1
|
Thakur S, Ankita, Dash S, Verma R, Kaur C, Kumar R, Mazumder A, Singh G. Understanding CFTR Functionality: A Comprehensive Review of Tests and Modulator Therapy in Cystic Fibrosis. Cell Biochem Biophys 2024; 82:15-34. [PMID: 38048024 DOI: 10.1007/s12013-023-01200-w] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/11/2023] [Accepted: 11/13/2023] [Indexed: 12/05/2023]
Abstract
Cystic fibrosis is a genetic disorder inherited in an autosomal recessive manner. It is caused by a mutation in the Cystic Fibrosis Transmembrane Conductance Regulator (CFTR) gene on chromosome 7, which leads to abnormal regulation of chloride and bicarbonate ions in cells that line organs like the lungs and pancreas. The CFTR protein plays a crucial role in regulating chloride ion flow, and its absence or malfunction causes the production of thick mucus that affects several organs. There are more than 2000 identified mutations that are classified into seven categories based on their dysfunction mechanisms. In this article, we have conducted a thorough examination and consolidation of the diverse array of tests essential for the quantification of CFTR functionality. Furthermore, we have engaged in a comprehensive discourse regarding the recent advancements in CFTR modulator therapy, a pivotal approach utilized for the management of cystic fibrosis, alongside its concomitant relevance in evaluating CFTR functionality.
Collapse
Affiliation(s)
- Shorya Thakur
- School of Pharmaceutical Sciences, Lovely Professional University, Phagwara, Panjab, India
| | - Ankita
- School of Pharmaceutical Sciences, Lovely Professional University, Phagwara, Panjab, India
| | - Shubham Dash
- School of Pharmaceutical Sciences, Lovely Professional University, Phagwara, Panjab, India
| | - Rupali Verma
- School of Pharmaceutical Sciences, Lovely Professional University, Phagwara, Panjab, India
| | - Charanjit Kaur
- School of Pharmaceutical Sciences, Lovely Professional University, Phagwara, Panjab, India
| | - Rajesh Kumar
- School of Pharmaceutical Sciences, Lovely Professional University, Phagwara, Panjab, India
| | - Avijit Mazumder
- Noida Institute of Engineering and Technology (Pharmacy Institute), Greater Noida, UP, India
| | - Gurvinder Singh
- School of Pharmaceutical Sciences, Lovely Professional University, Phagwara, Panjab, India.
| |
Collapse
|
2
|
Galles GD, Infield DT, Clark CJ, Hemshorn ML, Manikandan S, Fazan F, Rasouli A, Tajkhorshid E, Galpin JD, Cooley RB, Mehl RA, Ahern CA. Tuning phenylalanine fluorination to assess aromatic contributions to protein function and stability in cells. Nat Commun 2023; 14:59. [PMID: 36599844 PMCID: PMC9813137 DOI: 10.1038/s41467-022-35761-w] [Citation(s) in RCA: 4] [Impact Index Per Article: 4.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/13/2022] [Accepted: 12/27/2022] [Indexed: 01/05/2023] Open
Abstract
The aromatic side-chains of phenylalanine, tyrosine, and tryptophan interact with their environments via both hydrophobic and electrostatic interactions. Determining the extent to which these contribute to protein function and stability is not possible with conventional mutagenesis. Serial fluorination of a given aromatic is a validated method in vitro and in silico to specifically alter electrostatic characteristics, but this approach is restricted to a select few experimental systems. Here, we report a group of pyrrolysine-based aminoacyl-tRNA synthetase/tRNA pairs (tRNA/RS pairs) that enable the site-specific encoding of a varied spectrum of fluorinated phenylalanine amino acids in E. coli and mammalian (HEK 293T) cells. By allowing the cross-kingdom expression of proteins bearing these unnatural amino acids at biochemical scale, these tools may potentially enable the study of biological mechanisms which utilize aromatic interactions in structural and cellular contexts.
Collapse
Affiliation(s)
- Grace D Galles
- Department of Molecular Physiology and Biophysics, University of Iowa College of Medicine, Iowa City, IA, USA
- The GCE4All Research Center, Department of Biochemistry & Biophysics, Oregon State University, Corvallis, OR, USA
| | - Daniel T Infield
- Department of Molecular Physiology and Biophysics, University of Iowa College of Medicine, Iowa City, IA, USA
| | - Colin J Clark
- Department of Molecular Physiology and Biophysics, University of Iowa College of Medicine, Iowa City, IA, USA
| | - Marcus L Hemshorn
- The GCE4All Research Center, Department of Biochemistry & Biophysics, Oregon State University, Corvallis, OR, USA
| | - Shivani Manikandan
- Department of Molecular Physiology and Biophysics, University of Iowa College of Medicine, Iowa City, IA, USA
| | - Frederico Fazan
- Department of Molecular Physiology and Biophysics, University of Iowa College of Medicine, Iowa City, IA, USA
| | - Ali Rasouli
- Theoretical and Computational Biophysics Group, NIH Center for Macromolecular Modeling and Bioinformatics, Beckman Institute for Advanced Science and Technology, University of Illinois at Urbana-Champaign, Urbana, IL, USA
| | - Emad Tajkhorshid
- Theoretical and Computational Biophysics Group, NIH Center for Macromolecular Modeling and Bioinformatics, Beckman Institute for Advanced Science and Technology, University of Illinois at Urbana-Champaign, Urbana, IL, USA
| | - Jason D Galpin
- Department of Molecular Physiology and Biophysics, University of Iowa College of Medicine, Iowa City, IA, USA
| | - Richard B Cooley
- The GCE4All Research Center, Department of Biochemistry & Biophysics, Oregon State University, Corvallis, OR, USA
| | - Ryan A Mehl
- The GCE4All Research Center, Department of Biochemistry & Biophysics, Oregon State University, Corvallis, OR, USA
| | - Christopher A Ahern
- Department of Molecular Physiology and Biophysics, University of Iowa College of Medicine, Iowa City, IA, USA.
| |
Collapse
|
3
|
Raraigh KS, Paul KC, Goralski JL, Worthington EN, Faino AV, Sciortino S, Wang Y, Aksit MA, Ling H, Osorio DL, Onchiri FM, Patel SU, Merlo CA, Montemayor K, Gibson RL, West NE, Thakerar A, Bridges RJ, Sheppard DN, Sharma N, Cutting GR. CFTR bearing variant p.Phe312del exhibits function inconsistent with phenotype and negligible response to ivacaftor. JCI Insight 2022; 7:148841. [PMID: 35315358 PMCID: PMC8986068 DOI: 10.1172/jci.insight.148841] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/19/2021] [Accepted: 02/09/2022] [Indexed: 11/17/2022] Open
Abstract
The chloride channel dysfunction caused by deleterious cystic fibrosis transmembrane conductance regulator (CFTR) variants generally correlates with severity of cystic fibrosis (CF). However, 3 adults bearing the common severe variant p.Phe508del (legacy: F508del) and a deletion variant in an ivacaftor binding region of CFTR (p.Phe312del; legacy: F312del) manifested only elevated sweat chloride concentration (sw[Cl-]; 87-105 mEq/L). A database review of 25 individuals with F312del and a CF-causing variant revealed elevated sw[Cl-] (75-123 mEq/L) and variable CF features. F312del occurs at a higher-than-expected frequency in the general population, confirming that individuals with F312del and a CF-causing variant do not consistently develop overt CF features. In primary nasal cells, CFTR bearing F312del and F508del generated substantial chloride transport (66.0% ± 4.5% of WT-CFTR) but did not respond to ivacaftor. Single-channel analysis demonstrated that F312del did not affect current flow through CFTR, minimally altered gating, and ablated the ivacaftor response. When expressed stably in CF bronchial epithelial (CFBE41o-) cells, F312del-CFTR demonstrated residual function (50.9% ± 3.3% WT-CFTR) and a subtle decrease in forskolin response compared with WT-CFTR. F312del provides an exception to the established correlation between CFTR chloride transport and CF phenotype and informs our molecular understanding of ivacaftor response.
Collapse
Affiliation(s)
| | | | - Jennifer L Goralski
- University of North Carolina at Chapel Hill, Chapel Hill, North Carolina, USA
| | - Erin N Worthington
- University of North Carolina at Chapel Hill, Chapel Hill, North Carolina, USA
| | - Anna V Faino
- Seattle Children's Research Institute, Seattle, Washington, USA
| | - Stanley Sciortino
- California Department of Public Health, Genetic Disease Screening Program, Richmond, California, USA
| | - Yiting Wang
- University of Bristol, Bristol, United Kingdom
| | | | - Hua Ling
- Johns Hopkins University, Baltimore, Maryland, USA
| | | | | | | | | | | | | | | | - Amita Thakerar
- Rosalind Franklin University of Medicine and Science, Center for Genetic Diseases, North Chicago, Illinois, USA
| | - Robert J Bridges
- Rosalind Franklin University of Medicine and Science, Center for Genetic Diseases, North Chicago, Illinois, USA
| | | | | | | |
Collapse
|
4
|
Assays of CFTR Function In Vitro, Ex Vivo and In Vivo. Int J Mol Sci 2022; 23:ijms23031437. [PMID: 35163362 PMCID: PMC8836180 DOI: 10.3390/ijms23031437] [Citation(s) in RCA: 13] [Impact Index Per Article: 6.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/23/2021] [Revised: 01/12/2022] [Accepted: 01/21/2022] [Indexed: 12/22/2022] Open
Abstract
Cystic fibrosis, a multi-organ genetic disease, is characterized by abnormal function of the cystic fibrosis transmembrane conductance regulator (CFTR) protein, a chloride channel at the apical membrane of several epithelia. In recent years, therapeutic strategies have been developed to correct the CFTR defect. To evaluate CFTR function at baseline for diagnosis, or the efficacy of CFTR-restoring therapy, reliable tests are needed to measure CFTR function, in vitro, ex vivo and in vivo. In vitro techniques either directly or indirectly measure ion fluxes; direct measurement of ion fluxes and quenching of fluorescence in cell-based assays, change in transmembrane voltage or current in patch clamp or Ussing chamber, swelling of CFTR-containing organoids by secondary water influx upon CFTR activation. Several cell or tissue types can be used. Ex vivo and in vivo assays similarly evaluate current (intestinal current measurement) and membrane potential differences (nasal potential difference), on tissues from individual patients. In the sweat test, the most frequently used in vivo evaluation of CFTR function, chloride concentration or stimulated sweat rate can be directly measured. Here, we will describe the currently available bio-assays for quantitative evaluation of CFTR function, their indications, advantages and disadvantages, and correlation with clinical outcome measures.
Collapse
|
5
|
Liu J, Berg AP, Wang Y, Jantarajit W, Sutcliffe KJ, Stevens EB, Cao L, Pregel MJ, Sheppard DN. A small molecule CFTR potentiator restores ATP-dependent channel gating to the cystic fibrosis mutant G551D-CFTR. Br J Pharmacol 2021; 179:1319-1337. [PMID: 34644413 PMCID: PMC9304199 DOI: 10.1111/bph.15709] [Citation(s) in RCA: 6] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/18/2021] [Accepted: 08/30/2021] [Indexed: 11/29/2022] Open
Abstract
BACKGROUND AND PURPOSE Cystic fibrosis transmembrane conductance regulator (CFTR) potentiators are small molecules developed to treat the genetic disease cystic fibrosis (CF). They interact directly with CFTR Cl- channels at the plasma membrane to enhance channel gating. Here, we investigate the action of a new CFTR potentiator, CP-628006 with a distinct chemical structure. EXPERIMENTAL APPROACH Using electrophysiological assays with CFTR-expressing heterologous cells and CF patient-derived human bronchial epithelial (hBE) cells, we compared the effects of CP-628006 with the marketed CFTR potentiator ivacaftor. KEY RESULTS CP-628006 efficaciously potentiated CFTR function in epithelia from cultured hBE cells. Its effects on the predominant CFTR variant F508del-CFTR were larger than those with the gating variant G551D-CFTR. In excised inside-out membrane patches, CP-628006 potentiated wild-type, F508del- and G551D-CFTR by increasing the frequency and duration of channel openings. CP-628006 increased the affinity and efficacy of F508del-CFTR gating by ATP. In these respects, CP-628006 behaved like ivacaftor. CP-628006 also demonstrated notable differences with ivacaftor. Its potency and efficacy were lower than those of ivacaftor. CP-628006 conferred ATP-dependent gating on G551D-CFTR, whereas the action of ivacaftor was ATP-independent. For G551D-CFTR, but not F508del-CFTR, the action of CP-628006 plus ivacaftor was greater than ivacaftor alone. CP-628006 delayed, but did not prevent, the deactivation of F508del-CFTR at the plasma membrane, whereas ivacaftor accentuated F508del-CFTR deactivation. CONCLUSIONS AND IMPLICATIONS CP-628006 has distinct effects compared to ivacaftor, suggesting a different mechanism of CFTR potentiation. The emergence of CFTR potentiators with diverse modes of action makes therapy with combinations of potentiators a possibility.
Collapse
Affiliation(s)
- Jia Liu
- Neuroscience and Pain Research Unit, Pfizer Inc., Granta Park, Great Abington, Cambridge, UK.,School of Physiology, Pharmacology and Neuroscience, University of Bristol, Biomedical Sciences Building, University Walk, Bristol, UK
| | - Allison P Berg
- Rare Disease Research Unit, Pfizer Inc., Cambridge, MA, USA
| | - Yiting Wang
- School of Physiology, Pharmacology and Neuroscience, University of Bristol, Biomedical Sciences Building, University Walk, Bristol, UK
| | - Walailak Jantarajit
- School of Physiology, Pharmacology and Neuroscience, University of Bristol, Biomedical Sciences Building, University Walk, Bristol, UK.,Center of Calcium and Bone Research and Department of Physiology, Faculty of Science, Mahidol University, Bangkok, Thailand
| | - Katy J Sutcliffe
- School of Physiology, Pharmacology and Neuroscience, University of Bristol, Biomedical Sciences Building, University Walk, Bristol, UK
| | - Edward B Stevens
- Neuroscience and Pain Research Unit, Pfizer Inc., Granta Park, Great Abington, Cambridge, UK
| | - Lishuang Cao
- Neuroscience and Pain Research Unit, Pfizer Inc., Granta Park, Great Abington, Cambridge, UK
| | - Marko J Pregel
- Rare Disease Research Unit, Pfizer Inc., Cambridge, MA, USA
| | - David N Sheppard
- School of Physiology, Pharmacology and Neuroscience, University of Bristol, Biomedical Sciences Building, University Walk, Bristol, UK
| |
Collapse
|
6
|
Fortea E, Accardi A. A quantitative flux assay for the study of reconstituted Cl - channels and transporters. Methods Enzymol 2021; 652:243-272. [PMID: 34059284 DOI: 10.1016/bs.mie.2021.01.026] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Key Words] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/22/2022]
Abstract
The recent deluge of high-resolution structural information on membrane proteins has not been accompanied by a comparable increase in our ability to functionally interrogate these proteins. Current functional assays often are not quantitative or are performed in conditions that significantly differ from those used in structural experiments, thus limiting the mechanistic correspondence between structural and functional experiments. A flux assay to determine quantitatively the functional properties of purified and reconstituted Cl- channels and transporters in membranes of defined lipid compositions is described. An ion-sensitive electrode is used to measure the rate of Cl- efflux from proteoliposomes reconstituted with the desired protein and the fraction of vesicles containing at least one active protein. These measurements enable the quantitative determination of key molecular parameters such as the unitary transport rate, the fraction of proteins that are active, and the molecular mass of the transport protein complex. The approach is illustrated using CLC-ec1, a CLC-type H+/Cl- exchanger as an example. The assay enables the quantitative study of a wide range of Cl- transporting molecules and proteins whose activity is modulated by ligands, voltage, and membrane composition as well as the investigation of the effects of compounds that directly inhibit or activate the reconstituted transport systems. The present assay is readily adapted to the study of transport systems with diverse substrate specificities and molecular characteristics, and the necessary modifications needed are discussed.
Collapse
Affiliation(s)
- Eva Fortea
- Department of Physiology and Biophysics, Weill Cornell Medical College, New York, NY, United States
| | - Alessio Accardi
- Department of Physiology and Biophysics, Weill Cornell Medical College, New York, NY, United States; Department of Anesthesiology, Weill Cornell Medical College, New York, NY, United States; Department of Biochemistry, Weill Cornell Medical College, New York, NY, United States.
| |
Collapse
|
7
|
Meng X, Clews J, Ciuta AD, Martin ER, Ford RC. CFTR structure, stability, function and regulation. Biol Chem 2020; 400:1359-1370. [PMID: 30738013 DOI: 10.1515/hsz-2018-0470] [Citation(s) in RCA: 8] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/19/2018] [Accepted: 01/30/2019] [Indexed: 12/15/2022]
Abstract
Cystic fibrosis transmembrane conductance regulator (CFTR) is a unique member of the ATP-binding cassette family of proteins because it has evolved into a channel. Mutations in CFTR cause cystic fibrosis, the most common genetic disease in people of European origin. The F508del mutation is found in about 90% of patients and here we present data that suggest its main effect is on CFTR stability rather than on the three-dimensional (3D) folded state. A survey of recent cryo-electron microscopy studies was carried out and this highlighted differences in terms of CFTR conformation despite similarities in experimental conditions. We further studied CFTR structure under various phosphorylation states and with the CFTR-interacting protein NHERF1. The coexistence of outward-facing and inward-facing conformations under a range of experimental conditions was suggested from these data. These results are discussed in terms of structural models for channel gating, and favour the model where the mostly disordered regulatory-region of the protein acts as a channel plug.
Collapse
Affiliation(s)
- Xin Meng
- School of Biological Sciences, Faculty of Biology Medicine and Health, Michael Smith Building, The University of Manchester, Oxford Road, Manchester M13 9PL, UK
| | - Jack Clews
- School of Biological Sciences, Faculty of Biology Medicine and Health, Michael Smith Building, The University of Manchester, Oxford Road, Manchester M13 9PL, UK
| | - Anca D Ciuta
- School of Biological Sciences, Faculty of Biology Medicine and Health, Michael Smith Building, The University of Manchester, Oxford Road, Manchester M13 9PL, UK
| | - Eleanor R Martin
- School of Biological Sciences, Faculty of Biology Medicine and Health, Michael Smith Building, The University of Manchester, Oxford Road, Manchester M13 9PL, UK
| | - Robert C Ford
- School of Biological Sciences, Faculty of Biology Medicine and Health, Michael Smith Building, The University of Manchester, Oxford Road, Manchester M13 9PL, UK
| |
Collapse
|
8
|
Berg A, Hallowell S, Tibbetts M, Beasley C, Brown-Phillips T, Healy A, Pustilnik L, Doyonnas R, Pregel M. High-Throughput Surface Liquid Absorption and Secretion Assays to Identify F508del CFTR Correctors Using Patient Primary Airway Epithelial Cultures. SLAS DISCOVERY 2019; 24:724-737. [PMID: 31107611 DOI: 10.1177/2472555219849375] [Citation(s) in RCA: 13] [Impact Index Per Article: 2.6] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 11/16/2022]
Abstract
High-throughput screening for drug discovery is increasingly utilizing cellular systems of high physiological relevance, such as patient primary cells and organoid cultures. We used 3D-cultured cystic fibrosis patient bronchial epithelial cells to screen for new small-molecule correctors of the disease-causing F508del mutation in CFTR. Impaired mucociliary clearance due to insufficient airway hydration is a hallmark of cystic fibrosis and we used a simple measure of surface liquid levels to quantify F508del CFTR correction in cultured bronchial epithelial cells. Two robust assay formats were configured and used to screen more than 100,000 compounds as mixtures or individual compounds in 96-well format. The corrector discovery success rate, as measured by the number of hits confirmed by an electrophysiology assay on patient primary bronchial epithelial cells, was superior to screens in cell lines expressing recombinant F508del CFTR. Several novel corrector scaffolds were discovered that when combined with the clinical corrector VX-809 delivered combination responses greater than double that of VX-809 alone. This work exemplifies the advantages of a disease-relevant readout and 3D-cultured patient primary cells for the discovery of new drug candidates.
Collapse
Affiliation(s)
- Allison Berg
- 1 Rare Disease Research, Pfizer Inc., Cambridge, MA, USA
| | - Shawn Hallowell
- 2 Primary Pharmacology Group, Medicine Design, Pfizer Inc., Groton, CT, USA
| | - Mark Tibbetts
- 2 Primary Pharmacology Group, Medicine Design, Pfizer Inc., Groton, CT, USA
| | - Chad Beasley
- 2 Primary Pharmacology Group, Medicine Design, Pfizer Inc., Groton, CT, USA
| | | | - Anita Healy
- 2 Primary Pharmacology Group, Medicine Design, Pfizer Inc., Groton, CT, USA
| | - Leslie Pustilnik
- 2 Primary Pharmacology Group, Medicine Design, Pfizer Inc., Groton, CT, USA
| | - Regis Doyonnas
- 2 Primary Pharmacology Group, Medicine Design, Pfizer Inc., Groton, CT, USA
| | - Marko Pregel
- 1 Rare Disease Research, Pfizer Inc., Cambridge, MA, USA
| |
Collapse
|
9
|
Abstract
Cystic fibrosis transmembrane conductance regulator (CFTR) is an anion channel expressed in the apical membrane of epithelia. Mutations in the CFTR gene are the cause of cystsic fibrosis. CFTR is the only ABC-protein that constitutes an ion channel pore forming subunit. CFTR gating is regulated in complex manner as phosphorylation is mandatory for channel activity and gating is directly regulated by binding of ATP to specific intracellular sites on the CFTR protein. This review covers our current understanding on the gating mechanism in CFTR and illustrates the relevance of alteration of these mechanisms in the onset of cystic fibrosis.
Collapse
Affiliation(s)
- Oscar Moran
- Istituto di Biofisica, CNR. Via De Marini, 6, 16149, Genoa, Italy.
| |
Collapse
|
10
|
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: 27] [Impact Index Per Article: 3.4] [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.
Collapse
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.)
| |
Collapse
|
11
|
Eckford PDW, Li C, Bear CE. Functional reconstitution and channel activity measurements of purified wildtype and mutant CFTR protein. J Vis Exp 2015:52427. [PMID: 25867140 PMCID: PMC4401239 DOI: 10.3791/52427] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/19/2023] Open
Abstract
The Cystic Fibrosis Transmembrane Conductance Regulator (CFTR) is a unique channel-forming member of the ATP Binding Cassette (ABC) superfamily of transporters. The phosphorylation and nucleotide dependent chloride channel activity of CFTR has been frequently studied in whole cell systems and as single channels in excised membrane patches. Many Cystic Fibrosis-causing mutations have been shown to alter this activity. While a small number of purification protocols have been published, a fast reconstitution method that retains channel activity and a suitable method for studying population channel activity in a purified system have been lacking. Here rapid methods are described for purification and functional reconstitution of the full-length CFTR protein into proteoliposomes of defined lipid composition that retains activity as a regulated halide channel. This reconstitution method together with a novel flux-based assay of channel activity is a suitable system for studying the population channel properties of wild type CFTR and the disease-causing mutants F508del- and G551D-CFTR. Specifically, the method has utility in studying the direct effects of phosphorylation, nucleotides and small molecules such as potentiators and inhibitors on CFTR channel activity. The methods are also amenable to the study of other membrane channels/transporters for anionic substrates.
Collapse
Affiliation(s)
- Paul D W Eckford
- Programme in Molecular Structure and Function, Hospital for Sick Children
| | - Canhui Li
- Programme in Molecular Structure and Function, Hospital for Sick Children
| | - Christine E Bear
- Programme in Molecular Structure and Function, Hospital for Sick Children; Department of Biochemistry, University of Toronto; Department of Physiology, University of Toronto;
| |
Collapse
|