1
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Yeh HI, Sutcliffe KJ, Sheppard DN, Hwang TC. CFTR Modulators: From Mechanism to Targeted Therapeutics. Handb Exp Pharmacol 2024; 283:219-247. [PMID: 35972584 DOI: 10.1007/164_2022_597] [Citation(s) in RCA: 3] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 06/15/2023]
Abstract
People with cystic fibrosis (CF) suffer from a multi-organ disorder caused by loss-of-function variants in the gene encoding the epithelial anion channel cystic fibrosis transmembrane conductance regulator (CFTR). Tremendous progress has been made in both basic and clinical sciences over the past three decades since the identification of the CFTR gene. Over 90% of people with CF now have access to therapies targeting dysfunctional CFTR. This success was made possible by numerous studies in the field that incrementally paved the way for the development of small molecules known as CFTR modulators. The advent of CFTR modulators transformed this life-threatening illness into a treatable disease by directly binding to the CFTR protein and correcting defects induced by pathogenic variants. In this chapter, we trace the trajectory of structural and functional studies that brought CF therapies from bench to bedside, with an emphasis on mechanistic understanding of CFTR modulators.
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Affiliation(s)
- Han-I Yeh
- Department of Pharmacology, National Yang Ming Chiao Tung University, Taipei City, Taiwan
- Department of Medical Pharmacology and Physiology, University of Missouri, Columbia, MO, USA
- Dalton Cardiovascular Research Center, University of Missouri, Columbia, MO, USA
| | - Katy J Sutcliffe
- School of Physiology, Pharmacology and Neuroscience, University of Bristol, Bristol, UK
| | - David N Sheppard
- School of Physiology, Pharmacology and Neuroscience, University of Bristol, Bristol, UK
| | - Tzyh-Chang Hwang
- Department of Pharmacology, National Yang Ming Chiao Tung University, Taipei City, Taiwan.
- Department of Medical Pharmacology and Physiology, University of Missouri, Columbia, MO, USA.
- Dalton Cardiovascular Research Center, University of Missouri, Columbia, MO, USA.
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2
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Ersoy A, Altintel B, Livnat Levanon N, Ben-Tal N, Haliloglu T, Lewinson O. Computational analysis of long-range allosteric communications in CFTR. eLife 2023; 12:RP88659. [PMID: 38109179 PMCID: PMC10727502 DOI: 10.7554/elife.88659] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/19/2023] Open
Abstract
Malfunction of the CFTR protein results in cystic fibrosis, one of the most common hereditary diseases. CFTR functions as an anion channel, the gating of which is controlled by long-range allosteric communications. Allostery also has direct bearings on CF treatment: the most effective CFTR drugs modulate its activity allosterically. Herein, we integrated Gaussian network model, transfer entropy, and anisotropic normal mode-Langevin dynamics and investigated the allosteric communications network of CFTR. The results are in remarkable agreement with experimental observations and mutational analysis and provide extensive novel insight. We identified residues that serve as pivotal allosteric sources and transducers, many of which correspond to disease-causing mutations. We find that in the ATP-free form, dynamic fluctuations of the residues that comprise the ATP-binding sites facilitate the initial binding of the nucleotide. Subsequent binding of ATP then brings to the fore and focuses on dynamic fluctuations that were present in a latent and diffuse form in the absence of ATP. We demonstrate that drugs that potentiate CFTR's conductance do so not by directly acting on the gating residues, but rather by mimicking the allosteric signal sent by the ATP-binding sites. We have also uncovered a previously undiscovered allosteric 'hotspot' located proximal to the docking site of the phosphorylated regulatory (R) domain, thereby establishing a molecular foundation for its phosphorylation-dependent excitatory role. This study unveils the molecular underpinnings of allosteric connectivity within CFTR and highlights a novel allosteric 'hotspot' that could serve as a promising target for the development of novel therapeutic interventions.
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Affiliation(s)
- Ayca Ersoy
- Department of Chemical Engineering, Bogazici UniversityIstanbulTurkey
- Polymer Research Center, Bogazici UniversityIstanbulTurkey
| | - Bengi Altintel
- Department of Chemical Engineering, Bogazici UniversityIstanbulTurkey
- Polymer Research Center, Bogazici UniversityIstanbulTurkey
| | - Nurit Livnat Levanon
- Department of Molecular Microbiology, Bruce and Ruth Rappaport Faculty of Medicine, Technion-Israel Institute of TechnologyTel AvivIsrael
| | - Nir Ben-Tal
- Department of Biochemistry and Molecular Biology, Faculty of Life Sciences, Tel-Aviv UniversityTel-AvivIsrael
| | - Turkan Haliloglu
- Department of Chemical Engineering, Bogazici UniversityIstanbulTurkey
- Polymer Research Center, Bogazici UniversityIstanbulTurkey
| | - Oded Lewinson
- Department of Molecular Microbiology, Bruce and Ruth Rappaport Faculty of Medicine, Technion-Israel Institute of TechnologyTel AvivIsrael
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3
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Lam AKM, Dutzler R. Mechanistic basis of ligand efficacy in the calcium-activated chloride channel TMEM16A. EMBO J 2023; 42:e115030. [PMID: 37984335 PMCID: PMC10711664 DOI: 10.15252/embj.2023115030] [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: 07/19/2023] [Revised: 10/27/2023] [Accepted: 11/02/2023] [Indexed: 11/22/2023] Open
Abstract
Agonist binding in ligand-gated ion channels is coupled to structural rearrangements around the binding site, followed by the opening of the channel pore. In this process, agonist efficacy describes the equilibrium between open and closed conformations in a fully ligand-bound state. Calcium-activated chloride channels in the TMEM16 family are important sensors of intracellular calcium signals and are targets for pharmacological modulators, yet a mechanistic understanding of agonist efficacy has remained elusive. Using a combination of cryo-electron microscopy, electrophysiology, and autocorrelation analysis, we now show that agonist efficacy in the ligand-gated channel TMEM16A is dictated by the conformation of the pore-lining helix α6 around the Ca2+ -binding site. The closure of the binding site, which involves the formation of a π-helix below a hinge region in α6, appears to be coupled to the opening of the inner pore gate, thereby governing the channel's open probability and conductance. Our results provide a mechanism for agonist binding and efficacy and a structural basis for the design of potentiators and partial agonists in the TMEM16 family.
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Affiliation(s)
- Andy KM Lam
- Department of BiochemistryUniversity of ZurichZurichSwitzerland
| | - Raimund Dutzler
- Department of BiochemistryUniversity of ZurichZurichSwitzerland
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4
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Simon MA, Iordanov I, Szollosi A, Csanády L. Estimating the true stability of the prehydrolytic outward-facing state in an ABC protein. eLife 2023; 12:e90736. [PMID: 37782012 PMCID: PMC10569789 DOI: 10.7554/elife.90736] [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: 07/06/2023] [Accepted: 10/01/2023] [Indexed: 10/03/2023] Open
Abstract
CFTR, the anion channel mutated in cystic fibrosis patients, is a model ABC protein whose ATP-driven conformational cycle is observable at single-molecule level in patch-clamp recordings. Bursts of CFTR pore openings are coupled to tight dimerization of its two nucleotide-binding domains (NBDs) and in wild-type (WT) channels are mostly terminated by ATP hydrolysis. The slow rate of non-hydrolytic closure - which determines how tightly bursts and ATP hydrolysis are coupled - is unknown, as burst durations of catalytic site mutants span a range of ~200-fold. Here, we show that Walker A mutation K1250A, Walker B mutation D1370N, and catalytic glutamate mutations E1371S and E1371Q all completely disrupt ATP hydrolysis. True non-hydrolytic closing rate of WT CFTR approximates that of K1250A and E1371S. That rate is slowed ~15-fold in E1371Q by a non-native inter-NBD H-bond, and accelerated ~15-fold in D1370N. These findings uncover unique features of the NBD interface in human CFTR.
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Affiliation(s)
- Márton A Simon
- Department of Biochemistry, Semmelweis UniversityBudapestHungary
- HCEMM-SE Molecular Channelopathies Research GroupBudapestHungary
- HUN-REN-SE Ion Channel Research GroupBudapestHungary
| | - Iordan Iordanov
- Department of Biochemistry, Semmelweis UniversityBudapestHungary
- HCEMM-SE Molecular Channelopathies Research GroupBudapestHungary
- HUN-REN-SE Ion Channel Research GroupBudapestHungary
| | - Andras Szollosi
- Department of Biochemistry, Semmelweis UniversityBudapestHungary
- HCEMM-SE Molecular Channelopathies Research GroupBudapestHungary
- HUN-REN-SE Ion Channel Research GroupBudapestHungary
| | - László Csanády
- Department of Biochemistry, Semmelweis UniversityBudapestHungary
- HCEMM-SE Molecular Channelopathies Research GroupBudapestHungary
- HUN-REN-SE Ion Channel Research GroupBudapestHungary
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5
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Wong SL, Awatade NT, Astore MA, Allan KM, Carnell MJ, Slapetova I, Chen PC, Setiadi J, Pandzic E, Fawcett LK, Widger JR, Whan RM, Griffith R, Ooi CY, Kuyucak S, Jaffe A, Waters SA. Molecular Dynamics and Theratyping in Airway and Gut Organoids Reveal R352Q-CFTR Conductance Defect. Am J Respir Cell Mol Biol 2022; 67:99-111. [PMID: 35471184 PMCID: PMC9273222 DOI: 10.1165/rcmb.2021-0337oc] [Citation(s) in RCA: 2] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/24/2022] Open
Abstract
A significant challenge to making targeted cystic fibrosis transmembrane conductance regulator (CFTR) modulator therapies accessible to all individuals with cystic fibrosis (CF) are many mutations in the CFTR gene that can cause CF, most of which remain uncharacterized. Here, we characterized the structural and functional defects of the rare CFTR mutation R352Q, with a potential role contributing to intrapore chloride ion permeation, in patient-derived cell models of the airway and gut. CFTR function in differentiated nasal epithelial cultures and matched intestinal organoids was assessed using an ion transport assay and forskolin-induced swelling assay, respectively. CFTR potentiators (VX-770, GLPG1837, and VX-445) and correctors (VX-809, VX-445, with or without VX-661) were tested. Data from R352Q-CFTR were compared with data of 20 participants with mutations with known impact on CFTR function. R352Q-CFTR has residual CFTR function that was restored to functional CFTR activity by CFTR potentiators but not the corrector. Molecular dynamics simulations of R352Q-CFTR were carried out, which indicated the presence of a chloride conductance defect, with little evidence supporting a gating defect. The combination approach of in vitro patient-derived cell models and in silico molecular dynamics simulations to characterize rare CFTR mutations can improve the specificity and sensitivity of modulator response predictions and aid in their translational use for CF precision medicine.
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Affiliation(s)
- Sharon L Wong
- University of New South Wales, 7800, School of Women's and Children's Health, Faculty of Medicine, Sydney, New South Wales, Australia.,University of New South Wales, 7800, Molecular and Integrative Cystic Fibrosis Research Centre (miCF_RC), Sydney, New South Wales, Australia
| | - Nikhil T Awatade
- University of New South Wales, 7800, School of Women's and Children's Health, Faculty of Medicine, Sydney, New South Wales, Australia.,University of New South Wales, 7800, Molecular and Integrative Cystic Fibrosis Research Centre (miCF_RC), Sydney, New South Wales, Australia
| | - Miro A Astore
- The University of Sydney, 4334, School of Physics, Sydney, New South Wales, Australia
| | - Katelin M Allan
- University of New South Wales, 7800, School of Women's and Children's Health, Faculty of Medicine, Sydney, New South Wales, Australia.,University of New South Wales, 7800, Molecular and Integrative Cystic Fibrosis Research Centre (miCF_RC), Sydney, New South Wales, Australia
| | - Michael J Carnell
- University of New South Wales, 7800, Biomedical Imaging Facility, Mark Wainwright Analytical Centre, Sydney, New South Wales, Australia
| | - Iveta Slapetova
- University of New South Wales, 7800, Biomedical Imaging Facility, Mark Wainwright Analytical Centre, Sydney, New South Wales, Australia
| | - Po-Chia Chen
- The University of Sydney, 4334, School of Physics, Sydney, New South Wales, Australia
| | - Jeffry Setiadi
- The University of Sydney, 4334, School of Physics, Sydney, New South Wales, Australia
| | - Elvis Pandzic
- University of New South Wales, 7800, Biomedical Imaging Facility, Mark Wainwright Analytical Cen, Sydney, New South Wales, Australia
| | - Laura K Fawcett
- University of New South Wales, 7800, School of Women's and Children's Health, Faculty of Medicine, Sydney, New South Wales, Australia.,University of New South Wales, 7800, Molecular and Integrative Cystic Fibrosis Research Centre (miCF_RC), Sydney, New South Wales, Australia.,Sydney Children's Hospital Randwick, 63623, Department of Respiratory Medicine, Randwick, New South Wales, Australia
| | - John R Widger
- University of New South Wales, 7800, School of Women's and Children's Health, Faculty of Medicine, Sydney, New South Wales, Australia.,University of New South Wales, 7800, Molecular and Integrative Cystic Fibrosis Research Centre (miCF_RC), Sydney, New South Wales, Australia.,Sydney Children's Hospital Randwick, 63623, Department of Respiratory Medicine, Randwick, New South Wales, Australia
| | - Renee M Whan
- University of New South Wales, 7800, Biomedical Imaging Facility, Mark Wainwright Analytical Centre, Sydney, New South Wales, Australia
| | - Renate Griffith
- University of New South Wales, 7800, School of Chemistry, Sydney, New South Wales, Australia
| | - Chee Y Ooi
- Sydney Children's Hospital Randwick, Gastroenterology, Sydney, New South Wales, Australia
| | - Serdar Kuyucak
- The University of Sydney, 4334, School of Physics, Sydney, New South Wales, Australia
| | - Adam Jaffe
- Sydney Children`s Hospital, Respiratory Medicine, Sydney, New South Wales, Australia.,University of New South Wales, 7800, School of Women`s and Children`s Health, Sydney, New South Wales, Australia
| | - Shafagh A Waters
- Sydney Children's Hospital, Department of Respiratory Medicine, Sydney, New South Wales, Australia.,Univeristy of New South Wales, School of Women's and Children's Health, Sydney, New South Wales, Australia;
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6
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Prins S, Corradi V, Sheppard DN, Tieleman DP, Vergani P. Can two wrongs make a right? F508del-CFTR ion channel rescue by second-site mutations in its transmembrane domains. J Biol Chem 2022; 298:101615. [PMID: 35065958 PMCID: PMC8861112 DOI: 10.1016/j.jbc.2022.101615] [Citation(s) in RCA: 4] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/01/2021] [Revised: 01/13/2022] [Accepted: 01/17/2022] [Indexed: 11/20/2022] Open
Abstract
Deletion of phenylalanine 508 (F508del) in the cystic fibrosis transmembrane conductance regulator (CFTR) anion channel is the most common cause of cystic fibrosis. The F508 residue is located on nucleotide-binding domain 1 (NBD1) in contact with the cytosolic extensions of the transmembrane helices, in particular intracellular loop 4 (ICL4). To investigate how absence of F508 at this interface impacts the CFTR protein, we carried out a mutagenesis scan of ICL4 by introducing second-site mutations at 11 positions in cis with F508del. Using an image-based fluorescence assay, we measured how each mutation affected membrane proximity and ion-channel function. The scan strongly validated the effectiveness of R1070W at rescuing F508del defects. Molecular dynamics simulations highlighted two features characterizing the ICL4/NBD1 interface of F508del/R1070W-CFTR: flexibility, with frequent transient formation of interdomain hydrogen bonds, and loosely stacked aromatic sidechains (F1068, R1070W, and F1074, mimicking F1068, F508, and F1074 in WT CFTR). F508del-CFTR displayed a distorted aromatic stack, with F1068 displaced toward the space vacated by F508, while in F508del/R1070F-CFTR, which largely retained F508del defects, R1070F could not form hydrogen bonds and the interface was less flexible. Other ICL4 second-site mutations which partially rescued F508del-CFTR included F1068M and F1074M. Methionine side chains allow hydrophobic interactions without the steric rigidity of aromatic rings, possibly conferring flexibility to accommodate the absence of F508 and retain a dynamic interface. These studies highlight how both hydrophobic interactions and conformational flexibility might be important at the ICL4/NBD1 interface, suggesting possible structural underpinnings of F508del-induced dysfunction.
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Affiliation(s)
- Stella Prins
- Department of Neuroscience, Physiology and Pharmacology, University College London, London, UK
| | - Valentina Corradi
- Department of Biological Sciences, Centre for Molecular Simulation, University of Calgary, Calgary, Alberta, Canada
| | - David N Sheppard
- School of Physiology, Pharmacology and Neuroscience, University of Bristol, Bristol, UK
| | - D Peter Tieleman
- Department of Biological Sciences, Centre for Molecular Simulation, University of Calgary, Calgary, Alberta, Canada
| | - Paola Vergani
- Department of Neuroscience, Physiology and Pharmacology, University College London, London, UK.
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7
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Infield DT, Strickland KM, Gaggar A, McCarty NA. The molecular evolution of function in the CFTR chloride channel. J Gen Physiol 2021; 153:212705. [PMID: 34647973 PMCID: PMC8640958 DOI: 10.1085/jgp.202012625] [Citation(s) in RCA: 4] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/10/2020] [Revised: 08/11/2021] [Accepted: 09/09/2021] [Indexed: 12/13/2022] Open
Abstract
The ATP-binding cassette (ABC) transporter superfamily includes many proteins of clinical relevance, with genes expressed in all domains of life. Although most members use the energy of ATP binding and hydrolysis to accomplish the active import or export of various substrates across membranes, the cystic fibrosis transmembrane conductance regulator (CFTR) is the only known animal ABC transporter that functions primarily as an ion channel. Defects in CFTR, which is closely related to ABCC subfamily members that bear function as bona fide transporters, underlie the lethal genetic disease cystic fibrosis. This article seeks to integrate structural, functional, and genomic data to begin to answer the critical question of how the function of CFTR evolved to exhibit regulated channel activity. We highlight several examples wherein preexisting features in ABCC transporters were functionally leveraged as is, or altered by molecular evolution, to ultimately support channel function. This includes features that may underlie (1) construction of an anionic channel pore from an anionic substrate transport pathway, (2) establishment and tuning of phosphoregulation, and (3) optimization of channel function by specialized ligand–channel interactions. We also discuss how divergence and conservation may help elucidate the pharmacology of important CFTR modulators.
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Affiliation(s)
- Daniel T Infield
- Department of Molecular Physiology and Biophysics, University of Iowa, Iowa City, IA
| | | | - Amit Gaggar
- Department of Medicine, University of Alabama at Birmingham, Birmingham, AL.,Gregory Fleming James Cystic Fibrosis Research Center, University of Alabama at Birmingham, Birmingham, AL.,Program in Protease and Matrix Biology, University of Alabama at Birmingham, Birmingham, AL.,Birmingham Veterans Administration Medical Center, Birmingham, AL
| | - Nael A McCarty
- Department of Pediatrics, Emory University, Atlanta, GA.,Children's Healthcare of Atlanta Center for Cystic Fibrosis and Airways Disease Research, Emory University, Atlanta, GA
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8
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Simon MA, Csanády L. Molecular pathology of the R117H cystic fibrosis mutation is explained by loss of a hydrogen bond. eLife 2021; 10:74693. [PMID: 34870594 PMCID: PMC8673840 DOI: 10.7554/elife.74693] [Citation(s) in RCA: 3] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/13/2021] [Accepted: 12/03/2021] [Indexed: 11/21/2022] Open
Abstract
The phosphorylation-activated anion channel cystic fibrosis transmembrane conductance regulator (CFTR) is gated by an ATP hydrolysis cycle at its two cytosolic nucleotide-binding domains, and is essential for epithelial salt-water transport. A large number of CFTR mutations cause cystic fibrosis. Since recent breakthrough in targeted pharmacotherapy, CFTR mutants with impaired gating are candidates for stimulation by potentiator drugs. Thus, understanding the molecular pathology of individual mutations has become important. The relatively common R117H mutation affects an extracellular loop, but nevertheless causes a strong gating defect. Here, we identify a hydrogen bond between the side chain of arginine 117 and the backbone carbonyl group of glutamate 1124 in the cryo-electronmicroscopic structure of phosphorylated, ATP-bound CFTR. We address the functional relevance of that interaction for CFTR gating using macroscopic and microscopic inside-out patch-clamp recordings. Employing thermodynamic double-mutant cycles, we systematically track gating-state-dependent changes in the strength of the R117-E1124 interaction. We find that the H-bond is formed only in the open state, but neither in the short-lived ‘flickery’ nor in the long-lived ‘interburst’ closed state. Loss of this H-bond explains the strong gating phenotype of the R117H mutant, including robustly shortened burst durations and strongly reduced intraburst open probability. The findings may help targeted potentiator design.
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Affiliation(s)
- Márton A Simon
- Department of Biochemistry, Semmelweis University, Budapest, Hungary.,HCEMM-SE Molecular Channelopathies Research Group, Budapest, Hungary
| | - László Csanády
- Department of Biochemistry, Semmelweis University, Budapest, Hungary.,HCEMM-SE Molecular Channelopathies Research Group, Budapest, Hungary.,MTA-SE Ion Channel Research Group, Semmelweis University, Budapest, Hungary
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9
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Rietmeijer RA, Sorum B, Li B, Brohawn SG. Physical basis for distinct basal and mechanically gated activity of the human K + channel TRAAK. Neuron 2021; 109:2902-2913.e4. [PMID: 34390650 PMCID: PMC8448962 DOI: 10.1016/j.neuron.2021.07.009] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/17/2021] [Revised: 06/10/2021] [Accepted: 07/12/2021] [Indexed: 12/24/2022]
Abstract
TRAAK is a mechanosensitive two-pore domain K+ (K2P) channel localized to nodes of Ranvier in myelinated neurons. TRAAK deletion in mice results in mechanical and thermal allodynia, and gain-of-function mutations cause the human neurodevelopmental disorder FHEIG. TRAAK displays basal and stimulus-gated activities typical of K2Ps, but the mechanistic and structural differences between these modes are unknown. Here, we demonstrate that basal and mechanically gated openings are distinguished by their conductance, kinetics, and structure. Basal openings are low conductance, short duration, and due to a conductive channel conformation with the interior cavity exposed to the surrounding membrane. Mechanically gated openings are high conductance, long duration, and due to a channel conformation in which the interior cavity is sealed to the surrounding membrane. Our results explain how dual modes of activity are produced by a single ion channel and provide a basis for the development of state-selective pharmacology with the potential to treat disease.
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Affiliation(s)
- Robert A Rietmeijer
- Department of Molecular & Cell Biology, University of California Berkeley, Berkeley, CA 94720, USA; Helen Wills Neuroscience Institute, University of California Berkeley, Berkeley, CA 94720, USA; Biophysics Graduate Program, University of California Berkeley, Berkeley, CA 94720, USA; California Institute for Quantitative Biology (QB3), University of California Berkeley, Berkeley, CA 94720, USA
| | - Ben Sorum
- Department of Molecular & Cell Biology, University of California Berkeley, Berkeley, CA 94720, USA; Helen Wills Neuroscience Institute, University of California Berkeley, Berkeley, CA 94720, USA; California Institute for Quantitative Biology (QB3), University of California Berkeley, Berkeley, CA 94720, USA
| | - Baobin Li
- Department of Molecular & Cell Biology, University of California Berkeley, Berkeley, CA 94720, USA; Helen Wills Neuroscience Institute, University of California Berkeley, Berkeley, CA 94720, USA; California Institute for Quantitative Biology (QB3), University of California Berkeley, Berkeley, CA 94720, USA
| | - Stephen G Brohawn
- Department of Molecular & Cell Biology, University of California Berkeley, Berkeley, CA 94720, USA; Helen Wills Neuroscience Institute, University of California Berkeley, Berkeley, CA 94720, USA; California Institute for Quantitative Biology (QB3), University of California Berkeley, Berkeley, CA 94720, USA.
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10
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Della Sala A, Prono G, Hirsch E, Ghigo A. Role of Protein Kinase A-Mediated Phosphorylation in CFTR Channel Activity Regulation. Front Physiol 2021; 12:690247. [PMID: 34211404 PMCID: PMC8240754 DOI: 10.3389/fphys.2021.690247] [Citation(s) in RCA: 11] [Impact Index Per Article: 3.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/13/2021] [Accepted: 05/10/2021] [Indexed: 11/17/2022] Open
Abstract
Cystic fibrosis transmembrane conductance regulator (CFTR) is an anion channel expressed on the apical membrane of epithelial cells, where it plays a pivotal role in chloride transport and overall tissue homeostasis. CFTR constitutes a unique member of the ATP-binding cassette transporter superfamily, due to its distinctive cytosolic regulatory (R) domain carrying multiple phosphorylation sites that allow the tight regulation of channel activity and gating. Mutations in the CFTR gene cause cystic fibrosis, the most common lethal autosomal genetic disease in the Caucasian population. In recent years, major efforts have led to the development of CFTR modulators, small molecules targeting the underlying genetic defect of CF and ultimately rescuing the function of the mutant channel. Recent evidence has highlighted that this class of drugs could also impact on the phosphorylation of the R domain of the channel by protein kinase A (PKA), a key regulatory mechanism that is altered in various CFTR mutants. Therefore, the aim of this review is to summarize the current knowledge on the regulation of the CFTR by PKA-mediated phosphorylation and to provide insights into the different factors that modulate this essential CFTR modification. Finally, the discussion will focus on the impact of CF mutations on PKA-mediated CFTR regulation, as well as on how small molecule CFTR regulators and PKA interact to rescue dysfunctional channels.
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Affiliation(s)
- Angela Della Sala
- Molecular Biotechnology Center, Department of Molecular Biotechnology and Health Sciences, University of Turin, Turin, Italy
| | | | - Emilio Hirsch
- Molecular Biotechnology Center, Department of Molecular Biotechnology and Health Sciences, University of Turin, Turin, Italy.,Kither Biotech S.r.l, Turin, Italy
| | - Alessandra Ghigo
- Molecular Biotechnology Center, Department of Molecular Biotechnology and Health Sciences, University of Turin, Turin, Italy.,Kither Biotech S.r.l, Turin, Italy
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11
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Abstract
Ultrasound modulates the electrical activity of excitable cells and offers advantages over other neuromodulatory techniques; for example, it can be noninvasively transmitted through the skull and focused to deep brain regions. However, the fundamental cellular, molecular, and mechanistic bases of ultrasonic neuromodulation are largely unknown. Here, we demonstrate ultrasound activation of the mechanosensitive K+ channel TRAAK with submillisecond kinetics to an extent comparable to canonical mechanical activation. Single-channel recordings reveal a common basis for ultrasonic and mechanical activation with stimulus-graded destabilization of long-duration closures and promotion of full conductance openings. Ultrasonic energy is transduced to TRAAK through the membrane in the absence of other cellular components, likely increasing membrane tension to promote channel opening. We further demonstrate ultrasonic modulation of neuronally expressed TRAAK. These results suggest mechanosensitive channels underlie physiological responses to ultrasound and could serve as sonogenetic actuators for acoustic neuromodulation of genetically targeted cells.
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12
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Lam AKM, Dutzler R. Mechanism of pore opening in the calcium-activated chloride channel TMEM16A. Nat Commun 2021; 12:786. [PMID: 33542228 PMCID: PMC7862263 DOI: 10.1038/s41467-020-20788-8] [Citation(s) in RCA: 18] [Impact Index Per Article: 6.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/05/2020] [Accepted: 12/16/2020] [Indexed: 01/14/2023] Open
Abstract
The anion channel TMEM16A is activated by intracellular Ca2+ in a highly cooperative process. By combining electrophysiology and autocorrelation analysis, we investigated the mechanism of channel activation and the concurrent rearrangement of the gate in the narrow part of the pore. Features in the fluctuation characteristics of steady-state current indicate the sampling of intermediate conformations that are successively occupied during gating. The initial step is related to conformational changes induced by Ca2+ binding, which is ensued by rearrangements that open the pore. Mutations in the gate shift the equilibrium of transitions in a manner consistent with a progressive destabilization of this region during pore opening. We come up with a mechanism of channel activation where the binding of Ca2+ induces conformational changes in the protein that, in a sequential manner, propagate from the binding site and couple to the gate in the narrow pore to allow ion permeation.
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Affiliation(s)
- Andy K M Lam
- Department of Biochemistry, University of Zurich, Winterthurerstrasse 190, CH-8057, Zurich, Switzerland.
| | - Raimund Dutzler
- Department of Biochemistry, University of Zurich, Winterthurerstrasse 190, CH-8057, Zurich, Switzerland.
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13
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Linsdell P. On the relationship between anion binding and chloride conductance in the CFTR anion channel. BIOCHIMICA ET BIOPHYSICA ACTA-BIOMEMBRANES 2021; 1863:183558. [PMID: 33444622 DOI: 10.1016/j.bbamem.2021.183558] [Citation(s) in RCA: 3] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Subscribe] [Scholar Register] [Received: 10/21/2020] [Revised: 12/21/2020] [Accepted: 12/29/2020] [Indexed: 12/26/2022]
Abstract
Mutations at many sites within the cystic fibrosis transmembrane conductance regulator (CFTR) chloride channel pore region result in changes in chloride conductance. Although chloride binding in the pore - as well as interactions between concurrently bound chloride ions - are thought to be important facets of the chloride permeation mechanism, little is known about the relationship between anion binding and chloride conductance. The present work presents a comprehensive investigation of a number of anion binding properties in different pore mutants with differential effects on chloride conductance. When multiple pore mutants are compared, conductance appears best correlated with the ability of anions to bind to the pore when it is already occupied by chloride ions. In contrast, conductance was not correlated with biophysical measures of anion:anion interactions inside the pore. Although these findings suggest anion binding is required for high conductance, mutations that strengthened anion binding had very little effect on conductance, especially at high chloride concentrations, suggesting that the wild-type CFTR pore is already close to saturated with chloride ions. These results are used to support a revised model of chloride permeation in CFTR in which the overall chloride occupancy of multiple loosely-defined chloride binding sites results in high chloride conductance through the pore.
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Affiliation(s)
- Paul Linsdell
- Department of Physiology & Biophysics, Dalhousie University, Halifax, Nova Scotia, Canada.
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14
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Huysmans GHM, Ciftci D, Wang X, Blanchard SC, Boudker O. The high-energy transition state of the glutamate transporter homologue GltPh. EMBO J 2021; 40:e105415. [PMID: 33185289 PMCID: PMC7780239 DOI: 10.15252/embj.2020105415] [Citation(s) in RCA: 17] [Impact Index Per Article: 5.7] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/24/2020] [Revised: 09/16/2020] [Accepted: 09/18/2020] [Indexed: 01/03/2023] Open
Abstract
Membrane transporters mediate cellular uptake of nutrients, signaling molecules, and drugs. Their overall mechanisms are often well understood, but the structural features setting their rates are mostly unknown. Earlier single-molecule fluorescence imaging of the archaeal model glutamate transporter homologue GltPh from Pyrococcus horikoshii suggested that the slow conformational transition from the outward- to the inward-facing state, when the bound substrate is translocated from the extracellular to the cytoplasmic side of the membrane, is rate limiting to transport. Here, we provide insight into the structure of the high-energy transition state of GltPh that limits the rate of the substrate translocation process. Using bioinformatics, we identified GltPh gain-of-function mutations in the flexible helical hairpin domain HP2 and applied linear free energy relationship analysis to infer that the transition state structurally resembles the inward-facing conformation. Based on these analyses, we propose an approach to search for allosteric modulators for transporters.
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Affiliation(s)
- Gerard H M Huysmans
- Department of Physiology and BiophysicsWeill Cornell MedicineNew YorkNYUSA
- Mass Spectrometry for Biology Unit, USR 2000CNRSInstitut PasteurParisFrance
| | - Didar Ciftci
- Department of Physiology and BiophysicsWeill Cornell MedicineNew YorkNYUSA
- Tri‐Institutional Training Program in Chemical BiologyNew YorkNYUSA
| | - Xiaoyu Wang
- Department of Physiology and BiophysicsWeill Cornell MedicineNew YorkNYUSA
| | - Scott C Blanchard
- Department of Physiology and BiophysicsWeill Cornell MedicineNew YorkNYUSA
- Tri‐Institutional Training Program in Chemical BiologyNew YorkNYUSA
- St. Jude Children’s Research HospitalMemphisTNUSA
| | - Olga Boudker
- Department of Physiology and BiophysicsWeill Cornell MedicineNew YorkNYUSA
- Tri‐Institutional Training Program in Chemical BiologyNew YorkNYUSA
- Howard Hughes Medical InstituteChevy ChaseMDUSA
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15
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de Jonge HR, Ardelean MC, Bijvelds MJC, Vergani P. Strategies for cystic fibrosis transmembrane conductance regulator inhibition: from molecular mechanisms to treatment for secretory diarrhoeas. FEBS Lett 2020; 594:4085-4108. [PMID: 33113586 PMCID: PMC7756540 DOI: 10.1002/1873-3468.13971] [Citation(s) in RCA: 8] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/19/2020] [Revised: 09/22/2020] [Accepted: 10/15/2020] [Indexed: 02/06/2023]
Abstract
Cystic fibrosis transmembrane conductance regulator (CFTR) is an unusual ABC transporter. It acts as an anion‐selective channel that drives osmotic fluid transport across many epithelia. In the gut, CFTR is crucial for maintaining fluid and acid‐base homeostasis, and its activity is tightly controlled by multiple neuro‐endocrine factors. However, microbial toxins can disrupt this intricate control mechanism and trigger protracted activation of CFTR. This results in the massive faecal water loss, metabolic acidosis and dehydration that characterize secretory diarrhoeas, a major cause of malnutrition and death of children under 5 years of age. Compounds that inhibit CFTR could improve emergency treatment of diarrhoeal disease. Drawing on recent structural and functional insight, we discuss how existing CFTR inhibitors function at the molecular and cellular level. We compare their mechanisms of action to those of inhibitors of related ABC transporters, revealing some unexpected features of drug action on CFTR. Although challenges remain, especially relating to the practical effectiveness of currently available CFTR inhibitors, we discuss how recent technological advances might help develop therapies to better address this important global health need.
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Affiliation(s)
- Hugo R. de Jonge
- Department of Gastroenterology & HepatologyErasmus University Medical CenterRotterdamThe Netherlands
| | - Maria C. Ardelean
- Department of Neuroscience, Physiology and PharmacologyUniversity College LondonUK
- Department of Natural SciencesUniversity College LondonUK
| | - Marcel J. C. Bijvelds
- Department of Gastroenterology & HepatologyErasmus University Medical CenterRotterdamThe Netherlands
| | - Paola Vergani
- Department of Neuroscience, Physiology and PharmacologyUniversity College LondonUK
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16
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Rodrat M, Jantarajit W, Ng DRS, Harvey BSJ, Liu J, Wilkinson WJ, Charoenphandhu N, Sheppard DN. Carbon monoxide-releasing molecules inhibit the cystic fibrosis transmembrane conductance regulator Cl - channel. Am J Physiol Lung Cell Mol Physiol 2020; 319:L997-L1009. [PMID: 32936026 DOI: 10.1152/ajplung.00440.2019] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Key Words] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/08/2023] Open
Abstract
The gasotransmitter carbon monoxide (CO) regulates fluid and electrolyte movements across epithelial tissues. However, its action on anion channels is incompletely understood. Here, we investigate the direct action of CO on the cystic fibrosis transmembrane conductance regulator (CFTR) by applying CO-releasing molecules (CO-RMs) to the intracellular side of excised inside-out membrane patches from cells heterologously expressing wild-type human CFTR. Addition of increasing concentrations of tricarbonyldichlororuthenium(II) dimer (CORM-2) (1-300 μM) inhibited CFTR channel activity, whereas the control RuCl3 (100 μM) was without effect. CORM-2 predominantly inhibited CFTR by decreasing the frequency of channel openings and, hence, open probability (Po). But, it also reduced current flow through open channels with very fast kinetics, particularly at elevated concentrations. By contrast, the chemically distinct CO-releasing molecule CORM-3 inhibited CFTR by decreasing Po without altering current flow through open channels. Neither depolarizing the membrane voltage nor raising the ATP concentration on the intracellular side of the membrane affected CFTR inhibition by CORM-2. Interestingly, CFTR inhibition by CORM-2, but not by CFTRinh-172, was prevented by prior enhancement of channel activity by the clinically approved CFTR potentiator ivacaftor. Similarly, when added after CORM-2, ivacaftor completely relieved CFTR inhibition. In conclusion, CORM-2 has complex effects on wild-type human CFTR consistent with allosteric inhibition and open-channel blockade. Inhibition of CFTR by CO-releasing molecules suggests that CO regulates CFTR activity and that the gasotransmitter has tissue-specific effects on epithelial ion transport. The action of ivacaftor on CFTR Cl- channels inhibited by CO potentially expands the drug's clinical utility.
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Affiliation(s)
- Mayuree Rodrat
- School of Physiology, Pharmacology and Neuroscience, University of Bristol, Bristol, United Kingdom.,Center of Calcium and Bone Research (COCAB), Faculty of Science, Mahidol University, Bangkok, Thailand.,Department of Physiology, Faculty of Science, Mahidol University, Bangkok, Thailand
| | - Walailak Jantarajit
- School of Physiology, Pharmacology and Neuroscience, University of Bristol, Bristol, United Kingdom.,Center of Calcium and Bone Research (COCAB), Faculty of Science, Mahidol University, Bangkok, Thailand.,Department of Physiology, Faculty of Science, Mahidol University, Bangkok, Thailand
| | - Demi R S Ng
- School of Physiology, Pharmacology and Neuroscience, University of Bristol, Bristol, United Kingdom
| | - Bartholomew S J Harvey
- School of Physiology, Pharmacology and Neuroscience, University of Bristol, Bristol, United Kingdom
| | - Jia Liu
- School of Physiology, Pharmacology and Neuroscience, University of Bristol, Bristol, United Kingdom
| | | | - Narattaphol Charoenphandhu
- Center of Calcium and Bone Research (COCAB), Faculty of Science, Mahidol University, Bangkok, Thailand.,Department of Physiology, Faculty of Science, Mahidol University, Bangkok, Thailand.,Institute of Molecular Biosciences, Mahidol University, Nakhon Pathom, Thailand.,The Academy of Science, The Royal Society of Thailand, Dusit, Bangkok, Thailand
| | - David N Sheppard
- School of Physiology, Pharmacology and Neuroscience, University of Bristol, Bristol, United Kingdom
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17
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Human Sperm Capacitation Involves the Regulation of the Tyr-Phosphorylation Level of the Anion Exchanger 1 (AE1). Int J Mol Sci 2020; 21:ijms21114063. [PMID: 32517126 PMCID: PMC7311965 DOI: 10.3390/ijms21114063] [Citation(s) in RCA: 6] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/17/2020] [Revised: 06/02/2020] [Accepted: 06/03/2020] [Indexed: 12/22/2022] Open
Abstract
Bicarbonate uptake is one of the early steps of capacitation, but the identification of proteins regulating anion fluxes remains elusive. The aim of this study is to investigate the role of sperm solute carrier 4 (SLC4) A1 (spAE1) in the capacitation process. The expression, location, and tyrosine-phosphorylation (Tyr-P) level of spAE1 were assessed. Thereby, it was found that 4,4′-Diisothiocyano-2,2′-stilbenedisulfonic acid (DIDS), an SLC4 family channel blocker, inhibited capacitation in a dose-dependent manner by decreasing acrosome reaction (ARC% 24.5 ± 3.3 vs. 64.9 ± 4.3, p < 0.05) and increasing the percentage of not viable cells (NVC%), comparable to the inhibition by I-172, a cystic fibrosis transmembrane conductance regulator (CFTR) blocker (AR% 30.5 ± 4.4 and NVC% 18.6 ± 2.2). When used in combination, a synergistic inhibitory effect was observed with a remarkable increase of the percentage of NVC (45.3 ± 4.1, p < 0.001). spAE1 was identified in sperm membrane as a substrate for Tyr-protein kinases Lyn and Syk, which were identified as both soluble and membrane-bound pools. spAE1-Tyr-P level increased in the apical region of sperm under capacitating conditions and was negatively affected by I-172 or DIDS, and, to a far greater extent, by a combination of both. In conclusion, we demonstrated that spAE1 is expressed in sperm membranes and it is phosphorylated by Syk, but above all by Lyn on Tyr359, which are involved in sperm viability and capacitation.
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18
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Yeh HI, Qiu L, Sohma Y, Conrath K, Zou X, Hwang TC. Identifying the molecular target sites for CFTR potentiators GLPG1837 and VX-770. J Gen Physiol 2019; 151:912-928. [PMID: 31164398 PMCID: PMC6605684 DOI: 10.1085/jgp.201912360] [Citation(s) in RCA: 50] [Impact Index Per Article: 10.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/27/2019] [Revised: 04/29/2019] [Accepted: 05/10/2019] [Indexed: 01/14/2023] Open
Abstract
Identification of the binding sites for small molecules that alleviate gating
defects in CFTR would assist rational drug design for the treatment of cystic
fibrosis. Yeh et al. identify two potential binding sites for prototypical CFTR
potentiators at the interface of CFTR’s two transmembrane domains. The past two decades have witnessed major breakthroughs in developing compounds
that target the chloride channel CFTR for the treatment of patients with cystic
fibrosis. However, further improvement in affinity and efficacy for these CFTR
modulators will require insights into the molecular interactions between CFTR
modulators and their binding targets. In this study, we use in silico molecular
docking to identify potential binding sites for GLPG1837, a CFTR potentiator
that may share a common mechanism and binding site with VX-770, the FDA-approved
drug for patients carrying mutations with gating defects. Among the five binding
sites predicted by docking, the two top-scoring sites are located at the
interface between CFTR’s two transmembrane domains: site I consists of
D924, N1138, and S1141, and site IIN includes F229, F236, Y304, F312,
and F931. Using mutagenesis to probe the importance of these sites for GLPG187
binding, we find that disruption of predicted hydrogen-bonding interactions by
mutation of D924 decreases apparent affinity, while hydrophobic amino acids
substitutions at N1138 and introduction of positively charged amino acids at
S1141 improve the apparent affinity for GLPG1837. Alanine substitutions at Y304,
F312, and F931 (site IIN) decrease the affinity for GLPG1837, whereas
alanine substitutions at F229 and F236 (also site IIN), or at
residues in the other three lower-scoring sites, have little effect. In
addition, current relaxation analysis to assess the apparent dissociation rate
of VX-770 yields results consistent with the dose–response experiments
for GLPG8137, with the dissociation rate of VX-770 accelerated by D924N, F236A,
Y304A, and F312A, but decelerated by N1138L and S1141K mutations. Collectively,
these data identify two potential binding sites for GLPG1837 and VX-770 in CFTR.
We discuss the pros and cons of evidence for these two loci and the implications
for future drug design.
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Affiliation(s)
- Han-I Yeh
- Dalton Cardiovascular Research Center and Department of Medical Pharmacology and Physiology, University of Missouri, Columbia, MO
| | - Liming Qiu
- Dalton Cardiovascular Research Center, Department of Physics and Astronomy, Department of Biochemistry, and Informatics Institute, University of Missouri, Columbia, MO
| | - Yoshiro Sohma
- Dalton Cardiovascular Research Center and Department of Medical Pharmacology and Physiology, University of Missouri, Columbia, MO.,Department of Pharmaceutical Sciences, School of Pharmacy and Center for Medical Science, International University of Health and Welfare, Tochigi, Japan
| | | | - Xiaoqin Zou
- Dalton Cardiovascular Research Center, Department of Physics and Astronomy, Department of Biochemistry, and Informatics Institute, University of Missouri, Columbia, MO
| | - Tzyh-Chang Hwang
- Dalton Cardiovascular Research Center and Department of Medical Pharmacology and Physiology, University of Missouri, Columbia, MO
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19
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The extracellular gate shapes the energy profile of an ABC exporter. Nat Commun 2019; 10:2260. [PMID: 31113958 PMCID: PMC6529423 DOI: 10.1038/s41467-019-09892-6] [Citation(s) in RCA: 44] [Impact Index Per Article: 8.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/15/2018] [Accepted: 04/04/2019] [Indexed: 11/08/2022] Open
Abstract
ABC exporters harness the energy of ATP to pump substrates across membranes. Extracellular gate opening and closure are key steps of the transport cycle, but the underlying mechanism is poorly understood. Here, we generated a synthetic single domain antibody (sybody) that recognizes the heterodimeric ABC exporter TM287/288 exclusively in the presence of ATP, which was essential to solve a 3.2 Å crystal structure of the outward-facing transporter. The sybody binds to an extracellular wing and strongly inhibits ATPase activity by shifting the transporter's conformational equilibrium towards the outward-facing state, as shown by double electron-electron resonance (DEER). Mutations that facilitate extracellular gate opening result in a comparable equilibrium shift and strongly reduce ATPase activity and drug transport. Using the sybody as conformational probe, we demonstrate that efficient extracellular gate closure is required to dissociate the NBD dimer after ATP hydrolysis to reset the transporter back to its inward-facing state.
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20
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Csanády L, Vergani P, Gadsby DC. STRUCTURE, GATING, AND REGULATION OF THE CFTR ANION CHANNEL. Physiol Rev 2019; 99:707-738. [PMID: 30516439 DOI: 10.1152/physrev.00007.2018] [Citation(s) in RCA: 142] [Impact Index Per Article: 28.4] [Reference Citation Analysis] [Abstract] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/17/2022] Open
Abstract
The cystic fibrosis transmembrane conductance regulator (CFTR) belongs to the ATP binding cassette (ABC) transporter superfamily but functions as an anion channel crucial for salt and water transport across epithelial cells. CFTR dysfunction, because of mutations, causes cystic fibrosis (CF). The anion-selective pore of the CFTR protein is formed by its two transmembrane domains (TMDs) and regulated by its cytosolic domains: two nucleotide binding domains (NBDs) and a regulatory (R) domain. Channel activation requires phosphorylation of the R domain by cAMP-dependent protein kinase (PKA), and pore opening and closing (gating) of phosphorylated channels is driven by ATP binding and hydrolysis at the NBDs. This review summarizes available information on structure and mechanism of the CFTR protein, with a particular focus on atomic-level insight gained from recent cryo-electron microscopic structures and on the molecular mechanisms of channel gating and its regulation. The pharmacological mechanisms of small molecules targeting CFTR's ion channel function, aimed at treating patients suffering from CF and other diseases, are briefly discussed.
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Affiliation(s)
- László Csanády
- Department of Medical Biochemistry, Semmelweis University , Budapest , Hungary ; MTA-SE Ion Channel Research Group, Budapest , Hungary ; Department of Neuroscience, Physiology and Pharmacology, University College London , London , United Kingdom ; and Laboratory of Cardiac/Membrane Physiology, The Rockefeller University , New York, New York
| | - Paola Vergani
- Department of Medical Biochemistry, Semmelweis University , Budapest , Hungary ; MTA-SE Ion Channel Research Group, Budapest , Hungary ; Department of Neuroscience, Physiology and Pharmacology, University College London , London , United Kingdom ; and Laboratory of Cardiac/Membrane Physiology, The Rockefeller University , New York, New York
| | - David C Gadsby
- Department of Medical Biochemistry, Semmelweis University , Budapest , Hungary ; MTA-SE Ion Channel Research Group, Budapest , Hungary ; Department of Neuroscience, Physiology and Pharmacology, University College London , London , United Kingdom ; and Laboratory of Cardiac/Membrane Physiology, The Rockefeller University , New York, New York
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21
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Learning the ABCs one at a time: structure and mechanism of ABC transporters. Biochem Soc Trans 2019; 47:23-36. [PMID: 30626703 DOI: 10.1042/bst20180147] [Citation(s) in RCA: 94] [Impact Index Per Article: 18.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/28/2018] [Revised: 11/16/2018] [Accepted: 11/29/2018] [Indexed: 12/21/2022]
Abstract
ATP-binding cassette (ABC) transporters are essential proteins that are found across all kingdoms of life. ABC transporters harness the energy of ATP hydrolysis to drive the import of nutrients inside bacterial cells or the export of toxic compounds or essential lipids across bacteria and eukaryotic membranes. Typically, ABC transporters consist of transmembrane domains (TMDs) and nucleotide-binding domains (NBDs) to bind their substrate and ATP, respectively. The TMDs dictate what ligands can be recognised, whereas the NBDs are the power engine of the ABC transporter, carrying out ATP binding and hydrolysis. It has been proposed that they utilise the alternating access mechanism, inward- to outward-facing conformation, to transport their substrates. Here, we will review the recent progress on the structure determination of eukaryotic and bacterial ABC transporters as well as the novel mechanisms that have also been proposed, that fall out of the alternating access mechanism model.
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22
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Wang Y, Cai Z, Gosling M, Sheppard DN. Potentiation of the cystic fibrosis transmembrane conductance regulator Cl− channel by ivacaftor is temperature independent. Am J Physiol Lung Cell Mol Physiol 2018; 315:L846-L857. [DOI: 10.1152/ajplung.00235.2018] [Citation(s) in RCA: 10] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/14/2022] Open
Abstract
Ivacaftor is the first drug to target directly defects in the cystic fibrosis transmembrane conductance regulator (CFTR), which causes cystic fibrosis (CF). To understand better how ivacaftor potentiates CFTR channel gating, here we investigated the effects of temperature on its action. As a control, we studied the benzimidazolone UCCF-853, which potentiates CFTR by a different mechanism. Using the patch-clamp technique and cells expressing recombinant CFTR, we studied the single-channel behavior of wild-type and F508del-CFTR, the most common CF mutation. Raising the temperature of the intracellular solution from 23 to 37°C increased the frequency but reduced the duration of wild-type and F508del-CFTR channel openings. Although the open probability ( Po) of wild-type CFTR increased progressively as temperature was elevated, the relationship between Po and temperature for F508del-CFTR was bell-shaped with a maximum Po at ~30°C. For wild-type CFTR and to a greatly reduced extent F508del-CFTR, the temperature dependence of channel gating was asymmetric with the opening rate demonstrating greater temperature sensitivity than the closing rate. At all temperatures tested, ivacaftor and UCCF-853 potentiated wild-type and F508del-CFTR. Strikingly, ivacaftor but not UCCF-853 abolished the asymmetric temperature dependence of CFTR channel gating. At all temperatures tested, Po values of wild-type CFTR in the presence of ivacaftor were approximately double those of F508del-CFTR, which were equivalent to or greater than those of wild-type CFTR at 37°C in the absence of the drug. We conclude that the principal effect of ivacaftor is to promote channel opening to abolish the temperature dependence of CFTR channel gating.
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Affiliation(s)
- Yiting Wang
- School of Physiology, Pharmacology and Neuroscience, University of Bristol, Biomedical Sciences Building, University Walk, Bristol, United Kingdom
| | - Zhiwei Cai
- School of Physiology, Pharmacology and Neuroscience, University of Bristol, Biomedical Sciences Building, University Walk, Bristol, United Kingdom
| | - Martin Gosling
- Enterprise Therapeutics, Sussex Innovation Centre, University of Sussex, Science Park Square, Brighton, United Kingdom
- Sussex Drug Discovery Centre, School of Life Sciences, University of Sussex, Brighton, United Kingdom
| | - David N. Sheppard
- School of Physiology, Pharmacology and Neuroscience, University of Bristol, Biomedical Sciences Building, University Walk, Bristol, United Kingdom
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23
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Hoffmann B, Elbahnsi A, Lehn P, Décout JL, Pietrucci F, Mornon JP, Callebaut I. Combining theoretical and experimental data to decipher CFTR 3D structures and functions. Cell Mol Life Sci 2018; 75:3829-3855. [PMID: 29779042 PMCID: PMC11105360 DOI: 10.1007/s00018-018-2835-7] [Citation(s) in RCA: 21] [Impact Index Per Article: 3.5] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/31/2017] [Revised: 05/04/2018] [Accepted: 05/07/2018] [Indexed: 12/15/2022]
Abstract
Cryo-electron microscopy (cryo-EM) has recently provided invaluable experimental data about the full-length cystic fibrosis transmembrane conductance regulator (CFTR) 3D structure. However, this experimental information deals with inactive states of the channel, either in an apo, quiescent conformation, in which nucleotide-binding domains (NBDs) are widely separated or in an ATP-bound, yet closed conformation. Here, we show that 3D structure models of the open and closed forms of the channel, now further supported by metadynamics simulations and by comparison with the cryo-EM data, could be used to gain some insights into critical features of the conformational transition toward active CFTR forms. These critical elements lie within membrane-spanning domains but also within NBD1 and the N-terminal extension, in which conformational plasticity is predicted to occur to help the interaction with filamin, one of the CFTR cellular partners.
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Affiliation(s)
- Brice Hoffmann
- Sorbonne Université, Muséum National d'Histoire Naturelle, UMR CNRS 7590, IRD, Institut de Minéralogie, de Physique des Matériaux et de Cosmochimie, IMPMC, 75005, Paris, France
- Iktos, Paris, France
| | - Ahmad Elbahnsi
- Sorbonne Université, Muséum National d'Histoire Naturelle, UMR CNRS 7590, IRD, Institut de Minéralogie, de Physique des Matériaux et de Cosmochimie, IMPMC, 75005, Paris, France
| | - Pierre Lehn
- INSERM U1078, SFR ScInBioS, Université de Bretagne Occidentale, Brest, France
| | | | - Fabio Pietrucci
- Sorbonne Université, Muséum National d'Histoire Naturelle, UMR CNRS 7590, IRD, Institut de Minéralogie, de Physique des Matériaux et de Cosmochimie, IMPMC, 75005, Paris, France
| | - Jean-Paul Mornon
- Sorbonne Université, Muséum National d'Histoire Naturelle, UMR CNRS 7590, IRD, Institut de Minéralogie, de Physique des Matériaux et de Cosmochimie, IMPMC, 75005, Paris, France.
| | - Isabelle Callebaut
- Sorbonne Université, Muséum National d'Histoire Naturelle, UMR CNRS 7590, IRD, Institut de Minéralogie, de Physique des Matériaux et de Cosmochimie, IMPMC, 75005, Paris, France
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24
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Langron E, Prins S, Vergani P. Potentiation of the cystic fibrosis transmembrane conductance regulator by VX-770 involves stabilization of the pre-hydrolytic, O 1 state. Br J Pharmacol 2018; 175:3990-4002. [PMID: 30107029 DOI: 10.1111/bph.14475] [Citation(s) in RCA: 15] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/30/2018] [Revised: 07/30/2018] [Accepted: 08/05/2018] [Indexed: 12/16/2022] Open
Abstract
BACKGROUND AND PURPOSE Cystic fibrosis (CF) is a debilitating hereditary disease caused by mutations in the cystic fibrosis transmembrane conductance regulator (CFTR) gene, which encodes an anion channel. Wild type-CFTR gating is a non-equilibrium process. After ATP binding, CFTR enters a stable open state (O1 ). ATP hydrolysis leads it to a short-lived post-hydrolytic open state (O2 ), from which channels close. Here, we use mutations to probe the mechanism of VX-770, the first compound directly targeting the CFTR protein approved for treatment of CF. D1370N and K1250R mutations reduce or abolish catalytic activity, simplifying the gating scheme to an equilibrium (C↔O1 ); K464A-CFTR has a destabilized O1 state and rarely closes via hydrolysis. EXPERIMENTAL APPROACH Potentiation by VX-770 was measured using microscopic imaging of HEK293 cells expressing an anion-sensitive YFP-CFTR. A simple mathematical model was used to predict fluorescence quenching following extracellular iodide addition and estimate CFTR conductance. Membrane density of CFTR channels was measured in a parallel assay, using CFTR-pHTomato. KEY RESULTS VX-770 strongly potentiated WT-CFTR, D1370N-CFTR and K1250R-CFTR. K464A-CFTR was also strongly potentiated, regardless of whether it retained catalytic activity or not. CONCLUSIONS AND IMPLICATIONS Similar potentiation of hydrolytic and non-hydrolytic mutants suggests that VX-770 increases CFTR open probability mainly by stabilizing pre-hydrolytic O1 states with respect to closed states. Potentiation of K464A-CFTR channels suggests action of VX-770 did not strongly alter conformational dynamics at site 1. Understanding potentiator mechanism could help develop improved treatment for CF patients. The fluorescence assay presented here is a robust tool for such investigations.
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Affiliation(s)
- Emily Langron
- Neuroscience, Physiology and Pharmacology, University College London, London, UK
| | - Stella Prins
- Neuroscience, Physiology and Pharmacology, University College London, London, UK
| | - Paola Vergani
- Neuroscience, Physiology and Pharmacology, University College London, London, UK
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25
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Negoda A, Cowley EA, El Hiani Y, Linsdell P. Conformational change of the extracellular parts of the CFTR protein during channel gating. Cell Mol Life Sci 2018; 75:3027-3038. [PMID: 29441426 PMCID: PMC11105745 DOI: 10.1007/s00018-018-2777-0] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/28/2017] [Revised: 01/24/2018] [Accepted: 02/08/2018] [Indexed: 12/21/2022]
Abstract
Cystic fibrosis can be treated by potentiators, drugs that interact directly with the cystic fibrosis transmembrane conductance regulator (CFTR) Cl- channel to increase its open probability. These substances likely target key conformational changes occurring during channel opening and closing, however, the molecular bases of these conformational changes, and their susceptibility to manipulation are poorly understood. We have used patch clamp recording to identify changes in the three-dimensional organization of the extracellularly accessible parts of the CFTR protein during channel opening and closing. State-dependent formation of both disulfide bonds and Cd2+ bridges occurred for pairs of cysteine side-chains introduced into the extreme extracellular ends of transmembrane helices (TMs) 1, 6, and 12. Between each of these three TMs, we found that both disulfide bonds and metal bridges formed preferentially or exclusively in the closed state and that these inter-TM cross-links stabilized the closed state. These results indicate that the extracellular ends of these TMs are close together when the channel is closed and that they separate from each other when the channel opens. These findings identify for the first time key conformational changes in the extracellular parts of the CFTR protein that can potentially be manipulated to control channel activity.
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Affiliation(s)
- Alexander Negoda
- Department of Physiology and Biophysics, Dalhousie University, PO Box 15000, Halifax, NS, B3H 4R2, Canada
| | - Elizabeth A Cowley
- Department of Physiology and Biophysics, Dalhousie University, PO Box 15000, Halifax, NS, B3H 4R2, Canada
| | - Yassine El Hiani
- Department of Physiology and Biophysics, Dalhousie University, PO Box 15000, Halifax, NS, B3H 4R2, Canada
| | - Paul Linsdell
- Department of Physiology and Biophysics, Dalhousie University, PO Box 15000, Halifax, NS, B3H 4R2, Canada.
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26
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Puga Molina LC, Luque GM, Balestrini PA, Marín-Briggiler CI, Romarowski A, Buffone MG. Molecular Basis of Human Sperm Capacitation. Front Cell Dev Biol 2018; 6:72. [PMID: 30105226 PMCID: PMC6078053 DOI: 10.3389/fcell.2018.00072] [Citation(s) in RCA: 135] [Impact Index Per Article: 22.5] [Reference Citation Analysis] [Abstract] [Key Words] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/20/2018] [Accepted: 06/19/2018] [Indexed: 12/31/2022] Open
Abstract
In the early 1950s, Austin and Chang independently described the changes that are required for the sperm to fertilize oocytes in vivo. These changes were originally grouped under name of “capacitation” and were the first step in the development of in vitro fertilization (IVF) in humans. Following these initial and fundamental findings, a remarkable number of observations led to characterization of the molecular steps behind this process. The discovery of certain sperm-specific molecules and the possibility to record ion currents through patch-clamp approaches helped to integrate the initial biochemical observation with the activity of ion channels. This is of particular importance in the male gamete due to the fact that sperm are transcriptionally inactive. Therefore, sperm must control all these changes that occur during their transit through the male and female reproductive tracts by complex signaling cascades that include post-translational modifications. This review is focused on the principal molecular mechanisms that govern human sperm capacitation with particular emphasis on comparing all the reported pieces of evidence with the mouse model.
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Affiliation(s)
- Lis C Puga Molina
- Instituto de Biología y Medicina Experimental, Consejo Nacional de Investigaciones Científicas y Tecnológicas, Buenos Aires, Argentina
| | - Guillermina M Luque
- Instituto de Biología y Medicina Experimental, Consejo Nacional de Investigaciones Científicas y Tecnológicas, Buenos Aires, Argentina
| | - Paula A Balestrini
- Instituto de Biología y Medicina Experimental, Consejo Nacional de Investigaciones Científicas y Tecnológicas, Buenos Aires, Argentina
| | - Clara I Marín-Briggiler
- Instituto de Biología y Medicina Experimental, Consejo Nacional de Investigaciones Científicas y Tecnológicas, Buenos Aires, Argentina
| | - Ana Romarowski
- Instituto de Biología y Medicina Experimental, Consejo Nacional de Investigaciones Científicas y Tecnológicas, Buenos Aires, Argentina
| | - Mariano G Buffone
- Instituto de Biología y Medicina Experimental, Consejo Nacional de Investigaciones Científicas y Tecnológicas, Buenos Aires, Argentina
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27
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Yang F, Xiao X, Lee BH, Vu S, Yang W, Yarov-Yarovoy V, Zheng J. The conformational wave in capsaicin activation of transient receptor potential vanilloid 1 ion channel. Nat Commun 2018; 9:2879. [PMID: 30038260 PMCID: PMC6056546 DOI: 10.1038/s41467-018-05339-6] [Citation(s) in RCA: 50] [Impact Index Per Article: 8.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/21/2017] [Accepted: 06/19/2018] [Indexed: 01/17/2023] Open
Abstract
The capsaicin receptor TRPV1 has been intensively studied by cryo-electron microscopy and functional tests. However, though the apo and capsaicin-bound structural models are available, the dynamic process of capsaicin activation remains intangible, largely due to the lack of a capsaicin-induced open structural model and the low occupancy of the transition states. Here we report that reducing temperature toward the freezing point substantially increased channel closure events even in the presence of saturating capsaicin. We further used a combination of fluorescent unnatural amino acid (fUAA) incorporation, computational modeling, and rate-equilibrium linear free-energy relationships analysis (Φ-analysis) to derive the fully open capsaicin-bound state model, and reveal how the channel transits from the apo to the open state. We observed that capsaicin initiates a conformational wave that propagates through the S4–S5 linker towards the S6 bundle and finally reaching the selectivity filter. Our study provides a temporal mechanism for capsaicin activation of TRPV1. The capsaicin receptor TRPV1 has been structurally characterized, but the capsaicin activation dynamics remain elusive. Here authors use fluorescent unnatural amino acid incorporation, computational modeling and Φ-analysis to derive the capsaicin-bound open state model and reveal the capsaicin induced conformational changes.
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Affiliation(s)
- Fan Yang
- Department of Biophysics and Kidney Disease Center, First Affiliated Hospital, Institute of Neuroscience, National Health Commission and Chinese Academy of Medical Sciences Key Laboratory of Medical Neurobiology, Zhejiang University School of Medicine, Hangzhou, 310058, Zhejiang Province, China. .,Department of Physiology and Membrane Biology, University of California, Davis, CA, 95616, USA.
| | - Xian Xiao
- Department of Physiology and Membrane Biology, University of California, Davis, CA, 95616, USA.,Institute for Basic Medical Sciences, Westlake Institute for Advanced Study, Westlake University, Shilongshan Road No. 18, Xihu District, Hangzhou, 310024, Zhejiang Province, China
| | - Bo Hyun Lee
- Department of Physiology and Membrane Biology, University of California, Davis, CA, 95616, USA.,University of Washington, Department of Physiology and Biophysics, Seattle, WA, 98195, USA
| | - Simon Vu
- Department of Physiology and Membrane Biology, University of California, Davis, CA, 95616, USA
| | - Wei Yang
- Department of Biophysics and Kidney Disease Center, First Affiliated Hospital, Institute of Neuroscience, National Health Commission and Chinese Academy of Medical Sciences Key Laboratory of Medical Neurobiology, Zhejiang University School of Medicine, Hangzhou, 310058, Zhejiang Province, China
| | - Vladimir Yarov-Yarovoy
- Department of Physiology and Membrane Biology, University of California, Davis, CA, 95616, USA
| | - Jie Zheng
- Department of Physiology and Membrane Biology, University of California, Davis, CA, 95616, USA.
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28
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DeStefano S, Gees M, Hwang TC. Physiological and pharmacological characterization of the N1303K mutant CFTR. J Cyst Fibros 2018; 17:573-581. [PMID: 29887518 DOI: 10.1016/j.jcf.2018.05.011] [Citation(s) in RCA: 18] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/03/2018] [Revised: 05/13/2018] [Accepted: 05/21/2018] [Indexed: 11/18/2022]
Abstract
BACKGROUND N1303K, one of the common, severe disease-causing mutations in the CFTR gene, causes both defective biogenesis and gating abnormalities of the CFTR protein. The goals of the present study are to quantitatively assess the gating defects associated with the N1303K mutation and its pharmacological response to CFTR modulators including potentiators VX-770 and GLPG1837 and correctors VX-809, and VX-661. METHODS Gating behavior and pharmacological responses to CFTR potentiators were assessed using patch-clamp technique in the excised, inside-out mode. We also examined the effects of GLPG1837, VX-770, VX-809 and VX-661 on N1303K-CFTR surface expression using Western blot analysis. RESULTS Like wild-type (WT) CFTR, N1303K-CFTR channels were activated by protein kinase A-dependent phosphorylation, but the open probability (Po) of phosphorylated N1303K-CFTR was extremely low (~0.03 vs ~0.45 in WT channels). N1303K mutants showed abnormal responses to ATP analogs or mutations that disrupt ATP hydrolysis and/or dimerization of CFTR's two nucleotide-binding domains (NBDs). However, the Po of N1303K-CFTR was dramatically increased by GLPG1837 (~17-fold) and VX-770 (~8-fold). VX-809 or VX-661 enhanced N1303K-CFTR maturation by 2-3 fold, and co-treatment with GLPG1837 or VX-770 did not show any negative drug-drug interaction. CONCLUSION N1303K has a severe gating defect, reduced ATP-dependence and aberrant response to ATP analogs. These results suggest a defective function of the NBDs in N1303K-CFTR. An improvement of channel function by GLPG1837 or VX-770 and an increase of Band C protein by VX-809 or VX-661 support a therapeutic strategy of combining CFTR potentiator and corrector for patients carrying the N1303K mutation.
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Affiliation(s)
- Samantha DeStefano
- Dalton Cardiovascular Research Center, University of Missouri, Columbia, MO 65211, United States; Department of Medical Pharmacology and Physiology, University of Missouri, Columbia, MO 65211, United States
| | | | - Tzyh-Chang Hwang
- Dalton Cardiovascular Research Center, University of Missouri, Columbia, MO 65211, United States; Department of Medical Pharmacology and Physiology, University of Missouri, Columbia, MO 65211, United States.
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29
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Puga Molina LC, Pinto NA, Torres NI, González-Cota AL, Luque GM, Balestrini PA, Romarowski A, Krapf D, Santi CM, Treviño CL, Darszon A, Buffone MG. CFTR/ENaC-dependent regulation of membrane potential during human sperm capacitation is initiated by bicarbonate uptake through NBC. J Biol Chem 2018; 293:9924-9936. [PMID: 29743243 DOI: 10.1074/jbc.ra118.003166] [Citation(s) in RCA: 34] [Impact Index Per Article: 5.7] [Reference Citation Analysis] [Abstract] [Key Words] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/28/2018] [Revised: 04/29/2018] [Indexed: 12/16/2022] Open
Abstract
To fertilize an egg, sperm must reside in the female reproductive tract to undergo several maturational changes that are collectively referred to as capacitation. From a molecular point of view, the HCO3--dependent activation of the atypical soluble adenylyl cyclase (ADCY10) is one of the first events that occurs during capacitation and leads to the subsequent cAMP-dependent activation of protein kinase A (PKA). Capacitation is also accompanied by hyperpolarization of the sperm plasma membrane. We previously reported that PKA activation is necessary for CFTR (cystic fibrosis transmembrane conductance regulator channel) activity and for the modulation of membrane potential (Em). However, the main HCO3- transporters involved in the initial transport and the PKA-dependent Em changes are not well known nor characterized. Here, we analyzed how the activity of CFTR regulates Em during capacitation and examined its relationship with an electrogenic Na+/HCO3- cotransporter (NBC) and epithelial Na+ channels (ENaCs). We observed that inhibition of both CFTR and NBC decreased HCO3- influx, resulting in lower PKA activity, and that events downstream of the cAMP activation of PKA are essential for the regulation of Em. Addition of a permeable cAMP analog partially rescued the inhibitory effects caused by these inhibitors. HCO3- also produced a rapid membrane hyperpolarization mediated by ENaC channels, which contribute to the regulation of Em during capacitation. Altogether, we demonstrate for the first time, that NBC cotransporters and ENaC channels are essential in the CFTR-dependent activation of the cAMP/PKA signaling pathway and Em regulation during human sperm capacitation.
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Affiliation(s)
- Lis C Puga Molina
- From the Instituto de Biología y Medicina Experimental (IBYME), Consejo Nacional de Investigaciones Científicas y Tecnológicas (CONICET), C1425FQB Buenos Aires, Argentina
| | - Nicolás A Pinto
- From the Instituto de Biología y Medicina Experimental (IBYME), Consejo Nacional de Investigaciones Científicas y Tecnológicas (CONICET), C1425FQB Buenos Aires, Argentina
| | - Nicolás I Torres
- From the Instituto de Biología y Medicina Experimental (IBYME), Consejo Nacional de Investigaciones Científicas y Tecnológicas (CONICET), C1425FQB Buenos Aires, Argentina
| | - Ana L González-Cota
- the Department of Obstetrics and Gynecology, Washington University School of Medicine, St. Louis, Missouri 63110
| | - Guillermina M Luque
- From the Instituto de Biología y Medicina Experimental (IBYME), Consejo Nacional de Investigaciones Científicas y Tecnológicas (CONICET), C1425FQB Buenos Aires, Argentina
| | - Paula A Balestrini
- From the Instituto de Biología y Medicina Experimental (IBYME), Consejo Nacional de Investigaciones Científicas y Tecnológicas (CONICET), C1425FQB Buenos Aires, Argentina
| | - Ana Romarowski
- From the Instituto de Biología y Medicina Experimental (IBYME), Consejo Nacional de Investigaciones Científicas y Tecnológicas (CONICET), C1425FQB Buenos Aires, Argentina
| | - Dario Krapf
- the Instituto de Biología Molecular y Celular de Rosario (IBR), CONICET-UNR, Rosario 2000, Argentina, and
| | - Celia M Santi
- the Department of Obstetrics and Gynecology, Washington University School of Medicine, St. Louis, Missouri 63110
| | - Claudia L Treviño
- the Departamento de Genética del Desarrollo y Fisiología Molecular, Instituto de Biotecnología, Universidad Nacional Autónoma de México (UNAM), Cuernavaca, 62210 Morelos, México
| | - Alberto Darszon
- the Departamento de Genética del Desarrollo y Fisiología Molecular, Instituto de Biotecnología, Universidad Nacional Autónoma de México (UNAM), Cuernavaca, 62210 Morelos, México
| | - Mariano G Buffone
- From the Instituto de Biología y Medicina Experimental (IBYME), Consejo Nacional de Investigaciones Científicas y Tecnológicas (CONICET), C1425FQB Buenos Aires, Argentina,
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30
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Hwang TC, Yeh JT, Zhang J, Yu YC, Yeh HI, Destefano S. Structural mechanisms of CFTR function and dysfunction. J Gen Physiol 2018; 150:539-570. [PMID: 29581173 PMCID: PMC5881446 DOI: 10.1085/jgp.201711946] [Citation(s) in RCA: 67] [Impact Index Per Article: 11.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/16/2017] [Accepted: 03/05/2018] [Indexed: 12/18/2022] Open
Abstract
Hwang et al. integrate new structural insights with prior functional studies to reveal the functional anatomy of CFTR chloride channels. Cystic fibrosis (CF) transmembrane conductance regulator (CFTR) chloride channel plays a critical role in regulating transepithelial movement of water and electrolyte in exocrine tissues. Malfunction of the channel because of mutations of the cftr gene results in CF, the most prevalent lethal genetic disease among Caucasians. Recently, the publication of atomic structures of CFTR in two distinct conformations provides, for the first time, a clear overview of the protein. However, given the highly dynamic nature of the interactions among CFTR’s various domains, better understanding of the functional significance of these structures requires an integration of these new structural insights with previously established biochemical/biophysical studies, which is the goal of this review.
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Affiliation(s)
- Tzyh-Chang Hwang
- Dalton Cardiovascular Research Center, University of Missouri, Columbia, MO .,Department of Medical Pharmacology and Physiology, University of Missouri, Columbia, MO.,Department of Biological Engineering, University of Missouri, Columbia, MO
| | - Jiunn-Tyng Yeh
- Dalton Cardiovascular Research Center, University of Missouri, Columbia, MO
| | - Jingyao Zhang
- Dalton Cardiovascular Research Center, University of Missouri, Columbia, MO.,Department of Biological Engineering, University of Missouri, Columbia, MO
| | - Ying-Chun Yu
- Dalton Cardiovascular Research Center, University of Missouri, Columbia, MO.,Department of Medical Pharmacology and Physiology, University of Missouri, Columbia, MO
| | - Han-I Yeh
- Dalton Cardiovascular Research Center, University of Missouri, Columbia, MO.,Department of Medical Pharmacology and Physiology, University of Missouri, Columbia, MO
| | - Samantha Destefano
- Dalton Cardiovascular Research Center, University of Missouri, Columbia, MO.,Department of Medical Pharmacology and Physiology, University of Missouri, Columbia, MO
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31
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Sites associated with Kalydeco binding on human Cystic Fibrosis Transmembrane Conductance Regulator revealed by Hydrogen/Deuterium Exchange. Sci Rep 2018; 8:4664. [PMID: 29549268 PMCID: PMC5856801 DOI: 10.1038/s41598-018-22959-6] [Citation(s) in RCA: 19] [Impact Index Per Article: 3.2] [Reference Citation Analysis] [Abstract] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/20/2017] [Accepted: 01/31/2018] [Indexed: 12/18/2022] Open
Abstract
Cystic Fibrosis (CF) is caused by mutations in the Cystic Fibrosis Transmembrane Conductance Regulator (CFTR). Mutations associated with CF cause loss-of-function in CFTR leading to salt imbalance in epithelial tissues. Kalydeco (also called VX-770 or ivacaftor) was approved for CF treatment in 2012 but little is known regarding the compound’s interactions with CFTR including the site of binding or mechanisms of action. In this study we use hydrogen/deuterium exchange (HDX) coupled with mass spectrometry to assess the conformational dynamics of a thermostabilized form of CFTR in apo and ligand-bound states. We observe HDX protection at a known binding site for AMPPNP and significant protection for several regions of CFTR in the presence of Kalydeco. The ligand-induced changes of CFTR in the presence of Kalydeco suggest a potential binding site.
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32
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Muimo R, Alothaid HM, Mehta A. NM23 proteins: innocent bystanders or local energy boosters for CFTR? J Transl Med 2018; 98:272-282. [PMID: 29251738 DOI: 10.1038/labinvest.2017.121] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/20/2017] [Revised: 08/25/2017] [Accepted: 09/12/2017] [Indexed: 12/17/2022] Open
Abstract
NM23 proteins NDPK-A and -B bind to the cystic fibrosis (CF) protein CFTR in different ways from kinases such as PKA, CK2 and AMPK or linkers to cell calcium such as calmodulin and annexins. NDPK-A (not -B) interacts with CFTR through reciprocal AMPK binding/control, whereas NDPK-B (not -A) binds directly to CFTR. NDPK-B can activate G proteins without ligand-receptor coupling, so perhaps NDPK-B's binding influences energy supply local to a nucleotide-binding site (NBD1) needed for CFTR to function. Curiously, CFTR (ABC-C7) is a member of the ATP-binding cassette (ABC) protein family that does not obey 'clan rules'; CFTR channels anions and is not a pump, regulates disparate processes, is itself regulated by multiple means and is so pleiotropic that it acts as a hub that orchestrates calcium signaling through its consorts such as calmodulin/annexins. Furthermore, its multiple partners make CFTR dance to different tunes in different cellular and subcellular locations as it recycles from the plasma membrane to endosomes. CFTR function in airway apical membranes is inhibited by smoking which has been dubbed 'acquired CF'. CFTR alone among family members possesses a trap for other proteins that it unfurls as a 'fish-net' and which bears consensus phosphorylation sites for many protein kinases, with PKA being the most canonical. Recently, the site of CFTR's commonest mutation has been proposed as a knock-in mutant that alters allosteric control of kinase CK2 by log orders of activity towards calmodulin and other substrates after CFTR fragmentation. This link from CK2 to calmodulin that binds the R region invokes molecular paths that control lumen formation, which is incomplete in the tracheas of some CF-affected babies. Thus, we are poised to understand the many roles of NDPK-A and -B in CFTR function and, especially lumen formation, which is defective in the gut and lungs of many CF babies.
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Affiliation(s)
- Richmond Muimo
- Department of Infection, Immunity and Cardiovascular Disease, The Medical School, University of Sheffield, Sheffield, UK
| | - Hani Mm Alothaid
- Department of Infection, Immunity and Cardiovascular Disease, The Medical School, University of Sheffield, Sheffield, UK
| | - Anil Mehta
- Medical Research Institute, Ninewells Hospital and Medical School, University of Dundee, Dundee, UK
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33
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Yang Z, Hildebrandt E, Jiang F, Aleksandrov AA, Khazanov N, Zhou Q, An J, Mezzell AT, Xavier BM, Ding H, Riordan JR, Senderowitz H, Kappes JC, Brouillette CG, Urbatsch IL. Structural stability of purified human CFTR is systematically improved by mutations in nucleotide binding domain 1. BIOCHIMICA ET BIOPHYSICA ACTA-BIOMEMBRANES 2018; 1860:1193-1204. [PMID: 29425673 DOI: 10.1016/j.bbamem.2018.02.006] [Citation(s) in RCA: 13] [Impact Index Per Article: 2.2] [Reference Citation Analysis] [Abstract] [Key Words] [Subscribe] [Scholar Register] [Received: 09/27/2017] [Revised: 01/19/2018] [Accepted: 02/05/2018] [Indexed: 12/17/2022]
Abstract
The Cystic Fibrosis Transmembrane Conductance Regulator (CFTR) is an ABC transporter containing two transmembrane domains forming a chloride ion channel, and two nucleotide binding domains (NBD1 and NBD2). CFTR has presented a formidable challenge to obtain monodisperse, biophysically stable protein. Here we report a comprehensive study comparing effects of single and multiple NBD1 mutations on stability of both the NBD1 domain alone and on purified full length human CFTR. Single mutations S492P, A534P, I539T acted additively, and when combined with M470V, S495P, and R555K cumulatively yielded an NBD1 with highly improved structural stability. Strategic combinations of these mutations strongly stabilized the domain to attain a calorimetric Tm > 70 °C. Replica exchange molecular dynamics simulations on the most stable 6SS-NBD1 variant implicated fluctuations, electrostatic interactions and side chain packing as potential contributors to improved stability. Progressive stabilization of NBD1 directly correlated with enhanced structural stability of full-length CFTR protein. Thermal unfolding of the stabilized CFTR mutants, monitored by changes in intrinsic fluorescence, demonstrated that Tm could be shifted as high as 67.4 °C in 6SS-CFTR, more than 20 °C higher than wild-type. H1402S, an NBD2 mutation, conferred CFTR with additional thermal stability, possibly by stabilizing an NBD-dimerized conformation. CFTR variants with NBD1-stabilizing mutations were expressed at the cell surface in mammalian cells, exhibited ATPase and channel activity, and retained these functions to higher temperatures. The capability to produce enzymatically active CFTR with improved structural stability amenable to biophysical and structural studies will advance mechanistic investigations and future cystic fibrosis drug development.
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Affiliation(s)
- Zhengrong Yang
- Department of Chemistry, University of Alabama at Birmingham, Birmingham, AL, USA
| | - Ellen Hildebrandt
- Department of Cell Biology and Biochemistry, Center for Membrane Protein Research, Texas Tech University Health Sciences Center, 3601 4th Street, Stop 6540, Lubbock, TX 79430, USA
| | - Fan Jiang
- Department of Medicine, University of Alabama at Birmingham, 701 19th Street South, Birmingham, AL 35294-0007, USA
| | - Andrei A Aleksandrov
- Department of Biochemistry and Biophysics and Cystic Fibrosis Treatment and Research Center, University of North Carolina at Chapel Hill, Chapel Hill, NC 27599, USA
| | - Netaly Khazanov
- Department of Chemistry, Bar-Ilan University, Ramat-Gan, 5290002, Israel
| | - Qingxian Zhou
- Department of Chemistry, University of Alabama at Birmingham, Birmingham, AL, USA
| | - Jianli An
- Department of Chemistry, University of Alabama at Birmingham, Birmingham, AL, USA
| | - Andrew T Mezzell
- Department of Medicine, University of Alabama at Birmingham, 701 19th Street South, Birmingham, AL 35294-0007, USA
| | - Bala M Xavier
- Department of Cell Biology and Biochemistry, Center for Membrane Protein Research, Texas Tech University Health Sciences Center, 3601 4th Street, Stop 6540, Lubbock, TX 79430, USA
| | - Haitao Ding
- Department of Medicine, University of Alabama at Birmingham, 701 19th Street South, Birmingham, AL 35294-0007, USA
| | - John R Riordan
- Department of Biochemistry and Biophysics and Cystic Fibrosis Treatment and Research Center, University of North Carolina at Chapel Hill, Chapel Hill, NC 27599, USA
| | - Hanoch Senderowitz
- Department of Chemistry, Bar-Ilan University, Ramat-Gan, 5290002, Israel
| | - John C Kappes
- Department of Medicine, University of Alabama at Birmingham, 701 19th Street South, Birmingham, AL 35294-0007, USA; Birmingham Veterans Affairs Medical Center, Research Service, Birmingham, AL 35233, USA
| | | | - Ina L Urbatsch
- Department of Cell Biology and Biochemistry, Center for Membrane Protein Research, Texas Tech University Health Sciences Center, 3601 4th Street, Stop 6540, Lubbock, TX 79430, USA.
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34
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Ion channels as targets to treat cystic fibrosis lung disease. J Cyst Fibros 2017; 17:S22-S27. [PMID: 29102290 DOI: 10.1016/j.jcf.2017.10.006] [Citation(s) in RCA: 24] [Impact Index Per Article: 3.4] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/16/2017] [Revised: 10/09/2017] [Accepted: 10/09/2017] [Indexed: 11/21/2022]
Abstract
Lung health relies on effective mucociliary clearance and innate immune defence mechanisms. In cystic fibrosis (CF), an imbalance in ion transport due to an absence of chloride ion secretion, caused by mutations in the cystic fibrosis transmembrane conductance regulator (CFTR) and a concomitant sodium hyperabsorption, caused by dyregulation of the epithelial sodium channel (ENaC), results in mucus stasis which predisposes the lungs to cycles of chronic infection and inflammation leading to lung function decline. An increased understanding of CFTR structure and function has provided opportunity for the development of a number of novel modulators targeting mutant CFTR however, it is important to also consider other ion channels and transporters present in the airways as putative targets for drug development. In this review, we discuss recent advances in CFTR biology which will contribute to further drug discovery in the field. We also examine developments to inhibit the epithelial sodium channel (ENaC) and potentially activate alternative chloride channels and transporters as a multi-tracked strategy to hydrate CF airways and restore normal mucociliary clearance mechanisms in a manner independent of CFTR mutation.
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35
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Sorum B, Töröcsik B, Csanády L. Asymmetry of movements in CFTR's two ATP sites during pore opening serves their distinct functions. eLife 2017; 6:29013. [PMID: 28944753 PMCID: PMC5626490 DOI: 10.7554/elife.29013] [Citation(s) in RCA: 23] [Impact Index Per Article: 3.3] [Reference Citation Analysis] [Abstract] [Key Words] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/26/2017] [Accepted: 09/25/2017] [Indexed: 11/13/2022] Open
Abstract
CFTR, the chloride channel mutated in cystic fibrosis (CF) patients, is opened by ATP binding to two cytosolic nucleotide binding domains (NBDs), but pore-domain mutations may also impair gating. ATP-bound NBDs dimerize occluding two nucleotides at interfacial binding sites; one site hydrolyzes ATP, the other is inactive. The pore opens upon tightening, and closes upon disengagement, of the catalytic site following ATP hydrolysis. Extent, timing, and role of non-catalytic-site movements are unknown. Here we exploit equilibrium gating of a hydrolysis-deficient mutant and apply Φ value analysis to compare timing of opening-associated movements at multiple locations, from the cytoplasmic ATP sites to the extracellular surface. Marked asynchrony of motion in the two ATP sites reveals their distinct roles in channel gating. The results clarify the molecular mechanisms of functional cross-talk between canonical and degenerate ATP sites in asymmetric ABC proteins, and of the gating defects caused by two common CF mutations.
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Affiliation(s)
- Ben Sorum
- Department of Medical Biochemistry, Semmelweis University, Budapest, Hungary
| | - Beáta Töröcsik
- Department of Medical Biochemistry, Semmelweis University, Budapest, Hungary.,MTA-SE Ion Channel Research Group, Semmelweis University, Budapest, Hungary
| | - László Csanády
- Department of Medical Biochemistry, Semmelweis University, Budapest, Hungary.,MTA-SE Ion Channel Research Group, Semmelweis University, Budapest, Hungary
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36
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Zhang Z, Liu F, Chen J. Conformational Changes of CFTR upon Phosphorylation and ATP Binding. Cell 2017; 170:483-491.e8. [PMID: 28735752 DOI: 10.1016/j.cell.2017.06.041] [Citation(s) in RCA: 171] [Impact Index Per Article: 24.4] [Reference Citation Analysis] [Abstract] [Key Words] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/12/2017] [Revised: 06/21/2017] [Accepted: 06/26/2017] [Indexed: 02/01/2023]
Abstract
The cystic fibrosis transmembrane conductance regulator (CFTR) is an anion channel evolved from an ATP-binding cassette transporter. CFTR channel gating is strictly coupled to phosphorylation and ATP hydrolysis. Previously, we reported essentially identical structures of zebrafish and human CFTR in the dephosphorylated, ATP-free form. Here, we present the structure of zebrafish CFTR in the phosphorylated, ATP-bound conformation, determined by cryoelectron microscopy to 3.4 Å resolution. Comparison of the two conformations shows major structural rearrangements leading to channel opening. The phosphorylated regulatory domain is disengaged from its inhibitory position; the nucleotide-binding domains (NBDs) form a "head-to-tail" dimer upon binding ATP; and the cytoplasmic pathway, found closed off in other ATP-binding cassette transporters, is cracked open, consistent with CFTR's unique channel function. Unexpectedly, the extracellular mouth of the ion pore remains closed, indicating that local movements of the transmembrane helices can control ion access to the pore even in the NBD-dimerized conformation.
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Affiliation(s)
- Zhe Zhang
- Laboratory of Membrane Biophysics and Biology, The Rockefeller University, New York, NY, USA; Howard Hughes Medical Institute, Chevy Chase, MD 20815, USA
| | - Fangyu Liu
- Laboratory of Membrane Biophysics and Biology, The Rockefeller University, New York, NY, USA; Tri-Institutional Training Program in Chemical Biology, The Rockefeller University, New York, NY, USA
| | - Jue Chen
- Laboratory of Membrane Biophysics and Biology, The Rockefeller University, New York, NY, USA; Howard Hughes Medical Institute, Chevy Chase, MD 20815, USA.
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37
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Das J, Aleksandrov AA, Cui L, He L, Riordan JR, Dokholyan NV. Transmembrane helical interactions in the CFTR channel pore. PLoS Comput Biol 2017. [PMID: 28640808 PMCID: PMC5501672 DOI: 10.1371/journal.pcbi.1005594] [Citation(s) in RCA: 9] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/23/2022] Open
Abstract
Mutations in the Cystic Fibrosis Transmembrane Conductance Regulator (CFTR) gene affect CFTR protein biogenesis or its function as a chloride channel, resulting in dysregulation of epithelial fluid transport in the lung, pancreas and other organs in cystic fibrosis (CF). Development of pharmaceutical strategies to treat CF requires understanding of the mechanisms underlying channel function. However, incomplete 3D structural information on the unique ABC ion channel, CFTR, hinders elucidation of its functional mechanism and correction of cystic fibrosis causing mutants. Several CFTR homology models have been developed using bacterial ABC transporters as templates but these have low sequence similarity to CFTR and are not ion channels. Here, we refine an earlier model in an outward (OWF) and develop an inward (IWF) facing model employing an integrated experimental-molecular dynamics simulation (200 ns) approach. Our IWF structure agrees well with a recently solved cryo-EM structure of a CFTR IWF state. We utilize cysteine cross-linking to verify positions and orientations of residues within trans-membrane helices (TMHs) of the OWF conformation and to reconstruct a physiologically relevant pore structure. Comparison of pore profiles of the two conformations reveal a radius sufficient to permit passage of hydrated Cl- ions in the OWF but not the IWF model. To identify structural determinants that distinguish the two conformations and possible rearrangements of TMHs within them responsible for channel gating, we perform cross-linking by bifunctional reagents of multiple predicted pairs of cysteines in TMH 6 and 12 and 6 and 9. To determine whether the effects of cross-linking on gating observed are the result of switching of the channel from open to close state, we also treat the same residue pairs with monofunctional reagents in separate experiments. Both types of reagents prevent ion currents indicating that pore blockage is primarily responsible.
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Affiliation(s)
- Jhuma Das
- Department of Biochemistry and Biophysics, University of North Carolina at Chapel Hill, Chapel Hill, North Carolina, United States of America
| | - Andrei A. Aleksandrov
- Department of Biochemistry and Biophysics, University of North Carolina at Chapel Hill, Chapel Hill, North Carolina, United States of America
- Cystic Fibrosis Treatment and Research Center, University of North Carolina at Chapel Hill, Chapel Hill, North Carolina, United States of America
| | - Liying Cui
- Department of Biochemistry and Biophysics, University of North Carolina at Chapel Hill, Chapel Hill, North Carolina, United States of America
- Cystic Fibrosis Treatment and Research Center, University of North Carolina at Chapel Hill, Chapel Hill, North Carolina, United States of America
| | - Lihua He
- Department of Biochemistry and Biophysics, University of North Carolina at Chapel Hill, Chapel Hill, North Carolina, United States of America
- Cystic Fibrosis Treatment and Research Center, University of North Carolina at Chapel Hill, Chapel Hill, North Carolina, United States of America
| | - John R. Riordan
- Department of Biochemistry and Biophysics, University of North Carolina at Chapel Hill, Chapel Hill, North Carolina, United States of America
- Cystic Fibrosis Treatment and Research Center, University of North Carolina at Chapel Hill, Chapel Hill, North Carolina, United States of America
- * E-mail: (JRR); (NVD)
| | - Nikolay V. Dokholyan
- Department of Biochemistry and Biophysics, University of North Carolina at Chapel Hill, Chapel Hill, North Carolina, United States of America
- Cystic Fibrosis Treatment and Research Center, University of North Carolina at Chapel Hill, Chapel Hill, North Carolina, United States of America
- * E-mail: (JRR); (NVD)
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38
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Zhang J, Hwang TC. Electrostatic tuning of the pre- and post-hydrolytic open states in CFTR. J Gen Physiol 2017; 149:355-372. [PMID: 28242630 PMCID: PMC5339510 DOI: 10.1085/jgp.201611664] [Citation(s) in RCA: 13] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/08/2016] [Revised: 11/17/2016] [Accepted: 01/20/2017] [Indexed: 12/28/2022] Open
Abstract
Gating of the CFTR channel is coupled to ATP hydrolysis such that two open states can be identified under certain conditions. Zhang and Hwang find that pore-lining mutations differentially affect the permeation properties of these open states and suggest that the internal vestibule expands upon ATP hydrolysis. Cystic fibrosis transmembrane conductance regulator (CFTR) is an ion channel that couples adenosine triphosphate (ATP) hydrolysis at its nucleotide-binding domains to gating transitions in its transmembrane domains. We previously reported that the charge-neutralized mutant R352C shows two distinct open states, O1 and O2. The two states could be distinguished by their single-channel current amplitudes: O1 having a smaller amplitude (representing a prehydrolytic open state) and O2 having a larger amplitude (representing a post-hydrolytic open state). In this study, a similar phenotype is described for two mutations of another pore-lining residue, N306D and N306E, suggesting that alterations of the net charge within CFTR’s pore confer this unique conductance aberration. Because moving either of the two endogenous charges, R303 and R352, to positions further along TM5 and TM6, respectively, also results in this O1O2 phenotype, we conclude that the position of the charged residue in the internal vestibule affects hydrolysis-dependent conductance changes. Furthermore, our data show that the buffer and CFTR blocker morpholino propane sulfonic acid (MOPS−) occludes the O1 state more than it does the O2 state when the net charge of the internal vestibule is unchanged or increased. In contrast, when the net charge in the internal vestibule is decreased, the differential sensitivity to MOPS− block is diminished. We propose a three-state blocking mechanism to explain the charge-dependent sensitivity of prehydrolytic and post-hydrolytic open states to MOPS− block. We further posit that the internal vestibule expands during the O1 to O2 transition so that mutation-induced electrostatic perturbations within the pore are amplified by the smaller internal vestibule of the O1 state and thus result in the O1O2 phenotype and the charge-dependent sensitivity of the two open states to MOPS− block. Our study not only relates the O1O2 phenotype to the charge distribution in CFTR’s internal vestibule but also provides a toolbox for mechanistic studies of CFTR gating by ATP hydrolysis.
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Affiliation(s)
- Jingyao Zhang
- Department of Biological Engineering, University of Missouri, Columbia, MO 65211.,Dalton Cardiovascular Research Center, University of Missouri, Columbia, MO 65211
| | - Tzyh-Chang Hwang
- Department of Biological Engineering, University of Missouri, Columbia, MO 65211 .,Dalton Cardiovascular Research Center, University of Missouri, Columbia, MO 65211.,Department of Medical Pharmacology and Physiology, University of Missouri, Columbia, MO 65211
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39
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Timachi MH, Hutter CA, Hohl M, Assafa T, Böhm S, Mittal A, Seeger MA, Bordignon E. Exploring conformational equilibria of a heterodimeric ABC transporter. eLife 2017; 6. [PMID: 28051765 PMCID: PMC5216877 DOI: 10.7554/elife.20236] [Citation(s) in RCA: 55] [Impact Index Per Article: 7.9] [Reference Citation Analysis] [Abstract] [Key Words] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/02/2016] [Accepted: 12/01/2016] [Indexed: 01/04/2023] Open
Abstract
ABC exporters pump substrates across the membrane by coupling ATP-driven movements of nucleotide binding domains (NBDs) to the transmembrane domains (TMDs), which switch between inward- and outward-facing (IF, OF) orientations. DEER measurements on the heterodimeric ABC exporter TM287/288 from Thermotoga maritima, which contains a non-canonical ATP binding site, revealed that in the presence of nucleotides the transporter exists in an IF/OF equilibrium. While ATP binding was sufficient to partially populate the OF state, nucleotide trapping in the pre- or post-hydrolytic state was required for a pronounced conformational shift. At physiologically high temperatures and in the absence of nucleotides, the NBDs disengage asymmetrically while the conformation of the TMDs remains unchanged. Nucleotide binding at the degenerate ATP site prevents complete NBD separation, a molecular feature differentiating heterodimeric from homodimeric ABC exporters. Our data suggest hydrolysis-independent closure of the NBD dimer, which is further stabilized as the consensus site nucleotide is committed to hydrolysis. DOI:http://dx.doi.org/10.7554/eLife.20236.001
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Affiliation(s)
- M Hadi Timachi
- Faculty of Chemistry and Biochemistry, Ruhr-Universität Bochum, Bochum, Germany.,Department of Physics, Freie Universität Berlin, Berlin, Germany
| | - Cedric Aj Hutter
- Institute of Medical Microbiology, University of Zurich, Zurich, Switzerland
| | - Michael Hohl
- Institute of Medical Microbiology, University of Zurich, Zurich, Switzerland
| | - Tufa Assafa
- Faculty of Chemistry and Biochemistry, Ruhr-Universität Bochum, Bochum, Germany.,Department of Physics, Freie Universität Berlin, Berlin, Germany
| | - Simon Böhm
- Laboratory of Physical Chemistry, ETH Zurich, Zurich, Switzerland
| | - Anshumali Mittal
- Department of Biochemistry, University of Zurich, Zurich, Switzerland
| | - Markus A Seeger
- Institute of Medical Microbiology, University of Zurich, Zurich, Switzerland
| | - Enrica Bordignon
- Faculty of Chemistry and Biochemistry, Ruhr-Universität Bochum, Bochum, Germany.,Department of Physics, Freie Universität Berlin, Berlin, Germany
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40
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Chen JH, Xu W, Sheppard DN. Altering intracellular pH reveals the kinetic basis of intraburst gating in the CFTR Cl - channel. J Physiol 2017; 595:1059-1076. [PMID: 27779763 DOI: 10.1113/jp273205] [Citation(s) in RCA: 9] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Key Words] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/28/2016] [Accepted: 10/21/2016] [Indexed: 01/14/2023] Open
Abstract
KEY POINTS The cystic fibrosis transmembrane conductance regulator (CFTR), which is defective in the genetic disease cystic fibrosis (CF), forms a gated pathway for chloride movement regulated by intracellular ATP. To understand better CFTR function, we investigated the regulation of channel openings by intracellular pH. We found that short-lived channel closures during channel openings represent subtle changes in the structure of CFTR that are regulated by intracellular pH, in part, at ATP-binding site 1 formed by the nucleotide-binding domains. Our results provide a framework for future studies to understand better the regulation of channel openings, the dysfunction of CFTR in CF and the action of drugs that repair CFTR gating defects. ABSTRACT Cystic fibrosis transmembrane conductance regulator (CFTR) is an ATP-gated Cl- channel defective in the genetic disease cystic fibrosis (CF). The gating behaviour of CFTR is characterized by bursts of channel openings interrupted by brief, flickery closures, separated by long closures between bursts. Entry to and exit from an open burst is controlled by the interaction of ATP with two ATP-binding sites, sites 1 and 2, in CFTR. To understand better the kinetic basis of CFTR intraburst gating, we investigated the single-channel activity of human CFTR at different intracellular pH (pHi ) values. When compared with the control (pHi 7.3), acidifying pHi to 6.3 or alkalinizing pHi to 8.3 and 8.8 caused small reductions in the open-time constant (τo ) of wild-type CFTR. By contrast, the fast closed-time constant (τcf ), which describes the short-lived closures that interrupt open bursts, was greatly increased at pHi 5.8 and 6.3. To analyse intraburst kinetics, we used linear three-state gating schemes. All data were satisfactorily modelled by the C1 ↔ O ↔ C2 kinetic scheme. Changing the intracellular ATP concentration was without effect on τo , τcf and their responses to pHi changes. However, mutations that disrupt the interaction of ATP with ATP-binding site 1, including K464A, D572N and the CF-associated mutation G1349D all abolished the prolongation of τcf at pHi 6.3. Taken together, our data suggest that the regulation of CFTR intraburst gating is distinct from the ATP-dependent mechanism that controls channel opening and closing. However, our data also suggest that ATP-binding site 1 modulates intraburst gating.
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Affiliation(s)
- Jeng-Haur Chen
- School of Biomedical Sciences, University of Hong Kong, Hong Kong.,The University of Hong Kong Shenzhen Institute of Research and Innovation, Shenzhen, China.,School of Physiology, Pharmacology and Neuroscience, University of Bristol, Bristol, UK
| | - Weiyi Xu
- School of Biomedical Sciences, University of Hong Kong, Hong Kong.,The University of Hong Kong Shenzhen Institute of Research and Innovation, Shenzhen, China
| | - David N Sheppard
- School of Physiology, Pharmacology and Neuroscience, University of Bristol, Bristol, UK
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41
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Linsdell P. Architecture and functional properties of the CFTR channel pore. Cell Mol Life Sci 2017; 74:67-83. [PMID: 27699452 PMCID: PMC11107662 DOI: 10.1007/s00018-016-2389-5] [Citation(s) in RCA: 37] [Impact Index Per Article: 5.3] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/27/2016] [Accepted: 09/28/2016] [Indexed: 12/12/2022]
Abstract
The main function of the cystic fibrosis transmembrane conductance regulator (CFTR) is as an ion channel for the movement of small anions across epithelial cell membranes. As an ion channel, CFTR must form a continuous pathway across the cell membrane-referred to as the channel pore-for the rapid electrodiffusional movement of ions. This review summarizes our current understanding of the architecture of the channel pore, as defined by electrophysiological analysis and molecular modeling studies. This includes consideration of the characteristic functional properties of the pore, definition of the overall shape of the entire extent of the pore, and discussion of how the molecular structure of distinct regions of the pore might control different facets of pore function. Comparisons are drawn with closely related proteins that are not ion channels, and also with structurally unrelated proteins with anion channel function. A simple model of pore function is also described.
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Affiliation(s)
- Paul Linsdell
- Department of Physiology and Biophysics, Dalhousie University, PO Box 15000, Halifax, NS, B3H 4R2, Canada.
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42
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Chin S, Yang D, Miles AJ, Eckford PDW, Molinski S, Wallace BA, Bear CE. Attenuation of Phosphorylation-dependent Activation of Cystic Fibrosis Transmembrane Conductance Regulator (CFTR) by Disease-causing Mutations at the Transmission Interface. J Biol Chem 2016; 292:1988-1999. [PMID: 28003367 PMCID: PMC5290968 DOI: 10.1074/jbc.m116.762633] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/10/2016] [Revised: 12/07/2016] [Indexed: 12/21/2022] Open
Abstract
Cystic fibrosis transmembrane conductance regulator (CFTR) is a multidomain membrane protein that functions as a phosphorylation-regulated anion channel. The interface between its two cytosolic nucleotide binding domains and coupling helices conferred by intracellular loops extending from the channel pore domains has been referred to as a transmission interface and is thought to be critical for the regulated channel activity of CFTR. Phosphorylation of the regulatory domain of CFTR by protein kinase A (PKA) is required for its channel activity. However, it was unclear if phosphorylation modifies the transmission interface. Here, we studied purified full-length CFTR protein using spectroscopic techniques to determine the consequences of PKA-mediated phosphorylation. Synchrotron radiation circular dichroism spectroscopy confirmed that purified full-length wild-type CFTR is folded and structurally responsive to phosphorylation. Intrinsic tryptophan fluorescence studies of CFTR showed that phosphorylation reduced iodide-mediated quenching, consistent with an effect of phosphorylation in burying tryptophans at the transmission interface. Importantly, the rate of phosphorylation-dependent channel activation was compromised by the introduction of disease-causing mutations in either of the two coupling helices predicted to interact with nucleotide binding domain 1 at the interface. Together, these results suggest that phosphorylation modifies the interface between the catalytic and pore domains of CFTR and that this modification facilitates CFTR channel activation.
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Affiliation(s)
- Stephanie Chin
- From the Programme of Molecular Structure and Function, Hospital for Sick Children, Toronto M5G 0A4, Canada; the Department of Biochemistry, University of Toronto, Toronto, Canada
| | - Donghe Yang
- From the Programme of Molecular Structure and Function, Hospital for Sick Children, Toronto M5G 0A4, Canada
| | - Andrew J Miles
- the Institute of Structural and Molecular Biology, Birkbeck College, University of London, London WC1E 7HX, United Kingdom
| | - Paul D W Eckford
- From the Programme of Molecular Structure and Function, Hospital for Sick Children, Toronto M5G 0A4, Canada
| | - Steven Molinski
- From the Programme of Molecular Structure and Function, Hospital for Sick Children, Toronto M5G 0A4, Canada; the Department of Biochemistry, University of Toronto, Toronto, Canada
| | - B A Wallace
- the Institute of Structural and Molecular Biology, Birkbeck College, University of London, London WC1E 7HX, United Kingdom
| | - Christine E Bear
- From the Programme of Molecular Structure and Function, Hospital for Sick Children, Toronto M5G 0A4, Canada; the Department of Biochemistry, University of Toronto, Toronto, Canada; the Department of Physiology, University of Toronto, Toronto, Canada.
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43
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Gupta S, Chakraborty S, Vij R, Auerbach A. A mechanism for acetylcholine receptor gating based on structure, coupling, phi, and flip. J Gen Physiol 2016; 149:85-103. [PMID: 27932572 PMCID: PMC5217088 DOI: 10.1085/jgp.201611673] [Citation(s) in RCA: 36] [Impact Index Per Article: 4.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/21/2016] [Revised: 09/20/2016] [Accepted: 11/10/2016] [Indexed: 01/29/2023] Open
Abstract
Gupta et al. use single-channel electrophysiology to investigate the gating mechanism of acetylcholine receptor ion channels. They propose that channel opening starts at the M2–M3 linker and ligand-binding sites and proceeds through four brief intermediate conformations before ending with the collapse of a gate bubble. Nicotinic acetylcholine receptors are allosteric proteins that generate membrane currents by isomerizing (“gating”) between resting and active conformations under the influence of neurotransmitters. Here, to explore the mechanisms that link the transmitter-binding sites (TBSs) with the distant gate, we use mutant cycle analyses to measure coupling between residue pairs, phi value analyses to sequence domain rearrangements, and current simulations to reproduce a microsecond shut component (“flip”) apparent in single-channel recordings. Significant interactions between amino acids separated by >15 Å are rare; an exception is between the αM2–M3 linkers and the TBSs that are ∼30 Å apart. Linker residues also make significant, local interactions within and between subunits. Phi value analyses indicate that without agonists, the linker is the first region in the protein to reach the gating transition state. Together, the phi pattern and flip component suggest that a complete, resting↔active allosteric transition involves passage through four brief intermediate states, with brief shut events arising from sojourns in all or a subset. We derive energy landscapes for gating with and without agonists, and propose a structure-based model in which resting→active starts with spontaneous rearrangements of the M2–M3 linkers and TBSs. These conformational changes stabilize a twisted extracellular domain to promote transmembrane helix tilting, gate dilation, and the formation of a “bubble” that collapses to initiate ion conduction. The energy landscapes suggest that twisting is the most energetically unfavorable step in the resting→active conformational change and that the rate-limiting step in the reverse process is bubble formation.
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Affiliation(s)
- Shaweta Gupta
- Department of Physiology and Biophysics, State University of New York at Buffalo, Buffalo, NY 14214
| | - Srirupa Chakraborty
- Department of Physiology and Biophysics, State University of New York at Buffalo, Buffalo, NY 14214
| | - Ridhima Vij
- Department of Physiology and Biophysics, State University of New York at Buffalo, Buffalo, NY 14214
| | - Anthony Auerbach
- Department of Physiology and Biophysics, State University of New York at Buffalo, Buffalo, NY 14214
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44
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Puga Molina LC, Pinto NA, Torres Rodríguez P, Romarowski A, Vicens Sanchez A, Visconti PE, Darszon A, Treviño CL, Buffone MG. Essential Role of CFTR in PKA-Dependent Phosphorylation, Alkalinization, and Hyperpolarization During Human Sperm Capacitation. J Cell Physiol 2016; 232:1404-1414. [PMID: 27714810 DOI: 10.1002/jcp.25634] [Citation(s) in RCA: 48] [Impact Index Per Article: 6.0] [Reference Citation Analysis] [Abstract] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/14/2016] [Accepted: 10/05/2016] [Indexed: 12/17/2022]
Abstract
Mammalian sperm require to spend a limited period of time in the female reproductive tract to become competent to fertilize in a process called capacitation. It is well established that HCO3- is essential for capacitation because it activates the atypical soluble adenylate cyclase ADCY10 leading to cAMP production, and promotes alkalinization of cytoplasm, and membrane hyperpolarization. However, how HCO3- is transported into the sperm is not well understood. There is evidence that CFTR activity is involved in the human sperm capacitation but how this channel is integrated in the complex signaling cascades associated with this process remains largely unknown. In the present work, we have analyzed the extent to which CFTR regulates different events in human sperm capacitation. We observed that inhibition of CFTR affects HCO3- -entrance dependent events resulting in lower PKA activity. CFTR inhibition also affected cAMP/PKA-downstream events such as the increase in tyrosine phosphorylation, hyperactivated motility, and acrosome reaction. In addition, we demonstrated for the first time, that CFTR and PKA activity are essential for the regulation of intracellular pH, and membrane potential in human sperm. Addition of permeable cAMP partially recovered all the PKA-dependent events altered in the presence of inh-172 which is consistent with a role of CFTR upstream of PKA activation. J. Cell. Physiol. 232: 1404-1414, 2017. © 2016 Wiley Periodicals, Inc.
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Affiliation(s)
- Lis C Puga Molina
- Instituto de Biología y Medicina Experimental (IBYME), Consejo Nacional de Investigaciones Científicas y Tecnológicas (CONICET), Buenos Aires, Argentina
| | - Nicolás A Pinto
- Instituto de Biología y Medicina Experimental (IBYME), Consejo Nacional de Investigaciones Científicas y Tecnológicas (CONICET), Buenos Aires, Argentina
| | - Paulina Torres Rodríguez
- Departamento de Genética del Desarrollo y Fisiología Molecular, Instituto de Biotecnología, Universidad Nacional Autónoma de México (UNAM), Cuernavaca, Morelos, México
| | - Ana Romarowski
- Instituto de Biología y Medicina Experimental (IBYME), Consejo Nacional de Investigaciones Científicas y Tecnológicas (CONICET), Buenos Aires, Argentina
| | - Alberto Vicens Sanchez
- Departamento de Genética del Desarrollo y Fisiología Molecular, Instituto de Biotecnología, Universidad Nacional Autónoma de México (UNAM), Cuernavaca, Morelos, México
| | - Pablo E Visconti
- Department of Veterinary and Animal Science, Paige Labs, University of Massachusetts, Amherst, Massachusetts
| | - Alberto Darszon
- Departamento de Genética del Desarrollo y Fisiología Molecular, Instituto de Biotecnología, Universidad Nacional Autónoma de México (UNAM), Cuernavaca, Morelos, México
| | - Claudia L Treviño
- Departamento de Genética del Desarrollo y Fisiología Molecular, Instituto de Biotecnología, Universidad Nacional Autónoma de México (UNAM), Cuernavaca, Morelos, México
| | - Mariano G Buffone
- Instituto de Biología y Medicina Experimental (IBYME), Consejo Nacional de Investigaciones Científicas y Tecnológicas (CONICET), Buenos Aires, Argentina
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45
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Janssens A, Gees M, Toth BI, Ghosh D, Mulier M, Vennekens R, Vriens J, Talavera K, Voets T. Definition of two agonist types at the mammalian cold-activated channel TRPM8. eLife 2016; 5. [PMID: 27449282 PMCID: PMC4985286 DOI: 10.7554/elife.17240] [Citation(s) in RCA: 16] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/25/2016] [Accepted: 07/22/2016] [Indexed: 11/13/2022] Open
Abstract
Various TRP channels act as polymodal sensors of thermal and chemical stimuli, but the mechanisms whereby chemical ligands impact on TRP channel gating are poorly understood. Here we show that AITC (allyl isothiocyanate; mustard oil) and menthol represent two distinct types of ligands at the mammalian cold sensor TRPM8. Kinetic analysis of channel gating revealed that AITC acts by destabilizing the closed channel, whereas menthol stabilizes the open channel, relative to the transition state. Based on these differences, we classify agonists as either type I (menthol-like) or type II (AITC-like), and provide a kinetic model that faithfully reproduces their differential effects. We further demonstrate that type I and type II agonists have a distinct impact on TRPM8 currents and TRPM8-mediated calcium signals in excitable cells. These findings provide a theoretical framework for understanding the differential actions of TRP channel ligands, with important ramifications for TRP channel structure-function analysis and pharmacology. DOI:http://dx.doi.org/10.7554/eLife.17240.001 Sensory neurons in our skin detect cues from the environment – such as temperature and touch – and pass the information onto other cells in the nervous system. A protein called TRPM8 in sensory neurons is responsible for our ability to detect cool temperatures. TRPM8 sits in the membrane that surrounds the cell and forms a channel that can allow sodium and calcium ions to enter the cell. Cold temperatures activate TRPM8, which opens the channel and triggers electrical activity in the sensory neurons. Chemicals that cause a cold sensation – such as menthol, the refreshing substance found in mint plants – can also open the TRPM8 channel. Janssens, Gees, Toth et al. investigated how menthol, and another natural compound called mustard oil, influence the opening of TRPM8. The experiments show that menthol and mustard oil both stimulate sensory neurons by opening the TRPM8 ion channel, but using different mechanisms. Mustard oil forces the channel to open faster than it normally would, whereas menthol prevents the channel from closing. Further experiments show that these mechanisms explain why some compounds stimulate sensory neurons more strongly than others. The findings of Janssens, Gees, Toth et al. will help to understand how chemicals act on this class of ion channels, and how this affects the roles of the ion channels in cells. Altering the activity of TRPM8 and related ion channels may help to reduce pain in humans so a future challenge is to use these new insights to develop drugs that target these channels more efficiently. DOI:http://dx.doi.org/10.7554/eLife.17240.002
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Affiliation(s)
- Annelies Janssens
- Laboratory of Ion Channel Research and TRP channel Research Platform Leuven, Department of Cellular and Molecular Medicine, University of Leuven, Leuven, Belgium
| | - Maarten Gees
- Laboratory of Ion Channel Research and TRP channel Research Platform Leuven, Department of Cellular and Molecular Medicine, University of Leuven, Leuven, Belgium
| | - Balazs Istvan Toth
- Laboratory of Ion Channel Research and TRP channel Research Platform Leuven, Department of Cellular and Molecular Medicine, University of Leuven, Leuven, Belgium
| | - Debapriya Ghosh
- Laboratory of Ion Channel Research and TRP channel Research Platform Leuven, Department of Cellular and Molecular Medicine, University of Leuven, Leuven, Belgium
| | - Marie Mulier
- Laboratory of Ion Channel Research and TRP channel Research Platform Leuven, Department of Cellular and Molecular Medicine, University of Leuven, Leuven, Belgium
| | - Rudi Vennekens
- Laboratory of Ion Channel Research and TRP channel Research Platform Leuven, Department of Cellular and Molecular Medicine, University of Leuven, Leuven, Belgium
| | - Joris Vriens
- Laboratory of Ion Channel Research and TRP channel Research Platform Leuven, Department of Cellular and Molecular Medicine, University of Leuven, Leuven, Belgium.,Laboratory of Experimental Gynaecology, University of Leuven, Leuven, Belgium
| | - Karel Talavera
- Laboratory of Ion Channel Research and TRP channel Research Platform Leuven, Department of Cellular and Molecular Medicine, University of Leuven, Leuven, Belgium
| | - Thomas Voets
- Laboratory of Ion Channel Research and TRP channel Research Platform Leuven, Department of Cellular and Molecular Medicine, University of Leuven, Leuven, Belgium
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Mihályi C, Töröcsik B, Csanády L. Obligate coupling of CFTR pore opening to tight nucleotide-binding domain dimerization. eLife 2016; 5. [PMID: 27328319 PMCID: PMC4956468 DOI: 10.7554/elife.18164] [Citation(s) in RCA: 18] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [Key Words] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/24/2016] [Accepted: 06/20/2016] [Indexed: 12/20/2022] Open
Abstract
In CFTR, the chloride channel mutated in cystic fibrosis (CF) patients, ATP-binding-induced dimerization of two cytosolic nucleotide binding domains (NBDs) opens the pore, and dimer disruption following ATP hydrolysis closes it. Spontaneous openings without ATP are rare in wild-type CFTR, but in certain CF mutants constitute the only gating mechanism, stimulated by ivacaftor, a clinically approved CFTR potentiator. The molecular motions underlying spontaneous gating are unclear. Here we correlate energetic coupling between residues across the dimer interface with spontaneous pore opening/closure in single CFTR channels. We show that spontaneous openings are also strictly coupled to NBD dimerization, which may therefore occur even without ATP. Coordinated NBD/pore movements are therefore intrinsic to CFTR: ATP alters the stability, but not the fundamental structural architecture, of open- and closed-pore conformations. This explains correlated effects of phosphorylation, mutations, and drugs on ATP-driven and spontaneous activity, providing insights for understanding CF mutation and drug mechanisms. DOI:http://dx.doi.org/10.7554/eLife.18164.001 A protein pore called the CFTR channel allows chloride ions to move through the membrane of the cells that line the airways and some other parts of the human body. Mutations in the genes that encode CFTR may reduce the number of pores at the cell surface or stop them from working properly. When this happens, these cells cannot transport enough chloride, which causes the disease cystic fibrosis. CFTR contains two regions that lie inside the cell known as nucleotide binding domains (NBDs). These domains bind to the chemical energy molecule ATP, and when ATP does bind, two NBDs associate to form a dimer and the pore in CFTR opens. The CFTR channel can occasionally open in a spontaneous way that does not require ATP. However, it was not clear whether NBDs also formed dimers when CFTR opened in this way. This is because spontaneous opening could reflect NBDs occasionally forming a dimer without ATP binding or it could occur when the pore occasionally opens without the NBDs forming a dimer. To explore whether opening of the pore always requires NBD dimerization, Mihályi et al. studied the behaviour of single human CFTR channels produced in frog eggs. Normal channels and mutant ones (which show differences in spontaneous opening) were used, and the change in the way NBDs interacted when the channels spontaneously opened or closed was investigated. Mihályi et al. found that the NBD dimer forms when the pore spontaneously opens, demonstrating that this step happens both with and without ATP. The result demonstrates that NBD dimer formation and pore movement are strictly coupled and that this is an inbuilt property of the CFTR protein. When ATP binds, this only changes how stable the open-pore and closed-pore structures of CFTR are but does not alter the fundamental architecture of the channel. These new findings will be of interest to researchers studying a large group of transport proteins related to CFTR called ABC proteins. Furthermore, a drug called ivacaftor stimulates spontaneous opening of CFTR, and has recently been approved for clinical use to treat people with mutations in CFTR. As such, the new findings will be also useful to help researchers understand how ivacaftor stimulates the CFTR pore to open. DOI:http://dx.doi.org/10.7554/eLife.18164.002
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Affiliation(s)
- Csaba Mihályi
- Department of Medical Biochemistry, Semmelweis University, Budapest, Hungary.,MTA-SE Ion Channel Research Group, Semmelweis University, Budapest, Hungary
| | - Beáta Töröcsik
- Department of Medical Biochemistry, Semmelweis University, Budapest, Hungary.,MTA-SE Ion Channel Research Group, Semmelweis University, Budapest, Hungary
| | - László Csanády
- Department of Medical Biochemistry, Semmelweis University, Budapest, Hungary.,MTA-SE Ion Channel Research Group, Semmelweis University, Budapest, Hungary
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Linsdell P. Anion conductance selectivity mechanism of the CFTR chloride channel. BIOCHIMICA ET BIOPHYSICA ACTA-BIOMEMBRANES 2016; 1858:740-7. [DOI: 10.1016/j.bbamem.2016.01.009] [Citation(s) in RCA: 16] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Track Full Text] [Subscribe] [Scholar Register] [Received: 11/04/2015] [Revised: 01/11/2016] [Accepted: 01/13/2016] [Indexed: 02/08/2023]
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Role of Interaction and Nucleoside Diphosphate Kinase B in Regulation of the Cystic Fibrosis Transmembrane Conductance Regulator Function by cAMP-Dependent Protein Kinase A. PLoS One 2016; 11:e0149097. [PMID: 26950439 PMCID: PMC4780765 DOI: 10.1371/journal.pone.0149097] [Citation(s) in RCA: 10] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/26/2015] [Accepted: 01/27/2016] [Indexed: 02/05/2023] Open
Abstract
Cystic fibrosis results from mutations in the cystic fibrosis transmembrane conductance regulator (CFTR), a cAMP-dependent protein kinase A (PKA) and ATP-regulated chloride channel. Here, we demonstrate that nucleoside diphosphate kinase B (NDPK-B, NM23-H2) forms a functional complex with CFTR. In airway epithelia forskolin/IBMX significantly increases NDPK-B co-localisation with CFTR whereas PKA inhibitors attenuate complex formation. Furthermore, an NDPK-B derived peptide (but not its NDPK-A equivalent) disrupts the NDPK-B/CFTR complex in vitro (19-mers comprising amino acids 36–54 from NDPK-B or NDPK-A). Overlay (Far-Western) and Surface Plasmon Resonance (SPR) analysis both demonstrate that NDPK-B binds CFTR within its first nucleotide binding domain (NBD1, CFTR amino acids 351–727). Analysis of chloride currents reflective of CFTR or outwardly rectifying chloride channels (ORCC, DIDS-sensitive) showed that the 19-mer NDPK-B peptide (but not its NDPK-A equivalent) reduced both chloride conductances. Additionally, the NDPK-B (but not NDPK-A) peptide also attenuated acetylcholine-induced intestinal short circuit currents. In silico analysis of the NBD1/NDPK-B complex reveals an extended interaction surface between the two proteins. This binding zone is also target of the 19-mer NDPK-B peptide, thus confirming its capability to disrupt NDPK-B/CFTR complex. We propose that NDPK-B forms part of the complex that controls chloride currents in epithelia.
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Structural Changes Fundamental to Gating of the Cystic Fibrosis Transmembrane Conductance Regulator Anion Channel Pore. ADVANCES IN EXPERIMENTAL MEDICINE AND BIOLOGY 2016; 925:13-32. [PMID: 27311317 DOI: 10.1007/5584_2016_33] [Citation(s) in RCA: 8] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 12/18/2022]
Abstract
Cystic fibrosis is caused by mutations in the cystic fibrosis transmembrane conductance regulator (CFTR), an epithelial cell anion channel. Potentiator drugs used in the treatment of cystic fibrosis act on the channel to increase overall channel function, by increasing the stability of its open state and/or decreasing the stability of its closed state. The structure of the channel in either the open state or the closed state is not currently known. However, changes in the conformation of the protein as it transitions between these two states have been studied using functional investigation and molecular modeling techniques. This review summarizes our current understanding of the architecture of the transmembrane channel pore that controls the movement of chloride and other small anions, both in the open state and in the closed state. Evidence for different kinds of changes in the conformation of the pore as it transitions between open and closed states is described, as well as the mechanisms by which these conformational changes might be controlled to regulate normal channel gating. The ways that key conformational changes might be targeted by small compounds to influence overall CFTR activity are also discussed. Understanding the changes in pore structure that might be manipulated by such small compounds is key to the development of novel therapeutic strategies for the treatment of cystic fibrosis.
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