1
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Cui G, Strickland KM, Vazquez Cegla AJ, McCarty NA. Comparing ATPase activity of ATP-binding cassette subfamily C member 4, lamprey CFTR, and human CFTR using an antimony-phosphomolybdate assay. Front Pharmacol 2024; 15:1363456. [PMID: 38440176 PMCID: PMC10910009 DOI: 10.3389/fphar.2024.1363456] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/30/2023] [Accepted: 02/05/2024] [Indexed: 03/06/2024] Open
Abstract
Introduction: ATP-binding cassette (ABC) transporters use the hydrolysis of ATP to power the active transport of molecules, but paradoxically the cystic fibrosis transmembrane regulator (CFTR, ABCC7) forms an ion channel. We previously showed that ATP-binding cassette subfamily C member 4 (ABCC4) is the closest mammalian paralog to CFTR, compared to other ABC transporters. In addition, Lamprey CFTR (Lp-CFTR) is the oldest known CFTR ortholog and has unique structural and functional features compared to human CFTR (hCFTR). The availability of these evolutionarily distant orthologs gives us the opportunity to study the changes in ATPase activity that may be related to their disparate functions. Methods: We utilized the baculovirus expression system with Sf9 insect cells and made use of the highly sensitive antimony-phosphomolybdate assay for testing the ATPase activity of human ABCC4 (hABCC4), Lp-CFTR, and hCFTR under similar experimental conditions. This assay measures the production of inorganic phosphate (Pi) in the nanomolar range. Results: Crude plasma membranes were purified, and protein concentration, determined semi-quantitatively, of hABCC4, Lp-CFTR, and hCFTR ranged from 0.01 to 0.36 μg/μL. No significant difference in expression level was found although hABCC4 trended toward the highest level. hABCC4 was activated by ATP with the equilibrium constant (Kd) 0.55 ± 0.28 mM (n = 8). Estimated maximum ATPase rate (Vmax) for hABCC4 was about 0.2 nmol/μg/min when the protein was activated with 1 mM ATP at 37°C (n = 7). Estimated maximum ATPase rate for PKA-phosphorylated Lp-CFTR reached about half of hCFTR levels in the same conditions. Vmax for both Lp-CFTR and hCFTR were significantly increased in high PKA conditions compared to low PKA conditions. Maximum intrinsic ATPase rate of hABCC4 in the absence of substrate was twice that of hCFTR when activated in 1 mM ATP. Conclusion: The findings here suggest that while both ABCC4 and hCFTR bear one consensus and one degenerate ATPase site, the hCFTR exhibited a reduced intrinsic ATPase activity. In addition, ATPase activity in the CFTR lineage increased from Lp-CFTR to hCFTR. Finally, the studies pave the way to purify hABCC4, Lp-CFTR, and hCFTR from Sf9 cells for their structural investigation, including by cryo-EM, and for studies of evolution in the ABC transporter superfamily.
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Affiliation(s)
| | | | | | - Nael A. McCarty
- Division of Pulmonology, Asthma, Cystic Fibrosis, and Sleep, Department of Pediatrics, Emory + Children’s Center for Cystic Fibrosis and Airways Disease Research, Emory University School of Medicine and Children’s Healthcare of Atlanta, Atlanta, GA, United States
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2
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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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3
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Cholesterol Interaction Directly Enhances Intrinsic Activity of the Cystic Fibrosis Transmembrane Conductance Regulator (CFTR). Cells 2019; 8:cells8080804. [PMID: 31370288 PMCID: PMC6721619 DOI: 10.3390/cells8080804] [Citation(s) in RCA: 20] [Impact Index Per Article: 4.0] [Reference Citation Analysis] [Abstract] [Key Words] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/09/2019] [Revised: 07/23/2019] [Accepted: 07/29/2019] [Indexed: 12/15/2022] Open
Abstract
The recent cryo-electron microscopy structures of zebrafish and the human cystic fibrosis transmembrane conductance regulator (CFTR) provided unprecedented insights into putative mechanisms underlying gating of its anion channel activity. Interestingly, despite predictions based on channel activity measurements in biological membranes, the structure of the detergent purified, phosphorylated, and ATP-bound human CFTR protein did not reveal a stably open conduction pathway. This study tested the hypothesis that the functional properties of the detergent solubilized CFTR protein used for structural determinations are different from those exhibited by CFTR purified under conditions that retain associated lipids native to the membrane. It was found that CFTR purified together with phospholipids and cholesterol using amphipol: A8-35, exhibited higher rates of catalytic activity, phosphorylation dependent channel activation and potentiation by the therapeutic compound, ivacaftor, than did CFTR purified in detergent. The catalytic activity of phosphorylated CFTR detergent micelles was rescued by the addition of phospholipids plus cholesterol, but not by phospholipids alone, arguing for a specific role for cholesterol in modulating this function. In summary, these studies highlight the importance of lipid interactions in the intrinsic activities and pharmacological potentiation of CFTR.
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4
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Yeh HI, Qiu L, Sohma Y, Conrath K, Zou X, Hwang TC. Identifying the molecular target sites for CFTR potentiators GLPG1837 and VX-770. J Gen Physiol 2019; 151:912-928. [PMID: 31164398 PMCID: PMC6605684 DOI: 10.1085/jgp.201912360] [Citation(s) in RCA: 54] [Impact Index Per Article: 10.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/27/2019] [Revised: 04/29/2019] [Accepted: 05/10/2019] [Indexed: 01/14/2023] Open
Abstract
Identification of the binding sites for small molecules that alleviate gating
defects in CFTR would assist rational drug design for the treatment of cystic
fibrosis. Yeh et al. identify two potential binding sites for prototypical CFTR
potentiators at the interface of CFTR’s two transmembrane domains. The past two decades have witnessed major breakthroughs in developing compounds
that target the chloride channel CFTR for the treatment of patients with cystic
fibrosis. However, further improvement in affinity and efficacy for these CFTR
modulators will require insights into the molecular interactions between CFTR
modulators and their binding targets. In this study, we use in silico molecular
docking to identify potential binding sites for GLPG1837, a CFTR potentiator
that may share a common mechanism and binding site with VX-770, the FDA-approved
drug for patients carrying mutations with gating defects. Among the five binding
sites predicted by docking, the two top-scoring sites are located at the
interface between CFTR’s two transmembrane domains: site I consists of
D924, N1138, and S1141, and site IIN includes F229, F236, Y304, F312,
and F931. Using mutagenesis to probe the importance of these sites for GLPG187
binding, we find that disruption of predicted hydrogen-bonding interactions by
mutation of D924 decreases apparent affinity, while hydrophobic amino acids
substitutions at N1138 and introduction of positively charged amino acids at
S1141 improve the apparent affinity for GLPG1837. Alanine substitutions at Y304,
F312, and F931 (site IIN) decrease the affinity for GLPG1837, whereas
alanine substitutions at F229 and F236 (also site IIN), or at
residues in the other three lower-scoring sites, have little effect. In
addition, current relaxation analysis to assess the apparent dissociation rate
of VX-770 yields results consistent with the dose–response experiments
for GLPG8137, with the dissociation rate of VX-770 accelerated by D924N, F236A,
Y304A, and F312A, but decelerated by N1138L and S1141K mutations. Collectively,
these data identify two potential binding sites for GLPG1837 and VX-770 in CFTR.
We discuss the pros and cons of evidence for these two loci and the implications
for future drug design.
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Affiliation(s)
- Han-I Yeh
- Dalton Cardiovascular Research Center and Department of Medical Pharmacology and Physiology, University of Missouri, Columbia, MO
| | - Liming Qiu
- Dalton Cardiovascular Research Center, Department of Physics and Astronomy, Department of Biochemistry, and Informatics Institute, University of Missouri, Columbia, MO
| | - Yoshiro Sohma
- Dalton Cardiovascular Research Center and Department of Medical Pharmacology and Physiology, University of Missouri, Columbia, MO.,Department of Pharmaceutical Sciences, School of Pharmacy and Center for Medical Science, International University of Health and Welfare, Tochigi, Japan
| | | | - Xiaoqin Zou
- Dalton Cardiovascular Research Center, Department of Physics and Astronomy, Department of Biochemistry, and Informatics Institute, University of Missouri, Columbia, MO
| | - Tzyh-Chang Hwang
- Dalton Cardiovascular Research Center and Department of Medical Pharmacology and Physiology, University of Missouri, Columbia, MO
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5
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Csanády L, Vergani P, Gadsby DC. STRUCTURE, GATING, AND REGULATION OF THE CFTR ANION CHANNEL. Physiol Rev 2019; 99:707-738. [PMID: 30516439 DOI: 10.1152/physrev.00007.2018] [Citation(s) in RCA: 147] [Impact Index Per Article: 29.4] [Reference Citation Analysis] [Abstract] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/17/2022] Open
Abstract
The cystic fibrosis transmembrane conductance regulator (CFTR) belongs to the ATP binding cassette (ABC) transporter superfamily but functions as an anion channel crucial for salt and water transport across epithelial cells. CFTR dysfunction, because of mutations, causes cystic fibrosis (CF). The anion-selective pore of the CFTR protein is formed by its two transmembrane domains (TMDs) and regulated by its cytosolic domains: two nucleotide binding domains (NBDs) and a regulatory (R) domain. Channel activation requires phosphorylation of the R domain by cAMP-dependent protein kinase (PKA), and pore opening and closing (gating) of phosphorylated channels is driven by ATP binding and hydrolysis at the NBDs. This review summarizes available information on structure and mechanism of the CFTR protein, with a particular focus on atomic-level insight gained from recent cryo-electron microscopic structures and on the molecular mechanisms of channel gating and its regulation. The pharmacological mechanisms of small molecules targeting CFTR's ion channel function, aimed at treating patients suffering from CF and other diseases, are briefly discussed.
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Affiliation(s)
- László Csanády
- Department of Medical Biochemistry, Semmelweis University , Budapest , Hungary ; MTA-SE Ion Channel Research Group, Budapest , Hungary ; Department of Neuroscience, Physiology and Pharmacology, University College London , London , United Kingdom ; and Laboratory of Cardiac/Membrane Physiology, The Rockefeller University , New York, New York
| | - Paola Vergani
- Department of Medical Biochemistry, Semmelweis University , Budapest , Hungary ; MTA-SE Ion Channel Research Group, Budapest , Hungary ; Department of Neuroscience, Physiology and Pharmacology, University College London , London , United Kingdom ; and Laboratory of Cardiac/Membrane Physiology, The Rockefeller University , New York, New York
| | - David C Gadsby
- Department of Medical Biochemistry, Semmelweis University , Budapest , Hungary ; MTA-SE Ion Channel Research Group, Budapest , Hungary ; Department of Neuroscience, Physiology and Pharmacology, University College London , London , United Kingdom ; and Laboratory of Cardiac/Membrane Physiology, The Rockefeller University , New York, New York
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6
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Hopfner KP. Invited review: Architectures and mechanisms of ATP binding cassette proteins. Biopolymers 2017; 105:492-504. [PMID: 27037766 DOI: 10.1002/bip.22843] [Citation(s) in RCA: 45] [Impact Index Per Article: 6.4] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/19/2016] [Revised: 03/24/2016] [Accepted: 03/28/2016] [Indexed: 12/29/2022]
Abstract
ATP binding cassette (ABC) ATPases form chemo-mechanical engines and switches that function in a broad range of biological processes. Most prominently, a very large family of integral membrane NTPases-ABC transporters-catalyzes the import or export of a diverse molecules across membranes. ABC proteins are also important components of the chromosome segregation, recombination, and DNA repair machineries and regulate or catalyze critical steps of ribosomal protein synthesis. Recent structural and mechanistic studies draw interesting architectural and mechanistic parallels between diverse ABC proteins. Here, I review this state of our understanding how NTP-dependent conformational changes of ABC proteins drive diverse biological processes. © 2016 Wiley Periodicals, Inc. Biopolymers 105: 492-504, 2016.
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Affiliation(s)
- Karl-Peter Hopfner
- Department Biochemistry, Ludwig-Maximilians-Universität München, Feodor-Lynen-Str. 25, 81377 Munich, Germany.,Gene Center, Ludwig-Maximilians-Universität München, Feodor-Lynen-Str. 25, 81377 Munich, Germany.,Center for Integrated Protein Science Munich, Ludwigs-Maximilians-Universität München, Feodor-Lynen-Str. 25, 81377 Munich, Germany
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7
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Chin S, Hung M, Bear CE. Current insights into the role of PKA phosphorylation in CFTR channel activity and the pharmacological rescue of cystic fibrosis disease-causing mutants. Cell Mol Life Sci 2017; 74:57-66. [PMID: 27722768 PMCID: PMC11107731 DOI: 10.1007/s00018-016-2388-6] [Citation(s) in RCA: 16] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/27/2016] [Accepted: 09/28/2016] [Indexed: 12/21/2022]
Abstract
Cystic fibrosis transmembrane conductance regulator (CFTR) channel gating is predominantly regulated by protein kinase A (PKA)-dependent phosphorylation. In addition to regulating CFTR channel activity, PKA phosphorylation is also involved in enhancing CFTR trafficking and mediating conformational changes at the interdomain interfaces of the protein. The major cystic fibrosis (CF)-causing mutation is the deletion of phenylalanine at position 508 (F508del); it causes many defects that affect CFTR trafficking, stability, and gating at the cell surface. Due to the multiple roles of PKA phosphorylation, there is growing interest in targeting PKA-dependent signaling for rescuing the trafficking and functional defects of F508del-CFTR. This review will discuss the effects of PKA phosphorylation on wild-type CFTR, the consequences of CF mutations on PKA phosphorylation, and the development of therapies that target PKA-mediated signaling.
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Affiliation(s)
- Stephanie Chin
- Programme of Molecular Structure and Function, Research Institute, Hospital for Sick Children, Toronto, Canada
- Department of Biochemistry, University of Toronto, Toronto, Canada
| | - Maurita Hung
- Programme of Molecular Structure and Function, Research Institute, Hospital for Sick Children, Toronto, Canada
| | - Christine E Bear
- Programme of Molecular Structure and Function, Research Institute, Hospital for Sick Children, Toronto, Canada.
- Department of Biochemistry, University of Toronto, Toronto, Canada.
- Department of Physiology, University of Toronto, Toronto, Canada.
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8
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Strug LJ, Gonska T, He G, Keenan K, Ip W, Boëlle PY, Lin F, Panjwani N, Gong J, Li W, Soave D, Xiao B, Tullis E, Rabin H, Parkins MD, Price A, Zuberbuhler PC, Corvol H, Ratjen F, Sun L, Bear CE, Rommens JM. Cystic fibrosis gene modifier SLC26A9 modulates airway response to CFTR-directed therapeutics. Hum Mol Genet 2016; 25:4590-4600. [PMID: 28171547 PMCID: PMC5886039 DOI: 10.1093/hmg/ddw290] [Citation(s) in RCA: 48] [Impact Index Per Article: 6.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/20/2016] [Revised: 07/12/2016] [Accepted: 08/25/2016] [Indexed: 12/18/2022] Open
Abstract
Cystic fibrosis is realizing the promise of personalized medicine. Recent advances in drug development that target the causal CFTR directly result in lung function improvement, but variability in response is demanding better prediction of outcomes to improve management decisions. The genetic modifier SLC26A9 contributes to disease severity in the CF pancreas and intestine at birth and here we assess its relationship with disease severity and therapeutic response in the airways. SLC26A9 association with lung disease was assessed in individuals from the Canadian and French CF Gene Modifier consortia with CFTR-gating mutations and in those homozygous for the common Phe508del mutation. Variability in response to a CFTR-directed therapy attributed to SLC26A9 genotype was assessed in Canadian patients with gating mutations. A primary airway model system determined if SLC26A9 shows modification of Phe508del CFTR function upon treatment with a CFTR corrector. In those with gating mutations that retain cell surface-localized CFTR we show that SLC26A9 modifies lung function while this is not the case in individuals homozygous for Phe508del where cell surface expression is lacking. Treatment response to ivacaftor, which aims to improve CFTR-channel opening probability in patients with gating mutations, shows substantial variability in response, 28% of which can be explained by rs7512462 in SLC26A9 (P = 0.0006). When homozygous Phe508del primary bronchial cells are treated to restore surface CFTR, SLC26A9 likewise modifies treatment response (P = 0.02). Our findings indicate that SLC26A9 airway modification requires CFTR at the cell surface, and that a common variant in SLC26A9 may predict response to CFTR-directed therapeutics.
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Affiliation(s)
- Lisa J. Strug
- Program in Genetics and Genome Biology, Research Institute, The Hospital for Sick Children, Toronto, Ontario, Canada
- Division of Biostatistics, Dalla Lana School of Public Health, University of Toronto, Ontario, Canada
- The Centre for Applied Genomics, The Hospital for Sick Children, Toronto, Ontario, Canada
| | - Tanja Gonska
- Department of Pediatrics, University of Toronto, Toronto, Ontario, Canada
- Division of Gastroenterology, Hepatology and Nutrition, The Hospital for Sick Children, Toronto, Ontario, Canada
- Program in Physiology and Experimental Medicine, The Hospital for Sick Children, Toronto, Ontario, Canada
| | - Gengming He
- Program in Genetics and Genome Biology, Research Institute, The Hospital for Sick Children, Toronto, Ontario, Canada
| | - Katherine Keenan
- Program in Physiology and Experimental Medicine, The Hospital for Sick Children, Toronto, Ontario, Canada
| | - Wan Ip
- Program in Physiology and Experimental Medicine, The Hospital for Sick Children, Toronto, Ontario, Canada
| | - Pierre-Yves Boëlle
- Sorbonne Universités, Université Pierre et Marie Curie (UPMC) Paris 06, Paris, France
- Assistance Publique-Hôpitaux de Paris (AP-HP), Hôpital St. Antoine, Biostatistics Department; Inserm U1136, Paris, France
| | - Fan Lin
- Program in Genetics and Genome Biology, Research Institute, The Hospital for Sick Children, Toronto, Ontario, Canada
| | - Naim Panjwani
- Program in Genetics and Genome Biology, Research Institute, The Hospital for Sick Children, Toronto, Ontario, Canada
| | - Jiafen Gong
- Program in Genetics and Genome Biology, Research Institute, The Hospital for Sick Children, Toronto, Ontario, Canada
| | - Weili Li
- Program in Genetics and Genome Biology, Research Institute, The Hospital for Sick Children, Toronto, Ontario, Canada
- The Centre for Applied Genomics, The Hospital for Sick Children, Toronto, Ontario, Canada
| | - David Soave
- Program in Genetics and Genome Biology, Research Institute, The Hospital for Sick Children, Toronto, Ontario, Canada
- Division of Biostatistics, Dalla Lana School of Public Health, University of Toronto, Ontario, Canada
| | - Bowei Xiao
- Program in Genetics and Genome Biology, Research Institute, The Hospital for Sick Children, Toronto, Ontario, Canada
| | - Elizabeth Tullis
- Department of Respiratory Medicine and Li Ka Shing Knowledge Institute, St. Michael’s Hospital, University of Toronto, Toronto, Ontario, Canada
| | - Harvey Rabin
- Department of Medicine, University of Calgary, Calgary, Alberta, Canada
- The Department of Microbiology, Immunology and Infectious Disease, University of Calgary, Calgary, Alberta, Canada
| | - Michael D. Parkins
- Department of Medicine, University of Calgary, Calgary, Alberta, Canada
- The Department of Microbiology, Immunology and Infectious Disease, University of Calgary, Calgary, Alberta, Canada
| | - April Price
- Division of Paediatric Respirology, Department of Paediatrics, Children's Hospital at London Health Sciences Centre, London, Ontario, Canada
| | | | - Harriet Corvol
- Sorbonne Universités, Université Pierre et Marie Curie (UPMC) Paris 06, Paris, France
- AP-HP, Hôpital Trousseau, Pediatric Pulmonary Department; Institut National de la Santé et al Recherche Medicale (INSERM) U938, Paris, France
| | - Felix Ratjen
- Program in Physiology and Experimental Medicine, The Hospital for Sick Children, Toronto, Ontario, Canada
- Division of Respiratory Medicine, The Hospital for Sick Children, Toronto, Ontario, Canada
| | - Lei Sun
- Division of Biostatistics, Dalla Lana School of Public Health, University of Toronto, Ontario, Canada
- Department of Statistical Sciences, University of Toronto, Toronto, Ontario, Canada
| | - Christine E. Bear
- Program in Molecular Structure and Function, The Hospital for Sick Children, Toronto, Ontario, CanadaDepartments of
- Biochemistry
- Physiology
| | - Johanna M. Rommens
- Program in Genetics and Genome Biology, Research Institute, The Hospital for Sick Children, Toronto, Ontario, Canada
- Molecular Genetics, University of Toronto, Toronto, Ontario, Canada
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9
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Huang W, Liao JL. Catalytic Mechanism of the Maltose Transporter Hydrolyzing ATP. Biochemistry 2015; 55:224-31. [PMID: 26666844 DOI: 10.1021/acs.biochem.5b00970] [Citation(s) in RCA: 12] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Abstract
We use quantum mechanical and molecular mechanical (QM/MM) simulations to study ATP hydrolysis catalyzed by the maltose transporter. This protein is a prototypical member of a large family that consists of ATP-binding cassette (ABC) transporters. The ABC proteins catalyze ATP hydrolysis to perform a variety of biological functions. Despite extensive research efforts, the precise molecular mechanism of ATP hydrolysis catalyzed by the ABC enzymes remains elusive. In this work, the reaction pathway for ATP hydrolysis in the maltose transporter is evaluated using a QM/MM implementation of the nudged elastic band method without presuming reaction coordinates. The potential of mean force along the reaction pathway is obtained with an activation free energy of 19.2 kcal/mol in agreement with experiments. The results demonstrate that the reaction proceeds via a dissociative-like pathway with a trigonal bipyramidal transition state in which the cleavage of the γ-phosphate P-O bond occurs and the O-H bond of the lytic water molecule is not yet broken. Our calculations clearly show that the Walker B glutamate as well as the switch histidine stabilizes the transition state via electrostatic interactions rather than serving as a catalytic base. The results are consistent with biochemical and structural experiments, providing novel insight into the molecular mechanism of ATP hydrolysis in the ABC proteins.
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Affiliation(s)
- Wenting Huang
- Department of Chemical Physics, University of Science and Technology of China , 96 Jinzhai Road, Hefei, Anhui Province, People's Republic of China 230026
| | - Jie-Lou Liao
- Department of Chemical Physics, University of Science and Technology of China , 96 Jinzhai Road, Hefei, Anhui Province, People's Republic of China 230026
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10
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Ehrhardt A, Chung WJ, Pyle LC, Wang W, Nowotarski K, Mulvihill CM, Ramjeesingh M, Hong J, Velu SE, Lewis HA, Atwell S, Aller S, Bear CE, Lukacs GL, Kirk KL, Sorscher EJ. Channel Gating Regulation by the Cystic Fibrosis Transmembrane Conductance Regulator (CFTR) First Cytosolic Loop. J Biol Chem 2015; 291:1854-1865. [PMID: 26627831 DOI: 10.1074/jbc.m115.704809] [Citation(s) in RCA: 14] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [Key Words] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/16/2015] [Indexed: 11/06/2022] Open
Abstract
In this study, we present data indicating a robust and specific domain interaction between the cystic fibrosis transmembrane conductance regulator (CFTR) first cytosolic loop (CL1) and nucleotide binding domain 1 (NBD1) that allows ion transport to proceed in a regulated fashion. We used co-precipitation and ELISA to establish the molecular contact and showed that binding kinetics were not altered by the common clinical mutation F508del. Both intrinsic ATPase activity and CFTR channel gating were inhibited severely by CL1 peptide, suggesting that NBD1/CL1 binding is a crucial requirement for ATP hydrolysis and channel function. In addition to cystic fibrosis, CFTR dysregulation has been implicated in the pathogenesis of prevalent diseases such as chronic obstructive pulmonary disease, acquired rhinosinusitis, pancreatitis, and lethal secretory diarrhea (e.g. cholera). On the basis of clinical relevance of the CFTR as a therapeutic target, a cell-free drug screen was established to identify modulators of NBD1/CL1 channel activity independent of F508del CFTR and pharmacologic rescue. Our findings support a targetable mechanism of CFTR regulation in which conformational changes in the NBDs cause reorientation of transmembrane domains via interactions with CL1 and result in channel gating.
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Affiliation(s)
- Annette Ehrhardt
- From the Gregory Fleming James Cystic Fibrosis Research Center and; the Department of Pediatrics, Emory University, Atlanta, Georgia 30322
| | - W Joon Chung
- From the Gregory Fleming James Cystic Fibrosis Research Center and; Departments of Neurobiology
| | - Louise C Pyle
- From the Gregory Fleming James Cystic Fibrosis Research Center and
| | - Wei Wang
- Cellular, Integrative, and Developmental Biology
| | | | - Cory M Mulvihill
- the Hospital for Sick Children Research Institute, Toronto M5G 1X8, Canada
| | | | - Jeong Hong
- From the Gregory Fleming James Cystic Fibrosis Research Center and; Cellular, Integrative, and Developmental Biology
| | - Sadanandan E Velu
- Chemistry, University of Alabama at Birmingham, Birmingham, Alabama 35294
| | - Hal A Lewis
- Bristol-Myers Squibb, Princeton, New Jersey 08543
| | | | - Steve Aller
- From the Gregory Fleming James Cystic Fibrosis Research Center and; Pharmacology, and
| | - Christine E Bear
- the Hospital for Sick Children Research Institute, Toronto M5G 1X8, Canada,; the Departments of Biochemistry and; Physiology, University of Toronto, Toronto M5G 1X8, Canada, and
| | - Gergely L Lukacs
- the Department of Physiology, McGill University, Montreal H3G 1Y6, Canada
| | - Kevin L Kirk
- From the Gregory Fleming James Cystic Fibrosis Research Center and; Cellular, Integrative, and Developmental Biology
| | - Eric J Sorscher
- the Department of Pediatrics, Emory University, Atlanta, Georgia 30322,.
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11
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Schneider EK, Huang JX, Carbone V, Baker M, Azad MAK, Cooper MA, Li J, Velkov T. Drug-drug plasma protein binding interactions of ivacaftor. J Mol Recognit 2015; 28:339-48. [PMID: 25707701 DOI: 10.1002/jmr.2447] [Citation(s) in RCA: 29] [Impact Index Per Article: 3.2] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/16/2014] [Revised: 11/04/2014] [Accepted: 11/05/2014] [Indexed: 11/11/2022]
Abstract
Ivacaftor is a novel cystic fibrosis (CF) transmembrane conductance regulator (CFTR) potentiator that improves the pulmonary function for patients with CF bearing a G551D CFTR-protein mutation. Because ivacaftor is highly bound (>97%) to plasma proteins, there is the strong possibility that co-administered CF drugs may compete for the same plasma protein binding sites and impact the free drug concentration. This, in turn, could lead to drastic changes in the in vivo efficacy of ivacaftor and therapeutic outcomes. This biochemical study compares the binding affinity of ivacaftor and co-administered CF drugs for human serum albumin (HSA) and α1 -acid glycoprotein (AGP) using surface plasmon resonance and fluorimetric binding assays that measure the displacement of site-selective probes. Because of their ability to strongly compete for the ivacaftor binding sites on HSA and AGP, drug-drug interactions between ivacaftor are to be expected with ducosate, montelukast, ibuprofen, dicloxacillin, omeprazole, and loratadine. The significance of these plasma protein drug-drug interactions is also interpreted in terms of molecular docking simulations. This in vitro study provides valuable insights into the plasma protein drug-drug interactions of ivacaftor with co-administered CF drugs. The data may prove useful in future clinical trials for a staggered treatment that aims to maximize the effective free drug concentration and clinical efficacy of ivacaftor.
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Affiliation(s)
- Elena K Schneider
- Drug Delivery, Disposition and Dynamics, Monash Institute of Pharmaceutical Sciences, Monash University, Parkville, Victoria, 3052, Australia; Department of Pharmacology and Toxicology, Leopold-Franzen-Universität Innsbruck, Innsbruck, 6020, Austria
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12
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Pasyk S, Molinski S, Ahmadi S, Ramjeesingh M, Huan LJ, Chin S, Du K, Yeger H, Taylor P, Moran MF, Bear CE. The major cystic fibrosis causing mutation exhibits defective propensity for phosphorylation. Proteomics 2014; 15:447-61. [PMID: 25330774 DOI: 10.1002/pmic.201400218] [Citation(s) in RCA: 23] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/15/2014] [Revised: 09/24/2014] [Accepted: 10/16/2014] [Indexed: 11/11/2022]
Abstract
The major cystic fibrosis causing mutation, F508del-CFTR (where CFTR is cystic fibrosis transmembrane conductance regulator), impairs biosynthetic maturation of the CFTR protein, limiting its expression as a phosphorylation-dependent channel on the cell surface. The maturation defect can be partially rescued by low-temperature (27°C) cell culture conditions or small-molecule corrector compounds. Following its partial rescue, the open probability of F508del-CFTR is enhanced by the potentiator compound, VX-770. However, the channel activity of rescued F508del-CFTR remains less than that of the Wt-CFTR protein in the presence of VX-770. In this study, we asked if there are allosteric effects of F508del on the phosphorylation-regulated R domain. To identify defects in the R domain, we compared the phosphorylation status at protein kinase A sites in the R domain of Wt and F508del-CFTR. Here we show that phosphorylation of Ser-660, quantified by SRM-MS, is reduced in F508del-CFTR. Although the generation of a phosphomimic at this site (substituting aspartic acid for serine) did not modify the maturation defect, it did enhance F508del-CFTR channel function after pharmacological rescue with corrector VX-809, and treatment with the potentiator, VX-770. These findings support the concept that defective phosphorylation of F508del-CFTR partially accounts for its altered channel activity at the cell surface.
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Affiliation(s)
- Stan Pasyk
- Programme in Molecular Structure and Function, Research Institute, The Hospital for Sick Children, Toronto, ON, Canada; Department of Biochemistry, The University of Toronto, Toronto, ON, Canada
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13
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Broadbent SD, Ramjeesingh M, Bear CE, Argent BE, Linsdell P, Gray MA. The cystic fibrosis transmembrane conductance regulator is an extracellular chloride sensor. Pflugers Arch 2014; 467:1783-94. [PMID: 25277268 PMCID: PMC4502298 DOI: 10.1007/s00424-014-1618-8] [Citation(s) in RCA: 15] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/01/2014] [Revised: 09/22/2014] [Accepted: 09/23/2014] [Indexed: 02/07/2023]
Abstract
The cystic fibrosis transmembrane conductance regulator (CFTR) is a Cl(-) channel that governs the quantity and composition of epithelial secretions. CFTR function is normally tightly controlled as dysregulation can lead to life-threatening diseases such as secretory diarrhoea and cystic fibrosis. CFTR activity is regulated by phosphorylation of its cytosolic regulatory (R) domain, and ATP binding and hydrolysis at two nucleotide-binding domains (NBDs). Here, we report that CFTR activity is also controlled by extracellular Cl(-) concentration ([Cl(-)]o). Patch clamp current recordings show that a rise in [Cl(-)]o stimulates CFTR channel activity, an effect conferred by a single arginine residue, R899, in extracellular loop 4 of the protein. Using NBD mutants and ATP dose response studies in WT channels, we determined that [Cl(-)]o sensing was linked to changes in ATP binding energy at NBD1, which likely impacts NBD dimer stability. Biochemical measurements showed that increasing [Cl(-)]o decreased the intrinsic ATPase activity of CFTR mainly through a reduction in maximal ATP turnover. Our studies indicate that sensing [Cl(-)]o is a novel mechanism for regulating CFTR activity and suggest that the luminal ionic environment is an important physiological arbiter of CFTR function, which has significant implications for salt and fluid homeostasis in epithelial tissues.
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Affiliation(s)
- Steven D. Broadbent
- Epithelial Research Group, Institute for Cell & Molecular Biosciences, Newcastle University, Newcastle upon Tyne, NE2 4HH UK
- Department of Physiology & Biophysics, Dalhousie University, Halifax, NS Canada
| | - Mohabir Ramjeesingh
- Hospital for Sick Children and Departments of Biochemistry and Physiology, University of Toronto, Toronto, ON Canada
| | - Christine E. Bear
- Hospital for Sick Children and Departments of Biochemistry and Physiology, University of Toronto, Toronto, ON Canada
| | - Barry E. Argent
- Epithelial Research Group, Institute for Cell & Molecular Biosciences, Newcastle University, Newcastle upon Tyne, NE2 4HH UK
| | - Paul Linsdell
- Department of Physiology & Biophysics, Dalhousie University, Halifax, NS Canada
| | - Michael A. Gray
- Epithelial Research Group, Institute for Cell & Molecular Biosciences, Newcastle University, Newcastle upon Tyne, NE2 4HH UK
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14
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Yang Z, Wang C, Zhou Q, An J, Hildebrandt E, Aleksandrov LA, Kappes JC, DeLucas LJ, Riordan JR, Urbatsch IL, Hunt JF, Brouillette CG. Membrane protein stability can be compromised by detergent interactions with the extramembranous soluble domains. Protein Sci 2014; 23:769-89. [PMID: 24652590 PMCID: PMC4093953 DOI: 10.1002/pro.2460] [Citation(s) in RCA: 67] [Impact Index Per Article: 6.7] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/14/2013] [Revised: 03/07/2014] [Accepted: 03/17/2014] [Indexed: 11/06/2022]
Abstract
Detergent interaction with extramembranous soluble domains (ESDs) is not commonly considered an important determinant of integral membrane protein (IMP) behavior during purification and crystallization, even though ESDs contribute to the stability of many IMPs. Here we demonstrate that some generally nondenaturing detergents critically destabilize a model ESD, the first nucleotide-binding domain (NBD1) from the human cystic fibrosis transmembrane conductance regulator (CFTR), a model IMP. Notably, the detergents show equivalent trends in their influence on the stability of isolated NBD1 and full-length CFTR. We used differential scanning calorimetry (DSC) and circular dichroism (CD) spectroscopy to monitor changes in NBD1 stability and secondary structure, respectively, during titration with a series of detergents. Their effective harshness in these assays mirrors that widely accepted for their interaction with IMPs, i.e., anionic > zwitterionic > nonionic. It is noteworthy that including lipids or nonionic detergents is shown to mitigate detergent harshness, as will limiting contact time. We infer three thermodynamic mechanisms from the observed thermal destabilization by monomer or micelle: (i) binding to the unfolded state with no change in the native structure (all detergent classes); (ii) native state binding that alters thermodynamic properties and perhaps conformation (nonionic detergents); and (iii) detergent binding that directly leads to denaturation of the native state (anionic and zwitterionic). These results demonstrate that the accepted model for the harshness of detergents applies to their interaction with an ESD. It is concluded that destabilization of extramembranous soluble domains by specific detergents will influence the stability of some IMPs during purification.
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Affiliation(s)
- Zhengrong Yang
- Department of Chemistry, University of Alabama at BirminghamBirmingham, Alabama
- Center for Structural Biology, University of Alabama at BirminghamBirmingham, Alabama
| | - Chi Wang
- Department of Biological Sciences, Columbia UniversityNew York, New York
| | - Qingxian Zhou
- Center for Structural Biology, University of Alabama at BirminghamBirmingham, Alabama
| | - Jianli An
- Center for Structural Biology, University of Alabama at BirminghamBirmingham, Alabama
| | - Ellen Hildebrandt
- Department of Cell Biology and Biochemistry, Texas Tech University Health Sciences CenterLubbock, Texas
| | - Luba A Aleksandrov
- Department of Biochemistry and Biophysics, The University of North Carolina at Chapel HillChapel Hill, North Carolina
- Cystic Fibrosis Treatment and Research Center, The University of North Carolina at Chapel HillChapel Hill, North Carolina
| | - John C Kappes
- Department of Medicine, University of Alabama at BirminghamBirmingham, Alabama
- Birmingham Veterans Affairs Medical Center, Research ServiceBirmingham, Alabama
| | - Lawrence J DeLucas
- Center for Structural Biology, University of Alabama at BirminghamBirmingham, Alabama
- Department of Optometry, University of Alabama at BirminghamBirmingham, Alabama
| | - John R Riordan
- Department of Biochemistry and Biophysics, The University of North Carolina at Chapel HillChapel Hill, North Carolina
- Cystic Fibrosis Treatment and Research Center, The University of North Carolina at Chapel HillChapel Hill, North Carolina
| | - Ina L Urbatsch
- Department of Cell Biology and Biochemistry, Texas Tech University Health Sciences CenterLubbock, Texas
- Center for Membrane Protein Research, Texas Tech University Health Sciences CenterLubbock, TX
| | - John F Hunt
- Department of Biological Sciences, Columbia UniversityNew York, New York
| | - Christie G Brouillette
- Department of Chemistry, University of Alabama at BirminghamBirmingham, Alabama
- Center for Structural Biology, University of Alabama at BirminghamBirmingham, Alabama
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15
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Randak CO, Dong Q, Ver Heul AR, Elcock AH, Welsh MJ. ATP and AMP mutually influence their interaction with the ATP-binding cassette (ABC) adenylate kinase cystic fibrosis transmembrane conductance regulator (CFTR) at separate binding sites. J Biol Chem 2013; 288:27692-27701. [PMID: 23921386 PMCID: PMC3779764 DOI: 10.1074/jbc.m113.479675] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/18/2022] Open
Abstract
Cystic fibrosis transmembrane conductance regulator (CFTR) is an anion channel in the ATP-binding cassette (ABC) transporter protein family. In the presence of ATP and physiologically relevant concentrations of AMP, CFTR exhibits adenylate kinase activity (ATP + AMP ⇆ 2 ADP). Previous studies suggested that the interaction of nucleotide triphosphate with CFTR at ATP-binding site 2 is required for this activity. Two other ABC proteins, Rad50 and a structural maintenance of chromosome protein, also have adenylate kinase activity. All three ABC adenylate kinases bind and hydrolyze ATP in the absence of other nucleotides. However, little is known about how an ABC adenylate kinase interacts with ATP and AMP when both are present. Based on data from non-ABC adenylate kinases, we hypothesized that ATP and AMP mutually influence their interaction with CFTR at separate binding sites. We further hypothesized that only one of the two CFTR ATP-binding sites is involved in the adenylate kinase reaction. We found that 8-azidoadenosine 5′-triphosphate (8-N3-ATP) and 8-azidoadenosine 5′-monophosphate (8-N3-AMP) photolabeled separate sites in CFTR. Labeling of the AMP-binding site with 8-N3-AMP required the presence of ATP. Conversely, AMP enhanced photolabeling with 8-N3-ATP at ATP-binding site 2. The adenylate kinase active center probe P1,P5-di(adenosine-5′) pentaphosphate interacted simultaneously with an AMP-binding site and ATP-binding site 2. These results show that ATP and AMP interact with separate binding sites but mutually influence their interaction with the ABC adenylate kinase CFTR. They further indicate that the active center of the adenylate kinase comprises ATP-binding site 2.
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Affiliation(s)
| | | | | | | | - Michael J Welsh
- Departments of Internal Medicine; Molecular Physiology and Biophysics, University of Iowa, Iowa City, Iowa 52242; Howard Hughes Medical Institute, Iowa City, Iowa 52242
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16
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Jih KY, Hwang TC. Vx-770 potentiates CFTR function by promoting decoupling between the gating cycle and ATP hydrolysis cycle. Proc Natl Acad Sci U S A 2013; 110:4404-9. [PMID: 23440202 PMCID: PMC3600496 DOI: 10.1073/pnas.1215982110] [Citation(s) in RCA: 162] [Impact Index Per Article: 14.7] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/18/2022] Open
Abstract
Vx-770 (Ivacaftor), a Food and Drug Administration (FDA)-approved drug for clinical application to patients with cystic fibrosis (CF), shifts the paradigm from conventional symptomatic treatments to therapeutics directly tackling the root of the disease: functional defects of the cystic fibrosis transmembrane conductance regulator (CFTR) chloride channel caused by pathogenic mutations. The underlying mechanism for the action of Vx-770 remains elusive partly because this compound not only increases the activity of wild-type (WT) channels whose gating is primarily controlled by ATP binding/hydrolysis, but also improves the function of G551D-CFTR, a disease-associated mutation that abolishes CFTR's responsiveness to ATP. Here we provide a unified theory to account for this dual effect of Vx-770. We found that Vx-770 enhances spontaneous, ATP-independent activity of WT-CFTR to a similar magnitude as its effects on G551D channels, a result essentially explaining Vx-770's effect on G551D-CFTR. Furthermore, Vx-770 increases the open time of WT-CFTR in an [ATP]-dependent manner. This distinct kinetic effect is accountable with a newly proposed CFTR gating model depicting an [ATP]-dependent "reentry" mechanism that allows CFTR shuffling among different open states by undergoing multiple rounds of ATP hydrolysis. We further examined the effect of Vx-770 on R352C-CFTR, a unique mutant that allows direct observation of hydrolysis-triggered gating events. Our data corroborate that Vx-770 increases the open time of WT-CFTR by stabilizing a posthydrolytic open state and thereby fosters decoupling between the gating cycle and ATP hydrolysis cycle. The current study also suggests that this unique mechanism of drug action can be further exploited to develop strategies that enhance the function of CFTR.
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Affiliation(s)
- Kang-Yang Jih
- Dalton Cardiovascular Research Center, University of Missouri, Columbia, MO 65211; and
- Department of Medical Pharmacology and Physiology, University of Missouri, Columbia, MO 65212
| | - Tzyh-Chang Hwang
- Dalton Cardiovascular Research Center, University of Missouri, Columbia, MO 65211; and
- Department of Medical Pharmacology and Physiology, University of Missouri, Columbia, MO 65212
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17
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Randak CO, Ver Heul AR, Welsh MJ. Demonstration of phosphoryl group transfer indicates that the ATP-binding cassette (ABC) transporter cystic fibrosis transmembrane conductance regulator (CFTR) exhibits adenylate kinase activity. J Biol Chem 2012; 287:36105-10. [PMID: 22948143 PMCID: PMC3476278 DOI: 10.1074/jbc.m112.408450] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/06/2012] [Revised: 08/30/2012] [Indexed: 01/18/2023] Open
Abstract
Cystic fibrosis transmembrane conductance regulator (CFTR) is a membrane-spanning adenosine 5'-triphosphate (ATP)-binding cassette (ABC) transporter. ABC transporters and other nuclear and cytoplasmic ABC proteins have ATPase activity that is coupled to their biological function. Recent studies with CFTR and two nonmembrane-bound ABC proteins, the DNA repair enzyme Rad50 and a structural maintenance of chromosome (SMC) protein, challenge the model that the function of all ABC proteins depends solely on their associated ATPase activity. Patch clamp studies indicated that in the presence of physiologically relevant concentrations of adenosine 5'-monophosphate (AMP), CFTR Cl(-) channel function is coupled to adenylate kinase activity (ATP+AMP <==> 2 ADP). Work with Rad50 and SMC showed that these enzymes catalyze both ATPase and adenylate kinase reactions. However, despite the supportive electrophysiological results with CFTR, there are no biochemical data demonstrating intrinsic adenylate kinase activity of a membrane-bound ABC transporter. We developed a biochemical assay for adenylate kinase activity, in which the radioactive γ-phosphate of a nucleotide triphosphate could transfer to a photoactivatable AMP analog. UV irradiation could then trap the (32)P on the adenylate kinase. With this assay, we discovered phosphoryl group transfer that labeled CFTR, thereby demonstrating its adenylate kinase activity. Our results also suggested that the interaction of nucleotide triphosphate with CFTR at ATP-binding site 2 is required for adenylate kinase activity. These biochemical data complement earlier biophysical studies of CFTR and indicate that the ABC transporter CFTR can function as an adenylate kinase.
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Affiliation(s)
- Christoph O Randak
- Department of Pediatrics, University of Iowa, Iowa City, Iowa 52242, USA.
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18
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Eckford PDW, Li C, Ramjeesingh M, Bear CE. Cystic fibrosis transmembrane conductance regulator (CFTR) potentiator VX-770 (ivacaftor) opens the defective channel gate of mutant CFTR in a phosphorylation-dependent but ATP-independent manner. J Biol Chem 2012; 287:36639-49. [PMID: 22942289 DOI: 10.1074/jbc.m112.393637] [Citation(s) in RCA: 216] [Impact Index Per Article: 18.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/13/2023] Open
Abstract
The cystic fibrosis transmembrane conductance regulator (CFTR) acts as a channel on the apical membrane of epithelia. Disease-causing mutations in the cystic fibrosis gene can lead to CFTR protein misfolding as in the case of the F508del mutation and/or channel dysfunction. Recently, a small molecule, VX-770 (ivacaftor), has shown efficacy in restoring lung function in patients bearing the G551D mutation, and this has been linked to repair of its channel gating defect. However, these studies did not reveal the mechanism of action of VX-770 in detail. Normally, CFTR channel activity is regulated by phosphorylation, ATP binding, and hydrolysis. Hence, it has been hypothesized that VX-770 modifies one or more of these metabolic events. In this study, we examined VX-770 activity using a reconstitution system for purified CFTR protein, a system that enables control of known regulatory factors. We studied the consequences of VX-770 interaction with CFTR incorporated in planar lipid bilayers and in proteoliposomes, using a novel flux-based assay. We found that purified and phosphorylated CFTR was potentiated in the presence of Mg-ATP, suggesting that VX-770 bound directly to the CFTR protein, rather than associated kinases or phosphatases. Interestingly, we also found that VX-770 enhanced the channel activity of purified and mutant CFTR in the nominal absence of Mg-ATP. These findings suggest that VX-770 can cause CFTR channel opening through a nonconventional ATP-independent mechanism. This work sets the stage for future studies of the structural properties that mediate CFTR gating using VX-770 as a probe.
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Affiliation(s)
- Paul D W Eckford
- Programme of Molecular Structure and Function, Research Institute, Hospital for Sick Children, Toronto M5G 1X8, Canada
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19
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Zoghbi ME, Fuson KL, Sutton RB, Altenberg GA. Kinetics of the association/dissociation cycle of an ATP-binding cassette nucleotide-binding domain. J Biol Chem 2012; 287:4157-64. [PMID: 22158619 PMCID: PMC3281709 DOI: 10.1074/jbc.m111.318378] [Citation(s) in RCA: 26] [Impact Index Per Article: 2.2] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/28/2011] [Revised: 12/07/2011] [Indexed: 11/06/2022] Open
Abstract
Most ATP binding cassette (ABC) proteins are pumps that transport substrates across biological membranes using the energy of ATP hydrolysis. Functional ABC proteins have two nucleotide-binding domains (NBDs) that bind and hydrolyze ATP, but the molecular mechanism of nucleotide hydrolysis is unresolved. This is due in part to the limited kinetic information on NBD association and dissociation. Here, we show dimerization of a catalytically active NBD and follow in real time the association and dissociation of NBDs from the changes in fluorescence emission of a tryptophan strategically located at the center of the dimer interface. Spectroscopic and structural studies demonstrated that the tryptophan can be used as dimerization probe, and we showed that under hydrolysis conditions (millimolar MgATP), not only the dimer dissociation rate increases, but also the dimerization rate. Neither dimer formation or dissociation are clearly favored, and the end result is a dynamic equilibrium where the concentrations of monomer and dimer are very similar. We proposed that based on their variable rates of hydrolysis, the rate-limiting step of the hydrolysis cycle may differ among full-length ABC proteins.
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Affiliation(s)
- Maria E. Zoghbi
- From the Department of Cell Physiology and Molecular Biophysics and Center for Membrane Protein Research, Texas Tech Health Sciences Center, Lubbock, Texas 79430-6551
| | - Kerry L. Fuson
- From the Department of Cell Physiology and Molecular Biophysics and Center for Membrane Protein Research, Texas Tech Health Sciences Center, Lubbock, Texas 79430-6551
| | - Roger B. Sutton
- From the Department of Cell Physiology and Molecular Biophysics and Center for Membrane Protein Research, Texas Tech Health Sciences Center, Lubbock, Texas 79430-6551
| | - Guillermo A. Altenberg
- From the Department of Cell Physiology and Molecular Biophysics and Center for Membrane Protein Research, Texas Tech Health Sciences Center, Lubbock, Texas 79430-6551
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20
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Insights into the mechanisms underlying CFTR channel activity, the molecular basis for cystic fibrosis and strategies for therapy. Essays Biochem 2012; 50:233-48. [PMID: 21967060 DOI: 10.1042/bse0500233] [Citation(s) in RCA: 33] [Impact Index Per Article: 2.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/07/2023]
Abstract
Mutations in the CFTR (cystic fibrosis transmembrane conductance regulator) cause CF (cystic fibrosis), a fatal genetic disease commonly leading to airway obstruction with recurrent airway inflammation and infection. Pulmonary obstruction in CF has been linked to the loss of CFTR function as a regulated Cl- channel on the lumen-facing membrane of the epithelium lining the airways. We have learned much about the molecular basis for nucleotide- and phosphorylation-dependent regulation of channel activity of the normal (wild-type) version of the CFTR protein through electrophysiological studies. The major CF-causing mutation, F508del-CFTR, causes the protein to misfold and be retained in the ER (endoplasmic reticulum). Importantly, recent studies in cell culture have shown that retention in the ER can be 'corrected' through the application of certain small-molecule modulators and, once at the surface, the altered channel function of the major mutant can be 'potentiated', pharmacologically. Importantly, two such small molecules, a 'corrector' (VX-809) and a 'potentiator' (VX-770) compound are undergoing clinical trial for the treatment of CF. In this chapter, we describe recent discoveries regarding the wild-type CFTR and F508del-CFTR protein, in the context of molecular models based on X-ray structures of prokaryotic ABC (ATP-binding cassette) proteins. Finally, we discuss the promise of small-molecule modulators to probe the relationship between structure and function in the wild-type protein, the molecular defects caused by the most common mutation and the structural changes required to correct these defects.
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21
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Peng X, Wang L, Chen G, Wang X. Dynamic Expression of Adenylate Kinase 2 in the Hippocampus of Pilocarpine Model Rats. J Mol Neurosci 2012; 47:150-7. [DOI: 10.1007/s12031-011-9703-3] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/18/2011] [Accepted: 12/23/2011] [Indexed: 01/24/2023]
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22
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Miki H, Zhou Z, Li M, Hwang TC, Bompadre SG. Potentiation of disease-associated cystic fibrosis transmembrane conductance regulator mutants by hydrolyzable ATP analogs. J Biol Chem 2010; 285:19967-75. [PMID: 20406820 PMCID: PMC2888408 DOI: 10.1074/jbc.m109.092684] [Citation(s) in RCA: 51] [Impact Index Per Article: 3.6] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/08/2009] [Revised: 03/31/2010] [Indexed: 11/06/2022] Open
Abstract
The cystic fibrosis transmembrane conductance regulator (CFTR) is a chloride channel belonging to the ATP-binding cassette transporter superfamily. CFTR is gated by ATP binding and hydrolysis at its two nucleotide-binding domains (NBDs), which dimerize in the presence of ATP to form two ATP-binding pockets (ABP1 and ABP2). Mutations reducing the activity of CFTR result in the genetic disease cystic fibrosis. Two of the most common mutations causing a severe phenotype are G551D and DeltaF508. Previously we found that the ATP analog N(6)-(2-phenylethyl)-ATP (P-ATP) potentiates the activity of G551D by approximately 7-fold. Here we show that 2'-deoxy-ATP (dATP), but not 3'-deoxy-ATP, increases the activity of G551D-CFTR by approximately 8-fold. We custom synthesized N(6)-(2-phenylethyl)-2'-deoxy-ATP (P-dATP), an analog combining the chemical modifications in dATP and P-ATP. This new analog enhances G551D current by 36.2 +/- 5.4-fold suggesting an independent but energetically additive action of these two different chemical modifications. We show that P-dATP binds to ABP1 to potentiate the activity of G551D, and mutations in both sides of ABP1 (W401G and S1347G) decrease its potentiation effect, suggesting that the action of P-dATP takes place at the interface of both NBDs. Interestingly, P-dATP completely rectified the gating abnormality of DeltaF508-CFTR by increasing its activity by 19.5 +/- 3.8-fold through binding to both ABPs. This result highlights the severity of the gating defect associated with DeltaF508, the most prevalent disease-associated mutation. The new analog P-dATP can be not only an invaluable tool to study CFTR gating, but it can also serve as a proof-of-principle that, by combining elements that potentiate the channel activity independently, the increase in chloride transport necessary to reach a therapeutic target is attainable.
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Affiliation(s)
- Haruna Miki
- From the Dalton Cardiovascular Research Center and
- the Osaka University of Pharmaceutical Sciences, Takatsuki, Osaka 569-1094, Japan
| | - Zhen Zhou
- From the Dalton Cardiovascular Research Center and
| | - Min Li
- From the Dalton Cardiovascular Research Center and
| | - Tzyh-Chang Hwang
- From the Dalton Cardiovascular Research Center and
- the Department of Medical Pharmacology and Physiology, University of Missouri, Columbia, Missouri 65211 and
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23
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Lammens A, Hopfner KP. Structural basis for adenylate kinase activity in ABC ATPases. J Mol Biol 2010; 401:265-73. [PMID: 20600125 DOI: 10.1016/j.jmb.2010.06.029] [Citation(s) in RCA: 9] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/10/2010] [Revised: 05/31/2010] [Accepted: 06/15/2010] [Indexed: 01/24/2023]
Abstract
ATP-binding cassette (ABC) enzymes are involved in diverse biological processes ranging from transmembrane transport to chromosome cohesion and DNA repair. They typically use ATP hydrolysis to conduct energy-dependent biological reactions. However, the cystic fibrosis transmembrane conductance regulator and the DNA repair protein Rad50 can also catalyze the adenylate kinase reaction (ATP+AMP<-->2ADP). To clarify and provide a mechanistic basis for the adenylate kinase activity of ABC enzymes, we report the crystal structure of the nucleotide-binding domain of the Pyrococcus furiosus structural maintenance of chromosome protein (pfSMC(nbd)) in complex with the adenylate kinase inhibitor P(1),P(5)-di(adenosine-5')pentaphosphate. We show that pfSMC(nbd) possesses reverse adenylate kinase activity. Our results suggest that in adenylate kinase reactions, ATP binds to its canonical binding site while AMP binds to the Q-loop glutamine and a hydration water of the Mg(2+) ion. Furthermore, mutational analysis indicates that adenylate kinase reaction occurs in the engaged pfSMC(nbd) dimer and requires the Signature motif for phosphate transfer. Our results explain how ATP hydrolysis and adenylate kinase reactions can be catalyzed by the same functional motifs within the structural framework of ABC enzymes. Thus, adenylate kinase activity is likely to be a latent activity in many ABC enzymes.
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Affiliation(s)
- Alfred Lammens
- Center for Integrated Protein Science and Gene Center, Department of Biochemistry, Ludwig-Maximilians University of Munich, Feodor-Lynen-Str. 25, 81377 Munich, Germany
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Chiaw PK, Wellhauser L, Huan LJ, Ramjeesingh M, Bear CE. A Chemical Corrector Modifies the Channel Function of F508del-CFTR. Mol Pharmacol 2010; 78:411-8. [DOI: 10.1124/mol.110.065862] [Citation(s) in RCA: 51] [Impact Index Per Article: 3.6] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/06/2023] Open
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25
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ATP-independent CFTR channel gating and allosteric modulation by phosphorylation. Proc Natl Acad Sci U S A 2010; 107:3888-93. [PMID: 20133716 DOI: 10.1073/pnas.0913001107] [Citation(s) in RCA: 60] [Impact Index Per Article: 4.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/18/2022] Open
Abstract
Cystic fibrosis (CF) is caused by mutations in the cystic fibrosis transmembrane conductance regulator (CFTR) channel, an ATP binding cassette (ABC) transporter. CFTR gating is linked to ATP binding and dimerization of its two nucleotide binding domains (NBDs). Channel activation also requires phosphorylation of the R domain by poorly understood mechanisms. Unlike conventional ligand-gated channels, CFTR is an ATPase for which ligand (ATP) release typically involves nucleotide hydrolysis. The extent to which CFTR gating conforms to classic allosteric schemes of ligand activation is unclear. Here, we describe point mutations in the CFTR cytosolic loops that markedly increase ATP-independent (constitutive) channel activity. This finding is consistent with an allosteric gating mechanism in which ligand shifts the equilibrium between inactive and active states but is not essential for channel opening. Constitutive mutations mapped to the putative symmetry axis of CFTR based on the crystal structures of related ABC transporters, a common theme for activating mutations in ligand-gated channels. Furthermore, the ATP sensitivity of channel activation was strongly enhanced by these constitutive mutations, as predicted for an allosteric mechanism (reciprocity between protein activation and ligand occupancy). Introducing constitutive mutations into CFTR channels that cannot open in response to ATP (i.e., the G551D CF mutant and an NBD2-deletion mutant) substantially rescued their activities. Importantly, constitutive mutants that opened without ATP or NBD2 still required R domain phosphorylation for optimal activity. Our results confirm that (i) CFTR gating exhibits features of protein allostery that are shared with conventional ligand-gated channels and (ii) the R domain modulates CFTR activity independent of ATP-induced NBD dimerization.
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Kloch M, Milewski M, Nurowska E, Dworakowska B, Cutting GR, Dołowy K. The H-loop in the second nucleotide-binding domain of the cystic fibrosis transmembrane conductance regulator is required for efficient chloride channel closing. Cell Physiol Biochem 2010; 25:169-80. [PMID: 20110677 DOI: 10.1159/000276549] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Accepted: 10/23/2009] [Indexed: 11/19/2022] Open
Abstract
The cystic fibrosis transmembrane conductance regulator (CFTR) is an ATP-binding cassette (ABC) transporter that functions as a cAMP-activated chloride channel. The recent model of CFTR gating predicts that the ATP binding to both nucleotide-binding domains (NBD1 and NBD2) of CFTR is required for the opening of the channel, while the ATP hydrolysis at NBD2 induces subsequent channel closing. In most ABC proteins, efficient hydrolysis of ATP requires the presence of the invariant histidine residue within the H-loop located in the C-terminal part of the NBD. However, the contribution of the corresponding region (H-loop) of NBD2 to the CFTR channel gating has not been examined so far. Here we report that the alanine substitution of the conserved dipeptide HR motif (HR-->AA) in the H-loop of NBD2 leads to prolonged open states of CFTR channel, indicating that the H-loop is required for efficient channel closing. On the other hand, the HR-->AA substitution lead to the substantial decrease of CFTR-mediated current density (pA/pF) in transfected HEK 293 cells, as recorded in the whole-cell patch-clamp analysis. These results suggest that the H-loop of NBD2, apart from being required for CFTR channel closing, may be involved in regulating CFTR trafficking to the cell surface.
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Affiliation(s)
- Monika Kloch
- Department of Biophysics, Warsaw University of Life Sciences SGGW, Warsaw, Poland
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Wellhauser L, Chiaw PK, Pasyk S, Li C, Ramjeesingh M, Bear CE. A Small-Molecule Modulator Interacts Directly with ΔPhe508-CFTR to Modify Its ATPase Activity and Conformational Stability. Mol Pharmacol 2009; 75:1430-8. [DOI: 10.1124/mol.109.055608] [Citation(s) in RCA: 61] [Impact Index Per Article: 4.1] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022] Open
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Direct interaction of a small-molecule modulator with G551D-CFTR, a cystic fibrosis-causing mutation associated with severe disease. Biochem J 2009; 418:185-90. [PMID: 18945216 DOI: 10.1042/bj20081424] [Citation(s) in RCA: 28] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/17/2022]
Abstract
CF (cystic fibrosis) is caused by mutations in CFTR (CF transmembrane conductance regulator), which cause its mistrafficking and/or dysfunction as a regulated chloride channel on the apical surface of epithelia. CFTR is a member of the ABC (ATP-binding-cassette) superfamily of membrane proteins and a disease-causing missense mutation within the ABC signature sequence; G551D-CFTR exhibits defective phosphorylation and ATP-dependent channel gating. Studies of the purified and reconstituted G551D-CFTR protein revealed that faulty gating is associated with defective ATP binding and ATPase activity, reflecting the key role of G551 in these functions. Recently, high-throughput screens of chemical libraries led to identification of modulators that enhance channel activity of G551D-CFTR. However, the molecular target(s) for these modulators and their mechanism of action remain unclear. In the present study, we evaluated the mechanism of action of one small-molecule modulator, VRT-532, identified as a specific modulator of CF-causing mutants. First, we confirmed that VRT-532 causes a significant increase in channel activity of G551D-CFTR using a novel assay of CFTR function in inside-out membrane vesicles. Biochemical studies of purified and reconstituted G551D-CFTR revealed that potentiation of the ATPase activity of VRT-532 is mediated by enhancing the affinity of the mutant for ATP. Interestingly, VRT-532 did not affect the ATPase activity of the Wt (wild-type) CFTR, supporting the idea that this compound corrects the specific molecular defect in this mutant. To summarize, these studies provide direct evidence that this compound binds to G551D-CFTR to rescue its specific defect in ATP binding and hydrolysis.
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A mutation in CFTR modifies the effects of the adenylate kinase inhibitor Ap5A on channel gating. Biophys J 2008; 95:5178-85. [PMID: 18805924 DOI: 10.1529/biophysj.108.140897] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/02/2023] Open
Abstract
Mutations in the gene that encodes the cystic fibrosis transmembrane conductance regulator (CFTR) cause cystic fibrosis. The CFTR anion channel is controlled by ATP binding and enzymatic activity at the two nucleotide-binding domains. CFTR exhibits two types of enzymatic activity: 1), ATPase activity in the presence of ATP and 2), adenylate kinase activity in the presence of ATP plus physiologic concentrations of AMP or ADP. Previous work showed that P(1),P(5)-di(adenosine-5')pentaphosphate (Ap(5)A), a specific adenylate kinases inhibitor, inhibited wild-type CFTR. In this study, we report that Ap(5)A increased activity of CFTR with an L1254A mutation. This mutation increased the EC50 for ATP by >10-fold and reduced channel activity by prolonging the closed state. Ap(5)A did not elicit current on its own nor did it alter ATP EC50 or maximal current. However, it changed the relationship between ATP concentration and current. At submaximal ATP concentrations, Ap(5)A stimulated current by stabilizing the channel open state. Whereas previous work indicated that adenylate kinase activity regulated channel opening, our data suggest that Ap(5)A binding may also influence channel closing. These results also suggest that a better understanding of the adenylate kinase activity of CFTR may be of value in developing new therapeutic strategies for cystic fibrosis.
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