1
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Levring J, Terry DS, Kilic Z, Fitzgerald G, Blanchard SC, Chen J. CFTR function, pathology and pharmacology at single-molecule resolution. Nature 2023; 616:606-614. [PMID: 36949202 PMCID: PMC10115640 DOI: 10.1038/s41586-023-05854-7] [Citation(s) in RCA: 18] [Impact Index Per Article: 18.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/29/2022] [Accepted: 02/16/2023] [Indexed: 03/24/2023]
Abstract
The cystic fibrosis transmembrane conductance regulator (CFTR) is an anion channel that regulates salt and fluid homeostasis across epithelial membranes1. Alterations in CFTR cause cystic fibrosis, a fatal disease without a cure2,3. Electrophysiological properties of CFTR have been analysed for decades4-6. The structure of CFTR, determined in two globally distinct conformations, underscores its evolutionary relationship with other ATP-binding cassette transporters. However, direct correlations between the essential functions of CFTR and extant structures are lacking at present. Here we combine ensemble functional measurements, single-molecule fluorescence resonance energy transfer, electrophysiology and kinetic simulations to show that the two nucleotide-binding domains (NBDs) of human CFTR dimerize before channel opening. CFTR exhibits an allosteric gating mechanism in which conformational changes within the NBD-dimerized channel, governed by ATP hydrolysis, regulate chloride conductance. The potentiators ivacaftor and GLPG1837 enhance channel activity by increasing pore opening while NBDs are dimerized. Disease-causing substitutions proximal (G551D) or distal (L927P) to the ATPase site both reduce the efficiency of NBD dimerization. These findings collectively enable the framing of a gating mechanism that informs on the search for more efficacious clinical therapies.
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Affiliation(s)
- Jesper Levring
- Laboratory of Membrane Biology and Biophysics, The Rockefeller University, New York, NY, USA
| | - Daniel S Terry
- Department of Structural Biology, St. Jude Children's Research Hospital, Memphis, TN, USA
| | - Zeliha Kilic
- Department of Structural Biology, St. Jude Children's Research Hospital, Memphis, TN, USA
| | - Gabriel Fitzgerald
- Department of Physiology and Biophysics, Weill Cornell Medicine, New York, NY, USA
| | - Scott C Blanchard
- Department of Structural Biology, St. Jude Children's Research Hospital, Memphis, TN, USA.
| | - Jue Chen
- Laboratory of Membrane Biology and Biophysics, The Rockefeller University, New York, NY, USA.
- Howard Hughes Medical Institute, The Rockefeller University, New York, NY, USA.
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2
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Xiong C, Jia LN, Xiong WX, Wu XT, Xiong LL, Wang TH, Zhou D, Hong Z, Liu Z, Tang L. Structural insights into substrate recognition and translocation of human peroxisomal ABC transporter ALDP. Signal Transduct Target Ther 2023; 8:74. [PMID: 36810450 PMCID: PMC9944889 DOI: 10.1038/s41392-022-01280-9] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/15/2022] [Revised: 06/22/2022] [Accepted: 11/30/2022] [Indexed: 02/24/2023] Open
Abstract
Dysfunctions of ATP-binding cassette, subfamily D, member 1 (ABCD1) cause X-linked adrenoleukodystrophy, a rare neurodegenerative disease that affects all human tissues. Residing in the peroxisome membrane, ABCD1 plays a role in the translocation of very long-chain fatty acids for their β-oxidation. Here, the six cryo-electron microscopy structures of ABCD1 in four distinct conformational states were presented. In the transporter dimer, two transmembrane domains form the substrate translocation pathway, and two nucleotide-binding domains form the ATP-binding site that binds and hydrolyzes ATP. The ABCD1 structures provide a starting point for elucidating the substrate recognition and translocation mechanism of ABCD1. Each of the four inward-facing structures of ABCD1 has a vestibule that opens to the cytosol with variable sizes. Hexacosanoic acid (C26:0)-CoA substrate binds to the transmembrane domains (TMDs) and stimulates the ATPase activity of the nucleotide-binding domains (NBDs). W339 from the transmembrane helix 5 (TM5) is essential for binding substrate and stimulating ATP hydrolysis by substrate. ABCD1 has a unique C-terminal coiled-coil domain that negatively modulates the ATPase activity of the NBDs. Furthermore, the structure of ABCD1 in the outward-facing state indicates that ATP molecules pull the two NBDs together and open the TMDs to the peroxisomal lumen for substrate release. The five structures provide a view of the substrate transport cycle and mechanistic implication for disease-causing mutations.
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Affiliation(s)
- Chao Xiong
- Department of Neurology, State Key Lab of Biotherapy and Cancer Center, West China Hospital, Sichuan University and Collaborative Innovation Center for Biotherapy, 610041, Chengdu, Sichuan, China.,Institute of Brain Science and Brain-inspired Technology of West China Hospital, Sichuan University, Chengdu, China
| | - Li-Na Jia
- Department of Neurology, State Key Lab of Biotherapy and Cancer Center, West China Hospital, Sichuan University and Collaborative Innovation Center for Biotherapy, 610041, Chengdu, Sichuan, China.,Institute of Brain Science and Brain-inspired Technology of West China Hospital, Sichuan University, Chengdu, China
| | - Wei-Xi Xiong
- Department of Neurology, State Key Lab of Biotherapy and Cancer Center, West China Hospital, Sichuan University and Collaborative Innovation Center for Biotherapy, 610041, Chengdu, Sichuan, China.,Institute of Brain Science and Brain-inspired Technology of West China Hospital, Sichuan University, Chengdu, China
| | - Xin-Tong Wu
- Department of Neurology, State Key Lab of Biotherapy and Cancer Center, West China Hospital, Sichuan University and Collaborative Innovation Center for Biotherapy, 610041, Chengdu, Sichuan, China.,Institute of Brain Science and Brain-inspired Technology of West China Hospital, Sichuan University, Chengdu, China
| | - Liu-Lin Xiong
- Institute of Neurological Disease, State Key Lab of Biotherapy, West China Hospital, Sichuan University, 610041, Chengdu, Sichuan, China
| | - Ting-Hua Wang
- Institute of Neurological Disease, State Key Lab of Biotherapy, West China Hospital, Sichuan University, 610041, Chengdu, Sichuan, China
| | - Dong Zhou
- Department of Neurology, State Key Lab of Biotherapy and Cancer Center, West China Hospital, Sichuan University and Collaborative Innovation Center for Biotherapy, 610041, Chengdu, Sichuan, China.,Institute of Brain Science and Brain-inspired Technology of West China Hospital, Sichuan University, Chengdu, China
| | - Zhen Hong
- Department of Neurology, State Key Lab of Biotherapy and Cancer Center, West China Hospital, Sichuan University and Collaborative Innovation Center for Biotherapy, 610041, Chengdu, Sichuan, China. .,Institute of Brain Science and Brain-inspired Technology of West China Hospital, Sichuan University, Chengdu, China.
| | - Zheng Liu
- School of Life and Health, Kobilka Institute of Innovative Drug Discovery, the Chinese University of Hong Kong (Shenzhen), Shenzhen, China.
| | - Lin Tang
- Department of Neurology, State Key Lab of Biotherapy and Cancer Center, West China Hospital, Sichuan University and Collaborative Innovation Center for Biotherapy, 610041, Chengdu, Sichuan, China. .,Institute of Brain Science and Brain-inspired Technology of West China Hospital, Sichuan University, Chengdu, China.
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3
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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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4
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Yeh HI, Yu YC, Kuo PL, Tsai CK, Huang HT, Hwang TC. Functional stability of CFTR depends on tight binding of ATP at its degenerate ATP-binding site. J Physiol 2021; 599:4625-4642. [PMID: 34411298 DOI: 10.1113/jp281933] [Citation(s) in RCA: 8] [Impact Index Per Article: 2.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/23/2021] [Accepted: 08/13/2021] [Indexed: 01/28/2023] Open
Abstract
Opening of the cystic fibrosis transmembrane conductance regulator (CFTR) channel is coupled to the motion of its two nucleotide-binding domains: they form a heterodimer sandwiching two functionally distinct ATP-binding sites (sites 1 and 2). While active ATP hydrolysis in site 2 triggers rapid channel closure, the functional role of stable ATP binding in the catalysis-incompetent (or degenerate) site 1, a feature conserved in many other ATP-binding cassette (ABC) transporter proteins, remains elusive. Here, we found that CFTR loses its prompt responsiveness to ATP after the channel is devoid of ATP for tens to hundreds of seconds. Mutants with weakened ATP binding in site 1 and the most prevalent disease-causing mutation, F508del, are more vulnerable to ATP depletion. In contrast, strengthening ligand binding in site 1 with N6 -(2-phenylethyl)-ATP, a high-affinity ATP analogue, or abolishing ATP hydrolysis in site 2 by the mutation D1370N, helps sustain a durable function of the otherwise unstable mutant channels. Thus, tight binding of ATP in the degenerate ATP-binding site is crucial to the functional stability of CFTR. Small molecules targeting site 1 may bear therapeutic potential to overcome the membrane instability of F508del-CFTR. KEY POINTS: During evolution, many ATP-binding cassette transporters - including the cystic fibrosis transmembrane conductance regulator (CFTR) chloride channel, whose dysfunction causes cystic fibrosis (CF) - lose the ability to hydrolyse ATP in one of the two ATP-binding sites. Here we show that tight ATP binding at this degenerate site in CFTR is central for maintaining the stable, robust function of normal CFTR. We also demonstrate that membrane instability of the most common CF-causing mutant, F508del-CFTR, can be rescued by strengthening ATP binding at CFTR's degenerate site. Our data thus explain an evolutionary puzzle and offer a potential therapeutic strategy for CF.
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Affiliation(s)
- Han-I Yeh
- Dalton Cardiovascular Research Center and Department of Medical Pharmacology and Physiology, University of Missouri-Columbia, Columbia, MO, 65211, USA.,Department of Pharmacology, School of Medicine, National Yang Ming Chiao Tung University, Taipei, Taiwan
| | - Ying-Chun Yu
- Dalton Cardiovascular Research Center and Department of Medical Pharmacology and Physiology, University of Missouri-Columbia, Columbia, MO, 65211, USA
| | - Pei-Lun Kuo
- School of Medicine, National Yang Ming Chiao Tung University, Taipei, Taiwan
| | - Chun-Kuang Tsai
- School of Medicine, National Yang Ming Chiao Tung University, Taipei, Taiwan
| | - Hsin-Tuan Huang
- School of Medicine, National Yang Ming Chiao Tung University, Taipei, Taiwan
| | - Tzyh-Chang Hwang
- Dalton Cardiovascular Research Center and Department of Medical Pharmacology and Physiology, University of Missouri-Columbia, Columbia, MO, 65211, USA.,Department of Pharmacology, School of Medicine, National Yang Ming Chiao Tung University, Taipei, Taiwan
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5
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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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6
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Linsdell P. Cystic fibrosis transmembrane conductance regulator (CFTR): Making an ion channel out of an active transporter structure. Channels (Austin) 2019; 12:284-290. [PMID: 30152709 PMCID: PMC6986785 DOI: 10.1080/19336950.2018.1502585] [Citation(s) in RCA: 18] [Impact Index Per Article: 3.6] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/07/2023] Open
Abstract
Cystic fibrosis is caused by mutations in the cystic fibrosis transmembrane conductance regulator (CFTR). CFTR is a member of the ATP-binding cassette (ABC) family of membrane transport proteins, most members of which function as ATP-dependent pumps. CFTR is unique among human ABC proteins in functioning not as a pump, but as an ion channel. Recent structural data has indicated that CFTR shares broadly similar overall architecture and ATP-dependent conformational changes as other ABC proteins. Functional investigations suggest that CFTR has a unique open portal connecting the cytoplasm to the transmembrane channel pore, that allows for a continuous pathway for Cl− ions to cross the membrane in one conformation. This lateral portal may be what allows CFTR to function as an ion channel rather than as a pump, suggesting a plausible mechanism by which channel function may have evolved in CFTR.
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Affiliation(s)
- Paul Linsdell
- a Department of Physiology & Biophysics , Dalhousie University , Halifax , Canada
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7
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Strickland KM, Stock G, Cui G, Hwang H, Infield DT, Schmidt-Krey I, McCarty NA, Gumbart JC. ATP-Dependent Signaling in Simulations of a Revised Model of Cystic Fibrosis Transmembrane Conductance Regulator (CFTR). J Phys Chem B 2019; 123:3177-3188. [PMID: 30921517 DOI: 10.1021/acs.jpcb.8b11970] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/17/2022]
Abstract
Cystic fibrosis transmembrane conductance regulator (CFTR) is a member of the ATP-binding cassette (ABC) transporter superfamily that has uniquely evolved to function as a chloride channel. It binds and hydrolyzes ATP at its nucleotide binding domains to form a pore providing a diffusive pathway within its transmembrane domains. CFTR is the only known protein from the ABC superfamily with channel activity, and its dysfunction causes the disease cystic fibrosis. While much is known about the functional aspects of CFTR, significant gaps remain, such as the structure-function relationship underlying signaling of ATP binding. In the present work, we refined an existing homology model using an intermediate-resolution (9 Å) published cryo-electron microscopy map. The newly derived models have been simulated in equilibrium molecular dynamics simulations for a total of 2.5 μs in multiple ATP-occupancy states. Putative conformational movements connecting ATP binding with pore formation are elucidated and quantified. Additionally, new interdomain interactions between E543, K968, and K1292 have been identified and confirmed experimentally; these interactions may be relevant for signaling ATP binding and hydrolysis to the transmembrane domains and induction of pore opening.
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Affiliation(s)
- Kerry M Strickland
- School of Chemistry and Biochemistry , Georgia Institute of Technology , Atlanta , Georgia 30332 , United States
| | - Gorman Stock
- School of Chemistry and Biochemistry , Georgia Institute of Technology , Atlanta , Georgia 30332 , United States
| | - Guiying Cui
- Division of Pulmonology, Allergy and Immunology, Cystic Fibrosis, and Sleep, Department of Pediatrics, Center for Cystic Fibrosis and Airways Disease Research, Emory+Children's Pediatric Research Center , Emory University School of Medicine and Children's Healthcare of Atlanta , Atlanta , Georgia 30322 , United States
| | - Hyea Hwang
- School of Materials Science and Engineering , Georgia Institute of Technology , Atlanta , Georgia 30332 , United States
| | - Daniel T Infield
- Division of Pulmonology, Allergy and Immunology, Cystic Fibrosis, and Sleep, Department of Pediatrics, Center for Cystic Fibrosis and Airways Disease Research, Emory+Children's Pediatric Research Center , Emory University School of Medicine and Children's Healthcare of Atlanta , Atlanta , Georgia 30322 , United States
| | - Ingeborg Schmidt-Krey
- School of Chemistry and Biochemistry , Georgia Institute of Technology , Atlanta , Georgia 30332 , United States.,School of Biological Sciences , Georgia Institute of Technology , Atlanta , Georgia 30332 , United States.,Parker H. Petit Institute for Bioengineering and Bioscience , Georgia Institute of Technology , Atlanta , Georgia 30332 , United States
| | - Nael A McCarty
- Division of Pulmonology, Allergy and Immunology, Cystic Fibrosis, and Sleep, Department of Pediatrics, Center for Cystic Fibrosis and Airways Disease Research, Emory+Children's Pediatric Research Center , Emory University School of Medicine and Children's Healthcare of Atlanta , Atlanta , Georgia 30322 , United States.,Parker H. Petit Institute for Bioengineering and Bioscience , Georgia Institute of Technology , Atlanta , Georgia 30332 , United States
| | - James C Gumbart
- School of Chemistry and Biochemistry , Georgia Institute of Technology , Atlanta , Georgia 30332 , United States.,School of Biological Sciences , Georgia Institute of Technology , Atlanta , Georgia 30332 , United States.,Parker H. Petit Institute for Bioengineering and Bioscience , Georgia Institute of Technology , Atlanta , Georgia 30332 , United States.,School of Physics , Georgia Institute of Technology , Atlanta , Georgia 30332 , United States
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8
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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: 144] [Impact Index Per Article: 28.8] [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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9
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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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10
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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: 74] [Impact Index Per Article: 12.3] [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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11
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Barth K, Hank S, Spindler PE, Prisner TF, Tampé R, Joseph B. Conformational Coupling and trans-Inhibition in the Human Antigen Transporter Ortholog TmrAB Resolved with Dipolar EPR Spectroscopy. J Am Chem Soc 2018; 140:4527-4533. [DOI: 10.1021/jacs.7b12409] [Citation(s) in RCA: 34] [Impact Index Per Article: 5.7] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/17/2022]
Affiliation(s)
- Katja Barth
- Institute of Physical and Theoretical Chemistry, Goethe University Frankfurt, Max-von-Laue-Str. 7, 60438 Frankfurt/Main, Germany
| | - Susanne Hank
- Institute of Biochemistry, Biocenter, Goethe University Frankfurt, Max-von-Laue-Str. 9, 60438 Frankfurt/Main, Germany
| | - Philipp E. Spindler
- Institute of Physical and Theoretical Chemistry, Goethe University Frankfurt, Max-von-Laue-Str. 7, 60438 Frankfurt/Main, Germany
| | - Thomas F. Prisner
- Institute of Physical and Theoretical Chemistry, Goethe University Frankfurt, Max-von-Laue-Str. 7, 60438 Frankfurt/Main, Germany
| | - Robert Tampé
- Institute of Biochemistry, Biocenter, Goethe University Frankfurt, Max-von-Laue-Str. 9, 60438 Frankfurt/Main, Germany
| | - Benesh Joseph
- Institute of Physical and Theoretical Chemistry, Goethe University Frankfurt, Max-von-Laue-Str. 7, 60438 Frankfurt/Main, Germany
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12
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Dai F, Yoo WG, Lee JY, Lu Y, Pak JH, Sohn WM, Hong SJ. Multidrug resistance-associated protein 4 is a bile transporter of Clonorchis sinensis simulated by in silico docking. Parasit Vectors 2017; 10:578. [PMID: 29157307 PMCID: PMC5697364 DOI: 10.1186/s13071-017-2523-8] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/31/2017] [Accepted: 11/05/2017] [Indexed: 12/14/2022] Open
Abstract
BACKGROUND Multidrug resistance-associated protein 4 (MRP4) is a member of the C subfamily of the ABC family of ATP-binding cassette (ABC) transporters. MRP4 regulates ATP-dependent efflux of various organic anionic substrates and bile acids out of cells. Since Clonorchis sinensis lives in host's bile duct, accumulation of bile juice can be toxic to the worm's tissues and cells. Therefore, C. sinensis needs bile transporters to reduce accumulation of bile acids within its body. RESULTS We cloned MRP4 (CsMRP4) from C. sinensis and obtained a cDNA encoding an open reading frame of 1469 amino acids. Phylogenetic analysis revealed that CsMRP4 belonged to the MRP/SUR/CFTR subfamily. A tertiary structure of CsMRP4 was generated by homology modeling based on multiple structures of MRP1 and P-glycoprotein. CsMRP4 had two membrane-spanning domains (MSD1 & 2) and two nucleotide-binding domains (NBD1 & 2) as common structural folds. Docking simulation with nine bile acids showed that CsMRP4 transports bile acids through the inner cavity. Moreover, it was found that CsMRP4 mRNA was more abundant in the metacercariae than in the adults. Mouse immune serum, generated against the CsMRP4-NBD1 (24.9 kDa) fragment, localized CsMRP4 mainly in mesenchymal tissues and oral and ventral suckers of the metacercariae and the adults. CONCLUSIONS Our findings shed new light on MRPs and their homologs and provide a platform for further structural and functional investigations on the bile transporters and parasites' survival.
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Affiliation(s)
- Fuhong Dai
- Department of Medical Environmental Biology, Chung-Ang University College of Medicine, Seoul, 06974, South Korea
| | - Won Gi Yoo
- Department of Medical Environmental Biology, Chung-Ang University College of Medicine, Seoul, 06974, South Korea
| | - Ji-Yun Lee
- Department of Medical Environmental Biology, Chung-Ang University College of Medicine, Seoul, 06974, South Korea
| | - Yanyan Lu
- Department of Medical Environmental Biology, Chung-Ang University College of Medicine, Seoul, 06974, South Korea
| | - Jhang Ho Pak
- Department of Convergence Medicine, University of Ulsan College of Medicine and Asan Institute for Life Sciences, Asan Medical Center, Seoul, 05505, South Korea
| | - Woon-Mok Sohn
- Department of Parasitology and Institute of Health Sciences, Gyeongsang National University School of Medicine, Jinju, 52828, South Korea
| | - Sung-Jong Hong
- Department of Medical Environmental Biology, Chung-Ang University College of Medicine, Seoul, 06974, South Korea.
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13
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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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14
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Yeh HI, Sohma Y, Conrath K, Hwang TC. A common mechanism for CFTR potentiators. J Gen Physiol 2017; 149:1105-1118. [PMID: 29079713 PMCID: PMC5715911 DOI: 10.1085/jgp.201711886] [Citation(s) in RCA: 44] [Impact Index Per Article: 6.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/25/2017] [Accepted: 10/10/2017] [Indexed: 01/29/2023] Open
Abstract
VX-770 is a potentiator of the CFTR channel and an approved therapy for cystic fibrosis. Yeh et al. find that the apparent affinity of a new potentiator, GLPG1837, is state dependent and propose an allosteric modulation model to explain the potency and efficacy of CFTR potentiators. Cystic fibrosis (CF) is a channelopathy caused by loss-of-function mutations of the cystic fibrosis transmembrane conductance regulator (CFTR) gene, which encodes a phosphorylation-activated and adenosine triphosphate (ATP)–gated chloride channel. In the past few years, high-throughput drug screening has successfully realized the first US Food and Drug Administration–approved therapy for CF, called ivacaftor (or VX-770). A more recent CFTR potentiator, GLPG1837 (N-(3-carbamoyl-5,5,7,7-tetramethyl-4,7-dihydro-5H-thieno[2,3-c]pyran-2-yl)-1H-pyrazole-3-carboxamide), has been shown to exhibit a higher efficacy than ivacaftor for the G551D mutation, yet the underlying mechanism of GLPG1837 remains unclear. Here we find that despite their differences in potency and efficacy, GLPG1837 and VX-770 potentiate CFTR gating in a remarkably similar manner. Specifically, they share similar effects on single-channel kinetics of wild-type CFTR. Their actions are independent of nucleotide-binding domain (NBD) dimerization and ATP hydrolysis, critical steps controlling CFTR’s gate opening and closing, respectively. By applying the two reagents together, we provide evidence that GLPG1837 and VX-770 likely compete for the same site, whereas GLPG1837 and the high-affinity ATP analogue 2′-deoxy-N6-(2-phenylethyl)-adenosine-5′-O-triphosphate (dPATP) work synergistically through two different sites. We also find that the apparent affinity for GLPG1837 is dependent on the open probability of the channel, suggesting a state-dependent binding of the drug to CFTR (higher binding affinity for the open state than the closed state), which is consistent with the classic mechanism for allosteric modulation. We propose a simple four-state kinetic model featuring an energetic coupling between CFTR gating and potentiator binding to explain our experimental results.
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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
| | - 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
| | | | - Tzyh-Chang Hwang
- Dalton Cardiovascular Research Center and Department of Medical Pharmacology and Physiology, University of Missouri, Columbia, MO
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15
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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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16
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Molecular dynamics of the cryo-EM CFTR structure. Biochem Biophys Res Commun 2017; 491:986-993. [DOI: 10.1016/j.bbrc.2017.07.165] [Citation(s) in RCA: 14] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/24/2017] [Accepted: 07/30/2017] [Indexed: 12/11/2022]
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17
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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: 178] [Impact Index Per Article: 25.4] [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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18
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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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19
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Zhang Z, Chen J. Atomic Structure of the Cystic Fibrosis Transmembrane Conductance Regulator. Cell 2017; 167:1586-1597.e9. [PMID: 27912062 DOI: 10.1016/j.cell.2016.11.014] [Citation(s) in RCA: 230] [Impact Index Per Article: 32.9] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/09/2016] [Revised: 10/28/2016] [Accepted: 11/04/2016] [Indexed: 02/07/2023]
Abstract
The cystic fibrosis transmembrane conductance regulator (CFTR) is an anion channel evolved from the ATP-binding cassette (ABC) transporter family. In this study, we determined the structure of zebrafish CFTR in the absence of ATP by electron cryo-microscopy to 3.7 Å resolution. Human and zebrafish CFTR share 55% sequence identity, and 42 of the 46 cystic-fibrosis-causing missense mutational sites are identical. In CFTR, we observe a large anion conduction pathway lined by numerous positively charged residues. A single gate near the extracellular surface closes the channel. The regulatory domain, dephosphorylated, is located in the intracellular opening between the two nucleotide-binding domains (NBDs), preventing NBD dimerization and channel opening. The structure also reveals why many cystic-fibrosis-causing mutations would lead to defects either in folding, ion conduction, or gating and suggests new avenues for therapeutic intervention.
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Affiliation(s)
- Zhe Zhang
- The Rockefeller University and Howard Hughes Medical Institute, 1230 York Avenue, New York, NY 10065, USA
| | - Jue Chen
- The Rockefeller University and Howard Hughes Medical Institute, 1230 York Avenue, New York, NY 10065, USA.
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20
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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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21
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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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22
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Wang G, Linsley R, Norimatsu Y. External Zn2+binding to cysteine-substituted cystic fibrosis transmembrane conductance regulator constructs regulates channel gating and curcumin potentiation. FEBS J 2016; 283:2458-75. [DOI: 10.1111/febs.13752] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/01/2015] [Revised: 05/02/2016] [Accepted: 05/11/2016] [Indexed: 01/22/2023]
Affiliation(s)
- Guangyu Wang
- Department of Physiology and Pharmacology; Oregon Health & Sciences University; Portland OR USA
- Department of Drug Research and Development; Institute of Biophysical Medico-chemistry; Reno NV USA
- Department of Physiology and Membrane Biology; University of California School of Medicine; Davis CA USA
| | | | - Yohei Norimatsu
- Department of Physiology; Kirksville College of Osteopathic Medicine; A.T. Still University; Kirksville MO USA
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23
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Sorum B, Czégé D, Csanády L. Timing of CFTR pore opening and structure of its transition state. Cell 2015; 163:724-33. [PMID: 26496611 DOI: 10.1016/j.cell.2015.09.052] [Citation(s) in RCA: 49] [Impact Index Per Article: 5.4] [Reference Citation Analysis] [Abstract] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/02/2015] [Revised: 08/25/2015] [Accepted: 09/18/2015] [Indexed: 12/12/2022]
Abstract
In CFTR, the chloride ion channel mutated in cystic fibrosis (CF) patients, pore opening is coupled to ATP-binding-induced dimerization of two cytosolic nucleotide binding domains (NBDs) and closure to dimer disruption following ATP hydrolysis. CFTR opening rate, unusually slow because of its high-energy transition state, is further slowed by CF mutation ΔF508. Here, we exploit equilibrium gating of hydrolysis-deficient CFTR mutant D1370N and apply rate-equilibrium free-energy relationship analysis to estimate relative timing of opening movements in distinct protein regions. We find clear directionality of motion along the longitudinal protein axis and identify an opening transition-state structure with the NBD dimer formed but the pore still closed. Thus, strain at the NBD/pore-domain interface, the ΔF508 mutation locus, underlies the energetic barrier for opening. Our findings suggest a therapeutic opportunity to stabilize this transition-state structure pharmacologically in ΔF508-CFTR to correct its opening defect, an essential step toward restoring CFTR function.
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Affiliation(s)
- Ben Sorum
- Department of Medical Biochemistry, Semmelweis University, Tűzoltó u. 37-47, Budapest 1094, Hungary; MTA-SE Ion Channel Research Group, Semmelweis University, Tűzoltó u. 37-47, Budapest 1094, Hungary
| | - Dávid Czégé
- MTA-SE Ion Channel Research Group, Semmelweis University, Tűzoltó u. 37-47, Budapest 1094, Hungary
| | - László Csanády
- Department of Medical Biochemistry, Semmelweis University, Tűzoltó u. 37-47, Budapest 1094, Hungary; MTA-SE Ion Channel Research Group, Semmelweis University, Tűzoltó u. 37-47, Budapest 1094, Hungary.
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24
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Corradi V, Vergani P, Tieleman DP. Cystic Fibrosis Transmembrane Conductance Regulator (CFTR): CLOSED AND OPEN STATE CHANNEL MODELS. J Biol Chem 2015; 290:22891-906. [PMID: 26229102 PMCID: PMC4645605 DOI: 10.1074/jbc.m115.665125] [Citation(s) in RCA: 45] [Impact Index Per Article: 5.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/13/2015] [Indexed: 01/06/2023] Open
Abstract
The cystic fibrosis transmembrane conductance regulator (CFTR) is a member of the ATP-binding cassette (ABC) transporter superfamily. CFTR controls the flow of anions through the apical membrane of epithelia. Dysfunctional CFTR causes the common lethal genetic disease cystic fibrosis. Transitions between open and closed states of CFTR are regulated by ATP binding and hydrolysis on the cytosolic nucleotide binding domains, which are coupled with the transmembrane (TM) domains forming the pathway for anion permeation. Lack of structural data hampers a global understanding of CFTR and thus the development of "rational" approaches directly targeting defective CFTR. In this work, we explored possible conformational states of the CFTR gating cycle by means of homology modeling. As templates, we used structures of homologous ABC transporters, namely TM(287-288), ABC-B10, McjD, and Sav1866. In the light of published experimental results, structural analysis of the transmembrane cavity suggests that the TM(287-288)-based CFTR model could correspond to a commonly occupied closed state, whereas the McjD-based model could represent an open state. The models capture the important role played by Phe-337 as a filter/gating residue and provide structural information on the conformational transition from closed to open channel.
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Affiliation(s)
- Valentina Corradi
- From the Department of Biological Sciences and Centre for Molecular Simulation, University of Calgary, Calgary, Alberta T2N 1N4, Canada and
| | - Paola Vergani
- Research Department of Neuroscience, Physiology and Pharmacology, University College London, Gower Street, London WC1E 6BT, United Kingdom
| | - D Peter Tieleman
- From the Department of Biological Sciences and Centre for Molecular Simulation, University of Calgary, Calgary, Alberta T2N 1N4, Canada and
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25
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Affiliation(s)
- Michael C Puljung
- Department of Physiology, Anatomy & Genetics, University of Oxford, Oxford OX1 3PT, England, UK
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