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Chen J, Tomich JM. Free energy analysis of conductivity and charge selectivity of M2GlyR-derived synthetic channels. BIOCHIMICA ET BIOPHYSICA ACTA-BIOMEMBRANES 2014; 1838:2319-25. [PMID: 24582709 DOI: 10.1016/j.bbamem.2014.02.016] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Received: 01/13/2014] [Accepted: 02/21/2014] [Indexed: 12/16/2022]
Abstract
Significant progresses have been made in the design, synthesis, modeling and in vitro testing of channel-forming peptides derived from the second transmembrane domain of the α-subunit of the glycine receptor (GlyR). The latest designs, including p22 (KKKKP ARVGL GITTV LTMTT QS), are highly soluble in water with minimal aggregation propensity and insert efficiently into cell membranes to form highly conductive ion channels. The last obstacle to a potential lead sequence for channel replacement treatment of CF patients is achieving adequate chloride selectivity. We have performed free energy simulation to analyze the conductance and charge selectivity of M2GlyR-derived synthetic channels. The results reveal that the pentameric p22 pore is non-selective. Moderate barriers for permeation of both K(+) and Cl(-) are dominated by the desolvation cost. Despite previous evidence suggesting a potential role of threonine side chains in anion selectivity, the hydroxyl group is not a good surrogate of water for coordinating these ions. We have also tested initial ideas of introducing additional rings of positive changes to various positions along the pore to increase anion selectivity. The results support the feasibility of achieving anion selectivity by modifying the electrostatic properties of the pore, but at the same time suggest that the peptide assembly and pore topology may also be dramatically modified, which could abolish the effects of modified electrostatics on anion selectivity. This was confirmed by subsequent two-electrode voltage clamp measurements showing that none of the tested mono-, di- and tri-Dap substituted sequences was selective. The current study thus highlights the importance of controlling channel topology besides modifying pore electrostatics for achieving anion selectivity. Several strategies are now being explored in our continued efforts to design an anion selective peptide channel with suitable biophysical, physiological and pharmacological properties as a potential treatment modality for channel replacement therapy. This article is part of a Special Issue entitled: Interfacially Active Peptides and Proteins. Guest Editors: William C. Wimley and Kalina Hristova.
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Affiliation(s)
- Jianhan Chen
- Department of Biochemistry and Molecular Biophysics, Kansas State University, Manhattan, KS 66506, USA.
| | - John M Tomich
- Department of Biochemistry and Molecular Biophysics, Kansas State University, Manhattan, KS 66506, USA.
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2
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Bukovnik U, Sala-Rabanal M, Francis S, Frazier SJ, Schultz BD, Nichols CG, Tomich JM. Effect of diaminopropionic acid (Dap) on the biophysical properties of a modified synthetic channel-forming peptide. Mol Pharm 2013; 10:3959-66. [PMID: 24010543 DOI: 10.1021/mp4002377] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/18/2022]
Abstract
Channel replacement therapy, based on synthetic channel-forming peptides (CFPs) with the ability to supersede defective endogenous ion channels, is a novel treatment modality that may augment existing interventions against multiple diseases. Previously, we derived CFPs from the second transmembrane segment of the α-subunit of the glycine receptor, M2GlyR, which forms chloride-selective channels in its native form. The best candidate, NK4-M2GlyR T19R, S22W (p22-T19R, S22W), was water-soluble, incorporated into cell membranes and was nonimmunogenic, but lacked the structural properties for high conductance and anion selectivity when assembled into a pore. Further studies suggested that the threonine residues at positions 13, 17, and 20 line the pore of assembled p22-T19R, S22W, and here we used 2,3-diaminopropionic acid (Dap) substitutions to introduce positive charges to the pore-lining interface of the predicted p22-T19R, S22W channel. Dap-substituted p22-T19R, S22W peptides retained the α-helical secondary structure characteristic of their parent peptide, and induced short-circuit transepithelial currents when exposed to the apical membrane of Madin-Darby canine kidney (MDCK) cells; the sequences containing multiple Dap-substituted residues induced larger currents than the peptides with single or no Dap substitutions. To gain further insights into the effects of Dap residues on the properties of the putative pore, we performed two-electrode voltage clamp electrophysiology on Xenopus oocytes exposed to p22-T19R, S22W or its Dap-modified analogues. We observed that Dap-substituted peptides also induced significantly larger voltage-dependent currents than the parent compound, but there was no apparent change in reversal potential upon replacement of external Na+, Cl- or K+, indicating that these currents remained nonselective. These results suggest that the introduction of positively charged side chains in predicted pore-lining residues does not improve anion-to-cation selectivity, but results in higher conductance, perhaps due to higher oligomerization numbers.
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Affiliation(s)
- Urska Bukovnik
- Department of Biochemistry and ⊥Department of Anatomy and Physiology, Kansas State University , Manhattan, Kansas 66506, United States
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3
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Elie CR, Hébert A, Charbonneau M, Haiun A, Schmitzer AR. Benzimidazolium-based synthetic chloride and calcium transporters in bacterial membranes. Org Biomol Chem 2013; 11:923-8. [DOI: 10.1039/c2ob26966j] [Citation(s) in RCA: 41] [Impact Index Per Article: 3.7] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/13/2023]
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Yau KH, Mak JCW, Leung SWS, Yang D, Vanhoutte PM. A synthetic chloride channel relaxes airway smooth muscle of the rat. PLoS One 2012; 7:e45340. [PMID: 23049786 PMCID: PMC3458840 DOI: 10.1371/journal.pone.0045340] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/18/2012] [Accepted: 08/16/2012] [Indexed: 02/03/2023] Open
Abstract
Synthetic ion channels may have potential therapeutic applications, provided they possess appropriate biological activities. The present study was designed to examine the ability of small molecule-based synthetic Cl– channels to modulate airway smooth muscle responsiveness. Changes in isometric tension were measured in rat tracheal rings. Relaxations to the synthetic chloride channel SCC-1 were obtained during sustained contractions to KCl. The anion dependency of the effect of SCC-1 was evaluated by ion substitution experiments. The sensitivity to conventional Cl– transport inhibitors was also tested. SCC-1 caused concentration-dependent relaxations during sustained contractions to potassium chloride. This relaxing effect was dependent on the presence of extracellular Cl– and HCO3−. It was insensitive to conventional Cl– channels/transport inhibitors that blocked the cystic fibrosis transmembrane conductance regulator and calcium-activated Cl– channels. SCC-1 did not inhibit contractions induced by carbachol, endothelin-1, 5-hydroxytryptamine or the calcium ionophore A23187. SCC-1 relaxes airway smooth muscle during contractions evoked by depolarizing solutions. The Cl– conductance conferred by this synthetic compound is distinct from the endogenous transport systems for chloride anions.
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Affiliation(s)
- Kwok-hei Yau
- Morningside Laboratory for Chemical Biology, Department of Chemistry, Faculty of Science, The University of Hong Kong, Hong Kong SAR, China
| | - Judith Choi-wo Mak
- Department of Pharmacology and Pharmacy, Li Ka Shing Faculty of Medicine, The University of Hong Kong, Hong Kong SAR, China
- Department of Medicine, Li Ka Shing Faculty of Medicine, The University of Hong Kong, Hong Kong SAR, China
| | - Susan Wai-sum Leung
- Department of Pharmacology and Pharmacy, Li Ka Shing Faculty of Medicine, The University of Hong Kong, Hong Kong SAR, China
| | - Dan Yang
- Morningside Laboratory for Chemical Biology, Department of Chemistry, Faculty of Science, The University of Hong Kong, Hong Kong SAR, China
| | - Paul M. Vanhoutte
- Department of Pharmacology and Pharmacy, Li Ka Shing Faculty of Medicine, The University of Hong Kong, Hong Kong SAR, China
- * E-mail:
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Shen B, Li X, Wang F, Yao X, Yang D. A synthetic chloride channel restores chloride conductance in human cystic fibrosis epithelial cells. PLoS One 2012; 7:e34694. [PMID: 22514656 PMCID: PMC3326041 DOI: 10.1371/journal.pone.0034694] [Citation(s) in RCA: 55] [Impact Index Per Article: 4.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/18/2011] [Accepted: 03/05/2012] [Indexed: 11/25/2022] Open
Abstract
Mutations in the gene-encoding cystic fibrosis transmembrane conductance regulator (CFTR) cause defective transepithelial transport of chloride (Cl−) ions and fluid, thereby becoming responsible for the onset of cystic fibrosis (CF). One strategy to reduce the pathophysiology associated with CF is to increase Cl− transport through alternative pathways. In this paper, we demonstrate that a small synthetic molecule which forms Cl− channels to mediate Cl− transport across lipid bilayer membranes is capable of restoring Cl− permeability in human CF epithelial cells; as a result, it has the potential to become a lead compound for the treatment of human diseases associated with Cl− channel dysfunction.
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Affiliation(s)
- Bing Shen
- Department of Physiology, The Chinese University of Hong Kong, Shatin, Hong Kong, China
- Department of Physiology, Anhui Medical University, Hefei, China
| | - Xiang Li
- Morningside Laboratory for Chemical Biology, Department of Chemistry, The University of Hong Kong, Hong Kong, China
| | - Fei Wang
- Department of Physiology, Anhui Medical University, Hefei, China
| | - Xiaoqiang Yao
- Department of Physiology, The Chinese University of Hong Kong, Shatin, Hong Kong, China
- * E-mail: (XY) (XY); (DY) (DY)
| | - Dan Yang
- Morningside Laboratory for Chemical Biology, Department of Chemistry, The University of Hong Kong, Hong Kong, China
- * E-mail: (XY) (XY); (DY) (DY)
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Elie CR, Charbonneau M, Schmitzer AR. An anion structure–activity relationship of imidazolium-based synthetic transporters. MEDCHEMCOMM 2012. [DOI: 10.1039/c2md20107k] [Citation(s) in RCA: 22] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 11/21/2022]
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Bukovnik U, Gao J, Cook GA, Shank LP, Seabra MB, Schultz BD, Iwamoto T, Chen J, Tomich JM. Structural and biophysical properties of a synthetic channel-forming peptide: designing a clinically relevant anion selective pore. BIOCHIMICA ET BIOPHYSICA ACTA-BIOMEMBRANES 2011; 1818:1039-48. [PMID: 21835162 DOI: 10.1016/j.bbamem.2011.07.037] [Citation(s) in RCA: 15] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 06/01/2011] [Accepted: 07/25/2011] [Indexed: 12/15/2022]
Abstract
The design, synthesis, modeling and in vitro testing of channel-forming peptides derived from the cys-loop superfamily of ligand-gated ion channels are part of an ongoing research focus. Over 300 different sequences have been prepared based on the M2 transmembrane segment of the spinal cord glycine receptor α-subunit. A number of these sequences are water-soluble monomers that readily insert into biological membranes where they undergo supramolecular assembly, yielding channels with a range of selectivities and conductances. Selection of a sequence for further modifications to yield an optimal lead compound came down to a few key biophysical properties: low solution concentrations that yield channel activity, greater ensemble conductance, and enhanced ion selectivity. The sequence NK(4)-M2GlyR T19R, S22W (KKKKPARVGLGITTVLTMRTQW) addressed these criteria. The structure of this peptide has been analyzed by solution NMR as a monomer in detergent micelles, simulated as five-helix bundles in a membrane environment, modified by cysteine-scanning and studied for insertion efficiency in liposomes of selected lipid compositions. Taken together, these results define the structural and key biophysical properties of this sequence in a membrane. This model provides an initial scaffold from which rational substitutions can be proposed and tested to modulate anion selectivity. This article is part of a Special Issue entitled: Protein Folding in Membranes.
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Affiliation(s)
- U Bukovnik
- Department of Biochemistry, Kansas State University, Manhattan, KS 66506, USA
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Herrera AI, Al-Rawi A, Cook GA, Gao J, Iwamoto T, Prakash O, Tomich JM, Chen J. Structural characterization of two pore-forming peptides: consequences of introducing a C-terminal tryptophan. Proteins 2010; 78:2238-50. [PMID: 20544961 PMCID: PMC2909830 DOI: 10.1002/prot.22736] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/16/2022]
Abstract
Synthetic channel-forming peptides that can restore chloride conductance across epithelial membranes could provide a novel treatment of channelopathies such as cystic fibrosis. Among a series of 22-residue peptides derived from the second transmembrane segment of the glycine receptor alpha(1)-subunit (M2GlyR), p22-S22W (KKKKP ARVGL GITTV LTMTT QW) is particularly promising with robust membrane insertion and assembly. The concentration to reach one-half maximal short circuit current is reduced to 45 +/- 6 microM from that of 210 +/- 70 microM of peptide p22 (KKKKP ARVGL GITTV LTMTT QS). However, this is accompanied with nearly 50% reduction in conductance. Toward obtaining a molecular level understanding of the channel activities, we combine information from solution NMR, existing biophysical data, and molecular modeling to construct atomistic models of the putative pentameric channels of p22 and p22-S22W. Simulations in membrane bilayers demonstrate that these structural models, even though highly flexible, are stable and remain adequately open for ion conductance. The membrane-anchoring tryptophan residues not only rigidify the whole channel, suggesting increased stability, but also lead to global changes in the pore profile. Specifically, the p22-S22W pore has a smaller opening on average, consistent with lower measured conductance. Direct observation of several incidences of chloride transport suggests several qualitative features of how these channels might selectively conduct anions. The current study thus helps to rationalize the functional consequences of introducing a single C-terminal tryptophan. Availability of these structural models also paves the way for future work to rationally modify and improve M2GlyR-derived peptides toward potential peptide-based channel replacement therapy.
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Affiliation(s)
| | | | | | - Jian Gao
- Department of Biochemistry, Kansas State University, Manhattan KS 66506, USA
| | - Takeo Iwamoto
- Department of Biochemistry, Kansas State University, Manhattan KS 66506, USA
| | - Om Prakash
- Department of Biochemistry, Kansas State University, Manhattan KS 66506, USA
| | - John M. Tomich
- Department of Biochemistry, Kansas State University, Manhattan KS 66506, USA
| | - Jianhan Chen
- Department of Biochemistry, Kansas State University, Manhattan KS 66506, USA
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Bordag N, Keller S. α-Helical transmembrane peptides: A “Divide and Conquer” approach to membrane proteins. Chem Phys Lipids 2010; 163:1-26. [PMID: 19682979 DOI: 10.1016/j.chemphyslip.2009.07.009] [Citation(s) in RCA: 86] [Impact Index Per Article: 6.1] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/19/2009] [Revised: 07/21/2009] [Accepted: 07/21/2009] [Indexed: 11/26/2022]
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Li X, Shen B, Yao XQ, Yang D. Synthetic Chloride Channel Regulates Cell Membrane Potentials and Voltage-Gated Calcium Channels. J Am Chem Soc 2009; 131:13676-80. [DOI: 10.1021/ja902352g] [Citation(s) in RCA: 87] [Impact Index Per Article: 5.8] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
Affiliation(s)
- Xiang Li
- Morningside Laboratory for Chemical Biology, Department of Chemistry, The University of Hong Kong, Pokfulam Road, Hong Kong, People's Republic of China, and Department of Physiology, The Chinese University of Hong Kong, Shatin, N.T., Hong Kong, People's Republic of China
| | - Bing Shen
- Morningside Laboratory for Chemical Biology, Department of Chemistry, The University of Hong Kong, Pokfulam Road, Hong Kong, People's Republic of China, and Department of Physiology, The Chinese University of Hong Kong, Shatin, N.T., Hong Kong, People's Republic of China
| | - Xiao-Qiang Yao
- Morningside Laboratory for Chemical Biology, Department of Chemistry, The University of Hong Kong, Pokfulam Road, Hong Kong, People's Republic of China, and Department of Physiology, The Chinese University of Hong Kong, Shatin, N.T., Hong Kong, People's Republic of China
| | - Dan Yang
- Morningside Laboratory for Chemical Biology, Department of Chemistry, The University of Hong Kong, Pokfulam Road, Hong Kong, People's Republic of China, and Department of Physiology, The Chinese University of Hong Kong, Shatin, N.T., Hong Kong, People's Republic of China
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11
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Somasekharan S, Brandt R, Iwamoto T, Tomich JM, Schultz BD. Epithelial barrier modulation by a channel forming peptide. J Membr Biol 2008; 222:17-30. [PMID: 18418541 DOI: 10.1007/s00232-008-9099-3] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/12/2007] [Accepted: 02/21/2008] [Indexed: 01/07/2023]
Abstract
NC-1059 is a synthetic channel-forming peptide that provides for ion transport across, and transiently reduces the barrier integrity of, cultured epithelial monolayers derived from canine kidney (MDCK cells). Experiments were conducted to determine whether epithelial cells derived from other sources were similarly affected. Epithelial cells derived from human intestine (T-84), airway (Calu-3), porcine intestine (IPEC-J2) and reproductive duct (PVD9902) were grown on permeable supports. Basal short circuit current (Isc) was <3 microA cm(-2) for T-84, IPEC-J2 and PVD9902 cell monolayers and <8 microA cm(-2) for Calu-3 cells. Apical NC-1059 exposure caused, in all cell types, an increase in Isc to >15 microA cm(-2), indicative of net anion secretion or cation absorption, which was followed by an increase in transepithelial conductance (in mS cm(-2): T-84, 1.6 to 62; PVD9902, 0.2 to 51; IPEC-J2, 0.3 to 26; Calu-3, 2.3 to 13). These results are consistent with the peptide affecting transcellular ion movement, with a likely effect also on the paracellular route. NC-1059 exposure increased dextran permeation when compared to basal permeation, which documents an effect on the paracellular pathway. In order to evaluate membrane ion channels, experiments were conducted to study the dose dependence and stability of the NC-1059-induced membrane conductance in Xenopus laevis oocytes. NC-1059 induced a dose-dependent increase in oocyte membrane conductance that remained stable for greater than 2 h. The results demonstrate that NC-1059 increases transcellular conductance and paracellular permeation in a wide range of epithelia. These effects might be exploited to promote drug delivery across barrier epithelia.
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Affiliation(s)
- Suma Somasekharan
- Yale School of Medicine Cellular and Molecular Physiology, New Haven, CT, USA.
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12
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Immunity to a self-derived, channel-forming peptide in the respiratory tract. CLINICAL AND VACCINE IMMUNOLOGY : CVI 2007; 15:260-6. [PMID: 18094111 DOI: 10.1128/cvi.00319-07] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 11/20/2022]
Abstract
The channel-forming peptide NC-1130 was generated based on the amino acid sequence of the M2 segment of the spinal cord alpha-subunit of the glycine receptor and has been proposed as a therapeutic agent for anion channelopathies such as cystic fibrosis. Lysine adduction and amino acid substitutions at positions T19R and S22W of the peptide improved its performance as an ion channel. However, these modifications generated an altered self, potentially making this NC-1130 peptide immunogenic, which could preclude the repeated use of NC-1130 as a therapeutic agent. To measure the ability of NC-1130 to induce an immune response, it was administered nasally with or without cholera toxin (CT). The NC-1130 peptide, when given alone without adjuvant, induced very little peptide-specific immunity based on analyses of peptide-specific antibodies by enzyme-linked immunosorbent assay and enzyme-linked immunospot assay, induction of cytokine production, and delayed-type hypersensitivity (DTH) responses. The administration of NC-1130 with the mucosal adjuvant CT induced peptide-specific immunoglobulin G (IgG) antibodies and DTH responses and a Th2-dominant cytokine response. The coadministration of the strong mucosal adjuvant CT induced a systemic NC-1130-specific IgG response but not a mucosal peptide-specific antibody response. The lack of peptide-specific immunity and specifically mucosal immunity should allow repeated NC-1130 peptide applications to epithelial surfaces to correct anion channelopathies.
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Abstract
Amphiphilic peptides typically consist of a peptide portion that may be 5-25 (or more) amino acids in length. The hydrophobic portion may be a single fatty acid residue, but can also be more elaborate. The main focus of this article lies on the family of synthetic anion binders (SATs) of the general structure (R(1))(2)N-COCH(2)OCH(2)CO-(Aaa)(n)-OR(3). The most-common R(1) group is the octadecyl (C(18)H(37)) group. The most studied peptide sequence in this family is (Gly)(3)-Pro-(Gly)(3), although different sequences (and longer and shorter peptides) have been prepared as well. The C-terminal ester residue providing the most effective anion release from liposomes is heptyl (C(7)H(15)), although many others have been examined. The compound (C(18)H(37))(2)N-COCH(2)OCH(2)CO-(Gly)(3)-Pro-(Gly)(3)-OBn (Bn=benzyl) was found to mediate Cl(-) transport in mouse epithelial cells.
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Affiliation(s)
- Carl R Yamnitz
- Department of Chemistry, Washington University, Saint Louis, MO 63130, USA
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Li X, Shen B, Yao XQ, Yang D. A Small Synthetic Molecule Forms Chloride Channels to Mediate Chloride Transport across Cell Membranes. J Am Chem Soc 2007; 129:7264-5. [PMID: 17503826 DOI: 10.1021/ja071961h] [Citation(s) in RCA: 90] [Impact Index Per Article: 5.3] [Reference Citation Analysis] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Affiliation(s)
- Xiang Li
- Department of Chemistry, The University of Hong Kong, Pokfulam Road, Hong Kong, China
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Abstract
The development of low molecular weight anion transporters is an emerging topic in supramolecular chemistry. The major focus of this tutorial review is on synthetic chloride transport systems that operate in vesicle and cell membranes. The transporters alter transmembrane concentration gradients, and thus they have applications as reagents for cell biology research and as potential chemotherapeutic agents. The molecular designs include monomolecular channels, self-assembled channels and mobile carriers. Also discussed are the experimental assays that measure transport rates across model bilayer membranes.
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Affiliation(s)
- Anthony P. Davis
- School of Chemistry, University of Bristol, Cantock's Close, Bristol, BS8 1TS, UK.
| | - David N. Sheppard
- Department of Physiology, School of Medical Sciences, University of Bristol, University Walk, Bristol, BS8 1TD, UK.
| | - Bradley D. Smith
- Department of Chemistry and Biochemistry and Walther Cancer Research Center, University of Notre Dame, Notre Dame, Indiana 46556, USA.
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Shank LP, Broughman JR, Takeguchi W, Cook G, Robbins AS, Hahn L, Radke G, Iwamoto T, Schultz BD, Tomich JM. Redesigning channel-forming peptides: amino acid substitutions that enhance rates of supramolecular self-assembly and raise ion transport activity. Biophys J 2005; 90:2138-50. [PMID: 16387776 PMCID: PMC1386792 DOI: 10.1529/biophysj.105.070078] [Citation(s) in RCA: 25] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/18/2022] Open
Abstract
Three series of 22-residue peptides derived from the transmembrane M2 segment of the glycine receptor alpha1-subunit (M2GlyR) have been designed, synthesized, and tested to determine the plasticity of a channel-forming sequence and to define whether channel pores with enhanced conductive properties could be created. Sixteen sequences were examined for aqueous solubility, solution-association tendency, secondary structure, and half-maximal concentration for supramolecular assembly, channel activity, and ion transport properties across epithelial monolayers. All peptides interact strongly with membranes: associating with, inserting across, and assembling to form homooligomeric bundles when in micromolar concentrations. Single and double amino acid replacements involving arginine and/or aromatic amino acids within the final five C-terminal residues of the peptide cause dramatic effects on the concentration dependence, yielding a range of K1/2 values from 36 +/- 5 to 390 +/- 220 microM for transport activity. New water/lipid interfacial boundaries were established for the transmembrane segment using charged or aromatic amino acids, thus limiting the peptides' ability to move perpendicularly to the plane of the bilayer. Formation of discrete water/lipid interfacial boundaries appears to be necessary for efficient supramolecular assembly and high anion transport activity. A peptide sequence is identified that may show efficacy in channel replacement therapy for channelopathies such as cystic fibrosis.
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Affiliation(s)
- Lalida P Shank
- Department of Biochemistry, and Department of Anatomy and Physiology, Kansas State University, Manhattan, Kansas 66506, USA
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Djedovič N, Ferdani R, Harder E, Pajewska J, Pajewski R, Weber ME, Schlesinger PH, Gokel GW. The C- and N-Terminal Residues of Synthetic Heptapeptide Ion Channels Influence Transport Efficacy Through Phospholipid Bilayers. NEW J CHEM 2005; 29:291-305. [PMID: 19633728 PMCID: PMC2714648 DOI: 10.1039/b417091c] [Citation(s) in RCA: 46] [Impact Index Per Article: 2.4] [Reference Citation Analysis] [Abstract] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022]
Abstract
The synthetic peptide, R(2)N-COCH(2)OCH(2)CO-Gly-Gly-Gly-Pro-Gly-Gly-Gly-OR', was shown to be selective for Cl(-) over K(+) when R is n-octadecyl and R' is benzyl. Nineteen heptapeptides have now been prepared in which the N-terminal and C-terminal residues have been varied. All of the N-terminal residues are dialkyl but the C-terminal chains are esters, 2 degrees amides, or 3 degrees amides. The compounds having varied N-terminal anchors and C-terminal benzyl groups are as follows: 1, R = n-propyl; 2, R = n-hexyl; 3, R = n-octyl; 4, R = n-decyl; 5, R = n-dodecyl; 6, R = n-tetradecyl; 7, R = n-hexadecyl; 8, R = n-octadecyl. Compounds 9-19 have R = n-octadecyl and C-terminal residues as follows: 9, OR' = OCH(2)CH(3); 10, OR' = OCH(CH(3))(2); 11, OR' = O(CH(2))(6)CH(3); 12, OR' = OCH(2)-c-C(6)H(11); 13, OR' = O(CH(2))(9)CH(3); 14, OR' = O (CH(2))(17)CH(3); 15, NR'(2) = N[(CH(2))(6)CH(3)](2); 16, NHR' = NH(CH(2))(9)CH(3); 17, NR'(2) = N[(CH(2))(9)CH(3)](2); 18, NHR' = NH(CH(2))(17)CH(3); 19, NR'(2) = N[(CH(2))(17)CH(3)](2). The highest anion transport activities were observed as follows. For the benzyl esters whose N-terminal residues were varied, i.e.1-8, compound 3 was most active. For the C(18) anchored esters 10-14, n-heptyl ester 11 was most active. For the C(18) anchored, C-terminal amides 15-19, di-n-decylamide 17 was most active. It was concluded that both the C- and N-terminal anchors were important for channel function in the bilayer but that activity was lost unless only one of the two anchoring groups was dominant.
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Affiliation(s)
- Natasha Djedovič
- Department of Molecular Biology & Pharmacology, Washington University School of Medicine, 660 S. Euclid Ave., Campus Box 8103, St. Louis, MO 63110 U. S. A
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18
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Cook GA, Prakash O, Zhang K, Shank LP, Takeguchi WA, Robbins A, Gong YX, Iwamoto T, Schultz BD, Tomich JM. Activity and structural comparisons of solution associating and monomeric channel-forming peptides derived from the glycine receptor m2 segment. Biophys J 2004; 86:1424-35. [PMID: 14990471 PMCID: PMC1303979 DOI: 10.1016/s0006-3495(04)74212-5] [Citation(s) in RCA: 15] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/21/2022] Open
Abstract
A number of channel-forming peptides derived from the second transmembrane (TM) segment (M2) of the glycine receptor alpha(1) subunit (M2GlyR), including the 22-residue sequence NK(4)-M2GlyR p22 wild type (WT) (KKKKPARVGLGITTVLTMTTQS), induce anion permeation across epithelial cell monolayers. In vitro assays suggest that this peptide or related sequences might function as a candidate for ion channel replacement therapy in treating channelopathies such as cystic fibrosis (CF). The wild-type sequence forms soluble associations in water that diminish its efficacy. Introduction of a single substitution S22W at the C-terminus, NK(4)-M2GlyR p22 S22W, eliminates the formation of higher molecular weight associations in solution. The S22W peptide also reduces the concentration of peptide required for half-maximal anion transport induced across Madin-Darby canine kidney cells (MDCK) monolayers. A combination of 2D double quantum filtered correlation spectroscopy (DQF-COSY), total correlation spectroscopy (TOCSY), nuclear Overhauser effect spectroscopy (NOESY), and rotating frame nuclear Overhauser effect spectroscopy (ROESY) data were recorded for both the associating WT and nonassociating S22W peptides and used to compare the primary structures and to assign the secondary structures. High-resolution structural studies were recorded in the solvent system (40% 2,2,2-Trifluoroethanol (TFE)/water), which gave the largest structural difference between the two peptides. Nuclear Overhauser effect crosspeak intensity provided interproton distances and the torsion angles were measured by spin-spin coupling constants. These constraints were put into the DYANA modeling program to generate a group of structures. These studies yielded energy-minimized structures for this mixed solvent environment. Structure for both peptides is confined to the 15-residue transmembrane segments. The energy-minimized structure for the WT peptide shows a partially helical extended structure. The S22W peptide adopts a bent conformation forming a hydrophobic pocket by hydrophobic interactions.
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Affiliation(s)
- Gabriel A Cook
- Department of Biochemistry, Kansas State University, Manhattan, Kansas 66506, USA
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Broughman JR, Brandt RM, Hastings C, Iwamoto T, Tomich JM, Schultz BD. Channel-forming peptide modulates transepithelial electrical conductance and solute permeability. Am J Physiol Cell Physiol 2004; 286:C1312-23. [PMID: 15151917 DOI: 10.1152/ajpcell.00426.2002] [Citation(s) in RCA: 20] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022]
Abstract
NC-1059, a synthetic channel-forming peptide, transiently increases transepithelial electrical conductance (g(TE)) and ion transport (as indicated by short-circuit current) across Madin-Darby canine kidney (MDCK) cell monolayers in a time- and concentration-dependent manner when apically exposed. g(TE) increases from <2 to >40 mS/cm(2) over the low to middle micromolar range. Dextran polymer (9.5 but not 77 kDa) permeates the monolayer following apical NC-1059 exposure, suggesting that modulation of the paracellular pathway accounts for changes in g(TE). However, concomitant alterations in junctional protein localization (zonula occludens-1, occludin) and cellular morphology are not observed. Effects of NC-1059 on MDCK g(TE) occur in nominally Cl(-)- and Na(+)-free apical media, indicating that permeation by these ions is not required for effects on g(TE), although two-electrode voltage-clamp assays with Xenopus oocytes suggest that both Cl(-) and Na(+) permeate NC-1059 channels with a modest Cl(-) permselectivity (P(Cl):P(Na) = 1.3). MDCK monolayers can be exposed to multiple NC-1059 treatments over days to weeks without diminution of response, alteration in the time course, or loss of responsiveness to physiological and pharmacological secretagogues. Together, these results suggest that NC-1059 represents a valuable tool to investigate tight junction regulation and may be a lead compound for therapeutic interventions.
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Affiliation(s)
- James R Broughman
- Department of Anatomy and Physiology, 228 Coles Hall, Kansas State University, Manhattan, KS 66506, USA
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20
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Matsumoto N, Tsuruoka S, Iwamoto T, Tomich JM, Ito K, Imai M, Suzuki M. Expression of an artificial Cl- channel in microperfused renal proximal tubules. J Membr Biol 2003; 193:195-200. [PMID: 12962280 DOI: 10.1007/s00232-003-2018-8] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/07/2002] [Indexed: 10/26/2022]
Abstract
To better understand the process of fluid movement driven by Cl- conductance, a Cl- channel-forming peptide was delivered to the luminal membrane of microperfused rabbit renal proximal tubules. When the peptide (NK4-M2GlyR) was perfused, a significant new conductance was observed within 3 min and stabilized at 10 min. Alteration of the ion composition revealed it to be a Cl(-)-specific conductance. Reabsorption of Cl- (JCl) was increased by NK4-M2GlyR, but not by a scramble NK4-M2GlyR sequence, suggesting that the active peptide formed de novo Cl- channels in the luminal membrane of the perfused tubules. In the presence of the peptide, reabsorption of fluid (Jv) was dramatically increased and JNa and JCa were concomitantly increased. We propose that introduction of the new Cl- conductance in the luminal membrane leads to a coordinated efflux of water across the membrane and an increase in cation translocation via the paracellular pathway, resulting in an increase in Jv. This novel method could prove useful in characterizing mechanisms of fluid transport driven by Cl- gradients.
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Affiliation(s)
- N Matsumoto
- Department of Pharmacology, Jichi Medical School, Tochigi, Japan
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21
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Sidorov V, Kotch FW, Kuebler JL, Lam YF, Davis JT. Chloride transport across lipid bilayers and transmembrane potential induction by an oligophenoxyacetamide. J Am Chem Soc 2003; 125:2840-1. [PMID: 12617627 DOI: 10.1021/ja029372t] [Citation(s) in RCA: 69] [Impact Index Per Article: 3.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/30/2022]
Abstract
This contribution describes the discovery and properties of a synthetic, low-molecular weight compound that transports Cl- across bilayer membranes. Such compounds have potential as therapeutics for cystic fibrosis and cancer. The H+/Cl- co-transport activities of acyclic tetrabutylamides 1-6 were compared by using a pH-stat assay with synthetic EYPC liposomes. The ion transport activity of the most active compound, trimer 3, was an order of magnitude greater than that of calix[4]arene tetrabutylamide C1 a macrocycle known to function as a synthetic ion channel. Trimer 3 has an unprecedented function for a synthetic compound, as it induces a stable potential in liposomes experiencing a transmembrane Cl-/SO42- gradient. Data from both pH-stat and 35Cl NMR experiments indicate that 3 co-transports H+/Cl-. Although 3 transports both Cl- and H+ the overall process is not electrically silent. Thus, trimer 3 induces a stable potential in LUVs due to a transmembrane anionic gradient. The ability of trimer 3 to transport Cl-, to maintain a transmembrane potential, along with its high activity at uM concentrations, its low molecular weight, and its simple preparation, make this compound a valuable lead in drug development for diseases caused by Cl- transport malfunction.
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Affiliation(s)
- Vladimir Sidorov
- Department of Chemistry and Biochemistry, University of Maryland at College Park, College Park, MD, 20742, USA
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The lipid bilayer concept: Experimental realization and current applications. ACTA ACUST UNITED AC 2003. [DOI: 10.1016/s0927-5193(03)80025-6] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register]
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23
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Abstract
An increasing number of synthetic compounds have been shown to facilitate ion and polar molecule transport across bilayer membranes. Most notably, recent advances in anion transport have yielded synthetic chloride channels and phospholipid translocases. Attention has also turned to the ability of short amino acid sequences to transport peptides and proteins across cellular membranes.
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Affiliation(s)
- J Middleton Boon
- Department of Chemistry and Biochemistry, University of Notre Dame, Notre Dame, IN 46556, USA
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Broughman JR, Shank LP, Takeguchi W, Schultz BD, Iwamoto T, Mitchell KE, Tomich JM. Distinct structural elements that direct solution aggregation and membrane assembly in the channel-forming peptide M2GlyR. Biochemistry 2002; 41:7350-8. [PMID: 12044167 DOI: 10.1021/bi016053q] [Citation(s) in RCA: 52] [Impact Index Per Article: 2.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Abstract
Restoration of chloride conductance via the introduction of an anion selective pore, formed by a channel-forming peptide, has been hypothesized as a novel treatment modality for patients with cystic fibrosis (CF). Delivery of these peptide sequences to airway cells from an aqueous environment in the absence of organic solvents is paramount. New highly soluble COOH- and NH(2)-terminal truncated peptides, derived from the second transmembrane segment of the glycine receptor alpha-subunit (M2GlyR), were generated, with decreasing numbers of amino acid residues. NH(2)-terminal lysyl-adducted truncated peptides with lengths of 22, 25, and 27 amino acid residues are equally able to stimulate short circuit current (I(SC)). Peptides with as few as 16 amino acid residues are able to stimulate I(SC), although to a lesser degree. In contrast, COOH-terminal truncated peptides show greatly reduced induced I(SC) values for all peptides fewer than 27 residues in length and show no measurable activity for peptides fewer than 21 residues in length. CD spectra for both the NH(2)- and COOH-truncated peptides have random structure in aqueous solution, and those sequences that stimulated the highest maximal I(SC) are predominantly helical in 40% trifluoroethanol. Peptides with a decreased propensity to form helical structures in TFE also failed to stimulate I(SC). Palindromic peptide sequences based on both the NH(2)- and COOH-terminal halves of M2GlyR were synthesized to test roles of the COOH- and NH(2)-terminal halves of the molecule in solution aggregation and channel forming ability. On the basis of the study presented here, there are distinct, nonoverlapping regions of the M2GlyR sequence that define solution aggregation and membrane channel assembly. Peptides that eliminate solution aggregation with complete retention of channel forming activity were generated.
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Affiliation(s)
- James R Broughman
- Department of Biochemistry, Kansas State University, Manhattan, KS 66506, USA
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Sidorov V, Kotch FW, Abdrakhmanova G, Mizani R, Fettinger JC, Davis JT. Ion channel formation from a calix[4]arene amide that binds HCl. J Am Chem Soc 2002; 124:2267-78. [PMID: 11878981 DOI: 10.1021/ja012338e] [Citation(s) in RCA: 178] [Impact Index Per Article: 8.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Abstract
The ion transport activity of calix[4]arene tetrabutylamide 1,3-alt 2 was studied in liposomes, planar lipid bilayers, and HEK-293 cells. These experiments, when considered together with (1)H NMR and X-ray crystallography data, indicate that calix[4]arene tetrabutylamide 2 (1) forms ion channels in bilayer membranes, (2) mediates ion transport across cell membranes at positive holding potential, (3) alters the pH inside liposomes experiencing a Cl(-) gradient, and (4) shows a significant Cl(-)/SO(4)(2)(-) transport selectivity. An analogue, calix[4]arene tetramethylamide 1, self-assembles in the presence of HCl to generate solid-state structures with chloride-filled and water-filled channels. Structureminus signactivity studies indicate that the hydrophobicity, amide substitution, and macrocyclic framework of the calixarene are essential for HCl binding and transport. Calix[4]arene tetrabutylamide 2 is a rare example of an anion-dependent, synthetic ion channel.
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Affiliation(s)
- Vladimir Sidorov
- Department of Chemistry and Biochemistry, University of Maryland, College Park, Maryland 20742, USA
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Gao L, Broughman JR, Iwamoto T, Tomich JM, Venglarik CJ, Forman HJ. Synthetic chloride channel restores glutathione secretion in cystic fibrosis airway epithelia. Am J Physiol Lung Cell Mol Physiol 2001; 281:L24-30. [PMID: 11404241 DOI: 10.1152/ajplung.2001.281.1.l24] [Citation(s) in RCA: 40] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022] Open
Abstract
Cystic fibrosis (CF), an inherited disease characterized by defective epithelial Cl- transport, damages lungs via chronic inflammation and oxidative stress. Glutathione, a major antioxidant in the epithelial lung lining fluid, is decreased in the apical fluid of CF airway epithelia due to reduced glutathione efflux (Gao L, Kim KJ, Yankaskas JR, and Forman HJ. Am J Physiol Lung Cell Mol Physiol 277: L113-L118, 1999). The present study examined the question of whether restoration of chloride transport would also restore glutathione secretion. We found that a Cl- channel-forming peptide (N-K4-M2GlyR) and a K+ channel activator (chlorzoxazone) increased Cl- secretion, measured as bumetanide-sensitive short-circuit current, and glutathione efflux, measured by high-performance liquid chromatography, in a human CF airway epithelial cell line (CFT1). Addition of the peptide alone increased glutathione secretion (181 +/- 8% of the control value), whereas chlorzoxazone alone did not significantly affect glutathione efflux; however, chlorzoxazone potentiated the effect of the peptide on glutathione release (359 +/- 16% of the control value). These studies demonstrate that glutathione efflux is associated with apical chloride secretion, not with the CF transmembrane conductance regulator per se, and the defect of glutathione efflux in CF can be overcome pharmacologically.
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Affiliation(s)
- L Gao
- Department of Environmental Health Sciences, University of Alabama at Birmingham, Birmingham, Alabama 35294, USA
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