1
|
Kim Y, Song S, Kim M, Sim E. Soft‐wall
ion transfer channel accurately predicts sterically hindered ion channel permeability. B KOREAN CHEM SOC 2022. [DOI: 10.1002/bkcs.12486] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/11/2022]
Affiliation(s)
- Youngsam Kim
- Department of Chemistry Yonsei University Seoul South Korea
| | - Suhwan Song
- Department of Chemistry Yonsei University Seoul South Korea
| | - Min‐Cheol Kim
- Department of Chemistry Yonsei University Seoul South Korea
| | - Eunji Sim
- Department of Chemistry Yonsei University Seoul South Korea
| |
Collapse
|
2
|
Gao X, Hwang TC. Spatial positioning of CFTR's pore-lining residues affirms an asymmetrical contribution of transmembrane segments to the anion permeation pathway. J Gen Physiol 2017; 147:407-22. [PMID: 27114613 PMCID: PMC4845689 DOI: 10.1085/jgp.201511557] [Citation(s) in RCA: 11] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/10/2015] [Accepted: 03/28/2016] [Indexed: 12/22/2022] Open
Abstract
CFTR is a chloride channel and a member of the ABC transporter superfamily; however, its structure is unknown. By making a series of cysteine mutants, Gao and Hwang show that CFTR lacks the twofold pseudo-symmetry seen in the permeation pathway of bone fide ABC transporters. The structural composition of CFTR’s anion permeation pathway has been proposed to consist of a short narrow region, flanked by two wide inner and outer vestibules, based on systematic cysteine scanning studies using thiol-reactive probes of various sizes. Although these studies identified several of the transmembrane segments (TMs) as pore lining, the exact spatial relationship between pore-lining elements remains under debate. Here, we introduce cysteine pairs in several key pore-lining positions in TM1, 6, and 12 and use Cd2+ as a probe to gauge the spatial relationship of these residues within the pore. We find that inhibition of single cysteine CFTR mutants, such as 102C in TM1 or 341C in TM6, by intracellular Cd2+ is readily reversible upon removal of the metal ion. However, the inhibitory effect of Cd2+ on the double mutant 102C/341C requires the chelating agent dithiothreitol (DTT) for rapid reversal, indicating that 102C and 341C are close enough to the internal edge of the narrow region to coordinate one Cd2+ ion between them. We observe similar effects of extracellular Cd2+ on TM1/TM6 cysteine pairs 106C/337C, 107C/337C, and 107C/338C, corroborating the idea that these paired residues are physically close to each other at the external edge of the narrow region. Although these data paint a picture of relatively symmetrical contributions to CFTR’s pore by TM1 and TM6, introducing cysteine pairs between TM6 and TM12 (348C/1141C, 348C/1144C, and 348C/1145C) or between TM1 and TM12 (95C/1141C) yields results that contest the long-held principle of twofold pseudo-symmetry in the assembly of ABC transporters’ TMs. Collectively, these findings not only advance our current understanding of the architecture of CFTR’s pore, but could serve as a guide for refining computational models of CFTR by imposing physical constraints among pore-lining residues.
Collapse
Affiliation(s)
- Xiaolong Gao
- Dalton Cardiovascular Research Center, University of Missouri, Columbia, MO 65211 Department of Biological Engineering, University of Missouri, Columbia, MO 65211
| | - Tzyh-Chang Hwang
- Dalton Cardiovascular Research Center, University of Missouri, Columbia, MO 65211 Department of Biological Engineering, University of Missouri, Columbia, MO 65211 Department of Medical Pharmacology and Physiology, University of Missouri, Columbia, MO 65211
| |
Collapse
|
3
|
Simhaev L, McCarty NA, Ford RC, Senderowitz H. Molecular Dynamics Flexible Fitting Simulations Identify New Models of the Closed State of the Cystic Fibrosis Transmembrane Conductance Regulator Protein. J Chem Inf Model 2017; 57:1932-1946. [DOI: 10.1021/acs.jcim.7b00091] [Citation(s) in RCA: 7] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/02/2023]
Affiliation(s)
- Luba Simhaev
- Department
of Chemistry, Bar Ilan University, Ramat-Gan 5290002, Israel
| | - Nael A. McCarty
- Division
of Pulmonology, Allergy/Immunology, Cystic Fibrosis, and Sleep, Department
of Pediatrics, Emory + Children’s Center for Cystic Fibrosis
and Airways Disease Research, Emory University School of Medicine and Children’s Healthcare of Atlanta, 2015 Uppergate Drive, Atlanta, Georgia 30322, United States
| | - Robert C. Ford
- Faculty
of Biology Medicine and Health, University of Manchester, Oxford
Road, Manchester, M13 9PL, U.K
| | | |
Collapse
|
4
|
Yu K, Whitlock JM, Lee K, Ortlund EA, Yuan Cui Y, Hartzell HC. Identification of a lipid scrambling domain in ANO6/TMEM16F. eLife 2015; 4:e06901. [PMID: 26057829 PMCID: PMC4477620 DOI: 10.7554/elife.06901] [Citation(s) in RCA: 138] [Impact Index Per Article: 15.3] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/08/2015] [Accepted: 06/08/2015] [Indexed: 12/22/2022] Open
Abstract
Phospholipid scrambling (PLS) is a ubiquitous cellular mechanism involving the regulated bidirectional transport of phospholipids down their concentration gradient between membrane leaflets. ANO6/TMEM16F has been shown to be essential for Ca(2+)-dependent PLS, but controversy surrounds whether ANO6 is a phospholipid scramblase or an ion channel like other ANO/TMEM16 family members. Combining patch clamp recording with measurement of PLS, we show that ANO6 elicits robust Ca(2+)-dependent PLS coinciding with ionic currents that are explained by ionic leak during phospholipid translocation. By analyzing ANO1-ANO6 chimeric proteins, we identify a domain in ANO6 necessary for PLS and sufficient to confer this function on ANO1, which normally does not scramble. Homology modeling shows that the scramblase domain forms an unusual hydrophilic cleft that faces the lipid bilayer and may function to facilitate translocation of phospholipid between membrane leaflets. These findings provide a mechanistic framework for understanding PLS and how ANO6 functions in this process.
Collapse
Affiliation(s)
- Kuai Yu
- Department of Cell Biology, Emory University School of Medicine, Atlanta, United States
| | - Jarred M Whitlock
- Department of Cell Biology, Emory University School of Medicine, Atlanta, United States
| | - Kyleen Lee
- Department of Cell Biology, Emory University School of Medicine, Atlanta, United States
| | - Eric A Ortlund
- Department of Cell Biology, Emory University School of Medicine, Atlanta, United States
- Department of Biochemistry, Emory University School of Medicine, Atlanta, United States
| | - Yuan Yuan Cui
- Department of Cell Biology, Emory University School of Medicine, Atlanta, United States
| | - H Criss Hartzell
- Department of Cell Biology, Emory University School of Medicine, Atlanta, United States
| |
Collapse
|
5
|
Rubaiy HN, Linsdell P. Location of a permeant anion binding site in the cystic fibrosis transmembrane conductance regulator chloride channel pore. J Physiol Sci 2015; 65:233-41. [PMID: 25673337 PMCID: PMC10717427 DOI: 10.1007/s12576-015-0359-6] [Citation(s) in RCA: 11] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/15/2014] [Accepted: 01/24/2015] [Indexed: 01/15/2023]
Abstract
In the cystic fibrosis transmembrane conductance regulator (CFTR) chloride channel, lyotropic anions with high permeability also bind relatively tightly within the pore. However, the location of permeant anion binding sites, as well as their relationship to anion permeability, is not known. We have identified lysine residue K95 as a key determinant of permeant anion binding in the CFTR pore. Lyotropic anion binding affinity is related to the number of positively charged amino acids located in the inner vestibule of the pore. However, mutations that change the number of positive charges in this pore region have minimal effects on anion permeability. In contrast, a mutation at the narrow pore region alters permeability with minimal effects on anion binding. Our results suggest that a localized permeant anion binding site exists in the pore; however, anion binding to this site has little influence over anion permeability. Implications of this work for the mechanisms of anion recognition and permeability in CFTR are discussed.
Collapse
Affiliation(s)
- Hussein N. Rubaiy
- Department of Physiology and Biophysics, Dalhousie University, PO Box 15000, Halifax, NS B3H 4R2 Canada
| | - Paul Linsdell
- Department of Physiology and Biophysics, Dalhousie University, PO Box 15000, Halifax, NS B3H 4R2 Canada
| |
Collapse
|
6
|
Ju M, Scott-Ward TS, Liu J, Khuituan P, Li H, Cai Z, Husbands SM, Sheppard DN. Loop diuretics are open-channel blockers of the cystic fibrosis transmembrane conductance regulator with distinct kinetics. Br J Pharmacol 2014; 171:265-78. [PMID: 24117047 DOI: 10.1111/bph.12458] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/11/2013] [Revised: 09/21/2013] [Accepted: 09/26/2013] [Indexed: 12/26/2022] Open
Abstract
BACKGROUND AND PURPOSE Loop diuretics are widely used to inhibit the Na(+), K(+), 2Cl(-) co-transporter, but they also inhibit the cystic fibrosis transmembrane conductance regulator (CFTR) Cl(-) channel. Here, we investigated the mechanism of CFTR inhibition by loop diuretics and explored the effects of chemical structure on channel blockade. EXPERIMENTAL APPROACH Using the patch-clamp technique, we tested the effects of bumetanide, furosemide, piretanide and xipamide on recombinant wild-type human CFTR. KEY RESULTS When added to the intracellular solution, loop diuretics inhibited CFTR Cl(-) currents with potency approaching that of glibenclamide, a widely used CFTR blocker with some structural similarity to loop diuretics. To begin to study the kinetics of channel blockade, we examined the time dependence of macroscopic current inhibition following a hyperpolarizing voltage step. Like glibenclamide, piretanide blockade of CFTR was time and voltage dependent. By contrast, furosemide blockade was voltage dependent, but time independent. Consistent with these data, furosemide blocked individual CFTR Cl(-) channels with 'very fast' speed and drug-induced blocking events overlapped brief channel closures, whereas piretanide inhibited individual channels with 'intermediate' speed and drug-induced blocking events were distinct from channel closures. CONCLUSIONS AND IMPLICATIONS Structure-activity analysis of the loop diuretics suggests that the phenoxy group present in bumetanide and piretanide, but absent in furosemide and xipamide, might account for the different kinetics of channel block by locking loop diuretics within the intracellular vestibule of the CFTR pore. We conclude that loop diuretics are open-channel blockers of CFTR with distinct kinetics, affected by molecular dimensions and lipophilicity.
Collapse
Affiliation(s)
- Min Ju
- School of Physiology and Pharmacology, University of Bristol, Bristol, UK
| | | | | | | | | | | | | | | |
Collapse
|
7
|
Abstract
Cystic fibrosis is caused by mutations in the cystic fibrosis transmembrane conductance regulator (CFTR), a member of the ATP-binding cassette (ABC) family of membrane transport proteins. CFTR is unique among ABC proteins in that it functions not as an active transporter but as an ATP-gated Cl(-) channel. As an ion channel, the function of the CFTR transmembrane channel pore that mediates Cl(-) movement has been studied in great detail. On the other hand, only low resolution structural data is available on the transmembrane parts of the protein. The structure of the channel pore has, however, been modeled on the known structure of active transporter ABC proteins. Currently, significant barriers exist to building a unified view of CFTR pore structure and function. Reconciling functional data on the channel with indirect structural data based on other proteins with very different transport functions and substrates has proven problematic. This review summarizes current structural and functional models of the CFTR Cl(-) channel pore, including a comprehensive review of previous electrophysiological investigations of channel structure and function. In addition, functional data on the three-dimensional arrangement of pore-lining helices, as well as contemporary hypotheses concerning conformational changes in the pore that occur during channel opening and closing, are discussed. Important similarities and differences between different models of the pore highlight current gaps in our knowledge of CFTR structure and function. In order to fill these gaps, structural and functional models of the membrane-spanning pore need to become better integrated.
Collapse
Affiliation(s)
- Paul Linsdell
- Department of Physiology & Biophysics, Dalhousie University , Halifax, Nova Scotia , Canada
| |
Collapse
|
8
|
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
|
9
|
Hwang TC, Kirk KL. The CFTR ion channel: gating, regulation, and anion permeation. Cold Spring Harb Perspect Med 2013; 3:a009498. [PMID: 23284076 DOI: 10.1101/cshperspect.a009498] [Citation(s) in RCA: 94] [Impact Index Per Article: 8.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/23/2022]
Abstract
Cystic fibrosis transmembrane conductance regulator (CFTR) is an ATP-gated anion channel with two remarkable distinctions. First, it is the only ATP-binding cassette (ABC) transporter that is known to be an ion channel--almost all others function as transport ATPases. Second, CFTR is the only ligand-gated channel that consumes its ligand (ATP) during the gating cycle--a consequence of its enzymatic activity as an ABC transporter. We discuss these special properties of CFTR in the context of its evolutionary history as an ABC transporter. Other topics include the mechanisms by which CFTR gating is regulated by phosphorylation of its unique regulatory domain and our current view of the CFTR permeation pathway (or pore). Understanding these basic operating principles of the CFTR channel is central to defining the mechanisms of action of prospective cystic fibrosis drugs and to the development of new, rational treatment strategies.
Collapse
Affiliation(s)
- Tzyh-Chang Hwang
- Dalton Cardiovascular Research Center, University of Missouri-Columbia, Columbia, MO 65211, USA
| | | |
Collapse
|
10
|
El Hiani Y, Linsdell P. Tuning of CFTR chloride channel function by location of positive charges within the pore. Biophys J 2012; 103:1719-26. [PMID: 23083715 DOI: 10.1016/j.bpj.2012.09.020] [Citation(s) in RCA: 24] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/22/2012] [Revised: 09/14/2012] [Accepted: 09/19/2012] [Indexed: 11/27/2022] Open
Abstract
High unitary Cl(-) conductance in the cystic fibrosis transmembrane conductance regulator Cl(-) channel requires a functionally unique, positively charged lysine residue (K95) in the inner vestibule of the channel pore. Here we used a mutagenic approach to investigate the ability of other sites in the pore to host this important positive charge. The loss of conductance observed in the K95Q mutation was >50% rescued by substituting a lysine for each of five different pore-lining amino acids, suggesting that the exact location of the fixed positive charge is not crucial to support high conductance. Moving the positive charge also restored open-channel blocker interactions that are lost in K95Q. Introducing a second positive charge in addition to that at K95 did not increase conductance at any site, but did result in a striking increase in the strength of block by divalent Pt(NO(2))(4)(2-) ions. Based on the site dependence of these effects, we propose that although the exact location of the positive charge is not crucial for normal pore properties, transplanting this charge to other sites results in a diminution of its effectiveness that appears to depend on its location along the axis of the pore.
Collapse
Affiliation(s)
- Yassine El Hiani
- Department of Physiology and Biophysics, Dalhousie University, Halifax, Nova Scotia, Canada
| | | |
Collapse
|
11
|
Norimatsu Y, Ivetac A, Alexander C, Kirkham J, O’Donnell N, Dawson DC, Sansom MS. Cystic fibrosis transmembrane conductance regulator: a molecular model defines the architecture of the anion conduction path and locates a "bottleneck" in the pore. Biochemistry 2012; 51:2199-212. [PMID: 22352759 PMCID: PMC3316148 DOI: 10.1021/bi201888a] [Citation(s) in RCA: 50] [Impact Index Per Article: 4.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/23/2022]
Abstract
We developed molecular models for the cystic fibrosis transmembrane conductance regulator chloride channel based on the prokaryotic ABC transporter, Sav1866. Here we analyze predicted pore geometry and side-chain orientations for TM3, TM6, TM9, and TM12, with particular attention being paid to the location of the rate-limiting barrier for anion conduction. Side-chain orientations assayed by cysteine scanning were found to be from 77 to 90% in accord with model predictions. The predicted geometry of the anion conduction path was defined by a space-filling model of the pore and confirmed by visualizing the distribution of water molecules from a molecular dynamics simulation. The pore shape is that of an asymmetric hourglass, comprising a shallow outward-facing vestibule that tapers rapidly toward a narrow "bottleneck" linking the outer vestibule to a large inner cavity extending toward the cytoplasmic extent of the lipid bilayer. The junction between the outer vestibule and the bottleneck features an outward-facing rim marked by T338 in TM6 and I1131 in TM12, consistent with the observation that cysteines at both of these locations reacted with both channel-permeant and channel-impermeant, thiol-directed reagents. Conversely, cysteines substituted for S341 in TM6 or T1134 in TM12, predicted by the model to lie below the rim of the bottleneck, were found to react exclusively with channel-permeant reagents applied from the extracellular side. The predicted dimensions of the bottleneck are consistent with the demonstrated permeation of Cl(-), pseudohalide anions, water, and urea.
Collapse
Affiliation(s)
- Yohei Norimatsu
- Department of Physiology and Pharmacology, Oregon Health & Science University, Portland, Oregon 97239
| | - Anthony Ivetac
- Department of Biochemistry, University of Oxford, South Parks Road, Oxford, OX1 3QU, U.K
| | - Christopher Alexander
- Department of Physiology and Pharmacology, Oregon Health & Science University, Portland, Oregon 97239
| | - John Kirkham
- Department of Physiology and Pharmacology, Oregon Health & Science University, Portland, Oregon 97239
| | - Nicolette O’Donnell
- Department of Physiology and Pharmacology, Oregon Health & Science University, Portland, Oregon 97239
| | - David C. Dawson
- Department of Physiology and Pharmacology, Oregon Health & Science University, Portland, Oregon 97239
| | - Mark S.P. Sansom
- Department of Biochemistry, University of Oxford, South Parks Road, Oxford, OX1 3QU, U.K
| |
Collapse
|
12
|
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
|
13
|
Zhou JJ, Fatehi M, Linsdell P. Direct and indirect effects of mutations at the outer mouth of the cystic fibrosis transmembrane conductance regulator chloride channel pore. J Membr Biol 2007; 216:129-42. [PMID: 17673962 DOI: 10.1007/s00232-007-9056-6] [Citation(s) in RCA: 24] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/05/2007] [Accepted: 06/11/2007] [Indexed: 02/08/2023]
Abstract
The cystic fibrosis transmembrane conductance regulator (CFTR) Cl(-) channel pore is thought to contain multiple binding sites for permeant and impermeant anions. Here, we investigate the effects of mutation of different positively charged residues in the pore on current inhibition by impermeant Pt(NO(2)) (4) (2-) and suramin anions. We show that mutations that remove positive charges (K95, R303) influence interactions with intracellular, but not extracellular, Pt(NO(2))(4)(2-) ions, consistent with these residues being situated within the pore inner vestibule. In contrast, mutation of R334, supposedly located in the outer vestibule of the pore, affects block by both extracellular and intracellular Pt(NO(2))(4)(2-). Inhibition by extracellular Pt(NO(2))(4)(2-) requires a positive charge at position 334, consistent with a direct electrostatic interaction resulting in either open channel block or surface charge screening. In contrast, inhibition by intracellular Pt(NO(2))(4)(2-) is weakened in all R334-mutant forms of the channel studied, inconsistent with a direct interaction. Furthermore, mutation of R334 had similar effects on block by intracellular suramin, a large organic molecule that is apparently unable to enter deeply into the channel pore. Mutation of R334 altered interactions between intracellular Pt(NO(2))(4)(2-) and extracellular Cl(-) but not those between intracellular Pt(NO(2))(4)(2-) and extracellular Pt(NO(2))(4)(2-). We propose that while the positive charge of R334 interacts directly with extracellular anions, mutation of this residue also alters interactions with intracellular anions by an indirect mechanism, due to mutation-induced conformational changes in the protein that are propagated some distance from the site of the mutation in the outer mouth of the pore.
Collapse
Affiliation(s)
- Jing-Jun Zhou
- Department of Physiology and Biophysics, Dalhousie University, 5850 College Street, Halifax, NS, Canada, B3H 1X5
| | | | | |
Collapse
|
14
|
Melin P, Hosy E, Vivaudou M, Becq F. CFTR inhibition by glibenclamide requires a positive charge in cytoplasmic loop three. BIOCHIMICA ET BIOPHYSICA ACTA-BIOMEMBRANES 2007; 1768:2438-46. [PMID: 17582383 DOI: 10.1016/j.bbamem.2007.05.013] [Citation(s) in RCA: 14] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 02/20/2007] [Revised: 05/02/2007] [Accepted: 05/14/2007] [Indexed: 10/23/2022]
Abstract
The sulfonylurea glibenclamide is widely used as an open-channel blocker of the CFTR chloride channel. Here, we used site-directed mutagenesis to identify glibenclamide site of interaction: a positively charged residue K978, located in the cytoplasmic loop 3. Charge-neutralizing mutations K978A, K978Q, K978S abolished the inhibition of forskolin-activated CFTR chloride current by glibenclamide but not by CFTR(inh)-172. The charge-conservative mutation K978R did not alter glibenclamide sensitivity of CFTR current. Mutations of the neighbouring R975 (R975A, R975S, R975Q) did not affect electrophysiological and pharmacological properties of CFTR. No alteration of halide selectivity was observed with any of these CFTR mutant channels. This study identifies a novel potential inhibitor site within the CFTR molecule, and suggests a novel role of cytoplasmic loop three, within the second transmembrane domain of CFTR protein. This work is the first to report on the role of a residue in a cytoplasmic loop in the mechanism of action of the channel blocker glibenclamide.
Collapse
Affiliation(s)
- Patricia Melin
- Institut de Physiologie et Biologie Cellulaires, Université de Poitiers, CNRS UMR 6187, 86022 Poitiers cedex, France.
| | | | | | | |
Collapse
|
15
|
Fatehi M, St Aubin CN, Linsdell P. On the origin of asymmetric interactions between permeant anions and the cystic fibrosis transmembrane conductance regulator chloride channel pore. Biophys J 2006; 92:1241-53. [PMID: 17142267 PMCID: PMC1783888 DOI: 10.1529/biophysj.106.095349] [Citation(s) in RCA: 21] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/11/2023] Open
Abstract
Single channel and macroscopic current recording was used to investigate block of the cystic fibrosis transmembrane conductance regulator (CFTR) Cl(-) channel pore by the permeant anion Au(CN)2(-). Block was 1-2 orders of magnitude stronger when Au(CN)2(-) was added to the intracellular versus the extracellular solution, depending on membrane potential. A point mutation within the pore, T-338A, strongly decreased the asymmetry of block, by weakening block by intracellular Au(CN)2(-) and at the same time strengthening block by external Au(CN)2(-). Block of T-338A, but not wild-type, was strongest at the current reversal potential and weakened by either depolarization or hyperpolarization. In contrast to these effects, the T-338A mutation had no impact on block by the impermeant Pt(NO2)4(2-) ion. We suggest that the CFTR pore has at least two anion binding sites at which Au(CN)2(-) and Pt(NO2)4(2-) block Cl- permeation. The T-338A mutation decreases a barrier for Au(CN)2(-) movement between different sites, leading to significant changes in its blocking action. Our finding that apparent blocker binding affinity can be altered by mutagenesis of a residue which does not contribute to a blocker binding site has important implications for interpreting the effects of mutagenesis on channel blocker effects.
Collapse
Affiliation(s)
- Mohammad Fatehi
- Department of Physiology and Biophysics, Dalhousie University, Halifax, Nova Scotia B3H 1X5, Canada
| | | | | |
Collapse
|
16
|
Linsdell P. Mechanism of chloride permeation in the cystic fibrosis transmembrane conductance regulator chloride channel. Exp Physiol 2005; 91:123-9. [PMID: 16157656 DOI: 10.1113/expphysiol.2005.031757] [Citation(s) in RCA: 85] [Impact Index Per Article: 4.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/08/2022]
Abstract
The cystic fibrosis transmembrane conductance regulator (CFTR) functions as a Cl- channel important in transepithelial salt and water transport. While there is a paucity of direct structural information on CFTR, much has been learned about the molecular determinants of the CFTR Cl- channel pore region and the mechanism of Cl- permeation through the pore from indirect structure-function studies. The first and sixth transmembrane regions of the CFTR protein play major roles in forming the channel pore and determining its functional properties by interacting with permeating Cl- ions. Positively charged amino acid side-chains are involved in attracting negatively charged Cl- ions into the pore region, where they interact briefly with a number of discrete sites on the pore walls. The pore appears able to accommodate more than one Cl- ion at a time, and Cl- ions bound inside the pore are probably sensitive to one another's presence. Repulsive interactions between Cl- ions bound concurrently within the pore may be important in ensuring rapid movement of Cl- ions through the pore. Chloride ion binding sites also interact with larger anions that can occlude the pore and block Cl- permeation, thus inhibiting CFTR function. Other ions besides Cl- are capable of passing through the pore, and specific amino acid residues that may be important in allowing the channel to discriminate between different anions have been identified. This brief review summarizes these mechanistic insights and tries to incorporate them into a simple cartoon model depicting the interactions between the channel and Cl- ions that are important for ion translocation.
Collapse
Affiliation(s)
- Paul Linsdell
- Department of Physiology & Biophysics, Dalhousie University, Halifax, Canada.
| |
Collapse
|