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Levring J, Chen J. Structural identification of a selectivity filter in CFTR. Proc Natl Acad Sci U S A 2024; 121:e2316673121. [PMID: 38381791 PMCID: PMC10907310 DOI: 10.1073/pnas.2316673121] [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: 09/25/2023] [Accepted: 01/19/2024] [Indexed: 02/23/2024] Open
Abstract
The cystic fibrosis transmembrane conductance regulator (CFTR) is a chloride channel that regulates transepithelial salt and fluid homeostasis. CFTR dysfunction leads to reduced chloride secretion into the mucosal lining of epithelial tissues, thereby causing the inherited disease cystic fibrosis. Although several structures of CFTR are available, our understanding of the ion-conduction pathway is incomplete. In particular, the route that connects the cytosolic vestibule with the extracellular space has not been clearly defined, and the structure of the open pore remains elusive. Furthermore, although many residues have been implicated in altering the selectivity of CFTR, the structure of the "selectivity filter" has yet to be determined. In this study, we identify a chloride-binding site at the extracellular ends of transmembrane helices 1, 6, and 8, where a dehydrated chloride is coordinated by residues G103, R334, F337, T338, and Y914. Alterations to this site, consistent with its function as a selectivity filter, affect ion selectivity, conductance, and open channel block. This selectivity filter is accessible from the cytosol through a large inner vestibule and opens to the extracellular solvent through a narrow portal. The identification of a chloride-binding site at the intra- and extracellular bridging point leads us to propose a complete conductance path that permits dehydrated chloride ions to traverse the lipid bilayer.
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Affiliation(s)
- Jesper Levring
- Laboratory of Membrane Biology and Biophysics, The Rockefeller University, New York, NY10065
| | - Jue Chen
- Laboratory of Membrane Biology and Biophysics, The Rockefeller University, New York, NY10065
- HHMI, The Rockefeller University, New York, NY10065
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2
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Linsdell P. Role of Hydrophobic Amino-Acid Side-Chains in the Narrow Selectivity Filter of the CFTR Chloride Channel Pore in Conductance and Selectivity. J Membr Biol 2023; 256:433-442. [PMID: 37823914 DOI: 10.1007/s00232-023-00294-w] [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: 04/26/2023] [Accepted: 09/26/2023] [Indexed: 10/13/2023]
Abstract
Cystic fibrosis is caused by mutations in the cystic fibrosis transmembrane conductance regulator (CFTR) anion channel. Structural analysis of CFTR has identified a narrow, hydrophobic region close to the extracellular end of the open channel pore that may function as a selectivity filter. The present study combines comprehensive mutagenesis of hydrophobic amino-acid side-chains within the selectivity filter with functional evaluation of channel Cl- conductance and anion selectivity. Among these hydrophobic amino-acids, one (F337) appears to play a dominant role in determining both conductance and selectivity. Anion selectivity appears to depend on both side-chain size and hydrophobicity at this position. In contrast, conductance is disrupted by all F337 mutations, suggesting that unique interactions between permeating Cl- ions and the native phenylalanine side-chain are important for conductance. Surprisingly, a positively charged lysine side-chain can be substituted for several hydrophobic residues within the selectivity filter (including F337) with only minor changes in pore function, arguing against a crucial role for overall hydrophobicity. These results suggest that localized interactions between permeating anions and amino-acid side-chains within the selectivity filter may be more important in determining pore functional properties than are global features such as overall hydrophobicity.
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Affiliation(s)
- Paul Linsdell
- Department of Physiology & Biophysics, Dalhousie University, PO Box 15000, Halifax, NS, B3H 4R2, Canada.
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3
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Kleizen B, de Mattos E, Papaioannou O, Monti M, Tartaglia GG, van der Sluijs P, Braakman I. Transmembrane Helices 7 and 8 Confer Aggregation Sensitivity to the Cystic Fibrosis Transmembrane Conductance Regulator. Int J Mol Sci 2023; 24:15741. [PMID: 37958724 PMCID: PMC10648718 DOI: 10.3390/ijms242115741] [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: 09/04/2023] [Revised: 10/18/2023] [Accepted: 10/19/2023] [Indexed: 11/15/2023] Open
Abstract
The Cystic Fibrosis Transmembrane Conductance Regulator (CFTR) is a large multi-spanning membrane protein that is susceptible to misfolding and aggregation. We have identified here the region responsible for this instability. Temperature-induced aggregation of C-terminally truncated versions of CFTR demonstrated that all truncations up to the second transmembrane domain (TMD2), including the R region, largely resisted aggregation. Limited proteolysis identified a folded structure that was prone to aggregation and consisted of TMD2 and at least part of the Regulatory Region R. Only when both TM7 (TransMembrane helix 7) and TM8 were present, TMD2 fragments became as aggregation-sensitive as wild-type CFTR, in line with increased thermo-instability of late CFTR nascent chains and in silico prediction of aggregation propensity. In accord, isolated TMD2 was degraded faster in cells than isolated TMD1. We conclude that TMD2 extended at its N-terminus with part of the R region forms a protease-resistant structure that induces heat instability in CFTR and may be responsible for its limited intracellular stability.
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Affiliation(s)
- Bertrand Kleizen
- Cellular Protein Chemistry, Bijvoet Centre for Biomolecular Research, Utrecht University, 3584 CH Utrecht, The Netherlands; (B.K.); (E.d.M.); (O.P.); (P.v.d.S.)
| | - Eduardo de Mattos
- Cellular Protein Chemistry, Bijvoet Centre for Biomolecular Research, Utrecht University, 3584 CH Utrecht, The Netherlands; (B.K.); (E.d.M.); (O.P.); (P.v.d.S.)
| | - Olga Papaioannou
- Cellular Protein Chemistry, Bijvoet Centre for Biomolecular Research, Utrecht University, 3584 CH Utrecht, The Netherlands; (B.K.); (E.d.M.); (O.P.); (P.v.d.S.)
| | - Michele Monti
- Center for Life Nano- & Neuro-Science, Fondazione Istituto Italiano di Tecnologia (IIT), 00161 Rome, Italy; (M.M.); (G.G.T.)
- Centre for Human Technologies (CHT), Istituto Italiano di Tecnologia (IIT), 16152 Genoa, Italy
| | - Gian Gaetano Tartaglia
- Center for Life Nano- & Neuro-Science, Fondazione Istituto Italiano di Tecnologia (IIT), 00161 Rome, Italy; (M.M.); (G.G.T.)
- Centre for Human Technologies (CHT), Istituto Italiano di Tecnologia (IIT), 16152 Genoa, Italy
| | - Peter van der Sluijs
- Cellular Protein Chemistry, Bijvoet Centre for Biomolecular Research, Utrecht University, 3584 CH Utrecht, The Netherlands; (B.K.); (E.d.M.); (O.P.); (P.v.d.S.)
| | - Ineke Braakman
- Cellular Protein Chemistry, Bijvoet Centre for Biomolecular Research, Utrecht University, 3584 CH Utrecht, The Netherlands; (B.K.); (E.d.M.); (O.P.); (P.v.d.S.)
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4
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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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5
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Zeng ZW, Linsdell P, Pomès R. Molecular dynamics study of Cl - permeation through cystic fibrosis transmembrane conductance regulator (CFTR). Cell Mol Life Sci 2023; 80:51. [PMID: 36694009 PMCID: PMC9873711 DOI: 10.1007/s00018-022-04621-7] [Citation(s) in RCA: 3] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/31/2021] [Revised: 10/26/2022] [Accepted: 10/31/2022] [Indexed: 01/25/2023]
Abstract
The recent elucidation of atomistic structures of Cl- channel CFTR provides opportunities for understanding the molecular basis of cystic fibrosis. Despite having been activated through phosphorylation and provided with ATP ligands, several near-atomistic cryo-EM structures of CFTR are in a closed state, as inferred from the lack of a continuous passage through a hydrophobic bottleneck region located in the extracellular portion of the pore. Here, we present repeated, microsecond-long molecular dynamics simulations of human CFTR solvated in a lipid bilayer and aqueous NaCl. At equilibrium, Cl- ions enter the channel through a lateral intracellular portal and bind to two distinct cationic sites inside the channel pore but do not traverse the narrow, de-wetted bottleneck. Simulations conducted in the presence of a strong hyperpolarizing electric field led to spontaneous Cl- translocation events through the bottleneck region of the channel, suggesting that the protein relaxed to a functionally open state. Conformational changes of small magnitude involving transmembrane helices 1 and 6 preceded ion permeation through diverging exit routes at the extracellular end of the pore. The pore bottleneck undergoes wetting prior to Cl- translocation, suggesting that it acts as a hydrophobic gate. Although permeating Cl- ions remain mostly hydrated, partial dehydration occurs at the binding sites and in the bottleneck. The observed Cl- pathway is largely consistent with the loci of mutations that alter channel conductance, anion binding, and ion selectivity, supporting the model of the open state of CFTR obtained in the present study.
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Affiliation(s)
- Zhi Wei Zeng
- Molecular Medicine, Hospital for Sick Children, 686 Bay Street, Toronto, ON, M5G 0A4, Canada
- Department of Biochemistry, University of Toronto, Toronto, ON, M5S 1A8, Canada
| | - Paul Linsdell
- Department of Physiology and Biophysics, Dalhousie University, PO Box 15000, Halifax, NS, B3H 1X5, Canada
| | - Régis Pomès
- Molecular Medicine, Hospital for Sick Children, 686 Bay Street, Toronto, ON, M5G 0A4, Canada.
- Department of Biochemistry, University of Toronto, Toronto, ON, M5S 1A8, Canada.
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Yang J, Wang MJ, Huang WJ, Zhou Q, Ying X, Tian YH, Zhu YM, Lu YC. High expression of CFTR in cumulus cells from mature oocytes is associated with high-quality of oocyte and subsequent embryonic development. J Assist Reprod Genet 2022; 39:2239-2247. [PMID: 36044164 PMCID: PMC9596676 DOI: 10.1007/s10815-022-02599-6] [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: 03/14/2022] [Accepted: 08/18/2022] [Indexed: 11/28/2022] Open
Abstract
OBJECTIVE The purpose of this study was to explore the association of expression of cystic fibrosis transmembrane conductance regulator (CFTR) in cumulus cells (CCs) from mature oocytes with oocyte quality and embryonic development. METHODS A total of 338 infertile women who underwent ovarian stimulation cycle of oocyte retrieval in Zhejiang University School of Medicine were retrospectively enrolled in this study. The relative mRNA expression levels of CFTR, bone morphogenetic protein 15 (BMP15), and growth differentiation factor 9 (GDF9) in CCs were detected by qPCR technology. ROC curve was applied for the diagnosis of oocyte maturation. The serum levels of anti-Müllerian hormone (AMH), E2, follicle-stimulating hormone (FSH), luteinizing hormone (LH), and androstenedione were measured. Oocyte maturation rate, fertilization rate, cleavage rate, high-quality embryo formation rate, and implantation rate after embryo transfer were also determined. RESULTS The mRNA expression levels of CFTR in CCs were significantly increased in metaphase II (MII) oocytes compared to that in metaphase I (MI) or germinal vesicle (GV) oocytes. The ROC curve analysis illustrated that CFTR mRNA expression could efficiently discriminate MII oocytes from MI or GV oocytes (AUC = 0.954), and revealed that 0.695 RQU is the optimal cut-off value for diagnosis. So the cut-off value of 2-ΔΔCT = 0.70 was used to divide the patients into two groups: low- (n = 114) and high-CFTR group (n = 224). The mRNA expression of CFTR in CCs was positively correlated with the antral follicular count (AFC), number of oocytes retrieved, number of MII oocytes, serum E2 level on hCG day, and BMP15 and GDF9 expression in CCs. Under continuous stimulation with the same dose of recombinant follicle-stimulating hormone (rFSH), the number of follicles, average recovered oocytes, recovered oocytes, MII oocytes, as well as the oocyte recovery rate, fertilization rate, oocyte cleavage rate, high-quality embryo formation rate, and implantation rate were decreased in patients with lower CFTR. CONCLUSIONS This study suggests that CFTR expression in CCs is associated with the developmental potential of human oocytes.
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Affiliation(s)
- Jing Yang
- Department of Reproductive Endocrinology, Women's Hospital, Zhejiang University School of Medicine, 1 Xueshi Road, Hangzhou, 310006, Zhejiang, China
- Department of Assisted Reproduction, Shanghai Ninth People's Hospital, Shanghai Jiaotong University School of Medicine, Shanghai, 200011, China
| | - Ming-Juan Wang
- Department of Reproductive Endocrinology, Women's Hospital, Zhejiang University School of Medicine, 1 Xueshi Road, Hangzhou, 310006, Zhejiang, China
| | - Wen-Jie Huang
- Department of Reproductive Endocrinology, Women's Hospital, Zhejiang University School of Medicine, 1 Xueshi Road, Hangzhou, 310006, Zhejiang, China
| | - Qian Zhou
- Department of Reproductive Endocrinology, Women's Hospital, Zhejiang University School of Medicine, 1 Xueshi Road, Hangzhou, 310006, Zhejiang, China
| | - Xue Ying
- Department of Reproductive Endocrinology, Women's Hospital, Zhejiang University School of Medicine, 1 Xueshi Road, Hangzhou, 310006, Zhejiang, China
| | - Yong-Hong Tian
- Department of Reproductive Endocrinology, Women's Hospital, Zhejiang University School of Medicine, 1 Xueshi Road, Hangzhou, 310006, Zhejiang, China
| | - Yi-Min Zhu
- Department of Reproductive Endocrinology, Women's Hospital, Zhejiang University School of Medicine, 1 Xueshi Road, Hangzhou, 310006, Zhejiang, China.
| | - Yong-Chao Lu
- Department of Reproductive Endocrinology, Women's Hospital, Zhejiang University School of Medicine, 1 Xueshi Road, Hangzhou, 310006, Zhejiang, China.
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7
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Molecular mechanisms of Cystic Fibrosis - how mutations lead to misfunction and guide therapy. Biosci Rep 2022; 42:231430. [PMID: 35707985 PMCID: PMC9251585 DOI: 10.1042/bsr20212006] [Citation(s) in RCA: 8] [Impact Index Per Article: 4.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/03/2022] [Revised: 06/03/2022] [Accepted: 06/13/2022] [Indexed: 11/17/2022] Open
Abstract
Cystic fibrosis, the most common autosomal recessive disorder in Caucasians, is caused by mutations in the cystic fibrosis transmembrane conductance regulator (CFTR) gene, which encodes a cAMP-activated chloride and bicarbonate channel that regulates ion and water transport in secretory epithelia. Although all mutations lead to the lack or reduction in channel function, the mechanisms through which this occurs are diverse – ranging from lack of full-length mRNA, reduced mRNA levels, impaired folding and trafficking, targeting to degradation, decreased gating or conductance, and reduced protein levels to decreased half-life at the plasma membrane. Here, we review the different molecular mechanisms that cause cystic fibrosis and detail how these differences identify theratypes that can inform the use of directed therapies aiming at correcting the basic defect. In summary, we travel through CFTR life cycle from the gene to function, identifying what can go wrong and what can be targeted in terms of the different types of therapeutic approaches.
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8
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Allan KM, Astore MA, Fawcett LK, Wong SL, Chen PC, Griffith R, Jaffe A, Kuyucak S, Waters SA. S945L-CFTR molecular dynamics, functional characterization and tezacaftor/ivacaftor efficacy in vivo and in vitro in matched pediatric patient-derived cell models. Front Pediatr 2022; 10:1062766. [PMID: 36467478 PMCID: PMC9709344 DOI: 10.3389/fped.2022.1062766] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 10/06/2022] [Accepted: 10/28/2022] [Indexed: 11/18/2022] Open
Abstract
Cystic Fibrosis (CF) results from over 400 different disease-causing mutations in the CF Transmembrane Conductance Regulator (CFTR) gene. These CFTR mutations lead to numerous defects in CFTR protein function. A novel class of targeted therapies (CFTR modulators) have been developed that can restore defects in CFTR folding and gating. This study aimed to characterize the functional and structural defects of S945L-CFTR and interrogate the efficacy of modulators with two modes of action: gating potentiator [ivacaftor (IVA)] and folding corrector [tezacaftor (TEZ)]. The response to these modulators in vitro in airway differentiated cell models created from a participant with S945L/G542X-CFTR was correlated with in vivo clinical outcomes of that participant at least 12 months pre and post modulator therapy. In this participants' airway cell models, CFTR-mediated chloride transport was assessed via ion transport electrophysiology. Monotherapy with IVA or TEZ increased CFTR activity, albeit not reaching statistical significance. Combination therapy with TEZ/IVA significantly (p = 0.02) increased CFTR activity 1.62-fold above baseline. Assessment of CFTR expression and maturation via western blot validated the presence of mature, fully glycosylated CFTR, which increased 4.1-fold in TEZ/IVA-treated cells. The in vitro S945L-CFTR response to modulator correlated with an improvement in in vivo lung function (ppFEV1) from 77.19 in the 12 months pre TEZ/IVA to 80.79 in the 12 months post TEZ/IVA. The slope of decline in ppFEV1 significantly (p = 0.02) changed in the 24 months post TEZ/IVA, becoming positive. Furthermore, there was a significant improvement in clinical parameters and a fall in sweat chloride from 68 to 28 mmol/L. The mechanism of dysfunction of S945L-CFTR was elucidated by in silico molecular dynamics (MD) simulations. S945L-CFTR caused misfolding of transmembrane helix 8 and disruption of the R domain, a CFTR domain critical to channel gating. This study showed in vitro and in silico that S945L causes both folding and gating defects in CFTR and demonstrated in vitro and in vivo that TEZ/IVA is an efficacious modulator combination to address these defects. As such, we support the utility of patient-derived cell models and MD simulations in predicting and understanding the effect of modulators on CFTR function on an individualized basis.
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Affiliation(s)
- Katelin M Allan
- School of Clinical Medicine, Discipline of Paediatrics and Child Health, Faculty of Medicine and Health, UNSW Sydney, Sydney, NSW, Australia.,Molecular and Integrative Cystic Fibrosis Research Centre, UNSW Sydney, Sydney, NSW, Australia
| | - Miro A Astore
- School of Physics, The University of Sydney, Sydney, NSW, Australia
| | - Laura K Fawcett
- School of Clinical Medicine, Discipline of Paediatrics and Child Health, Faculty of Medicine and Health, UNSW Sydney, Sydney, NSW, Australia.,Molecular and Integrative Cystic Fibrosis Research Centre, UNSW Sydney, Sydney, NSW, Australia.,Department of Respiratory Medicine, Sydney Children's Hospital, Sydney, NSW, Australia
| | - Sharon L Wong
- School of Clinical Medicine, Discipline of Paediatrics and Child Health, Faculty of Medicine and Health, UNSW Sydney, Sydney, NSW, Australia.,Molecular and Integrative Cystic Fibrosis Research Centre, UNSW Sydney, Sydney, NSW, Australia
| | - Po-Chia Chen
- School of Physics, The University of Sydney, Sydney, NSW, Australia
| | - Renate Griffith
- School of Natural Sciences (Chemistry), University of Tasmania, Hobart, TAS, Australia
| | - Adam Jaffe
- School of Clinical Medicine, Discipline of Paediatrics and Child Health, Faculty of Medicine and Health, UNSW Sydney, Sydney, NSW, Australia.,Molecular and Integrative Cystic Fibrosis Research Centre, UNSW Sydney, Sydney, NSW, Australia.,Department of Respiratory Medicine, Sydney Children's Hospital, Sydney, NSW, Australia
| | - Serdar Kuyucak
- School of Physics, The University of Sydney, Sydney, NSW, Australia
| | - Shafagh A Waters
- School of Clinical Medicine, Discipline of Paediatrics and Child Health, Faculty of Medicine and Health, UNSW Sydney, Sydney, NSW, Australia.,Molecular and Integrative Cystic Fibrosis Research Centre, UNSW Sydney, Sydney, NSW, Australia.,Department of Respiratory Medicine, Sydney Children's Hospital, Sydney, NSW, Australia.,School of Biomedical Sciences, Faculty of Medicine and Health, UNSW Sydney, Sydney, NSW, Australia
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9
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Infield DT, Strickland KM, Gaggar A, McCarty NA. The molecular evolution of function in the CFTR chloride channel. J Gen Physiol 2021; 153:212705. [PMID: 34647973 PMCID: PMC8640958 DOI: 10.1085/jgp.202012625] [Citation(s) in RCA: 4] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/10/2020] [Revised: 08/11/2021] [Accepted: 09/09/2021] [Indexed: 12/13/2022] Open
Abstract
The ATP-binding cassette (ABC) transporter superfamily includes many proteins of clinical relevance, with genes expressed in all domains of life. Although most members use the energy of ATP binding and hydrolysis to accomplish the active import or export of various substrates across membranes, the cystic fibrosis transmembrane conductance regulator (CFTR) is the only known animal ABC transporter that functions primarily as an ion channel. Defects in CFTR, which is closely related to ABCC subfamily members that bear function as bona fide transporters, underlie the lethal genetic disease cystic fibrosis. This article seeks to integrate structural, functional, and genomic data to begin to answer the critical question of how the function of CFTR evolved to exhibit regulated channel activity. We highlight several examples wherein preexisting features in ABCC transporters were functionally leveraged as is, or altered by molecular evolution, to ultimately support channel function. This includes features that may underlie (1) construction of an anionic channel pore from an anionic substrate transport pathway, (2) establishment and tuning of phosphoregulation, and (3) optimization of channel function by specialized ligand–channel interactions. We also discuss how divergence and conservation may help elucidate the pharmacology of important CFTR modulators.
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Affiliation(s)
- Daniel T Infield
- Department of Molecular Physiology and Biophysics, University of Iowa, Iowa City, IA
| | | | - Amit Gaggar
- Department of Medicine, University of Alabama at Birmingham, Birmingham, AL.,Gregory Fleming James Cystic Fibrosis Research Center, University of Alabama at Birmingham, Birmingham, AL.,Program in Protease and Matrix Biology, University of Alabama at Birmingham, Birmingham, AL.,Birmingham Veterans Administration Medical Center, Birmingham, AL
| | - Nael A McCarty
- Department of Pediatrics, Emory University, Atlanta, GA.,Children's Healthcare of Atlanta Center for Cystic Fibrosis and Airways Disease Research, Emory University, Atlanta, GA
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10
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Laselva O, Qureshi Z, Zeng ZW, Petrotchenko EV, Ramjeesingh M, Hamilton CM, Huan LJ, Borchers CH, Pomès R, Young R, Bear CE. Identification of binding sites for ivacaftor on the cystic fibrosis transmembrane conductance regulator. iScience 2021; 24:102542. [PMID: 34142049 PMCID: PMC8184517 DOI: 10.1016/j.isci.2021.102542] [Citation(s) in RCA: 29] [Impact Index Per Article: 9.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/11/2021] [Revised: 03/22/2021] [Accepted: 05/11/2021] [Indexed: 11/25/2022] Open
Abstract
Ivacaftor (VX-770) was the first cystic fibrosis transmembrane conductance regulator (CFTR) modulatory drug approved for the treatment of patients with cystic fibrosis. Electron cryomicroscopy (cryo-EM) studies of detergent-solubilized CFTR indicated that VX-770 bound to a site at the interface between solvent and a hinge region in the CFTR protein conferred by transmembrane (tm) helices: tm4, tm5, and tm8. We re-evaluated VX-770 binding to CFTR in biological membranes using photoactivatable VX-770 probes. One such probe covalently labeled CFTR at two sites as determined following trypsin digestion and analysis by tandem-mass spectrometry. One labeled peptide resides in the cytosolic loop 4 of CFTR and the other is located in tm8, proximal to the site identified by cryo-EM. Complementary data from functional and molecular dynamic simulation studies support a model, where VX-770 mediates potentiation via multiple sites in the CFTR protein.
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Affiliation(s)
- Onofrio Laselva
- Programme in Molecular Medicine, Hospital for Sick Children, 686 Bay Street, Toronto, ON M5G 0A4, Canada
- Department of Medical and Surgical Sciences, University of Foggia, Foggia, Italy
| | - Zafar Qureshi
- Department of Chemistry, Simon Fraser University, Burnaby, Canada
| | - Zhi-Wei Zeng
- Programme in Molecular Medicine, Hospital for Sick Children, 686 Bay Street, Toronto, ON M5G 0A4, Canada
- Department of Biochemistry, University of Toronto, Toronto, Canada
| | - Evgeniy V. Petrotchenko
- Segal Cancer Proteomics Center, Lady Davis Institute, Jewish General Hospital, McGill University, Montreal, Canada
- Center for Computational and Data-Intensive Science and Engineering, Skolkovo Institute of Science and Technology, Moscow 121205, Russia
| | - Mohabir Ramjeesingh
- Programme in Molecular Medicine, Hospital for Sick Children, 686 Bay Street, Toronto, ON M5G 0A4, Canada
| | | | - Ling-Jun Huan
- Programme in Molecular Medicine, Hospital for Sick Children, 686 Bay Street, Toronto, ON M5G 0A4, Canada
| | - Christoph H. Borchers
- Segal Cancer Proteomics Center, Lady Davis Institute, Jewish General Hospital, McGill University, Montreal, Canada
- Center for Computational and Data-Intensive Science and Engineering, Skolkovo Institute of Science and Technology, Moscow 121205, Russia
- Gerald Bronfman Department of Oncology, Jewish General Hospital, McGill University, Montreal, Quebec H3T 1E2, Canada
| | - Régis Pomès
- Programme in Molecular Medicine, Hospital for Sick Children, 686 Bay Street, Toronto, ON M5G 0A4, Canada
- Department of Biochemistry, University of Toronto, Toronto, Canada
| | - Robert Young
- Department of Chemistry, Simon Fraser University, Burnaby, Canada
| | - Christine E. Bear
- Programme in Molecular Medicine, Hospital for Sick Children, 686 Bay Street, Toronto, ON M5G 0A4, Canada
- Department of Physiology, University of Toronto, Toronto, Canada
- Department of Biochemistry, University of Toronto, Toronto, Canada
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11
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Linsdell P, Irving CL, Cowley EA, El Hiani Y. Two positively charged amino acid side-chains in the inner vestibule of the CFTR channel pore play analogous roles in controlling anion binding and anion conductance. Cell Mol Life Sci 2021; 78:5213-5223. [PMID: 34023918 PMCID: PMC11073087 DOI: 10.1007/s00018-021-03859-x] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/23/2021] [Revised: 05/06/2021] [Accepted: 05/15/2021] [Indexed: 12/18/2022]
Abstract
Positively charged amino acid side-chains play important roles in anion binding and permeation through the CFTR chloride channel. One pore-lining lysine residue in particular (K95) has been shown to be indispensable for anion binding, conductance, and selectivity. Here, we use functional investigation of CFTR to show that a nearby arginine (R134) plays a functionally analogous role. Removal of this positive charge (in the R134Q mutant) drastically reduces single-channel conductance, weakens binding of both permeant and blocking anions, and abolishes the normal anion conductance selectivity pattern. Each of these functional effects was reversed by a second-site mutation (S1141K) that introduces an ectopic positive charge to a nearby pore-lining residue. Substituted cysteine accessibility experiments confirm that R134-but not nearby residues in the same transmembrane helix-is accessible within the pore lumen. These results suggest that K95 and R134, which are very close together within the inner vestibule of the pore, play analogous, important roles, and that both are required for the normal anion binding and anion conductance properties of the pore. Nevertheless, that fact that both positive charges can be "transplanted" to other sites in the inner vestibule with little effect on channel permeation properties indicates that it is the overall number of charges-rather than their exact locations-that controls pore function.
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Affiliation(s)
- Paul Linsdell
- Department of Physiology and Biophysics, Dalhousie University, PO Box 15000, Halifax, NS, B3H 4R2, Canada.
| | - Christina L Irving
- Department of Physiology and Biophysics, Dalhousie University, PO Box 15000, Halifax, NS, B3H 4R2, Canada
| | - Elizabeth A Cowley
- Department of Physiology and Biophysics, Dalhousie University, PO Box 15000, Halifax, NS, B3H 4R2, Canada
| | - Yassine El Hiani
- Department of Physiology and Biophysics, Dalhousie University, PO Box 15000, Halifax, NS, B3H 4R2, Canada
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Linsdell P. On the relationship between anion binding and chloride conductance in the CFTR anion channel. BIOCHIMICA ET BIOPHYSICA ACTA-BIOMEMBRANES 2021; 1863:183558. [PMID: 33444622 DOI: 10.1016/j.bbamem.2021.183558] [Citation(s) in RCA: 3] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Subscribe] [Scholar Register] [Received: 10/21/2020] [Revised: 12/21/2020] [Accepted: 12/29/2020] [Indexed: 12/26/2022]
Abstract
Mutations at many sites within the cystic fibrosis transmembrane conductance regulator (CFTR) chloride channel pore region result in changes in chloride conductance. Although chloride binding in the pore - as well as interactions between concurrently bound chloride ions - are thought to be important facets of the chloride permeation mechanism, little is known about the relationship between anion binding and chloride conductance. The present work presents a comprehensive investigation of a number of anion binding properties in different pore mutants with differential effects on chloride conductance. When multiple pore mutants are compared, conductance appears best correlated with the ability of anions to bind to the pore when it is already occupied by chloride ions. In contrast, conductance was not correlated with biophysical measures of anion:anion interactions inside the pore. Although these findings suggest anion binding is required for high conductance, mutations that strengthened anion binding had very little effect on conductance, especially at high chloride concentrations, suggesting that the wild-type CFTR pore is already close to saturated with chloride ions. These results are used to support a revised model of chloride permeation in CFTR in which the overall chloride occupancy of multiple loosely-defined chloride binding sites results in high chloride conductance through the pore.
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Affiliation(s)
- Paul Linsdell
- Department of Physiology & Biophysics, Dalhousie University, Halifax, Nova Scotia, Canada.
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Electrostatic Tuning of Anion Attraction from the Cytoplasm to the Pore of the CFTR Chloride Channel. Cell Biochem Biophys 2019; 78:15-22. [PMID: 31893350 DOI: 10.1007/s12013-019-00899-w] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/22/2019] [Accepted: 12/17/2019] [Indexed: 10/25/2022]
Abstract
Anions enter from the cytoplasm into the channel pore of the cystic fibrosis transmembrane conductance regulator (CFTR) Cl- channel not via a central pathway but via a single lateral portal or fenestration. High Cl- conductance is dependent on electrostatic attraction of cytoplasmic Cl- ions by four positively charged amino acid side-chains located within this portal. Here we use a mutagenic approach to investigate the functional effects of transplanting or supplementing these positive charges at nearby portal-lining sites. Using patch clamp recording, we find that the functionally important positive charges at K190 and R303 can be transplanted to four nearby sites (N186, L197, W356, and A367) with little loss of Cl- conductance. Introduction of additional positive charge at these sites had almost no effect on Cl- conductance, but did increase the sensitivity to channel block by intracellular suramin and Pt(NO2)42- anions. We suggest that it is the number of positive charges within the portal, rather than their exact location, that is the most important factor influencing Cl- conductance. The portal appears well optimized in terms of charge distribution to maximize Cl- conductance.
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