1
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Stockbridge RB, Wackett LP. The link between ancient microbial fluoride resistance mechanisms and bioengineering organofluorine degradation or synthesis. Nat Commun 2024; 15:4593. [PMID: 38816380 PMCID: PMC11139923 DOI: 10.1038/s41467-024-49018-1] [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: 01/10/2024] [Accepted: 05/20/2024] [Indexed: 06/01/2024] Open
Abstract
Fluorinated organic chemicals, such as per- and polyfluorinated alkyl substances (PFAS) and fluorinated pesticides, are both broadly useful and unusually long-lived. To combat problems related to the accumulation of these compounds, microbial PFAS and organofluorine degradation and biosynthesis of less-fluorinated replacement chemicals are under intense study. Both efforts are undermined by the substantial toxicity of fluoride, an anion that powerfully inhibits metabolism. Microorganisms have contended with environmental mineral fluoride over evolutionary time, evolving a suite of detoxification mechanisms. In this perspective, we synthesize emerging ideas on microbial defluorination/fluorination and fluoride resistance mechanisms and identify best approaches for bioengineering new approaches for degrading and making organofluorine compounds.
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Affiliation(s)
- Randy B Stockbridge
- Department of Molecular, Cellular, and Developmental Biology, University of Michigan, Ann Arbor, MI, 48109, USA.
| | - Lawrence P Wackett
- Department of Biochemistry, Biophysics & Molecular Biology and Biotechnology Institute, University of Minnesota, Minneapolis, MN, 55455, USA.
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2
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Chon NL, Lin H. Fluoride Ion Binding and Translocation in the CLC F Fluoride/Proton Antiporter: Molecular Insights from Combined Quantum-Mechanical/Molecular-Mechanical Modeling. J Phys Chem B 2024; 128:2697-2706. [PMID: 38447081 PMCID: PMC10962343 DOI: 10.1021/acs.jpcb.4c00079] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/04/2024] [Revised: 02/15/2024] [Accepted: 02/20/2024] [Indexed: 03/08/2024]
Abstract
CLCF fluoride/proton antiporters move fluoride ions out of bacterial cells, leading to fluoride resistance in these bacteria. However, many details about their operating mechanisms remain unclear. Here, we report a combined quantum-mechanical/molecular-mechanical (QM/MM) study of a CLCF homologue from Enterococci casseliflavus (Eca), in accord with the previously proposed windmill mechanism. Our multiscale modeling sheds light on two critical steps in the transport cycle: (i) the external gating residue E118 pushing a fluoride in the external binding site into the extracellular vestibule and (ii) an incoming fluoride reconquering the external binding site by forcing out E118. Both steps feature competitions for the external binding site between the negatively charged carboxylate of E118 and the fluoride. Remarkably, the displaced E118 by fluoride accepts a proton from the nearby R117, initiating the next transport cycle. We also demonstrate the importance of accurate quantum descriptions of fluoride solvation. Our results provide clues to the mysterious E318 residue near the central binding site, suggesting that the transport activities are unlikely to be disrupted by the glutamate interacting with a well-solvated fluoride at the central binding site. This differs significantly from the structurally similar CLC chloride/proton antiporters, where a fluoride trapped deep in the hydrophobic pore causes the transporter to be locked down. A free-energy barrier of 10-15 kcal/mol was estimated via umbrella sampling for a fluoride ion traveling through the pore to repopulate the external binding site.
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Affiliation(s)
- Nara L. Chon
- Department of Chemistry, University of Colorado Denver, Denver, Colorado 80217, United States
| | - Hai Lin
- Department of Chemistry, University of Colorado Denver, Denver, Colorado 80217, United States
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3
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Kang CY, An M, Stockbridge RB. Lanthanum-fluoride electrode-based methods to monitor fluoride transport in cells and reconstituted lipid vesicles. Methods Enzymol 2024; 696:43-63. [PMID: 38658088 DOI: 10.1016/bs.mie.2024.01.012] [Citation(s) in RCA: 1] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 04/26/2024]
Abstract
Fluoride (F-) export proteins, including F- channels and F- transporters, are widespread in biology. They contribute to cellular resistance against fluoride ion, which has relevance as an ancient xenobiotic, and in more modern contexts like organofluorine biosynthesis and degradation or dental medicine. This chapter summarizes quantitative methods to measure fluoride transport across membranes using fluoride-specific lanthanum-fluoride electrodes. Electrode-based measurements can be used to measure unitary fluoride transport rates by membrane proteins that have been purified and reconstituted into lipid vesicles, or to monitor fluoride efflux into living microbial cells. Thus, fluoride electrode-based measurements yield quantitative mechanistic insight into one of the major determinants of fluoride resistance in microorganisms, fungi, yeasts, and plants.
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Affiliation(s)
- Chia-Yu Kang
- Program in Biophysics, University of Michigan, Ann Arbor, MI, United States
| | - Minjun An
- Department of Molecular, Cellular, and Developmental Biology, University of Michigan, Ann Arbor, MI, United States
| | - Randy B Stockbridge
- Program in Biophysics, University of Michigan, Ann Arbor, MI, United States; Department of Molecular, Cellular, and Developmental Biology, University of Michigan, Ann Arbor, MI, United States.
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4
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Asgharpour S, Chi LA, Spehr M, Carloni P, Alfonso-Prieto M. Fluoride Transport and Inhibition Across CLC Transporters. Handb Exp Pharmacol 2024; 283:81-100. [PMID: 36042142 DOI: 10.1007/164_2022_593] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/29/2022]
Abstract
The Chloride Channel (CLC) family includes proton-coupled chloride and fluoride transporters. Despite their similar protein architecture, the former exchange two chloride ions for each proton and are inhibited by fluoride, whereas the latter efficiently transport one fluoride in exchange for one proton. The combination of structural, mutagenesis, and functional experiments with molecular simulations has pinpointed several amino acid changes in the permeation pathway that capitalize on the different chemical properties of chloride and fluoride to fine-tune protein function. Here we summarize recent findings on fluoride inhibition and transport in the two prototypical members of the CLC family, the chloride/proton transporter from Escherichia coli (CLC-ec1) and the fluoride/proton transporter from Enterococcus casseliflavus (CLCF-eca).
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Affiliation(s)
- Somayeh Asgharpour
- Institute for Advanced Simulations IAS-5 and Institute of Neuroscience and Medicine INM-9, Computational Biomedicine, Forschungszentrum Jülich, Jülich, Germany
- Research Training Group 2416 MultiSenses-MultiScales, Institute for Biology II, RWTH Aachen University, Aachen, Germany
| | - L América Chi
- Laboratory for the Design and Development of New Drugs and Biotechnological Innovation, Escuela Superior de Medicina, Instituto Politécnico Nacional, Plan de San Luis y Díaz Mirón, Ciudad de México, Mexico
| | - Marc Spehr
- Research Training Group 2416 MultiSenses-MultiScales, Institute for Biology II, RWTH Aachen University, Aachen, Germany
- Department of Chemosensation, Institute for Biology II, RWTH Aachen University, Aachen, Germany
| | - Paolo Carloni
- Institute for Advanced Simulations IAS-5 and Institute of Neuroscience and Medicine INM-9, Computational Biomedicine, Forschungszentrum Jülich, Jülich, Germany.
- Research Training Group 2416 MultiSenses-MultiScales, Institute for Biology II, RWTH Aachen University, Aachen, Germany.
- Department of Physics, RWTH Aachen University, Aachen, Germany.
- JARA Institute Molecular Neuroscience and Neuroimaging (INM-11), Forschungszentrum Jülich, Jülich, Germany.
- JARA-HPC, Forschungszentrum Jülich, Jülich, Germany.
| | - Mercedes Alfonso-Prieto
- Institute for Advanced Simulations IAS-5 and Institute of Neuroscience and Medicine INM-9, Computational Biomedicine, Forschungszentrum Jülich, Jülich, Germany.
- Medical Faculty, Cécile and Oskar Vogt Institute for Brain Research, University Hospital Düsseldorf, Heinrich Heine University Düsseldorf, Düsseldorf, Germany.
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5
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Mills KR, Torabifard H. Uncovering the Mechanism of the Proton-Coupled Fluoride Transport in the CLC F Antiporter. J Chem Inf Model 2023; 63:2445-2455. [PMID: 37053383 DOI: 10.1021/acs.jcim.2c01228] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 04/15/2023]
Abstract
Fluoride is a natural antibiotic abundantly present in the environment and, in micromolar concentrations, is able to inhibit enzymes necessary for bacteria to survive. However, as is the case with many antibiotics, bacteria have evolved resistance methods, including through the use of recently discovered membrane proteins. One such protein is the CLCF F-/H+ antiporter protein, a member of the CLC superfamily of anion-transport proteins. Though previous studies have examined this F- transporter, many questions are still left unanswered. To reveal details of the transport mechanism used by CLCF, we have employed molecular dynamics simulations and umbrella sampling calculations. Our results have led to several discoveries, including the mechanism of proton import and how it is able to aid in the fluoride export. Additionally, we have determined the role of the previously identified residues Glu118, Glu318, Met79, and Tyr396. This work is among the first studies of the CLCF F-/H+ antiporter and is the first computational investigation to model the full transport process, proposing a mechanism which couples the F- export with the H+ import.
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Affiliation(s)
- Kira R Mills
- Department of Chemistry and Biochemistry, The University of Texas at Dallas, Richardson, Texas 75080, United States
| | - Hedieh Torabifard
- Department of Chemistry and Biochemistry, The University of Texas at Dallas, Richardson, Texas 75080, United States
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6
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Yue Z, Li C, Voth GA. The role of conformational change and key glutamic acid residues in the ClC-ec1 antiporter. Biophys J 2023; 122:1068-1085. [PMID: 36698313 PMCID: PMC10111279 DOI: 10.1016/j.bpj.2023.01.025] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/24/2022] [Revised: 01/16/2023] [Accepted: 01/20/2023] [Indexed: 01/26/2023] Open
Abstract
The triple glutamine (Q) mutant (QQQ) structure of a Cl-/H+ antiporter from Escherichia coli (ClC-ec1) displaying a novel backbone arrangement has been used to challenge the long-held notion that Cl-/H+ antiporters do not operate through large conformational motions. The QQQ mutant substitutes the glutamine residue for an external glutamate E148, an internal glutamate E203, and a third glutamate E113 that hydrogen-bonds with E203. However, it is unknown if QQQ represents a physiologically relevant state, as well as how the protonation of the wild-type glutamates relates to the global dynamics. We herein apply continuous constant-pH molecular dynamics to investigate the H+-coupled dynamics of ClC-ec1. Although any large-scale conformational rearrangement upon acidification would be due to the accumulation of excess charge within the protein, protonation of the glutamates significantly impacts mainly the local structure and dynamics. Despite the fact that the extracellular pore enlarges at acidic pHs, an occluded ClC-ec1 within the active pH range of 3.5-7.5 requires a protonated E148 to facilitate extracellular Cl- release. E203 is also involved in the intracellular H+ transfer as an H+ acceptor. The water wire connection of E148 with the intracellular solution is regulated by the charge states of the E113/E203 dyad with coupled proton titration. However, the dynamics extracted from our simulations are not QQQ-like, indicating that the QQQ mutant does not represent the behavior of the wild-type ClC-ec1. These findings reinforce the necessity of having a protonatable residue at the E203 position in ClC-ec1 and suggest that a higher level of complexity exists for the intracellular H+ transfer in Cl-/H+ antiporters.
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Affiliation(s)
- Zhi Yue
- Department of Chemistry, Chicago Center for Theoretical Chemistry, James Franck Institute, and Institute for Biophysical Dynamics, The University of Chicago, Chicago, Illinois
| | - Chenghan Li
- Department of Chemistry, Chicago Center for Theoretical Chemistry, James Franck Institute, and Institute for Biophysical Dynamics, The University of Chicago, Chicago, Illinois
| | - Gregory A Voth
- Department of Chemistry, Chicago Center for Theoretical Chemistry, James Franck Institute, and Institute for Biophysical Dynamics, The University of Chicago, Chicago, Illinois.
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7
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Kumar S, Mollo A, Rubino FA, Kahne D, Ruiz N. Chloride Ions Are Required for Thermosipho africanus MurJ Function. mBio 2023; 14:e0008923. [PMID: 36752629 PMCID: PMC9973255 DOI: 10.1128/mbio.00089-23] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/12/2023] [Accepted: 01/17/2023] [Indexed: 02/09/2023] Open
Abstract
Most bacteria have a peptidoglycan cell wall that determines their cell shape and helps them resist osmotic lysis. Peptidoglycan synthesis depends on the translocation of the lipid-linked precursor lipid II across the cytoplasmic membrane by the MurJ flippase. Structure-function analyses of MurJ from Thermosipho africanus (MurJTa) and Escherichia coli (MurJEc) have revealed that MurJ adopts multiple conformations and utilizes an alternating-access mechanism to flip lipid II. MurJEc activity relies on membrane potential, but the specific counterion has not been identified. Crystal structures of MurJTa revealed a chloride ion bound to the N-lobe of the flippase and a sodium ion in its C-lobe, but the role of these ions in transport is unknown. Here, we investigated the effect of various ions on the function of MurJTa and MurJEc in vivo. We found that chloride, and not sodium, ions are necessary for MurJTa function, but neither ion is required for MurJEc function. We also showed that murJTa alleles encoding changes at the crystallographically identified sodium-binding site still complement the loss of native murJEc, although they decreased protein stability and/or function. Based on our data and previous work, we propose that chloride ions are necessary for the conformational change that resets MurJTa after lipid II translocation and suggest that MurJ orthologs may function similarly but differ in their requirements for counterions. IMPORTANCE The biosynthetic pathway of the peptidoglycan cell wall is one of the most favorable targets for antibiotic development. Lipid II, the lipid-linked PG precursor, is made in the inner leaflet of the cytoplasmic membrane and then transported by the MurJ flippase so that it can be used to build the peptidoglycan cell wall. MurJ functions using an alternating-access mechanism thought to depend on a yet-to-be-identified counterion. This study fills a gap in our understanding of MurJ's energy-coupling mechanism by showing that chloride ions are required for MurJ in some, but not all, organisms. Based on our data and prior studies, we propose that, while the general transport mechanism of MurJ may be conserved, its specific mechanistic details may differ across bacteria, as is common in transporters. These findings are important to understand MurJ function and its development as an antibiotic target.
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Affiliation(s)
- Sujeet Kumar
- Department of Microbiology, The Ohio State University, Columbus, Ohio, USA
| | - Aurelio Mollo
- Department of Chemistry and Chemical Biology, Harvard University, Cambridge, Massachusetts, USA
| | - Frederick A. Rubino
- Department of Chemistry and Chemical Biology, Harvard University, Cambridge, Massachusetts, USA
| | - Daniel Kahne
- Department of Chemistry and Chemical Biology, Harvard University, Cambridge, Massachusetts, USA
- Department of Molecular and Cellular Biology, Harvard University, Cambridge, Massachusetts, USA
- Department of Biological Chemistry and Molecular Pharmacology, Harvard Medical School, Boston, Massachusetts, USA
| | - Natividad Ruiz
- Department of Microbiology, The Ohio State University, Columbus, Ohio, USA
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8
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Leisle L, Lam K, Dehghani-Ghahnaviyeh S, Fortea E, Galpin JD, Ahern CA, Tajkhorshid E, Accardi A. Backbone amides are determinants of Cl - selectivity in CLC ion channels. Nat Commun 2022; 13:7508. [PMID: 36473856 PMCID: PMC9726985 DOI: 10.1038/s41467-022-35279-1] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/30/2022] [Accepted: 11/23/2022] [Indexed: 12/12/2022] Open
Abstract
Chloride homeostasis is regulated in all cellular compartments. CLC-type channels selectively transport Cl- across biological membranes. It is proposed that side-chains of pore-lining residues determine Cl- selectivity in CLC-type channels, but their spatial orientation and contributions to selectivity are not conserved. This suggests a possible role for mainchain amides in selectivity. We use nonsense suppression to insert α-hydroxy acids at pore-lining positions in two CLC-type channels, CLC-0 and bCLC-k, thus exchanging peptide-bond amides with ester-bond oxygens which are incapable of hydrogen-bonding. Backbone substitutions functionally degrade inter-anion discrimination in a site-specific manner. The presence of a pore-occupying glutamate side chain modulates these effects. Molecular dynamics simulations show backbone amides determine ion energetics within the bCLC-k pore and how insertion of an α-hydroxy acid alters selectivity. We propose that backbone-ion interactions are determinants of Cl- specificity in CLC channels in a mechanism reminiscent of that described for K+ channels.
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Affiliation(s)
- Lilia Leisle
- Department of Anesthesiology, Weill Cornell Medical College, New York, NY, USA
| | - Kin Lam
- Theoretical and Computational Biophysics Group, University of Illinois at Urbana-Champaign, Urbana, IL, 61801, USA
- NIH Center for Macromolecular Modeling and Bioinformatics, University of Illinois at Urbana-Champaign, Urbana, IL, 61801, USA
- Beckman Institute for Advanced Science and Technology, University of Illinois at Urbana-Champaign, Urbana, IL, 61801, USA
- Department of Biochemistry, University of Illinois at Urbana-Champaign, Urbana, IL, 61801, USA
- Center for Biophysics and Quantitative Biology, University of Illinois at Urbana-Champaign, Urbana, IL, 61801, USA
| | - Sepehr Dehghani-Ghahnaviyeh
- Theoretical and Computational Biophysics Group, University of Illinois at Urbana-Champaign, Urbana, IL, 61801, USA
- NIH Center for Macromolecular Modeling and Bioinformatics, University of Illinois at Urbana-Champaign, Urbana, IL, 61801, USA
- Beckman Institute for Advanced Science and Technology, University of Illinois at Urbana-Champaign, Urbana, IL, 61801, USA
- Department of Biochemistry, University of Illinois at Urbana-Champaign, Urbana, IL, 61801, USA
- Center for Biophysics and Quantitative Biology, University of Illinois at Urbana-Champaign, Urbana, IL, 61801, USA
| | - Eva Fortea
- Department of Anesthesiology, Weill Cornell Medical College, New York, NY, USA
- Department of Physiology and Biophysics, Weill Cornell Medical College, New York, NY, USA
| | - Jason D Galpin
- Department of Molecular Physiology and Biophysics, University of Iowa, Iowa City, IA, USA
| | - Christopher A Ahern
- Department of Molecular Physiology and Biophysics, University of Iowa, Iowa City, IA, USA
| | - Emad Tajkhorshid
- Theoretical and Computational Biophysics Group, University of Illinois at Urbana-Champaign, Urbana, IL, 61801, USA
- NIH Center for Macromolecular Modeling and Bioinformatics, University of Illinois at Urbana-Champaign, Urbana, IL, 61801, USA
- Beckman Institute for Advanced Science and Technology, University of Illinois at Urbana-Champaign, Urbana, IL, 61801, USA
- Department of Biochemistry, University of Illinois at Urbana-Champaign, Urbana, IL, 61801, USA
- Center for Biophysics and Quantitative Biology, University of Illinois at Urbana-Champaign, Urbana, IL, 61801, USA
| | - Alessio Accardi
- Department of Anesthesiology, Weill Cornell Medical College, New York, NY, USA.
- Department of Physiology and Biophysics, Weill Cornell Medical College, New York, NY, USA.
- Department of Biochemistry, Weill Cornell Medical College, New York, NY, USA.
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9
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Yue Z, Bernardi A, Li C, Mironenko AV, Swanson JMJ. Toward a Multipathway Perspective: pH-Dependent Kinetic Selection of Competing Pathways and the Role of the Internal Glutamate in Cl -/H + Antiporters. J Phys Chem B 2021; 125:7975-7984. [PMID: 34260231 PMCID: PMC8409247 DOI: 10.1021/acs.jpcb.1c03304] [Citation(s) in RCA: 3] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/13/2022]
Abstract
Canonical descriptions of multistep biomolecular transformations generally follow a single-pathway viewpoint, with a series of transitions through intermediates converting reactants to products or repeating a conformational cycle. However, mounting evidence suggests that more complexity and pathway heterogeneity are mechanistically relevant due to the statistical distribution of multiple interconnected rate processes. Making sense of such pathway complexity remains a significant challenge. To better understand the role and relevance of pathway heterogeneity, we herein probe the chemical reaction network of a Cl-/H+ antiporter, ClC-ec1, and analyze reaction pathways using multiscale kinetic modeling (MKM). This approach allows us to describe the nature of the competing pathways and how they change as a function of pH. We reveal that although pH-dependent Cl-/H+ transport rates are largely regulated by the charge state of amino acid E148, the charge state of E203 determines relative contributions from coexisting pathways and can shift the flux pH-dependence. The selection of pathways via E203 explains how ionizable mutations (D/H/K/R) would impact the ClC-ec1 bioactivity from a kinetic perspective and lends further support to the indispensability of an internal glutamate in ClC antiporters. Our results demonstrate how quantifying the kinetic selection of competing pathways under varying conditions leads to a deeper understanding of the Cl-/H+ exchange mechanism and can suggest new approaches for mechanistic control.
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Affiliation(s)
- Zhi Yue
- Department of Chemistry, Chicago Center for Theoretical Chemistry, James Frank Institute, and Institute for Biophysical Dynamics, The University of Chicago, Chicago, Illinois 60637, United States
| | - Austen Bernardi
- Department of Chemistry, Biological Chemistry Program, and Center for Cell and Genome Science, The University of Utah, Salt Lake City, Utah 84112, United States
| | - Chenghan Li
- Department of Chemistry, Chicago Center for Theoretical Chemistry, James Frank Institute, and Institute for Biophysical Dynamics, The University of Chicago, Chicago, Illinois 60637, United States
| | - Alexander V. Mironenko
- Department of Chemistry, Chicago Center for Theoretical Chemistry, James Frank Institute, and Institute for Biophysical Dynamics, The University of Chicago, Chicago, Illinois 60637, United States
| | - Jessica M. J. Swanson
- Department of Chemistry, Biological Chemistry Program, and Center for Cell and Genome Science, The University of Utah, Salt Lake City, Utah 84112, United States
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10
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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.
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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
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11
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12
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Chiariello MG, Bolnykh V, Ippoliti E, Meloni S, Olsen JMH, Beck T, Rothlisberger U, Fahlke C, Carloni P. Molecular Basis of CLC Antiporter Inhibition by Fluoride. J Am Chem Soc 2020; 142:7254-7258. [PMID: 32233472 DOI: 10.1021/jacs.9b13588] [Citation(s) in RCA: 12] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/07/2023]
Abstract
CLC channels and transporters conduct or transport various kinds of anions, with the exception of fluoride, which acts as an effective inhibitor. Here, we performed sub-nanosecond DFT-based QM/MM simulations of the E. coli anion/proton exchanger ClC-ec1 and observed that fluoride binds incoming protons within the selectivity filter, with excess protons shared with the gating glutamate E148. Depending on E148 conformation, the competition for the proton can involve either a direct F-/E148 interaction or the modulation of water molecules bridging the two anions. The direct interaction locks E148 in a conformation that does not allow for proton transport, and thus inhibits protein function.
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Affiliation(s)
- Maria Gabriella Chiariello
- Institute for Advanced Simulation (IAS-5) and Institute of Neuroscience and Medicine (INM-9), Computational Biomedicine, Forschungszentrum Jülich, 52425 Jülich, Germany.,JARA-HPC, Forschungszentrum Jülich, D-54245 Jülich, Germany
| | - Viacheslav Bolnykh
- Laboratory of Computational Chemistry and Biochemistry, Ecole Polytechnique Fédérale de Lausanne, CH-1015 Lausanne, Switzerland
| | - Emiliano Ippoliti
- Institute for Advanced Simulation (IAS-5) and Institute of Neuroscience and Medicine (INM-9), Computational Biomedicine, Forschungszentrum Jülich, 52425 Jülich, Germany.,JARA-HPC, Forschungszentrum Jülich, D-54245 Jülich, Germany
| | - Simone Meloni
- Dipartimento di Scienze Chimiche e Farmaceutiche, Università degli Studi di Ferrara, Via Luigi Borsari 46, I-44121 Ferrara, Italy
| | - Jógvan Magnus Haugaard Olsen
- Hylleraas Centre for Quantum Molecular Sciences, Department of Chemistry, UiT The Arctic University of Norway, N-9037 Tromsø, Norway
| | - Thomas Beck
- Department of Chemistry, University of Cincinnati, Cincinnati, Ohio 45221, United States
| | - Ursula Rothlisberger
- Laboratory of Computational Chemistry and Biochemistry, Ecole Polytechnique Fédérale de Lausanne, CH-1015 Lausanne, Switzerland
| | - Christoph Fahlke
- Institute of Biological Information Processing (IBI-1), Molekular- und Zellphysiologie, Forschungszentrum Jülich, D-54245 Jülich, Germany
| | - Paolo Carloni
- Institute for Advanced Simulation (IAS-5) and Institute of Neuroscience and Medicine (INM-9), Computational Biomedicine, Forschungszentrum Jülich, 52425 Jülich, Germany.,JARA-HPC, Forschungszentrum Jülich, D-54245 Jülich, Germany.,Department of Physics, RWTH Aachen University, 52056 Aachen, Germany.,Institute of Neuroscience and Medicine (INM-11), Molecular Neuroscience and Neuroimaging, Forschungszentrum Julich, 52425 Julich, Germany
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13
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Johnston NR, Strobel SA. Principles of fluoride toxicity and the cellular response: a review. Arch Toxicol 2020; 94:1051-1069. [PMID: 32152649 PMCID: PMC7230026 DOI: 10.1007/s00204-020-02687-5] [Citation(s) in RCA: 111] [Impact Index Per Article: 27.8] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/09/2019] [Accepted: 02/21/2020] [Indexed: 02/04/2023]
Abstract
Fluoride is ubiquitously present throughout the world. It is released from minerals, magmatic gas, and industrial processing, and travels in the atmosphere and water. Exposure to low concentrations of fluoride increases overall oral health. Consequently, many countries add fluoride to their public water supply at 0.7-1.5 ppm. Exposure to high concentrations of fluoride, such as in a laboratory setting often exceeding 100 ppm, results in a wide array of toxicity phenotypes. This includes oxidative stress, organelle damage, and apoptosis in single cells, and skeletal and soft tissue damage in multicellular organisms. The mechanism of fluoride toxicity can be broadly attributed to four mechanisms: inhibition of proteins, organelle disruption, altered pH, and electrolyte imbalance. Recently, there has been renewed concern in the public sector as to whether fluoride is safe at the current exposure levels. In this review, we will focus on the impact of fluoride at the chemical, cellular, and multisystem level, as well as how organisms defend against fluoride. We also address public concerns about fluoride toxicity, including whether fluoride has a significant effect on neurodegeneration, diabetes, and the endocrine system.
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Affiliation(s)
- Nichole R Johnston
- Department of Molecular Biophysics and Biochemistry, Yale University, New Haven, CT, 06520, USA
| | - Scott A Strobel
- Department of Molecular Biophysics and Biochemistry, Yale University, New Haven, CT, 06520, USA.
- Department of Chemistry, Yale University, New Haven, CT, 06520, USA.
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14
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Xing A, Ma Y, Wu Z, Nong S, Zhu J, Sun H, Tao J, Wen B, Zhu X, Fang W, Li X, Wang Y. Genome-wide identification and expression analysis of the CLC superfamily genes in tea plants (Camellia sinensis). Funct Integr Genomics 2020; 20:497-508. [PMID: 31897824 DOI: 10.1007/s10142-019-00725-9] [Citation(s) in RCA: 6] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/12/2019] [Revised: 10/17/2019] [Accepted: 11/05/2019] [Indexed: 11/30/2022]
Abstract
The voltage-gated chloride channel (CLC) superfamily is one of the most important anion channels that is widely distributed in bacteria and plants. CLC is involved in transporting various anions such as chloride (Cl-) and fluoride (F-) in and out of cells. Although Camellia sinensis is a hyper-accumulated F plant, there is no studies on the CLC gene superfamily in the tea plant. Here, 8 CLC genes were identified from C. sinensis and they were named CsCLC1-8. The structure of CsCLC genes and the proteins were not conserved; the number of exons varied from 3 to 24, and the number of transmembrane domains contained 2 to 10. Furthermore, phylogenetic analysis revealed that CsCLC4-8 in subclass I contained the typical conserved domains GxGIPE (I), GKxGPxxH (II) and PxxGxLF (III), and CsCLC1-3 in subclass II did not contain any of the three conserved residues. We measured the expression levels of CsCLCs in roots, stems and leaves to assess the responses to different concentrations of Cl- and F-. The result indicated that CsCLCs participated in subfunctionalization in response to Cl- and F-, and CsCLC1-3 was more sensitive to F- treatments than CsCLC4-8, CsCLC6 and CsCLC7 may participate in absorption and long-distance transport of Cl-.
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Affiliation(s)
- Anqi Xing
- College of Horticulture, Nanjing Agricultural University, Nanjing, 210095, China
| | - Yuanchun Ma
- College of Horticulture, Nanjing Agricultural University, Nanjing, 210095, China
| | - Zichen Wu
- College of Horticulture, Nanjing Agricultural University, Nanjing, 210095, China
| | - Shouhua Nong
- College of Horticulture, Nanjing Agricultural University, Nanjing, 210095, China
| | - Jiaojiao Zhu
- College of Horticulture, Nanjing Agricultural University, Nanjing, 210095, China
| | - Hua Sun
- College of Horticulture, Nanjing Agricultural University, Nanjing, 210095, China
| | - Jing Tao
- College of Horticulture, Nanjing Agricultural University, Nanjing, 210095, China
| | - Bo Wen
- College of Landscape Architecture, Nanjing Forestry University, Nanjing, 210037, China
| | - Xujun Zhu
- College of Horticulture, Nanjing Agricultural University, Nanjing, 210095, China
| | - Wanping Fang
- College of Horticulture, Nanjing Agricultural University, Nanjing, 210095, China
| | - Xiaocheng Li
- Jiaozhou Vocational Education Center School, Qingdao, 266300, China
| | - Yuhua Wang
- College of Horticulture, Nanjing Agricultural University, Nanjing, 210095, China.
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15
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Araújo CET, Oliveira CMC, Barbosa JD, Oliveira-Filho JP, Resende LAL, Badial PR, Araujo-Junior JP, McCue ME, Borges AS. A large intragenic deletion in the CLCN1 gene causes Hereditary Myotonia in pigs. Sci Rep 2019; 9:15632. [PMID: 31666547 PMCID: PMC6821760 DOI: 10.1038/s41598-019-51286-7] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/18/2019] [Accepted: 09/11/2019] [Indexed: 12/14/2022] Open
Abstract
Mutations in the CLCN1 gene are the primary cause of non-dystrophic Hereditary Myotonia in several animal species. However, there are no reports of Hereditary Myotonia in pigs to date. Therefore, the objective of the present study was to characterize the clinical and molecular findings of Hereditary Myotonia in an inbred pedigree. The clinical, electromyographic, histopathological, and molecular findings were evaluated. Clinically affected pigs presented non-dystrophic recessive Hereditary Myotonia. Nucleotide sequence analysis of the entire coding region of the CLCN1 gene revealed the absence of the exons 15 and 16 in myotonic animals. Analysis of the genomic region flanking the deletion unveiled a large intragenic deletion of 4,165 nucleotides. Interestingly, non-related, non-myotonic pigs expressed transcriptional levels of an alternate transcript (i.e., X2) that was identical to the deleted X1 transcript of myotonic pigs. All myotonic pigs and their progenitors were homozygous recessive and heterozygous, respectively, for the 4,165-nucleotide deletion. This is the first study reporting Hereditary Myotonia in pigs and characterizing its clinical and molecular findings. Moreover, to the best of our knowledge, Hereditary Myotonia has never been associated with a genomic deletion in the CLCN1 gene in any other species.
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Affiliation(s)
- C E T Araújo
- São Paulo State University (UNESP), School of Veterinary Medicine and Animal Science, Botucatu, São Paulo, Brazil
| | - C M C Oliveira
- Instituto de Medicina Veterinária, Universidade Federal do Pará, Campus Castanhal, PA, Brazil
| | - J D Barbosa
- Instituto de Medicina Veterinária, Universidade Federal do Pará, Campus Castanhal, PA, Brazil
| | - J P Oliveira-Filho
- São Paulo State University (UNESP), School of Veterinary Medicine and Animal Science, Botucatu, São Paulo, Brazil
| | - L A L Resende
- São Paulo State University (UNESP), Medical School, Botucatu, Brazil
| | - P R Badial
- Department of Pathobiology and Population Medicine, College of Veterinary Medicine, Mississippi State University, Starkville, MS, USA
| | - J P Araujo-Junior
- São Paulo State University (UNESP), Institute of Bioscience, Botucatu, Brazil
| | - M E McCue
- College of Veterinary Medicine, University of Minnesota, St Paul, Minnesota, 55108, USA
| | - A S Borges
- São Paulo State University (UNESP), School of Veterinary Medicine and Animal Science, Botucatu, São Paulo, Brazil.
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16
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Mutation of external glutamate residue reveals a new intermediate transport state and anion binding site in a CLC Cl -/H + antiporter. Proc Natl Acad Sci U S A 2019; 116:17345-17354. [PMID: 31409705 DOI: 10.1073/pnas.1901822116] [Citation(s) in RCA: 8] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/21/2022] Open
Abstract
The CLC family of proteins are involved in a variety of physiological processes to control cellular chloride concentration. Two distinct classes of CLC proteins, Cl- channels and Cl-/H+ antiporters, have been functionally and structurally investigated over the last several decades. Previous studies have suggested that the conformational heterogeneity of the critical glutamate residue, Gluex, could explain the transport cycle of CLC-type Cl-/H+ antiporters. However, the presence of multiple conformations (Up, Middle, and Down) of the Gluex has been suggested from combined structural snapshots of 2 different CLC antiporters: CLC-ec1 from Escherichia coli and cmCLC from a thermophilic red alga, Cyanidioschyzon merolae Thus, we aimed to investigate further the heterogeneity of Gluex-conformations in CLC-ec1, the most deeply studied CLC antiporter, at both functional and structural levels. Here, we show that the crystal structures of the Gluex mutant E148D and wild-type CLC-ec1 with varying anion concentrations suggest a structural intermediate, the "Midlow" conformation. We also found that an extra anion can be located above the external Cl--binding site in the E148D mutant when the anion concentration is high. Moreover, we observed that a carboxylate in solution can occupy either the external or central Cl--binding site in the ungated E148A mutant using an anomalously detectable short carboxylic acid, bromoacetate. These results lend credibility to the idea that the Gluex can take at least 3 distinct conformational states during the transport cycle of a single CLC antiporter.
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17
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Wang Z, Swanson JMJ, Voth GA. Modulating the Chemical Transport Properties of a Transmembrane Antiporter via Alternative Anion Flux. J Am Chem Soc 2018; 140:16535-16543. [PMID: 30421606 PMCID: PMC6379079 DOI: 10.1021/jacs.8b07614] [Citation(s) in RCA: 21] [Impact Index Per Article: 3.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/16/2023]
Abstract
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ClC-ec1 is a prototype of the ClC
antiporters, proteins that stoichiometrically
exchange Cl– and H+ ions in opposite
directions across a membrane. It has been shown that other polyatomic
anions, such as NO3– and SCN–, can also be transported by ClC-ec1, but with partially or completely
uncoupled proton flux. Herein, with the help of multiscale computer
simulations in which the Grotthuss mechanism of proton transport (PT)
is treated explicitly, we demonstrate how the chemical nature of these
anions alters the coupling mechanism and qualitatively explain the
shifts in the ion stoichiometry. Multidimensional free energy profiles
for PT and the coupled changes in hydration are presented for NO3– and SCN–. The calculated
proton conductances agree with experiment, showing reduced or abolished
proton flux. Surprisingly, the proton affinity of the anion is less
influential on the PT, while its size and interactions with the protein
significantly alter hydration and shift its influence on PT from facilitating
to inhibiting. We find that the hydration of the cavity below the
anion is relatively fast, but connecting the water network past the
steric hindrance of these polyatomic anions is quite slow. Hence,
the most relevant coordinate to the PT free energy barrier is the
water connectivity along the PT pathway, but importantly only in the
presence of the excess proton, and this coordinate is significantly
affected by the nature of the bound anion. This work again demonstrates
how PT is intrinsically coupled with protein cavity hydration changes
as well as influenced by the protein environment. It additionally
suggests ways in which ion exchange can be modulated and exchange
stoichiometries altered.
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Affiliation(s)
- Zhi Wang
- Department of Chemistry, James Franck Institute, and Institute for Biophysical Dynamics , The University of Chicago , Chicago , Illinois 60637 , United States
| | - Jessica M J Swanson
- Department of Chemistry, James Franck Institute, and Institute for Biophysical Dynamics , The University of Chicago , Chicago , Illinois 60637 , United States
| | - Gregory A Voth
- Department of Chemistry, James Franck Institute, and Institute for Biophysical Dynamics , The University of Chicago , Chicago , Illinois 60637 , United States
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18
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Last NB, Stockbridge RB, Wilson AE, Shane T, Kolmakova-Partensky L, Koide A, Koide S, Miller C. A CLC-type F -/H + antiporter in ion-swapped conformations. Nat Struct Mol Biol 2018; 25:601-606. [PMID: 29941917 PMCID: PMC6044475 DOI: 10.1038/s41594-018-0082-0] [Citation(s) in RCA: 26] [Impact Index Per Article: 4.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/03/2018] [Accepted: 05/31/2018] [Indexed: 11/09/2022]
Abstract
Fluoride/proton antiporters of the CLCF family combat F- toxicity in bacteria by exporting this halide from the cytoplasm. These transporters belong to the widespread CLC superfamily but display transport properties different from those of the well-studied Cl-/H+ antiporters. Here, we report a structural and functional investigation of these F--transport proteins. Crystal structures of a CLCF homolog from Enterococcus casseliflavus are captured in two conformations with simultaneous accessibility of F- and H+ ions via separate pathways on opposite sides of the membrane. Manipulation of a key glutamate residue critical for H+ and F- transport reverses the anion selectivity of transport; replacement of the glutamate with glutamine or alanine completely inhibits F- and H+ transport while allowing for rapid uncoupled flux of Cl-. The structural and functional results lead to a 'windmill' model of CLC antiport wherein F- and H+ simultaneously move through separate ion-specific pathways that switch sidedness during the transport cycle.
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Affiliation(s)
- Nicholas B Last
- Department of Biochemistry, Howard Hughes Medical Institute, Brandeis University, Waltham, MA, USA
| | - Randy B Stockbridge
- Department of Biochemistry, Howard Hughes Medical Institute, Brandeis University, Waltham, MA, USA
| | - Ashley E Wilson
- Department of Biochemistry, Howard Hughes Medical Institute, Brandeis University, Waltham, MA, USA
| | - Tania Shane
- Department of Biochemistry, Howard Hughes Medical Institute, Brandeis University, Waltham, MA, USA
| | | | - Akiko Koide
- Perlmutter Cancer Center, New York University Langone Health, New York University School of Medicine, New York, NY, USA
- Department of Medicine, New York University School of Medicine, New York, NY, USA
| | - Shohei Koide
- Perlmutter Cancer Center, New York University Langone Health, New York University School of Medicine, New York, NY, USA
- Department of Biochemistry and Molecular Pharmacology, New York University School of Medicine, New York, NY, USA
| | - Christopher Miller
- Department of Biochemistry, Howard Hughes Medical Institute, Brandeis University, Waltham, MA, USA.
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19
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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.
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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
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20
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Mayes HB, Lee S, White AD, Voth GA, Swanson JMJ. Multiscale Kinetic Modeling Reveals an Ensemble of Cl -/H + Exchange Pathways in ClC-ec1 Antiporter. J Am Chem Soc 2018; 140:1793-1804. [PMID: 29332400 PMCID: PMC5812667 DOI: 10.1021/jacs.7b11463] [Citation(s) in RCA: 32] [Impact Index Per Article: 5.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/29/2023]
Abstract
Despite several years of research, the ion exchange mechanisms in chloride/proton antiporters and many other coupled transporters are not yet understood at the molecular level. Here, we present a novel approach to kinetic modeling and apply it to ion exchange in ClC-ec1. Our multiscale kinetic model is developed by (1) calculating the state-to-state rate coefficients with reactive and polarizable molecular dynamics simulations, (2) optimizing these rates in a global kinetic network, and (3) predicting new electrophysiological results. The model shows that the robust Cl:H exchange ratio (2.2:1) can indeed arise from kinetic coupling without large protein conformational changes, indicating a possible facile evolutionary connection to chloride channels. The E148 amino acid residue is shown to couple chloride and proton transport through protonation-dependent blockage of the central anion binding site and an anion-dependent pKa value, which influences proton transport. The results demonstrate how an ensemble of different exchange pathways, as opposed to a single series of transitions, culminates in the macroscopic observables of the antiporter, such as transport rates, chloride/proton stoichiometry, and pH dependence.
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Affiliation(s)
- Heather B Mayes
- Department of Chemistry, The University of Chicago , Chicago, Illinois 60637, United States.,Department of Chemical Engineering, University of Michigan , Ann Arbor, Michigan 48109, United States
| | - Sangyun Lee
- Department of Chemistry, The University of Chicago , Chicago, Illinois 60637, United States.,Computational Biology Center, IBM Thomas J. Watson Research Center , Yorktown Heights, New York 10598, United States
| | - Andrew D White
- Department of Chemistry, The University of Chicago , Chicago, Illinois 60637, United States.,Department of Chemical Engineering, University of Rochester , Rochester, New York 14627-0166, United States
| | - Gregory A Voth
- Department of Chemistry, The University of Chicago , Chicago, Illinois 60637, United States.,James Franck Institute and Institute for Biophysical Dynamics, The University of Chicago , Chicago, Illinois 60637, United States
| | - Jessica M J Swanson
- Department of Chemistry, The University of Chicago , Chicago, Illinois 60637, United States
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21
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Abstract
Isothermal titration calorimetry (ITC) is an emerging, label-free technology used to measure ligand binding to membrane proteins. This technology utilizes a titration calorimeter to measure the heat exchange upon ligands binding to proteins, the magnitude of which is based on the overall enthalpy of the reaction. In this protocol, the steps we and others use to measure ion binding to ion transport proteins are described.
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Affiliation(s)
- Shian Liu
- Department of Biology, Texas A&M University, 3474 TAMU, College Station, TX, 77843-3474, USA
- Janelia Research Campus, Howard Hughes Medical Institute, 19700 Helix Drive, Ashburn, VA, 20148, USA
| | - Steve W Lockless
- Department of Biology, Texas A&M University, 3474 TAMU, College Station, TX, 77843-3474, USA.
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22
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Lacruz RS, Habelitz S, Wright JT, Paine ML. DENTAL ENAMEL FORMATION AND IMPLICATIONS FOR ORAL HEALTH AND DISEASE. Physiol Rev 2017; 97:939-993. [PMID: 28468833 DOI: 10.1152/physrev.00030.2016] [Citation(s) in RCA: 223] [Impact Index Per Article: 31.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/03/2016] [Revised: 01/10/2017] [Accepted: 01/10/2017] [Indexed: 12/16/2022] Open
Abstract
Dental enamel is the hardest and most mineralized tissue in extinct and extant vertebrate species and provides maximum durability that allows teeth to function as weapons and/or tools as well as for food processing. Enamel development and mineralization is an intricate process tightly regulated by cells of the enamel organ called ameloblasts. These heavily polarized cells form a monolayer around the developing enamel tissue and move as a single forming front in specified directions as they lay down a proteinaceous matrix that serves as a template for crystal growth. Ameloblasts maintain intercellular connections creating a semi-permeable barrier that at one end (basal/proximal) receives nutrients and ions from blood vessels, and at the opposite end (secretory/apical/distal) forms extracellular crystals within specified pH conditions. In this unique environment, ameloblasts orchestrate crystal growth via multiple cellular activities including modulating the transport of minerals and ions, pH regulation, proteolysis, and endocytosis. In many vertebrates, the bulk of the enamel tissue volume is first formed and subsequently mineralized by these same cells as they retransform their morphology and function. Cell death by apoptosis and regression are the fates of many ameloblasts following enamel maturation, and what cells remain of the enamel organ are shed during tooth eruption, or are incorporated into the tooth's epithelial attachment to the oral gingiva. In this review, we examine key aspects of dental enamel formation, from its developmental genesis to the ever-increasing wealth of data on the mechanisms mediating ionic transport, as well as the clinical outcomes resulting from abnormal ameloblast function.
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Affiliation(s)
- Rodrigo S Lacruz
- Department of Basic Science and Craniofacial Biology, College of Dentistry, New York University, New York, New York; Department of Preventive and Restorative Dental Sciences, University of California, San Francisco, San Francisco, California; Department of Pediatric Dentistry, School of Dentistry, University of North Carolina, Chapel Hill, North Carolina; Herman Ostrow School of Dentistry, Center for Craniofacial Molecular Biology, University of Southern California, Los Angeles, California
| | - Stefan Habelitz
- Department of Basic Science and Craniofacial Biology, College of Dentistry, New York University, New York, New York; Department of Preventive and Restorative Dental Sciences, University of California, San Francisco, San Francisco, California; Department of Pediatric Dentistry, School of Dentistry, University of North Carolina, Chapel Hill, North Carolina; Herman Ostrow School of Dentistry, Center for Craniofacial Molecular Biology, University of Southern California, Los Angeles, California
| | - J Timothy Wright
- Department of Basic Science and Craniofacial Biology, College of Dentistry, New York University, New York, New York; Department of Preventive and Restorative Dental Sciences, University of California, San Francisco, San Francisco, California; Department of Pediatric Dentistry, School of Dentistry, University of North Carolina, Chapel Hill, North Carolina; Herman Ostrow School of Dentistry, Center for Craniofacial Molecular Biology, University of Southern California, Los Angeles, California
| | - Michael L Paine
- Department of Basic Science and Craniofacial Biology, College of Dentistry, New York University, New York, New York; Department of Preventive and Restorative Dental Sciences, University of California, San Francisco, San Francisco, California; Department of Pediatric Dentistry, School of Dentistry, University of North Carolina, Chapel Hill, North Carolina; Herman Ostrow School of Dentistry, Center for Craniofacial Molecular Biology, University of Southern California, Los Angeles, California
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23
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Structure of a CLC chloride ion channel by cryo-electron microscopy. Nature 2016; 541:500-505. [PMID: 28002411 PMCID: PMC5576512 DOI: 10.1038/nature20812] [Citation(s) in RCA: 92] [Impact Index Per Article: 11.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/18/2016] [Accepted: 11/18/2016] [Indexed: 12/18/2022]
Abstract
CLC proteins transport chloride (Cl-) ions across cellular membranes to regulate muscle excitability, electrolyte movement across epithelia, and acidification of intracellular organelles. Some CLC proteins are channels that conduct Cl- ions passively, whereas others are secondary active transporters that exchange two Cl- ions for one H+. The structural basis underlying these distinctive transport mechanisms is puzzling because CLC channels and transporters are expected to share the same architecture on the basis of sequence homology. Here we determined the structure of a bovine CLC channel (CLC-K) using cryo-electron microscopy. A conserved loop in the Cl- transport pathway shows a structure markedly different from that of CLC transporters. Consequently, the cytosolic constriction for Cl- passage is widened in CLC-K such that the kinetic barrier previously postulated for Cl-/H+ transporter function would be reduced. Thus, reduction of a kinetic barrier in CLC channels enables fast flow of Cl- down its electrochemical gradient.
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24
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Clarke HJ, Howe ENW, Wu X, Sommer F, Yano M, Light ME, Kubik S, Gale PA. Transmembrane Fluoride Transport: Direct Measurement and Selectivity Studies. J Am Chem Soc 2016; 138:16515-16522. [PMID: 27998094 DOI: 10.1021/jacs.6b10694] [Citation(s) in RCA: 66] [Impact Index Per Article: 8.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Abstract
Fluoride has been overlooked as a target in the development of synthetic anion transporters despite natural fluoride transport channels being recently discovered. In this paper we report the direct measurement of fluoride transport across lipid bilayers facilitated by a series of strapped calix[4]pyrroles and show that these compounds facilitate transport via an electrogenic mechanism (determined using valinomycin and monensin coupled transport assays and an additional osmotic response assay). An HPTS transport assay was used to quantify this electrogenic process and assess the interference of naturally occurring fatty acids with the transport process and Cl- over H+/OH- transport selectivity.
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Affiliation(s)
- Harriet J Clarke
- Chemistry, University of Southampton , Southampton SO17 1BJ, U.K
| | - Ethan N W Howe
- Chemistry, University of Southampton , Southampton SO17 1BJ, U.K
| | - Xin Wu
- Chemistry, University of Southampton , Southampton SO17 1BJ, U.K
| | - Fabian Sommer
- Department of Chemistry-Organic Chemistry, Kaiserslautern University of Technology , Erwin-Schrödinger-Straße, 67663 Kaiserslautern, Germany
| | - Masafumi Yano
- Chemistry, University of Southampton , Southampton SO17 1BJ, U.K
| | - Mark E Light
- Chemistry, University of Southampton , Southampton SO17 1BJ, U.K
| | - Stefan Kubik
- Department of Chemistry-Organic Chemistry, Kaiserslautern University of Technology , Erwin-Schrödinger-Straße, 67663 Kaiserslautern, Germany
| | - Philip A Gale
- Chemistry, University of Southampton , Southampton SO17 1BJ, U.K
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25
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Lee S, Mayes HB, Swanson JMJ, Voth GA. The Origin of Coupled Chloride and Proton Transport in a Cl -/H + Antiporter. J Am Chem Soc 2016; 138:14923-14930. [PMID: 27783900 PMCID: PMC5114699 DOI: 10.1021/jacs.6b06683] [Citation(s) in RCA: 31] [Impact Index Per Article: 3.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/30/2022]
Abstract
![]()
The ClC family of transmembrane proteins
functions throughout nature
to control the transport of Cl– ions across biological
membranes. ClC-ec1 from Escherichia coli is an antiporter,
coupling the transport of Cl– and H+ ions
in opposite directions and driven by the concentration gradients of
the ions. Despite keen interest in this protein, the molecular mechanism
of the Cl–/H+ coupling has not been fully
elucidated. Here, we have used multiscale simulation to help identify
the essential mechanism of the Cl–/H+ coupling. We find that the highest barrier for proton transport
(PT) from the intra- to extracellular solution is attributable to
a chemical reaction, the deprotonation of glutamic acid 148 (E148).
This barrier is significantly reduced by the binding of Cl– in the “central” site (Cl–cen), which displaces E148 and thereby facilitates its deprotonation.
Conversely, in the absence of Cl–cen E148
favors the “down” conformation, which results in a much
higher cumulative rotation and deprotonation barrier that effectively
blocks PT to the extracellular solution. Thus, the rotation of E148
plays a critical role in defining the Cl–/H+ coupling. As a control, we have also simulated PT in the
ClC-ec1 E148A mutant to further understand the role of this residue.
Replacement with a non-protonatable residue greatly increases the
free energy barrier for PT from E203 to the extracellular solution,
explaining the experimental result that PT in E148A is blocked whether
or not Cl–cen is present. The results
presented here suggest both how a chemical reaction can control the
rate of PT and also how it can provide a mechanism for a coupling
of the two ion transport processes.
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Affiliation(s)
- Sangyun Lee
- Department of Chemistry, James Franck Institute, and Institute for Biophysical Dynamics, The University of Chicago , Chicago, Illinois 60637, United States
| | - Heather B Mayes
- Department of Chemistry, James Franck Institute, and Institute for Biophysical Dynamics, The University of Chicago , Chicago, Illinois 60637, United States
| | - Jessica M J Swanson
- Department of Chemistry, James Franck Institute, and Institute for Biophysical Dynamics, The University of Chicago , Chicago, Illinois 60637, United States
| | - Gregory A Voth
- Department of Chemistry, James Franck Institute, and Institute for Biophysical Dynamics, The University of Chicago , Chicago, Illinois 60637, United States
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26
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Chen Z, Beck TL. Free Energies of Ion Binding in the Bacterial CLC-ec1 Chloride Transporter with Implications for the Transport Mechanism and Selectivity. J Phys Chem B 2016; 120:3129-39. [DOI: 10.1021/acs.jpcb.6b01150] [Citation(s) in RCA: 9] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Affiliation(s)
- Zhihong Chen
- Department
of Physics, and ‡Department of Chemistry, University of Cincinnati, Cincinnati, Ohio 45221, United States
| | - Thomas L. Beck
- Department
of Physics, and ‡Department of Chemistry, University of Cincinnati, Cincinnati, Ohio 45221, United States
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27
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Jiang T, Han W, Maduke M, Tajkhorshid E. Molecular Basis for Differential Anion Binding and Proton Coupling in the Cl(-)/H(+) Exchanger ClC-ec1. J Am Chem Soc 2016; 138:3066-75. [PMID: 26880377 DOI: 10.1021/jacs.5b12062] [Citation(s) in RCA: 31] [Impact Index Per Article: 3.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/30/2022]
Abstract
Cl–/H+ transporters of the CLC superfamily form a ubiquitous class of membrane proteins that catalyze stoichiometrically coupled exchange of Cl– and H+ across biological membranes. CLC transporters exchange H+ for halides and certain polyatomic anions, but exclude cations, F–, and larger physiological anions, such as PO43– and SO42–. Despite comparable transport rates of different anions, the H+ coupling in CLC transporters varies significantly depending on the chemical nature of the transported anion. Although the molecular mechanism of exchange remains unknown, studies on bacterial ClC-ec1 transporter revealed that Cl– binding to the central anion-binding site (Scen) is crucial for the anion-coupled H+ transport. Here, we show that Cl–, F–, NO3–, and SCN– display distinct binding coordinations at the Scen site and are hydrated in different manners. Consistent with the observation of differential bindings, ClC-ec1 exhibits markedly variable ability to support the formation of the transient water wires, which are necessary to support the connection of the two H+ transfer sites (Gluin and Gluex), in the presence of different anions. While continuous water wires are frequently observed in the presence of physiologically transported Cl–, binding of F– or NO3– leads to the formation of pseudo-water-wires that are substantially different from the wires formed with Cl–. Binding of SCN–, however, eliminates the water wires altogether. These findings provide structural details of anion binding in ClC-ec1 and reveal a putative atomic-level mechanism for the decoupling of H+ transport to the transport of anions other than Cl–.
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Affiliation(s)
- Tao Jiang
- Department of Biochemistry, Center for Biophysics and Computational Biology, and Beckman Institute for Advanced Science and Technology, University of Illinois at Urbana-Champaign , Champaign, Illinois 61801, United States
| | - Wei Han
- Department of Biochemistry, Center for Biophysics and Computational Biology, and Beckman Institute for Advanced Science and Technology, University of Illinois at Urbana-Champaign , Champaign, Illinois 61801, United States
| | - Merritt Maduke
- Department of Molecular and Cellular Physiology, Stanford University School of Medicine , Stanford, California 94305-5207, United States
| | - Emad Tajkhorshid
- Department of Biochemistry, Center for Biophysics and Computational Biology, and Beckman Institute for Advanced Science and Technology, University of Illinois at Urbana-Champaign , Champaign, Illinois 61801, United States
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28
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Nagarajan Y, Rongala J, Luang S, Singh A, Shadiac N, Hayes J, Sutton T, Gilliham M, Tyerman SD, McPhee G, Voelcker NH, Mertens HDT, Kirby NM, Lee JG, Yingling YG, Hrmova M. A Barley Efflux Transporter Operates in a Na+-Dependent Manner, as Revealed by a Multidisciplinary Platform. THE PLANT CELL 2016; 28:202-18. [PMID: 26672067 PMCID: PMC4746678 DOI: 10.1105/tpc.15.00625] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 07/14/2015] [Accepted: 12/11/2015] [Indexed: 05/02/2023]
Abstract
Plant growth and survival depend upon the activity of membrane transporters that control the movement and distribution of solutes into, around, and out of plants. Although many plant transporters are known, their intrinsic properties make them difficult to study. In barley (Hordeum vulgare), the root anion-permeable transporter Bot1 plays a key role in tolerance to high soil boron, facilitating the efflux of borate from cells. However, its three-dimensional structure is unavailable and the molecular basis of its permeation function is unknown. Using an integrative platform of computational, biophysical, and biochemical tools as well as molecular biology, electrophysiology, and bioinformatics, we provide insight into the origin of transport function of Bot1. An atomistic model, supported by atomic force microscopy measurements, reveals that the protein folds into 13 transmembrane-spanning and five cytoplasmic α-helices. We predict a trimeric assembly of Bot1 and the presence of a Na(+) ion binding site, located in the proximity of a pore that conducts anions. Patch-clamp electrophysiology of Bot1 detects Na(+)-dependent polyvalent anion transport in a Nernstian manner with channel-like characteristics. Using alanine scanning, molecular dynamics simulations, and transport measurements, we show that conductance by Bot1 is abolished by removal of the Na(+) ion binding site. Our data enhance the understanding of the permeation functions of Bot1.
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Affiliation(s)
- Yagnesh Nagarajan
- Australian Centre for Plant Functional Genomics, School of Agriculture, Food, and Wine, University of Adelaide, Glen Osmond, South Australia 5064, Australia
| | - Jay Rongala
- Australian Centre for Plant Functional Genomics, School of Agriculture, Food, and Wine, University of Adelaide, Glen Osmond, South Australia 5064, Australia
| | - Sukanya Luang
- Australian Centre for Plant Functional Genomics, School of Agriculture, Food, and Wine, University of Adelaide, Glen Osmond, South Australia 5064, Australia
| | - Abhishek Singh
- Department of Materials Science and Engineering, North Carolina State University, Raleigh, North Carolina 27695-7907
| | - Nadim Shadiac
- Australian Centre for Plant Functional Genomics, School of Agriculture, Food, and Wine, University of Adelaide, Glen Osmond, South Australia 5064, Australia
| | - Julie Hayes
- Australian Centre for Plant Functional Genomics, School of Agriculture, Food, and Wine, University of Adelaide, Glen Osmond, South Australia 5064, Australia
| | - Tim Sutton
- Australian Centre for Plant Functional Genomics, School of Agriculture, Food, and Wine, University of Adelaide, Glen Osmond, South Australia 5064, Australia
| | - Matthew Gilliham
- Australian Research Council Centre of Excellence in Plant Energy Biology, School of Agriculture, Food, and Wine, University of Adelaide, Glen Osmond, South Australia 5064, Australia
| | - Stephen D Tyerman
- Australian Research Council Centre of Excellence in Plant Energy Biology, School of Agriculture, Food, and Wine, University of Adelaide, Glen Osmond, South Australia 5064, Australia
| | - Gordon McPhee
- Mawson Institute, University of South Australia, Mawson Lakes, South Australia 5095, Australia
| | - Nicolas H Voelcker
- Mawson Institute, University of South Australia, Mawson Lakes, South Australia 5095, Australia
| | - Haydyn D T Mertens
- Small- and Wide-Angle X-Ray Scattering Beamline, Australian Synchrotron, Clayton, Victoria 3168, Australia
| | - Nigel M Kirby
- Small- and Wide-Angle X-Ray Scattering Beamline, Australian Synchrotron, Clayton, Victoria 3168, Australia
| | - Jung-Goo Lee
- Department of Materials Science and Engineering, North Carolina State University, Raleigh, North Carolina 27695-7907
| | - Yaroslava G Yingling
- Department of Materials Science and Engineering, North Carolina State University, Raleigh, North Carolina 27695-7907
| | - Maria Hrmova
- Australian Centre for Plant Functional Genomics, School of Agriculture, Food, and Wine, University of Adelaide, Glen Osmond, South Australia 5064, Australia
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29
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De Jesús-Pérez JJ, Castro-Chong A, Shieh RC, Hernández-Carballo CY, De Santiago-Castillo JA, Arreola J. Gating the glutamate gate of CLC-2 chloride channel by pore occupancy. ACTA ACUST UNITED AC 2015; 147:25-37. [PMID: 26666914 PMCID: PMC4692487 DOI: 10.1085/jgp.201511424] [Citation(s) in RCA: 24] [Impact Index Per Article: 2.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/25/2015] [Accepted: 11/17/2015] [Indexed: 11/20/2022]
Abstract
Intracellular permeant anions, and not extracellular protons, are the predominant driver of fast gating in the hyperpolarization-activated CLC-2 chloride channel. CLC-2 channels are dimeric double-barreled chloride channels that open in response to hyperpolarization. Hyperpolarization activates protopore gates that independently regulate the permeability of the pore in each subunit and the common gate that affects the permeability through both pores. CLC-2 channels lack classic transmembrane voltage–sensing domains; instead, their protopore gates (residing within the pore and each formed by the side chain of a glutamate residue) open under repulsion by permeant intracellular anions or protonation by extracellular H+. Here, we show that voltage-dependent gating of CLC-2: (a) is facilitated when permeant anions (Cl−, Br−, SCN−, and I−) are present in the cytosolic side; (b) happens with poorly permeant anions fluoride, glutamate, gluconate, and methanesulfonate present in the cytosolic side; (c) depends on pore occupancy by permeant and poorly permeant anions; (d) is strongly facilitated by multi-ion occupancy; (e) is absent under likely protonation conditions (pHe = 5.5 or 6.5) in cells dialyzed with acetate (an impermeant anion); and (f) was the same at intracellular pH 7.3 and 4.2; and (g) is observed in both whole-cell and inside-out patches exposed to increasing [Cl−]i under unlikely protonation conditions (pHe = 10). Thus, based on our results we propose that hyperpolarization activates CLC-2 mainly by driving intracellular anions into the channel pores, and that protonation by extracellular H+ plays a minor role in dislodging the glutamate gate.
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Affiliation(s)
- José J De Jesús-Pérez
- Physics Institute, Universidad Autónoma de San Luis Potosí, 78290 San Luis Potosí, México
| | - Alejandra Castro-Chong
- Physics Institute, Universidad Autónoma de San Luis Potosí, 78290 San Luis Potosí, México
| | - Ru-Chi Shieh
- Institute of Biomedical Sciences, Academia Sinica, Taipei 115, Taiwan, R.O.C
| | | | | | - Jorge Arreola
- Physics Institute, Universidad Autónoma de San Luis Potosí, 78290 San Luis Potosí, México
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30
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Abstract
Many bacterial species protect themselves against environmental F(-) toxicity by exporting this anion from the cytoplasm via CLC(F) F(-)/H(+) antiporters, a subclass of CLC superfamily anion transporters. Strong F(-) over Cl(-) selectivity is biologically essential for these membrane proteins because Cl(-) is orders of magnitude more abundant in the biosphere than F(-). Sequence comparisons reveal differences between CLC(F)s and canonical Cl(-)-transporting CLCs within regions that, in the canonical CLCs, coordinate Cl(-) ion and govern anion transport. A phylogenetic split within the CLC(F) clade, manifested in sequence divergence in the vicinity of this ion-binding center, raises the possibility that these two CLC(F) subclades might exhibit differences in anion selectivity. Several CLC(F) homologues from each subclade were examined for F(-)/Cl(-) selectivity of anion transport and equilibrium binding. Differences in both of these anion-selectivity metrics correlate with sequence divergence among CLC(F)s. Chimeric constructs identify two residues in this region that largely account for the subclade differences in selectivity. In addition, these experiments serendipitously uncovered an unusually steep, Cl(-)-specific voltage dependence of transport that greatly enhances F(-) selectivity at low voltage.
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Affiliation(s)
- Ashley E Brammer
- Department of Biochemistry and Howard Hughes Medical Institute, Brandeis University, Waltham, MA 02453Department of Biochemistry and Howard Hughes Medical Institute, Brandeis University, Waltham, MA 02453
| | - Randy B Stockbridge
- Department of Biochemistry and Howard Hughes Medical Institute, Brandeis University, Waltham, MA 02453Department of Biochemistry and Howard Hughes Medical Institute, Brandeis University, Waltham, MA 02453
| | - Christopher Miller
- Department of Biochemistry and Howard Hughes Medical Institute, Brandeis University, Waltham, MA 02453Department of Biochemistry and Howard Hughes Medical Institute, Brandeis University, Waltham, MA 02453
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31
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Basilio D, Accardi A. A Proteoliposome-Based Efflux Assay to Determine Single-molecule Properties of Cl- Channels and Transporters. J Vis Exp 2015:52369. [PMID: 25938223 PMCID: PMC4541587 DOI: 10.3791/52369] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/31/2022] Open
Abstract
The last 15 years have been characterized by an explosion in the ability to overexpress and purify membrane proteins from prokaryotic organisms as well as from eukaryotes. This increase has been largely driven by the successful push to obtain structural information on membrane proteins. However, the ability to functionally interrogate these proteins has not advanced at the same rate and is often limited to qualitative assays of limited quantitative value, thereby limiting the mechanistic insights that they can provide. An assay to quantitatively investigate the transport activity of reconstituted Cl(-) channels or transporters is described. The assay is based on the measure of the efflux rate of Cl(-) from proteoliposomes following the addition of the K(+) ionophore valinomycin to shunt the membrane potential. An ion sensitive electrode is used to follow the time-course of ion efflux from proteoliposomes reconstituted with the desired protein. The method is highly suited for mechanistic studies, as it allows for the quantitative determination of key properties of the reconstituted protein, such as its unitary transport rate, the fraction of active protein and the molecular mass of the functional unit. The assay can also be utilized to determine the effect of small molecule compounds that directly inhibit/activate the reconstituted protein, as well as to test the modulatory effects of the membrane composition or lipid-modifying reagents. Where possible, direct comparison between results obtained using this method were found to be in good agreement with those obtained using electrophysiological approaches. The technique is illustrated using CLC-ec1, a CLC-type H(+)/Cl(-) exchanger, as a model system. The efflux assay can be utilized to study any Cl(-) conducting channel/transporter and, with minimal changes, can be adapted to study any ion-transporting protein.
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Affiliation(s)
- Daniel Basilio
- Department of Anesthesiology, Weill Cornell Medical College
| | - Alessio Accardi
- Department of Anesthesiology, Weill Cornell Medical College; Department of Physiology and Biophysics, Weill Cornell Medical College; Department of Biochemistry, Weill Cornell Medical College;
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32
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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(-).
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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
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33
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Boudker O, Oh S. Isothermal titration calorimetry of ion-coupled membrane transporters. Methods 2015; 76:171-182. [PMID: 25676707 PMCID: PMC4912014 DOI: 10.1016/j.ymeth.2015.01.012] [Citation(s) in RCA: 13] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/10/2014] [Revised: 01/20/2015] [Accepted: 01/21/2015] [Indexed: 11/17/2022] Open
Abstract
Binding of ligands, ranging from proteins to ions, to membrane proteins is associated with absorption or release of heat that can be detected by isothermal titration calorimetry (ITC). Such measurements not only provide binding affinities but also afford direct access to thermodynamic parameters of binding--enthalpy, entropy and heat capacity. These parameters can be interpreted in a structural context, allow discrimination between different binding mechanisms and guide drug design. In this review, we introduce advantages and limitations of ITC as a methodology to study molecular interactions of membrane proteins. We further describe case studies where ITC was used to analyze thermodynamic linkage between ions and substrates in ion-coupled transporters. Similar type of linkage analysis will likely be applicable to a wide range of transporters, channels, and receptors.
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Affiliation(s)
- Olga Boudker
- Department of Physiology & Biophysics, Weill Cornell Medical College, New York 10021, USA.
| | - SeCheol Oh
- Department of Physiology & Biophysics, Weill Cornell Medical College, New York 10021, USA.
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34
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Woo J, Kim G, Quintero K, Hanrahan MP, Palencia H, Cao H. Investigation of desilylation in the recognition mechanism to fluoride by a 1,8-naphthalimide derivative. Org Biomol Chem 2014; 12:8275-9. [DOI: 10.1039/c4ob01500b] [Citation(s) in RCA: 11] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022]
Abstract
Desilylation based fluorescence sensor (AF-1) gives a dual signal for quantitative detection of F− in MeCN.
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Affiliation(s)
- Jeeun Woo
- University of Nebraska at Kearney
- Department of Chemistry
- Kearney, USA
| | - Gunwoo Kim
- University of Nebraska at Kearney
- Department of Chemistry
- Kearney, USA
| | - Kevanie Quintero
- University of Nebraska at Kearney
- Department of Chemistry
- Kearney, USA
| | | | - Hector Palencia
- University of Nebraska at Kearney
- Department of Chemistry
- Kearney, USA
| | - Haishi Cao
- University of Nebraska at Kearney
- Department of Chemistry
- Kearney, USA
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35
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Abstract
CLC transporters catalyze transmembrane exchange of chloride for protons. Although a putative pathway for Cl(-) has been established, the pathway of H(+) translocation remains obscure. Through a highly concerted computational and experimental approach, we characterize microscopic details essential to understanding H(+)-translocation. An extended (0.4 µs) equilibrium molecular dynamics simulation of membrane-embedded, dimeric ClC-ec1, a CLC from Escherichia coli, reveals transient but frequent hydration of the central hydrophobic region by water molecules from the intracellular bulk phase via the interface between the two subunits. We characterize a portal region lined by E202, E203, and A404 as the main gateway for hydration. Supporting this mechanism, site-specific mutagenesis experiments show that ClC-ec1 ion transport rates decrease as the size of the portal residue at position 404 is increased. Beyond the portal, water wires form spontaneously and repeatedly to span the 15-Å hydrophobic region between the two known H(+) transport sites [E148 (Glu(ex)) and E203 (Glu(in))]. Our finding that the formation of these water wires requires the presence of Cl(-) explains the previously mystifying fact that Cl(-) occupancy correlates with the ability to transport protons. To further validate the idea that these water wires are central to the H(+) transport mechanism, we identified I109 as the residue that exhibits the greatest conformational coupling to water wire formation and experimentally tested the effects of mutating this residue. The results, by providing a detailed microscopic view of the dynamics of water wire formation and confirming the involvement of specific protein residues, offer a mechanism for the coupled transport of H(+) and Cl(-) ions in CLC transporters.
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