1
|
Raut S, Singh K, Sanghvi S, Loyo-Celis V, Varghese L, Singh E, Gururaja Rao S, Singh H. Chloride ions in health and disease. Biosci Rep 2024; 44:BSR20240029. [PMID: 38573803 PMCID: PMC11065649 DOI: 10.1042/bsr20240029] [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: 01/09/2024] [Revised: 03/26/2024] [Accepted: 04/04/2024] [Indexed: 04/06/2024] Open
Abstract
Chloride is a key anion involved in cellular physiology by regulating its homeostasis and rheostatic processes. Changes in cellular Cl- concentration result in differential regulation of cellular functions such as transcription and translation, post-translation modifications, cell cycle and proliferation, cell volume, and pH levels. In intracellular compartments, Cl- modulates the function of lysosomes, mitochondria, endosomes, phagosomes, the nucleus, and the endoplasmic reticulum. In extracellular fluid (ECF), Cl- is present in blood/plasma and interstitial fluid compartments. A reduction in Cl- levels in ECF can result in cell volume contraction. Cl- is the key physiological anion and is a principal compensatory ion for the movement of the major cations such as Na+, K+, and Ca2+. Over the past 25 years, we have increased our understanding of cellular signaling mediated by Cl-, which has helped in understanding the molecular and metabolic changes observed in pathologies with altered Cl- levels. Here, we review the concentration of Cl- in various organs and cellular compartments, ion channels responsible for its transportation, and recent information on its physiological roles.
Collapse
Affiliation(s)
- Satish K. Raut
- Department of Physiology and Cell Biology, College of Medicine, The Ohio State University, Columbus, OH, U.S.A
| | - Kulwinder Singh
- Department of Physiology and Cell Biology, College of Medicine, The Ohio State University, Columbus, OH, U.S.A
| | - Shridhar Sanghvi
- Department of Physiology and Cell Biology, College of Medicine, The Ohio State University, Columbus, OH, U.S.A
- Department of Molecular Cellular and Developmental Biology, The Ohio State University, Columbus, OH, U.S.A
| | - Veronica Loyo-Celis
- Department of Physiology and Cell Biology, College of Medicine, The Ohio State University, Columbus, OH, U.S.A
| | - Liyah Varghese
- Department of Physiology and Cell Biology, College of Medicine, The Ohio State University, Columbus, OH, U.S.A
| | - Ekam R. Singh
- Department of Physiology and Cell Biology, College of Medicine, The Ohio State University, Columbus, OH, U.S.A
| | | | - Harpreet Singh
- Department of Physiology and Cell Biology, College of Medicine, The Ohio State University, Columbus, OH, U.S.A
- Department of Molecular Cellular and Developmental Biology, The Ohio State University, Columbus, OH, U.S.A
| |
Collapse
|
2
|
Xu M, Neelands T, Powers AS, Liu Y, Miller SD, Pintilie G, Bois JD, Dror RO, Chiu W, Maduke M. CryoEM structures of the human CLC-2 voltage gated chloride channel reveal a ball and chain gating mechanism. BIORXIV : THE PREPRINT SERVER FOR BIOLOGY 2023:2023.08.13.553136. [PMID: 37645939 PMCID: PMC10462068 DOI: 10.1101/2023.08.13.553136] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 08/31/2023]
Abstract
CLC-2 is a voltage-gated chloride channel that contributes to electrical excitability and ion homeostasis in many different mammalian tissues and cell types. Among the nine mammalian CLC homologs, CLC-2 is uniquely activated by hyperpolarization, rather than depolarization, of the plasma membrane. The molecular basis for the divergence in polarity of voltage gating mechanisms among closely related CLC homologs has been a long-standing mystery, in part because few CLC channel structures are available, and those that exist exhibit high conformational similarity. Here, we report cryoEM structures of human CLC-2 at 2.46 - 2.76 Å, in the presence and absence of the potent and selective inhibitor AK-42. AK-42 binds within the extracellular entryway of the Cl--permeation pathway, occupying a pocket previously proposed through computational docking studies. In the apo structure, we observed two distinct apo conformations of CLC-2 involving rotation of one of the cytoplasmic C-terminal domains (CTDs). In the absence of CTD rotation, an intracellular N-terminal 15-residue hairpin peptide nestles against the TM domain to physically occlude the Cl--permeation pathway from the intracellular side. This peptide is highly conserved among species variants of CLC-2 but is not present in any other CLC homologs. Previous studies suggested that the N-terminal domain of CLC-2 influences channel properties via a "ball-and-chain" gating mechanism, but conflicting data cast doubt on such a mechanism, and thus the structure of the N-terminal domain and its interaction with the channel has been uncertain. Through electrophysiological studies of an N-terminal deletion mutant lacking the 15-residue hairpin peptide, we show that loss of this short sequence increases the magnitude and decreases the rectification of CLC-2 currents expressed in mammalian cells. Furthermore, we show that with repetitive hyperpolarization WT CLC-2 currents increase in resemblance to the hairpin-deleted CLC-2 currents. These functional results combined with our structural data support a model in which the N-terminal hairpin of CLC-2 stabilizes a closed state of the channel by blocking the cytoplasmic Cl--permeation pathway.
Collapse
Affiliation(s)
- Mengyuan Xu
- Department of Molecular and Cellular Physiology, Stanford University, Stanford, CA 94305
| | - Torben Neelands
- Department of Molecular and Cellular Physiology, Stanford University, Stanford, CA 94305
| | - Alexander S. Powers
- Department of Chemistry, Stanford University, Stanford, CA 94305
- Department of Computer Science, Stanford University, Stanford, CA 94305
- Department of Structural Biology, Stanford University, Stanford, CA 94305
- Institute for Computational and Mathematical Engineering, Stanford University, Stanford, CA 94305
| | - Yan Liu
- Division of CryoEM and Bioimaging, SSRL, SLAC National Accelerator Laboratory, Stanford University, Menlo Park 94025
| | - Steven D. Miller
- Department of Chemistry, Stanford University, Stanford, CA 94305
| | - Grigore Pintilie
- Department of Bioengineering and Department of Microbiology and Immunology, Stanford University, Stanford, 94305
| | - J. Du Bois
- Department of Chemistry, Stanford University, Stanford, CA 94305
| | - Ron O. Dror
- Department of Molecular and Cellular Physiology, Stanford University, Stanford, CA 94305
- Department of Computer Science, Stanford University, Stanford, CA 94305
- Department of Structural Biology, Stanford University, Stanford, CA 94305
- Institute for Computational and Mathematical Engineering, Stanford University, Stanford, CA 94305
| | - Wah Chiu
- Division of CryoEM and Bioimaging, SSRL, SLAC National Accelerator Laboratory, Stanford University, Menlo Park 94025
- Department of Bioengineering and Department of Microbiology and Immunology, Stanford University, Stanford, 94305
| | - Merritt Maduke
- Department of Molecular and Cellular Physiology, Stanford University, Stanford, CA 94305
| |
Collapse
|
3
|
Abstract
Microorganisms contend with numerous and unusual chemical threats and have evolved a catalog of resistance mechanisms in response. One particularly ancient, pernicious threat is posed by fluoride ion (F-), a common xenobiotic in natural environments that causes broad-spectrum harm to metabolic pathways. This review focuses on advances in the last ten years toward understanding the microbial response to cytoplasmic accumulation of F-, with a special emphasis on the structure and mechanisms of the proteins that microbes use to export fluoride: the CLCF family of F-/H+ antiporters and the Fluc/FEX family of F- channels.
Collapse
Affiliation(s)
- Benjamin C McIlwain
- Department of Molecular, Cellular, and Developmental Biology, University of Michigan, Ann Arbor, Michigan 48109, USA;
| | - Michal T Ruprecht
- Department of Molecular, Cellular, and Developmental Biology, University of Michigan, Ann Arbor, Michigan 48109, USA;
| | - Randy B Stockbridge
- Department of Molecular, Cellular, and Developmental Biology, University of Michigan, Ann Arbor, Michigan 48109, USA; .,Program in Biophysics, University of Michigan, Ann Arbor, Michigan 48109, USA
| |
Collapse
|
4
|
Teulon J, Planelles G, Sepúlveda FV, Andrini O, Lourdel S, Paulais M. Renal Chloride Channels in Relation to Sodium Chloride Transport. Compr Physiol 2018; 9:301-342. [DOI: 10.1002/cphy.c180024] [Citation(s) in RCA: 9] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/13/2022]
|
5
|
Jentsch TJ, Pusch M. CLC Chloride Channels and Transporters: Structure, Function, Physiology, and Disease. Physiol Rev 2018; 98:1493-1590. [DOI: 10.1152/physrev.00047.2017] [Citation(s) in RCA: 214] [Impact Index Per Article: 35.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/16/2022] Open
Abstract
CLC anion transporters are found in all phyla and form a gene family of eight members in mammals. Two CLC proteins, each of which completely contains an ion translocation parthway, assemble to homo- or heteromeric dimers that sometimes require accessory β-subunits for function. CLC proteins come in two flavors: anion channels and anion/proton exchangers. Structures of these two CLC protein classes are surprisingly similar. Extensive structure-function analysis identified residues involved in ion permeation, anion-proton coupling and gating and led to attractive biophysical models. In mammals, ClC-1, -2, -Ka/-Kb are plasma membrane Cl−channels, whereas ClC-3 through ClC-7 are 2Cl−/H+-exchangers in endolysosomal membranes. Biological roles of CLCs were mostly studied in mammals, but also in plants and model organisms like yeast and Caenorhabditis elegans. CLC Cl−channels have roles in the control of electrical excitability, extra- and intracellular ion homeostasis, and transepithelial transport, whereas anion/proton exchangers influence vesicular ion composition and impinge on endocytosis and lysosomal function. The surprisingly diverse roles of CLCs are highlighted by human and mouse disorders elicited by mutations in their genes. These pathologies include neurodegeneration, leukodystrophy, mental retardation, deafness, blindness, myotonia, hyperaldosteronism, renal salt loss, proteinuria, kidney stones, male infertility, and osteopetrosis. In this review, emphasis is laid on biophysical structure-function analysis and on the cell biological and organismal roles of mammalian CLCs and their role in disease.
Collapse
Affiliation(s)
- Thomas J. Jentsch
- Leibniz-Forschungsinstitut für Molekulare Pharmakologie (FMP) and Max-Delbrück-Centrum für Molekulare Medizin (MDC), Berlin, Germany; and Istituto di Biofisica, Consiglio Nazionale delle Ricerche, Genova, Italy
| | - Michael Pusch
- Leibniz-Forschungsinstitut für Molekulare Pharmakologie (FMP) and Max-Delbrück-Centrum für Molekulare Medizin (MDC), Berlin, Germany; and Istituto di Biofisica, Consiglio Nazionale delle Ricerche, Genova, Italy
| |
Collapse
|
6
|
Abstract
Miller recounts the distinct influences that Gilbert Ling and Efraim Racker had on his early career.
Collapse
|
7
|
Abstract
CLC proteins are a ubiquitously expressed family of chloride-selective ion channels and transporters. A dearth of pharmacological tools for modulating CLC gating and ion conduction limits investigations aimed at understanding CLC structure/function and physiology. Herein, we describe the design, synthesis, and evaluation of a collection of N-arylated benzimidazole derivatives (BIMs), one of which (BIM1) shows unparalleled (>20-fold) selectivity for CLC-Ka over CLC-Kb, the two most closely related human CLC homologs. Computational docking to a CLC-Ka homology model has identified a BIM1 binding site on the extracellular face of the protein near the chloride permeation pathway in a region previously identified as a binding site for other less selective inhibitors. Results from site-directed mutagenesis experiments are consistent with predictions of this docking model. The residue at position 68 is 1 of only ∼20 extracellular residues that differ between CLC-Ka and CLC-Kb. Mutation of this residue in CLC-Ka and CLC-Kb (N68D and D68N, respectively) reverses the preference of BIM1 for CLC-Ka over CLC-Kb, thus showing the critical role of residue 68 in establishing BIM1 selectivity. Molecular docking studies together with results from structure-activity relationship studies with 19 BIM derivatives give insight into the increased selectivity of BIM1 compared with other inhibitors and identify strategies for further developing this class of compounds.
Collapse
|
8
|
Gururaja Rao S, Ponnalagu D, Patel NJ, Singh H. Three Decades of Chloride Intracellular Channel Proteins: From Organelle to Organ Physiology. CURRENT PROTOCOLS IN PHARMACOLOGY 2018; 80:11.21.1-11.21.17. [PMID: 30040212 PMCID: PMC6060641 DOI: 10.1002/cpph.36] [Citation(s) in RCA: 33] [Impact Index Per Article: 5.5] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 12/13/2022]
Abstract
Intracellular organelles are membranous structures central for maintaining cellular physiology and the overall health of the cell. To maintain cellular function, intracellular organelles are required to tightly regulate their ionic homeostasis. Any imbalance in ionic concentrations can disrupt energy production (mitochondria), protein degradation (lysosomes), DNA replication (nucleus), or cellular signaling (endoplasmic reticulum). Ionic homeostasis is also important for volume regulation of intracellular organelles and is maintained by cation and anion channels as well as transporters. One of the major classes of ion channels predominantly localized to intracellular membranes is chloride intracellular channel proteins (CLICs). They are non-canonical ion channels with six homologs in mammals, existing as either soluble or integral membrane protein forms, with dual functions as enzymes and channels. Provided in this overview is a brief introduction to CLICs, and a summary of recent information on their localization, biophysical properties, and physiological roles. © 2018 by John Wiley & Sons, Inc.
Collapse
Affiliation(s)
- Shubha Gururaja Rao
- Department of Pharmacology and Physiology, Drexel University College of Medicine, Philadelphia, Pennsylvania
| | - Devasena Ponnalagu
- Department of Pharmacology and Physiology, Drexel University College of Medicine, Philadelphia, Pennsylvania
| | - Neel J Patel
- Department of Pharmacology and Physiology, Drexel University College of Medicine, Philadelphia, Pennsylvania
| | - Harpreet Singh
- Department of Pharmacology and Physiology, Drexel University College of Medicine, Philadelphia, Pennsylvania
| |
Collapse
|
9
|
Wingo CS, Stockand JD. Alkaline activation of ClC-K2 chloride channels switches renal cells from reabsorbing to secreting. J Gen Physiol 2018; 148:195-9. [PMID: 27574289 PMCID: PMC5004340 DOI: 10.1085/jgp.201611669] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/18/2016] [Accepted: 08/05/2016] [Indexed: 12/28/2022] Open
Affiliation(s)
- Charles S Wingo
- Department of Medicine, University of Florida, Gainesville, FL 32610 Department of Physiology and Functional Genomics, University of Florida, Gainesville, FL 32610 Nephrology Section, Department of Veteran Affairs Medical Center, Gainesville, FL 32608
| | - James D Stockand
- Department of Physiology, University of Texas Health Science Center at San Antonio, San Antonio, TX 78229
| |
Collapse
|
10
|
Chavan T, Maduke M, Swartz K. Protein ligands for studying ion channel proteins. J Gen Physiol 2017; 149:407-411. [PMID: 28270405 PMCID: PMC5379924 DOI: 10.1085/jgp.201711776] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022] Open
Abstract
Chavan et al. highlight work showing that a monobody can inhibit a fluoride channel using a mechanism similar to that of a scorpion toxin blocker of potassium channels.
Collapse
Affiliation(s)
- Tanmay Chavan
- Department of Molecular and Cellular Physiology, Stanford University School of Medicine, Stanford, CA 94305
| | - Merritt Maduke
- Department of Molecular and Cellular Physiology, Stanford University School of Medicine, Stanford, CA 94305
| | - Kenton Swartz
- Molecular Physiology and Biophysics Section, John Edward Porter Neuroscience Research Center, National Institute of Neurological Disorders and Stroke, National Institutes of Health, Bethesda, MD 20892
| |
Collapse
|
11
|
Last NB, Kolmakova-Partensky L, Shane T, Miller C. Mechanistic signs of double-barreled structure in a fluoride ion channel. eLife 2016; 5. [PMID: 27449280 PMCID: PMC4969038 DOI: 10.7554/elife.18767] [Citation(s) in RCA: 28] [Impact Index Per Article: 3.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/14/2016] [Accepted: 07/22/2016] [Indexed: 12/04/2022] Open
Abstract
The Fluc family of F− ion channels protects prokaryotes and lower eukaryotes from the toxicity of environmental F−. In bacteria, these channels are built as dual-topology dimers whereby the two subunits assemble in antiparallel transmembrane orientation. Recent crystal structures suggested that Fluc channels contain two separate ion-conduction pathways, each with two F− binding sites, but no functional correlates of this unusual architecture have been reported. Experiments here fill this gap by examining the consequences of mutating two conserved F−-coordinating phenylalanine residues. Substitution of each phenylalanine specifically extinguishes its associated F− binding site in crystal structures and concomitantly inhibits F− permeation. Functional analysis of concatemeric channels, which permit mutagenic manipulation of individual pores, show that each pore can be separately inactivated without blocking F− conduction through its symmetry-related twin. The results strongly support dual-pathway architecture of Fluc channels. DOI:http://dx.doi.org/10.7554/eLife.18767.001
Collapse
Affiliation(s)
- Nicholas B Last
- Department of Biochemistry, Howard Hughes Medical Institute, Brandeis University, Waltham, United States
| | | | - Tania Shane
- Department of Biochemistry, Howard Hughes Medical Institute, Brandeis University, Waltham, United States
| | - Christopher Miller
- Department of Biochemistry, Howard Hughes Medical Institute, Brandeis University, Waltham, United States
| |
Collapse
|
12
|
Khantwal CM, Abraham SJ, Han W, Jiang T, Chavan TS, Cheng RC, Elvington SM, Liu CW, Mathews II, Stein RA, Mchaourab HS, Tajkhorshid E, Maduke M. Revealing an outward-facing open conformational state in a CLC Cl(-)/H(+) exchange transporter. eLife 2016; 5. [PMID: 26799336 PMCID: PMC4769167 DOI: 10.7554/elife.11189] [Citation(s) in RCA: 33] [Impact Index Per Article: 4.1] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/27/2015] [Accepted: 01/14/2016] [Indexed: 11/22/2022] Open
Abstract
CLC secondary active transporters exchange Cl- for H+. Crystal structures have suggested that the conformational change from occluded to outward-facing states is unusually simple, involving only the rotation of a conserved glutamate (Gluex) upon its protonation. Using 19F NMR, we show that as [H+] is increased to protonate Gluex and enrich the outward-facing state, a residue ~20 Å away from Gluex, near the subunit interface, moves from buried to solvent-exposed. Consistent with functional relevance of this motion, constriction via inter-subunit cross-linking reduces transport. Molecular dynamics simulations indicate that the cross-link dampens extracellular gate-opening motions. In support of this model, mutations that decrease steric contact between Helix N (part of the extracellular gate) and Helix P (at the subunit interface) remove the inhibitory effect of the cross-link. Together, these results demonstrate the formation of a previously uncharacterized 'outward-facing open' state, and highlight the relevance of global structural changes in CLC function. DOI:http://dx.doi.org/10.7554/eLife.11189.001 Cells have transporter proteins on their surface to carry molecules in and out of the cell. For example, the CLC family of transporters move two chloride ions in one direction at the same time as moving one hydrogen ion in the opposite direction. To be able to move these ions in opposite directions, transporters have to cycle through a series of shapes in which the ions can only access alternate sides of the membrane. First, the transporter adopts an 'outward-facing' shape when the ions first bind to the transporter, then it switches into the 'occluded' shape to move the ions through the membrane. Finally, the transporter takes on the 'inward-facing' shape to release the ions on the other side of the membrane. However, structural studies of CLCs suggest that the structures of these proteins do not change much while they are moving ions, which suggests that they might work in a different way. Khantwal, Abraham et al. have now used techniques called “nuclear magnetic resonance” and "double electron-electron resonance" to investigate how a CLC from a bacterium moves ions. The experiments suggest that when the transporter adopts the outward-facing shape, points on the protein known as Y419 and D417 shift their positions. Chemically linking two regions of the CLC prevented this movement and inhibited the transport of chloride ions across the membrane. Khantwal, Abraham et al. then used a computer simulation to model how the protein changes shape in more detail. This model predicts that two regions of the transporter undergo major rearrangements resulting in a gate-opening motion that widens a passage to allow the chloride ions to bind to the protein. Khantwal, Abraham et al.’s findings will prompt future studies to reveal the other shapes and how CLCs transition between them. DOI:http://dx.doi.org/10.7554/eLife.11189.002
Collapse
Affiliation(s)
- Chandra M Khantwal
- Department of Molecular and Cellular Physiology, Stanford University School of Medicine, Stanford, United States
| | - Sherwin J Abraham
- Department of Molecular and Cellular Physiology, Stanford University School of Medicine, Stanford, United States
| | - Wei Han
- Department of Biochemistry, University of Illinois at Urbana-Champaign, Urbana, United States.,College of Medicine, University of Illinois at Urbana-Champaign, Urbana, United States.,Center for Biophysics and Computational Biology, University of Illinois at Urbana-Champaign, Urbana, United States.,Beckman Institute for Advanced Science and Technology, University of Illinois at Urbana-Champaign, Urbana, United States
| | - Tao Jiang
- Department of Biochemistry, University of Illinois at Urbana-Champaign, Urbana, United States.,College of Medicine, University of Illinois at Urbana-Champaign, Urbana, United States.,Center for Biophysics and Computational Biology, University of Illinois at Urbana-Champaign, Urbana, United States.,Beckman Institute for Advanced Science and Technology, University of Illinois at Urbana-Champaign, Urbana, United States
| | - Tanmay S Chavan
- Department of Molecular and Cellular Physiology, Stanford University School of Medicine, Stanford, United States
| | - Ricky C Cheng
- Department of Molecular and Cellular Physiology, Stanford University School of Medicine, Stanford, United States
| | - Shelley M Elvington
- Department of Molecular and Cellular Physiology, Stanford University School of Medicine, Stanford, United States
| | - Corey W Liu
- Stanford Magnetic Resonance Laboratory, Stanford University School of Medicine, Stanford, United States
| | - Irimpan I Mathews
- Stanford Synchrotron Radiation Lightsource, Stanford University, Menlo Park, United States
| | - Richard A Stein
- Department of Molecular Physiology and Biophysics, Vanderbilt University, Nashville, United States
| | - Hassane S Mchaourab
- Department of Molecular Physiology and Biophysics, Vanderbilt University, Nashville, United States
| | - Emad Tajkhorshid
- Department of Biochemistry, University of Illinois at Urbana-Champaign, Urbana, United States.,College of Medicine, University of Illinois at Urbana-Champaign, Urbana, United States.,Center for Biophysics and Computational Biology, University of Illinois at Urbana-Champaign, Urbana, United States.,Beckman Institute for Advanced Science and Technology, University of Illinois at Urbana-Champaign, Urbana, United States
| | - Merritt Maduke
- Department of Molecular and Cellular Physiology, Stanford University School of Medicine, Stanford, United States
| |
Collapse
|
13
|
Fong P. Twenty-five years of CLC chloride transport proteins. J Physiol 2015; 593:4083-4. [PMID: 26372836 DOI: 10.1113/jp271325] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/20/2015] [Accepted: 07/22/2015] [Indexed: 11/08/2022] Open
Affiliation(s)
- Peying Fong
- Kansas State University College of Veterinary Medicine, 1600 Denison Ave, 129 Coles Hall, Manhattan, KS, 66506, USA
| |
Collapse
|
14
|
Abraham SJ, Cheng RC, Chew TA, Khantwal CM, Liu CW, Gong S, Nakamoto RK, Maduke M. 13C NMR detects conformational change in the 100-kD membrane transporter ClC-ec1. JOURNAL OF BIOMOLECULAR NMR 2015; 61:209-26. [PMID: 25631353 PMCID: PMC4398623 DOI: 10.1007/s10858-015-9898-7] [Citation(s) in RCA: 17] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 10/16/2014] [Accepted: 01/13/2015] [Indexed: 05/03/2023]
Abstract
CLC transporters catalyze the exchange of Cl(-) for H(+) across cellular membranes. To do so, they must couple Cl(-) and H(+) binding and unbinding to protein conformational change. However, the sole conformational changes distinguished crystallographically are small movements of a glutamate side chain that locally gates the ion-transport pathways. Therefore, our understanding of whether and how global protein dynamics contribute to the exchange mechanism has been severely limited. To overcome the limitations of crystallography, we used solution-state (13)C-methyl NMR with labels on methionine, lysine, and engineered cysteine residues to investigate substrate (H(+)) dependent conformational change outside the restraints of crystallization. We show that methyl labels in several regions report H(+)-dependent spectral changes. We identify one of these regions as Helix R, a helix that extends from the center of the protein, where it forms the part of the inner gate to the Cl(-)-permeation pathway, to the extracellular solution. The H(+)-dependent spectral change does not occur when a label is positioned just beyond Helix R, on the unstructured C-terminus of the protein. Together, the results suggest that H(+) binding is mechanistically coupled to closing of the intracellular access-pathway for Cl(-).
Collapse
Affiliation(s)
- Sherwin J. Abraham
- Department of Molecular & Cellular Physiology, Stanford University School of Medicine, 279 Campus Drive West, Stanford, CA 94035
| | - Ricky C. Cheng
- Department of Molecular & Cellular Physiology, Stanford University School of Medicine, 279 Campus Drive West, Stanford, CA 94035
| | - Thomas A. Chew
- Department of Molecular & Cellular Physiology, Stanford University School of Medicine, 279 Campus Drive West, Stanford, CA 94035
| | - Chandra M. Khantwal
- Department of Molecular & Cellular Physiology, Stanford University School of Medicine, 279 Campus Drive West, Stanford, CA 94035
| | - Corey W. Liu
- Stanford Magnetic Resonance Laboratory, Stanford University School of Medicine, 299 Campus Drive West, D105 Fairchild Science Building, Stanford, CA 94305
| | - Shimei Gong
- Department of Molecular Physiology and Biological Physics, University of Virginia, PO Box 10011, Charlottesville, VA 22906-0011
| | - Robert K. Nakamoto
- Department of Molecular Physiology and Biological Physics, University of Virginia, PO Box 10011, Charlottesville, VA 22906-0011
| | - Merritt Maduke
- Department of Molecular & Cellular Physiology, Stanford University School of Medicine, 279 Campus Drive West, Stanford, CA 94035
- corresponding author, , tel (650)-723-9075, fax (650)-725-8021
| |
Collapse
|