1
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Nestorovich EM, Bezrukov SM. Beta-Barrel Channel Response to High Electric Fields: Functional Gating or Reversible Denaturation? Int J Mol Sci 2023; 24:16655. [PMID: 38068977 PMCID: PMC10706840 DOI: 10.3390/ijms242316655] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/30/2023] [Revised: 11/16/2023] [Accepted: 11/21/2023] [Indexed: 12/18/2023] Open
Abstract
Ion channels exhibit gating behavior, fluctuating between open and closed states, with the transmembrane voltage serving as one of the essential regulators of this process. Voltage gating is a fundamental functional aspect underlying the regulation of ion-selective, mostly α-helical, channels primarily found in excitable cell membranes. In contrast, there exists another group of larger, and less selective, β-barrel channels of a different origin, which are not directly associated with cell excitability. Remarkably, these channels can also undergo closing, or "gating", induced by sufficiently strong electric fields. Once the field is removed, the channels reopen, preserving a memory of the gating process. In this study, we explored the hypothesis that the voltage-induced closure of the β-barrel channels can be seen as a form of reversible protein denaturation by the high electric fields applied in model membranes experiments-typically exceeding twenty million volts per meter-rather than a manifestation of functional gating. Here, we focused on the bacterial outer membrane channel OmpF reconstituted into planar lipid bilayers and analyzed various characteristics of the closing-opening process that support this idea. Specifically, we considered the nearly symmetric response to voltages of both polarities, the presence of multiple closed states, the stabilization of the open conformation in channel clusters, the long-term gating memory, and the Hofmeister effects in closing kinetics. Furthermore, we contemplate the evolutionary aspect of the phenomenon, proposing that the field-induced denaturation of membrane proteins might have served as a starting point for their development into amazing molecular machines such as voltage-gated channels of nerve and muscle cells.
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Affiliation(s)
- Ekaterina M. Nestorovich
- Department of Biology, The Catholic University of America, Washington, DC 20064, USA
- Section on Molecular Transport, Eunice Kennedy Shriver National Institute of Child Health and Human Development, National Institutes of Health, Bethesda, MD 20892, USA;
| | - Sergey M. Bezrukov
- Section on Molecular Transport, Eunice Kennedy Shriver National Institute of Child Health and Human Development, National Institutes of Health, Bethesda, MD 20892, USA;
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2
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Bogard A, Finn PW, Smith AR, Flacau IM, Whiting R, Fologea D. Modulation of Voltage-Gating and Hysteresis of Lysenin Channels by Cu 2+ Ions. Int J Mol Sci 2023; 24:12996. [PMID: 37629177 PMCID: PMC10455686 DOI: 10.3390/ijms241612996] [Citation(s) in RCA: 1] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/18/2023] [Revised: 08/12/2023] [Accepted: 08/18/2023] [Indexed: 08/27/2023] Open
Abstract
The intricate voltage regulation presented by lysenin channels reconstituted in artificial lipid membranes leads to a strong hysteresis in conductance, bistability, and memory. Prior investigations on lysenin channels indicate that the hysteresis is modulated by multivalent cations which are also capable of eliciting single-step conformational changes and transitions to stable closed or sub-conducting states. However, the influence on voltage regulation of Cu2+ ions, capable of completely closing the lysenin channels in a two-step process, was not sufficiently addressed. In this respect, we employed electrophysiology approaches to investigate the response of lysenin channels to variable voltage stimuli in the presence of small concentrations of Cu2+ ions. Our experimental results showed that the hysteretic behavior, recorded in response to variable voltage ramps, is accentuated in the presence of Cu2+ ions. Using simultaneous AC/DC stimulation, we were able to determine that Cu2+ prevents the reopening of channels previously closed by depolarizing potentials and the channels remain in the closed state even in the absence of a transmembrane voltage. In addition, we showed that Cu2+ addition reinstates the voltage gating and hysteretic behavior of lysenin channels reconstituted in neutral lipid membranes in which lysenin channels lose their voltage-regulating properties. In the presence of Cu2+ ions, lysenin not only regained the voltage gating but also behaved like a long-term molecular memory controlled by electrical potentials.
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Affiliation(s)
- Andrew Bogard
- Department of Physics, Boise State University, Boise, ID 83725, USA
- Biomolecular Sciences Graduate Program, State University, Boise, ID 83725, USA
| | - Pangaea W. Finn
- Department of Physics, Boise State University, Boise, ID 83725, USA
| | - Aviana R. Smith
- Department of Physics, Boise State University, Boise, ID 83725, USA
| | - Ilinca M. Flacau
- Department of Physics, Boise State University, Boise, ID 83725, USA
| | - Rose Whiting
- Department of Physics, Boise State University, Boise, ID 83725, USA
- Biomolecular Sciences Graduate Program, State University, Boise, ID 83725, USA
| | - Daniel Fologea
- Department of Physics, Boise State University, Boise, ID 83725, USA
- Biomolecular Sciences Graduate Program, State University, Boise, ID 83725, USA
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3
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Whiting R, Stanton S, Kucheriava M, Smith AR, Pitts M, Robertson D, Kammer J, Li Z, Fologea D. Hypo-Osmotic Stress and Pore-Forming Toxins Adjust the Lipid Order in Sheep Red Blood Cell Membranes. MEMBRANES 2023; 13:620. [PMID: 37504986 PMCID: PMC10385129 DOI: 10.3390/membranes13070620] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 04/05/2023] [Revised: 06/07/2023] [Accepted: 06/22/2023] [Indexed: 07/29/2023]
Abstract
Lipid ordering in cell membranes has been increasingly recognized as an important factor in establishing and regulating a large variety of biological functions. Multiple investigations into lipid organization focused on assessing ordering from temperature-induced phase transitions, which are often well outside the physiological range. However, particular stresses elicited by environmental factors, such as hypo-osmotic stress or protein insertion into membranes, with respect to changes in lipid status and ordering at constant temperature are insufficiently described. To fill these gaps in our knowledge, we exploited the well-established ability of environmentally sensitive membrane probes to detect intramembrane changes at the molecular level. Our steady state fluorescence spectroscopy experiments focused on assessing changes in optical responses of Laurdan and diphenylhexatriene upon exposure of red blood cells to hypo-osmotic stress and pore-forming toxins at room temperature. We verified our utilized experimental systems by a direct comparison of the results with prior reports on artificial membranes and cholesterol-depleted membranes undergoing temperature changes. The significant changes observed in the lipid order after exposure to hypo-osmotic stress or pore-forming toxins resembled phase transitions of lipids in membranes, which we explained by considering the short-range interactions between membrane components and the hydrophobic mismatch between membrane thickness and inserted proteins. Our results suggest that measurements of optical responses from the membrane probes constitute an appropriate method for assessing the status of lipids and phase transitions in target membranes exposed to mechanical stresses or upon the insertion of transmembrane proteins.
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Affiliation(s)
- Rose Whiting
- Department of Physics, Boise State University, Boise, ID 83725, USA
- Biomolecular Sciences Graduate Program, Boise State University, Boise, ID 83725, USA
| | - Sevio Stanton
- Department of Physics, Boise State University, Boise, ID 83725, USA
| | | | - Aviana R Smith
- Department of Physics, Boise State University, Boise, ID 83725, USA
| | - Matt Pitts
- Department of Physics, Boise State University, Boise, ID 83725, USA
- Biomolecular Sciences Graduate Program, Boise State University, Boise, ID 83725, USA
| | - Daniel Robertson
- Department of Physics, Boise State University, Boise, ID 83725, USA
| | - Jacob Kammer
- Department of Physics, Boise State University, Boise, ID 83725, USA
- Department of Family Medicine, Idaho College of Osteopathic Medicine, Meridian, ID 83642, USA
| | - Zhiyu Li
- Department of Physics, Boise State University, Boise, ID 83725, USA
| | - Daniel Fologea
- Department of Physics, Boise State University, Boise, ID 83725, USA
- Biomolecular Sciences Graduate Program, Boise State University, Boise, ID 83725, USA
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4
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Bogard A, Finn PW, McKinney F, Flacau IM, Smith AR, Whiting R, Fologea D. The Ionic Selectivity of Lysenin Channels in Open and Sub-Conducting States. MEMBRANES 2021; 11:897. [PMID: 34832126 PMCID: PMC8622276 DOI: 10.3390/membranes11110897] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Download PDF] [Figures] [Subscribe] [Scholar Register] [Received: 10/30/2021] [Revised: 11/14/2021] [Accepted: 11/18/2021] [Indexed: 01/13/2023]
Abstract
The electrochemical gradients established across cell membranes are paramount for the execution of biological functions. Besides ion channels, other transporters, such as exogenous pore-forming toxins, may present ionic selectivity upon reconstitution in natural and artificial lipid membranes and contribute to the electrochemical gradients. In this context, we utilized electrophysiology approaches to assess the ionic selectivity of the pore-forming toxin lysenin reconstituted in planar bilayer lipid membranes. The membrane voltages were determined from the reversal potentials recorded upon channel exposure to asymmetrical ionic conditions, and the permeability ratios were calculated from the fit with the Goldman-Hodgkin-Katz equation. Our work shows that lysenin channels are ion-selective and the determined permeability coefficients are cation and anion-species dependent. We also exploited the unique property of lysenin channels to transition to a stable sub-conducting state upon exposure to calcium ions and assessed their subsequent change in ionic selectivity. The observed loss of selectivity was implemented in an electrical model describing the dependency of reversal potentials on calcium concentration. In conclusion, our work demonstrates that this pore-forming toxin presents ionic selectivity but this is adjusted by the particular conduction state of the channels.
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Affiliation(s)
- Andrew Bogard
- Department of Physics, Boise State University, Boise, ID 83725, USA; (A.B.); (P.W.F.); (F.M.); (I.M.F.); (A.R.S.); (R.W.)
- Biomolecular Sciences Graduate Program, Boise State University, Boise, ID 83725, USA
| | - Pangaea W. Finn
- Department of Physics, Boise State University, Boise, ID 83725, USA; (A.B.); (P.W.F.); (F.M.); (I.M.F.); (A.R.S.); (R.W.)
| | - Fulton McKinney
- Department of Physics, Boise State University, Boise, ID 83725, USA; (A.B.); (P.W.F.); (F.M.); (I.M.F.); (A.R.S.); (R.W.)
| | - Ilinca M. Flacau
- Department of Physics, Boise State University, Boise, ID 83725, USA; (A.B.); (P.W.F.); (F.M.); (I.M.F.); (A.R.S.); (R.W.)
| | - Aviana R. Smith
- Department of Physics, Boise State University, Boise, ID 83725, USA; (A.B.); (P.W.F.); (F.M.); (I.M.F.); (A.R.S.); (R.W.)
| | - Rosey Whiting
- Department of Physics, Boise State University, Boise, ID 83725, USA; (A.B.); (P.W.F.); (F.M.); (I.M.F.); (A.R.S.); (R.W.)
- Biomolecular Sciences Graduate Program, Boise State University, Boise, ID 83725, USA
| | - Daniel Fologea
- Department of Physics, Boise State University, Boise, ID 83725, USA; (A.B.); (P.W.F.); (F.M.); (I.M.F.); (A.R.S.); (R.W.)
- Biomolecular Sciences Graduate Program, Boise State University, Boise, ID 83725, USA
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5
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Rapid Production and Purification of Dye-Loaded Liposomes by Electrodialysis-Driven Depletion. MEMBRANES 2021; 11:membranes11060417. [PMID: 34072746 PMCID: PMC8228697 DOI: 10.3390/membranes11060417] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Subscribe] [Scholar Register] [Received: 05/03/2021] [Revised: 05/29/2021] [Accepted: 05/29/2021] [Indexed: 12/12/2022]
Abstract
Liposomes are spherical-shaped vesicles that enclose an aqueous milieu surrounded by bilayer or multilayer membranes formed by self-assembly of lipid molecules. They are intensively exploited as either model membranes for fundamental studies or as vehicles for delivery of active substances in vivo and in vitro. Irrespective of the method adopted for production of loaded liposomes, obtaining the final purified product is often achieved by employing multiple, time consuming steps. To alleviate this problem, we propose a simplified approach for concomitant production and purification of loaded liposomes by exploiting the Electrodialysis-Driven Depletion of charged molecules from solutions. Our investigations show that electrically-driven migration of charged detergent and dye molecules from solutions that include natural or synthetic lipid mixtures leads to rapid self-assembly of loaded, purified liposomes, as inferred from microscopy and fluorescence spectroscopy assessments. In addition, the same procedure was successfully applied for incorporating PEGylated lipids into the membranes for the purpose of enabling long-circulation times needed for potential in vivo applications. Dynamic Light Scattering analyses and comparison of electrically-formed liposomes with liposomes produced by sonication or extrusion suggest potential use for numerous in vitro and in vivo applications.
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6
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Liposomes Prevent In Vitro Hemolysis Induced by Streptolysin O and Lysenin. MEMBRANES 2021; 11:membranes11050364. [PMID: 34069894 PMCID: PMC8157566 DOI: 10.3390/membranes11050364] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Subscribe] [Scholar Register] [Received: 04/09/2021] [Revised: 05/08/2021] [Accepted: 05/12/2021] [Indexed: 12/12/2022]
Abstract
The need for alternatives to antibiotics in the fight against infectious diseases has inspired scientists to focus on antivirulence factors instead of the microorganisms themselves. In this respect, prior work indicates that tiny, enclosed bilayer lipid membranes (liposomes) have the potential to compete with cellular targets for toxin binding, hence preventing their biological attack and aiding with their clearance. The effectiveness of liposomes as decoy targets depends on their availability in the host and how rapidly they are cleared from the circulation. Although liposome PEGylation may improve their circulation time, little is known about how such a modification influences their interactions with antivirulence factors. To fill this gap in knowledge, we investigated regular and long-circulating liposomes for their ability to prevent in vitro red blood cell hemolysis induced by two potent lytic toxins, lysenin and streptolysin O. Our explorations indicate that both regular and long-circulating liposomes are capable of similarly preventing lysis induced by streptolysin O. In contrast, PEGylation reduced the effectiveness against lysenin-induced hemolysis and altered binding dynamics. These results suggest that toxin removal by long-circulating liposomes is feasible, yet dependent on the particular virulence factor under scrutiny.
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7
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Lysenin Channels as Sensors for Ions and Molecules. SENSORS 2020; 20:s20216099. [PMID: 33120957 PMCID: PMC7663491 DOI: 10.3390/s20216099] [Citation(s) in RCA: 4] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Subscribe] [Scholar Register] [Received: 09/30/2020] [Revised: 10/19/2020] [Accepted: 10/23/2020] [Indexed: 12/18/2022]
Abstract
Lysenin is a pore-forming protein extracted from the earthworm Eisenia fetida, which inserts large conductance pores in artificial and natural lipid membranes containing sphingomyelin. Its cytolytic and hemolytic activity is rather indicative of a pore-forming toxin; however, lysenin channels present intricate regulatory features manifested as a reduction in conductance upon exposure to multivalent ions. Lysenin pores also present a large unobstructed channel, which enables the translocation of analytes, such as short DNA and peptide molecules, driven by electrochemical gradients. These important features of lysenin channels provide opportunities for using them as sensors for a large variety of applications. In this respect, this literature review is focused on investigations aimed at the potential use of lysenin channels as analytical tools. The described explorations include interactions with multivalent inorganic and organic cations, analyses on the reversibility of such interactions, insights into the regulation mechanisms of lysenin channels, interactions with purines, stochastic sensing of peptides and DNA molecules, and evidence of molecular translocation. Lysenin channels present themselves as versatile sensing platforms that exploit either intrinsic regulatory features or the changes in ionic currents elicited when molecules thread the conducting pathway, which may be further developed into analytical tools of high specificity and sensitivity or exploited for other scientific biotechnological applications.
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8
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Temporary Membrane Permeabilization via the Pore-Forming Toxin Lysenin. Toxins (Basel) 2020; 12:toxins12050343. [PMID: 32456013 PMCID: PMC7290483 DOI: 10.3390/toxins12050343] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/29/2020] [Revised: 05/17/2020] [Accepted: 05/20/2020] [Indexed: 12/19/2022] Open
Abstract
Pore-forming toxins are alluring tools for delivering biologically-active, impermeable cargoes to intracellular environments by introducing large conductance pathways into cell membranes. However, the lack of regulation often leads to the dissipation of electrical and chemical gradients, which might significantly affect the viability of cells under scrutiny. To mitigate these problems, we explored the use of lysenin channels to reversibly control the barrier function of natural and artificial lipid membrane systems by controlling the lysenin's transport properties. We employed artificial membranes and electrophysiology measurements in order to identify the influence of labels and media on the lysenin channel's conductance. Two cell culture models: Jurkat cells in suspension and adherent ATDC5 cells were utilized to demonstrate that lysenin channels may provide temporary cytosol access to membrane non-permeant propidium iodide and phalloidin. Permeability and cell viability were assessed by fluorescence spectroscopy and microscopy. Membrane resealing by chitosan or specific media addition proved to be an effective way of maintaining cellular viability. In addition, we loaded non-permeant dyes into liposomes via lysenin channels by controlling their conducting state with multivalent metal cations. The improved control over membrane permeability might prove fruitful for a large variety of biological or biomedical applications that require only temporary, non-destructive access to the inner environment enclosed by natural and artificial membranes.
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9
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An Effective Electric Dipole Model for Voltage-induced Gating Mechanism of Lysenin. Sci Rep 2019; 9:11440. [PMID: 31391571 PMCID: PMC6686002 DOI: 10.1038/s41598-019-47725-0] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/19/2018] [Accepted: 07/08/2019] [Indexed: 11/30/2022] Open
Abstract
Lysenin is a pore-forming toxin, which self-inserts open channels into sphingomyelin containing membranes and is known to be voltage regulated. The mechanistic details of its voltage gating mechanism, however, remains elusive despite much recent efforts. Here, we have employed a novel combination of experimental and computational techniques to examine a model for voltage gating, that is based on the existence of an “effective electric dipole” inspired by recent reported structures of lysenin. We support this mechanism by the observations that (i) the charge-reversal and neutralization substitutions in lysenin result in changing its electrical gating properties by modifying the strength of the dipole, and (ii) an increase in the viscosity of the solvent increases the drag force and slows down the gating. In addition, our molecular dynamics (MD) simulations of membrane-embedded lysenin provide a mechanistic picture for lysenin conformational changes, which reveals, for the first time, the existence of a lipid-dependent bulge region in the pore-forming module of lysenin, which may explain the gating mechanism of lysenin at a molecular level.
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10
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Bryant SL, Clark T, Thomas CA, Ware KS, Bogard A, Calzacorta C, Prather D, Fologea D. Insights into the Voltage Regulation Mechanism of the Pore-Forming Toxin Lysenin. Toxins (Basel) 2018; 10:toxins10080334. [PMID: 30126104 PMCID: PMC6115918 DOI: 10.3390/toxins10080334] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/15/2018] [Revised: 08/02/2018] [Accepted: 08/15/2018] [Indexed: 11/30/2022] Open
Abstract
Lysenin, a pore forming toxin (PFT) extracted from Eisenia fetida, inserts voltage-regulated channels into artificial lipid membranes containing sphingomyelin. The voltage-induced gating leads to a strong static hysteresis in conductance, which endows lysenin with molecular memory capabilities. To explain this history-dependent behavior, we hypothesized a gating mechanism that implies the movement of a voltage domain sensor from an aqueous environment into the hydrophobic core of the membrane under the influence of an external electric field. In this work, we employed electrophysiology approaches to investigate the effects of ionic screening elicited by metal cations on the voltage-induced gating and hysteresis in conductance of lysenin channels exposed to oscillatory voltage stimuli. Our experimental data show that screening of the voltage sensor domain strongly affects the voltage regulation only during inactivation (channel closing). In contrast, channel reactivation (reopening) presents a more stable, almost invariant voltage dependency. Additionally, in the presence of anionic Adenosine 5′-triphosphate (ATP), which binds at a different site in the channel’s structure and occludes the conducting pathway, both inactivation and reactivation pathways are significantly affected. Therefore, the movement of the voltage domain sensor into a physically different environment that precludes electrostatically bound ions may be an integral part of the gating mechanism.
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Affiliation(s)
- Sheenah Lynn Bryant
- Department of Physics, Boise State University, Boise, ID 83725, USA.
- Biomolecular Sciences Graduate Program, Boise State University, Boise, ID 83725, USA.
| | - Tyler Clark
- Department of Physics, Boise State University, Boise, ID 83725, USA.
| | | | | | - Andrew Bogard
- Department of Physics, Boise State University, Boise, ID 83725, USA.
- Biomolecular Sciences Graduate Program, Boise State University, Boise, ID 83725, USA.
| | | | - Daniel Prather
- Department of Physics, Boise State University, Boise, ID 83725, USA.
| | - Daniel Fologea
- Department of Physics, Boise State University, Boise, ID 83725, USA.
- Biomolecular Sciences Graduate Program, Boise State University, Boise, ID 83725, USA.
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11
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Molecular mechanisms of action of sphingomyelin-specific pore-forming toxin, lysenin. Semin Cell Dev Biol 2018; 73:188-198. [DOI: 10.1016/j.semcdb.2017.07.036] [Citation(s) in RCA: 23] [Impact Index Per Article: 3.8] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/02/2017] [Revised: 07/18/2017] [Accepted: 07/19/2017] [Indexed: 11/21/2022]
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12
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Bryant SL, Eixenberger JE, Rossland S, Apsley H, Hoffmann C, Shrestha N, McHugh M, Punnoose A, Fologea D. ZnO nanoparticles modulate the ionic transport and voltage regulation of lysenin nanochannels. J Nanobiotechnology 2017; 15:90. [PMID: 29246155 PMCID: PMC5732404 DOI: 10.1186/s12951-017-0327-9] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/23/2017] [Accepted: 12/06/2017] [Indexed: 02/05/2023] Open
Abstract
Background The insufficient understanding of unintended biological impacts from nanomaterials (NMs) represents a serious impediment to their use for scientific, technological, and medical applications. While previous studies have focused on understanding nanotoxicity effects mostly resulting from cellular internalization, recent work indicates that NMs may interfere with transmembrane transport mechanisms, hence enabling contributions to nanotoxicity by affecting key biological activities dependent on transmembrane transport. In this line of inquiry, we investigated the effects of charged nanoparticles (NPs) on the transport properties of lysenin, a pore-forming toxin that shares fundamental features with ion channels such as regulation and high transport rate. Results The macroscopic conductance of lysenin channels greatly diminished in the presence of cationic ZnO NPs. The inhibitory effects were asymmetrical relative to the direction of the electric field and addition site, suggesting electrostatic interactions between ZnO NPs and a binding site. Similar changes in the macroscopic conductance were observed when lysenin channels were reconstituted in neutral lipid membranes, implicating protein-NP interactions as the major contributor to the reduced transport capabilities. In contrast, no inhibitory effects were observed in the presence of anionic SnO2 NPs. Additionally, we demonstrate that inhibition of ion transport is not due to the dissolution of ZnO NPs and subsequent interactions of zinc ions with lysenin channels. Conclusion We conclude that electrostatic interactions between positively charged ZnO NPs and negative charges within the lysenin channels are responsible for the inhibitory effects on the transport of ions. These interactions point to a potential mechanism of cytotoxicity, which may not require NP internalization. Electronic supplementary material The online version of this article (10.1186/s12951-017-0327-9) contains supplementary material, which is available to authorized users.
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Affiliation(s)
- Sheenah L Bryant
- Department of Physics, Boise State University, Boise, ID, 83725, USA.,Biomolecular Sciences Graduate Program, Boise State University, Boise, ID, 83725, USA
| | - Josh E Eixenberger
- Department of Physics, Boise State University, Boise, ID, 83725, USA.,Biomolecular Sciences Graduate Program, Boise State University, Boise, ID, 83725, USA
| | - Steven Rossland
- Department of Physics, Boise State University, Boise, ID, 83725, USA.,Department of Physics, University of Utah, Salt Lake City, UT, 84112, USA
| | - Holly Apsley
- Department of Physics, Boise State University, Boise, ID, 83725, USA.,Department of Social Sciences, Yale-NUS College, Singapore, 138610, Singapore
| | - Connor Hoffmann
- Department of Physics, Boise State University, Boise, ID, 83725, USA.,Department of Chemical and Biological Engineering, Montana State University, Bozeman, MT, 59717, USA
| | - Nisha Shrestha
- Department of Physics, Boise State University, Boise, ID, 83725, USA.,Biomolecular Sciences Graduate Program, Boise State University, Boise, ID, 83725, USA
| | - Michael McHugh
- Department of Physics, Boise State University, Boise, ID, 83725, USA
| | - Alex Punnoose
- Department of Physics, Boise State University, Boise, ID, 83725, USA.,Biomolecular Sciences Graduate Program, Boise State University, Boise, ID, 83725, USA
| | - Daniel Fologea
- Department of Physics, Boise State University, Boise, ID, 83725, USA. .,Biomolecular Sciences Graduate Program, Boise State University, Boise, ID, 83725, USA.
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13
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Abstract
The ability of pore-forming proteins to interact with various analytes has found vast applicability in single molecule sensing and characterization. In spite of their abundance in organisms from all kingdoms of life, only a few pore-forming proteins have been successfully reconstituted in artificial membrane systems for sensing purposes. Lysenin, a pore-forming toxin extracted from the earthworm E. fetida, inserts large conductance nanopores in lipid membranes containing sphingomyelin. Here we show that single lysenin channels may function as stochastic nanosensors by allowing the short cationic peptide angiotensin II to be electrophoretically driven through the conducting pathway. Long-term translocation experiments performed using large populations of lysenin channels allowed unequivocal identification of the unmodified analyte by Liquid Chromatography-Mass Spectrometry. However, application of reverse voltages or irreversible blockage of the macroscopic conductance of lysenin channels by chitosan addition prevented analyte translocation. This investigation demonstrates that lysenin channels have the potential to function as nano-sensing devices capable of single peptide molecule identification and characterization, which may be further extended to other macromolecular analytes.
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14
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Bryant S, Shrestha N, Carnig P, Kosydar S, Belzeski P, Hanna C, Fologea D. Purinergic control of lysenin's transport and voltage-gating properties. Purinergic Signal 2016; 12:549-59. [PMID: 27318938 DOI: 10.1007/s11302-016-9520-9] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [Key Words] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/13/2016] [Accepted: 06/08/2016] [Indexed: 02/07/2023] Open
Abstract
Lysenin, a pore-forming protein extracted from the coelomic fluid of the earthworm Eisenia foetida, manifests cytolytic activity by inserting large conductance pores in host membranes containing sphingomyelin. In the present study, we found that adenosine phosphates control the biological activity of lysenin channels inserted into planar lipid membranes with respect to their macroscopic conductance and voltage-induced gating. Addition of ATP, ADP, or AMP decreased the macroscopic conductance of lysenin channels in a concentration-dependent manner, with ATP being the most potent inhibitor and AMP the least. ATP removal from the bulk solutions by buffer exchange quickly reinstated the macroscopic conductance and demonstrated reversibility. Single-channel experiments pointed to an inhibition mechanism that most probably relies on electrostatic binding and partial occlusion of the channel-conducting pathway, rather than ligand gating induced by the highly charged phosphates. The Hill analysis of the changes in macroscopic conduction as a function of the inhibitor concentration suggested cooperative binding as descriptive of the inhibition process. Ionic screening significantly reduced the ATP inhibitory efficacy, in support of the electrostatic binding hypothesis. In addition to conductance modulation, purinergic control over the biological activity of lysenin channels has also been observed to manifest as changes of the voltage-induced gating profile. Our analysis strongly suggests that not only the inhibitor's charge but also its ability to adopt a folded conformation may explain the differences in the observed influence of ATP, ADP, and AMP on lysenin's biological activity.
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Affiliation(s)
- Sheenah Bryant
- Department of Physics, Boise State University, Boise, ID, 83725, USA.,Biomolecular Sciences PhD Program, Boise State University, Boise, ID, 83725, USA
| | - Nisha Shrestha
- Department of Physics, Boise State University, Boise, ID, 83725, USA.,Biomolecular Sciences PhD Program, Boise State University, Boise, ID, 83725, USA
| | - Paul Carnig
- Department of Physics, Boise State University, Boise, ID, 83725, USA
| | - Samuel Kosydar
- Department of Physics, Boise State University, Boise, ID, 83725, USA
| | - Philip Belzeski
- Department of Physics, Boise State University, Boise, ID, 83725, USA
| | - Charles Hanna
- Department of Physics, Boise State University, Boise, ID, 83725, USA.,Biomolecular Sciences PhD Program, Boise State University, Boise, ID, 83725, USA
| | - Daniel Fologea
- Department of Physics, Boise State University, Boise, ID, 83725, USA. .,Biomolecular Sciences PhD Program, Boise State University, Boise, ID, 83725, USA.
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15
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Intramembrane congestion effects on lysenin channel voltage-induced gating. EUROPEAN BIOPHYSICS JOURNAL: EBJ 2015; 45:187-94. [PMID: 26695013 DOI: 10.1007/s00249-015-1104-z] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Received: 08/18/2015] [Revised: 10/29/2015] [Accepted: 11/24/2015] [Indexed: 10/22/2022]
Abstract
All cell membranes are packed with proteins. The ability to investigate the regulatory mechanisms of protein channels in experimental conditions mimicking their congested native environment is crucial for understanding the environmental physicochemical cues that may fundamentally contribute to their functionality in natural membranes. Here we report on investigations of the voltage-induced gating of lysenin channels in congested conditions experimentally achieved by increasing the number of channels inserted into planar lipid membranes. Typical electrophysiology measurements reveal congestion-induced changes to the voltage-induced gating, manifested as a significant reduction of the response to external voltage stimuli. Furthermore, we demonstrate a similar diminished voltage sensitivity for smaller populations of channels by reducing the amount of sphingomyelin in the membrane. Given lysenin's preference for targeting lipid rafts, this result indicates the potential role of the heterogeneous organization of the membrane in modulating channel functionality. Our work indicates that local congestion within membranes may alter the energy landscape and the kinetics of conformational changes of lysenin channels in response to voltage stimuli. This level of understanding may be extended to better characterize the role of the specific membrane environment in modulating the biological functionality of protein channels in health and disease.
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16
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Cationic polymers inhibit the conductance of lysenin channels. ScientificWorldJournal 2013; 2013:316758. [PMID: 24191139 PMCID: PMC3804441 DOI: 10.1155/2013/316758] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/09/2013] [Accepted: 09/12/2013] [Indexed: 11/29/2022] Open
Abstract
The pore-forming toxin lysenin self-assembles large and stable conductance channels in natural and artificial lipid membranes. The lysenin channels exhibit unique regulation capabilities, which open unexplored possibilities to control the transport of ions and molecules through artificial and natural lipid membranes. Our investigations demonstrate that the positively charged polymers polyethyleneimine and chitosan inhibit the conducting properties of lysenin channels inserted into planar lipid membranes. The preservation of the inhibitory effect following addition of charged polymers on either side of the supporting membrane suggests the presence of multiple binding sites within the channel's structure and a multistep inhibition mechanism that involves binding and trapping. Complete blockage of the binding sites with divalent cations prevents further inhibition in conductance induced by the addition of cationic polymers and supports the hypothesis that the binding sites are identical for both multivalent metal cations and charged polymers. The investigation at the single-channel level has shown distinct complete blockages of each of the inserted channels. These findings reveal key structural characteristics which may provide insight into lysenin's functionality while opening innovative approaches for the development of applications such as transient cell permeabilization and advanced drug delivery systems.
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17
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Krueger E, Al Faouri R, Fologea D, Henry R, Straub D, Salamo G. A model for the hysteresis observed in gating of lysenin channels. Biophys Chem 2013; 184:126-30. [PMID: 24075493 DOI: 10.1016/j.bpc.2013.09.001] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/02/2013] [Revised: 08/28/2013] [Accepted: 09/03/2013] [Indexed: 11/19/2022]
Abstract
The pore-forming toxin lysenin self-inserts to form conductance channels in natural and artificial lipid membranes containing sphingomyelin. The inserted channels exhibit voltage regulation and hysteresis of the macroscopic current during the application of positive periodic voltage stimuli. We explored the bi-stable behavior of lysenin channels and present a theoretical approach for the mechanism of the hysteresis to explain its static and dynamic components. This investigation develops a model to incorporate the role of charge accumulation on the bilayer lipid membrane in influencing the channel conduction state. Our model is supported by experimental results and also provides insight into the temperature dependence of lysenin channel hysteresis. Through this work we gain perspective into the mechanism of how the response of a channel protein is determined by previous stimuli.
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Affiliation(s)
- Eric Krueger
- Department of Physics, University of Arkansas, Fayetteville, AR 72701, USA.
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18
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Earthworm-derived pore-forming toxin lysenin and screening of its inhibitors. Toxins (Basel) 2013; 5:1392-401. [PMID: 23965430 PMCID: PMC3760042 DOI: 10.3390/toxins5081392] [Citation(s) in RCA: 16] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/10/2013] [Revised: 07/08/2013] [Accepted: 07/31/2013] [Indexed: 11/16/2022] Open
Abstract
Lysenin is a pore-forming toxin from the coelomic fluid of earthworm Eisenia foetida. This protein specifically binds to sphingomyelin and induces erythrocyte lysis. Lysenin consists of 297 amino acids with a molecular weight of 41 kDa. We screened for cellular signal transduction inhibitors of low molecular weight from microorganisms and plants. The purpose of the screening was to study the mechanism of diseases using the obtained inhibitors and to develop new chemotherapeutic agents acting in the new mechanism. Therefore, our aim was to screen for inhibitors of Lysenin-induced hemolysis from plant extracts and microbial culture filtrates. As a result, we isolated all-E-lutein from an extract of Dalbergia latifolia leaves. All-E-lutein is likely to inhibit the process of Lysenin-membrane binding and/or oligomer formation rather than pore formation. Additionally, we isolated tyrosylproline anhydride from the culture filtrate of Streptomyces as an inhibitor of Lysenin-induced hemolysis.
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19
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Tomita N, Mohammad MM, Niedzwiecki DJ, Ohta M, Movileanu L. Does the lipid environment impact the open-state conductance of an engineered β-barrel protein nanopore? BIOCHIMICA ET BIOPHYSICA ACTA 2013; 1828:1057-65. [PMID: 23246446 PMCID: PMC3560310 DOI: 10.1016/j.bbamem.2012.12.003] [Citation(s) in RCA: 14] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 08/06/2012] [Revised: 11/16/2012] [Accepted: 12/04/2012] [Indexed: 12/11/2022]
Abstract
Using rational membrane protein design, we were recently able to obtain a β-barrel protein nanopore that was robust under an unusually broad range of experimental circumstances. This protein nanopore was based upon the native scaffold of the bacterial ferric hydroxamate uptake component A (FhuA) of Escherichia coli. In this work, we expanded the examinations of the open-state current of this engineered protein nanopore, also called FhuA ΔC/Δ4L, employing an array of lipid bilayer systems that contained charged and uncharged as well as conical and cylindrical lipids. Remarkably, systematical single-channel analysis of FhuA ΔC/Δ4L indicated that most of its biophysical features, such as the unitary conductance and the stability of the open-state current, were not altered under the conditions tested in this work. However, electrical recordings at high transmembrane potentials revealed that the presence of conical phospholipids within the bilayer catalyzes the first, stepwise current transition of the FhuA ΔC/Δ4L protein nanopore to a lower-conductance open state. This study reinforces the stability of the open-state current of the engineered FhuA ΔC/Δ4L protein nanopore under various experimental conditions, paving the way for further critical developments in biosensing and molecular biomedical diagnosis.
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Affiliation(s)
- Noriko Tomita
- Department of Physics, Syracuse University, Syracuse, New York 13244-1130, USA
- Institute of Fluid Science, Tohoku University, Sendai, Miyagi 980-8577, Japan
| | | | | | - Makoto Ohta
- Institute of Fluid Science, Tohoku University, Sendai, Miyagi 980-8577, Japan
| | - Liviu Movileanu
- Department of Physics, Syracuse University, Syracuse, New York 13244-1130, USA
- Structural Biology, Biochemistry, and Biophysics Program, Syracuse University, Syracuse, New York 13244-4100, USA
- Syracuse Biomaterials Institute, Syracuse University, Syracuse, New York 13244, USA
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20
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Fologea D, Krueger E, Mazur YI, Stith C, Okuyama Y, Henry R, Salamo GJ. Bi-stability, hysteresis, and memory of voltage-gated lysenin channels. BIOCHIMICA ET BIOPHYSICA ACTA-BIOMEMBRANES 2011; 1808:2933-9. [PMID: 21945404 DOI: 10.1016/j.bbamem.2011.09.005] [Citation(s) in RCA: 20] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 05/02/2011] [Revised: 08/28/2011] [Accepted: 09/06/2011] [Indexed: 10/17/2022]
Abstract
Lysenin, a 297 amino acid pore-forming protein extracted from the coelomic fluid of the earthworm E. foetida, inserts constitutively open large conductance channels in natural and artificial lipid membranes containing sphingomyelin. The inserted channels show voltage regulation and slowly close at positive applied voltages. We report on the consequences of slow voltage-induced gating of lysenin channels inserted into a planar Bilayer Lipid Membrane (BLM), and demonstrate that these pore-forming proteins constitute memory elements that manifest gating bi-stability in response to variable external voltages. The hysteresis in macroscopic currents dynamically changes when the time scale of the voltage variation is smaller or comparable to the characteristic conformational equilibration time, and unexpectedly persists for extremely slow-changing external voltage stimuli. The assay performed on a single lysenin channel reveals that hysteresis is a fundamental feature of the individual channel unit and an intrinsic component of the gating mechanism. The investigation conducted at different temperatures reveals a thermally stable reopening process, suggesting that major changes in the energy landscape and kinetics diagram accompany the conformational transitions of the channels. Our work offers new insights on the dynamics of pore-forming proteins and provides an understanding of how channel proteins may form an immediate record of the molecular history which then determines their future response to various stimuli. Such new functionalities may uncover a link between molecular events and macroscopic processing and transmission of information in cells, and may lead to applications such as high density biologically-compatible memories and learning networks.
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Affiliation(s)
- Daniel Fologea
- Department of Biological Sciences, University of Arkansas, Fayetteville, AR 72701, USA.
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21
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Potential analytical applications of lysenin channels for detection of multivalent ions. Anal Bioanal Chem 2011; 401:1871-9. [PMID: 21818682 DOI: 10.1007/s00216-011-5277-8] [Citation(s) in RCA: 11] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/26/2011] [Revised: 07/13/2011] [Accepted: 07/21/2011] [Indexed: 11/27/2022]
Abstract
Transmembrane protein transporters possessing binding sites for ions, toxins, pharmaceutical drugs, and other molecules constitute excellent candidates for developing sensitive and selective biosensing devices. Their attractiveness for analytical purposes is enhanced by the intrinsic amplification capabilities shown when the binding event leads to major changes in the transportation of ions or molecules other than the analyte itself. The large-scale implementation of such transmembrane proteins in biosensing devices is limited by the difficulties encountered in inserting functional transporters into artificial bilayer lipid membranes and by the limitations in understanding and exploiting the changes induced by the interaction with the analyte for sensing purposes. Here, we show that lysenin, a pore-forming toxin extracted from earthworm Eisenia foetida, which inserts stable and large conductance channels into artificial bilayer lipid membranes, functions as a multivalent ion-sensing device. The analytical response consists of concentration and ionic-species-dependent macroscopic conductance inhibition most probably linked to a ligand-induced gating mechanism. Multivalent ion removal by chelation or precipitation restores, in most cases, the initial conductance and demonstrates reversibility. Changes in lipid bilayer membrane compositions leading to the absence of voltage-induced gating do not affect the analytical response to multivalent ions. Microscopic current analysis performed on individual lysenin channels in the presence of Cu(2+) revealed complex open-closed transitions characterized by unstable intermediate sub-conducting states. Lysenin channels provide an analytical tool with a built-in sensing mechanism for inorganic and organic multivalent ions, and the excellent stability in an artificial environment recommend lysenin as a potential candidate for single-molecule detection and analysis.
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22
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Demarche S, Sugihara K, Zambelli T, Tiefenauer L, Vörös J. Techniques for recording reconstituted ion channels. Analyst 2011; 136:1077-89. [PMID: 21267480 DOI: 10.1039/c0an00828a] [Citation(s) in RCA: 43] [Impact Index Per Article: 3.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022]
Abstract
This review describes and discusses techniques useful for monitoring the activity of protein ion channels in vitro. In the first section the biological importance and the classification of ion channels are outlined in order to justify the strong motivation for dealing with this important class of membrane proteins. The expression, reconstitution and integration of recombinant proteins into lipid bilayers are crucial steps to obtain consistent data when working with ion channels. In the second section recording techniques used in research are presented. Since this review focuses on analytical systems bearing reconstituted ion channels the industrial most important patch-clamp techniques of cells are only briefly mentioned. In section three, artificial systems developed in the last decades are described while the emerging technologies using nanostructured supports or microfluidic systems are presented in section four. Finally, the remaining challenges of membrane protein analysis and its potential applications are briefly outlined.
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Affiliation(s)
- Sophie Demarche
- Biomolecular Research, Paul Scherrer Institut (PSI), CH-5232 Villigen, Switzerland
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23
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Fologea D, Krueger E, Al Faori R, Lee R, Mazur YI, Henry R, Arnold M, Salamo GJ. Multivalent ions control the transport through lysenin channels. Biophys Chem 2010; 152:40-5. [PMID: 20724059 DOI: 10.1016/j.bpc.2010.07.004] [Citation(s) in RCA: 17] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/18/2010] [Revised: 07/27/2010] [Accepted: 07/28/2010] [Indexed: 11/30/2022]
Abstract
We report the effect of different ions on the conducting properties of lysenin channels inserted into planar lipid bilayer membranes. Our observations indicated that multivalent ions inhibited the lysenin channels conductance in a concentration dependent manner. The analysis performed on single channels revealed that multivalent ions induced reversible sub-conducting or closed states depending on the ionic charge and size. Good agreement is reported between experimental results and a theoretical model that is proposed to describe the interaction between divalent ions and lysenin channels as a simple isothermal absorption process.
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Affiliation(s)
- Daniel Fologea
- Department of Biological Sciences, University of Arkansas, Fayetteville, AR 72701, USA.
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24
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AOKI T, HIRANO M, TAKEUCHI Y, KOBAYASHI T, YANAGIDA T, IDE T. Single channel properties of lysenin measured in artificial lipid bilayers and their applications to biomolecule detection. PROCEEDINGS OF THE JAPAN ACADEMY. SERIES B, PHYSICAL AND BIOLOGICAL SCIENCES 2010; 86:920-925. [PMID: 21084775 PMCID: PMC3035922 DOI: 10.2183/pjab.86.920] [Citation(s) in RCA: 11] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 01/26/2010] [Accepted: 09/14/2010] [Indexed: 05/28/2023]
Abstract
Single channel currents of lysenin were measured using artificial lipid bilayers formed on a glass micropipette tip. The single channel conductance for KCl, NaCl, CaCl(2), and Trimethylammonium-Cl were 474 ± 87, 537 ± 66, 210 ± 14, and 274 ± 10 pS, respectively, while the permeability ratio P(Na)/P(Cl) was 5.8. By adding poly(deoxy adenine) or poly(L-lysine) to one side of the bilayer, channel currents were influenced when membrane voltages were applied to pass the charged molecules through the channel pores. Current inhibition process was concentration-dependent with applied DNA. As the current fluctuations of α-hemolysin channels is often cited as the detector in a molecular sensor, these results suggest that by monitoring channel current changes, the lysenin channel has possibilities to detect interactions between it and certain biomolecules by its current fluctuations.
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Affiliation(s)
- Takaaki AOKI
- Network Center for Molecular and System Life Science, Graduate School of Frontier Biosciences, Osaka University, Osaka, Japan
| | - Minako HIRANO
- Laboratory for Nanobiology, Graduate School of Frontier Biosciences, Osaka University, Osaka, Japan
| | - Yuko TAKEUCHI
- Network Center for Molecular and System Life Science, Graduate School of Frontier Biosciences, Osaka University, Osaka, Japan
| | | | - Toshio YANAGIDA
- Network Center for Molecular and System Life Science, Graduate School of Frontier Biosciences, Osaka University, Osaka, Japan
- Laboratory for Nanobiology, Graduate School of Frontier Biosciences, Osaka University, Osaka, Japan
| | - Toru IDE
- Network Center for Molecular and System Life Science, Graduate School of Frontier Biosciences, Osaka University, Osaka, Japan
- Molecular-Informational Life Science Research Group, RIKEN, Saitama, Japan
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25
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Abstract
Lysenin forms unitary large conductance pores in artificial bilayer membranes containing sphingomyelin. A population of lysenin pores inserted into such a bilayer membrane exhibited a dynamic negative conductance region, as predicted by a simple two-state model for voltage-gated channels. The recorded I-V curves demonstrated that lysenin pores inserted into the bilayer are uniformly oriented. Additionally, the transition between the two-states was affected by changes in the monovalent ion concentration and pH, pointing towards an electrostatic interaction governing the gating mechanism.
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26
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Hereć M, Gagoś M, Kulma M, Kwiatkowska K, Sobota A, Gruszecki WI. Secondary structure and orientation of the pore-forming toxin lysenin in a sphingomyelin-containing membrane. BIOCHIMICA ET BIOPHYSICA ACTA-BIOMEMBRANES 2008; 1778:872-9. [DOI: 10.1016/j.bbamem.2007.12.004] [Citation(s) in RCA: 23] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Track Full Text] [Subscribe] [Scholar Register] [Received: 06/20/2007] [Revised: 10/29/2007] [Accepted: 12/07/2007] [Indexed: 11/25/2022]
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27
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Lysenin: A sphingomyelin specific pore-forming toxin. Biochim Biophys Acta Gen Subj 2008; 1780:612-8. [DOI: 10.1016/j.bbagen.2007.09.001] [Citation(s) in RCA: 69] [Impact Index Per Article: 4.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/11/2007] [Revised: 08/08/2007] [Accepted: 09/05/2007] [Indexed: 11/21/2022]
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28
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Lipid Bilayers at Gel/Gel Interface for Ion Channel Recordings. E-JOURNAL OF SURFACE SCIENCE AND NANOTECHNOLOGY 2008. [DOI: 10.1380/ejssnt.2008.130] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 11/20/2022]
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