin family G-protein coupled receptor. Our localization of OXTR to the retinal pigment epithelium (RPE), in close proximity to OXT in the adjacent photoreceptor neurons, leads us to propose that OXT plays an important role in RPE-retinal communication. An increase of RPE [Ca2+]i in response to OXT stimulation implies that the RPE may utilize oxytocinergic signaling as a mechanism by which it accomplishes some of its many roles. In this study, we used an established human RPE cell line, a HEK293 heterologous OXTR expression system, and pharmacological inhibitors of Ca2+ signaling to demonstrate that OXTR utilizes capacitative Ca2+ entry (CCE) mechanisms to sustain an increase in cytoplasmic Ca2+. These findings demonstrate how multiple functional outcomes of OXT-OXTR signaling could be integrated via a single pathway. In addition, the activated OXTR was able to inhibit the Kir7.1 channel, an important mediator of sub retinal waste transport and K+ homeostasis.
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Affiliation(s)
- Nathaniel York
- Endocrinology-Reproductive Physiology Program, The University of Wisconsin, Madison, WI 53715, United States; Division of Neonatology& Newborn Nursery, The University of Wisconsin, Madison, WI 53715, United States; Departments of Pediatrics, The University of Wisconsin, Madison, WI 53715, United States; The McPherson Eye Research Institute, The University of Wisconsin, Madison, WI 53715, United States
| | - Patrick Halbach
- Endocrinology-Reproductive Physiology Program, The University of Wisconsin, Madison, WI 53715, United States; Division of Neonatology& Newborn Nursery, The University of Wisconsin, Madison, WI 53715, United States; Departments of Pediatrics, The University of Wisconsin, Madison, WI 53715, United States; The McPherson Eye Research Institute, The University of Wisconsin, Madison, WI 53715, United States
| | - Michelle A Chiu
- Division of Neonatology& Newborn Nursery, The University of Wisconsin, Madison, WI 53715, United States; Departments of Pediatrics, The University of Wisconsin, Madison, WI 53715, United States; The McPherson Eye Research Institute, The University of Wisconsin, Madison, WI 53715, United States
| | - Ian M Bird
- Endocrinology-Reproductive Physiology Program, The University of Wisconsin, Madison, WI 53715, United States; Obstetrics & Gynecology, The University of Wisconsin, Madison, WI 53715, United States
| | - De-Ann M Pillers
- Division of Neonatology& Newborn Nursery, The University of Wisconsin, Madison, WI 53715, United States; Departments of Pediatrics, The University of Wisconsin, Madison, WI 53715, United States; Medical Genetics, The University of Wisconsin, Madison, WI 53715, United States; The McPherson Eye Research Institute, The University of Wisconsin, Madison, WI 53715, United States
| | - Bikash R Pattnaik
- Endocrinology-Reproductive Physiology Program, The University of Wisconsin, Madison, WI 53715, United States; Division of Neonatology& Newborn Nursery, The University of Wisconsin, Madison, WI 53715, United States; Departments of Pediatrics, The University of Wisconsin, Madison, WI 53715, United States; Ophthalmology &Visual Sciences, The University of Wisconsin, Madison, WI 53715, United States; The McPherson Eye Research Institute, The University of Wisconsin, Madison, WI 53715, United States.
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15
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Kirchner MK, Foehring RC, Wang L, Chandaka GK, Callaway JC, Armstrong WE. Phosphatidylinositol 4,5-bisphosphate (PIP 2 ) modulates afterhyperpolarizations in oxytocin neurons of the supraoptic nucleus. J Physiol 2017; 595:4927-4946. [PMID: 28383826 DOI: 10.1113/jp274219] [Citation(s) in RCA: 7] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/21/2017] [Accepted: 04/04/2017] [Indexed: 01/19/2023] Open
Abstract
KEY POINTS Afterhyperpolarizations (AHPs) generated by repetitive action potentials in supraoptic magnocellular neurons regulate repetitive firing and spike frequency adaptation but relatively little is known about PIP2 's control of these AHPs. We examined how changes in PIP2 levels affected AHPs, somatic [Ca2+ ]i , and whole cell Ca2+ currents. Manipulations of PIP2 levels affected both medium and slow AHP currents in oxytocin (OT) neurons of the supraoptic nucleus. Manipulations of PIP2 levels did not modulate AHPs by influencing Ca2+ release from IP3 -triggered Ca2+ stores, suggesting more direct modulation of channels by PIP2 . PIP2 depletion reduced spike-evoked Ca2+ entry and voltage-gated Ca2+ currents. PIP2 appears to influence AHPs in OT neurons by reducing Ca2+ influx during spiking. ABSTRACT Oxytocin (OT)- and vasopressin (VP)-secreting magnocellular neurons of the supraoptic nucleus (SON) display calcium-dependent afterhyperpolarizations (AHPs) following a train of action potentials that are critical to shaping the firing patterns of these cells. Previous work demonstrated that the lipid phosphatidylinositol 4,5-bisphosphate (PIP2 ) enabled the slow AHP component (sAHP) in cortical pyramidal neurons. We investigated whether this phenomenon occurred in OT and VP neurons of the SON. Using whole cell recordings in coronal hypothalamic slices from adult female rats, we demonstrated that inhibition of PIP2 synthesis with wortmannin robustly blocked both the medium and slow AHP currents (ImAHP and IsAHP ) of OT, but not VP neurons with high affinity. We further tested this by introducing a water-soluble PIP2 analogue (diC8 -PIP2 ) into neurons, which in OT neurons not only prevented wortmannin's inhibitory effect, but slowed rundown of the ImAHP and IsAHP . Inhibition of phospholipase C (PLC) with U73122 did not inhibit either ImAHP or IsAHP in OT neurons, consistent with wortmannin's effects not being due to reducing diacylglycerol (DAG) or IP3 availability, i.e. PIP2 modulation of AHPs is not likely to involve downstream Ca2+ release from inositol 1,4,5-trisphosphate (IP3 )-triggered Ca2+ -store release, or channel modulation via DAG and protein kinase C (PKC). We found that wortmannin reduced [Ca2+ ]i increase induced by spike trains in OT neurons, but had no effect on AHPs evoked by uncaging intracellular Ca2+ . Finally, wortmannin selectively reduced whole cell Ca2+ currents in OT neurons while leaving VP neurons unaffected. The results indicate that PIP2 modulates both the ImAHP and IsAHP in OT neurons, most likely by controlling Ca2+ entry through voltage-gated Ca2+ channels opened during spike trains.
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Affiliation(s)
- Matthew K Kirchner
- Department of Anatomy and Neurobiology and Neuroscience Institute, University of Tennessee Health Science Center, Memphis, TN, USA
| | - Robert C Foehring
- Department of Anatomy and Neurobiology and Neuroscience Institute, University of Tennessee Health Science Center, Memphis, TN, USA
| | - Lie Wang
- Department of Anatomy and Neurobiology and Neuroscience Institute, University of Tennessee Health Science Center, Memphis, TN, USA
| | - Giri Kumar Chandaka
- Department of Anatomy and Neurobiology and Neuroscience Institute, University of Tennessee Health Science Center, Memphis, TN, USA
| | - Joseph C Callaway
- Department of Anatomy and Neurobiology and Neuroscience Institute, University of Tennessee Health Science Center, Memphis, TN, USA
| | - William E Armstrong
- Department of Anatomy and Neurobiology and Neuroscience Institute, University of Tennessee Health Science Center, Memphis, TN, USA
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16
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Wang S, Borschel WF, Heyman S, Hsu P, Nichols CG. Conformational changes at cytoplasmic intersubunit interactions control Kir channel gating. J Biol Chem 2017; 292:10087-10096. [PMID: 28446610 DOI: 10.1074/jbc.m117.785154] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/10/2017] [Revised: 04/17/2017] [Indexed: 02/02/2023] Open
Abstract
The defining structural feature of inward-rectifier potassium (Kir) channels is the unique Kir cytoplasmic domain. Recently we showed that salt bridges located at the cytoplasmic domain subunit interfaces (CD-Is) of eukaryotic Kir channels control channel gating via stability of a novel inactivated closed state. The cytoplasmic domains of prokaryotic and eukaryotic Kir channels show similar conformational rearrangements to the common gating ligand, phosphatidylinositol bisphosphate (PIP2), although these exhibit opposite coupling to opening and closing transitions. In Kir2.1, mutation of one of these CD-I salt bridge residues (R204A) reduces apparent PIP2 sensitivity of channel activity, and here we show that Ala or Cys substitutions of the functionally equivalent residue (Arg-165) in the prokaryotic Kir channel KirBac1.1 also significantly decrease sensitivity of the channel to PIP2 (by 5-30-fold). To further understand the structural basis of CD-I control of Kir channel gating, we examined the effect of the R165A mutation on PIP2-induced changes in channel function and conformation. Single-channel analyses indicated that the R165A mutation disrupts the characteristic long interburst closed state of reconstituted KirBac1.1 in giant liposomes, resulting in a higher open probability due to more frequent opening bursts. Intramolecular FRET measurements indicate that, relative to wild-type channels, the R165A mutation results in splaying of the cytoplasmic domains away from the central axis and that PIP2 essentially induces opposite motions of the major β-sheet in this channel mutant. We conclude that the removal of stabilizing CD-I salt bridges results in a collapsed state of the Kir domain.
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Affiliation(s)
- Shizhen Wang
- From the Department of Cell Biology and Physiology and the Center for the Investigation of Membrane Excitability Diseases, Washington University School of Medicine, St. Louis, Missouri 63110
| | - William F Borschel
- From the Department of Cell Biology and Physiology and the Center for the Investigation of Membrane Excitability Diseases, Washington University School of Medicine, St. Louis, Missouri 63110
| | - Sarah Heyman
- From the Department of Cell Biology and Physiology and the Center for the Investigation of Membrane Excitability Diseases, Washington University School of Medicine, St. Louis, Missouri 63110
| | - Phillip Hsu
- From the Department of Cell Biology and Physiology and the Center for the Investigation of Membrane Excitability Diseases, Washington University School of Medicine, St. Louis, Missouri 63110
| | - Colin G Nichols
- From the Department of Cell Biology and Physiology and the Center for the Investigation of Membrane Excitability Diseases, Washington University School of Medicine, St. Louis, Missouri 63110
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17
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Scherer D, Schworm B, Seyler C, Xynogalos P, Scholz EP, Thomas D, Katus HA, Zitron E. Inhibition of inwardly rectifying Kir2.x channels by the novel anti-cancer agent gambogic acid depends on both pore block and PIP 2 interference. Naunyn Schmiedebergs Arch Pharmacol 2017; 390:701-710. [PMID: 28365825 DOI: 10.1007/s00210-017-1372-5] [Citation(s) in RCA: 7] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/23/2017] [Accepted: 03/23/2017] [Indexed: 12/21/2022]
Abstract
The caged xanthone gambogic acid (GA) is a novel anti-cancer agent which exhibits anti-proliferative, anti-inflammatory and cytotoxic effects in many types of cancer tissues. In a recent phase IIa study, GA exhibits a favourable safety profile. However, limited data are available concerning its interaction with cardiac ion channels. Heteromeric assembly of Kir2.x channels underlies the cardiac inwardly rectifying IK1 current which is responsible for the stabilization of the diastolic resting membrane potential. Inhibition of the cardiac IK1 current may lead to ventricular arrhythmia due to delayed afterdepolarizations. Compared to Kv2.1, hERG and Kir1.1, a slow, delayed inhibition of Kir2.1 channels by GA in a mammalian cell line was reported before but no data exist in literature concerning action of GA on homomeric Kir2.2 and Kir2.3 and heteromeric Kir2.x channels. Therefore, the aim of this study was to provide comparative data on the effect of GA on homomeric and heteromeric Kir2.x channels. Homomeric and heteromeric Kir2.x channels were heterologously expressed in Xenopus oocytes, and the two-microelectrode voltage-clamp technique was used to record Kir2.x currents. To investigate the mechanism of the channel inhibition by GA, alanine-mutated Kir2.x channels with modifications in the channels pore region or at phosphatidylinositol 4,5-bisphosphate (PIP2)-binding sites were employed. GA caused a slow inhibition of homomeric and heteromeric Kir2.x channels at low micromolar concentrations (with IC50 Kir2.1/2.2 < Kir2.2 < Kir2.2/2.3 < Kir2.3 < Kir2.1 < Kir2.1/2.3). The effect did not reach saturation within 60 min and was not reversible upon washout for 30 min. The inhibition showed no strong voltage dependence. We provide evidence for a combination of direct channel pore blockade and a PIP2-dependent mechanism as a molecular basis for the observed effect. We conclude that Kir2.x channel inhibition by GA may be relevant in patients with pre-existing cardiac disorders such as chronic heart failure or certain rhythm disorders and recommend a close cardiac monitoring for those patients when treated with GA.
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Affiliation(s)
- Daniel Scherer
- Department of Cardiology, Medical University Hospital Heidelberg, Im Neuenheimer Feld 410, D-69120, Heidelberg, Germany.
| | - Benedikt Schworm
- Department of Cardiology, Medical University Hospital Heidelberg, Im Neuenheimer Feld 410, D-69120, Heidelberg, Germany
| | - Claudia Seyler
- Department of Cardiology, Medical University Hospital Heidelberg, Im Neuenheimer Feld 410, D-69120, Heidelberg, Germany.,DZHK (German Centre for Cardiovascular Research), partner site Heidelberg/Mannheim, Heidelberg, Germany
| | - Panagiotis Xynogalos
- Department of Cardiology, Medical University Hospital Heidelberg, Im Neuenheimer Feld 410, D-69120, Heidelberg, Germany
| | - Eberhard P Scholz
- Department of Cardiology, Medical University Hospital Heidelberg, Im Neuenheimer Feld 410, D-69120, Heidelberg, Germany
| | - Dierk Thomas
- Department of Cardiology, Medical University Hospital Heidelberg, Im Neuenheimer Feld 410, D-69120, Heidelberg, Germany.,DZHK (German Centre for Cardiovascular Research), partner site Heidelberg/Mannheim, Heidelberg, Germany
| | - Hugo A Katus
- Department of Cardiology, Medical University Hospital Heidelberg, Im Neuenheimer Feld 410, D-69120, Heidelberg, Germany.,DZHK (German Centre for Cardiovascular Research), partner site Heidelberg/Mannheim, Heidelberg, Germany
| | - Edgar Zitron
- Department of Cardiology, Medical University Hospital Heidelberg, Im Neuenheimer Feld 410, D-69120, Heidelberg, Germany.,DZHK (German Centre for Cardiovascular Research), partner site Heidelberg/Mannheim, Heidelberg, Germany
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18
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Synergistic activation of G protein-gated inwardly rectifying potassium channels by cholesterol and PI(4,5)P 2. BIOCHIMICA ET BIOPHYSICA ACTA-BIOMEMBRANES 2017; 1859:1233-1241. [PMID: 28377218 DOI: 10.1016/j.bbamem.2017.03.023] [Citation(s) in RCA: 14] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Received: 12/19/2016] [Revised: 03/16/2017] [Accepted: 03/31/2017] [Indexed: 11/23/2022]
Abstract
G-protein gated inwardly rectifying potassium (GIRK or Kir3) channels play a major role in the control of the heart rate, and require the membrane phospholipid phosphatidylinositol-bis-phosphate (PI(4,5)P2) for activation. Recently, we have shown that the activity of the heterotetrameric Kir3.1/Kir3.4 channel that underlies atrial KACh currents was enhanced by cholesterol. Similarly, the activities of both the Kir3.4 homomer and its active pore mutant Kir3.4* (Kir3.4_S143T) were also enhanced by cholesterol. Here we employ planar lipid bilayers to investigate the crosstalk between PI(4,5)P2 and cholesterol, and demonstrate that these two lipids act synergistically to activate Kir3.4* currents. Further studies using the Xenopus oocytes heterologous expression system suggest that PI(4,5)P2 and cholesterol act via distinct binding sites. Whereas PI(4,5)P2 binds to the cytosolic domain of the channel, the putative binding region of cholesterol is located at the center of the transmembrane domain overlapping the central glycine hinge region of the channel. Together, our data suggest that changes in the levels of two key membrane lipids - cholesterol and PI(4,5)P2 - could act in concert to provide fine-tuning of Kir3 channel function.
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19
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Koepple C, Scherer D, Seyler C, Scholz E, Thomas D, Katus HA, Zitron E. Dual Mechanism for Inhibition of Inwardly Rectifying Kir2.x Channels by Quinidine Involving Direct Pore Block and PIP 2-interference. J Pharmacol Exp Ther 2017; 361:209-218. [PMID: 28188270 DOI: 10.1124/jpet.116.238287] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/13/2016] [Accepted: 02/08/2017] [Indexed: 11/22/2022] Open
Abstract
Class IA antiarrhythmic drug quinidine was one of the first clinically used compounds to terminate atrial fibrillation and acts as multichannel inhibitor with well-documented inhibitory effects on several cardiac potassium channels. In the mammalian heart, heteromeric assembly of Kir2.1-2.3 channels underlies IK1 current. Although a low-affinity block of quinidine on Kir2.1 has already been described, a comparative analysis of effects on other Kir2.x channels has not been performed to date. Therefore, we analyzed the effects of quinidine on wild-type and mutant Kir2.x channels in the Xenopus oocyte expression system. Quinidine exerted differential inhibitory effects on Kir2.x channels with the highest affinity toward Kir2.3 subunits. Onset of block was slow and solely reversible in Kir2.2 subunits. Quinidine inhibited Kir2.x currents in a voltage-independent manner. By means of comparative Ala-scanning mutagenesis, we further found that residues E224, F254, D259, and E299 are essential for quinidine block in Kir2.1 subunits. Analogously, quinidine mediated Kir2.3 inhibition by binding corresponding residues E216, D247, D251, and E291. In contrast, Kir2.2 current block merely involved corresponding residue D260. Using channel mutants with altered (phosphatidylinositol 4,5-bisphosphate PIP2) affinities, we were able to demonstrate that high PIP2 affinities (i.e., Kir2.3 I214L) correlate with low quinidine sensitivity. Inversely, mutant channels interacting only weakly with PIP2 (i.e., Kir2.1 K182Q, and L221I) are prone to a higher inhibitory effect. Thus, we conclude that inhibition of Kir2.x channels by quinidine is mediated by joint modes of action involving direct cytoplasmic pore block and an impaired channel stabilization via interference with PIP2.
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Affiliation(s)
- Christoph Koepple
- Department of Cardiology, Medical University Hospital Heidelberg, Heidelberg, Germany (C.K., D.S., C.S., E.S., D.T., H.A.K., E.Z.); DZHK (German Centre for Cardiovascular Research), partner site Heidelberg/Mannheim, University of Heidelberg, Heidelberg, Germany (C.S., E.S., D.T., H.A.K., E.Z.); and Department for Hand-, Plastic- and Reconstructive Surgery, BG Unfallklinik Ludwigshafen, University of Heidelberg, Heidelberg, Germany (C.K.)
| | - Daniel Scherer
- Department of Cardiology, Medical University Hospital Heidelberg, Heidelberg, Germany (C.K., D.S., C.S., E.S., D.T., H.A.K., E.Z.); DZHK (German Centre for Cardiovascular Research), partner site Heidelberg/Mannheim, University of Heidelberg, Heidelberg, Germany (C.S., E.S., D.T., H.A.K., E.Z.); and Department for Hand-, Plastic- and Reconstructive Surgery, BG Unfallklinik Ludwigshafen, University of Heidelberg, Heidelberg, Germany (C.K.)
| | - Claudia Seyler
- Department of Cardiology, Medical University Hospital Heidelberg, Heidelberg, Germany (C.K., D.S., C.S., E.S., D.T., H.A.K., E.Z.); DZHK (German Centre for Cardiovascular Research), partner site Heidelberg/Mannheim, University of Heidelberg, Heidelberg, Germany (C.S., E.S., D.T., H.A.K., E.Z.); and Department for Hand-, Plastic- and Reconstructive Surgery, BG Unfallklinik Ludwigshafen, University of Heidelberg, Heidelberg, Germany (C.K.)
| | - Eberhard Scholz
- Department of Cardiology, Medical University Hospital Heidelberg, Heidelberg, Germany (C.K., D.S., C.S., E.S., D.T., H.A.K., E.Z.); DZHK (German Centre for Cardiovascular Research), partner site Heidelberg/Mannheim, University of Heidelberg, Heidelberg, Germany (C.S., E.S., D.T., H.A.K., E.Z.); and Department for Hand-, Plastic- and Reconstructive Surgery, BG Unfallklinik Ludwigshafen, University of Heidelberg, Heidelberg, Germany (C.K.)
| | - Dierk Thomas
- Department of Cardiology, Medical University Hospital Heidelberg, Heidelberg, Germany (C.K., D.S., C.S., E.S., D.T., H.A.K., E.Z.); DZHK (German Centre for Cardiovascular Research), partner site Heidelberg/Mannheim, University of Heidelberg, Heidelberg, Germany (C.S., E.S., D.T., H.A.K., E.Z.); and Department for Hand-, Plastic- and Reconstructive Surgery, BG Unfallklinik Ludwigshafen, University of Heidelberg, Heidelberg, Germany (C.K.)
| | - Hugo A Katus
- Department of Cardiology, Medical University Hospital Heidelberg, Heidelberg, Germany (C.K., D.S., C.S., E.S., D.T., H.A.K., E.Z.); DZHK (German Centre for Cardiovascular Research), partner site Heidelberg/Mannheim, University of Heidelberg, Heidelberg, Germany (C.S., E.S., D.T., H.A.K., E.Z.); and Department for Hand-, Plastic- and Reconstructive Surgery, BG Unfallklinik Ludwigshafen, University of Heidelberg, Heidelberg, Germany (C.K.)
| | - Edgar Zitron
- Department of Cardiology, Medical University Hospital Heidelberg, Heidelberg, Germany (C.K., D.S., C.S., E.S., D.T., H.A.K., E.Z.); DZHK (German Centre for Cardiovascular Research), partner site Heidelberg/Mannheim, University of Heidelberg, Heidelberg, Germany (C.S., E.S., D.T., H.A.K., E.Z.); and Department for Hand-, Plastic- and Reconstructive Surgery, BG Unfallklinik Ludwigshafen, University of Heidelberg, Heidelberg, Germany (C.K.)
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20
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Meng XY, Liu S, Cui M, Zhou R, Logothetis DE. The Molecular Mechanism of Opening the Helix Bundle Crossing (HBC) Gate of a Kir Channel. Sci Rep 2016; 6:29399. [PMID: 27439597 PMCID: PMC4954981 DOI: 10.1038/srep29399] [Citation(s) in RCA: 22] [Impact Index Per Article: 2.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/15/2015] [Accepted: 06/20/2016] [Indexed: 11/19/2022] Open
Abstract
Inwardly rectifying K+ (Kir) channels, serving as natural molecular nanomachines, transport potassium ions across the plasma membrane of the cell. Along the ion permeation pathway, three relatively narrow regions (the selectivity filter (SF), the inner helix bundle crossing (HBC), and the cytosolic G loop) may serve as gates to control ion permeation. Our previous molecular dynamics simulations based on the crystal structure of a Kir3.1 chimera revealed the possible gating mechanism of the G loop gate. Here, we introduced a proline mutation in the inner helix and obtained a channel model of the open HBC gate. The open HBC gate reaches 0.6 nm in diameter, which allows partial hydrated K+ ions to pass through. During the gating process, both the transmembrane helices TM1 and TM2 cooperatively rotate in a counterclockwise direction (viewed from the extracellular side) with the aid of the phospholipid PIP2. Only when all the transmembrane helices adopt a counterclockwise rotation, the HBC gate can be stabilized in the open state. We estimate that introduction of the proline mutation decreases the energy required to open the HBC gate by about 1.4 kcal/mol (ΔΔG).
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Affiliation(s)
- Xuan-Yu Meng
- Institute of Quantitative Biology and Medicine, SRMP and RAD-X, Collaborative Innovation Center of Radiation Medicine of Jiangsu Higher Education Institutions, Soochow University, Suzhou 215123, China.,Department of Physiology and Biophysics, Virginia Commonwealth University, School of Medicine, Richmond, Virginia
| | - Shengtang Liu
- Institute of Quantitative Biology and Medicine, SRMP and RAD-X, Collaborative Innovation Center of Radiation Medicine of Jiangsu Higher Education Institutions, Soochow University, Suzhou 215123, China
| | - Meng Cui
- Department of Physiology and Biophysics, Virginia Commonwealth University, School of Medicine, Richmond, Virginia
| | - Ruhong Zhou
- Institute of Quantitative Biology and Medicine, SRMP and RAD-X, Collaborative Innovation Center of Radiation Medicine of Jiangsu Higher Education Institutions, Soochow University, Suzhou 215123, China.,IBM Thomas J. Watson Research Center, Yorktown Heights, NY 10598, USA.,Department of Chemistry, Columbia University, New York, NY 10027, USA
| | - Diomedes E Logothetis
- Department of Physiology and Biophysics, Virginia Commonwealth University, School of Medicine, Richmond, Virginia
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21
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Lee CH, Huang PT, Liou HH, Lin MY, Lou KL, Chen CY. Non-basic amino acids in the ROMK1 channels via an appropriate distance modulate PIP2 regulated pHi-gating. Biochem Biophys Res Commun 2016; 473:303-310. [PMID: 27016482 DOI: 10.1016/j.bbrc.2016.03.100] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/12/2016] [Accepted: 03/21/2016] [Indexed: 12/11/2022]
Abstract
The ROMK1 (Kir1.1) channel activity is predominantly regulated by intracellular pH (pHi) and phosphatidylinositol 4,5-bisphosphate (PIP2). Although several residues were reported to be involved in the regulation of pHi associated with PIP2 interaction, the detailed molecular mechanism remains unclear. We perform experiments in ROMK1 pHi-gating with electrophysiology combined with mutational and structural analysis. In the present study, non basic residues of C-terminal region (S219, N215, I192, L216 and L220) in ROMK1 channels have been found to mediate channel-PIP2 interaction and pHi gating. Further, our structural results show these residues with an appropriate distance to interact with membrane PIP2. Meanwhile, a cluster of basic residues (R188, R217 and K218), which was previously discovered regarding the interaction with PIP2, exists in this appropriate distance to discriminate the regulation of channel-PIP2 interaction and pHi-gating. This appropriate distance can be observed with high conservation in the Kir channel family. Our results provide insight that an appropriate distance cooperates with the electrostatics interaction of channel-PIP2 to regulate pHi-gating.
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Affiliation(s)
- Chien-Hsing Lee
- Institute of Pharmacology, College of Medicine, National Taiwan University, Taipei, 10051, Taiwan; Department of Nursing, Min-Hwei Junior College of Health Care Management, Tainan, 73658, Taiwan
| | - Po-Tsang Huang
- Institutes of Biochemistry and Molecular Biology, College of Medicine, National Taiwan University, Taipei, 10051, Taiwan; Graduate Institutes of Oral Biology, Medical College, National Taiwan University, Taipei, 10048, Taiwan
| | - Horng-Huei Liou
- Institute of Pharmacology, College of Medicine, National Taiwan University, Taipei, 10051, Taiwan; Divisions of Neurology, National Taiwan University Hospital, Taipei, 10002, Taiwan
| | - Mei-Ying Lin
- Cancer Center, Kaohsiung Medical University Hospital, Kaohsiung, 80708, Taiwan
| | - Kuo-Long Lou
- Institutes of Biochemistry and Molecular Biology, College of Medicine, National Taiwan University, Taipei, 10051, Taiwan; Graduate Institutes of Oral Biology, Medical College, National Taiwan University, Taipei, 10048, Taiwan; NTU-DRCP Lectures and Core for Membrane Proteins, Center for Biotechnology, National Taiwan University, Taipei, 10672, Taiwan.
| | - Chung-Yi Chen
- School of Medical and Health Sciences, Fooyin University, No.151, Jinxue Rd., Daliao Dist., Kaohsiung City, 83102, Taiwan.
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22
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The ICl,swell inhibitor DCPIB blocks Kir channels that possess weak affinity for PIP2. Pflugers Arch 2016; 468:817-24. [PMID: 26837888 DOI: 10.1007/s00424-016-1794-9] [Citation(s) in RCA: 13] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/23/2015] [Revised: 01/17/2016] [Accepted: 01/20/2016] [Indexed: 12/15/2022]
Abstract
Inwardly rectifying K(+) (Kir) channels are important contributors to the resting membrane potential and regulate cellular excitability. The activity of Kir channels depends critically on the phospholipid PIP2. Several modulators of the activity of Kir channels alter the apparent affinity of the channel to PIP2. Channels with high apparent affinity to PIP2 may not respond to a given modulator, but mutations that decrease such affinity can render the channel susceptible to modulation. Here, we identify a known inhibitor of the swelling-activated Cl(-) current, DCPIB, as an effective inhibitor of a number of Kir channels both in native cardiac cells and in heterologous expression systems. We show that the apparent affinity to PIP2 determines whether DCPIB will serve as an efficient blocker of Kir channels. These effects are consistent with a model in which DCPIB competes with PIP2 for a common binding site.
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23
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Wang S, Vafabakhsh R, Borschel WF, Ha T, Nichols CG. Structural dynamics of potassium-channel gating revealed by single-molecule FRET. Nat Struct Mol Biol 2015; 23:31-36. [PMID: 26641713 PMCID: PMC4833211 DOI: 10.1038/nsmb.3138] [Citation(s) in RCA: 59] [Impact Index Per Article: 6.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/11/2015] [Accepted: 11/06/2015] [Indexed: 01/06/2023]
Abstract
Crystallography has provided invaluable insights to ion channel selectivity and gating, but to advance understanding to a new level, dynamic views of channel structures within membranes are essential. We labeled tetrameric KirBac1.1 potassium channels with single donor and acceptor fluorophores at different sites, and examined structural dynamics within lipid membranes by single molecule FRET. We found that the extracellular region is structurally rigid in both closed and open states, whereas the N-terminal slide helix undergoes marked conformational fluctuations. The cytoplasmic C-terminal domain fluctuates between two major structural states both of which become less dynamic and move away from the pore axis and away from the membrane in closed channels. Our results reveal mobile and rigid conformations of functionally relevant KirBac1.1 channel motifs, implying similar dynamics for similar motifs in eukaryotic Kir channels and for cation channels in general.
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Affiliation(s)
- Shizhen Wang
- Center for Investigation of Membrane Excitability Diseases, Department of Cell Biology and Physiology, Washington University School of Medicine, St. Louis MO
| | - Reza Vafabakhsh
- Department of Physics and the Center for the Physics of Living Cells, University of Illinois at Urbana-Champaign, Urbana, IL
| | - William F Borschel
- Center for Investigation of Membrane Excitability Diseases, Department of Cell Biology and Physiology, Washington University School of Medicine, St. Louis MO
| | - Taekjip Ha
- Department of Physics and the Center for the Physics of Living Cells, University of Illinois at Urbana-Champaign, Urbana, IL.,Howard Hughes Medical Institute, Baltimore, MD.,Department of Biophysics and Biophysical Chemistry, Department of Biophysics, Department of Biomedical Engineering, Baltimore, MD
| | - Colin G Nichols
- Center for Investigation of Membrane Excitability Diseases, Department of Cell Biology and Physiology, Washington University School of Medicine, St. Louis MO
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Yakubovich D, Berlin S, Kahanovitch U, Rubinstein M, Farhy-Tselnicker I, Styr B, Keren-Raifman T, Dessauer CW, Dascal N. A Quantitative Model of the GIRK1/2 Channel Reveals That Its Basal and Evoked Activities Are Controlled by Unequal Stoichiometry of Gα and Gβγ. PLoS Comput Biol 2015; 11:e1004598. [PMID: 26544551 PMCID: PMC4636287 DOI: 10.1371/journal.pcbi.1004598] [Citation(s) in RCA: 14] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/27/2015] [Accepted: 10/13/2015] [Indexed: 12/02/2022] Open
Abstract
G protein-gated K+ channels (GIRK; Kir3), activated by Gβγ subunits derived from Gi/o proteins, regulate heartbeat and neuronal excitability and plasticity. Both neurotransmitter-evoked (Ievoked) and neurotransmitter-independent basal (Ibasal) GIRK activities are physiologically important, but mechanisms of Ibasal and its relation to Ievoked are unclear. We have previously shown for heterologously expressed neuronal GIRK1/2, and now show for native GIRK in hippocampal neurons, that Ibasal and Ievoked are interrelated: the extent of activation by neurotransmitter (activation index, Ra) is inversely related to Ibasal. To unveil the underlying mechanisms, we have developed a quantitative model of GIRK1/2 function. We characterized single-channel and macroscopic GIRK1/2 currents, and surface densities of GIRK1/2 and Gβγ expressed in Xenopus oocytes. Based on experimental results, we constructed a mathematical model of GIRK1/2 activity under steady-state conditions before and after activation by neurotransmitter. Our model accurately recapitulates Ibasal and Ievoked in Xenopus oocytes, HEK293 cells and hippocampal neurons; correctly predicts the dose-dependent activation of GIRK1/2 by coexpressed Gβγ and fully accounts for the inverse Ibasal-Ra correlation. Modeling indicates that, under all conditions and at different channel expression levels, between 3 and 4 Gβγ dimers are available for each GIRK1/2 channel. In contrast, available Gαi/o decreases from ~2 to less than one Gα per channel as GIRK1/2's density increases. The persistent Gβγ/channel (but not Gα/channel) ratio support a strong association of GIRK1/2 with Gβγ, consistent with recruitment to the cell surface of Gβγ, but not Gα, by GIRK1/2. Our analysis suggests a maximal stoichiometry of 4 Gβγ but only 2 Gαi/o per one GIRK1/2 channel. The unique, unequal association of GIRK1/2 with G protein subunits, and the cooperative nature of GIRK gating by Gβγ, underlie the complex pattern of basal and agonist-evoked activities and allow GIRK1/2 to act as a sensitive bidirectional detector of both Gβγ and Gα. Many neurotransmitters and hormones inhibit the electric activity of excitable cells (such as cardiac cells and neurons) by activating a K+ channel, GIRK (G protein-gated Inwardly Rectifying K+ channel). GIRK channels also possess constitutive “basal” activity which contributes to regulation of neuronal and cardiac excitability and certain disorders, but the mechanism of this activity and its interrelation with the neurotransmitter-evoked activity are poorly understood. In this work we show that key features of basal and neurotransmitter-evoked activities are similar in cultured hippocampal neurons and in two model systems (mammalian HEK293 cells and Xenopus oocytes). Using experimental data of the neuronal GIRK1/2 channel function upon changes in GIRK and G protein concentrations, we constructed a mathematical model that quantitatively accounts for basal and evoked activity, and for the inverse correlation between the two. Our analysis suggests a novel and unexpected mechanism of interaction of GIRK1/2 with the G protein subunits, where the tetrameric GIRK channel can assemble with 4 molecules of the Gβγ subunits but only 2 molecules of Gα. GIRK is a prototypical effector of Gβγ, and the unequal stoichiometry of interaction with G protein subunits may have general implications for G protein signaling.
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Affiliation(s)
- Daniel Yakubovich
- Department of Physiology and Pharmacology and Sagol School of Neuroscience, Tel Aviv University, Tel Aviv, Israel
| | - Shai Berlin
- Department of Physiology and Pharmacology and Sagol School of Neuroscience, Tel Aviv University, Tel Aviv, Israel
| | - Uri Kahanovitch
- Department of Physiology and Pharmacology and Sagol School of Neuroscience, Tel Aviv University, Tel Aviv, Israel
| | - Moran Rubinstein
- Department of Physiology and Pharmacology and Sagol School of Neuroscience, Tel Aviv University, Tel Aviv, Israel
| | - Isabella Farhy-Tselnicker
- Department of Physiology and Pharmacology and Sagol School of Neuroscience, Tel Aviv University, Tel Aviv, Israel
| | - Boaz Styr
- Department of Physiology and Pharmacology and Sagol School of Neuroscience, Tel Aviv University, Tel Aviv, Israel
| | - Tal Keren-Raifman
- Department of Physiology and Pharmacology and Sagol School of Neuroscience, Tel Aviv University, Tel Aviv, Israel
| | - Carmen W. Dessauer
- Department of Integrative Biology and Pharmacology, University of Texas Health Science Center, Houston, Texas, United States of America
| | - Nathan Dascal
- Department of Physiology and Pharmacology and Sagol School of Neuroscience, Tel Aviv University, Tel Aviv, Israel
- * E-mail:
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Bukiya AN, Osborn CV, Kuntamallappanavar G, Toth PT, Baki L, Kowalsky G, Oh MJ, Dopico AM, Levitan I, Rosenhouse-Dantsker A. Cholesterol increases the open probability of cardiac KACh currents. BIOCHIMICA ET BIOPHYSICA ACTA-BIOMEMBRANES 2015. [DOI: 10.1016/j.bbamem.2015.07.007] [Citation(s) in RCA: 11] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 01/19/2023]
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Rjasanow A, Leitner MG, Thallmair V, Halaszovich CR, Oliver D. Ion channel regulation by phosphoinositides analyzed with VSPs-PI(4,5)P2 affinity, phosphoinositide selectivity, and PI(4,5)P2 pool accessibility. Front Pharmacol 2015; 6:127. [PMID: 26150791 PMCID: PMC4472987 DOI: 10.3389/fphar.2015.00127] [Citation(s) in RCA: 24] [Impact Index Per Article: 2.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/27/2015] [Accepted: 06/05/2015] [Indexed: 11/13/2022] Open
Abstract
The activity of many proteins depends on the phosphoinositide (PI) content of the membrane. E.g., dynamic changes of the concentration of PI(4,5)P2 are cellular signals that regulate ion channels. The susceptibility of a channel to such dynamics depends on its affinity for PI(4,5)P2. Yet, measuring affinities for endogenous PIs has not been possible directly, but has relied largely on the response to soluble analogs, which may not quantitatively reflect binding to native lipids. Voltage-sensitive phosphatases (VSPs) turn over PI(4,5)P2 to PI(4)P when activated by depolarization. In combination with voltage-clamp electrophysiology VSPs are useful tools for rapid and reversible depletion of PI(4,5)P2. Because cellular PI(4,5)P2 is resynthesized rapidly, steady state PI(4,5)P2 changes with the degree of VSP activation and thus depends on membrane potential. Here we show that titration of endogenous PI(4,5)P2 with Ci-VSP allows for the quantification of relative PI(4,5)P2 affinities of ion channels. The sensitivity of inward rectifier and voltage-gated K+ channels to Ci-VSP allowed for comparison of PI(4,5)P2 affinities within and across channel subfamilies and detected changes of affinity in mutant channels. The results also reveal that VSPs are useful only for PI effectors with high binding specificity among PI isoforms, because PI(4,5)P2 depletion occurs at constant overall PI level. Thus, Kir6.2, a channel activated by PI(4,5)P2 and PI(4)P was insensitive to VSP. Surprisingly, despite comparable PI(4,5)P2 affinity as determined by Ci-VSP, the Kv7 and Kir channel families strongly differed in their sensitivity to receptor-mediated depletion of PI(4,5)P2. While Kv7 members were highly sensitive to activation of PLC by Gq-coupled receptors, Kir channels were insensitive even when PI(4,5)P2 affinity was lowered by mutation. We hypothesize that different channels may be associated with distinct pools of PI(4,5)P2 that differ in their accessibility to PLC and VSPs.
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Affiliation(s)
- Alexandra Rjasanow
- Department of Neurophysiology, Institute of Physiology and Pathophysiology, Philipps University Marburg, Germany ; Institute of Physiology, University of Freiburg Freiburg, Germany
| | - Michael G Leitner
- Department of Neurophysiology, Institute of Physiology and Pathophysiology, Philipps University Marburg, Germany
| | - Veronika Thallmair
- Department of Neurophysiology, Institute of Physiology and Pathophysiology, Philipps University Marburg, Germany
| | - Christian R Halaszovich
- Department of Neurophysiology, Institute of Physiology and Pathophysiology, Philipps University Marburg, Germany
| | - Dominik Oliver
- Department of Neurophysiology, Institute of Physiology and Pathophysiology, Philipps University Marburg, Germany
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Identification of the Conformational transition pathway in PIP2 Opening Kir Channels. Sci Rep 2015; 5:11289. [PMID: 26063437 PMCID: PMC4462750 DOI: 10.1038/srep11289] [Citation(s) in RCA: 20] [Impact Index Per Article: 2.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/20/2014] [Accepted: 04/29/2015] [Indexed: 11/08/2022] Open
Abstract
The gating of Kir channels depends critically on phosphatidylinositol 4,5-bisphosphate (PIP2), but the detailed mechanism by which PIP2 regulates Kir channels remains obscure. Here, we performed a series of Targeted molecular dynamics simulations on the full-length Kir2.1 channel and, for the first time, were able to achieve the transition from the closed to the open state. Our data show that with the upward motion of the cytoplasmic domain (CTD) the structure of the C-Linker changes from a loop to a helix. The twisting of the C-linker triggers the rotation of the CTD, which induces a small downward movement of the CTD and an upward motion of the slide helix toward the membrane that pulls the inner helix gate open. At the same time, the rotation of the CTD breaks the interaction between the CD- and G-loops thus releasing the G-loop. The G-loop then bounces away from the CD-loop, which leads to the opening of the G-loop gate and the full opening of the pore. We identified a series of interaction networks, between the N-terminus, CD loop, C linker and G loop one by one, which exquisitely regulates the global conformational changes during the opening of Kir channels by PIP2.
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Tang QY, Larry T, Hendra K, Yamamoto E, Bell J, Cui M, Logothetis DE, Boland LM. Mutations in Nature Conferred a High Affinity Phosphatidylinositol 4,5-Bisphosphate-binding Site in Vertebrate Inwardly Rectifying Potassium Channels. J Biol Chem 2015; 290:16517-29. [PMID: 25957411 DOI: 10.1074/jbc.m115.640409] [Citation(s) in RCA: 12] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/28/2015] [Indexed: 11/06/2022] Open
Abstract
All vertebrate inwardly rectifying potassium (Kir) channels are activated by phosphatidylinositol 4,5-bisphosphate (PIP2) (Logothetis, D. E., Petrou, V. I., Zhang, M., Mahajan, R., Meng, X. Y., Adney, S. K., Cui, M., and Baki, L. (2015) Annu. Rev. Physiol. 77, 81-104; Fürst, O., Mondou, B., and D'Avanzo, N. (2014) Front. Physiol. 4, 404-404). Structural components of a PIP2-binding site are conserved in vertebrate Kir channels but not in distantly related animals such as sponges and sea anemones. To expand our understanding of the structure-function relationships of PIP2 regulation of Kir channels, we studied AqKir, which was cloned from the marine sponge Amphimedon queenslandica, an animal that represents the phylogenetically oldest metazoans. A requirement for PIP2 in the maintenance of AqKir activity was examined in intact oocytes by activation of a co-expressed voltage-sensing phosphatase, application of wortmannin (at micromolar concentrations), and activation of a co-expressed muscarinic acetylcholine receptor. All three mechanisms to reduce the availability of PIP2 resulted in inhibition of AqKir current. However, time-dependent rundown of AqKir currents in inside-out patches could not be re-activated by direct application to the inside membrane surface of water-soluble dioctanoyl PIP2, and the current was incompletely re-activated by the more hydrophobic arachidonyl stearyl PIP2. When we introduced mutations to AqKir to restore two positive charges within the vertebrate PIP2-binding site, both forms of PIP2 strongly re-activated the mutant sponge channels in inside-out patches. Molecular dynamics simulations validate the additional hydrogen bonding potential of the sponge channel mutants. Thus, nature's mutations conferred a high affinity activation of vertebrate Kir channels by PIP2, and this is a more recent evolutionary development than the structures that explain ion channel selectivity and inward rectification.
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Affiliation(s)
- Qiong-Yao Tang
- From the Department of Physiology and Biophysics, Virginia Commonwealth University School of Medicine, Richmond, Virginia 23298, the Jiangsu Province Key Laboratory of Anesthesiology and Jiangsu Province Key Laboratory of Anesthesia and Analgesia Application Technology, XuZhou Medical College, Xuzhou, 221004 Jiangsu Province, China
| | - Trevor Larry
- the Department of Biology, University of Richmond, Richmond, Virginia 23173
| | - Kalen Hendra
- the Department of Biology, University of Richmond, Richmond, Virginia 23173
| | - Erica Yamamoto
- the Department of Biology, University of Richmond, Richmond, Virginia 23173
| | - Jessica Bell
- the Department of Chemistry and Biochemistry, University of San Diego, San Diego, California 92110, and
| | - Meng Cui
- From the Department of Physiology and Biophysics, Virginia Commonwealth University School of Medicine, Richmond, Virginia 23298
| | - Diomedes E Logothetis
- From the Department of Physiology and Biophysics, Virginia Commonwealth University School of Medicine, Richmond, Virginia 23298
| | - Linda M Boland
- the Department of Biology, University of Richmond, Richmond, Virginia 23173
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Dascal N, Kahanovitch U. The Roles of Gβγ and Gα in Gating and Regulation of GIRK Channels. INTERNATIONAL REVIEW OF NEUROBIOLOGY 2015; 123:27-85. [DOI: 10.1016/bs.irn.2015.06.001] [Citation(s) in RCA: 43] [Impact Index Per Article: 4.8] [Reference Citation Analysis] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 12/21/2022]
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Sheldon RE, Shmygol A, Van Den Berg HA, Blanks AM. Functional and morphological development of the womb throughout life. Sci Prog 2015; 98:103-27. [PMID: 26288915 PMCID: PMC10365438 DOI: 10.3184/003685015x14308363103415] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/17/2022]
Abstract
The uterus undergoes changes throughout a woman's life, beginning with her own embryonic development when she is still in the womb, commencing a monthly cycle at the onset of adulthood, and undergoing dramatic changes during pregnancy and parturition. The impact of preterm labour and other perinatal health problems is significant, both in human and financial terms; therefore the study of the physiological and regulatory changes which the uterus undergoes can be of enormous potential benefit. Here we briefly review the current state of knowledge, with an emphasis on the importance of changes in connectivity in the uterine smooth muscle cell network and on recent mathematical modelling work aimed at elucidating the role of spatial heterogeneity in this connected network.
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31
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Rusinova R, Kim DM, Nimigean CM, Andersen OS. Regulation of ion channel function by the host lipid bilayer examined by a stopped-flow spectrofluorometric assay. Biophys J 2014; 106:1070-8. [PMID: 24606931 DOI: 10.1016/j.bpj.2014.01.027] [Citation(s) in RCA: 27] [Impact Index Per Article: 2.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/24/2013] [Revised: 01/03/2014] [Accepted: 01/07/2014] [Indexed: 01/16/2023] Open
Abstract
To examine the function of ligand-gated ion channels in a defined membrane environment, we developed a robust sequential-mixing fluorescence-based stopped-flow assay. Channel activity is determined using a channel-permeable quencher (e.g., thallium, Tl(+)) of a water-soluble fluorophore (8-aminonaphthalene-1,3,6-trisulfonic acid) encapsulated in large unilamellar vesicles in which the channel of interest has been reconstituted, which allows for rapid solution changes. To validate the method, we explored the activation of wild-type KcsA channel, as well as it's noninactivating (E71A) KcsA mutant, by extravesicular protons (H(+)). For both channel types, the day-to-day variability in the reconstitution yield (as judged from the time course of fluorescence quenching) is <10%. The activation curve for E71A KcsA is similar to that obtained previously using single-channel electrophysiology, and the activation curves for wild-type and E71A KcsA are indistinguishable, indicating that channel activation and inactivation are separate processes. We then investigated the regulation of KcsA activation by changes in lipid bilayer composition. Increasing the acyl chain length (from C18:1 to C22:1 in diacylphosphatidylcholine), but not the mole fraction of POPG (>0.25) in the bilayer-forming phospholipid mixture, alters KcsA H(+) gating. The bilayer-thickness-dependent shift in the activation curve is suggestive of a decrease in an apparent H(+) affinity and cooperativity. The control over bilayer environment and time resolution makes this method a powerful assay for exploring ligand activation and inactivation of ion channels, and how channel gating varies with changes in the channels' lipid bilayer environment or other regulatory processes.
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Affiliation(s)
- Radda Rusinova
- Department of Physiology and Biophysics, Weill Cornell Medical College, New York, New York; Department of Anesthesiology, Weill Cornell Medical College, New York, New York.
| | - Dorothy M Kim
- Department of Anesthesiology, Weill Cornell Medical College, New York, New York
| | - Crina M Nimigean
- Department of Physiology and Biophysics, Weill Cornell Medical College, New York, New York; Department of Anesthesiology, Weill Cornell Medical College, New York, New York
| | - Olaf S Andersen
- Department of Physiology and Biophysics, Weill Cornell Medical College, New York, New York
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32
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Bista P, Pawlowski M, Cerina M, Ehling P, Leist M, Meuth P, Aissaoui A, Borsotto M, Heurteaux C, Decher N, Pape HC, Oliver D, Meuth SG, Budde T. Differential phospholipase C-dependent modulation of TASK and TREK two-pore domain K+ channels in rat thalamocortical relay neurons. J Physiol 2014; 593:127-44. [PMID: 25556792 DOI: 10.1113/jphysiol.2014.276527] [Citation(s) in RCA: 36] [Impact Index Per Article: 3.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/24/2014] [Accepted: 09/23/2014] [Indexed: 01/10/2023] Open
Abstract
KEY POINTS During the behavioural states of sleep and wakefulness thalamocortical relay neurons fire action potentials in high frequency bursts or tonic sequences, respectively. The modulation of specific K(+) channel types, termed TASK and TREK, allows these neurons to switch between the two modes of activity. In this study we show that the signalling lipids phosphatidylinositol 4,5-bisphosphate (PIP2) and diacylglycerol (DAG), which are components of their membrane environment, switch on and shut off TREK and TASK channels, respectively. These channel modulations contribute to a better understanding of the molecular basis of the effects of neurotransmitters such as ACh which are released by the brainstem arousal system. The present report introduces PIP2 and DAG as new elements of signal transduction in the thalamus. The activity of two-pore domain potassium channels (K2P ) regulates the excitability and firing modes of thalamocortical (TC) neurons. In particular, the inhibition of two-pore domain weakly inwardly rectifying K(+) channel (TWIK)-related acid-sensitive K(+) (TASK) channels and TWIK-related K(+) (TREK) channels, as a consequence of the stimulation of muscarinic ACh receptors (MAChRs) which are coupled to phosphoinositide-specific phospholipase C (PLCβ), induces a shift from burst to tonic firing. By using a whole cell patch-clamp approach, the contribution of the membrane-bound second messenger molecules phosphatidylinositol 4,5-bisphosphate (PIP2 ) and diacylglycerol (DAG) acting downstream of PLCβ was probed. The standing outward current (ISO ) was used to monitor the current through TASK and TREK channels in TC neurons. By exploiting different manoeuvres to change the intracellular PIP2 level in TC neurons, we here show that the scavenging of PIP2 (by neomycin) results in an increased muscarinic effect on ISO whereas increased availability of PIP2 (inclusion to the patch pipette; histone-based carrier) decreased muscarinic signalling. The degree of muscarinic inhibition specifically depends on phosphatidylinositol phosphate (PIP) and PIP2 but no other phospholipids (phosphatidic acid, phosphatidylserine). The use of specific blockers revealed that PIP2 is targeting TREK but not TASK channels. Furthermore, we demonstrate that the inhibition of TASK channels is induced by the application of the DAG analogue 1-oleoyl-2-acetyl-sn-glycerol (OAG). Under current clamp conditions the activation of MAChRs and PLCβ as well as the application of OAG resulted in membrane depolarization, while PIP2 application via histone carrier induced a hyperpolarization. These results demonstrate a differential role of PIP2 and DAG in K2P channel modulation in native neurons which allows a fine-tuned inhibition of TREK (via PIP2 depletion) and TASK (via DAG) channels following MAChR stimulation.
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Affiliation(s)
- Pawan Bista
- Institut für Physiologie I, Westfälische Wilhelms-Universität, Robert-Koch-Straße 27a, D-48149, Münster, Germany
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Itsuki K, Imai Y, Hase H, Okamura Y, Inoue R, Mori MX. PLC-mediated PI(4,5)P2 hydrolysis regulates activation and inactivation of TRPC6/7 channels. ACTA ACUST UNITED AC 2014; 143:183-201. [PMID: 24470487 PMCID: PMC4001779 DOI: 10.1085/jgp.201311033] [Citation(s) in RCA: 56] [Impact Index Per Article: 5.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022]
Abstract
Transient receptor potential classical (or canonical) (TRPC)3, TRPC6, and TRPC7 are a subfamily of TRPC channels activated by diacylglycerol (DAG) produced through the hydrolysis of phosphatidylinositol 4,5-bisphosphate (PI(4,5)P2) by phospholipase C (PLC). PI(4,5)P2 depletion by a heterologously expressed phosphatase inhibits TRPC3, TRPC6, and TRPC7 activity independently of DAG; however, the physiological role of PI(4,5)P2 reduction on channel activity remains unclear. We used Förster resonance energy transfer (FRET) to measure PI(4,5)P2 or DAG dynamics concurrently with TRPC6 or TRPC7 currents after agonist stimulation of receptors that couple to Gq and thereby activate PLC. Measurements made at different levels of receptor activation revealed a correlation between the kinetics of PI(4,5)P2 reduction and those of receptor-operated TRPC6 and TRPC7 current activation and inactivation. In contrast, DAG production correlated with channel activation but not inactivation; moreover, the time course of channel inactivation was unchanged in protein kinase C-insensitive mutants. These results suggest that inactivation of receptor-operated TRPC currents is primarily mediated by the dissociation of PI(4,5)P2. We determined the functional dissociation constant of PI(4,5)P2 to TRPC channels using FRET of the PLCδ Pleckstrin homology domain (PHd), which binds PI(4,5)P2, and used this constant to fit our experimental data to a model in which channel gating is controlled by PI(4,5)P2 and DAG. This model predicted similar FRET dynamics of the PHd to measured FRET in either human embryonic kidney cells or smooth muscle cells, whereas a model lacking PI(4,5)P2 regulation failed to reproduce the experimental data, confirming the inhibitory role of PI(4,5)P2 depletion on TRPC currents. Our model also explains various PLC-dependent characteristics of channel activity, including limitation of maximum open probability, shortening of the peak time, and the bell-shaped response of total current. In conclusion, our studies demonstrate a fundamental role for PI(4,5)P2 in regulating TRPC6 and TRPC7 activity triggered by PLC-coupled receptor stimulation.
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Affiliation(s)
- Kyohei Itsuki
- Department of Physiology, School of Medicine, Fukuoka University, Fukuoka 814-0180, Japan
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34
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Logothetis DE, Petrou VI, Zhang M, Mahajan R, Meng XY, Adney SK, Cui M, Baki L. Phosphoinositide control of membrane protein function: a frontier led by studies on ion channels. Annu Rev Physiol 2014; 77:81-104. [PMID: 25293526 DOI: 10.1146/annurev-physiol-021113-170358] [Citation(s) in RCA: 74] [Impact Index Per Article: 7.4] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/21/2022]
Abstract
Anionic phospholipids are critical constituents of the inner leaflet of the plasma membrane, ensuring appropriate membrane topology of transmembrane proteins. Additionally, in eukaryotes, the negatively charged phosphoinositides serve as key signals not only through their hydrolysis products but also through direct control of transmembrane protein function. Direct phosphoinositide control of the activity of ion channels and transporters has been the most convincing case of the critical importance of phospholipid-protein interactions in the functional control of membrane proteins. Furthermore, second messengers, such as [Ca(2+)]i, or posttranslational modifications, such as phosphorylation, can directly or allosterically fine-tune phospholipid-protein interactions and modulate activity. Recent advances in structure determination of membrane proteins have allowed investigators to obtain complexes of ion channels with phosphoinositides and to use computational and experimental approaches to probe the dynamic mechanisms by which lipid-protein interactions control active and inactive protein states.
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Affiliation(s)
- Diomedes E Logothetis
- Department of Physiology and Biophysics, School of Medicine, Virginia Commonwealth University, Richmond, Virginia 23298-0551;
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35
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Collins MD, Gordon SE. Short-chain phosphoinositide partitioning into plasma membrane models. Biophys J 2014; 105:2485-94. [PMID: 24314079 DOI: 10.1016/j.bpj.2013.09.035] [Citation(s) in RCA: 18] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/29/2013] [Revised: 08/20/2013] [Accepted: 09/23/2013] [Indexed: 10/26/2022] Open
Abstract
Phosphoinositides are vital for many cellular signaling processes, and therefore a number of approaches to manipulating phosphoinositide levels in cells or excised patches of cell membranes have been developed. Among the most common is the use of "short-chain" phosphoinositides, usually dioctanoyl phosphoinositol phosphates. We use isothermal titration calorimetry to determine partitioning of the most abundant phosphoinositol phosphates, PI(4)P and PI(4,5)P2 into models of the intracellular and extracellular facing leaflets of neuronal plasma membranes. We show that phosphoinositide mole fractions in the lipid membrane reach physiological levels at equilibrium with reasonable solution concentrations. Finally we explore the consequences of our results for cellular electrophysiology. In particular, we find that TRPV1 is more selective for PI(4,5)P2 than PI(4)P and activated by extremely low membrane mole fractions of PIPs. We conclude by discussing how the logic of our work extends to other experiments with short-chain phosphoinositides. For delayed rectifier K(+) channels, consideration of the membrane mole fraction of PI(4,5)P2 lipids with different acyl chain lengths suggests a different mechanism for PI(4,5)P2 regulation than previously proposed. Inward rectifier K(+) channels apparent lack of selectivity for certain short-chain PIPs may require reinterpretation in view of the PIPs different membrane partitioning.
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Affiliation(s)
- Marcus D Collins
- University of Washington School of Medicine, Department of Physiology and Biophysics, Seattle, WA
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36
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Rosenhouse-Dantsker A, Epshtein Y, Levitan I. Interplay Between Lipid Modulators of Kir2 Channels: Cholesterol and PIP2. Comput Struct Biotechnol J 2014; 11:131-7. [PMID: 25408847 PMCID: PMC4232564 DOI: 10.1016/j.csbj.2014.09.007] [Citation(s) in RCA: 15] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/30/2014] [Revised: 09/16/2014] [Accepted: 09/18/2014] [Indexed: 11/16/2022] Open
Abstract
We have shown earlier that Kir2 channels are suppressed by the elevation of membrane cholesterol. Moreover, it is also well known that activation of Kir channels is critically dependent on a regulatory phospholipid, phosphatidylinositol-4,5-bisphosphate (PIP2). In this study we examined the cross-talk between cholesterol and PIP2 in the regulation of Kir2 channels. The strength of Kir2-PIP2 interactions was assessed by acute sequestering of PIP2 with neomycin dialyzed into cells through a patch pipette while simultaneously recording whole cell currents. Consistent with a reduction in PIP2 levels, dialysis of neomycin resulted in a decrease in Kir2.1 and Kir2.3 current amplitudes (current rundown), however, this effect was significantly delayed by cholesterol depletion for both types of channels suggesting that cholesterol depletion strengthens the interaction between Kir2 channels and PIP2. Furthermore, mutation of Kir2.1 that renders the channels' cholesterol insensitive abrogated cholesterol depletion-induced delay in the current rundown whereas reverse mutation in Kir2.3 has the opposite effect. These observations provide further support for the functional cross-talk between cholesterol and PIP2 in regulating Kir2 channels. Consistent with these observations, there is a significant structural overlap between cytosolic residues that are critical for the sensitivity of Kir2 channels to the two lipid modulators but based on recent studies, there is little or no overlap between cholesterol and PIP2 binding sites. Taken together, these observations suggest that cholesterol and PIP2 regulate the channels through distinct binding sites but that the signals generated by the binding of the two modulators converge.
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Affiliation(s)
| | | | - Irena Levitan
- Section of Pulmonary, Critical Care, Sleep, and Allergy, Department of Medicine, University of Illinois at Chicago, Chicago, IL 60612, United States
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Bollepalli MK, Fowler PW, Rapedius M, Shang L, Sansom MSP, Tucker SJ, Baukrowitz T. State-dependent network connectivity determines gating in a K+ channel. Structure 2014; 22:1037-46. [PMID: 24980796 PMCID: PMC4087272 DOI: 10.1016/j.str.2014.04.018] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/14/2014] [Revised: 04/05/2014] [Accepted: 04/07/2014] [Indexed: 12/31/2022]
Abstract
X-ray crystallography has provided tremendous insight into the different structural states of membrane proteins and, in particular, of ion channels. However, the molecular forces that determine the thermodynamic stability of a particular state are poorly understood. Here we analyze the different X-ray structures of an inwardly rectifying potassium channel (Kir1.1) in relation to functional data we obtained for over 190 mutants in Kir1.1. This mutagenic perturbation analysis uncovered an extensive, state-dependent network of physically interacting residues that stabilizes the pre-open and open states of the channel, but fragments upon channel closure. We demonstrate that this gating network is an important structural determinant of the thermodynamic stability of these different gating states and determines the impact of individual mutations on channel function. These results have important implications for our understanding of not only K+ channel gating but also the more general nature of conformational transitions that occur in other allosteric proteins. Functional validation of different crystallographic states of Kir channels Presence of a state-dependent gating network revealed by large-scale mutagenesis Biased effect of mutations on Kir channel gating due to open-state destabilization Long-range allosteric coupling mediated by a physically connected residue network
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Affiliation(s)
- Murali K Bollepalli
- Physiological Institute, Christian-Albrechts University, 24118 Kiel, Germany
| | - Philip W Fowler
- Department of Biochemistry, University of Oxford, Oxford OX1 3QU, UK
| | - Markus Rapedius
- Physiological Institute, Christian-Albrechts University, 24118 Kiel, Germany
| | - Lijun Shang
- Clarendon Laboratory, Department of Physics, University of Oxford Oxford, OX1 3PU, UK
| | - Mark S P Sansom
- Department of Biochemistry, University of Oxford, Oxford OX1 3QU, UK; OXION Ion Channel Initiative, University of Oxford, Oxford OX1 3PT, UK
| | - Stephen J Tucker
- Clarendon Laboratory, Department of Physics, University of Oxford Oxford, OX1 3PU, UK; OXION Ion Channel Initiative, University of Oxford, Oxford OX1 3PT, UK.
| | - Thomas Baukrowitz
- Physiological Institute, Christian-Albrechts University, 24118 Kiel, Germany.
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38
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Levitan I, Singh DK, Rosenhouse-Dantsker A. Cholesterol binding to ion channels. Front Physiol 2014; 5:65. [PMID: 24616704 PMCID: PMC3935357 DOI: 10.3389/fphys.2014.00065] [Citation(s) in RCA: 143] [Impact Index Per Article: 14.3] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/09/2013] [Accepted: 02/03/2014] [Indexed: 11/13/2022] Open
Abstract
Numerous studies demonstrated that membrane cholesterol is a major regulator of ion channel function. The goal of this review is to discuss significant advances that have been recently achieved in elucidating the mechanisms responsible for cholesterol regulation of ion channels. The first major insight that comes from growing number of studies that based on the sterol specificity of cholesterol effects, show that several types of ion channels (nAChR, Kir, BK, TRPV) are regulated by specific sterol-protein interactions. This conclusion is supported by demonstrating direct saturable binding of cholesterol to a bacterial Kir channel. The second major advance in the field is the identification of putative cholesterol binding sites in several types of ion channels. These include sites at locations associated with the well-known cholesterol binding motif CRAC and its reversed form CARC in nAChR, BK, and TRPV, as well as novel cholesterol binding regions in Kir channels. Notably, in the majority of these channels, cholesterol is suggested to interact mainly with hydrophobic residues in non-annular regions of the channels being embedded in between transmembrane protein helices. We also discuss how identification of putative cholesterol binding sites is an essential step to understand the mechanistic basis of cholesterol-induced channel regulation. Clearly, however, these are only the first few steps in obtaining a general understanding of cholesterol-ion channels interactions and their roles in cellular and organ functions.
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Affiliation(s)
- Irena Levitan
- Division of Pulmonary, Critical Care, Sleep, and Allergy, Department of Medicine, University of Illinois at ChicagoChicago, IL, USA
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Lukacs V, Rives JM, Sun X, Zakharian E, Rohacs T. Promiscuous activation of transient receptor potential vanilloid 1 (TRPV1) channels by negatively charged intracellular lipids: the key role of endogenous phosphoinositides in maintaining channel activity. J Biol Chem 2013; 288:35003-13. [PMID: 24158445 PMCID: PMC3853253 DOI: 10.1074/jbc.m113.520288] [Citation(s) in RCA: 47] [Impact Index Per Article: 4.3] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/18/2013] [Revised: 10/18/2013] [Indexed: 11/06/2022] Open
Abstract
The regulation of the heat- and capsaicin-activated transient receptor potential vanilloid 1 (TRPV1) channels by phosphoinositides is controversial. Data in cellular systems support the dependence of TRPV1 activity on phosphoinositides. The purified TRPV1, however, was recently shown to be fully functional in artificial liposomes in the absence of phosphoinositides. Here, we show that several other negatively charged phospholipids, including phosphatidylglycerol, can also support TRPV1 activity in excised patches at high concentrations. When we incorporated TRPV1 into planar lipid bilayers consisting of neutral lipids, capsaicin-induced activity depended on phosphatidylinositol 4,5-bisphosphate. We also found that TRPV1 activity in excised patches ran down and that MgATP reactivated the channel. Inhibition of phosphatidylinositol 4-kinases or enzymatic removal of phosphatidylinositol abolished this effect of MgATP, suggesting that it activated TRPV1 by generating endogenous phosphoinositides. We conclude that endogenous phosphoinositides are positive cofactors for TRPV1 activity. Our data highlight the importance of specificity in lipid regulation of ion channels and may reconcile discordant data obtained in various experimental settings.
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Affiliation(s)
- Viktor Lukacs
- From the Department of Pharmacology and Physiology, Rutgers New Jersey Medical School, Newark, New Jersey 07103 and
| | - Jan-Michael Rives
- From the Department of Pharmacology and Physiology, Rutgers New Jersey Medical School, Newark, New Jersey 07103 and
| | - Xiaohui Sun
- Department of Cancer Biology and Pharmacology, University of Illinois College of Medicine, Peoria, Illinois 61605
| | - Eleonora Zakharian
- Department of Cancer Biology and Pharmacology, University of Illinois College of Medicine, Peoria, Illinois 61605
| | - Tibor Rohacs
- From the Department of Pharmacology and Physiology, Rutgers New Jersey Medical School, Newark, New Jersey 07103 and
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40
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Bernier LP, Ase AR, Séguéla P. Post-translational regulation of P2X receptor channels: modulation by phospholipids. Front Cell Neurosci 2013; 7:226. [PMID: 24324400 PMCID: PMC3838964 DOI: 10.3389/fncel.2013.00226] [Citation(s) in RCA: 25] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [Key Words] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/11/2013] [Accepted: 11/04/2013] [Indexed: 01/14/2023] Open
Abstract
P2X receptor channels mediate fast excitatory signaling by ATP and play major roles in sensory transduction, neuro-immune communication and inflammatory response. P2X receptors constitute a gene family of calcium-permeable ATP-gated cation channels therefore the regulation of P2X signaling is critical for both membrane potential and intracellular calcium homeostasis. Phosphoinositides (PIPn) are anionic signaling phospholipids that act as functional regulators of many types of ion channels. Direct PIPn binding was demonstrated for several ligand- or voltage-gated ion channels, however no generic motif emerged to accurately predict lipid-protein binding sites. This review presents what is currently known about the modulation of the different P2X subtypes by phospholipids and about critical determinants underlying their sensitivity to PIPn levels in the plasma membrane. All functional mammalian P2X subtypes tested, with the notable exception of P2X5, have been shown to be positively modulated by PIPn, i.e., homomeric P2X1, P2X2, P2X3, P2X4, and P2X7, as well as heteromeric P2X1/5 and P2X2/3 receptors. Based on various results reported on the aforementioned subtypes including mutagenesis of the prototypical PIPn-sensitive P2X4 and PIPn-insensitive P2X5 receptor subtypes, an increasing amount of functional, biochemical and structural evidence converges on the modulatory role of a short polybasic domain located in the proximal C-terminus of P2X subunits. This linear motif, semi-conserved in the P2X family, seems necessary and sufficient for encoding direct modulation of ATP-gated channels by PIPn. Furthermore, the physiological impact of the regulation of ionotropic purinergic responses by phospholipids on pain pathways was recently revealed in the context of native crosstalks between phospholipase C (PLC)-linked metabotropic receptors and P2X receptor channels in dorsal root ganglion sensory neurons and microglia.
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Affiliation(s)
- Louis-Philippe Bernier
- Department of Psychiatry, Brain Research Centre, University of British Columbia Vancouver, BC, Canada
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41
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Rosenhouse-Dantsker A, Noskov S, Durdagi S, Logothetis DE, Levitan I. Identification of novel cholesterol-binding regions in Kir2 channels. J Biol Chem 2013; 288:31154-64. [PMID: 24019518 DOI: 10.1074/jbc.m113.496117] [Citation(s) in RCA: 86] [Impact Index Per Article: 7.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
Inwardly rectifying potassium (Kir) channels play an important role in setting the resting membrane potential and modulating membrane excitability. We have recently shown that cholesterol regulates representative members of the Kir family and that in the majority of the cases, cholesterol suppresses channel function. Furthermore, recent data indicate that cholesterol regulates Kir channels by specific sterol-protein interactions, yet the location of the cholesterol binding site in Kir channels is unknown. Using a combined computational-experimental approach, we show that cholesterol may bind to two nonanular hydrophobic regions in the transmembrane domain of Kir2.1 located between adjacent subunits of the channel. The location of the binding regions suggests that cholesterol modulates channel function by affecting the hinging motion at the center of the pore-lining transmembrane helix that underlies channel gating either directly or through the interface between the N and C termini of the channel.
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Affiliation(s)
- Avia Rosenhouse-Dantsker
- From the Department of Medicine, Pulmonary Section, University of Illinois, Chicago, Illinois 60612
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42
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Membrane channels as integrators of G-protein-mediated signaling. BIOCHIMICA ET BIOPHYSICA ACTA-BIOMEMBRANES 2013; 1838:521-31. [PMID: 24028827 DOI: 10.1016/j.bbamem.2013.08.018] [Citation(s) in RCA: 22] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Received: 04/29/2013] [Revised: 08/14/2013] [Accepted: 08/21/2013] [Indexed: 01/03/2023]
Abstract
A variety of extracellular stimuli regulate cellular responses via membrane receptors. A well-known group of seven-transmembrane domain-containing proteins referred to as G protein-coupled receptors, directly couple with the intracellular GTP-binding proteins (G proteins) across cell membranes and trigger various cellular responses by regulating the activity of several enzymes as well as ion channels. Many specific populations of ion channels are directly controlled by G proteins; however, indirect modulation of some channels by G protein-dependent phosphorylation events and lipid metabolism is also observed. G protein-mediated diverse modifications affect the ion channel activities and spatio-temporally regulate membrane potentials as well as of intracellular Ca(2+) concentrations in both excitatory and non-excitatory cells. This article is part of a Special Issue entitled: Reciprocal influences between cell cytoskeleton and membrane channels, receptors and transporters. Guest Editor: Jean Claude Hervé.
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43
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Pattnaik BR, Tokarz S, Asuma MP, Schroeder T, Sharma A, Mitchell JC, Edwards AO, Pillers DAM. Snowflake vitreoretinal degeneration (SVD) mutation R162W provides new insights into Kir7.1 ion channel structure and function. PLoS One 2013; 8:e71744. [PMID: 23977131 PMCID: PMC3747230 DOI: 10.1371/journal.pone.0071744] [Citation(s) in RCA: 29] [Impact Index Per Article: 2.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/05/2013] [Accepted: 07/02/2013] [Indexed: 01/08/2023] Open
Abstract
Snowflake Vitreoretinal Degeneration (SVD) is associated with the R162W mutation of the Kir7.1 inwardly-rectifying potassium channel. Kir7.1 is found at the apical membrane of Retinal Pigment Epithelial (RPE) cells, adjacent to the photoreceptor neurons. The SVD phenotype ranges from RPE degeneration to an abnormal b-wave to a liquid vitreous. We sought to determine how this mutation alters the structure and function of the human Kir7.1 channel. In this study, we expressed a Kir7.1 construct with the R162W mutation in CHO cells to evaluate function of the ion channel. Compared to the wild-type protein, the mutant protein exhibited a non-functional Kir channel that resulted in depolarization of the resting membrane potential. Upon co-expression with wild-type Kir7.1, R162W mutant showed a reduction of IKir7.1 and positive shift in ‘0’ current potential. Homology modeling based on the structure of a bacterial Kir channel protein suggested that the effect of R162W mutation is a result of loss of hydrogen bonding by the regulatory lipid binding domain of the cytoplasmic structure.
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Affiliation(s)
- Bikash R. Pattnaik
- Department of Pediatrics, University of Wisconsin, Madison, Wisconsin, United States of America
- Department of Ophthalmology and Visual Sciences, University of Wisconsin, Madison, Wisconsin, United States of America
- McPherson Eye Research Institute, University of Wisconsin, Madison, Wisconsin, United States of America
- * E-mail:
| | - Sara Tokarz
- Department of Pediatrics, University of Wisconsin, Madison, Wisconsin, United States of America
| | - Matti P. Asuma
- Department of Pediatrics, University of Wisconsin, Madison, Wisconsin, United States of America
| | - Tyler Schroeder
- Department of Pediatrics, University of Wisconsin, Madison, Wisconsin, United States of America
| | - Anil Sharma
- Department of Experimental Pathology, Mayo Clinic, Rochester, Minnesota, United States of America
| | - Julie C. Mitchell
- Department of Biochemistry, University of Wisconsin, Madison, Wisconsin, United States of America
| | - Albert O. Edwards
- Institute for Molecular Biology, University of Oregon, and Oregon Retina, Eugene, Oregon, United States of America
| | - De-Ann M. Pillers
- Department of Pediatrics, University of Wisconsin, Madison, Wisconsin, United States of America
- McPherson Eye Research Institute, University of Wisconsin, Madison, Wisconsin, United States of America
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44
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Rosenhouse-Dantsker A, Noskov S, Logothetis DE, Levitan I. Cholesterol sensitivity of KIR2.1 depends on functional inter-links between the N and C termini. Channels (Austin) 2013; 7:303-12. [PMID: 23807091 DOI: 10.4161/chan.25437] [Citation(s) in RCA: 17] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/23/2023] Open
Abstract
In recent years, cholesterol has been emerging as a major regulator of ion channel function. We have previously shown that cholesterol suppresses Kir2 channels, a subfamily of constitutively active strongly rectifying K (+) channels. Furthermore, our earlier studies have shown that cholesterol sensitivity of Kir2 channels depends on a group of residues that form a belt-like structure around the cytosolic pore of the channel in proximity to the transmembrane domain. In this study, we focus on the contributions of different structural domains of Kir2 channels in the regulation of their cholesterol sensitivity. Focusing on the mildest mutation in the sensitivity belt, L222I, we show that the sensitivity of the channel to cholesterol can be restored by crosstalk between three distinct cytosolic regions: the C-terminal CD loop, the EF and GA loops of the C-terminus, and the βA sheet of the N-terminus. Thus, in addition to the importance of residues that affect the cytosolic G-loop gate in the sensitivity of Kir2 channels to cholesterol, our data suggest an important role to the interactions at the interface between the channel's N- and C- termini that couple the intracellular domains of its four subunits during gating.
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45
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Zylbergold P, Sleno R, Hébert TE. A novel, radiolabel-free pulse chase strategy to study Kir3 channel ontogeny. J Recept Signal Transduct Res 2013; 33:144-52. [DOI: 10.3109/10799893.2013.764898] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/26/2022]
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46
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The molecular mechanism by which PIP(2) opens the intracellular G-loop gate of a Kir3.1 channel. Biophys J 2012; 102:2049-59. [PMID: 22824268 DOI: 10.1016/j.bpj.2012.03.050] [Citation(s) in RCA: 52] [Impact Index Per Article: 4.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/19/2011] [Revised: 03/15/2012] [Accepted: 03/22/2012] [Indexed: 11/24/2022] Open
Abstract
Inwardly rectifying potassium (Kir) channels are characterized by a long pore comprised of continuous transmembrane and cytosolic portions. A high-resolution structure of a Kir3.1 chimera revealed the presence of the cytosolic (G-loop) gate captured in the closed or open conformations. Here, we conducted molecular-dynamics simulations of these two channel states in the presence and absence of phosphatidylinositol bisphosphate (PIP(2)), a phospholipid that is known to gate Kir channels. Simulations of the closed state with PIP(2) revealed an intermediate state between the closed and open conformations involving direct transient interactions with PIP(2), as well as a network of transitional inter- and intrasubunit interactions. Key elements in the G-loop gating transition involved a PIP(2)-driven movement of the N-terminus and C-linker that removed constraining intermolecular interactions and led to CD-loop stabilization of the G-loop gate in the open state. To our knowledge, this is the first dynamic molecular view of PIP(2)-induced channel gating that is consistent with existing experimental data.
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47
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Zamponi GW, Currie KPM. Regulation of Ca(V)2 calcium channels by G protein coupled receptors. BIOCHIMICA ET BIOPHYSICA ACTA-BIOMEMBRANES 2012; 1828:1629-43. [PMID: 23063655 DOI: 10.1016/j.bbamem.2012.10.004] [Citation(s) in RCA: 135] [Impact Index Per Article: 11.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 08/16/2012] [Revised: 10/02/2012] [Accepted: 10/04/2012] [Indexed: 12/29/2022]
Abstract
Voltage gated calcium channels (Ca²⁺ channels) are key mediators of depolarization induced calcium influx into excitable cells, and thereby play pivotal roles in a wide array of physiological responses. This review focuses on the inhibition of Ca(V)2 (N- and P/Q-type) Ca²⁺-channels by G protein coupled receptors (GPCRs), which exerts important autocrine/paracrine control over synaptic transmission and neuroendocrine secretion. Voltage-dependent inhibition is the most widespread mechanism, and involves direct binding of the G protein βγ dimer (Gβγ) to the α1 subunit of Ca(V)2 channels. GPCRs can also recruit several other distinct mechanisms including phosphorylation, lipid signaling pathways, and channel trafficking that result in voltage-independent inhibition. Current knowledge of Gβγ-mediated inhibition is reviewed, including the molecular interactions involved, determinants of voltage-dependence, and crosstalk with other cell signaling pathways. A summary of recent developments in understanding the voltage-independent mechanisms prominent in sympathetic and sensory neurons is also included. This article is part of a Special Issue entitled: Calcium channels.
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Affiliation(s)
- Gerald W Zamponi
- Department of Physiology & Pharmacology, Hotchkiss Brain Institute, University of Calgary, Canada
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48
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An HL, Lü SQ, Li JW, Meng XY, Zhan Y, Cui M, Long M, Zhang HL, Logothetis DE. The cytosolic GH loop regulates the phosphatidylinositol 4,5-bisphosphate-induced gating kinetics of Kir2 channels. J Biol Chem 2012; 287:42278-87. [PMID: 23033482 DOI: 10.1074/jbc.m112.418640] [Citation(s) in RCA: 16] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
Inwardly rectifying K(+) (Kir) channels set the resting membrane potential and regulate cellular excitability. The activity of Kir channels depends critically on the phospholipid PIP(2). The molecular mechanism by which PIP(2) regulates Kir channel gating is poorly understood. Here, we utilized a combination of computational and electrophysiological approaches to discern structural elements involved in regulating the PIP(2)-induced gating kinetics of Kir2 channels. We identify a novel role for the cytosolic GH loop. Mutations that directly or indirectly affect GH loop flexibility (e.g. V223L, E272G, D292G) increase both the on- and especially the off-gating kinetics. These effects are consistent with a model in which competing interactions between the CD and GH loops for the N terminus regulate the gating of the intracellular G loop gate.
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Affiliation(s)
- Hai-Long An
- Department of Physiology and Biophysics, School of Medicine, Virginia Commonwealth University, Richmond, Virginia 23298, USA
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49
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Rosenhouse-Dantsker A, Noskov S, Han H, Adney SK, Tang QY, Rodríguez-Menchaca AA, Kowalsky GB, Petrou VI, Osborn CV, Logothetis DE, Levitan I. Distant cytosolic residues mediate a two-way molecular switch that controls the modulation of inwardly rectifying potassium (Kir) channels by cholesterol and phosphatidylinositol 4,5-bisphosphate (PI(4,5)P(2)). J Biol Chem 2012; 287:40266-78. [PMID: 22995912 DOI: 10.1074/jbc.m111.336339] [Citation(s) in RCA: 22] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
BACKGROUND Cholesterol modulates inwardly rectifying potassium (Kir) channels. RESULTS A two-way molecular cytosolic switch controls channel modulation by cholesterol and PI(4,5)P(2). CONCLUSION Cholesterol and PI(4,5)P(2) induce a common gating pathway of Kir2.1 despite their opposite impact on channel function. SIGNIFICANCE These findings provide insights into structure-function relationship of ion channels and contribute to understanding of the mechanisms underlying their regulation by lipids. Inwardly rectifying potassium (Kir) channels play an important role in setting the resting membrane potential and modulating membrane excitability. An emerging feature of several Kir channels is that they are regulated by cholesterol. However, the mechanism by which cholesterol affects channel function is unclear. Here we show that mutations of two distant Kir2.1 cytosolic residues, Leu-222 and Asn-251, form a two-way molecular switch that controls channel modulation by cholesterol and affects critical hydrogen bonding. Notably, these two residues are linked by a residue chain that continues from Asn-251 to connect adjacent subunits. Furthermore, our data indicate that the same switch also regulates the sensitivity of the channels to phosphatidylinositol 4,5-bisphosphate, a phosphoinositide that is required for activation of Kir channels. Thus, although cholesterol and phosphatidylinositol 4,5-bisphosphate do not interact with the same region of Kir2.1, these different modulators induce a common gating pathway of the channel.
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50
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Bernier LP, Blais D, Boué-Grabot É, Séguéla P. A dual polybasic motif determines phosphoinositide binding and regulation in the P2X channel family. PLoS One 2012; 7:e40595. [PMID: 22792379 PMCID: PMC3394732 DOI: 10.1371/journal.pone.0040595] [Citation(s) in RCA: 16] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/14/2012] [Accepted: 06/11/2012] [Indexed: 01/05/2023] Open
Abstract
Phosphoinositides modulate the function of several ion channels, including most ATP-gated P2X receptor channels in neurons and glia, but little is known about the underlying molecular mechanism. We identified a phosphoinositide-binding motif formed of two clusters of positively charged amino acids located on the P2X cytosolic C-terminal domain, proximal to the second transmembrane domain. For all known P2X subtypes, the specific arrangement of basic residues in these semi-conserved clusters determines their sensitivity to membrane phospholipids. Neutralization of these positive charges disrupts the functional properties of the prototypical phosphoinositide-binding P2X4 subtype, mimicking wortmannin-induced phosphoinositide depletion, whereas adding basic residues at homologous positions to the natively insensitive P2X5 subtype establishes de novo phosphoinositide-mediated regulation. Moreover, biochemical evidence of in vitro P2X subunit-phospholipid interaction and functional intracellular phosphoinositide-binding assays demonstrate that the dual polybasic cluster is necessary and sufficient for regulation of P2X signaling by phospholipids.
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MESH Headings
- Amino Acid Motifs
- Amino Acid Sequence
- Animals
- Binding Sites
- Binding, Competitive
- Cell Line
- Conserved Sequence
- Humans
- Molecular Sequence Data
- Mutation
- Oocytes/metabolism
- Phenotype
- Phosphatidylinositols/metabolism
- Protein Binding
- Protein Interaction Domains and Motifs
- Protein Subunits/chemistry
- Protein Subunits/metabolism
- Rats
- Receptors, Purinergic P2X/chemistry
- Receptors, Purinergic P2X/genetics
- Receptors, Purinergic P2X/metabolism
- Receptors, Purinergic P2X1/chemistry
- Receptors, Purinergic P2X1/metabolism
- Receptors, Purinergic P2X5/chemistry
- Receptors, Purinergic P2X5/metabolism
- Receptors, Purinergic P2X7/chemistry
- Receptors, Purinergic P2X7/metabolism
- Sequence Alignment
- Signal Transduction
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Affiliation(s)
- Louis-Philippe Bernier
- Department of Neurology and Neurosurgery, Montreal Neurological Institute, Alan Edwards Centre for Research on Pain, McGill University, Montréal, Québec, Canada
| | - Dominique Blais
- Department of Neurology and Neurosurgery, Montreal Neurological Institute, Alan Edwards Centre for Research on Pain, McGill University, Montréal, Québec, Canada
| | - Éric Boué-Grabot
- Institut des Maladies Neurodégénératives, Université Bordeaux Segalen, CNRS UMR 5293, Bordeaux, France
| | - Philippe Séguéla
- Department of Neurology and Neurosurgery, Montreal Neurological Institute, Alan Edwards Centre for Research on Pain, McGill University, Montréal, Québec, Canada
- * E-mail:
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