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Bellacchio E. Exploring the Mechanism of Activation of CFTR by Curcuminoids: An Ensemble Docking Study. Int J Mol Sci 2023; 25:552. [PMID: 38203723 PMCID: PMC10778693 DOI: 10.3390/ijms25010552] [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: 11/07/2023] [Revised: 12/18/2023] [Accepted: 12/28/2023] [Indexed: 01/12/2024] Open
Abstract
Curcumin, a major constituent of turmeric (Curcuma longa L.), has beneficial effects against several diseases. In cystic fibrosis (CF), this compound improves patients' symptoms by recovering the activity of a number of mutants of the cystic fibrosis transmembrane conductance regulator (CFTR). Despite holding promise in the treatment of CF, the curcumin binding site in CFTR and the molecular mechanism of activation of this channel are still unknown. The results of this study, based on docking and molecular dynamics (MD) simulations, allow us to propose that curcumin binds the closed ATP-free CFTR near the nucleotide-binding domain 1 (NBD1)/ICl1/ICl4 interface. The bound ligand, once approached by the nucleotide-binding domain 2 (NBD2) during transient channel opening, lays at a multiple interdomain cross point. Thereafter, curcumin can bridge NBD1 and NBD2, and also ICL1/ICL4 and ICL2/ICL3, finally tightening the same interdomain interactions that normally uphold the open conformation in the wild-type ATP-bound CFTR. The proposed binding site is compatible with biochemical observations made in previous CFTR-curcumin interaction studies. These findings provide a framework for the design of novel drugs that activate CFTR mutants characterized by defects in ATP binding and/or NBD dimerization or even lacking NBD2.
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Affiliation(s)
- Emanuele Bellacchio
- Genetica Molecolare e Genomica Funzionale, Bambino Gesù Children's Hospital, IRCCS, 00165 Rome, Italy
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2
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Baharara H, Kesharwani P, Johnston TP, Sahebkar A. Therapeutic potential of phytochemicals for cystic fibrosis. Biofactors 2023; 49:984-1009. [PMID: 37191383 DOI: 10.1002/biof.1960] [Citation(s) in RCA: 2] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 11/14/2022] [Accepted: 05/01/2023] [Indexed: 05/17/2023]
Abstract
The aim of this review was to review and discuss various phytochemicals that exhibit beneficial effects on mutated membrane channels, and hence, improve transmembrane conductance. These therapeutic phytochemicals may have the potential to decrease mortality and morbidity of CF patients. Four databases were searched using keywords. Relevant studies were identified, and related articles were separated. Google Scholar, as well as gray literature (i.e., information that is not produced by commercial publishers), were also checked for related articles to locate/identify additional studies. The relevant databases were searched a second time to ensure that recent studies were included. In conclusion, while curcumin, genistein, and resveratrol have demonstrated effectiveness in this regard, it should be emphasized that coumarins, quercetin, and other herbal medicines also have beneficial effects on transporter function, transmembrane conductivity, and overall channel activity. Additional in vitro and in vivo studies should be conducted on mutant CFTR to unequivocally define the mechanism by which phytochemicals alter transmembrane channel function/activity, since the results of the studies evaluated in this review have a high degree of heterogenicity and discrepancy. Finally, continued research be undertaken to clearly define the mechanism(s) of action and the therapeutic effects that therapeutic phytochemicals have on the symptoms observed in CF patients in an effort to reduce mortality and morbidity.
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Affiliation(s)
- Hamed Baharara
- Department of Clinical Pharmacy, School of Pharmacy, Mashhad University of Medical Sciences, Mashhad, Iran
| | - Prashant Kesharwani
- Department of Pharmaceutics, School of Pharmaceutical Education and Research, Jamia Hamdard, New Delhi, India
- Center for Transdisciplinary Research, Department of Pharmacology, Saveetha Dental College, Saveetha Institute of Medical and Technical Science, Chennai, India
| | - Thomas P Johnston
- Division of Pharmacology and Pharmaceutical Sciences, School of Pharmacy, University of Missouri-Kansas City, Kansas City, Missouri, USA
| | - AmirHossein Sahebkar
- Biotechnology Research Center, Pharmaceutical Technology Institute, Mashhad University of Medical Sciences, Mashhad, Iran
- Applied Biomedical Research Center, Mashhad University of Medical Sciences, Mashhad, Iran
- Department of Biotechnology, School of Pharmacy, Mashhad University of Medical Sciences, Mashhad, Iran
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Wang G. Thermal Ring-Based Heat Switches in Hyperthermophilic Class II Bacterial Fructose Aldolase. ACS OMEGA 2023; 8:24624-24634. [PMID: 37457467 PMCID: PMC10339327 DOI: 10.1021/acsomega.3c03001] [Citation(s) in RCA: 4] [Impact Index Per Article: 4.0] [Reference Citation Analysis] [Abstract] [Grants] [Track Full Text] [Download PDF] [Figures] [Subscribe] [Scholar Register] [Received: 05/01/2023] [Accepted: 05/24/2023] [Indexed: 07/18/2023]
Abstract
Both thermophilic and hyperthermophilic enzymes in bacterial and archaeal species are activated above a specific temperature threshold but inactivated at another higher temperature. However, the underlying structural basis for these two heat switches is still unresolved. Here, graph theory was used to test if the temperature-dependent noncovalent interactions and metal bridges as identified in a series of crystal structures of the class II bacterial fructose 1,6-bisphosphate aldolase homodimer or homotetramer with or without natural substrates and products bound could form systematic fluidic grid-like mesh networks with topological grids as thermal rings to regulate their structural thermostability and functional thermoactivity. The results indicated that the second biggest grid in the Thermus aquaticus fructose 1,6-diphosphate aldolase dimer may control the specific temperature threshold to release the swapping flexible active sites at the dimeric interface for heat-evoked activation. Meanwhile, the third biggest grid may serve as a necessary structural motif against heat inactivation. Finally, the smallest grid may act as a stiff thermostable anchor. Its dissociation at the maximal melting temperature threshold may stop the catalytic activity. Taken as a whole, this computational study may render the structural motifs for the optimal growth temperature and the extreme heat stability of hyperthermophiles.
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Wang G. Network Basis for the Heat-Adapted Structural Thermostability of Bacterial Class II Fructose Bisphosphate Aldolase. ACS OMEGA 2023; 8:17731-17739. [PMID: 37251155 PMCID: PMC10210171 DOI: 10.1021/acsomega.3c00473] [Citation(s) in RCA: 5] [Impact Index Per Article: 5.0] [Reference Citation Analysis] [Abstract] [Grants] [Track Full Text] [Download PDF] [Figures] [Subscribe] [Scholar Register] [Received: 01/23/2023] [Accepted: 04/28/2023] [Indexed: 05/31/2023]
Abstract
The sufficient structural thermostability of a biological macromolecule is an overriding need for green nanoreactors and nanofactories to secure high activity. However, little is still known about what specific structural motif is responsible for it. Here, graph theory was employed to examine if the temperature-dependent noncovalent interactions and metal bridges, as identified in the structures of Escherichia coli class II fructose 1,6-bisphosphate aldolase, could shape a systematic fluidic grid-like mesh network with topological grids to regulate the structural thermostability of the wild-type construct and its evolved variants in each generation upon decyclization. The results indicated that the biggest grids may govern the temperature thresholds for their tertiary structural perturbations but without affecting the catalytic activities. Moreover, lower grid-based systematic thermal instability may facilitate structural thermostability, but a highly independent thermostable grid may still be required to serve as a critical anchor to secure the stereospecific thermoactivity. Its end melting temperature thresholds, together with the start ones of the biggest grids in the evolved variants, may confer high temperature sensitivity against thermal inactivation. Collectively, this computational study may have widespread significance in advancing our complete understanding and biotechnology of the thermoadaptive mechanism of the structural thermostability of a biological macromolecule.
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Wang G. Lipid-dependent sequential allosteric activation of heat-sensing TRPV1 channels by anchor-stereoselective "hot" vanilloid compounds and analogs. Biochem Biophys Rep 2021; 28:101109. [PMID: 34504955 PMCID: PMC8416642 DOI: 10.1016/j.bbrep.2021.101109] [Citation(s) in RCA: 6] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/31/2021] [Revised: 08/09/2021] [Accepted: 08/16/2021] [Indexed: 12/22/2022] Open
Abstract
Both a silent resident phosphatidylinositol lipid and a “hot” vanilloid agonist capsaicin or resiniferatoxin have been shown to share the same inter-subunit binding pocket between a voltage sensor like domain and a pore domain in TRPV1. However, how the vanilloid competes off the resident lipid for allosteric TRPV1 activation is unknown. Here, the in silico research suggested that anchor-stereoselective sequential cooperativity between an initial recessive transient silent weak ligand binding site and a subsequent dominant steady-state strong ligand binding site in the vanilloid pocket may facilitate the lipid release for allosteric activation of TRPV1 by vanilloids or analogs upon non-covalent interactions. Thus, the resident lipid may play a critical role in allosteric activation of TRPV1 by vanilloid compounds and analogs. Four active vanilloid binding pockets as revealed by the cryo-EM structure of TRPV1 have no cooperativity between subunits. Allosteric activation of TRPV1 by vanilloid compounds and analogs is lipid-dependent and anchor-stereoselective. The resident and occluded lipid must be competed off for allosteric activation of TRPV1 by vanilloid compounds and analogs. The first ligand binding is needed to release the resident lipid for the second ligand binding in the vanilloid pocket. A lipid-free anchor facilitates the vanilloid ligand binding to remove the resident lipid from the active site in TRPV1. Site accessibility controls sequential cooperative interactions of TRPV1 with vanilloids or analogs to open the channel. The anchor stereoselectivity depends on the formation of a vanilloid bridge between two separated residues at the active site. Different anchor stereoselectivities produce diverse recessive transient reaction intermediates or steps for TRPV1 opening. Membrane hyperpolarization and depolarization may stabilize and loosen the resident lipid for TRPV1 gating, respectively. Phospholipids at N- and C- terminal domains may affect the cooperativity or the potency of the vanilloid ligands.
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Affiliation(s)
- Guangyu Wang
- Department of Physiology and Membrane Biology, University of California School of Medicine, Davis, CA, USA.,Institute of Biophysical Medico-chemistry, Reno, NV, USA
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Wang G. Removal of the Fe(iii) site promotes activation of the human cystic fibrosis transmembrane conductance regulator by high-affinity Zn(ii) binding. Metallomics 2019; 10:240-247. [PMID: 29372915 DOI: 10.1039/c7mt00315c] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022]
Abstract
The cystic fibrosis transmembrane conductance regulator (CFTR) chloride channel is activated by ATP binding at the interface of two cytoplasmic nucleotide binding domains (NBDs) and phosphorylation of the regulatory (R) domain by protein kinase A (PKA). The human CFTR has two functionally active thiol groups for gating regulation by chemical modification. Although modification of C832 in the R domain with N-ethylmaleimide promotes channel opening, glutathionylation of C1344 in NBD2 inhibits channel opening. Our recent studies demonstrated that the N-ethylmaleimide-induced potentiation involves a high-affinity inhibitory Fe3+ site at the interface between the R domain and intracellular loop 3 (ICL3). However, it is unknown whether the glutathionylation-evoked inhibition implies another stimulatory metal site. Here, Fe3+-insensitive mutations at the R-ICL3 interface were employed to further examine whether Zn2+ potentiated the activity of the human CFTR channel by targeting C1344 once the interfacial Fe3+ bridge was disrupted. The results showed that internal nanomolar Zn2+ increased its activity by about two- to threefold at a low level of protein kinase A, and the increase was reversed by EDTA or DTT or reduced glutathione but suppressed by a high level of protein kinase A, N-ethylmaleimide modification or a C1344A mutation. It is interesting that this Zn2+-triggered potentiation is not found in the wild type human CFTR to which endogenous Fe3+ is bound. Thus, the high-affinity binding of Zn2+ to C1344 in NBD2 may stimulate human CFTR activity in a phosphorylation-dependent manner, but the primary binding of Fe3+ to the ICL3-R interface may prohibit this stimulation.
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Affiliation(s)
- Guangyu Wang
- Department of Physiology and Biophysics and Gregory Fleming James Cystic Fibrosis Research Center, University of Alabama at Birmingham, Birmingham, AL 39254, USA
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Wang G. Mechanistic insight into the heme-independent interplay between iron and carbon monoxide in CFTR and Slo1 BK Ca channels. Metallomics 2017; 9:634-645. [PMID: 28474046 DOI: 10.1039/c7mt00065k] [Citation(s) in RCA: 9] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/15/2022]
Abstract
Ion channels have been extensively reported as effectors of carbon monoxide (CO). However, the mechanisms of heme-independent CO action are still not known. Because most ion channels are heterologously expressed on human embryonic kidney cells that are cultured in Fe3+-containing media, CO may act as a small and strong iron chelator to disrupt a putative iron bridge in ion channels and thus to tune their activity. In this review CFTR and Slo1 BKCa channels are employed to discuss the possible heme-independent interplay between iron and CO. Our recent studies demonstrated a high-affinity Fe3+ site at the interface between the regulatory domain and intracellular loop 3 of CFTR. Because the binding of Fe3+ to CFTR prevents channel opening, the stimulatory effect of CO on the Cl- and HCO3- currents across the apical membrane of rat distal colon may be due to the release of inhibitive Fe3+ by CO. In contrast, CO repeatedly stimulates the human Slo1 BKCa channel opening, possibly by binding to an unknown iron site, because cyanide prohibits this heme-independent CO stimulation. Here, in silico research on recent structural data of the slo1 BKCa channels indicates two putative binuclear Fe2+-binding motifs in the gating ring in which CO may compete with protein residues to bind to either Fe2+ bowl to disrupt the Fe2+ bridge but not to release Fe2+ from the channel. Thus, these two new regulation models of CO, with iron releasing from and retaining in the ion channel, may have significant and extensive implications for other metalloproteins.
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Affiliation(s)
- Guangyu Wang
- Department of Physiology and Membrane Biology, University of California School of Medicine, Davis, CA, USA. and Institute of Biophysical Medico-chemistry, Reno, NV, USA
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Lelli D, Sahebkar A, Johnston TP, Pedone C. Curcumin use in pulmonary diseases: State of the art and future perspectives. Pharmacol Res 2016; 115:133-148. [PMID: 27888157 DOI: 10.1016/j.phrs.2016.11.017] [Citation(s) in RCA: 174] [Impact Index Per Article: 21.8] [Reference Citation Analysis] [Abstract] [Key Words] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 07/22/2016] [Revised: 10/13/2016] [Accepted: 11/19/2016] [Indexed: 01/18/2023]
Abstract
Curcumin (diferuloylmethane) is a yellow pigment present in the spice turmeric (Curcuma longa). It has been used for centuries in Ayurveda (Indian traditional medicine) for the treatment of several diseases. Over the last several decades, the therapeutic properties of curcumin have slowly been elucidated. It has been shown that curcumin has pleiotropic effects, regulating transcription factors (e.g., NF-kB), cytokines (e.g., IL6, TNF-alpha), adhesion molecules (e.g., ICAM-1), and enzymes (e.g., MMPs) that play a major role in inflammation and cancerogenesis. These effects may be relevant for several pulmonary diseases that are characterized by abnormal inflammatory responses, such as asthma or chronic obstructive pulmonary disease, acute respiratory distress syndrome, pulmonary fibrosis, and acute lung injury. Furthermore, some preliminary evidence suggests that curcumin may have a role in the treatment of lung cancer. The evidence for the use of curcumin in pulmonary disease is still sparse and has mostly been obtained using either in vitro or animal models. The most important issue with the use of curcumin in humans is its poor bioavailability, which makes it necessary to use adjuvants or curcumin nanoparticles or liposomes. The aim of this review is to summarize the available evidence on curcumin's effectiveness in pulmonary diseases, including lung cancer, and to provide our perspective on future research with curcumin so as to improve its pharmacological effects, as well as provide additional evidence of curcumin's efficacy in the treatment of pulmonary diseases.
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Affiliation(s)
- Diana Lelli
- Area di Geriatria, Università Campus Bio-Medico di Roma, via Alvaro del Portillo 21, 00128 Roma, Italy.
| | - Amirhossein Sahebkar
- Biotechnology Research Center, Mashhad University of Medical Sciences, BuAli Square, Mashhad, 9196773117 Iran.
| | - Thomas P Johnston
- Division of Pharmaceutical Sciences, School of Pharmacy, University of Missouri-Kansas City, 2464 Charlotte Street, Kansas City, MO, 64108,USA.
| | - Claudio Pedone
- Area di Geriatria, Università Campus Bio-Medico di Roma, via Alvaro del Portillo 21, 00128 Roma, Italy.
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Wang G, Linsley R, Norimatsu Y. External Zn2+binding to cysteine-substituted cystic fibrosis transmembrane conductance regulator constructs regulates channel gating and curcumin potentiation. FEBS J 2016; 283:2458-75. [DOI: 10.1111/febs.13752] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/01/2015] [Revised: 05/02/2016] [Accepted: 05/11/2016] [Indexed: 01/22/2023]
Affiliation(s)
- Guangyu Wang
- Department of Physiology and Pharmacology; Oregon Health & Sciences University; Portland OR USA
- Department of Drug Research and Development; Institute of Biophysical Medico-chemistry; Reno NV USA
- Department of Physiology and Membrane Biology; University of California School of Medicine; Davis CA USA
| | | | - Yohei Norimatsu
- Department of Physiology; Kirksville College of Osteopathic Medicine; A.T. Still University; Kirksville MO USA
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Dong ZW, Chen J, Ruan YC, Zhou T, Chen Y, Chen Y, Tsang LL, Chan HC, Peng YZ. CFTR-regulated MAPK/NF-κB signaling in pulmonary inflammation in thermal inhalation injury. Sci Rep 2015; 5:15946. [PMID: 26515683 PMCID: PMC4626762 DOI: 10.1038/srep15946] [Citation(s) in RCA: 35] [Impact Index Per Article: 3.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/12/2015] [Accepted: 09/30/2015] [Indexed: 12/17/2022] Open
Abstract
The mechanism underlying pulmonary inflammation in thermal inhalation injury remains elusive. Cystic fibrosis, also hallmarked with pulmonary inflammation, is caused by mutations in CFTR, the expression of which is temperature-sensitive. We investigated whether CFTR is involved in heat-induced pulmonary inflammation. We applied heat-treatment in 16HBE14o- cells with CFTR knockdown or overexpression and heat-inhalation in rats in vivo. Heat-treatment caused significant reduction in CFTR and, reciprocally, increase in COX-2 at early stages both in vitro and in vivo. Activation of ERK/JNK, NF-κB and COX-2/PGE2 were detected in heat-treated cells, which were mimicked by knockdown, and reversed by overexpression of CFTR or VX-809, a reported CFTR mutation corrector. JNK/ERK inhibition reversed heat-/CFTR-knockdown-induced NF-κB activation, whereas NF-κB inhibitor showed no effect on JNK/ERK. IL-8 was augmented by heat-treatment or CFTR-knockdown, which was abolished by inhibition of NF-κB, JNK/ERK or COX-2. Moreover, in vitro or in vivo treatment with curcumin, a natural phenolic compound, significantly enhanced CFTR expression and reversed the heat-induced increases in COX-2/PGE2/IL-8, neutrophil infiltration and tissue damage in the airway. These results have revealed a CFTR-regulated MAPK/NF-κB pathway leading to COX-2/PGE2/IL-8 activation in thermal inhalation injury, and demonstrated therapeutic potential of curcumin for alleviating heat-induced pulmonary inflammation.
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Affiliation(s)
- Zhi Wei Dong
- State Key Laboratory of Trauma, Burns and Combined Injury, Chongqing Key Laboratory for Proteomics Disease, Institute of Burn Research, Southwest Hospital, the Third Military Medical University, Chongqing, China
| | - Jing Chen
- State Key Laboratory of Trauma, Burns and Combined Injury, Chongqing Key Laboratory for Proteomics Disease, Institute of Burn Research, Southwest Hospital, the Third Military Medical University, Chongqing, China
| | - Ye Chun Ruan
- Epithelial Cell Biology Research Center, School of Biomedical Sciences, Faculty of Medicine, The Chinese University of Hong Kong, Hong Kong, People's Republic of China
| | - Tao Zhou
- State Key Laboratory of Trauma, Burns and Combined Injury, Chongqing Key Laboratory for Proteomics Disease, Institute of Burn Research, Southwest Hospital, the Third Military Medical University, Chongqing, China
| | - Yu Chen
- State Key Laboratory of Trauma, Burns and Combined Injury, Chongqing Key Laboratory for Proteomics Disease, Institute of Burn Research, Southwest Hospital, the Third Military Medical University, Chongqing, China
| | - YaJie Chen
- State Key Laboratory of Trauma, Burns and Combined Injury, Chongqing Key Laboratory for Proteomics Disease, Institute of Burn Research, Southwest Hospital, the Third Military Medical University, Chongqing, China
| | - Lai Ling Tsang
- Epithelial Cell Biology Research Center, School of Biomedical Sciences, Faculty of Medicine, The Chinese University of Hong Kong, Hong Kong, People's Republic of China
| | - Hsiao Chang Chan
- Epithelial Cell Biology Research Center, School of Biomedical Sciences, Faculty of Medicine, The Chinese University of Hong Kong, Hong Kong, People's Republic of China
| | - Yi Zhi Peng
- State Key Laboratory of Trauma, Burns and Combined Injury, Chongqing Key Laboratory for Proteomics Disease, Institute of Burn Research, Southwest Hospital, the Third Military Medical University, Chongqing, China
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Corradi V, Vergani P, Tieleman DP. Cystic Fibrosis Transmembrane Conductance Regulator (CFTR): CLOSED AND OPEN STATE CHANNEL MODELS. J Biol Chem 2015; 290:22891-906. [PMID: 26229102 PMCID: PMC4645605 DOI: 10.1074/jbc.m115.665125] [Citation(s) in RCA: 45] [Impact Index Per Article: 5.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/13/2015] [Indexed: 01/06/2023] Open
Abstract
The cystic fibrosis transmembrane conductance regulator (CFTR) is a member of the ATP-binding cassette (ABC) transporter superfamily. CFTR controls the flow of anions through the apical membrane of epithelia. Dysfunctional CFTR causes the common lethal genetic disease cystic fibrosis. Transitions between open and closed states of CFTR are regulated by ATP binding and hydrolysis on the cytosolic nucleotide binding domains, which are coupled with the transmembrane (TM) domains forming the pathway for anion permeation. Lack of structural data hampers a global understanding of CFTR and thus the development of "rational" approaches directly targeting defective CFTR. In this work, we explored possible conformational states of the CFTR gating cycle by means of homology modeling. As templates, we used structures of homologous ABC transporters, namely TM(287-288), ABC-B10, McjD, and Sav1866. In the light of published experimental results, structural analysis of the transmembrane cavity suggests that the TM(287-288)-based CFTR model could correspond to a commonly occupied closed state, whereas the McjD-based model could represent an open state. The models capture the important role played by Phe-337 as a filter/gating residue and provide structural information on the conformational transition from closed to open channel.
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Affiliation(s)
- Valentina Corradi
- From the Department of Biological Sciences and Centre for Molecular Simulation, University of Calgary, Calgary, Alberta T2N 1N4, Canada and
| | - Paola Vergani
- Research Department of Neuroscience, Physiology and Pharmacology, University College London, Gower Street, London WC1E 6BT, United Kingdom
| | - D Peter Tieleman
- From the Department of Biological Sciences and Centre for Molecular Simulation, University of Calgary, Calgary, Alberta T2N 1N4, Canada and
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