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van der Sluijs P, Hoelen H, Schmidt A, Braakman I. The Folding Pathway of ABC Transporter CFTR: Effective and Robust. J Mol Biol 2024; 436:168591. [PMID: 38677493 DOI: 10.1016/j.jmb.2024.168591] [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: 02/23/2024] [Revised: 04/16/2024] [Accepted: 04/23/2024] [Indexed: 04/29/2024]
Abstract
De novo protein folding into a native three-dimensional structure is indispensable for biological function, is instructed by its amino acid sequence, and occurs along a vectorial trajectory. The human proteome contains thousands of membrane-spanning proteins, whose biosynthesis begins on endoplasmic reticulum-associated ribosomes. Nearly half of all membrane proteins traverse the membrane more than once, including therapeutically important protein families such as solute carriers, G-protein-coupled receptors, and ABC transporters. These mediate a variety of functions like signal transduction and solute transport and are often of vital importance for cell function and tissue homeostasis. Missense mutations in multispan membrane proteins can lead to misfolding and cause disease; an example is the ABC transporter Cystic Fibrosis Transmembrane Conductance Regulator (CFTR). Even though our understanding of multispan membrane-protein folding still is rather rudimental, the cumulative knowledge of 20 years of basic research on CFTR folding has led to development of drugs that modulate the misfolded protein. This has provided the prospect of a life without CF to the vast majority of patients. In this review we describe our understanding of the folding pathway of CFTR in cells, which is modular and tolerates many defects, making it effective and robust. We address how modulator drugs affect folding and function of CFTR, and distinguish protein stability from its folding process. Since the domain architecture of (mammalian) ABC transporters are highly conserved, we anticipate that the insights we discuss here for folding of CFTR may lay the groundwork for understanding the general rules of ABC-transporter folding.
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Affiliation(s)
- Peter van der Sluijs
- Cellular Protein Chemistry, Bijvoet Centre for Biomolecular Research, Utrecht University, 3584 CH Utrecht, the Netherlands.
| | - Hanneke Hoelen
- Cellular Protein Chemistry, Bijvoet Centre for Biomolecular Research, Utrecht University, 3584 CH Utrecht, the Netherlands; Present address: GenDx, Yalelaan 48, 3584 CM Utrecht, The Netherlands
| | - Andre Schmidt
- Cellular Protein Chemistry, Bijvoet Centre for Biomolecular Research, Utrecht University, 3584 CH Utrecht, the Netherlands; 3D-Pharmxchange, Tilburg, the Netherlands
| | - Ineke Braakman
- Cellular Protein Chemistry, Bijvoet Centre for Biomolecular Research, Utrecht University, 3584 CH Utrecht, the Netherlands
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2
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Poroca DR, Amer N, Li A, Hanrahan JW, Chappe VM. Changes in the R-region interactions depend on phosphorylation and contribute to PKA and PKC regulation of the cystic fibrosis transmembrane conductance regulator chloride channel. FASEB Bioadv 2020; 2:33-48. [PMID: 32123855 PMCID: PMC6996395 DOI: 10.1096/fba.2019-00053] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/26/2019] [Accepted: 11/19/2019] [Indexed: 01/30/2023] Open
Abstract
The CFTR chloride channel is regulated by phosphorylation at PKA and PKC consensus sites within its regulatory region (R-region) through a mechanism, which is still not completely understood. We used a split-CFTR construct expressing the N-term-TMD1-NBD1 (Front Half; FH), TMD2-NBD2-C-Term (Back Half; BH), and the R-region as separate polypeptides (Split-R) in BHK cells, to investigate in situ how different phosphorylation conditions affect the R-region interactions with other parts of the protein. In proximity ligation assays, we studied the formation of complexes between the R-region and each half of the Split-CFTR. We found that at basal conditions, the density of complexes formed between the R-region and both halves of the split channel were equal. PKC stimulation alone had no effect, whereas PKA stimulation induced the formation of more complexes between the R-region and both halves compared to basal conditions. Moreover, PKC + PKA stimulation further enhanced the formation of FH-R complexes by 40% from PKA level. In cells expressing the Split-R with the two inhibitory PKC sites on the R-region inactivated (SR-S641A/T682A), density of FH-R complexes was much higher than in Split-R WT expressing cells after PKC or PKC + PKA stimulation. No differences were observed for BH-R complexes measured at all phosphorylation conditions. Since full-length CFTR channels display large functional responses to PKC + PKA in WT and S641A/T682A mutant, we conclude that FH-R interactions are important for CFTR function. Inactivation of consensus PKC site serine 686 (S686A) significantly reduced the basal BH-R interaction and prevented the PKC enhancing effect on CFTR function and FH-R interaction. The phospho-mimetic mutation (S686D) restored basal BH-R interaction and the PKC enhancing effect on CFTR function with enhanced FH-R interaction. As the channel function is mainly stimulated by PKA phosphorylation of the R-region, and this response is known to be enhanced by PKC phosphorylation, our data support a model in which the regulation of CFTR activation results from increased interactions of the R-region with the N-term-TMD1-NBD1. Also, serine S686 was found to be critical for the PKC enhancing effect which requires a permissive BH-R interaction at basal level and increased FH-R interaction after PKC + PKA phosphorylation.
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Affiliation(s)
- Diogo R. Poroca
- Department of Physiology & BiophysicsDalhousie UniversityHalifaxNSCanada
| | - Noha Amer
- Department of Physiology & BiophysicsDalhousie UniversityHalifaxNSCanada
| | - Audrey Li
- Department of Physiology & BiophysicsDalhousie UniversityHalifaxNSCanada
| | | | - Valerie M. Chappe
- Department of Physiology & BiophysicsDalhousie UniversityHalifaxNSCanada
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3
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Csanády L, Vergani P, Gadsby DC. STRUCTURE, GATING, AND REGULATION OF THE CFTR ANION CHANNEL. Physiol Rev 2019; 99:707-738. [PMID: 30516439 DOI: 10.1152/physrev.00007.2018] [Citation(s) in RCA: 144] [Impact Index Per Article: 28.8] [Reference Citation Analysis] [Abstract] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/17/2022] Open
Abstract
The cystic fibrosis transmembrane conductance regulator (CFTR) belongs to the ATP binding cassette (ABC) transporter superfamily but functions as an anion channel crucial for salt and water transport across epithelial cells. CFTR dysfunction, because of mutations, causes cystic fibrosis (CF). The anion-selective pore of the CFTR protein is formed by its two transmembrane domains (TMDs) and regulated by its cytosolic domains: two nucleotide binding domains (NBDs) and a regulatory (R) domain. Channel activation requires phosphorylation of the R domain by cAMP-dependent protein kinase (PKA), and pore opening and closing (gating) of phosphorylated channels is driven by ATP binding and hydrolysis at the NBDs. This review summarizes available information on structure and mechanism of the CFTR protein, with a particular focus on atomic-level insight gained from recent cryo-electron microscopic structures and on the molecular mechanisms of channel gating and its regulation. The pharmacological mechanisms of small molecules targeting CFTR's ion channel function, aimed at treating patients suffering from CF and other diseases, are briefly discussed.
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Affiliation(s)
- László Csanády
- Department of Medical Biochemistry, Semmelweis University , Budapest , Hungary ; MTA-SE Ion Channel Research Group, Budapest , Hungary ; Department of Neuroscience, Physiology and Pharmacology, University College London , London , United Kingdom ; and Laboratory of Cardiac/Membrane Physiology, The Rockefeller University , New York, New York
| | - Paola Vergani
- Department of Medical Biochemistry, Semmelweis University , Budapest , Hungary ; MTA-SE Ion Channel Research Group, Budapest , Hungary ; Department of Neuroscience, Physiology and Pharmacology, University College London , London , United Kingdom ; and Laboratory of Cardiac/Membrane Physiology, The Rockefeller University , New York, New York
| | - David C Gadsby
- Department of Medical Biochemistry, Semmelweis University , Budapest , Hungary ; MTA-SE Ion Channel Research Group, Budapest , Hungary ; Department of Neuroscience, Physiology and Pharmacology, University College London , London , United Kingdom ; and Laboratory of Cardiac/Membrane Physiology, The Rockefeller University , New York, New York
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4
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Hoffmann B, Elbahnsi A, Lehn P, Décout JL, Pietrucci F, Mornon JP, Callebaut I. Combining theoretical and experimental data to decipher CFTR 3D structures and functions. Cell Mol Life Sci 2018; 75:3829-3855. [PMID: 29779042 PMCID: PMC11105360 DOI: 10.1007/s00018-018-2835-7] [Citation(s) in RCA: 21] [Impact Index Per Article: 3.5] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/31/2017] [Revised: 05/04/2018] [Accepted: 05/07/2018] [Indexed: 12/15/2022]
Abstract
Cryo-electron microscopy (cryo-EM) has recently provided invaluable experimental data about the full-length cystic fibrosis transmembrane conductance regulator (CFTR) 3D structure. However, this experimental information deals with inactive states of the channel, either in an apo, quiescent conformation, in which nucleotide-binding domains (NBDs) are widely separated or in an ATP-bound, yet closed conformation. Here, we show that 3D structure models of the open and closed forms of the channel, now further supported by metadynamics simulations and by comparison with the cryo-EM data, could be used to gain some insights into critical features of the conformational transition toward active CFTR forms. These critical elements lie within membrane-spanning domains but also within NBD1 and the N-terminal extension, in which conformational plasticity is predicted to occur to help the interaction with filamin, one of the CFTR cellular partners.
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Affiliation(s)
- Brice Hoffmann
- Sorbonne Université, Muséum National d'Histoire Naturelle, UMR CNRS 7590, IRD, Institut de Minéralogie, de Physique des Matériaux et de Cosmochimie, IMPMC, 75005, Paris, France
- Iktos, Paris, France
| | - Ahmad Elbahnsi
- Sorbonne Université, Muséum National d'Histoire Naturelle, UMR CNRS 7590, IRD, Institut de Minéralogie, de Physique des Matériaux et de Cosmochimie, IMPMC, 75005, Paris, France
| | - Pierre Lehn
- INSERM U1078, SFR ScInBioS, Université de Bretagne Occidentale, Brest, France
| | | | - Fabio Pietrucci
- Sorbonne Université, Muséum National d'Histoire Naturelle, UMR CNRS 7590, IRD, Institut de Minéralogie, de Physique des Matériaux et de Cosmochimie, IMPMC, 75005, Paris, France
| | - Jean-Paul Mornon
- Sorbonne Université, Muséum National d'Histoire Naturelle, UMR CNRS 7590, IRD, Institut de Minéralogie, de Physique des Matériaux et de Cosmochimie, IMPMC, 75005, Paris, France.
| | - Isabelle Callebaut
- Sorbonne Université, Muséum National d'Histoire Naturelle, UMR CNRS 7590, IRD, Institut de Minéralogie, de Physique des Matériaux et de Cosmochimie, IMPMC, 75005, Paris, France
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5
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Abbas NAT, Kabil SL. Liraglutide ameliorates cardiotoxicity induced by doxorubicin in rats through the Akt/GSK-3β signaling pathway. Naunyn Schmiedebergs Arch Pharmacol 2017; 390:1145-1153. [PMID: 28780599 DOI: 10.1007/s00210-017-1414-z] [Citation(s) in RCA: 17] [Impact Index Per Article: 2.4] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/08/2017] [Accepted: 07/27/2017] [Indexed: 12/21/2022]
Abstract
Doxorubicin (Dox)-induced cardiotoxicity constitutes the major adverse effect that limited its use. We investigated the possible protective effects of liraglutide on Dox-induced cardiotoxicity in rats. Rats were divided into the following groups: control group rats received normal saline [1 ml/kg, intraperitoneal (i.p.)]; doxorubicin group rats received doxorubicin (1.25 mg/kg, i.p.), four times per week for 4 weeks; and liraglutide group rats received doxorubicin (1.25 mg/kg, i.p.) four times per week for 4 weeks then received liraglutide (100 μg/kg, i.p) daily for 4 weeks. At the end of the study, animals were sacrificed and serum creatine kinase-MB (CK-MB) and troponin I levels were determined. Malondialdehyde (MDA), superoxide dismutase (SOD), tumor necrosis factor-α (TNF-α), interleukin-6 (IL-6), and caspase-3 levels of the heart were determined. Cardiac AMPK, phosphorylated-Akt, tissue growth factor-β1 (TGF-β1), and GSK3-β levels of the heart were determined. Hematoxylin and eosin (H&E) stained sections form the heart were examined as well as immunohistochemical sections for detection of Bcl-2 expression. Dox treatment increased serum level of troponin I and CK-MB while decreased SOD activity, decreased AMPK, and p-Akt cardiac levels with increased in MDA, IL-6, TNF-α,GSK-3b, TGFB1, and caspase-3 levels in the heart with inflammation and necrosis in cardiac histopathology with decreased Bcl-2. Treatment with liraglutide decreased troponin I and CK-MB while increased SOD activity, AMPK, p-Akt with decrements in MDA, IL-6, TNF-α, GSK-3β, TGF-β1, and caspase-3 levels with attenuation of inflammation and necrosis while increased Bcl-2 expression. Liraglutide may thus represent a new clinical tool for the treatment of Dox-induced cardiotoxicity.
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Affiliation(s)
- Noha A T Abbas
- Department of Pharmacology, Faculty of Medicine, Zagazig University, Zagazig, Egypt.
| | - Soad L Kabil
- Department of Pharmacology, Faculty of Medicine, Zagazig University, Zagazig, Egypt
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6
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Sorum B, Czégé D, Csanády L. Timing of CFTR pore opening and structure of its transition state. Cell 2015; 163:724-33. [PMID: 26496611 DOI: 10.1016/j.cell.2015.09.052] [Citation(s) in RCA: 49] [Impact Index Per Article: 5.4] [Reference Citation Analysis] [Abstract] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/02/2015] [Revised: 08/25/2015] [Accepted: 09/18/2015] [Indexed: 12/12/2022]
Abstract
In CFTR, the chloride ion channel mutated in cystic fibrosis (CF) patients, pore opening is coupled to ATP-binding-induced dimerization of two cytosolic nucleotide binding domains (NBDs) and closure to dimer disruption following ATP hydrolysis. CFTR opening rate, unusually slow because of its high-energy transition state, is further slowed by CF mutation ΔF508. Here, we exploit equilibrium gating of hydrolysis-deficient CFTR mutant D1370N and apply rate-equilibrium free-energy relationship analysis to estimate relative timing of opening movements in distinct protein regions. We find clear directionality of motion along the longitudinal protein axis and identify an opening transition-state structure with the NBD dimer formed but the pore still closed. Thus, strain at the NBD/pore-domain interface, the ΔF508 mutation locus, underlies the energetic barrier for opening. Our findings suggest a therapeutic opportunity to stabilize this transition-state structure pharmacologically in ΔF508-CFTR to correct its opening defect, an essential step toward restoring CFTR function.
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Affiliation(s)
- Ben Sorum
- Department of Medical Biochemistry, Semmelweis University, Tűzoltó u. 37-47, Budapest 1094, Hungary; MTA-SE Ion Channel Research Group, Semmelweis University, Tűzoltó u. 37-47, Budapest 1094, Hungary
| | - Dávid Czégé
- MTA-SE Ion Channel Research Group, Semmelweis University, Tűzoltó u. 37-47, Budapest 1094, Hungary
| | - László Csanády
- Department of Medical Biochemistry, Semmelweis University, Tűzoltó u. 37-47, Budapest 1094, Hungary; MTA-SE Ion Channel Research Group, Semmelweis University, Tűzoltó u. 37-47, Budapest 1094, Hungary.
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7
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Wang G. Molecular Basis for Fe(III)-Independent Curcumin Potentiation of Cystic Fibrosis Transmembrane Conductance Regulator Activity. Biochemistry 2015; 54:2828-40. [DOI: 10.1021/acs.biochem.5b00219] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/30/2022]
Affiliation(s)
- Guangyu Wang
- Department of Physiology
and Biophysics and Gregory Fleming James Cystic Fibrosis Research
Center, University of Alabama at Birmingham School of Medicine, Birmingham, Alabama 35294, United States
- Department of Pharmacology, University of Nevada School of Medicine, Reno, Nevada 89557, United States
- Department of Physiology
and Membrane Biology, University of California School of Medicine, Davis, California 95616, United States
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8
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On the structural organization of the intracellular domains of CFTR. Int J Biochem Cell Biol 2014; 52:7-14. [PMID: 24513531 DOI: 10.1016/j.biocel.2014.01.024] [Citation(s) in RCA: 13] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/15/2013] [Revised: 01/17/2014] [Accepted: 01/21/2014] [Indexed: 12/17/2022]
Abstract
The cystic fibrosis transmembrane conductance regulator (CFTR) is a multidomain membrane protein forming an anion selective channel. Mutations in the gene encoding CFTR cause cystic fibrosis (CF). The intracellular side of CFTR constitutes about 80% of the total mass of the protein. This region includes domains involved in ATP-dependent gating and regulatory protein kinase-A phosphorylation sites. The high-resolution molecular structure of CFTR has not yet been solved. However, a range of lower resolution structural data, as well as functional biochemical and electrophysiological data, are now available. This information has enabled the proposition of a working model for the structural architecture of the intracellular domains of the CFTR protein.
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9
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Marasini C, Galeno L, Moran O. A SAXS-based ensemble model of the native and phosphorylated regulatory domain of the CFTR. Cell Mol Life Sci 2013; 70:923-33. [PMID: 23052212 PMCID: PMC11113146 DOI: 10.1007/s00018-012-1172-5] [Citation(s) in RCA: 18] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/15/2012] [Revised: 08/24/2012] [Accepted: 09/17/2012] [Indexed: 11/26/2022]
Abstract
The cystic fibrosis transmembrane conductance regulator (CFTR), the defective protein in cystic fibrosis, is an anion channel activated by protein kinase A phosphorylation. The regulatory domain (RD) of CFTR has multiple phosphorylation sites, and is responsible for channel activation. This domain is intrinsically disordered, rendering the structural analysis a difficult task, as high-resolution techniques are barely applicable. In this work, we obtained a biophysical characterization of the native and phosphorylated RD in solution by employing complementary structural methods. The native RD has a gyration radius of 3.25 nm, and a maximum molecular dimension of 11.4 nm, larger than expected for a globular protein of the same molecular mass. Phosphorylation causes compaction of the structure, yielding a significant reduction of the gyration radius, to 2.92 nm, and on the maximum molecular dimension to 10.2 nm. Using an ensemble optimization method, we were able to generate a low-resolution, three-dimensional model of the native and the phosphorylated RD based on small-angle X-ray scattering data. We have obtained the first experiment-based model of the CFTR regulatory domain, which will be useful to understand the molecular mechanisms of normal and pathological CFTR functioning.
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Affiliation(s)
- Carlotta Marasini
- Istituto di Biofisica, Consiglio Nazionale delle Ricerche (CNR), Via De Marini, 6, 16149 Genoa, Italy
| | - Lauretta Galeno
- Istituto di Biofisica, Consiglio Nazionale delle Ricerche (CNR), Via De Marini, 6, 16149 Genoa, Italy
| | - Oscar Moran
- Istituto di Biofisica, Consiglio Nazionale delle Ricerche (CNR), Via De Marini, 6, 16149 Genoa, Italy
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Seavilleklein G, Amer N, Evagelidis A, Chappe F, Irvine T, Hanrahan JW, Chappe V. PKC phosphorylation modulates PKA-dependent binding of the R domain to other domains of CFTR. Am J Physiol Cell Physiol 2008; 295:C1366-75. [PMID: 18799655 DOI: 10.1152/ajpcell.00034.2008] [Citation(s) in RCA: 25] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022]
Abstract
Activity of the CFTR channel is regulated by phosphorylation of its regulatory domain (RD). In a previous study, we developed a bicistronic construct called DeltaR-Split CFTR, which encodes the front and back halves of CFTR as separate polypeptides without the RD. These fragments assemble to form a constitutively active CFTR channel. Coexpression of the third fragment corresponding to the missing RD restores regulation by PKA, and this is associated with dramatically enhanced binding of the phosphorylated RD. In the present study, we examined the effect of PKC phosphorylation on this PKA-induced interaction. We report here that PKC alone enhanced association of the RD with DeltaR-Split CFTR and that binding was further enhanced when the RD was phosphorylated by both kinases. Mutation of all seven PKC consensus sequences on the RD (7CA-RD) did not affect its association under basal (unphosphorylated) conditions but abolished phosphorylation-induced binding by both kinases. Iodide efflux responses provided further support for the essential role of RD binding in channel regulation. The basal activity of DeltaR-Split/7CA-RD channels was similar to that of DeltaR-Split/wild type (WT)-RD channels, whereas cAMP-stimulated iodide efflux was greatly diminished by removal of the PKC sites, indicating that 7CA-RD binding maintains channels in an inactive state that is unresponsive to PKA. These results suggest a novel mechanism for CFTR regulation in which PKC modulates PKA-induced domain-domain interactions.
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Affiliation(s)
- Gage Seavilleklein
- Dept. of Physiology and Biophysics, 5850 College St., Halifax, NS, Canada B3H 1X5
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Hegedus T, Serohijos AWR, Dokholyan NV, He L, Riordan JR. Computational studies reveal phosphorylation-dependent changes in the unstructured R domain of CFTR. J Mol Biol 2008; 378:1052-63. [PMID: 18423665 DOI: 10.1016/j.jmb.2008.03.033] [Citation(s) in RCA: 45] [Impact Index Per Article: 2.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/27/2007] [Revised: 03/11/2008] [Accepted: 03/15/2008] [Indexed: 01/09/2023]
Abstract
The cystic fibrosis transmembrane conductance regulator (CFTR) is a cAMP-dependent chloride channel that is mutated in cystic fibrosis, an inherited disease of high morbidity and mortality. The phosphorylation of its approximately 200 amino acid R domain by protein kinase A is obligatory for channel gating under normal conditions. The R domain contains more than ten PKA phosphorylation sites. No individual site is essential but phosphorylation of increasing numbers of sites enables progressively greater channel activity. In spite of numerous studies of the role of the R domain in CFTR regulation, its mechanism of action remains largely unknown. This is because neither its structure nor its interactions with other parts of CFTR have been completely elucidated. Studies have shown that the R domain lacks well-defined secondary structural elements and is an intrinsically disordered region of the channel protein. Here, we have analyzed the disorder pattern and employed computational methods to explore low-energy conformations of the R domain. The specific disorder and secondary structure patterns detected suggest the presence of molecular recognition elements (MoREs) that may mediate phosphorylation-regulated intra- and inter-domain interactions. Simulations were performed to generate an ensemble of accessible R domain conformations. Although the calculated structures may represent more compact conformers than occur in vivo, their secondary structure propensities are consistent with predictions and published experimental data. Equilibrium simulations of a mimic of a phosphorylated R domain showed that it exhibited an increased radius of gyration. In one possible interpretation of these findings, by changing its size, the globally unstructured R domain may act as an entropic spring to perturb the packing of membrane-spanning sequences that constitute the ion permeability pathway and thereby activate channel gating.
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Affiliation(s)
- Tamás Hegedus
- Department of Biochemistry and Biophysics, University of North Carolina-Chapel Hill, Chapel Hill, NC 27599, USA.
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Yu Y, Platoshyn O, Safrina O, Tsigelny I, Yuan JXJ, Keller SH. Cystic fibrosis transmembrane conductance regulator (CFTR) functionality is dependent on coatomer protein I (COPI). Biol Cell 2007; 99:433-44. [PMID: 17388782 DOI: 10.1042/bc20060114] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/17/2022]
Abstract
BACKGROUND INFORMATION Cystic fibrosis results from mutations in the ABC transporter CFTR (cystic fibrosis transmembrane conductance regulator), which functions as a cAMP-regulated anion channel. The most prevalent mutation in CFTR, the Phe(508) deletion, results in the generation of a trafficking and functionally deficient channel. The cellular machineries involved in modulating CFTR trafficking and function have not been fully characterized. In the present study, we identified a role for the COPI (coatomer protein I) cellular trafficking machinery in the development of the CFTR polypeptide into a functional chloride channel. To examine the role of COPI in CFTR biosynthesis, we employed the cell line ldlF, which harbours a temperature-sensitive mutation in epsilon-COP, a COPI subunit, to inhibit COPI function and then determined whether the CFTR polypeptide produced from the transfected gene developed into a cAMP-regulated chloride channel. RESULTS When COPI was inactivated in the ldlF cells by an elevated temperature pulse (39 degrees C), the CFTR polypeptide was detected on the cell surface by immunofluorescence microscopy and cell-surface biotinylation. Therefore, CFTR proceeded upstream in the secretory pathway in the absence of COPI function, a result demonstrated previously by others. In contrast, electrophysiological measurements indicated an absence of cAMP-stimulated chloride efflux, suggesting that channel function was impaired. In comparison, expression of CFTR at the same elevated temperature (39 degrees C) in an epsilon-COP-rescued cell line [ldlF(ldlF)], which has an introduced wild-type epsilon-COP gene in addition to the mutant epsilon-COP gene, showed restoration of cAMP-stimulated channel activity, confirming the requirement of COPI for channel function. CONCLUSIONS These results therefore suggest that generation of the folded-functional conformation of CFTR requires COPI.
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Affiliation(s)
- Ying Yu
- Department of Medicine, University of California, San Diego, La Jolla, CA 92093-0725, USA
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Gross CH, Abdul-Manan N, Fulghum J, Lippke J, Liu X, Prabhakar P, Brennan D, Willis MS, Faerman C, Connelly P, Raybuck S, Moore J. Nucleotide-binding domains of cystic fibrosis transmembrane conductance regulator, an ABC transporter, catalyze adenylate kinase activity but not ATP hydrolysis. J Biol Chem 2005; 281:4058-68. [PMID: 16361259 DOI: 10.1074/jbc.m511113200] [Citation(s) in RCA: 21] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
The cystic fibrosis transmembrane conductance regulator (CFTR) is an anion channel in the ATP-binding cassette (ABC) transporter family. CFTR consists of two transmembrane domains, two nucleotide-binding domains (NBD1 and NBD2), and a regulatory domain. Previous biochemical reports suggest NBD1 is a site of stable nucleotide interaction with low ATPase activity, whereas NBD2 is the site of active ATP hydrolysis. It has also been reported that NBD2 additionally possessed adenylate kinase (AK) activity. Knowledge about the intrinsic biochemical activities of the NBDs is essential to understanding the Cl(-) ion gating mechanism. We find that purified mouse NBD1, human NBD1, and human NBD2 function as adenylate kinases but not as ATPases. AK activity is strictly dependent on the addition of the adenosine monophosphate (AMP) substrate. No liberation of [(33)P]phosphate is observed from the gamma-(33)P-labeled ATP substrate in the presence or absence of AMP. AK activity is intrinsic to both human NBDs, as the Walker A box lysine mutations abolish this activity. At low protein concentration, the NBDs display an initial slower nonlinear phase in AK activity, suggesting that the activity results from homodimerization. Interestingly, the G551D gating mutation has an exaggerated nonlinear phase compared with the wild type and may indicate this mutation affects the ability of NBD1 to dimerize. hNBD1 and hNBD2 mixing experiments resulted in an 8-57-fold synergistic enhancement in AK activity suggesting heterodimer formation, which supports a common theme in ABC transporter models. A CFTR gating mechanism model based on adenylate kinase activity is proposed.
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McGinniss MJ, Chen C, Redman JB, Buller A, Quan F, Peng M, Giusti R, Hantash FM, Huang D, Sun W, Strom CM. Extensive Sequencing of the CFTR gene: lessons learned from the first 157 patient samples. Hum Genet 2005; 118:331-8. [PMID: 16189704 DOI: 10.1007/s00439-005-0065-1] [Citation(s) in RCA: 26] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/23/2005] [Accepted: 08/29/2005] [Indexed: 11/30/2022]
Abstract
Cystic fibrosis (CF) is one of the most common monogenic diseases affecting Caucasians and has an incidence of approximately 1:3,300 births. Currently recommended screening panels for mutations in the responsible gene (CF transmembrane regulator gene, CFTR) do not detect all disease-associated mutations. Our laboratory offers extensive sequencing of the CFTR (ABCC7) gene (including the promoter, all exons and splice junction sites, and regions of selected introns) as a clinical test to detect mutations which are not found with conventional screening. The objective of this report is to summarize the findings of extensive CFTR sequencing from our first 157 consecutive patient samples. In most patients with classic CF symptoms (18/24, 75%), extensive CFTR sequencing confirmed the diagnosis by finding two disease-associated mutations. In contrast, only 5 of 75 (7%) patients with atypical CF had been identified with two CFTR mutations. A diagnosis of CF was confirmed in 10 of 17 (58%) newborns with either positive sweat chloride readings or positive immunoreactive trypsinogen (IRT) screen results. We ascertained ten novel sequence variants that are potentially disease-associated: two deletions (c.1641AG>T, c.2949_2853delTACTC), seven missense mutations (p.S158T, p.G451V, p.K481E, p.C491S, p.H949L, p.T1036N, p.F1099L), and one complex allele ([p.356_A357del; p.358I]). We ascertained three other apparently novel complex alleles. Finally, several patients were found to carry partial CFTR gene deletions. In summary, extensive CFTR gene sequencing can detect rare mutations which are not found with other screening and diagnostic tests, and can thus establish a definitive diagnosis in symptomatic patients with previously negative results. This enables carrier detection and prenatal diagnosis in additional family members.
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Affiliation(s)
- Matthew J McGinniss
- Molecular Genetics Laboratory, Quest Diagnostics Nichols Institute, 33608 Ortega Highway, San Juan Capistrano, CA, 92690-6130, USA.
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15
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Chappe V, Irvine T, Liao J, Evagelidis A, Hanrahan JW. Phosphorylation of CFTR by PKA promotes binding of the regulatory domain. EMBO J 2005; 24:2730-40. [PMID: 16001079 PMCID: PMC1182242 DOI: 10.1038/sj.emboj.7600747] [Citation(s) in RCA: 61] [Impact Index Per Article: 3.2] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/15/2004] [Accepted: 06/21/2005] [Indexed: 11/08/2022] Open
Abstract
The unphosphorylated regulatory (R) domain of the Cystic Fibrosis Transmembrane conductance Regulator (CFTR) is often viewed as an inhibitor that is released by phosphorylation. To test this notion, we studied domain interactions using CFTR channels assembled from three polypeptides. Nucleotides encoding the R domain (aa 635-836) were replaced with an internal ribosome entry sequence so that amino- and carboxyl-terminal half-molecules would be translated from the same mRNA transcript. Although only core glycosylation was detected on SplitDeltaR, biotinylation, immunostaining, and functional studies clearly demonstrated its trafficking to the plasma membrane. SplitDeltaR generated a constitutive halide permeability, which became responsive to cAMP when the missing R domain was coexpressed. Each half-molecule was co-precipitated by antibody against the other half. Contrary to expectations, GST-R domain was pulled down only if prephosphorylated by protein kinase A, and coexpressed R domain was precipitated with SplitDeltaR much more efficiently when cells were stimulated with cAMP. These results indicate that phosphorylation regulates CFTR by promoting association of the R domain with other domains rather than by causing its dissociation from an inhibitory site.
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Affiliation(s)
- Valerie Chappe
- Department of Physiology, McGill University, Montréal, QC, Canada
- Department of Physiology and Biophysics, Dalhousie University, Halifax, NS, Canada
| | - Thomas Irvine
- Department of Physiology, McGill University, Montréal, QC, Canada
| | - Jie Liao
- Department of Physiology, McGill University, Montréal, QC, Canada
| | | | - John W Hanrahan
- Department of Physiology, McGill University, Montréal, QC, Canada
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16
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Howell LD, Borchardt R, Kole J, Kaz AM, Randak C, Cohn JA. Protein kinase A regulates ATP hydrolysis and dimerization by a CFTR (cystic fibrosis transmembrane conductance regulator) domain. Biochem J 2004; 378:151-9. [PMID: 14602047 PMCID: PMC1223935 DOI: 10.1042/bj20021428] [Citation(s) in RCA: 26] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/10/2002] [Revised: 10/02/2003] [Accepted: 11/06/2003] [Indexed: 11/17/2022]
Abstract
Gating of the CFTR Cl- channel is associated with ATP hydrolysis at the nucleotide-binding domains (NBD1, NBD2) and requires PKA (protein kinase A) phosphorylation of the R domain. The manner in which the NBD1, NBD2 and R domains of CFTR (cystic fibrosis transmembrane conductance regulator) interact to achieve a properly regulated ion channel is largely unknown. In this study we used bacterially expressed recombinant proteins to examine interactions between these soluble domains of CFTR in vitro. PKA phosphorylated a fusion protein containing NBD1 and R (NBD1-R-GST) on CFTR residues Ser-660, Ser-700, Ser-712, Ser-737, Ser-768, Ser-795 and Ser-813. Phosphorylation of these serine residues regulated ATP hydrolysis by NBD1-R-GST by increasing the apparent K(m) for ATP (from 70 to 250 microM) and the Hill coefficient (from 1 to 1.7) without changing the V(max). When fusion proteins were photolabelled with 8-azido-[alpha-32P]ATP, PKA phosphorylation increased the apparent k(d) for nucleotide binding and it caused binding to become co-operative. PKA phosphorylation also resulted in dimerization of NBD1-R-GST but not of R-GST, a related fusion protein lacking the NBD1 domain. Finally, an MBP (maltose-binding protein) fusion protein containing the NBD2 domain (NBD2-MBP) associated with and regulated the ATPase activity of PKA-phosphorylated NBD1-R-GST. Thus when the R domain in NBD1-R-GST is phosphorylated by PKA, ATP binding and hydrolysis becomes co-operative and NBD dimerization occurs. These findings suggest that during the activation of native CFTR, phosphorylation of the R domain by PKA can control the ability of the NBD1 domain to hydrolyse ATP and to interact with other NBD domains.
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Affiliation(s)
- L Daniel Howell
- Department of Medicine, Duke University and VA Medical Centers, Durham, NC 27710-3378, USA
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17
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Grimard V, Li C, Ramjeesingh M, Bear CE, Goormaghtigh E, Ruysschaert JM. Phosphorylation-induced Conformational Changes of Cystic Fibrosis Transmembrane Conductance Regulator Monitored by Attenuated Total Reflection-Fourier Transform IR Spectroscopy and Fluorescence Spectroscopy. J Biol Chem 2004; 279:5528-36. [PMID: 14660584 DOI: 10.1074/jbc.m311014200] [Citation(s) in RCA: 24] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
Cystic fibrosis transmembrane conductance regulator (CFTR) is a member of the ABC protein superfamily. Phosphorylation of a regulatory domain of this protein is a prerequisite for activity. We analyzed the effect of protein kinase A (PKA) phosphorylation on the structure of purified and reconstituted CFTR protein. 1H/2H exchange monitored by attenuated total reflection Fourier transform IR spectroscopy demonstrates that CFTR is highly accessible to aqueous medium. Phosphorylation of the regulatory (R) domain by PKA further increases this accessibility. More specifically, fluorescence quenching of cytosolic tryptophan residues revealed that the accessibility of the cytoplasmic part of the protein is modified by phosphorylation. Moreover, the combination of polarized IR spectroscopy with 1H/2H exchange suggested an increase of the accessibility of the transmembrane domains of CFTR. This suggests that CFTR phosphorylation can induce a large conformational change that could correspond either to a displacement of the R domain or to long range conformational changes transmitted from the phosphorylation sites to the nucleotide binding domains and the transmembrane segments. Such structural changes may provide better access for the solutes to the nucleotide binding domains and the ion binding site.
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Affiliation(s)
- Vinciane Grimard
- Center for Structural Biology and Bioinformatics, Free University of Brussels, Campus Plaine CP206/2, 1050 Brussels, Belgium
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18
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Lewis HA, Buchanan SG, Burley SK, Conners K, Dickey M, Dorwart M, Fowler R, Gao X, Guggino WB, Hendrickson WA, Hunt JF, Kearins MC, Lorimer D, Maloney PC, Post KW, Rajashankar KR, Rutter ME, Sauder JM, Shriver S, Thibodeau PH, Thomas PJ, Zhang M, Zhao X, Emtage S. Structure of nucleotide-binding domain 1 of the cystic fibrosis transmembrane conductance regulator. EMBO J 2003; 23:282-93. [PMID: 14685259 PMCID: PMC1271750 DOI: 10.1038/sj.emboj.7600040] [Citation(s) in RCA: 311] [Impact Index Per Article: 14.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/23/2003] [Accepted: 11/25/2003] [Indexed: 11/08/2022] Open
Abstract
Cystic fibrosis transmembrane conductance regulator (CFTR) is an ATP-binding cassette (ABC) transporter that functions as a chloride channel. Nucleotide-binding domain 1 (NBD1), one of two ABC domains in CFTR, also contains sites for the predominant CF-causing mutation and, potentially, for regulatory phosphorylation. We have determined crystal structures for mouse NBD1 in unliganded, ADP- and ATP-bound states, with and without phosphorylation. This NBD1 differs from typical ABC domains in having added regulatory segments, a foreshortened subdomain interconnection, and an unusual nucleotide conformation. Moreover, isolated NBD1 has undetectable ATPase activity and its structure is essentially the same independent of ligand state. Phe508, which is commonly deleted in CF, is exposed at a putative NBD1-transmembrane interface. Our results are consistent with a CFTR mechanism, whereby channel gating occurs through ATP binding in an NBD1-NBD2 nucleotide sandwich that forms upon displacement of NBD1 regulatory segments.
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Affiliation(s)
- Hal A Lewis
- Structural GenomiX Inc., San Diego, CA, USA.
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19
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Annereau JP, Ko YH, Pedersen PL. Cystic fibrosis transmembrane conductance regulator: the NBF1+R (nucleotide-binding fold 1 and regulatory domain) segment acting alone catalyses a Co2+/Mn2+/Mg2+-ATPase activity markedly inhibited by both Cd2+ and the transition-state analogue orthovanadate. Biochem J 2003; 371:451-62. [PMID: 12523935 PMCID: PMC1223294 DOI: 10.1042/bj20021318] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/21/2002] [Revised: 11/08/2002] [Accepted: 01/10/2003] [Indexed: 11/17/2022]
Abstract
Cystic fibrosis (CF) is caused by mutations in the gene encoding CFTR (cystic fibrosis transmembrane conductance regulator), a regulated anion channel and member of the ATP-binding-cassette transporter (ABC transporter) superfamily. Of CFTR's five domains, the first nucleotide-binding fold (NBF1) has been of greatest interest both because it is the major 'hotspot' for mutations that cause CF, and because it is connected to a unique regulatory domain (R). However, attempts have failed to obtain a catalytically active NBF1+R protein in the absence of a fusion partner. Here, we report that such a protein can be obtained following its overexpression in bacteria. The pure NBF1+R protein exhibits significant ATPase activity [catalytic-centre activity (turnover number) 6.7 min(-1)] and an apparent affinity for ATP ( K (m), 8.7 microM) higher than reported previously for CFTR or segments thereof. As predicted, the ATPase activity is inhibited by mutations in the Walker A motif. It is also inhibited by vanadate, a transition-state analogue. Surprisingly, however, the best divalent metal activator is Co(2+), followed by Mn(2+) and Mg(2+). In contrast, Ca(2+) is ineffective and Cd(2+) is a potent inhibitor. These novel studies, while demonstrating clearly that CFTR's NBF1+R segment can act independently as an active, vanadate-sensitive ATPase, also identify its unique cation activators and a new inhibitor, thus providing insight into the nature of its active site.
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Affiliation(s)
- Jean Philippe Annereau
- Department of Biological Chemistry, The Johns Hopkins University School of Medicine, Baltimore, MD 21205-2185, USA
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