1
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Gao X, Yeh HI, Yang Z, Fan C, Jiang F, Howard RJ, Lindahl E, Kappes JC, Hwang TC. Allosteric inhibition of CFTR gating by CFTRinh-172 binding in the pore. Nat Commun 2024; 15:6668. [PMID: 39107303 PMCID: PMC11303713 DOI: 10.1038/s41467-024-50641-1] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/22/2023] [Accepted: 07/09/2024] [Indexed: 08/10/2024] Open
Abstract
Loss-of-function mutations of the CFTR gene cause the life-shortening genetic disease cystic fibrosis (CF), whereas overactivity of CFTR may lead to secretory diarrhea and polycystic kidney disease. While effective drugs targeting the CFTR protein have been developed for the treatment of CF, little progress has been made for diseases caused by hyper-activated CFTR. Here, we solve the cryo-EM structure of CFTR in complex with CFTRinh-172 (Inh-172), a CFTR gating inhibitor with promising potency and efficacy. We find that Inh-172 binds inside the pore of CFTR, interacting with amino acid residues from transmembrane segments (TMs) 1, 6, 8, 9, and 12 through mostly hydrophobic interactions and a salt bridge. Substitution of these residues lowers the apparent affinity of Inh-172. The inhibitor-bound structure reveals re-orientations of the extracellular segment of TMs 1, 8, and 12, supporting an allosteric modulation mechanism involving post-binding conformational changes. This allosteric inhibitory mechanism readily explains our observations that pig CFTR, which preserves all the amino acid residues involved in Inh-172 binding, exhibits a much-reduced sensitivity to Inh-172 and that the apparent affinity of Inh-172 is altered by the CF drug ivacaftor (i.e., VX-770) which enhances CFTR's activity through binding to a site also comprising TM8.
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Affiliation(s)
- Xiaolong Gao
- Dalton Cardiovascular Research Center, University of Missouri-Columbia, Columbia, MO, 65211, USA.
| | - Han-I Yeh
- Dalton Cardiovascular Research Center, University of Missouri-Columbia, Columbia, MO, 65211, USA
- Institute of Pharmacology, National Yang Ming Chiao Tung University, College of Medicine, Taipei, Taiwan
- Membrane Protein Structural Biology Research Center, National Yang Ming Chiao Tung University, Taipei, Taiwan
| | - Zhengrong Yang
- Heersink School of Medicine, University of Alabama School of Medicine, Birmingham, AL, 35233, USA
| | - Chen Fan
- Department of Applied Physics, Science for Life Laboratory, KTH Royal Institute of Technology, Solna, Sweden
- Department of Biochemistry and Biophysics, Science for Life Laboratory, Stockholm University, Solna, Sweden
| | - Fan Jiang
- Heersink School of Medicine, University of Alabama School of Medicine, Birmingham, AL, 35233, USA
| | - Rebecca J Howard
- Department of Applied Physics, Science for Life Laboratory, KTH Royal Institute of Technology, Solna, Sweden
- Department of Biochemistry and Biophysics, Science for Life Laboratory, Stockholm University, Solna, Sweden
| | - Erik Lindahl
- Department of Applied Physics, Science for Life Laboratory, KTH Royal Institute of Technology, Solna, Sweden
- Department of Biochemistry and Biophysics, Science for Life Laboratory, Stockholm University, Solna, Sweden
| | - John C Kappes
- Heersink School of Medicine, University of Alabama School of Medicine, Birmingham, AL, 35233, USA
- Research Service, Birmingham Veterans Affairs Medical Center, Veterans Health Administration, Birmingham, AL, 35233, USA
| | - Tzyh-Chang Hwang
- Dalton Cardiovascular Research Center, University of Missouri-Columbia, Columbia, MO, 65211, USA.
- Institute of Pharmacology, National Yang Ming Chiao Tung University, College of Medicine, Taipei, Taiwan.
- Membrane Protein Structural Biology Research Center, National Yang Ming Chiao Tung University, Taipei, Taiwan.
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2
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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: 4] [Impact Index Per Article: 4.0] [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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3
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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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4
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Abstract
ABC transporters are essential for cellular physiology. Humans have 48 ABC genes organized into seven distinct families. Of these genes, 44 (in five distinct families) encode for membrane transporters, of which several are involved in drug resistance and disease pathways resulting from transporter dysfunction. Over the last decade, advances in structural biology have vastly expanded our mechanistic understanding of human ABC transporter function, revealing details of their molecular arrangement, regulation, and interactions, facilitated in large part by advances in cryo-EM that have rendered hitherto inaccessible targets amenable to high-resolution structural analysis. As a result, experimentally determined structures of multiple members of each of the five families of ABC transporters in humans are now available. Here we review this recent progress, highlighting the physiological relevance of human ABC transporters and mechanistic insights gleaned from their direct structure determination. We also discuss the impact and limitations of model systems and structure prediction methods in understanding human ABC transporters and discuss current challenges and future research directions.
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Affiliation(s)
- Amer Alam
- The Hormel Institute, University of Minnesota, Austin, Minnesota, USA
| | - Kaspar P Locher
- Institute of Molecular Biology and Biophysics, ETH Zurich, Switzerland;
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5
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Simon MA, Csanády L. Optimization of CFTR gating through the evolution of its extracellular loops. J Gen Physiol 2023; 155:e202213264. [PMID: 36723516 PMCID: PMC9929929 DOI: 10.1085/jgp.202213264] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/15/2022] [Revised: 12/02/2022] [Accepted: 01/17/2023] [Indexed: 02/02/2023] Open
Abstract
CFTR chloride channel mutations cause the lethal and incurable disease cystic fibrosis (CF). CFTR is activated by phosphorylation, and phosphorylated channels exhibit "bursting" behavior-"bursts" of openings separated by short "flickery" closures and flanked by long "interburst" closures-driven by ATP binding/hydrolysis at two nucleotide-binding domains. The human channel (hCFTR) and the distant zebrafish ortholog (zCFTR) display differences both in their gating properties and structures. In phosphorylated ATP-bound hCFTR, the hR117 side chain, conserved across evolution, forms an H-bond that stabilizes the open state. Lack of that bond in the hR117H mutant causes CF. In the phosphorylated ATP-bound zCFTR structure that H-bond is not observable. Here, we show that the zR118H mutation does not affect the function of zCFTR. Instead, we identify an H-bond between the zS109 and zS120 side chains of phosphorylated ATP-bound, but not of unphosphorylated apo-, zCFTR. We investigate the role of that interaction using thermodynamic mutant cycles built on gating parameters determined in inside-out patch clamp recordings. We find that zS109 indeed forms an H-bond with zN120 in the flickery closed state, but not in the open or interburst closed states. Although in hCFTR an isoleucine (hI119) replaces the asparagine, mutation hS108A produces a strong hR117H-like phenotype. Since the effects of the latter two mutations are not additive, we conclude that in hCFTR these two positions interact, and the hS108-hR117 and hR117-hE1124 H-bonds cooperate to stabilize the open state. These findings highlight an example of how the gating mechanism was optimized during CFTR molecular evolution.
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Affiliation(s)
- Márton A. Simon
- Department of Biochemistry, Semmelweis University, Budapest, Hungary
- HCEMM-SE Molecular Channelopathies Research Group, Budapest, Hungary
- ELKH-SE Ion Channel Research Group, Budapest, Hungary
| | - László Csanády
- Department of Biochemistry, Semmelweis University, Budapest, Hungary
- HCEMM-SE Molecular Channelopathies Research Group, Budapest, Hungary
- ELKH-SE Ion Channel Research Group, Budapest, Hungary
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6
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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: 19] [Impact Index Per Article: 19.0] [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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7
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Hwang TC, Braakman I, van der Sluijs P, Callebaut I. Structure basis of CFTR folding, function and pharmacology. J Cyst Fibros 2023; 22 Suppl 1:S5-S11. [PMID: 36216744 DOI: 10.1016/j.jcf.2022.09.010] [Citation(s) in RCA: 5] [Impact Index Per Article: 5.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/28/2022] [Revised: 09/19/2022] [Accepted: 09/26/2022] [Indexed: 11/05/2022]
Abstract
The root cause of cystic fibrosis (CF), the most common life-shortening genetic disease in the Caucasian population, is the loss of function of the CFTR protein, which serves as a phosphorylation-activated, ATP-gated anion channel in numerous epithelia-lining tissues. In the past decade, high-throughput drug screening has made a significant stride in developing highly effective CFTR modulators for the treatment of CF. Meanwhile, structural-biology studies have succeeded in solving the high-resolution three-dimensional (3D) structure of CFTR in different conformations. Here, we provide a brief overview of some striking features of CFTR folding, function and pharmacology, in light of its specific structural features within the ABC-transporter superfamily. A particular focus is given to CFTR's first nucleotide-binding domain (NBD1), because folding of NBD1 constitutes a bottleneck in the CFTR protein biogenesis pathway, and ATP binding to this domain plays a unique role in the functional stability of CFTR. Unraveling the molecular basis of CFTR folding, function, and pharmacology would inspire the development of next-generation mutation-specific CFTR modulators.
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Affiliation(s)
- Tzyh-Chang Hwang
- Institute of Pharmacology, School of Medicine, National Yang Ming Chiao Tung University, Taiwan; Department of Medical Pharmacology and Physiology, Dalton Cardiovascular Research Center, University of Missouri, Columbia, MO, USA
| | - Ineke Braakman
- Cellular Protein Chemistry, Bijvoet Centre for Biomolecular Research, Utrecht University, 3584 CH Utrecht, The Netherlands
| | - Peter van der Sluijs
- Cellular Protein Chemistry, Bijvoet Centre for Biomolecular Research, Utrecht University, 3584 CH Utrecht, The Netherlands
| | - Isabelle Callebaut
- Sorbonne Université, Muséum National d'Histoire Naturelle, UMR CNRS 7590, Institut de Minéralogie, de Physique des Matériaux et de Cosmochimie, IMPMC, 75005 Paris, France.
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8
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Recovery of ΔF508-CFTR Function by Citrate. Nutrients 2022; 14:nu14204283. [PMID: 36296967 PMCID: PMC9610893 DOI: 10.3390/nu14204283] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/26/2022] [Revised: 10/09/2022] [Accepted: 10/10/2022] [Indexed: 11/13/2022] Open
Abstract
Treatment of cystic fibrosis relies so far on expensive and sophisticated drugs. A logical approach to rescuing the defective ΔF508-CFTR protein has not yet been published. Therefore, virtual docking of ATP and CFTR activators to the open conformation of the CFTR protein was performed. A new ATP binding site outside of the two known locations was identified. It was located in the cleft between the nucleotide binding domains NBD1 and NBD2 and comprised six basic amino acids in close proximity. Citrate and isocitrate were also bound to this site. Citrate was evaluated for its action on epithelial cells with intact CFTR and defective ΔF508-CFTR. It activated hyaluronan export from human breast carcinoma cells and iodide efflux, and recovered ΔF508-CFTR from premature intracellular degradation. In conclusion, citrate is an activator for ΔF508-CFTR and increases export by defective ΔF508-CFTR into the extracellular matrix of epithelial cells.
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9
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Csanády L. Degenerate but indispensable: How CFTR channel activity depends on the catalytically inactive ATP binding site. J Physiol 2021; 599:4523-4524. [PMID: 34487359 DOI: 10.1113/jp282278] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/27/2021] [Accepted: 09/02/2021] [Indexed: 11/08/2022] Open
Affiliation(s)
- László Csanády
- HCEMM-SE Molecular Channelopathies Research Group.,MTA-SE Ion Channel Research Group.,Department of Biochemistry, Semmelweis University, Budapest, Hungary
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10
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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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11
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Stockner T, Gradisch R, Schmitt L. The role of the degenerate nucleotide binding site in type I ABC exporters. FEBS Lett 2020; 594:3815-3838. [PMID: 33179257 PMCID: PMC7756269 DOI: 10.1002/1873-3468.13997] [Citation(s) in RCA: 26] [Impact Index Per Article: 6.5] [Reference Citation Analysis] [Abstract] [Key Words] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/24/2020] [Revised: 09/26/2020] [Accepted: 10/15/2020] [Indexed: 12/18/2022]
Abstract
ATP‐binding cassette (ABC) transporters are fascinating molecular machines that are capable of transporting a large variety of chemically diverse compounds. The energy required for translocation is derived from binding and hydrolysis of ATP. All ABC transporters share a basic architecture and are composed of two transmembrane domains and two nucleotide binding domains (NBDs). The latter harbor all conserved sequence motifs that hallmark the ABC transporter superfamily. The NBDs form the nucleotide binding sites (NBSs) in their interface. Transporters with two active NBSs are called canonical transporters, while ABC exporters from eukaryotic organisms, including humans, frequently have a degenerate NBS1 containing noncanonical residues that strongly impair ATP hydrolysis. Here, we summarize current knowledge on degenerate ABC transporters. By integrating structural information with biophysical and biochemical evidence of asymmetric function, we develop a model for the transport cycle of degenerate ABC transporters. We will elaborate on the unclear functional advantages of a degenerate NBS.
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Affiliation(s)
- Thomas Stockner
- Institute of Pharmacology, Center for Physiology and Pharmacology, Medical University of Vienna, Vienna, Austria
| | - Ralph Gradisch
- Institute of Pharmacology, Center for Physiology and Pharmacology, Medical University of Vienna, Vienna, Austria
| | - Lutz Schmitt
- Institute of Biochemistry, Heinrich Heine University, Düsseldorf, Germany
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12
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Simple binding of protein kinase A prior to phosphorylation allows CFTR anion channels to be opened by nucleotides. Proc Natl Acad Sci U S A 2020; 117:21740-21746. [PMID: 32817533 PMCID: PMC7474675 DOI: 10.1073/pnas.2007910117] [Citation(s) in RCA: 11] [Impact Index Per Article: 2.8] [Reference Citation Analysis] [Abstract] [Key Words] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/22/2022] Open
Abstract
The Cystic Fibrosis Transmembrane Conductance Regulator (CFTR) anion channel is essential for epithelial salt-water balance. CFTR mutations cause cystic fibrosis, a lethal incurable disease. In cells CFTR is activated through the cAMP signaling pathway, overstimulation of which during cholera leads to CFTR-mediated intestinal salt-water loss. Channel activation is achieved by phosphorylation of its regulatory (R) domain by cAMP-dependent protein kinase catalytic subunit (PKA). Here we show using two independent approaches--an ATP analog that can drive CFTR channel gating but is unsuitable for phosphotransfer by PKA, and CFTR mutants lacking phosphorylatable serines--that PKA efficiently opens CFTR channels through simple binding, under conditions that preclude phosphorylation. Unlike when phosphorylation happens, CFTR activation by PKA binding is completely reversible. Thus, PKA binding promotes release of the unphosphorylated R domain from its inhibitory position, causing full channel activation, whereas phosphorylation serves only to maintain channel activity beyond termination of the PKA signal. The results suggest two levels of CFTR regulation in cells: irreversible through phosphorylation, and reversible through R-domain binding to PKA--and possibly also to other members of a large network of proteins known to interact with the channel.
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13
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Abstract
Energy-coupling factor (ECF)-type ATP-binding cassette (ABC) transporters catalyze membrane transport of micronutrients in prokaryotes. Crystal structures and biochemical characterization have revealed that ECF transporters are mechanistically distinct from other ABC transport systems. Notably, ECF transporters make use of small integral membrane subunits (S-components) that are predicted to topple over in the membrane when carrying the bound substrate from the extracellular side of the bilayer to the cytosol. Here, we review the phylogenetic diversity of ECF transporters as well as recent structural and biochemical advancements that have led to the postulation of conceptually different mechanistic models. These models can be described as power stroke and thermal ratchet. Structural data indicate that the lipid composition and bilayer structure are likely to have great impact on the transport function. We argue that study of ECF transporters could lead to generic insight into membrane protein structure, dynamics, and interaction.
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Affiliation(s)
- S Rempel
- Gr oningen Biomolecular Sciences and Biotechnology Institute, University of Groningen, 9747 AG Groningen, The Netherlands; , ,
| | - W K Stanek
- Gr oningen Biomolecular Sciences and Biotechnology Institute, University of Groningen, 9747 AG Groningen, The Netherlands; , ,
| | - D J Slotboom
- Gr oningen Biomolecular Sciences and Biotechnology Institute, University of Groningen, 9747 AG Groningen, The Netherlands; , , .,Zernike Institute for Advanced Materials, University of Groningen, 9747 AG Groningen, The Netherlands
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14
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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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15
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Abreu B, Lopes EF, Oliveira ASF, Soares CM. F508del disturbs the dynamics of the nucleotide binding domains of CFTR before and after ATP hydrolysis. Proteins 2019; 88:113-126. [PMID: 31298435 DOI: 10.1002/prot.25776] [Citation(s) in RCA: 12] [Impact Index Per Article: 2.4] [Reference Citation Analysis] [Abstract] [Key Words] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/11/2019] [Revised: 06/17/2019] [Accepted: 07/06/2019] [Indexed: 12/20/2022]
Abstract
The cystic fibrosis transmembrane conductance regulator (CFTR) channel is an ion channel responsible for chloride transport in epithelia and it belongs to the class of ABC transporters. The deletion of phenylalanine 508 (F508del) in CFTR is the most common mutation responsible for cystic fibrosis. Little is known about the effect of the mutation in the isolated nucleotide binding domains (NBDs), on dimer dynamics, ATP hydrolysis and even on nucleotide binding. Using molecular dynamics simulations of the human CFTR NBD dimer, we showed that F508del increases, in the prehydrolysis state, the inter-motif distance in both ATP binding sites (ABP) when ATP is bound. Additionally, a decrease in the number of catalytically competent conformations was observed in the presence of F508del. We used the subtraction technique to study the first 300 ps after ATP hydrolysis in the catalytic competent site and found that the F508del dimer evidences lower conformational changes than the wild type. Using longer simulation times, the magnitude of the conformational changes in both forms increases. Nonetheless, the F508del dimer shows lower C-α RMS values in comparison to the wild-type, on the F508del loop, on the residues surrounding the catalytic site and the portion of NBD2 adjacent to ABP1. These results provide evidence that F508del interferes with the NBD dynamics before and after ATP hydrolysis. These findings shed a new light on the effect of F508del on NBD dynamics and reveal a novel mechanism for the influence of F508del on CFTR.
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Affiliation(s)
- Bárbara Abreu
- Protein Modelling Lab, ITQB-NOVA, Universidade Nova de Lisboa, Oeiras, Portugal
| | - Emanuel F Lopes
- Protein Modelling Lab, ITQB-NOVA, Universidade Nova de Lisboa, Oeiras, Portugal
| | - A S F Oliveira
- Protein Modelling Lab, ITQB-NOVA, Universidade Nova de Lisboa, Oeiras, Portugal.,School of Biochemistry & Center for Computational Chemistry, University of Bristol, Bristol, UK
| | - Cláudio M Soares
- Protein Modelling Lab, ITQB-NOVA, Universidade Nova de Lisboa, Oeiras, Portugal
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16
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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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17
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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: 147] [Impact Index Per Article: 29.4] [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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18
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Functional characterization reveals that zebrafish CFTR prefers to occupy closed channel conformations. PLoS One 2018; 13:e0209862. [PMID: 30596737 PMCID: PMC6312236 DOI: 10.1371/journal.pone.0209862] [Citation(s) in RCA: 12] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/24/2018] [Accepted: 12/12/2018] [Indexed: 12/19/2022] Open
Abstract
Cystic fibrosis transmembrane conductance regulator (CFTR), the culprit behind the genetic disease cystic fibrosis (CF), is a phosphorylation-activated, but ATP-gated anion channel. Studies of human CFTR over the past two decades have provided an in-depth understanding of how CFTR works as an ion channel despite its structural resemblance to ABC transporters. Recently-solved cryo-EM structures of unphosphorylated human and zebrafish CFTR (hCFTR and zCFTR), as well as phosphorylated ATP-bound zebrafish and human CFTR offer an unprecedented opportunity to understand CFTR's function at a molecular level. Interestingly, despite millions of years of phylogenetic distance between human and zebrafish, the structures of zCFTR and hCFTR exhibit remarkable similarities. In the current study, we characterized biophysical and pharmacological properties of zCFTR with the patch-clamp technique, and showed surprisingly very different functional properties between these two orthologs. First, while hCFTR has a single-channel conductance of 8.4 pS with a linear I-V curve, zCFTR shows an inwardly-rectified I-V relationship with a single-channel conductance of ~3.5 pS. Second, single-channel gating behaviors of phosphorylated zCFTR are very different from those of hCFTR, featuring a very low open probability Po (0.03 ± 0.02, vs. ~0.50 for hCFTR) with exceedingly long closed events and brief openings. In addition, unlike hCFTR where each open burst is clearly defined with rare short-lived flickery closures, the open bursts of zCFTR are not easily resolved. Third, although abolishing ATP hydrolysis by replacing the catalytic glutamate with glutamine (i.e., E1372Q) drastically prolongs the open bursts defined by the macroscopic relaxation analysis in zCFTR, the Po within a "locked-open" burst of E1372Q-zCFTR is only ~ 0.35 (vs. Po > 0.94 in E1371Q-hCFTR). Collectively, our data not only provide a reasonable explanation for the unexpected closed-state structure of phosphorylated E1372Q-zCFTR with a canonical ATP-bound dimer of the nucleotide binding domains (NBDs), but also implicate significant structural and functional differences between these two evolutionarily distant orthologs.
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19
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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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20
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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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21
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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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22
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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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23
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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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24
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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: 46] [Impact Index Per Article: 6.6] [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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25
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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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26
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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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27
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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: 233] [Impact Index Per Article: 33.3] [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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28
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The Synergetic Effects of Combining Structural Biology and EPR Spectroscopy on Membrane Proteins. CRYSTALS 2017. [DOI: 10.3390/cryst7040117] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 02/07/2023]
Abstract
Protein structures as provided by structural biology such as X-ray crystallography, cryo-electron microscopy and NMR spectroscopy are key elements to understand the function of a protein on the molecular level. Nonetheless, they might be error-prone due to crystallization artifacts or, in particular in case of membrane-imbedded proteins, a mostly artificial environment. In this review, we will introduce different EPR spectroscopy methods as powerful tools to complement and validate structural data gaining insights in the dynamics of proteins and protein complexes such that functional cycles can be derived. We will highlight the use of EPR spectroscopy on membrane-embedded proteins and protein complexes ranging from receptors to secondary active transporters as structural information is still limited in this field and the lipid environment is a particular challenge.
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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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30
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Villalona S, Glover-López G, Ortega-García JA, Moya-Quiles R, Mondejar-López P, Martínez-Romero MC, Rigabert-Montiel M, Pastor-Vivero MD, Sánchez-Solís M. R248G cystic fibrosis transmembrane conductance regulator mutation in three siblings presenting with recurrent acute pancreatitis and reproductive issues: a case series. J Med Case Rep 2017; 11:42. [PMID: 28196530 PMCID: PMC5310058 DOI: 10.1186/s13256-016-1181-3] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/29/2015] [Accepted: 12/14/2016] [Indexed: 11/10/2022] Open
Abstract
Background Mutational combinations of the cystic fibrosis transmembrane conductance regulator, CFTR, gene have different phenotypic manifestations at the molecular level with varying clinical consequences for individuals possessing such mutations. Reporting cystic fibrosis transmembrane conductance regulator mutations is important in understanding the genotype-phenotype correlations and associated clinical presentations in patients with cystic fibrosis. Understanding the effects of mutations is critical in developing appropriate treatments for individuals affected with cystic fibrosis, non-classic cystic fibrosis, or cystic fibrosis transmembrane conductance regulator-related disorders. This is the first report of related individuals possessing the R248G missense cystic fibrosis transmembrane conductance regulator mutation and we present their associated clinical histories. Case presentation All three patients are of Spanish descent. Deoxyribonucleic acid analysis revealed that all three siblings possessed a novel c.742A>G mutation, resulting in a p.Arg248Gly (R248G) amino acid change in exon 6 in trans with the known N1303K mutant allele. Case 1 patient is a 39-year-old infertile man presenting with congenital unilateral absence of the vas deferens and recurrent episodes of epigastric pain. Case 2 patient is a 32-year-old woman presenting with periods of infertility, two previous spontaneous abortions, recurrent epigastric pain, and recurrent pancreatitis. Case 3 patient is a 29-year-old woman presenting with recurrent pancreatitis and epigastric pain. Conclusions We report the genotype-phenotype correlations and clinical manifestations of a novel R248G cystic fibrosis transmembrane conductance regulator mutation: congenital unilateral absence of the vas deferens in males, reduced female fertility, and recurrent acute pancreatitis. In addition, we discuss the possible functional consequences of the mutations at the molecular level. Electronic supplementary material The online version of this article (doi:10.1186/s13256-016-1181-3) contains supplementary material, which is available to authorized users.
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Affiliation(s)
- Seiichi Villalona
- Pediatric Environmental Health Specialty Unit, University Hospital Virgen of Arrixaca, Murcia, Spain
| | | | | | - Rosa Moya-Quiles
- Center of Clinical Genetics, University Hospital Virgen of Arrixaca, Murcia, Spain
| | - Pedro Mondejar-López
- Cystic Fibrosis Unit, Pediatric Neumology, University Hospital Virgen of Arrixaca, Murcia, Spain
| | | | | | - María D Pastor-Vivero
- Cystic Fibrosis Unit, Pediatric Neumology, University Hospital Virgen of Arrixaca, Murcia, Spain
| | - Manuel Sánchez-Solís
- Cystic Fibrosis Unit, Pediatric Neumology, University Hospital Virgen of Arrixaca, Murcia, Spain
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31
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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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32
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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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33
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Callebaut I, Hoffmann B, Lehn P, Mornon JP. Molecular modelling and molecular dynamics of CFTR. Cell Mol Life Sci 2017; 74:3-22. [PMID: 27717958 PMCID: PMC11107702 DOI: 10.1007/s00018-016-2385-9] [Citation(s) in RCA: 25] [Impact Index Per Article: 3.6] [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: 12/11/2022]
Abstract
The cystic fibrosis transmembrane conductance regulator (CFTR) protein is a member of the ATP-binding cassette (ABC) transporter superfamily that functions as an ATP-gated channel. Considerable progress has been made over the last years in the understanding of the molecular basis of the CFTR functions, as well as dysfunctions causing the common genetic disease cystic fibrosis (CF). This review provides a global overview of the theoretical studies that have been performed so far, especially molecular modelling and molecular dynamics (MD) simulations. A special emphasis is placed on the CFTR-specific evolution of an ABC transporter framework towards a channel function, as well as on the understanding of the effects of disease-causing mutations and their specific modulation. This in silico work should help structure-based drug discovery and design, with a view to develop CFTR-specific pharmacotherapeutic approaches for the treatment of CF in the context of precision medicine.
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Affiliation(s)
- Isabelle Callebaut
- UMR CNRS 7590, Museum National d'Histoire Naturelle, IRD UMR 206, IUC, Case 115, IMPMC, Sorbonne Universités, UPMC Univ Paris 06, 4 Place Jussieu, 75005, Paris Cedex 05, France.
| | - Brice Hoffmann
- UMR CNRS 7590, Museum National d'Histoire Naturelle, IRD UMR 206, IUC, Case 115, IMPMC, Sorbonne Universités, UPMC Univ Paris 06, 4 Place Jussieu, 75005, Paris Cedex 05, France
| | - Pierre Lehn
- INSERM U1078, SFR ScInBioS, Université de Bretagne Occidentale, Brest, France
| | - Jean-Paul Mornon
- UMR CNRS 7590, Museum National d'Histoire Naturelle, IRD UMR 206, IUC, Case 115, IMPMC, Sorbonne Universités, UPMC Univ Paris 06, 4 Place Jussieu, 75005, Paris Cedex 05, France
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34
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Vedovato N, Ashcroft FM, Puljung MC. The Nucleotide-Binding Sites of SUR1: A Mechanistic Model. Biophys J 2016; 109:2452-2460. [PMID: 26682803 PMCID: PMC4699857 DOI: 10.1016/j.bpj.2015.10.026] [Citation(s) in RCA: 22] [Impact Index Per Article: 2.8] [Reference Citation Analysis] [Abstract] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/07/2015] [Revised: 10/22/2015] [Accepted: 10/22/2015] [Indexed: 12/19/2022] Open
Abstract
ATP-sensitive potassium (KATP) channels comprise four pore-forming Kir6.2 subunits and four modulatory sulfonylurea receptor (SUR) subunits. The latter belong to the ATP-binding cassette family of transporters. KATP channels are inhibited by ATP (or ADP) binding to Kir6.2 and activated by Mg-nucleotide interactions with SUR. This dual regulation enables the KATP channel to couple the metabolic state of a cell to its electrical excitability and is crucial for the KATP channel’s role in regulating insulin secretion, cardiac and neuronal excitability, and vascular tone. Here, we review the regulation of the KATP channel by adenine nucleotides and present an equilibrium allosteric model for nucleotide activation and inhibition. The model can account for many experimental observations in the literature and provides testable predictions for future experiments.
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Affiliation(s)
- Natascia Vedovato
- Department of Physiology, Anatomy and Genetics, University of Oxford, Oxford, United Kingdom
| | - Frances M Ashcroft
- Department of Physiology, Anatomy and Genetics, University of Oxford, Oxford, United Kingdom
| | - Michael C Puljung
- Department of Physiology, Anatomy and Genetics, University of Oxford, Oxford, United Kingdom.
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35
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Lin WY, Sohma Y, Hwang TC. Synergistic Potentiation of Cystic Fibrosis Transmembrane Conductance Regulator Gating by Two Chemically Distinct Potentiators, Ivacaftor (VX-770) and 5-Nitro-2-(3-Phenylpropylamino) Benzoate. Mol Pharmacol 2016; 90:275-85. [PMID: 27413118 PMCID: PMC4998663 DOI: 10.1124/mol.116.104570] [Citation(s) in RCA: 28] [Impact Index Per Article: 3.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/04/2016] [Accepted: 07/12/2016] [Indexed: 01/12/2023] Open
Abstract
Cystic fibrosis (CF) is caused by loss-of-function mutations of the cystic fibrosis transmembrane conductance regulator (CFTR) gene encoding a phosphorylation-activated but ATP-gated chloride channel. Previous studies suggested that VX-770 [ivacaftor, N-(2,4-di-tert-butyl-5-hydroxyphenyl)-4-oxo-1,4-dihydroquinoline-3-carboxamide], a CFTR potentiator now used in clinics, increases the open probability of CFTR by shifting the gating conformational changes to favor the open channel configuration. Recently the chloride channel blocker and CFTR potentiator 5-nitro-2-(3-phenylpropylamino) benzoate (NPPB) has been reported to enhance CFTR activity by a mechanism that exploits the ATP hydrolysis-driven, nonequilibrium gating mechanism unique to CFTR. Surprisingly however, NPPB increased the activity of nonhydrolytic G551D-CFTR, the third most common disease-associated mutation. Here, we further investigated the mechanism of NPPB's effects on CFTR gating by assessing its interaction with well-studied VX-770. Interestingly, once G551D-CFTR was maximally potentiated by VX-770, NPPB further increased its activity. However, quantitative analysis of this drug-drug interaction suggests that this pharmacologic synergism is not due to independent actions of NPPB and VX-770 on CFTR gating; instead, our data support a dependent mechanism involving two distinct binding sites. This latter idea is further supported by the observation that the locked-open time of a hydrolysis-deficient mutant K1250A was shortened by NPPB but prolonged by VX-770. In addition, the effectiveness of NPPB, but not of VX-770, was greatly diminished in a mutant whose second nucleotide-binding domain was completely removed. Interpreting these results under the framework of current understanding of CFTR gating not only reveals insights into the mechanism of action for different CFTR potentiators but also brings us one step forward to a more complete schematic for CFTR gating.
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Affiliation(s)
- Wen-Ying Lin
- Department of Medical Pharmacology and Physiology, Dalton Cardiovascular Research Center, University of Missouri, Columbia, Missouri (W.-Y.L., T.-C.H.); Department of Pharmacology, School of Medicine, Keio University, Tokyo Japan (Y.S.)
| | - Yoshiro Sohma
- Department of Medical Pharmacology and Physiology, Dalton Cardiovascular Research Center, University of Missouri, Columbia, Missouri (W.-Y.L., T.-C.H.); Department of Pharmacology, School of Medicine, Keio University, Tokyo Japan (Y.S.)
| | - Tzyh-Chang Hwang
- Department of Medical Pharmacology and Physiology, Dalton Cardiovascular Research Center, University of Missouri, Columbia, Missouri (W.-Y.L., T.-C.H.); Department of Pharmacology, School of Medicine, Keio University, Tokyo Japan (Y.S.)
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36
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Molecular action of sulphonylureas on KATP channels: a real partnership between drugs and nucleotides. Biochem Soc Trans 2016; 43:901-7. [PMID: 26517901 PMCID: PMC4613533 DOI: 10.1042/bst20150096] [Citation(s) in RCA: 30] [Impact Index Per Article: 3.8] [Reference Citation Analysis] [Abstract] [Key Words] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/25/2022]
Abstract
Sulphonylureas stimulate insulin secretion from pancreatic β-cells primarily by closing ATP-sensitive K+ channels in the β-cell plasma membrane. The mechanism of channel inhibition by these drugs is unusually complex. As direct inhibitors of channel activity, sulphonylureas act only as partial antagonists at therapeutic concentrations. However, they also exert an additional indirect inhibitory effect via modulation of nucleotide-dependent channel gating. In this review, we summarize current knowledge and recent advances in our understanding of the molecular mechanism of action of these drugs.
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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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38
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Yu YC, Sohma Y, Hwang TC. On the mechanism of gating defects caused by the R117H mutation in cystic fibrosis transmembrane conductance regulator. J Physiol 2016; 594:3227-44. [PMID: 26846474 DOI: 10.1113/jp271723] [Citation(s) in RCA: 30] [Impact Index Per Article: 3.8] [Reference Citation Analysis] [Abstract] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/11/2015] [Accepted: 01/29/2016] [Indexed: 01/05/2023] Open
Abstract
KEY POINTS Two functional abnormalities of cystic fibrosis transmembrane conductance regulator (CFTR), a 25% reduction of the single-channel conductance (g) and a ∼13-fold lower open probability (Po ), were found with the R117H mutation that is associated with mild forms of cystic fibrosis. Characterizations of the gating defects of R117H-CFTR led to the conclusion that the mutation decreases Po by perturbing the gating conformational changes in CFTR's transmembrane domains (TMDs) without altering the function of the nucleotide binding domains (NBDs). Nonetheless, gating of the R117H-CFTR can be improved by a variety of pharmacological reagents supposedly acting on NBDs such as ATP analogues, or TMDs (e.g. VX-770 or nitrate). These reagents potentiate synergistically R117H-CFTR gating to a level that allows accurate assessments of its gating deficits. Our studies not only elucidate the mechanism underpinning gating dysfunction of R117H-CFTR, but also provide a mechanistic understanding of how VX-770 ameliorates the gating defects in the R117H mutant. ABSTRACT Cystic fibrosis (CF) is caused by loss-of-function mutations of the cystic fibrosis transmembrane conductance regulator (CFTR) gene encoding a phosphorylation-activated, but ATP-gated chloride channel. In the current study, we investigated the mechanism responsible for the gating defects manifested in R117H-CFTR, an arginine-to-histidine substitution at position 117 of CFTR that is associated with mild forms of CF. We confirmed previous findings of a 25% decrease of the single-channel conductance (g) in R117H-CFTR, but found a ∼13-fold lower open probability (Po ). This dramatic gating deficit is not due to dysfunctional nucleotide binding domains (NBDs) as the mutation does not alter the apparent affinity for ATP, and the mutant channels respond to ATP analogues in a similar manner as wild-type CFTR. Furthermore, once ATP hydrolysis is abolished, the R117H mutant can be trapped in a prolonged 'burst opening' conformation that is proposed to be equipped with a stable NBD dimer. On the other hand, our results support the conclusion that the R117H mutation decreases Po by perturbing the gating conformational changes in CFTR's transmembrane domains as even when NBDs are kept at a dimerized configuration, Po is reduced by ∼10-fold. Moreover, our data demonstrate that a synergistic improvement of R117H-CFTR function can be accomplished with a combined regiment of VX-770 (Ivacaftor), nitrate ion (NO3 (-) ) and N(6) -(2-phenylethyl)-2'-deoxy-ATP (d-PATP), which almost completely rectifies the gating defect of R117H-CFTR. Clinical implications of our results are discussed.
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Affiliation(s)
- Ying-Chun Yu
- Dalton Cardiovascular Research Center, University of Missouri-Columbia, MO, 65211, USA.,Department of Medical Pharmacology and Physiology, University of Missouri-Columbia, MO, 65211, USA
| | - Yoshiro Sohma
- Dalton Cardiovascular Research Center, University of Missouri-Columbia, MO, 65211, USA.,Department of Pharmacology, Keio University School of Medicine, Shinjuku, Tokyo, 160-8582, Japan
| | - Tzyh-Chang Hwang
- Dalton Cardiovascular Research Center, University of Missouri-Columbia, MO, 65211, USA.,Department of Medical Pharmacology and Physiology, University of Missouri-Columbia, MO, 65211, USA
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Chaves LAP, Gadsby DC. Cysteine accessibility probes timing and extent of NBD separation along the dimer interface in gating CFTR channels. ACTA ACUST UNITED AC 2015; 145:261-83. [PMID: 25825169 PMCID: PMC4380215 DOI: 10.1085/jgp.201411347] [Citation(s) in RCA: 25] [Impact Index Per Article: 2.8] [Reference Citation Analysis] [Abstract] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/21/2023]
Abstract
Cystic fibrosis transmembrane conductance regulator (CFTR) channel opening and closing are driven by cycles of adenosine triphosphate (ATP) binding-induced formation and hydrolysis-triggered disruption of a heterodimer of its cytoplasmic nucleotide-binding domains (NBDs). Although both composite sites enclosed within the heterodimer interface contain ATP in an open CFTR channel, ATP hydrolysis in the sole catalytically competent site causes channel closure. Opening of the NBD interface at that site then allows ADP-ATP exchange. But how frequently, and how far, the NBD surfaces separate at the other, inactive composite site remains unclear. We assessed separation at each composite site by monitoring access of nucleotide-sized hydrophilic, thiol-specific methanothiosulfonate (MTS) reagents to interfacial target cysteines introduced into either LSGGQ-like ATP-binding cassette signature sequence (replacing equivalent conserved serines: S549 and S1347). Covalent MTS-dependent modification of either cysteine while channels were kept closed by the absence of ATP impaired subsequent opening upon ATP readdition. Modification while channels were opening and closing in the presence of ATP caused macroscopic CFTR current to decline at the same speed as when the unmodified channels shut upon sudden ATP withdrawal. These results suggest that the target cysteines can be modified only in closed channels; that after modification the attached MTS adduct interferes with ATP-mediated opening; and that modification in the presence of ATP occurs rapidly once channels close, before they can reopen. This interpretation was corroborated by the finding that, for either cysteine target, the addition of the hydrolysis-impairing mutation K1250R (catalytic site Walker A Lys) similarly slowed, by an order of magnitude, channel closing on ATP removal and the speed of modification by MTS reagent in ATP. We conclude that, in every CFTR channel gating cycle, the NBD dimer interface separates simultaneously at both composite sites sufficiently to allow MTS reagents to access both signature-sequence serines. Relatively rapid modification of S1347C channels by larger reagents-MTS-glucose, MTS-biotin, and MTS-rhodamine-demonstrates that, at the noncatalytic composite site, this separation must exceed 8 Å.
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Affiliation(s)
- Luiz A Poletto Chaves
- The Laboratory of Cardiac/Membrane Physiology, The Rockefeller University, New York, NY 10065
| | - David C Gadsby
- The Laboratory of Cardiac/Membrane Physiology, The Rockefeller University, New York, NY 10065
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40
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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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41
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Csanády L, Töröcsik B. Structure-activity analysis of a CFTR channel potentiator: Distinct molecular parts underlie dual gating effects. ACTA ACUST UNITED AC 2015; 144:321-36. [PMID: 25267914 PMCID: PMC4178936 DOI: 10.1085/jgp.201411246] [Citation(s) in RCA: 12] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/31/2022]
Abstract
The head and tail regions of 5-nitro-2-(3-phenylpropylamino)benzoate increase CFTR open probability through distinct mechanisms. The cystic fibrosis (CF) transmembrane conductance regulator (CFTR) is a member of the ATP-binding cassette transporter superfamily that functions as an epithelial chloride channel. Gating of the CFTR ion conduction pore involves a conserved irreversible cyclic mechanism driven by ATP binding and hydrolysis at two cytosolic nucleotide-binding domains (NBDs): formation of an intramolecular NBD dimer that occludes two ATP molecules opens the pore, whereas dimer disruption after ATP hydrolysis closes it. CFTR dysfunction resulting from inherited mutations causes CF. The most common CF mutation, deletion of phenylalanine 508 (ΔF508), impairs both protein folding and processing and channel gating. Development of ΔF508 CFTR correctors (to increase cell surface expression) and potentiators (to enhance open probability, Po) is therefore a key focus of CF research. The practical utility of 5-nitro-2-(3-phenylpropylamino)benzoate (NPPB), one of the most efficacious potentiators of ΔF508 CFTR identified to date, is limited by its pore-blocking side effect. NPPB-mediated stimulation of Po is unique in that it involves modulation of gating transition state stability. Although stabilization by NPPB of the transition state for pore opening enhances both the rate of channel opening and the very slow rate of nonhydrolytic closure, because of CFTR’s cyclic gating mechanism, the net effect is Po stimulation. In addition, slowing of ATP hydrolysis by NPPB delays pore closure, further enhancing Po. Here we show that NPPB stimulates gating at a site outside the pore and that these individual actions of NPPB on CFTR are fully attributable to one or the other of its two complementary molecular parts, 3-nitrobenzoate (3NB) and 3-phenylpropylamine (3PP), both of which stimulate Po: the pore-blocking 3NB selectively stabilizes the transition state for opening, whereas the nonblocking 3PP selectively slows the ATP hydrolysis step. Understanding structure–activity relationships of NPPB might prove useful for designing potent, clinically relevant CFTR potentiators.
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Affiliation(s)
- László Csanády
- Department of Medical Biochemistry and MTA-SE Ion Channel Research Group, Semmelweis University, Budapest H-1094, Hungary Department of Medical Biochemistry and MTA-SE Ion Channel Research Group, Semmelweis University, Budapest H-1094, Hungary
| | - Beáta Töröcsik
- Department of Medical Biochemistry and MTA-SE Ion Channel Research Group, Semmelweis University, Budapest H-1094, Hungary
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42
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Golin J, Ambudkar SV. The multidrug transporter Pdr5 on the 25th anniversary of its discovery: an important model for the study of asymmetric ABC transporters. Biochem J 2015; 467:353-63. [PMID: 25886173 PMCID: PMC4784962 DOI: 10.1042/bj20150042] [Citation(s) in RCA: 49] [Impact Index Per Article: 5.4] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/17/2022]
Abstract
Asymmetric ABC (ATP-binding cassette) transporters make up a significant proportion of this important superfamily of integral membrane proteins. These proteins contain one canonical (catalytic) ATP-binding site and a second atypical site with little enzymatic capability. The baker's yeast (Saccharomyces cerevisiae) Pdr5 multidrug transporter is the founding member of the Pdr subfamily of asymmetric ABC transporters, which exist only in fungi and slime moulds. Because these organisms are of considerable medical and agricultural significance, Pdr5 has been studied extensively, as has its medically important homologue Cdr1 from Candida albicans. Genetic and biochemical analyses of Pdr5 have contributed important observations that are likely to be applicable to mammalian asymmetric ABC multidrug transporter proteins, including the basis of transporter promiscuity, the function of the non-catalytic deviant ATP-binding site, the most complete description of an in vivo transmission interface, and the recent discovery that Pdr5 is a molecular diode (one-way gate). In the present review, we discuss the observations made with Pdr5 and compare them with findings from clinically important asymmetric ABC transporters, such as CFTR (cystic fibrosis transmembrane conductance regulator), Cdr1 and Tap1/Tap2.
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Affiliation(s)
- John Golin
- Department of Biology, The Catholic University of America, Washington, DC 20064, U.S.A
| | - Suresh V. Ambudkar
- The Laboratory of Cell Biology, Center for Cancer Research, NCI, NIH, Bethesda, MD 20892, U.S.A
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43
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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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44
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Abstract
Cystic fibrosis transmembrane conductance regulator (CFTR) is unique among ion channels in that after its phosphorylation by protein kinase A (PKA), its ATP-dependent gating violates microscopic reversibility caused by the intimate involvement of ATP hydrolysis in controlling channel closure. Recent studies suggest a gating model featuring an energetic coupling between opening and closing of the gate in CFTR's transmembrane domains and association and dissociation of its two nucleotide-binding domains (NBDs). We found that permeant ions such as nitrate can increase the open probability (Po) of wild-type (WT) CFTR by increasing the opening rate and decreasing the closing rate. Nearly identical effects were seen with a construct in which activity does not require phosphorylation of the regulatory domain, indicating that nitrate primarily affects ATP-dependent gating steps rather than PKA-dependent phosphorylation. Surprisingly, the effects of nitrate on CFTR gating are remarkably similar to those of VX-770 (N-(2,4-Di-tert-butyl-5-hydroxyphenyl)-4-oxo-1,4-dihydroquinoline-3-carboxamide), a potent CFTR potentiator used in clinics. These include effects on single-channel kinetics of WT CFTR, deceleration of the nonhydrolytic closing rate, and potentiation of the Po of the disease-associated mutant G551D. In addition, both VX-770 and nitrate increased the activity of a CFTR construct lacking NBD2 (ΔNBD2), indicating that these gating effects are independent of NBD dimerization. Nonetheless, whereas VX-770 is equally effective when applied from either side of the membrane, nitrate potentiates gating mainly from the cytoplasmic side, implicating a common mechanism for gating modulation mediated through two separate sites of action.
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Affiliation(s)
- Han-I Yeh
- Physician-Scientist Program, School of Medicine, National Yang-Ming University, Taipei, 112 Taiwan Dalton Cardiovascular Research Center and Department of Medical Pharmacology and Physiology, University of Missouri, Columbia, MO 65211
| | - Jiunn-Tyng Yeh
- Physician-Scientist Program, School of Medicine, National Yang-Ming University, Taipei, 112 Taiwan Dalton Cardiovascular Research Center and Department of Medical Pharmacology and Physiology, University of Missouri, Columbia, MO 65211
| | - Tzyh-Chang Hwang
- Dalton Cardiovascular Research Center and Department of Medical Pharmacology and Physiology, University of Missouri, Columbia, MO 65211 Dalton Cardiovascular Research Center and Department of Medical Pharmacology and Physiology, University of Missouri, Columbia, MO 65211
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45
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Qian F, Li T, Yang F, Liu L. Stoichiometry and novel gating mechanism within the cystic fibrosis transmembrane conductance regulator channel. Exp Physiol 2014; 99:1611-23. [DOI: 10.1113/expphysiol.2014.081034] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/27/2023]
Affiliation(s)
- Feng Qian
- Department of Medical Function; School of Medicine; Yangtze University; Jingzhou Hubei Province 434023 China
| | - Tao Li
- Department of Biology; College of Chemistry and Life Sciences; Zhejiang Normal University; Jinhua Zhejiang Province 321004 China
| | - Fei Yang
- Department of Medical Function; School of Medicine; Yangtze University; Jingzhou Hubei Province 434023 China
| | - Lian Liu
- Department of Medical Function; School of Medicine; Yangtze University; Jingzhou Hubei Province 434023 China
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46
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Lin WY, Jih KY, Hwang TC. A single amino acid substitution in CFTR converts ATP to an inhibitory ligand. ACTA ACUST UNITED AC 2014; 144:311-20. [PMID: 25225552 PMCID: PMC4178940 DOI: 10.1085/jgp.201411247] [Citation(s) in RCA: 22] [Impact Index Per Article: 2.2] [Reference Citation Analysis] [Abstract] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/06/2023]
Abstract
Cystic fibrosis (CF), one of the most common lethal genetic diseases, is caused by loss-of-function mutations of the cystic fibrosis transmembrane conductance regulator (CFTR) gene, which encodes a chloride channel that, when phosphorylated, is gated by ATP. The third most common pathogenic mutation, a glycine-to-aspartate mutation at position 551 or G551D, shows a significantly decreased open probability (Po) caused by failure of the mutant channel to respond to ATP. Recently, a CFTR-targeted drug, VX-770 (Ivacaftor), which potentiates G551D-CFTR function in vitro by boosting its Po, has been approved by the FDA to treat CF patients carrying this mutation. Here, we show that, in the presence of VX-770, G551D-CFTR becomes responsive to ATP, albeit with an unusual time course. In marked contrast to wild-type channels, which are stimulated by ATP, sudden removal of ATP in excised inside-out patches elicits an initial increase in macroscopic G551D-CFTR current followed by a slow decrease. Furthermore, decreasing [ATP] from 2 mM to 20 µM resulted in a paradoxical increase in G551D-CFTR current. These results suggest that the two ATP-binding sites in the G551D mutant mediate opposite effects on channel gating. We introduced mutations that specifically alter ATP-binding affinity in either nucleotide-binding domain (NBD1 or NBD2) into the G551D background and determined that this disease-associated mutation converts site 2, formed by the head subdomain of NBD2 and the tail subdomain of NBD1, into an inhibitory site, whereas site 1 remains stimulatory. G551E, but not G551K or G551S, exhibits a similar phenotype, indicating that electrostatic repulsion between the negatively charged side chain of aspartate and the γ-phosphate of ATP accounts for the observed mutational effects. Understanding the molecular mechanism of this gating defect lays a foundation for rational drug design for the treatment of CF.
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Affiliation(s)
- Wen-Ying Lin
- Department of Medical Pharmacology and Physiology, Dalton Cardiovascular Research Center, University of Missouri-Columbia, Columbia, MO 65211 Department of Medical Pharmacology and Physiology, Dalton Cardiovascular Research Center, University of Missouri-Columbia, Columbia, MO 65211
| | - Kang-Yang Jih
- Department of Medical Pharmacology and Physiology, Dalton Cardiovascular Research Center, University of Missouri-Columbia, Columbia, MO 65211 Physician-Scientist Program, National Yang-Ming University, Taipei, 112 Taiwan
| | - Tzyh-Chang Hwang
- Department of Medical Pharmacology and Physiology, Dalton Cardiovascular Research Center, University of Missouri-Columbia, Columbia, MO 65211 Department of Medical Pharmacology and Physiology, Dalton Cardiovascular Research Center, University of Missouri-Columbia, Columbia, MO 65211
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47
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Structural basis for allosteric cross-talk between the asymmetric nucleotide binding sites of a heterodimeric ABC exporter. Proc Natl Acad Sci U S A 2014; 111:11025-30. [PMID: 25030449 DOI: 10.1073/pnas.1400485111] [Citation(s) in RCA: 89] [Impact Index Per Article: 8.9] [Reference Citation Analysis] [Abstract] [Key Words] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/18/2022] Open
Abstract
ATP binding cassette (ABC) transporters mediate vital transport processes in every living cell. ATP hydrolysis, which fuels transport, displays positive cooperativity in numerous ABC transporters. In particular, heterodimeric ABC exporters exhibit pronounced allosteric coupling between a catalytically impaired degenerate site, where nucleotides bind tightly, and a consensus site, at which ATP is hydrolyzed in every transport cycle. Whereas the functional phenomenon of cooperativity is well described, its structural basis remains poorly understood. Here, we present the apo structure of the heterodimeric ABC exporter TM287/288 and compare it to the previously solved structure with adenosine 5'-(β,γ-imido)triphosphate (AMP-PNP) bound at the degenerate site. In contrast to other ABC exporter structures, the nucleotide binding domains (NBDs) of TM287/288 remain in molecular contact even in the absence of nucleotides, and the arrangement of the transmembrane domains (TMDs) is not influenced by AMP-PNP binding, a notion confirmed by double electron-electron resonance (DEER) measurements. Nucleotide binding at the degenerate site results in structural rearrangements, which are transmitted to the consensus site via two D-loops located at the NBD interface. These loops owe their name from a highly conserved aspartate and are directly connected to the catalytically important Walker B motif. The D-loop at the degenerate site ties the NBDs together even in the absence of nucleotides and substitution of its aspartate by alanine is well-tolerated. By contrast, the D-loop of the consensus site is flexible and the aspartate to alanine mutation and conformational restriction by cross-linking strongly reduces ATP hydrolysis and substrate transport.
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48
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Guo JH, Chen H, Ruan YC, Zhang XL, Zhang XH, Fok KL, Tsang LL, Yu MK, Huang WQ, Sun X, Chung YW, Jiang X, Sohma Y, Chan HC. Glucose-induced electrical activities and insulin secretion in pancreatic islet β-cells are modulated by CFTR. Nat Commun 2014; 5:4420. [PMID: 25025956 PMCID: PMC4104438 DOI: 10.1038/ncomms5420] [Citation(s) in RCA: 123] [Impact Index Per Article: 12.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/28/2014] [Accepted: 06/17/2014] [Indexed: 01/08/2023] Open
Abstract
The cause of insulin insufficiency remains unknown in many diabetic cases. Up to 50% adult patients with cystic fibrosis (CF), a disease caused by mutations in the gene encoding the CF transmembrane conductance regulator (CFTR), develop CF-related diabetes (CFRD) with most patients exhibiting insulin insufficiency. Here we show that CFTR is a regulator of glucose-dependent electrical acitivities and insulin secretion in β-cells. We demonstrate that glucose elicited whole-cell currents, membrane depolarization, electrical bursts or action potentials, Ca(2+) oscillations and insulin secretion are abolished or reduced by inhibitors or knockdown of CFTR in primary mouse β-cells or RINm5F β-cell line, or significantly attenuated in CFTR mutant (DF508) mice compared with wild-type mice. VX-809, a newly discovered corrector of DF508 mutation, successfully rescues the defects in DF508 β-cells. Our results reveal a role of CFTR in glucose-induced electrical activities and insulin secretion in β-cells, shed light on the pathogenesis of CFRD and possibly other idiopathic diabetes, and present a potential treatment strategy.
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Affiliation(s)
- Jing Hui Guo
- Epithelial Cell Biology Research Center, Key Laboratory of Regenerative Medicine of Ministry of Education of China, CUHK-SJTU Joint Center for Human Reproduction and Related Disease, Faculty of Medicine, School of Biomedical Sciences, The Chinese University of Hong Kong, Hong Kong, China
| | - Hui Chen
- Epithelial Cell Biology Research Center, Key Laboratory of Regenerative Medicine of Ministry of Education of China, CUHK-SJTU Joint Center for Human Reproduction and Related Disease, Faculty of Medicine, School of Biomedical Sciences, The Chinese University of Hong Kong, Hong Kong, China
| | - Ye Chun Ruan
- 1] Epithelial Cell Biology Research Center, Key Laboratory of Regenerative Medicine of Ministry of Education of China, CUHK-SJTU Joint Center for Human Reproduction and Related Disease, Faculty of Medicine, School of Biomedical Sciences, The Chinese University of Hong Kong, Hong Kong, China [2] Sichuan University-The Chinese University of Hong Kong Joint Laboratory for Reproductive Medicine, Key Laboratory of Obstetric, Gynecologic and Pediatric Diseases and Birth Defects of Ministry of Education of China, West China Second University Hospital, Sichuan University, Chengdu 610041, China [3] Lui Che Woo Institute of Innovative Medicine, Faculty of Medicine, The Chinese University of Hong Kong, Hong Kong, China
| | - Xue Lian Zhang
- Department of Endocrinology, Beijing Tongren Hospital, Capital Medical University, Beijing 100730, China
| | - Xiao Hu Zhang
- Epithelial Cell Biology Research Center, Key Laboratory of Regenerative Medicine of Ministry of Education of China, CUHK-SJTU Joint Center for Human Reproduction and Related Disease, Faculty of Medicine, School of Biomedical Sciences, The Chinese University of Hong Kong, Hong Kong, China
| | - Kin Lam Fok
- Epithelial Cell Biology Research Center, Key Laboratory of Regenerative Medicine of Ministry of Education of China, CUHK-SJTU Joint Center for Human Reproduction and Related Disease, Faculty of Medicine, School of Biomedical Sciences, The Chinese University of Hong Kong, Hong Kong, China
| | - Lai Ling Tsang
- Epithelial Cell Biology Research Center, Key Laboratory of Regenerative Medicine of Ministry of Education of China, CUHK-SJTU Joint Center for Human Reproduction and Related Disease, Faculty of Medicine, School of Biomedical Sciences, The Chinese University of Hong Kong, Hong Kong, China
| | - Mei Kuen Yu
- Epithelial Cell Biology Research Center, Key Laboratory of Regenerative Medicine of Ministry of Education of China, CUHK-SJTU Joint Center for Human Reproduction and Related Disease, Faculty of Medicine, School of Biomedical Sciences, The Chinese University of Hong Kong, Hong Kong, China
| | - Wen Qing Huang
- Epithelial Cell Biology Research Center, Key Laboratory of Regenerative Medicine of Ministry of Education of China, CUHK-SJTU Joint Center for Human Reproduction and Related Disease, Faculty of Medicine, School of Biomedical Sciences, The Chinese University of Hong Kong, Hong Kong, China
| | - Xiao Sun
- Epithelial Cell Biology Research Center, Key Laboratory of Regenerative Medicine of Ministry of Education of China, CUHK-SJTU Joint Center for Human Reproduction and Related Disease, Faculty of Medicine, School of Biomedical Sciences, The Chinese University of Hong Kong, Hong Kong, China
| | - Yiu Wa Chung
- Epithelial Cell Biology Research Center, Key Laboratory of Regenerative Medicine of Ministry of Education of China, CUHK-SJTU Joint Center for Human Reproduction and Related Disease, Faculty of Medicine, School of Biomedical Sciences, The Chinese University of Hong Kong, Hong Kong, China
| | - Xiaohua Jiang
- 1] Epithelial Cell Biology Research Center, Key Laboratory of Regenerative Medicine of Ministry of Education of China, CUHK-SJTU Joint Center for Human Reproduction and Related Disease, Faculty of Medicine, School of Biomedical Sciences, The Chinese University of Hong Kong, Hong Kong, China [2] Sichuan University-The Chinese University of Hong Kong Joint Laboratory for Reproductive Medicine, Key Laboratory of Obstetric, Gynecologic and Pediatric Diseases and Birth Defects of Ministry of Education of China, West China Second University Hospital, Sichuan University, Chengdu 610041, China [3] Lui Che Woo Institute of Innovative Medicine, Faculty of Medicine, The Chinese University of Hong Kong, Hong Kong, China
| | - Yoshiro Sohma
- Department of Pharmacology, Keio University School of Medicine, Shinjuku, Tokyo 160-8582, Japan
| | - Hsiao Chang Chan
- 1] Epithelial Cell Biology Research Center, Key Laboratory of Regenerative Medicine of Ministry of Education of China, CUHK-SJTU Joint Center for Human Reproduction and Related Disease, Faculty of Medicine, School of Biomedical Sciences, The Chinese University of Hong Kong, Hong Kong, China [2] Sichuan University-The Chinese University of Hong Kong Joint Laboratory for Reproductive Medicine, Key Laboratory of Obstetric, Gynecologic and Pediatric Diseases and Birth Defects of Ministry of Education of China, West China Second University Hospital, Sichuan University, Chengdu 610041, China [3] Lui Che Woo Institute of Innovative Medicine, Faculty of Medicine, The Chinese University of Hong Kong, Hong Kong, China
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49
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Wei S, Roessler BC, Chauvet S, Guo J, Hartman JL, Kirk KL. Conserved allosteric hot spots in the transmembrane domains of cystic fibrosis transmembrane conductance regulator (CFTR) channels and multidrug resistance protein (MRP) pumps. J Biol Chem 2014; 289:19942-57. [PMID: 24876383 DOI: 10.1074/jbc.m114.562116] [Citation(s) in RCA: 17] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [Key Words] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/18/2022] Open
Abstract
ATP-binding cassette (ABC) transporters are an ancient family of transmembrane proteins that utilize ATPase activity to move substrates across cell membranes. The ABCC subfamily of the ABC transporters includes active drug exporters (the multidrug resistance proteins (MRPs)) and a unique ATP-gated ion channel (cystic fibrosis transmembrane conductance regulator (CFTR)). The CFTR channel shares gating principles with conventional ligand-gated ion channels, but the allosteric network that couples ATP binding at its nucleotide binding domains (NBDs) with conformational changes in its transmembrane helices (TMs) is poorly defined. It is also unclear whether the mechanisms that govern CFTR gating are conserved with the thermodynamically distinct MRPs. Here we report a new class of gain of function (GOF) mutation of a conserved proline at the base of the pore-lining TM6. Multiple substitutions of this proline promoted ATP-free CFTR activity and activation by the weak agonist, 5'-adenylyl-β,γ-imidodiphosphate (AMP-PNP). TM6 proline mutations exhibited additive GOF effects when combined with a previously reported GOF mutation located in an outer collar of TMs that surrounds the pore-lining TMs. Each TM substitution allosterically rescued the ATP sensitivity of CFTR gating when introduced into an NBD mutant with defective ATP binding. Both classes of GOF mutations also rescued defective drug export by a yeast MRP (Yor1p) with ATP binding defects in its NBDs. We conclude that the conserved TM6 proline helps set the energy barrier to both CFTR channel opening and MRP-mediated drug efflux and that CFTR channels and MRP pumps utilize similar allosteric mechanisms for coupling conformational changes in their translocation pathways to ATP binding at their NBDs.
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Affiliation(s)
- Shipeng Wei
- From the Departments of Cell, Developmental, and Integrative Biology
| | - Bryan C Roessler
- From the Departments of Cell, Developmental, and Integrative Biology
| | - Sylvain Chauvet
- From the Departments of Cell, Developmental, and Integrative Biology
| | | | | | - Kevin L Kirk
- From the Departments of Cell, Developmental, and Integrative Biology, Neurobiology and the Gregory Fleming James Cystic Fibrosis Research Center, University of Alabama at Birmingham, Birmingham Alabama 35294-0005
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50
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Kopeikin Z, Yuksek Z, Yang HY, Bompadre SG. Combined effects of VX-770 and VX-809 on several functional abnormalities of F508del-CFTR channels. J Cyst Fibros 2014; 13:508-14. [PMID: 24796242 DOI: 10.1016/j.jcf.2014.04.003] [Citation(s) in RCA: 48] [Impact Index Per Article: 4.8] [Reference Citation Analysis] [Abstract] [Key Words] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/11/2014] [Accepted: 04/08/2014] [Indexed: 12/11/2022]
Abstract
BACKGROUND The most common cystic fibrosis-associated mutation, the deletion of phenylalanine 508 (F508del), results in channels with poor membrane expression and impaired function. VX-770, a clinically approved drug for treatment of CF patients carrying the G551D mutation, and VX-809, a corrector shown in vitro to increase membrane expression of mutant channels, are currently undergoing clinical trials, but functional data at the molecular level is still lacking. METHODS The effect of VX-770 and VX-809 on the multiple functional defects of F508del-CFTR was assessed via excised inside-out patch-clamp experiments. RESULTS VX-770 completely restores the low opening-rate of F508del-CFTR, with smaller open-time increase, in temperature-corrected and VX-809-treated channels. The shorter locked-open time of hydrolysis-deficient F508del-CFTR is also prolonged by VX-770. VX-809 does not improve channel function by itself as previously reported. CONCLUSIONS The results from these studies can be interpreted as an equilibrium shift toward the open-channel conformation of F508del-CFTR channels.
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Affiliation(s)
- Z Kopeikin
- Department of Physics and Astronomy, University of Missouri, Columbia, MO 65211, USA; Dalton Cardiovascular Research Center, University of Missouri, Columbia, MO 65211, USA
| | - Z Yuksek
- Department of Physics and Astronomy, University of Missouri, Columbia, MO 65211, USA; Dalton Cardiovascular Research Center, University of Missouri, Columbia, MO 65211, USA
| | - H-Y Yang
- Dalton Cardiovascular Research Center, University of Missouri, Columbia, MO 65211, USA
| | - S G Bompadre
- Department of Physics and Astronomy, University of Missouri, Columbia, MO 65211, USA; Dalton Cardiovascular Research Center, University of Missouri, Columbia, MO 65211, USA.
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