1
|
Zhu Y, Xing X, Wang F, Chen L, Zhong C, Lu X, Yu Z, Yang Y, Yao Y, Song Q, Han S, Liu Z, Zhang P. The ATP-bound inward-open conformation of ABCC4 reveals asymmetric ATP binding for substrate transport. FEBS Lett 2024. [PMID: 38886124 DOI: 10.1002/1873-3468.14955] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/16/2024] [Revised: 04/25/2024] [Accepted: 05/27/2024] [Indexed: 06/20/2024]
Abstract
The multidrug resistance-associated protein (MRP) ABCC4 facilitates substrate transport across the cytoplasmic membrane, crucial for normal physiology and mediating multidrug resistance in tumor cells. Despite intensive studies on MRPs, ABCC4's transport mechanism remains incompletely understood. In this study, we unveiled an inward-open conformation with an ATP bound to degenerate NBD1. Additionally, we captured the structure with both ATP and substrate co-bound in the inward-open state. Our findings uncover the asymmetric ATP binding in ABCC4 and provide insights into substrate binding and transport mechanisms. ATP binding to NBD1 is parallel to substrate binding to ABCC4, and is a prerequisite for ATP-bound NBD2-induced global conformational changes. Our findings shed new light on targeting ABCC4 in combination with anticancer therapy.
Collapse
Affiliation(s)
- Yue Zhu
- Department of Radiation Oncology, The First Affiliated Hospital of Xi'an Jiaotong University, China
- Cancer Center, Renmin Hospital of Wuhan University, China
| | - Xiaoke Xing
- Cancer Center, Renmin Hospital of Wuhan University, China
| | - Fuxing Wang
- Kobilka Institute of Innovative Drug Discovery, School of Medicine, Chinese University of Hong Kong, Shenzhen, China
| | - Luojun Chen
- Cancer Center, Renmin Hospital of Wuhan University, China
| | - Chunhui Zhong
- Kobilka Institute of Innovative Drug Discovery, School of Medicine, Chinese University of Hong Kong, Shenzhen, China
| | - Xiting Lu
- School of Applied Biology, Shenzhen Institute of Technology, China
| | - Zhanwang Yu
- School of Applied Biology, Shenzhen Institute of Technology, China
| | - Yongbo Yang
- School of Life Sciences, Central China Normal University, Wuhan, China
| | - Yi Yao
- Cancer Center, Renmin Hospital of Wuhan University, China
| | - Qibin Song
- Cancer Center, Renmin Hospital of Wuhan University, China
| | - Suxia Han
- Department of Radiation Oncology, The First Affiliated Hospital of Xi'an Jiaotong University, China
| | - Zheng Liu
- Kobilka Institute of Innovative Drug Discovery, School of Medicine, Chinese University of Hong Kong, Shenzhen, China
| | - Pingfeng Zhang
- Cancer Center, Renmin Hospital of Wuhan University, China
| |
Collapse
|
2
|
Piccolo D, Zarouchlioti C, Bellingham J, Guarascio R, Ziaka K, Molday RS, Cheetham ME. A Proximity Complementation Assay to Identify Small Molecules That Enhance the Traffic of ABCA4 Misfolding Variants. Int J Mol Sci 2024; 25:4521. [PMID: 38674104 PMCID: PMC11050442 DOI: 10.3390/ijms25084521] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/29/2024] [Revised: 04/16/2024] [Accepted: 04/18/2024] [Indexed: 04/28/2024] Open
Abstract
ABCA4-related retinopathy is the most common inherited Mendelian eye disorder worldwide, caused by biallelic variants in the ATP-binding cassette transporter ABCA4. To date, over 2200 ABCA4 variants have been identified, including missense, nonsense, indels, splice site and deep intronic defects. Notably, more than 60% are missense variants that can lead to protein misfolding, mistrafficking and degradation. Currently no approved therapies target ABCA4. In this study, we demonstrate that ABCA4 misfolding variants are temperature-sensitive and reduced temperature growth (30 °C) improves their traffic to the plasma membrane, suggesting the folding of these variants could be rescuable. Consequently, an in vitro platform was developed for the rapid and robust detection of ABCA4 traffic to the plasma membrane in transiently transfected cells. The system was used to assess selected candidate small molecules that were reported to improve the folding or traffic of other ABC transporters. Two candidates, 4-PBA and AICAR, were identified and validated for their ability to enhance both wild-type ABCA4 and variant trafficking to the cell surface in cell culture. We envision that this platform could serve as a primary screen for more sophisticated in vitro testing, enabling the discovery of breakthrough agents to rescue ABCA4 protein defects and mitigate ABCA4-related retinopathy.
Collapse
Affiliation(s)
- Davide Piccolo
- UCL Institute of Ophthalmology, 11-43 Bath Street, London EC1V 9EL, UK; (D.P.); (C.Z.); (R.G.); (K.Z.)
| | - Christina Zarouchlioti
- UCL Institute of Ophthalmology, 11-43 Bath Street, London EC1V 9EL, UK; (D.P.); (C.Z.); (R.G.); (K.Z.)
| | - James Bellingham
- UCL Institute of Ophthalmology, 11-43 Bath Street, London EC1V 9EL, UK; (D.P.); (C.Z.); (R.G.); (K.Z.)
| | - Rosellina Guarascio
- UCL Institute of Ophthalmology, 11-43 Bath Street, London EC1V 9EL, UK; (D.P.); (C.Z.); (R.G.); (K.Z.)
| | - Kalliopi Ziaka
- UCL Institute of Ophthalmology, 11-43 Bath Street, London EC1V 9EL, UK; (D.P.); (C.Z.); (R.G.); (K.Z.)
| | - Robert S. Molday
- Department of Biochemistry and Molecular Biology, University of British Columbia, Vancouver, BC V6T 1Z3, Canada;
| | - Michael E. Cheetham
- UCL Institute of Ophthalmology, 11-43 Bath Street, London EC1V 9EL, UK; (D.P.); (C.Z.); (R.G.); (K.Z.)
| |
Collapse
|
3
|
Haque MS, Emi Y, Sakaguchi M. A conserved WXXE motif is an apical delivery determinant of ABC transporter C subfamily isoforms. Cell Struct Funct 2023; 48:71-82. [PMID: 36696993 PMCID: PMC10721954 DOI: 10.1247/csf.22049] [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: 06/30/2022] [Accepted: 07/15/2022] [Indexed: 01/25/2023] Open
Abstract
ATP-binding cassette transporter isoform C7 (ABCC7), also designated as cystic fibrosis transmembrane conductance regulator (CFTR), is exclusively targeted to the apical plasma membrane of polarized epithelial cells. Although the apical localization of ABCC7 in epithelia is crucial for the Cl- excretion into lumens, the mechanism regulating its apical localization is poorly understood. In the present study, an apical localization determinant was identified in the N-terminal 80-amino acid long cytoplasmic region of ABCC7 (NT80). In HepG2 cells, overexpression of NT80 significantly disturbed the apical expression of ABCC7 in a competitive manner, suggesting the presence of a sorting determinant in this region. Deletion analysis identified a potential sorting information within a 20-amino acid long peptide (aa 41-60) of NT80. Alanine scanning mutagenesis of this region in full-length ABCC7 further narrowed down the apical localization determinant to four amino acids, W57DRE60. This WDRE sequence was conserved among vertebrate ABCC7 orthologs. Site-directed mutagenesis showed that W57 and E60 were critical for the apical expression of ABCC7, confirming a novel apical sorting determinant of ABCC7. Furthermore, a WXXE motif (tryptophan and glutamic acid residues with two-amino acid spacing) was found to be conserved among the N-terminal regions of apically localized ABCC members with 12-TM configuration. The significance of the WXXE motif was demonstrated for proper trafficking of ABCC4 to the apical plasma membrane.Key words: apical plasma membrane, sorting, ATP-binding cassette transporter, CFTR, MRP4.
Collapse
Affiliation(s)
- Md Shajedul Haque
- Graduate School of Science, University of Hyogo, Harima Science Park City, Hyogo 678-1297, Japan
| | - Yoshikazu Emi
- Graduate School of Science, University of Hyogo, Harima Science Park City, Hyogo 678-1297, Japan
| | - Masao Sakaguchi
- Graduate School of Science, University of Hyogo, Harima Science Park City, Hyogo 678-1297, Japan
| |
Collapse
|
4
|
Si Y, Ma K, Hu Y, Si H, Zhai H. QSAR Model Study of 2,3,4,5-tetrahydro-1H-pyrido[4,3-b]indole of Cystic-brosis-transmembrane Conductance-regulator Gene Potentiators. LETT DRUG DES DISCOV 2021. [DOI: 10.2174/1570180818666211022142920] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022]
Abstract
Background:
Cystic fibrosis (CF) is a genetic disease, which has no effective treatment.
Objective:
The aim of this study is to predict the EC50 value of 2,3,4,5-tetrahydro-1H-pyrido[4,3-b]indole core as a novel chemotype of potentiators to establish a highly predicting quantitative structure-activity relationship model.
Methods:
41 products were optimized, and a linear model was built by a heuristic method in CODESSA program. In this study, 3 descriptors were selected and utilized to build a nonlinear model in gene expression programming.
Results:
The square of the correlation coefficient of the heuristic method is 0.57, and the s2 is 0.30. In gene expression programming, the square of correlation coefficient and the mean square error for the training set are 0.74 and 0.13, respectively. The square of correlation coefficient and the mean square error for the test set are 0.70 and 0.27, respectively.
Conclusion:
The GEP model has stronger predictive ability to help develop the novel structure of 2,3,4,5-tetrahydro-1H-pyrido[4,3-b]indole of cystic-brosis-transmembrane conductance-regulator gene potentiators.
Collapse
Affiliation(s)
- Yaru Si
- School of Biology, Qingdao University, Qingdao, 266071, China
| | - Kang Ma
- School of Basic Medicine, Ningxia Medical University, Yinchuan, Ningxia Hui Autonomous Region, 750004, China
| | - Yingfeng Hu
- School of Biology, Qingdao University, Qingdao, 266071, China
| | - Hongzong Si
- State Key Laboratory of Biopolysaccharide Fiber Forming and Ecological Textile; Qingdao University, Qingdao, 266071, China
| | - Honglin Zhai
- Department of Chemistry, Lanzhou University, Lanzhou 730000, China
| |
Collapse
|
5
|
CFTR Lifecycle Map-A Systems Medicine Model of CFTR Maturation to Predict Possible Active Compound Combinations. Int J Mol Sci 2021; 22:ijms22147590. [PMID: 34299207 PMCID: PMC8306775 DOI: 10.3390/ijms22147590] [Citation(s) in RCA: 4] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Key Words] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/18/2021] [Revised: 07/07/2021] [Accepted: 07/13/2021] [Indexed: 02/07/2023] Open
Abstract
Different causative therapeutics for CF patients have been developed. There are still no mutation-specific therapeutics for some patients, especially those with rare CFTR mutations. For this purpose, high-throughput screens have been performed which result in various candidate compounds, with mostly unclear modes of action. In order to elucidate the mechanism of action for promising candidate substances and to be able to predict possible synergistic effects of substance combinations, we used a systems biology approach to create a model of the CFTR maturation pathway in cells in a standardized, human- and machine-readable format. It is composed of a core map, manually curated from small-scale experiments in human cells, and a coarse map including interactors identified in large-scale efforts. The manually curated core map includes 170 different molecular entities and 156 reactions from 221 publications. The coarse map encompasses 1384 unique proteins from four publications. The overlap between the two data sources amounts to 46 proteins. The CFTR Lifecycle Map can be used to support the identification of potential targets inside the cell and elucidate the mode of action for candidate substances. It thereby provides a backbone to structure available data as well as a tool to develop hypotheses regarding novel therapeutics.
Collapse
|
6
|
Zhang L, Huang P, Huang C, Jiang L, Lu Z, Wang P. Varied clinical significance of ATP-binding cassette C sub-family members for lung adenocarcinoma. Medicine (Baltimore) 2021; 100:e25246. [PMID: 33879658 PMCID: PMC8078454 DOI: 10.1097/md.0000000000025246] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 03/18/2020] [Accepted: 03/01/2021] [Indexed: 12/25/2022] Open
Abstract
Lung adenocarcinoma (LUAD) is a lethal malignancy worldwide and a major public health concern. We explored the potential clinical significance for LUAD of ATP-binding cassette (ABC), sub-family C, consisting of ABCC1-6, 8-12, and cystic fibrosis transmembrane conductance regulator (CFTR).Five hundred LUAD patients from The Cancer Genome Atlas database were used for analysis, including differential expression and diagnostic and prognostic significance. Oncomine and MERAV databases were used to validate differential expression and diagnostic significance. A risk score model was constructed using prognosis-related ABCC members. Prognosis-related genes were further explored to correlate their expression with tumor stage progression. Interaction networks, including biological processes and metabolic pathways, were constructed using Cytoscape software and STRING website.ABCC1-3 consistently showed high expression in tumor tissues (all P ≤ 0.05). Most datasets indicated that ABCC5, 10, and 11 were highly expressed in tumor tissues whereas ABCC6, 9, and CFTR were highly expressed in nontumor tissues (all P ≤ 0.05). Diagnostic significance of ABCC3 and ABCC5 was consistently assessed and validated in three datasets (all area under the curve > 0.700) whereas ABCC6, 8, 10, 11, and CFTR were assessed in The Cancer Genome Atlas dataset and validated in one dataset (all area under the curve > 0.700). Prognostic analysis indicated that ABCC2, 6, and 8 mRNA expression was associated with survival of LUAD (all adjusted P ≤ .037). The risk score model constructed using ABCC2, 6, and 8 suggested prognostic significance for survival predictions. ABCC2 expression was associated with tumor stage, whereas ABCC6 and 8 were not. Interaction networks indicated that they were involved in establishment of localization, ion transport, plasma membrane, apical plasma membrane, adenylyl nucleotide binding, ABC transporters, ABC transporter disorders, ABC-family-protein-mediated transport, and bile secretion.Differentially expressed ABCC2 and ABCC5 might be diagnostic whereas ABCC2, 6, and 8 may be prognostic biomarkers for LUAD, possibly through ABC-family-mediated transporter disorders.
Collapse
|
7
|
Stieger B, Steiger J, Locher KP. Membrane lipids and transporter function. Biochim Biophys Acta Mol Basis Dis 2021; 1867:166079. [PMID: 33476785 DOI: 10.1016/j.bbadis.2021.166079] [Citation(s) in RCA: 28] [Impact Index Per Article: 9.3] [Reference Citation Analysis] [Abstract] [Key Words] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/15/2020] [Revised: 12/12/2020] [Accepted: 01/07/2021] [Indexed: 02/07/2023]
Abstract
Transport proteins are essential for cells in allowing the exchange of substances between cells and their environment across the lipid bilayer forming a tight barrier. Membrane lipids modulate the function of transmembrane proteins such as transporters in two ways: Lipids are tightly and specifically bound to transport proteins and in addition they modulate from the bulk of the lipid bilayer the function of transport proteins. This overview summarizes currently available information at the ultrastructural level on lipids tightly bound to transport proteins and the impact of altered bulk membrane lipid composition. Human diseases leading to altered lipid homeostasis will lead to altered membrane lipid composition, which in turn affect the function of transporter proteins.
Collapse
Affiliation(s)
- Bruno Stieger
- Department of Clinical Pharmacology and Toxicology, University Hospital Zurich, University of Zurich, 8091 Zurich, Switzerland.
| | - Julia Steiger
- Department of Clinical Pharmacology and Toxicology, University Hospital Zurich, University of Zurich, 8091 Zurich, Switzerland
| | - Kaspar P Locher
- Department of Biology, Institute of Molecular Biology and Biophysics, ETH Zurich, 8093 Zurich, Switzerland
| |
Collapse
|
8
|
Fougere B, Barnes KR, Francis ME, Claus LN, Cozzi RRF, Marshall WS. Focal adhesion kinase and osmotic responses in ionocytes of Fundulus heteroclitus, a euryhaline teleost fish. Comp Biochem Physiol A Mol Integr Physiol 2019; 241:110639. [PMID: 31863842 DOI: 10.1016/j.cbpa.2019.110639] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/21/2019] [Revised: 12/12/2019] [Accepted: 12/13/2019] [Indexed: 11/17/2022]
Abstract
Cystic Fibrosis Transmembrane conductance Regulator (CFTR) anion channels are the regulated exit pathway in Cl- secretion by teleost salt secreting ionocytes of the gill and opercular epithelia of euryhaline teleosts. By confocal light immunocytochemistry using regular and phospho-antibodies directed against conserved sites, we found that killifish CFTR (kfCFTR) and the tyrosine kinase Focal Adhesion Kinase (FAK) phosphorylated at Y407 (FAKpY407) and FAKpY397 are colocalized at the apical membrane and in subjacent membrane vesicles of ionocytes. Hypotonic shock and the α-2 adrenergic agonist clonidine rapidly and reversibly inhibit Cl- secretion by isolated opercular epithelia, simultaneous with dephosphorylation of FAKpY407 and increased FAKpY397, located in the apical membrane of ionocytes in the opercular epithelium. FAKpY407 is re-phosphorylated at the apical membrane of ionocytes and Cl- secretion rapidly restored by hypertonic shock, detectable at 2 min., maximum at 5 min and still elevated at 30 min. In isolated opercular epithelia, the FAK phosphorylation inhibitor Y15 and p38MAP kinase inhibitor SB203580 significantly blunted the recovery of short-circuit current (Isc, equal to Cl- secretion rate) after hypertonic shock. The cSRC inhibitor saracatinib dephosphorylated FAKpY861 seen near tight junctions of pavement cells, and reduced the increase in epithelial resistance normally seen with clonidine inhibition of ion transport, while FAKpY397 was unaffected. The results show rapid osmosensitive responses in teleost fish ionocytes involve phosphorylation of CFTR by FAKpY407, an opposing role for FAKpY397 and a possible role for FAKpY861 in tight junction dynamics.
Collapse
Affiliation(s)
- Breton Fougere
- Department of Biology, St. Francis Xavier University, P.O. Box 5000, Antigonish, Nova Scotia B2G 2W5, Canada
| | - Katelyn R Barnes
- Department of Biology, St. Francis Xavier University, P.O. Box 5000, Antigonish, Nova Scotia B2G 2W5, Canada
| | - Magen E Francis
- Department of Biology, St. Francis Xavier University, P.O. Box 5000, Antigonish, Nova Scotia B2G 2W5, Canada
| | - Lauren N Claus
- Department of Biology, St. Francis Xavier University, P.O. Box 5000, Antigonish, Nova Scotia B2G 2W5, Canada
| | - Regina R F Cozzi
- Department of Biology, St. Francis Xavier University, P.O. Box 5000, Antigonish, Nova Scotia B2G 2W5, Canada
| | - William S Marshall
- Department of Biology, St. Francis Xavier University, P.O. Box 5000, Antigonish, Nova Scotia B2G 2W5, Canada.
| |
Collapse
|
9
|
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.
Collapse
|
10
|
Jeong CB, Kim DH, Kang HM, Lee YH, Kim HS, Kim IC, Lee JS. Genome-wide identification of ATP-binding cassette (ABC) transporters and their roles in response to polycyclic aromatic hydrocarbons (PAHs) in the copepod Paracyclopina nana. AQUATIC TOXICOLOGY (AMSTERDAM, NETHERLANDS) 2017; 183:144-155. [PMID: 28073050 DOI: 10.1016/j.aquatox.2016.12.022] [Citation(s) in RCA: 8] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 11/24/2016] [Revised: 12/26/2016] [Accepted: 12/27/2016] [Indexed: 06/06/2023]
Abstract
The ATP-binding cassette (ABC) protein superfamily is one of the largest gene families and is highly conserved in all domains. The ABC proteins play roles in several biological processes, including multi-xenobiotic resistance (MXR), by functioning as transporters in the cellular membrane. They also mediate the cellular efflux of a wide range of substrates against concentration gradients. In this study, 37 ABC genes belonging to eight distinct subfamilies were identified in the marine copepod Paracyclopina nana and annotated based on a phylogenetic analysis. Also, the functions of P-glycoproteins (P-gp) and multidrug resistance-associated proteins (MRPs), conferring MXR, were verified using fluorescent substrates and specific inhibitors. The activities of MXR-mediated ABC proteins and their transcriptional level were examined in response to polyaromatic hydrocarbons (PAHs), main components of the water-accommodated fraction. This study increases the understanding of the protective role of MXR in response to PAHs over the comparative evolution of ABC gene families.
Collapse
Affiliation(s)
- Chang-Bum Jeong
- Department of Chemistry, College of Natural Sciences, Hanyang University, Seoul 04763, South Korea
| | - Duck-Hyun Kim
- Department of Biological Science, College of Science, Sungkyunkwan University, Suwon 16419, South Korea
| | - Hye-Min Kang
- Department of Biological Science, College of Science, Sungkyunkwan University, Suwon 16419, South Korea
| | - Young Hwan Lee
- Department of Biological Science, College of Science, Sungkyunkwan University, Suwon 16419, South Korea
| | - Hui-Su Kim
- Department of Biological Science, College of Science, Sungkyunkwan University, Suwon 16419, South Korea
| | - Il-Chan Kim
- Division of Polar Life Sciences, Korea Polar Research Institute, Incheon 21990, South Korea
| | - Jae-Seong Lee
- Department of Biological Science, College of Science, Sungkyunkwan University, Suwon 16419, South Korea.
| |
Collapse
|
11
|
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: 13] [Impact Index Per Article: 1.9] [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.
Collapse
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.
| |
Collapse
|
12
|
Vitzthum C, Clauss WG, Fronius M. Mechanosensitive activation of CFTR by increased cell volume and hydrostatic pressure but not shear stress. BIOCHIMICA ET BIOPHYSICA ACTA-BIOMEMBRANES 2015; 1848:2942-51. [PMID: 26357939 DOI: 10.1016/j.bbamem.2015.09.009] [Citation(s) in RCA: 15] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Received: 05/28/2015] [Revised: 09/03/2015] [Accepted: 09/05/2015] [Indexed: 12/20/2022]
Abstract
The cystic fibrosis transmembrane conductance regulator (CFTR) is a Cl(-) channel that is essential for electrolyte and fluid homeostasis. Preliminary evidence indicates that CFTR is a mechanosensitive channel. In lung epithelia, CFTR is exposed to different mechanical forces such as shear stress (Ss) and membrane distention. The present study questioned whether Ss and/or stretch influence CFTR activity (wild type, ∆F508, G551D). Human CFTR (hCFTR) was heterologously expressed in Xenopus oocytes and the response to the mechanical stimulus and forskolin/IBMX (FI) was measured by two-electrode voltage-clamp experiments. Ss had no influence on hCFTR activity. Injection of an intracellular analogous solution to increase cell volume alone did not affect hCFTR activity. However, hCFTR activity was augmented by injection after pre-stimulation with FI. The response to injection was similar in channels carrying the common mutations ∆F508 and G551D compared to wild type hCFTR. Stretch-induced CFTR activation was further assessed in Ussing chamber measurements using Xenopus lung preparations. Under control conditions increased hydrostatic pressure (HP) decreased the measured ion current including activation of a Cl(-) secretion that was unmasked by the CFTR inhibitor GlyH-101. These data demonstrate activation of CFTR in vitro and in a native pulmonary epithelium in response to mechanical stress. Mechanosensitive regulation of CFTR is highly relevant for pulmonary physiology that relies on ion transport processes facilitated by pulmonary epithelial cells.
Collapse
Affiliation(s)
- Constanze Vitzthum
- Institute of Animal Physiology, Justus-Liebig-University Giessen, Giessen, Germany
| | - Wolfgang G Clauss
- Institute of Animal Physiology, Justus-Liebig-University Giessen, Giessen, Germany
| | - Martin Fronius
- Department of Physiology, University of Otago, Dunedin, New Zealand.
| |
Collapse
|
13
|
Sabirzhanova I, Lopes Pacheco M, Rapino D, Grover R, Handa JT, Guggino WB, Cebotaru L. Rescuing Trafficking Mutants of the ATP-binding Cassette Protein, ABCA4, with Small Molecule Correctors as a Treatment for Stargardt Eye Disease. J Biol Chem 2015; 290:19743-55. [PMID: 26092729 DOI: 10.1074/jbc.m115.647685] [Citation(s) in RCA: 36] [Impact Index Per Article: 4.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/23/2015] [Indexed: 11/06/2022] Open
Abstract
Stargardt disease is the most common form of early onset macular degeneration. Mutations in ABCA4, a member of the ATP-binding cassette (ABC) family, are associated with Stargardt disease. Here, we have examined two disease-causing mutations in the NBD1 region of ABCA4, R1108C, and R1129C, which occur within regions of high similarity with CFTR, another ABC transporter gene, which is associated with cystic fibrosis. We show that R1108C and R1129C are both temperature-sensitive processing mutants that engage the cellular quality control mechanism and show a strong interaction with the chaperone Hsp 27. Both mutant proteins also interact with HDCAC6 and are degraded in the aggresome. We also demonstrate that novel corrector compounds that are being tested as treatment for cystic fibrosis, such as VX-809, can rescue the processing of the ABCA4 mutants, particularly their expression at the cell surface, and can reduce their binding to HDAC6. Thus, our data suggest that VX-809 can potentially be developed as a new therapy for Stargardt disease, for which there is currently no treatment.
Collapse
Affiliation(s)
- Inna Sabirzhanova
- From the Division of Gastroenterology, Department of Medicine, Johns Hopkins University, Baltimore, Maryland 21205, Physiology Center for Retinal Biology, and
| | - Miquéias Lopes Pacheco
- From the Division of Gastroenterology, Department of Medicine, Johns Hopkins University, Baltimore, Maryland 21205, Physiology Center for Retinal Biology, and
| | - Daniele Rapino
- From the Division of Gastroenterology, Department of Medicine, Johns Hopkins University, Baltimore, Maryland 21205, Physiology Center for Retinal Biology, and
| | - Rahul Grover
- From the Division of Gastroenterology, Department of Medicine, Johns Hopkins University, Baltimore, Maryland 21205, Physiology Center for Retinal Biology, and
| | - James T Handa
- Department of Ophthalmology, Johns Hopkins University, Baltimore, Maryland 21231
| | - William B Guggino
- From the Division of Gastroenterology, Department of Medicine, Johns Hopkins University, Baltimore, Maryland 21205
| | - Liudmila Cebotaru
- From the Division of Gastroenterology, Department of Medicine, Johns Hopkins University, Baltimore, Maryland 21205, Physiology Center for Retinal Biology, and Department of Ophthalmology, Johns Hopkins University, Baltimore, Maryland 21231
| |
Collapse
|
14
|
Dong Q, Ernst SE, Ostedgaard LS, Shah VS, Ver Heul AR, Welsh MJ, Randak CO. Mutating the Conserved Q-loop Glutamine 1291 Selectively Disrupts Adenylate Kinase-dependent Channel Gating of the ATP-binding Cassette (ABC) Adenylate Kinase Cystic Fibrosis Transmembrane Conductance Regulator (CFTR) and Reduces Channel Function in Primary Human Airway Epithelia. J Biol Chem 2015; 290:14140-53. [PMID: 25887396 PMCID: PMC4447984 DOI: 10.1074/jbc.m114.611616] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Key Words] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/12/2014] [Indexed: 11/06/2022] Open
Abstract
The ATP-binding cassette (ABC) transporter cystic fibrosis transmembrane conductance regulator (CFTR) and two other non-membrane-bound ABC proteins, Rad50 and a structural maintenance of chromosome (SMC) protein, exhibit adenylate kinase activity in the presence of physiologic concentrations of ATP and AMP or ADP (ATP + AMP ⇆ 2 ADP). The crystal structure of the nucleotide-binding domain of an SMC protein in complex with the adenylate kinase bisubstrate inhibitor P(1),P(5)-di(adenosine-5') pentaphosphate (Ap5A) suggests that AMP binds to the conserved Q-loop glutamine during the adenylate kinase reaction. Therefore, we hypothesized that mutating the corresponding residue in CFTR, Gln-1291, selectively disrupts adenylate kinase-dependent channel gating at physiologic nucleotide concentrations. We found that substituting Gln-1291 with bulky side-chain amino acids abolished the effects of Ap5A, AMP, and adenosine 5'-monophosphoramidate on CFTR channel function. 8-Azidoadenosine 5'-monophosphate photolabeling of the AMP-binding site and adenylate kinase activity were disrupted in Q1291F CFTR. The Gln-1291 mutations did not alter the potency of ATP at stimulating current or ATP-dependent gating when ATP was the only nucleotide present. However, when physiologic concentrations of ADP and AMP were added, adenylate kinase-deficient Q1291F channels opened significantly less than wild type. Consistent with this result, we found that Q1291F CFTR displayed significantly reduced Cl(-) channel function in well differentiated primary human airway epithelia. These results indicate that a highly conserved residue of an ABC transporter plays an important role in adenylate kinase-dependent CFTR gating. Furthermore, the results suggest that adenylate kinase activity is important for normal CFTR channel function in airway epithelia.
Collapse
Affiliation(s)
- Qian Dong
- From the Stead Family Department of Pediatrics
| | - Sarah E Ernst
- the Department of Internal Medicine, the Howard Hughes Medical Institute, Iowa City, Iowa 52242
| | | | - Viral S Shah
- the Department of Molecular Physiology and Biophysics, and the Medical Scientist Training Program, University of Iowa, Iowa City, Iowa 52242 and
| | | | - Michael J Welsh
- the Department of Internal Medicine, the Howard Hughes Medical Institute, Iowa City, Iowa 52242 the Department of Molecular Physiology and Biophysics, and
| | | |
Collapse
|
15
|
Wang W, Roessler BC, Kirk KL. An electrostatic interaction at the tetrahelix bundle promotes phosphorylation-dependent cystic fibrosis transmembrane conductance regulator (CFTR) channel opening. J Biol Chem 2014; 289:30364-30378. [PMID: 25190805 DOI: 10.1074/jbc.m114.595710] [Citation(s) in RCA: 30] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [Key Words] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/22/2022] Open
Abstract
The CFTR channel is an essential mediator of electrolyte transport across epithelial tissues. CFTR opening is promoted by ATP binding and dimerization of its two nucleotide binding domains (NBDs). Phosphorylation of its R domain (e.g. by PKA) is also required for channel activity. The CFTR structure is unsolved but homology models of the CFTR closed and open states have been produced based on the crystal structures of evolutionarily related ABC transporters. These models predict the formation of a tetrahelix bundle of intracellular loops (ICLs) during channel opening. Here we provide evidence that residues E267 in ICL2 and K1060 in ICL4 electrostatically interact at the interface of this predicted bundle to promote CFTR opening. Mutations or a thiol modifier that introduced like charges at these two positions substantially inhibited ATP-dependent channel opening. ATP-dependent activity was rescued by introducing a second site gain of function (GOF) mutation that was previously shown to promote ATP-dependent and ATP-independent opening (K978C). Conversely, the ATP-independent activity of the K978C GOF mutant was inhibited by charge- reversal mutations at positions 267 or 1060 either in the presence or absence of NBD2. The latter result indicates that this electrostatic interaction also promotes unliganded channel opening in the absence of ATP binding and NBD dimerization. Charge-reversal mutations at either position markedly reduced the PKA sensitivity of channel activation implying strong allosteric coupling between bundle formation and R domain phosphorylation. These findings support important roles of the tetrahelix bundle and the E267-K1060 electrostatic interaction in phosphorylation-dependent CFTR gating.
Collapse
Affiliation(s)
- Wei Wang
- Gregory Fleming James Cystic Fibrosis Research Center and Departments of Cell, Developmental, and Integrative Biology, and University of Alabama at Birmingham, Birmingham, Alabama 35294-0005.
| | - Bryan C Roessler
- Gregory Fleming James Cystic Fibrosis Research Center and Departments of Cell, Developmental, and Integrative Biology, and University of Alabama at Birmingham, Birmingham, Alabama 35294-0005
| | - Kevin L Kirk
- Gregory Fleming James Cystic Fibrosis Research Center and Departments of Cell, Developmental, and Integrative Biology, and University of Alabama at Birmingham, Birmingham, Alabama 35294-0005; Departments of Neurobiology, University of Alabama at Birmingham, Birmingham, Alabama 35294-0005.
| |
Collapse
|
16
|
Luckenbach T, Fischer S, Sturm A. Current advances on ABC drug transporters in fish. Comp Biochem Physiol C Toxicol Pharmacol 2014; 165:28-52. [PMID: 24858718 DOI: 10.1016/j.cbpc.2014.05.002] [Citation(s) in RCA: 72] [Impact Index Per Article: 7.2] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 12/19/2013] [Revised: 05/13/2014] [Accepted: 05/14/2014] [Indexed: 01/14/2023]
Abstract
Most members of the large ATP-binding cassette (ABC) gene family are transporters involved in substrate translocation across biological membranes. In eukaryotes, ABC proteins functioning as drug transporters are located in the plasma membrane and mediate the cellular efflux of a wide range of organic chemicals, with some transporters also transporting certain metals. As the enhanced expression of ABC drug transporters can confer multidrug resistance (MDR) to cancers and multixenobiotic resistance (MXR) to organisms from polluted habitats, these ABC family members are also referred to as MDR or MXR proteins. In mammals, ABC drug transporters show predominant expression in tissues involved in excretion or constituting internal or external body boundaries, where they facilitate the excretion of chemicals and their metabolites, and limit chemical uptake and penetration into "sanctuary" sites of the body. Available knowledge about ABC proteins is still limited in teleost fish, a large vertebrate group of high ecological and economic importance. Using transport activity measurements and immunochemical approaches, early studies demonstrated similarities in the tissue distribution of ABC drug transporters between teleosts and mammals, suggesting conserved roles of the transporters in the biochemical defence against toxicants. Recently, the availability of teleost genome assemblies has stimulated studies of the ABC family in this taxon. This review summarises the current knowledge regarding the genetics, functional properties, physiological function, and ecotoxicological relevance of teleostean ABC transporters. The available literature is reviewed with emphasis on recent studies addressing the tissue distribution, substrate spectrum, regulation, physiological function and phylogenetic origin of teleostean ABC transporters.
Collapse
Affiliation(s)
- Till Luckenbach
- Department of Bioanalytical Ecotoxicology, UFZ-Helmholtz Centre for Environmental Research, 04318 Leipzig, Germany
| | - Stephan Fischer
- Department of Environmental Toxicology, Eawag, Swiss Federal Institute of Aquatic Science and Technology, 8600 Dübendorf, Switzerland; Department of Environmental Systems Sciences, ETH Zürich, Institute of Biogeochemistry and Pollutant Dynamics, 8092 Zürich, Switzerland
| | - Armin Sturm
- Institute of Aquaculture, School of Natural Sciences, University of Stirling, Stirling FK9 4LA, Scotland, UK.
| |
Collapse
|
17
|
Strauss AS, Wang D, Stock M, Gretscher RR, Groth M, Boland W, Burse A. Tissue-specific transcript profiling for ABC transporters in the sequestering larvae of the phytophagous leaf beetle Chrysomela populi. PLoS One 2014; 9:e98637. [PMID: 24887102 PMCID: PMC4041752 DOI: 10.1371/journal.pone.0098637] [Citation(s) in RCA: 33] [Impact Index Per Article: 3.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/31/2014] [Accepted: 05/05/2014] [Indexed: 11/18/2022] Open
Abstract
BACKGROUND Insects evolved ingenious adaptations to use extraordinary food sources. Particularly, the diet of herbivores enriched with noxious plant secondary metabolites requires detoxification mechanisms. Sequestration, which involves the uptake, transfer, and concentration of occasionally modified phytochemicals into specialized tissues or hemolymph, is one of the most successful detoxification strategies found in most insect orders. Due to the ability of ATP-binding cassette (ABC) carriers to transport a wide range of molecules including phytochemicals and xenobiotics, it is highly likely that they play a role in this sequestration process. To shed light on the role of ABC proteins in sequestration, we describe an inventory of putative ABC transporters in various tissues in the sequestering juvenile poplar leaf beetle, Chrysomela populi. RESULTS In the transcriptome of C. populi, we predicted 65 ABC transporters. To link the proteins with a possible function, we performed comparative phylogenetic analyses with ABC transporters of other insects and of humans. While tissue-specific profiling of each ABC transporter subfamily suggests that ABCB, C and G influence the plant metabolite absorption in the gut, ABCC with 14 members is the preferred subfamily responsible for the excretion of these metabolites via Malpighian tubules. Moreover, salicin, which is sequestered from poplar plants, is translocated into the defensive glands for further deterrent production. In these glands and among all identified ABC transporters, an exceptionally high transcript level was observed only for Cpabc35 (Cpmrp). RNAi revealed the deficiency of other ABC pumps to compensate the function of CpABC35, demonstrating its key role during sequestration. CONCLUSION We provide the first comprehensive phylogenetic study of the ABC family in a phytophagous beetle species. RNA-seq data from different larval tissues propose the importance of ABC pumps to achieve a homeostasis of plant-derived compounds and offer a basis for future analyses of their physiological function in sequestration processes.
Collapse
Affiliation(s)
- Anja S. Strauss
- Max Planck Institute for Chemical Ecology, Beutenberg Campus, Hans-Knoell-Str. 8, D-07745 Jena, Thuringia, Germany
| | - Ding Wang
- Max Planck Institute for Chemical Ecology, Beutenberg Campus, Hans-Knoell-Str. 8, D-07745 Jena, Thuringia, Germany
| | - Magdalena Stock
- Max Planck Institute for Chemical Ecology, Beutenberg Campus, Hans-Knoell-Str. 8, D-07745 Jena, Thuringia, Germany
| | - René R. Gretscher
- Max Planck Institute for Chemical Ecology, Beutenberg Campus, Hans-Knoell-Str. 8, D-07745 Jena, Thuringia, Germany
| | - Marco Groth
- Leibniz Institute for Age Research – Fritz Lipmann Institute, Beutenbergstr. 11, D-07745 Jena, Thuringia, Germany
| | - Wilhelm Boland
- Max Planck Institute for Chemical Ecology, Beutenberg Campus, Hans-Knoell-Str. 8, D-07745 Jena, Thuringia, Germany
| | - Antje Burse
- Max Planck Institute for Chemical Ecology, Beutenberg Campus, Hans-Knoell-Str. 8, D-07745 Jena, Thuringia, Germany
- * E-mail:
| |
Collapse
|
18
|
Wei S, Roessler BC, Chauvet S, Guo J, Hartman JL, Kirk KL. Conserved allosteric hot spots in the transmembrane domains of cystic fibrosis transmembrane conductance regulator (CFTR) channels and multidrug resistance protein (MRP) pumps. J Biol Chem 2014; 289:19942-57. [PMID: 24876383 DOI: 10.1074/jbc.m114.562116] [Citation(s) in RCA: 17] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [Key Words] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/18/2022] Open
Abstract
ATP-binding cassette (ABC) transporters are an ancient family of transmembrane proteins that utilize ATPase activity to move substrates across cell membranes. The ABCC subfamily of the ABC transporters includes active drug exporters (the multidrug resistance proteins (MRPs)) and a unique ATP-gated ion channel (cystic fibrosis transmembrane conductance regulator (CFTR)). The CFTR channel shares gating principles with conventional ligand-gated ion channels, but the allosteric network that couples ATP binding at its nucleotide binding domains (NBDs) with conformational changes in its transmembrane helices (TMs) is poorly defined. It is also unclear whether the mechanisms that govern CFTR gating are conserved with the thermodynamically distinct MRPs. Here we report a new class of gain of function (GOF) mutation of a conserved proline at the base of the pore-lining TM6. Multiple substitutions of this proline promoted ATP-free CFTR activity and activation by the weak agonist, 5'-adenylyl-β,γ-imidodiphosphate (AMP-PNP). TM6 proline mutations exhibited additive GOF effects when combined with a previously reported GOF mutation located in an outer collar of TMs that surrounds the pore-lining TMs. Each TM substitution allosterically rescued the ATP sensitivity of CFTR gating when introduced into an NBD mutant with defective ATP binding. Both classes of GOF mutations also rescued defective drug export by a yeast MRP (Yor1p) with ATP binding defects in its NBDs. We conclude that the conserved TM6 proline helps set the energy barrier to both CFTR channel opening and MRP-mediated drug efflux and that CFTR channels and MRP pumps utilize similar allosteric mechanisms for coupling conformational changes in their translocation pathways to ATP binding at their NBDs.
Collapse
Affiliation(s)
- Shipeng Wei
- From the Departments of Cell, Developmental, and Integrative Biology
| | - Bryan C Roessler
- From the Departments of Cell, Developmental, and Integrative Biology
| | - Sylvain Chauvet
- From the Departments of Cell, Developmental, and Integrative Biology
| | | | | | - Kevin L Kirk
- From the Departments of Cell, Developmental, and Integrative Biology, Neurobiology and the Gregory Fleming James Cystic Fibrosis Research Center, University of Alabama at Birmingham, Birmingham Alabama 35294-0005
| |
Collapse
|
19
|
Mishra S, Verhalen B, Stein RA, Wen PC, Tajkhorshid E, Mchaourab HS. Conformational dynamics of the nucleotide binding domains and the power stroke of a heterodimeric ABC transporter. eLife 2014; 3:e02740. [PMID: 24837547 PMCID: PMC4046567 DOI: 10.7554/elife.02740] [Citation(s) in RCA: 103] [Impact Index Per Article: 10.3] [Reference Citation Analysis] [Abstract] [Key Words] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/02/2023] Open
Abstract
Multidrug ATP binding cassette (ABC) exporters are ubiquitous ABC transporters that extrude cytotoxic molecules across cell membranes. Despite recent progress in structure determination of these transporters, the conformational motion that transduces the energy of ATP hydrolysis to the work of substrate translocation remains undefined. Here, we have investigated the conformational cycle of BmrCD, a representative of the heterodimer family of ABC exporters that have an intrinsically impaired nucleotide binding site. We measured distances between pairs of spin labels monitoring the movement of the nucleotide binding (NBD) and transmembrane domains (TMD). The results expose previously unobserved structural intermediates of the NBDs arising from asymmetric configuration of catalytically inequivalent nucleotide binding sites. The two-state transition of the TMD, from an inward- to an outward-facing conformation, is driven exclusively by ATP hydrolysis. These findings provide direct evidence of divergence in the mechanism of ABC exporters.DOI: http://dx.doi.org/10.7554/eLife.02740.001.
Collapse
Affiliation(s)
- Smriti Mishra
- Department of Molecular Physiology and Biophysics, Vanderbilt University, Nashville, United States
| | - Brandy Verhalen
- Department of Molecular Physiology and Biophysics, Vanderbilt University, Nashville, United States
| | - Richard A Stein
- Department of Molecular Physiology and Biophysics, Vanderbilt University, Nashville, United States
| | - Po-Chao Wen
- Department of Biochemistry, College of Medicine, University of Illinois, Urbana, United States Center for Biophysics and Computational Biology, University of Illinois, Urbana, United States The Beckman Institute for Advanced Science and Technology, University of Illinois, Urbana, Unites States
| | - Emad Tajkhorshid
- Department of Biochemistry, College of Medicine, University of Illinois, Urbana, United States Center for Biophysics and Computational Biology, University of Illinois, Urbana, United States The Beckman Institute for Advanced Science and Technology, University of Illinois, Urbana, Unites States
| | - Hassane S Mchaourab
- Department of Molecular Physiology and Biophysics, Vanderbilt University, Nashville, United States
| |
Collapse
|
20
|
Pollock N, Cant N, Rimington T, Ford RC. Purification of the cystic fibrosis transmembrane conductance regulator protein expressed in Saccharomyces cerevisiae. J Vis Exp 2014. [PMID: 24893839 PMCID: PMC4181556 DOI: 10.3791/51447] [Citation(s) in RCA: 14] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/17/2022] Open
Abstract
Defects in the cystic fibrosis transmembrane conductance regulator (CFTR) protein cause cystic fibrosis (CF), an autosomal recessive disease that currently limits the average life expectancy of sufferers to <40 years of age. The development of novel drug molecules to restore the activity of CFTR is an important goal in the treatment CF, and the isolation of functionally active CFTR is a useful step towards achieving this goal. We describe two methods for the purification of CFTR from a eukaryotic heterologous expression system, S. cerevisiae. Like prokaryotic systems, S. cerevisiae can be rapidly grown in the lab at low cost, but can also traffic and posttranslationally modify large membrane proteins. The selection of detergents for solubilization and purification is a critical step in the purification of any membrane protein. Having screened for the solubility of CFTR in several detergents, we have chosen two contrasting detergents for use in the purification that allow the final CFTR preparation to be tailored to the subsequently planned experiments. In this method, we provide comparison of the purification of CFTR in dodecyl-β-D-maltoside (DDM) and 1-tetradecanoyl-sn-glycero-3-phospho-(1'-rac-glycerol) (LPG-14). Protein purified in DDM by this method shows ATPase activity in functional assays. Protein purified in LPG-14 shows high purity and yield, can be employed to study post-translational modifications, and can be used for structural methods such as small-angle X-ray scattering and electron microscopy. However it displays significantly lower ATPase activity.
Collapse
Affiliation(s)
| | - Natasha Cant
- Faculty of Life Sciences, University of Manchester
| | | | | |
Collapse
|
21
|
Abstract
ATP-binding cassette (ABC) transporters form a large superfamily of ATP-dependent protein complexes that mediate transport of a vast array of substrates across membranes. The 14 currently available structures of ABC transporters have greatly advanced insight into the transport mechanism and revealed a tremendous structural diversity. Whereas the domains that hydrolyze ATP are structurally related in all ABC transporters, the membrane-embedded domains, where the substrates are translocated, adopt four different unrelated folds. Here, we review the structural characteristics of ABC transporters and discuss the implications of this structural diversity for mechanistic diversity.
Collapse
Affiliation(s)
- Josy ter Beek
- Department of Biochemistry, Groningen Biomolecular Sciences and Biotechnology Institute, University of Groningen, 9747 AG Groningen, Netherlands
| | | | | |
Collapse
|
22
|
CFTR structure and cystic fibrosis. Int J Biochem Cell Biol 2014; 52:15-25. [PMID: 24534272 DOI: 10.1016/j.biocel.2014.02.004] [Citation(s) in RCA: 44] [Impact Index Per Article: 4.4] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/08/2014] [Revised: 02/04/2014] [Accepted: 02/06/2014] [Indexed: 12/31/2022]
Abstract
CFTR (cystic fibrosis transmembrane conductance regulator) is a member of the ATP-binding cassette family of membrane proteins. Although almost all members of this family are transporters, CFTR functions as a channel with specificity for anions, in particular chloride and bicarbonate. In this review we look at what is known about CFTR structure and function within the context of the ATP-binding cassette family. We also review current strategies aimed at obtaining the high resolution structure of the protein.
Collapse
|
23
|
Kempf J, Noujeim N, Schmitzer AR. 2,4,7-Triphenylbenzimidazole: the monomeric unit of supramolecular helical rod-like transmembrane transporters. RSC Adv 2014. [DOI: 10.1039/c4ra06887d] [Citation(s) in RCA: 14] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022] Open
Abstract
Supramolecular compact helical rod as transmembrane anion transporter.
Collapse
Affiliation(s)
- J. Kempf
- Département de Chimie
- Université de Montréal
- Montréal, Canada
| | - N. Noujeim
- Département de Chimie
- Université de Montréal
- Montréal, Canada
| | | |
Collapse
|
24
|
Alexander SPH, Benson HE, Faccenda E, Pawson AJ, Sharman JL, Catterall WA, Spedding M, Peters JA, Harmar AJ. The Concise Guide to PHARMACOLOGY 2013/14: ion channels. Br J Pharmacol 2013; 170:1607-51. [PMID: 24528239 PMCID: PMC3892289 DOI: 10.1111/bph.12447] [Citation(s) in RCA: 224] [Impact Index Per Article: 20.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/15/2022] Open
Abstract
The Concise Guide to PHARMACOLOGY 2013/14 provides concise overviews of the key properties of over 2000 human drug targets with their pharmacology, plus links to an open access knowledgebase of drug targets and their ligands (www.guidetopharmacology.org), which provides more detailed views of target and ligand properties. The full contents can be found at http://onlinelibrary.wiley.com/doi/10.1111/bph.12444/full. Ion channels are one of the seven major pharmacological targets into which the Guide is divided, with the others being G protein-coupled receptors, ligand-gated ion channels, catalytic receptors, nuclear hormone receptors, transporters and enzymes. These are presented with nomenclature guidance and summary information on the best available pharmacological tools, alongside key references and suggestions for further reading. A new landscape format has easy to use tables comparing related targets. It is a condensed version of material contemporary to late 2013, which is presented in greater detail and constantly updated on the website www.guidetopharmacology.org, superseding data presented in previous Guides to Receptors and Channels. It is produced in conjunction with NC-IUPHAR and provides the official IUPHAR classification and nomenclature for human drug targets, where appropriate. It consolidates information previously curated and displayed separately in IUPHAR-DB and the Guide to Receptors and Channels, providing a permanent, citable, point-in-time record that will survive database updates.
Collapse
Affiliation(s)
- Stephen PH Alexander
- School of Life Sciences, University of Nottingham Medical SchoolNottingham, NG7 2UH, UK
- *
Author for correspondence;
| | - Helen E Benson
- The University/BHF Centre for Cardiovascular Science, University of EdinburghEdinburgh, EH16 4TJ, UK
| | - Elena Faccenda
- The University/BHF Centre for Cardiovascular Science, University of EdinburghEdinburgh, EH16 4TJ, UK
| | - Adam J Pawson
- The University/BHF Centre for Cardiovascular Science, University of EdinburghEdinburgh, EH16 4TJ, UK
| | - Joanna L Sharman
- The University/BHF Centre for Cardiovascular Science, University of EdinburghEdinburgh, EH16 4TJ, UK
| | - William A Catterall
- University of Washington, School of Medicine, Department of PharmacologyBox 357280, Seattle, WA 98195-7280, USA
| | | | - John A Peters
- Neuroscience Division, Medical Education Institute, Ninewells Hospital and Medical School, University of DundeeDundee, DD1 9SY, UK
| | - Anthony J Harmar
- The University/BHF Centre for Cardiovascular Science, University of EdinburghEdinburgh, EH16 4TJ, UK
| |
Collapse
|
25
|
Abstract
Malfunction of cystic fibrosis transmembrane conductance regulator (CFTR), a member of the ABC protein superfamily that functions as an ATP-gated chloride channel, causes the lethal genetic disease, cystic fibrosis. This review focuses on the most recent findings on the gating mechanism of CFTR. Potential clinical relevance and implications to ABC transporter function are also discussed.
Collapse
Affiliation(s)
- Kang-Yang Jih
- Dalton Cardiovascular Research Center, University of Missouri-Columbia, Columbia, Missouri, USA
| | | |
Collapse
|
26
|
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.
Collapse
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
| |
Collapse
|
27
|
Okeyo G, Wang W, Wei S, Kirk KL. Converting nonhydrolyzable nucleotides to strong cystic fibrosis transmembrane conductance regulator (CFTR) agonists by gain of function (GOF) mutations. J Biol Chem 2013; 288:17122-33. [PMID: 23620589 DOI: 10.1074/jbc.m112.442582] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
Cystic fibrosis transmembrane conductance regulator (CFTR) is the only ligand-gated ion channel that hydrolyzes its agonist, ATP. CFTR gating has been argued to be tightly coupled to its enzymatic activity, but channels do open occasionally in the absence of ATP and are reversibly activated (albeit weakly) by nonhydrolyzable nucleotides. Why the latter only weakly activates CFTR is not understood. Here we show that CFTR activation by adenosine 5'-O-(thiotriphosphate) (ATPγS), adenosine 5'-(β,γ-imino)triphosphate (AMP-PNP), and guanosine 5'-3-O-(thio)triphosphate (GTPγS) is enhanced substantially by gain of function (GOF) mutations in the cytosolic loops that increase unliganded activity. This enhancement correlated with the base-line nucleotide-independent activity for several GOF mutations. AMP-PNP or ATPγS activation required both nucleotide binding domains (NBDs) and was disrupted by a cystic fibrosis mutation in NBD1 (G551D). GOF mutant channels deactivated very slowly upon AMP-PNP or ATPγS removal (τdeac ∼ 100 s) implying tight binding between the two NBDs. Despite this apparently tight binding, neither AMP-PNP nor ATPγS activated even the strongest GOF mutant as strongly as ATP. ATPγS-activated wild type channels deactivated more rapidly, indicating that GOF mutations in the cytosolic loops reciprocally/allosterically affect nucleotide occupancy of the NBDs. A GOF mutation substantially rescued defective ATP-dependent gating of G1349D-CFTR, a cystic fibrosis NBD2 signature sequence mutant. Interestingly, the G1349D mutation strongly disrupted activation by AMP-PNP but not by ATPγS, indicating that these analogs interact differently with the NBDs. We conclude that poorly hydrolyzable nucleotides are less effective than ATP at opening CFTR channels even when they bind tightly to the NBDs but are converted to stronger agonists by GOF mutations.
Collapse
Affiliation(s)
- George Okeyo
- Department of Cell, Developmental, and Integrative Biology, Gregory Fleming James Cystic Fibrosis Research Center, University of Alabama at Birmingham, Birmingham, Alabama 35294-0005, USA
| | | | | | | |
Collapse
|
28
|
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: 156] [Impact Index Per Article: 14.2] [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.
Collapse
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
| |
Collapse
|
29
|
Hunt JF, Wang C, Ford RC. Cystic fibrosis transmembrane conductance regulator (ABCC7) structure. Cold Spring Harb Perspect Med 2013; 3:a009514. [PMID: 23378596 DOI: 10.1101/cshperspect.a009514] [Citation(s) in RCA: 39] [Impact Index Per Article: 3.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/18/2022]
Abstract
Structural studies of the cystic fibrosis transmembrane conductance regulator (CFTR) are reviewed. Like many membrane proteins, full-length CFTR has proven to be difficult to express and purify, hence much of the structural data available is for the more tractable, independently expressed soluble domains. Therefore, this chapter covers structural data for individual CFTR domains in addition to the sparser data available for the full-length protein. To set the context for these studies, we will start by reviewing structural information on model proteins from the ATP-binding cassette (ABC) transporter superfamily, to which CFTR belongs.
Collapse
Affiliation(s)
- John F Hunt
- Department of Biological Sciences, Columbia University, New York, NY 10027, USA.
| | | | | |
Collapse
|
30
|
Spalding EP. Diverting the downhill flow of auxin to steer growth during tropisms. AMERICAN JOURNAL OF BOTANY 2013; 100:203-14. [PMID: 23284058 DOI: 10.3732/ajb.1200420] [Citation(s) in RCA: 28] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/21/2023]
Abstract
Polar auxin transport can be likened to water following the path of least resistance as it flows downhill. In the case of auxin, the hill is the difference in electrochemical potential of the auxin anion (IAA(-)). H(+)-ATPases and H(+)-IAA symporters at the plasma membrane create the electrical and IAA(-) concentration gradients that constitute this thermodynamic hill. PIN and ABCB transporters also at the plasma membrane bias the direction and limit the rate of downhill flow out of the cell. This article will present the thermodynamic basis for this view and critically examine how well the molecular biological descriptions of the polar auxin transport process fit the framework. An auxin concentration gradient across an organ has long been recognized as the cause of bending growth during tropisms. Its generation can be viewed as a result of redirected polar auxin transport. This article will examine how molecular regulation of the paths of least resistance to auxin efflux diverts the downhill flow of auxin to steer growth during tropisms.
Collapse
Affiliation(s)
- Edgar P Spalding
- Department of Botany, University of Wisconsin-Madison, 430 Lincoln Drive, Madison, Wisconsin 53706, USA.
| |
Collapse
|
31
|
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.
Collapse
Affiliation(s)
- Christoph O Randak
- Department of Pediatrics, University of Iowa, Iowa City, Iowa 52242, USA.
| | | | | |
Collapse
|
32
|
Affiliation(s)
- Ming-Feng Tsai
- Department of Biochemistry, Howard Hughes Medical Institute, Brandeis University, Waltham, MA 02454, USA.
| |
Collapse
|
33
|
Abstract
Cystic fibrosis is a lethal genetic disease caused by lack of functional cystic fibrosis transmembrane conductance regulator (CFTR) proteins at the apical surface of secretory epithelia. CFTR is a multidomain protein, containing five domains, and its functional structure is attained in a hierarchical folding process. Most CF-causing mutations in CFTR, including the most common mutation, a deletion of phenylalanine at position 508 (ΔF508), are unable to properly fold into this functional native three dimensional structure. Currently, no high-resolution structural information about full length CFTR exists. However, insight has been gained through examining homologous ABC transporter structures, molecular modeling, and high-resolution structures of individual, isolated CFTR domains. Taken together, these studies indicate that the prevalent ΔF508 mutation disrupts two essential steps during the development of the native structure: folding of the first nucleotide binding domain (NBD1) and its later association with the fourth intracellular loop (ICL4) in the second transmembrane domain (TMD2). Therapeutics to rescue ΔF508 and other mutants in CFTR can be targeted to correct defects that occur during the complex folding process. This article reviews the structural relationships between CFTR and ABC transporters and current knowledge about how CFTR attains its structure–with a focus on how this process is altered by CF-causing mutations in a manner targetable by therapeutics.
Collapse
Affiliation(s)
- Anna E Patrick
- Department of Physiology, University of Texas Southwestern Medical Center Dallas, TX, USA
| | | |
Collapse
|
34
|
Ip YK, Wilson JM, Loong AM, Chen XL, Wong WP, Delgado ILS, Lam SH, Chew SF. Cystic fibrosis transmembrane conductance regulator in the gills of the climbing perch, Anabas testudineus, is involved in both hypoosmotic regulation during seawater acclimation and active ammonia excretion during ammonia exposure. J Comp Physiol B 2012; 182:793-812. [PMID: 22526263 DOI: 10.1007/s00360-012-0664-9] [Citation(s) in RCA: 17] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/14/2011] [Revised: 03/26/2012] [Accepted: 04/02/2012] [Indexed: 01/20/2023]
Abstract
This study aimed to clone and sequence the cystic fibrosis transmembrane conductance regulator (cftr) from, and to determine the effects of seawater acclimation or exposure to 100 mmol l⁻¹ NH₄Cl in freshwater on its mRNA and protein expressions in, the gills of Anabas testudineus. There were 4,530 bp coding for 1,510 amino acids in the cftr cDNA sequence from A. testudineus. The branchial mRNA expression of cftr in fish kept in freshwater was low (<50 copies of transcript per ng cDNA), but significant increases were observed in fish acclimated to seawater for 1 day (92-fold) or 6 days (219-fold). Branchial Cftr expression was detected in fish acclimated to seawater but not in the freshwater control, indicating that Cl⁻ excretion through the apical Cftr of the branchial epithelium was essential to seawater acclimation. More importantly, fish exposed to ammonia also exhibited a significant increase (12-fold) in branchial mRNA expression of cftr, with Cftr being expressed in a type of Na⁺/K⁺-ATPase-immunoreactive cells that was apparently different from the type involved in seawater acclimation. It is probable that Cl⁻ excretion through Cftr generated a favorable electrical potential across the apical membrane to drive the excretion of NH₄⁺ against a concentration gradient through a yet to be determined transporter, but it led to a slight loss of endogenous Cl⁻. Since ammonia exposure also resulted in significant decreases in blood pH, [HCO₃⁻] and [total CO₂] in A. testudineus, it can be deduced that active NH₄⁺ excretion could also be driven by the exit of HCO₃⁻ through the apical Cftr. Furthermore, A. testudineus uniquely responded to ammonia exposure by increasing the ambient pH and decreasing the branchial bafilomycin-sensitive V-type H⁺-ATPase activity, which suggests that its gills might have low NH₃ permeability.
Collapse
Affiliation(s)
- Yuen K Ip
- Department of Biological Sciences, National University of Singapore, Kent Ridge, Singapore 117543, Republic of Singapore.
| | | | | | | | | | | | | | | |
Collapse
|
35
|
Rogan MP, Stoltz DA, Hornick DB. Cystic fibrosis transmembrane conductance regulator intracellular processing, trafficking, and opportunities for mutation-specific treatment. Chest 2011; 139:1480-1490. [PMID: 21652558 DOI: 10.1378/chest.10-2077] [Citation(s) in RCA: 96] [Impact Index Per Article: 7.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/01/2023] Open
Abstract
Recent advances in basic science have greatly expanded our understanding of the cystic fibrosis (CF) transmembrane conductance regulator (CFTR), the chloride and bicarbonate channel that is encoded by the gene, which is mutated in patients with CF. We review the structure, function, biosynthetic processing, and intracellular trafficking of CFTR and discuss the five classes of mutations and their impact on the CF phenotype. The therapeutic discussion is focused on the significant progress toward CFTR mutation-specific therapies. We review the results of encouraging clinical trials examining orally administered therapeutics, including agents that promote read-through of class I mutations (premature termination codons); correctors, which overcome the CFTR misfolding that characterizes the common class II mutation F508del; and potentiators, which enhance the function of class III or IV mutated CFTR at the plasma membrane. Long-term outcomes from successful mutation-specific treatments could finally answer the question that has been lingering since and even before the CFTR gene discovery: Will therapies that specifically restore CFTR-mediated chloride secretion slow or arrest the deleterious cascade of events leading to chronic infection, bronchiectasis, and end-stage lung disease?
Collapse
Affiliation(s)
- Mark P Rogan
- Department of Respiratory Medicine, Waterford Regional Hospital, Waterford, Ireland
| | - David A Stoltz
- Department of Internal Medicine, Division of Pulmonary, Critical Care, and Occupational Medicine, University of Iowa Roy J. and Lucille A. Carver College of Medicine, Iowa City, IA
| | - Douglas B Hornick
- Department of Internal Medicine, Division of Pulmonary, Critical Care, and Occupational Medicine, University of Iowa Roy J. and Lucille A. Carver College of Medicine, Iowa City, IA.
| |
Collapse
|
36
|
Stolarczyk EI, Reiling CJ, Paumi CM. Regulation of ABC transporter function via phosphorylation by protein kinases. Curr Pharm Biotechnol 2011; 12:621-35. [PMID: 21118091 DOI: 10.2174/138920111795164075] [Citation(s) in RCA: 53] [Impact Index Per Article: 4.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/28/2010] [Accepted: 04/07/2010] [Indexed: 11/22/2022]
Abstract
ATP-binding cassette (ABC) transporters are multispanning membrane proteins that utilize ATP to move a broad range of substrates across cellular membranes. ABC transporters are involved in a number of human disorders and diseases. Overexpression of a subset of the transporters has been closely linked to multidrug resistance in both bacteria and viruses and in cancer. A poorly understood and important aspect of ABC transporter biology is the role of phosphorylation as a mechanism to regulate transporter function. In this review, we summarize the current literature addressing the role of phosphorylation in regulating ABC transporter function. A comprehensive list of all the phosphorylation sites that have been identified for the human ABC transporters is presented, and we discuss the role of individual kinases in regulating transporter function. We address the potential pitfalls and difficulties associated with identifying phosphorylation sites and the corresponding kinase(s), and we discuss novel techniques that may circumvent these problems. We conclude by providing a brief perspective on studying ABC transporter phosphorylation.
Collapse
|
37
|
Tarling EJ, Edwards PA. Dancing with the sterols: critical roles for ABCG1, ABCA1, miRNAs, and nuclear and cell surface receptors in controlling cellular sterol homeostasis. Biochim Biophys Acta Mol Cell Biol Lipids 2011; 1821:386-95. [PMID: 21824529 DOI: 10.1016/j.bbalip.2011.07.011] [Citation(s) in RCA: 43] [Impact Index Per Article: 3.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/04/2011] [Revised: 07/13/2011] [Accepted: 07/15/2011] [Indexed: 12/29/2022]
Abstract
ATP binding cassette (ABC) transporters represent a large and diverse family of proteins that transport specific substrates across a membrane. The importance of these transporters is illustrated by the finding that inactivating mutations within 17 different family members are known to lead to specific human diseases. Clinical data from humans and/or studies with mice lacking functional transporters indicate that ABCA1, ABCG1, ABCG4, ABCG5 and ABCG8 are involved in cholesterol and/or phospholipid transport. This review discusses the multiple mechanisms that control cellular sterol homeostasis, including the roles of microRNAs, nuclear and cell surface receptors and ABC transporters, with particular emphasis on recent findings that have provided insights into the role(s) of ABCG1. This article is part of a Special Issue entitled Advances in High Density Lipoprotein Formation and Metabolism: A Tribute to John F. Oram (1945-2010).
Collapse
Affiliation(s)
- Elizabeth J Tarling
- Department of Biological Chemistry, David Geffen School of Medicine at UCLA, Los Angeles, CA 90095, USA
| | | |
Collapse
|
38
|
Krasilnikov OV, Sabirov RZ, Okada Y. ATP hydrolysis-dependent asymmetry of the conformation of CFTR channel pore. J Physiol Sci 2011; 61:267-78. [PMID: 21461971 PMCID: PMC10717511 DOI: 10.1007/s12576-011-0144-0] [Citation(s) in RCA: 9] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/09/2011] [Accepted: 03/20/2011] [Indexed: 01/13/2023]
Abstract
Despite substantial efforts, the entire cystic fibrosis transmembrane conductance regulator (CFTR) protein proved to be difficult for structural analysis at high resolution, and little is still known about the actual dimensions of the anion-transporting pathway of CFTR channel. In the present study, we therefore gauged geometrical features of the CFTR Cl(-) channel pore by a nonelectrolyte exclusion technique. Polyethylene glycols with a hydrodynamic radius (R (h)) smaller than 0.95 nm (PEG 300-1,000) added from the intracellular side greatly suppressed the inward unitary anionic conductance, whereas only molecules with R (h) ≤ 0.62 nm (PEG 200-400) applied extracellularly were able to affect the outward unitary anionic currents. Larger molecules with R (h) = 1.16-1.84 nm (PEG 1,540-3,400) added from either side were completely excluded from the pore and had no significant effect on the single-channel conductance. The cut-off radius of the inner entrance of CFTR channel pore was assessed to be 1.19 ± 0.02 nm. The outer entrance was narrower with its cut-off radius of 0.70 ± 0.16 nm and was dilated to 0.93 ± 0.23 nm when a non-hydrolyzable ATP analog, 5'-adenylylimidodiphosphate (AMP-PNP), was added to the intracellular solution. Thus, it is concluded that the structure of CFTR channel pore is highly asymmetric with a narrower extracellular entrance and that a dilating conformational change of the extracellular entrance is associated with the channel transition to a non-hydrolytic, locked-open state.
Collapse
Affiliation(s)
- Oleg V. Krasilnikov
- Department of Cell Physiology, National Institute for Physiological Sciences, Okazaki, 444-8585 Japan
- Department of Biophysics and Radiobiology, Federal University of Pernambuco, Recife, PE 50670-901 Brazil
| | - Ravshan Z. Sabirov
- Department of Cell Physiology, National Institute for Physiological Sciences, Okazaki, 444-8585 Japan
- Laboratory of Molecular Physiology, Institute of Physiology and Biophysics, Academy of Science RUz, Niyazova 1, 100095 Tashkent, Uzbekistan
- Department of Biophysics, National University, Niyazova 1, 100095 Tashkent, Uzbekistan
| | - Yasunobu Okada
- Department of Cell Physiology, National Institute for Physiological Sciences, Okazaki, 444-8585 Japan
| |
Collapse
|
39
|
Piro D, Piccoli C, Guerra L, Sassone F, D'Aprile A, Favia M, Castellani S, Di Gioia S, Lepore S, Garavaglia ML, Trotta T, Maffione AB, Casavola V, Meyer G, Capitanio N, Conese M. Hematopoietic stem/progenitor cells express functional mitochondrial energy-dependent cystic fibrosis transmembrane conductance regulator. Stem Cells Dev 2011; 21:634-46. [PMID: 21561312 DOI: 10.1089/scd.2011.0041] [Citation(s) in RCA: 12] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/31/2022] Open
Abstract
Bone marrow-derived hematopoietic stem/progenitor cells (HSPCs) encompass a wide array of cell subsets with different capacities of engraftment and injured tissue-regenerating potential. The characterization/isolation of the stem cell subpopulations represents a major challenge to improve the efficacy of transplantation protocols used in regenerative medicine. Cystic fibrosis (CF) is one of the diseases whose hope of cure relies on the successful application of cell-based gene therapy. This study was aimed at characterizing murine HSPCs on the basis of their bioenergetic competence and CF transmembrane conductance regulator (CFTR) expression. Positively immunoselected Sca-1(+) HSPCs encompassed 2 populations distinguished by their different size, Sca-1 expression and mitochondrial content. The smaller were the cells, the higher was Sca-1 expression and the lower was the intracellular density of functional mitochondria. Reverse transcription-polymerase chain reaction and western blotting revealed that HSPCs expressed CFTR mRNA and protein, which was also functional, as assessed by spectrofluorimetric and patch-clamp techniques. Inhibition of mitochondrial oxidative phosphorylation by oligomycin resulted in a 70% decrease of both the intracelluar adenosine triphosphate content and CFTR-mediated channel activity. Finally, HSPCs with lower Sca-1 expression and higher mitochondrial content displayed higher CFTR levels. Our findings identify 2 subpopulations in HSPCs and unveil a so-far unappreciated relationship between bioenergetic metabolism and CFTR in HSPC biology.
Collapse
Affiliation(s)
- Donatella Piro
- Department of Biomedical Sciences, University of Foggia, Foggia, Italy
| | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | |
Collapse
|
40
|
Venerando A, Pagano MA, Tosoni K, Meggio F, Cassidy D, Stobbart M, Pinna LA, Mehta A. Understanding protein kinase CK2 mis-regulation upon F508del CFTR expression. Naunyn Schmiedebergs Arch Pharmacol 2011; 384:473-88. [PMID: 21607646 PMCID: PMC3208816 DOI: 10.1007/s00210-011-0650-x] [Citation(s) in RCA: 10] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/11/2011] [Accepted: 04/28/2011] [Indexed: 12/17/2022]
Abstract
We review areas of overlap between nucleoside diphosphate kinase (NDPK; nm23) and two proteins manifesting an equivalent diversity of action, each with many thousands of publications. The first is a constitutively active protein kinase, CK2 (formerly casein kinase 2), that includes NDPK amongst its hundreds of targets. The second is an enigmatic member of the ATP-binding cassette (ABC) family of membrane pumps that normally hydrolyse ATP to transport substrates. Yet our unusual family member (ABCC7) is not a pump but, uniquely, acts as a regulated anion channel. ABCC7 is the cystic fibrosis transmembrane conductance regulator (CFTR), and we discuss the highly prevalent CFTR mutation (F508del CFTR) in terms of the uncertainties surrounding the molecular basis of cystic fibrosis that cloud approaches to corrective therapy. Using lysates from cells stably expressing either wild-type or F508del CFTR, incubated with the CK2 substrate GTP, we show that the phosphoproteome of F508del CFTR-expressing cells both differs from wild-type CFTR-expressing cells and is significantly enhanced in intensity by ∼1.5-fold (p < 0.05, paired t test with Bonferroni correction, n = 4). Phosphorylation is about 50% attenuated with a specific CK2 inhibitor. We propose that a new function may exist for the CFTR region that is commonly mutated, noting that its sequence (PGTIKENIIF508GVSYDEYRYR) is not only highly conserved within the C sub-family of ABC proteins but also a related sequence is found in NDPK. We conclude that a latent path may exist between mutation of this conserved sequence, CK2 hyperactivity and disease pathogenesis that might also explain the heterozygote advantage for the common F508del CFTR mutant .
Collapse
Affiliation(s)
- Andrea Venerando
- Department of Biological Chemistry and CNR Institute of Neurosciences, University of Padova, viale G. Colombo 3, 35131, Padua, Italy
| | | | | | | | | | | | | | | |
Collapse
|
41
|
Kirk KL, Wang W. A unified view of cystic fibrosis transmembrane conductance regulator (CFTR) gating: combining the allosterism of a ligand-gated channel with the enzymatic activity of an ATP-binding cassette (ABC) transporter. J Biol Chem 2011; 286:12813-9. [PMID: 21296873 PMCID: PMC3075628 DOI: 10.1074/jbc.r111.219634] [Citation(s) in RCA: 36] [Impact Index Per Article: 2.8] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
The cystic fibrosis transmembrane conductance regulator (CFTR) is a unique ion channel in that its gating is coupled to an intrinsic enzymatic activity (ATP hydrolysis). This enzymatic activity derives from the evolutionary origin of CFTR as an ATP-binding cassette transporter. CFTR gating is distinct from that of a typical ligand-gated channel because its ligand (ATP) is usually consumed during the gating cycle. However, recent findings indicate that CFTR gating exhibits allosteric properties that are common to conventional ligand-gated channels (e.g. unliganded openings and constitutive mutations). Here, we provide a unified view of CFTR gating that combines the allosterism of a ligand-gated channel with its unique enzymatic activity.
Collapse
Affiliation(s)
- Kevin L Kirk
- Department of Physiology and Biophysics and the Gregory Fleming James Cystic Fibrosis Research Center, University of Alabama at Birmingham, Birmingham, Alabama 35294, USA.
| | | |
Collapse
|
42
|
Gu X, Manautou JE. Regulation of hepatic ABCC transporters by xenobiotics and in disease states. Drug Metab Rev 2010; 42:482-538. [PMID: 20233023 DOI: 10.3109/03602531003654915] [Citation(s) in RCA: 51] [Impact Index Per Article: 3.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/19/2023]
Abstract
The subfamily of ABCC transporters consists of 13 members in mammals, including the multidrug resistance-associated proteins (MRPs), sulfonylurea receptors (SURs), and the cystic fibrosis transmembrane conductance regulator (CFTR). These proteins play roles in chemical detoxification, disposition, and normal cell physiology. ABCC transporters are expressed differentially in the liver and are regulated at the transcription and translation level. Their expression and function are also controlled by post-translational modification and membrane-trafficking events. These processes are tightly regulated. Information about alterations in the expression of hepatobiliary ABCC transporters could provide important insights into the pathogenesis of diseases and disposition of xenobiotics. In this review, we describe the regulation of hepatic ABCC transporters in humans and rodents by a variety of xenobiotics, under disease states and in genetically modified animal models deficient in transcription factors, transporters, and cell-signaling molecules.
Collapse
Affiliation(s)
- Xinsheng Gu
- Department of Pharmaceutical Sciences, University of Connecticut, Storrs, 06269, USA
| | | |
Collapse
|
43
|
Becq F, Billet A. Understanding nucleotide binding and CFTR ion channel gating: how many cycles? Expert Rev Respir Med 2010; 4:451-4. [PMID: 20658906 DOI: 10.1586/ers.10.47] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/08/2022]
Affiliation(s)
- Frédéric Becq
- Université de Poitiers/CNRS, 40 avenue du recteur Pineau, 86022 Poitiers, France.
| | | |
Collapse
|
44
|
Aleksandrov AA, Kota P, Aleksandrov LA, He L, Jensen T, Cui L, Gentzsch M, Dokholyan NV, Riordan JR. Regulatory insertion removal restores maturation, stability and function of DeltaF508 CFTR. J Mol Biol 2010; 401:194-210. [PMID: 20561529 DOI: 10.1016/j.jmb.2010.06.019] [Citation(s) in RCA: 82] [Impact Index Per Article: 5.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/26/2010] [Revised: 06/07/2010] [Accepted: 06/09/2010] [Indexed: 10/19/2022]
Abstract
The cystic fibrosis transmembrane conductance regulator (CFTR) epithelial anion channel is a large multidomain membrane protein that matures inefficiently during biosynthesis. Its assembly is further perturbed by the deletion of F508 from the first nucleotide-binding domain (NBD1) responsible for most cystic fibrosis. The mutant polypeptide is recognized by cellular quality control systems and is proteolyzed. CFTR NBD1 contains a 32-residue segment termed the regulatory insertion (RI) not present in other ATP-binding cassette transporters. We report here that RI deletion enabled F508 CFTR to mature and traffic to the cell surface where it mediated regulated anion efflux and exhibited robust single chloride channel activity. Long-term pulse-chase experiments showed that the mature DeltaRI/DeltaF508 had a T(1/2) of approximately 14 h in cells, similar to the wild type. RI deletion restored ATP occlusion by NBD1 of DeltaF508 CFTR and had a strong thermostabilizing influence on the channel with gating up to at least 40 degrees C. None of these effects of RI removal were achieved by deletion of only portions of RI. Discrete molecular dynamics simulations of NBD1 indicated that RI might indirectly influence the interaction of NBD1 with the rest of the protein by attenuating the coupling of the F508-containing loop with the F1-like ATP-binding core subdomain so that RI removal overcame the perturbations caused by F508 deletion. Restriction of RI to a particular conformational state may ameliorate the impact of the disease-causing mutation.
Collapse
Affiliation(s)
- Andrei A Aleksandrov
- Department of Biomedical Engineering, University of North Carolina-Chapel Hill, Chapel Hill, NC 27599, USA
| | | | | | | | | | | | | | | | | |
Collapse
|
45
|
Billet A, Melin P, Jollivet M, Mornon JP, Callebaut I, Becq F. C terminus of nucleotide binding domain 1 contains critical features for cystic fibrosis transmembrane conductance regulator trafficking and activation. J Biol Chem 2010; 285:22132-40. [PMID: 20435887 DOI: 10.1074/jbc.m110.120683] [Citation(s) in RCA: 12] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
The cystic fibrosis transmembrane conductance regulator (CFTR) is a Cl(-) channel physiologically important in fluid-transporting epithelia and pathologically relevant in several human diseases. Here, we show that mutations in the C terminus of the first nucleotide binding domain comprising the latest beta strands (beta(c)5 and beta(c)6) influence the trafficking, channel activity, and pharmacology of CFTR. We mutated CFTR amino acids located in the beta(c)5-beta(c)6 hairpin, within the beta(c)5 strand (H620Q), within the beta-turn linking the two beta strands (E621G, G622D), as well as within (S623A, S624A) and at the extremity (G628R) of the beta(c)6 strand. Functional analysis reveals that the current density was largely reduced for G622D and G628R channels compared with wt CFTR, similar for E621G and S624A, but increased for H620Q and S623A. For G622D and G628R, the abnormal activity is likely due to a defective maturation process, as assessed by the augmented activity and mature C-band observed in the presence of the trafficking corrector miglustat. In addition, in presence of the CFTR activator benzo[c]quinolizinium, the CFTR current density compared with that of wt CFTR was abolished for G622D and G628R channels, but similar for H620Q, S623A, and S624A or slightly increased for E621G. Finally, G622D and G628R were activated by the CFTR agonists genistein, RP-107, and isobutylmethylxanthine. Our results identify the C terminus of the CFTR first nucleotide binding domain as an important molecular site for the trafficking of CFTR protein, for the control of CFTR channel gating, and for the pharmacological effect of a dual activity agent.
Collapse
Affiliation(s)
- Arnaud Billet
- Institut de Physiologie et Biologie Cellulaires, Université de Poitiers, CNRS, 86022 Poitiers, France
| | | | | | | | | | | |
Collapse
|
46
|
Hibino H, Inanobe A, Furutani K, Murakami S, Findlay I, Kurachi Y. Inwardly rectifying potassium channels: their structure, function, and physiological roles. Physiol Rev 2010; 90:291-366. [PMID: 20086079 DOI: 10.1152/physrev.00021.2009] [Citation(s) in RCA: 1074] [Impact Index Per Article: 76.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/19/2022] Open
Abstract
Inwardly rectifying K(+) (Kir) channels allow K(+) to move more easily into rather than out of the cell. They have diverse physiological functions depending on their type and their location. There are seven Kir channel subfamilies that can be classified into four functional groups: classical Kir channels (Kir2.x) are constitutively active, G protein-gated Kir channels (Kir3.x) are regulated by G protein-coupled receptors, ATP-sensitive K(+) channels (Kir6.x) are tightly linked to cellular metabolism, and K(+) transport channels (Kir1.x, Kir4.x, Kir5.x, and Kir7.x). Inward rectification results from pore block by intracellular substances such as Mg(2+) and polyamines. Kir channel activity can be modulated by ions, phospholipids, and binding proteins. The basic building block of a Kir channel is made up of two transmembrane helices with cytoplasmic NH(2) and COOH termini and an extracellular loop which folds back to form the pore-lining ion selectivity filter. In vivo, functional Kir channels are composed of four such subunits which are either homo- or heterotetramers. Gene targeting and genetic analysis have linked Kir channel dysfunction to diverse pathologies. The crystal structure of different Kir channels is opening the way to understanding the structure-function relationships of this simple but diverse ion channel family.
Collapse
Affiliation(s)
- Hiroshi Hibino
- Department of Pharmacology, Graduate School of Medicine and The Center for Advanced Medical Engineering and Informatics, Osaka University, Osaka 565-0871, Japan
| | | | | | | | | | | |
Collapse
|
47
|
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.
Collapse
Affiliation(s)
- Monika Kloch
- Department of Biophysics, Warsaw University of Life Sciences SGGW, Warsaw, Poland
| | | | | | | | | | | |
Collapse
|
48
|
|
49
|
Csanády L. Application of rate-equilibrium free energy relationship analysis to nonequilibrium ion channel gating mechanisms. ACTA ACUST UNITED AC 2009; 134:129-36. [PMID: 19635854 PMCID: PMC2717696 DOI: 10.1085/jgp.200910268] [Citation(s) in RCA: 11] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022]
Abstract
Rate-equilibrium free energy relationship (REFER) analysis provides information on transition-state structures and has been applied to reveal the temporal sequence in which the different regions of an ion channel protein move during a closed-open conformational transition. To date, the theory used to interpret REFER relationships has been developed only for equilibrium mechanisms. Gating of most ion channels is an equilibrium process, but recently several ion channels have been identified to have retained nonequilibrium traits in their gating cycles, inherited from transporter-like ancestors. So far it has not been examined to what extent REFER analysis is applicable to such systems. By deriving the REFER relationships for a simple nonequilibrium mechanism, this paper addresses whether an equilibrium mechanism can be distinguished from a nonequilibrium one by the characteristics of their REFER plots, and whether information on the transition-state structures can be obtained from REFER plots for gating mechanisms that are known to be nonequilibrium cycles. The results show that REFER plots do not carry information on the equilibrium nature of the underlying gating mechanism. Both equilibrium and nonequilibrium mechanisms can result in linear or nonlinear REFER plots, and complementarity of REFER slopes for opening and closing transitions is a trivial feature true for any mechanism. Additionally, REFER analysis provides limited information about the transition-state structures for gating schemes that are known to be nonequilibrium cycles.
Collapse
Affiliation(s)
- László Csanády
- Department of Medical Biochemistry, Semmelweis University, Budapest, Hungary.
| |
Collapse
|
50
|
Marshall WS, Watters KD, Hovdestad LR, Cozzi RRF, Katoh F. CFTR Cl- channel functional regulation by phosphorylation of focal adhesion kinase at tyrosine 407 in osmosensitive ion transporting mitochondria rich cells of euryhaline killifish. ACTA ACUST UNITED AC 2009; 212:2365-77. [PMID: 19617429 DOI: 10.1242/jeb.030015] [Citation(s) in RCA: 36] [Impact Index Per Article: 2.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/27/2023]
Abstract
Cystic fibrosis transmembrane conductance regulator (CFTR) anion channels are the regulated exit pathway in Cl(-) secretion by teleost mitochondria rich salt secreting (MR) cells of the gill and opercular epithelia of euryhaline teleosts. By confocal light immunocytochemistry, immunogold transmission electron microscopy (TEM), and co-immunoprecipitation, using regular and phospho-antibodies directed against conserved sites, we found that killifish CFTR (kfCFTR) and the tyrosine kinase focal adhesion kinase (FAK) phosphorylated at Y407 (FAK pY407) are colocalized in the apical membrane and in subjacent membrane vesicles of MR cells. We showed previously that basolateral FAK pY407, unlike other FAK phosphorylation sites, is osmosensitive and dephosphorylates during hypotonic shock of epithelial cells (Marshall et al., 2008). In the present study, we found that hypotonic shock and the alpha(2)-adrenergic agonist clonidine (neither of which affects cAMP levels) rapidly and reversibly inhibit Cl(-) secretion by isolated opercular membranes, simultaneous with dephosphorylation of FAK pY407, located in the apical membrane. FAK pY407 is rephosphorylated and Cl(-) secretion rapidly restored by hypertonic shock as well as by forskolin and isoproterenol, which operate via cAMP and protein kinase A. We conclude that hormone mediated, cAMP dependent and osmotically mediated, cAMP independent pathways converge on a mechanism to activate CFTR and Cl(-) secretion, possibly through tyrosine phosphorylation of CFTR by FAK.
Collapse
Affiliation(s)
- William S Marshall
- Department of Biology, St Francis Xavier University, PO Box 5000 Antigonish, Nova Scotia, Canada B2G 2W5.
| | | | | | | | | |
Collapse
|