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Becucci L, Benci S, Nuti F, Real-Fernandez F, Vaezi Z, Stella L, Venanzi M, Rovero P, Papini AM. Interaction Study of Phospholipid Membranes with an N-Glucosylated β-Turn Peptide Structure Detecting Autoantibodies Biomarkers of Multiple Sclerosis. MEMBRANES 2015; 5:576-96. [PMID: 26437433 PMCID: PMC4704000 DOI: 10.3390/membranes5040576] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Subscribe] [Scholar Register] [Received: 06/27/2015] [Accepted: 09/24/2015] [Indexed: 11/18/2022]
Abstract
The interaction of lipid environments with the type I’ β-turn peptide structure called CSF114 and its N-glucosylated form CSF114(Glc), previously developed as a synthetic antigenic probe recognizing specific autoantibodies in a subpopulation of multiple sclerosis patients’ serum, was investigated by fluorescence spectroscopy and electrochemical experiments using large unilamellar vesicles, mercury supported lipid self-assembled monolayers (SAMs) and tethered bilayer lipid membranes (tBLMs). The synthetic antigenic probe N-glucosylated peptide CSF114(Glc) and its unglucosylated form interact with the polar heads of lipid SAMs of dioleoylphosphatidylcholine at nonzero transmembrane potentials, probably establishing a dual electrostatic interaction of the trimethylammonium and phosphate groups of the phosphatidylcholine polar head with the Glu5 and His9 residues on the opposite ends of the CSF114(Glc) β-turn encompassing residues 6-9. His9 protonation at pH 7 eliminates this dual interaction. CSF114(Glc) is adsorbed on top of SAMs of mixtures of dioleoylphosphatidylcholine with sphingomyelin, an important component of myelin, whose proteins are hypothesized to undergo an aberrant N-glucosylation triggering the autoimmune response. Incorporation of the type I’ β-turn peptide structure CSF114 into lipid SAMs by potential scans of electrochemical impedance spectroscopy induces defects causing a slight permeabilization toward cadmium ions. The N-glucopeptide CSF114(Glc) does not affect tBLMs to a detectable extent.
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Affiliation(s)
- Lucia Becucci
- Department of Chemistry "Ugo Schiff", University of Florence, Via della Lastruccia 13, 50019 Sesto Fiorentino, Italy.
- Department of Chemistry, University of Padova, Via Marzolo 1, 35131 Padova, Italy.
| | - Stefano Benci
- Department of Chemistry "Ugo Schiff", University of Florence, Via della Lastruccia 13, 50019 Sesto Fiorentino, Italy
- Interdepartmental Laboratory of Peptide and Protein Chemistry and Biology, Via della Lastruccia 13, 50019 Sesto Fiorentino, Italy
| | - Francesca Nuti
- Department of Chemistry "Ugo Schiff", University of Florence, Via della Lastruccia 13, 50019 Sesto Fiorentino, Italy
- Interdepartmental Laboratory of Peptide and Protein Chemistry and Biology, Via della Lastruccia 13, 50019 Sesto Fiorentino, Italy
| | - Feliciana Real-Fernandez
- Department of Chemistry "Ugo Schiff", University of Florence, Via della Lastruccia 13, 50019 Sesto Fiorentino, Italy
- Interdepartmental Laboratory of Peptide and Protein Chemistry and Biology, Via della Lastruccia 13, 50019 Sesto Fiorentino, Italy
| | - Zahra Vaezi
- Department of Chemical Sciences and Technologies, University of Rome 'Tor Vergata', Via Ricerca Scientifica 1, 00133 Rome, Italy
| | - Lorenzo Stella
- Department of Chemical Sciences and Technologies, University of Rome 'Tor Vergata', Via Ricerca Scientifica 1, 00133 Rome, Italy
| | - Mariano Venanzi
- Department of Chemical Sciences and Technologies, University of Rome 'Tor Vergata', Via Ricerca Scientifica 1, 00133 Rome, Italy
| | - Paolo Rovero
- Interdepartmental Laboratory of Peptide and Protein Chemistry and Biology, Via della Lastruccia 13, 50019 Sesto Fiorentino, Italy
- Department of Neurosciences, Psychology, Drug Research and Child Health-Section of Pharmaceutical Sciences and Nutraceutics, University of Florence, Via Ugo Schiff 6, 50019 Sesto Fiorentino, Italy
| | - Anna Maria Papini
- Department of Chemistry "Ugo Schiff", University of Florence, Via della Lastruccia 13, 50019 Sesto Fiorentino, Italy
- Interdepartmental Laboratory of Peptide and Protein Chemistry and Biology, Via della Lastruccia 13, 50019 Sesto Fiorentino, Italy
- PeptLab@UCP Platform and Laboratory of Chemical Biology EA4505, University of Cergy-Pontoise, 5 mail Gay-Lussac, 95031 Cergy-Pontoise CEDEX, France
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Role of electrolyte in the occurrence of the voltage induced phase transitions in a dioleoyl phosphatidylcholine monolayer on Hg. Electrochim Acta 2015. [DOI: 10.1016/j.electacta.2014.12.077] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/23/2022]
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Becucci L, Valensin D, Innocenti M, Guidelli R. Dermcidin, an anionic antimicrobial peptide: influence of lipid charge, pH and Zn2+ on its interaction with a biomimetic membrane. SOFT MATTER 2014; 10:616-626. [PMID: 24652391 DOI: 10.1039/c3sm52400k] [Citation(s) in RCA: 40] [Impact Index Per Article: 4.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/03/2023]
Abstract
The mechanism of membrane permeabilization by dermcidin (DCD-1L), an antimicrobial peptide present in human sweat, was investigated at a mercury-supported monolayer of dioleoylphosphatidylcholine (DOPC) or dioleoylphosphatidylserine (DOPS) and at a mercury-supported tethered bilayer lipid membrane (tBLM) consisting of a thiolipid (DPTL) with a DOPC or DOPS monolayer self-assembled on top of it. In an unbuffered solution of pH 5.4, DCD-1L is almost neutral and permeabilizes a DPTL/DOPS tBLM at transmembrane potentials, ϕtrans, which are physiological. In a pH 7 buffer solution DCD-1L bears two negative charges and has no effect on a DPTL/DOPC tBLM, whereas it permeabilizes a DPTL/DOPS tBLM only outside the physiological ϕtrans range; however, the presence of zinc ion induces DCD-1L to permeabilize the DPTL/DOPS tBLM at physiological ϕtrans values. The effect of zinc ions suggests a DCD-1L conformation with its positive N-terminus embedded in the lipid bilayer and the negative C terminus floating on the membrane surface. This conformation can be stabilized by a zinc ion bridge between the His(38) residue of the C terminus and the carboxyl group of DOPS. Chronocoulometric potential jumps from ϕtrans ≅ +160 mV to sufficiently negative values yield charge transients exhibiting a sigmoidal shape preceded by a relatively long "foot". This behavior is indicative of ion-channel formation characterized by disruption of DCD-1L clusters adsorbed on top of the lipid bilayer, incorporation of the resulting monomers and their aggregation into hydrophilic pores by a mechanism of nucleation and growth.
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Affiliation(s)
- Lucia Becucci
- Department of Chemistry, Florence University, Via della Lastruccia 3, 50019 Sesto Fiorentino (Firenze), Italy.
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Becucci L, Guidelli R. Mercury-supported biomimetic membranes for the investigation of antimicrobial peptides. Pharmaceuticals (Basel) 2014; 7:136-68. [PMID: 24463343 PMCID: PMC3942690 DOI: 10.3390/ph7020136] [Citation(s) in RCA: 21] [Impact Index Per Article: 2.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/16/2013] [Accepted: 01/17/2014] [Indexed: 11/16/2022] Open
Abstract
Tethered bilayer lipid membranes (tBLMs) consist of a lipid bilayer interposed between an aqueous solution and a hydrophilic "spacer" anchored to a gold or mercury electrode. There is great potential for application of these biomimetic membranes for the elucidation of structure-function relationships of membrane peptides and proteins. A drawback in the use of mercury-supported tBLMs with respect to gold-supported ones is represented by the difficulty in applying surface sensitive, spectroscopic and scanning probe microscopic techniques to gather information on the architecture of these biomimetic membranes. Nonetheless, mercury-supported tBLMs are definitely superior to gold-supported biomimetic membranes for the investigation of the function of membrane peptides and proteins, thanks to a fluidity and lipid lateral mobility comparable with those of bilayer lipid membranes interposed between two aqueous phases (BLMs), but with a much higher robustness and resistance to electric fields. The different features of mercury-supported tBLMs reconstituted with functionally active membrane proteins and peptides of bacteriological or pharmacological interest may be disclosed by a judicious choice of the most appropriate electrochemical techniques. We will describe the way in which electrochemical impedance spectroscopy, potential-step chronocoulometry, cyclic voltammetry and phase-sensitive AC voltammetry are conveniently employed to investigate the structure of mercury-supported tBLMs and the mode of interaction of antimicrobial peptides reconstituted into them.
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Affiliation(s)
- Lucia Becucci
- Department of Chemistry "Ugo Schiff", Florence University, Via della Lastruccia 3, Sesto Fiorentino (Firenze) 50019, Italy.
| | - Rolando Guidelli
- Retired professor from Florence University, Firenze 50121, Italy.
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Sagara T, Zamlynny V, Bizzotto D, Mcalees A, Mccrindle R, Lipkowski J. Spectroelectrochemical Investigations of the Spreading of 4-Pentadecyl Pyridine onto the Au(111) Electrode. Isr J Chem 2013. [DOI: 10.1002/ijch.199700024] [Citation(s) in RCA: 23] [Impact Index Per Article: 2.1] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/05/2022]
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Becucci L, Foresti ML, Schwan A, Guidelli R. Can proton pumping by SERCA enhance the regulatory role of phospholamban and sarcolipin? BIOCHIMICA ET BIOPHYSICA ACTA-BIOMEMBRANES 2013; 1828:2682-90. [DOI: 10.1016/j.bbamem.2013.07.012] [Citation(s) in RCA: 14] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Track Full Text] [Subscribe] [Scholar Register] [Received: 04/11/2013] [Revised: 06/22/2013] [Accepted: 07/08/2013] [Indexed: 11/26/2022]
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Musgrove A, Bridges CR, Sammis GM, Bizzotto D. Potential-dependent interaction of DOPC liposomes with an octadecanol-covered Au(111) surface investigated using electrochemical methods coupled with in situ fluorescence microscopy. LANGMUIR : THE ACS JOURNAL OF SURFACES AND COLLOIDS 2013; 29:3347-3360. [PMID: 23414099 DOI: 10.1021/la400042c] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/01/2023]
Abstract
The potential-controlled incorporation of DOPC liposomes (100 nm diameter) into an adsorbed octadecanol layer on Au(111) was studied using electrochemical and in situ fluorescence microscopy. The adsorbed layer of octadecanol included a small amount of a lipophilic fluorophore-octadecanol modified with BODIPY-to enable fluorescence imaging. The deposited octadecanol layer was found not to allow liposomes to interact unless the potential was less than -0.4 V/SCE, which introduces defects into the adsorbed layer. Small increases in the capacitance of the adsorbed layer were measured after introducing the defects, allowing the liposomes to interact with the defects and then annealing the defects at 0 V/SCE. A change in the adsorbed layer was also signified by a more positive desorption potential for the liposome-modified adsorbed layer as compared to that for an adsorbed layer that was porated in a similar fashion but without liposomes present in the electrolyte. These subtle changes in capacitance are difficult to interpret, so an in situ spectroscopic study was performed to provide a more direct measure of the interaction. The incorporation of liposomes should result in an increase in the fluorescence measured because the fluorophore should become further separated from the gold surface, reducing the efficiency of fluorescence quenching. No significant increase in the fluorescence of the adsorbed layer was observed during the potential pulses used in the poration procedure in the absence of liposomes. In the presence of liposomes, the fluorescence intensity was found to depend on the potential and time used for poration. At 0 V/SCE, no significant change in the fluorescence was observed for defect-free adsorbed layers. Changing the poration potential to -0.4 V/SCE caused significant increases in the fluorescence and the appearance of new structural features in the adsorbed layers that were more easily observed during the desorption procedure. The extent of fluorescence changes was found to be strongly dependent on the nature of the adsorbed layer under investigation, which suggests that the poration and liposome interaction are dependent on the quality of the adsorbed layer and its ease of poration through changes in the electrode potential.
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Affiliation(s)
- Amanda Musgrove
- Advanced Materials and Process Engineering Laboratory (AMPEL), Department of Chemistry, University of British Columbia, Vancouver, British Columbia, Canada
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Rueda Rueda M, Prieto Dapena F. Application of electrochemical impedance spectroscopy to the study of surface processes. ACTA ACUST UNITED AC 2012. [DOI: 10.1135/cccc2011118] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/05/2022]
Abstract
The application of Electrochemical Impedance Spectroscopy to the study of surface electrode processes is reviewed. The impedance expressions and the physical meaning of the parameters included in them are shown for three surface processes: adsorption kinetics, diffusion towards partially blocked electrodes and surface confined redox reactions. The models are applied to selected examples, showing the capability of Electrochemical Impedance Spectroscopy to obtain fundamental kinetic information of these processes. A review with 83 references.
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Probing membrane permeabilization by the antimicrobial peptide distinctin in mercury-supported biomimetic membranes. BIOCHIMICA ET BIOPHYSICA ACTA-BIOMEMBRANES 2011; 1808:2745-52. [DOI: 10.1016/j.bbamem.2011.07.033] [Citation(s) in RCA: 24] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Track Full Text] [Subscribe] [Scholar Register] [Received: 05/25/2011] [Revised: 06/27/2011] [Accepted: 07/21/2011] [Indexed: 02/01/2023]
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10
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Nelson A. Electrochemistry of mercury supported phospholipid monolayers and bilayers. Curr Opin Colloid Interface Sci 2010. [DOI: 10.1016/j.cocis.2010.07.004] [Citation(s) in RCA: 42] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/15/2022]
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11
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Phospholipid and gramicidin–phospholipid-coated mercury electrodes as model systems of partially blocked electrodes. J Electroanal Chem (Lausanne) 2010. [DOI: 10.1016/j.jelechem.2010.01.011] [Citation(s) in RCA: 10] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/16/2022]
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12
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Santos HA, García-Morales V, Pereira CM. Electrochemical properties of phospholipid monolayers at liquid-liquid interfaces. Chemphyschem 2010; 11:28-41. [PMID: 19943272 DOI: 10.1002/cphc.200900609] [Citation(s) in RCA: 28] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/11/2022]
Abstract
Biomembrane models built at the interface between two immiscible electrolytes (ITIES) are useful systems to study phenomena of biological relevance by means of their electrochemical processes. The unique properties of ITIES allow one either to control or measure the potential difference across the biomimetic membranes. Herein we focus on phospholipid monolayers adsorbed at liquid-liquid interfaces, and besides discussing recent developments on the subject, we describe electrochemical techniques that can be used to get insight on the interfacial processes and electrostatic properties of phospholipid membranes at the ITIES. In particular, we examine the electrochemical and physicochemical properties of (modified) phospholipid monolayers and their interaction with other biologically relevant compounds. The use of liquid-liquid electrochemistry as a powerful tool to characterize drug properties is outlined. Although this review is not a survey of all the work in the field, it provides a comprehensive referencing to current research.
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Affiliation(s)
- Hélder A Santos
- Division of Pharmaceutical Technology, Faculty of Pharmacy, University of Helsinki, P.O. Box 56 Viikinkaari 5 E, 00014, Finland.
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14
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Ringstad L, Protopapa E, Lindholm-Sethson B, Schmidtchen A, Nelson A, Malmsten M. An electrochemical study into the interaction between complement-derived peptides and DOPC mono- and bilayers. LANGMUIR : THE ACS JOURNAL OF SURFACES AND COLLOIDS 2008; 24:208-216. [PMID: 18052298 DOI: 10.1021/la702538k] [Citation(s) in RCA: 51] [Impact Index Per Article: 3.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/25/2023]
Abstract
Electrochemical methods employing the hanging mercury drop electrode were used to study the interaction between variants of the complement-derived antimicrobial peptide CNY21 (CNYITELRRQH ARASHLGLAR) and dioleoyl phosphatidylcholine (DOPC) monolayers. Capacitance potential and impedance measurements showed that the CNY21 analogues investigated interact with DOPC monolayers coating the mercury drop. Increasing the peptide hydrophobicity by substituting the two histidine residues with leucine resulted in a deeper peptide penetration into the hydrophobic region of the DOPC monolayer, indicated by an increase in the dielectric constant of the lipid monolayer (Deltaepsilon = 2.0 after 15 min interaction). Increasing the peptide net charge from +3 to +5 by replacing the histidines by lysines, on the other hand, arrests the peptide in the lipid head group region. Reduction of electroactive ions (Tl+, Pb2+, Cd2+, and Eu3+) at the monolayer-coated electrode was employed to further characterize the types of defects induced by the peptides. All peptides studied permeabilize the monolayer to Tl+ to an appreciable extent, but this effect is more pronounced for the more hydrophobic peptide (CNY21L), which also allows penetration of larger ions and ions of higher valency. The results for the various ions indicate that charge repulsion rather than ion size is the determining factor for cation penetration through peptide-induced defects in the DOPC monolayer. The effects obtained for monolayers were compared to results obtained with bilayers from liposome leakage and circular dichroism studies for unilamellar DOPC vesicles, and in situ ellipsometry for supported DOPC bilayers. Trends in peptide-induced liposome leakage were similar to peptide effects on electrochemical impedance and permeability of electroactive ions for the monolayer system, demonstrating that formation of transmembrane pores alone does not constitute the mechanism of action for the peptides investigated. Instead, our results point to the importance of local packing defects in the lipid membrane in close proximity to the adsorbed peptide molecules.
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Affiliation(s)
- Lovisa Ringstad
- Department of Pharmacy, Uppsala University, Uppsala, Sweden.
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Santos HA, Carlsson S, Murtomäki L, Kontturi K. Effect of Gramicidin on Phospholipid-Modified Monolayers and on Ion Transfer at a Liquid–Liquid Interface. Chemphyschem 2007; 8:913-20. [PMID: 17366646 DOI: 10.1002/cphc.200600767] [Citation(s) in RCA: 11] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/12/2022]
Abstract
The interaction of hybrid lipid/gramicidin A (gA) monolayers with dextran sulfate (DS) and the effect of this interaction on ion transfer at a liquid-liquid interface is reported. The interfacial and physicochemical properties are studied with Langmuir-Blodgett (LB) and electrochemical techniques. The results obtained from compression isotherms demonstrate that the interactions between the different species in the hybrid monolayer vary according to the chemical nature of the lipid (hydrocarbon region and charge of the head group). Interfacial capacitance measured with AC voltammetry indicates that the DS chains form a rather flat and compact layer when adsorbed to either zwitterionic or negatively charged phospholipid monolayers, and that calcium, even at low concentrations, interacts with the monolayers. These results are successfully described by a model based on the solution of the Poisson-Boltzmann equation in the interfacial region. Ion transfer and interactions with the lipid/gA/DS-modified monolayers were also studied with electrochemical techniques. Admittance data show that although the studied ions are not using gA channels for the transfer through the lipid membranes, the incorporation of gA in the lipid domain and the adsorption of DS at the interface have a significant effect on ion transfer across the monolayers. This effect can be explained as a consequence of the modified surface charge and of the compactness of the lipid domain due to its interaction with gA and to calcium and DS adsorption at the interface. The ion-transfer rate, therefore, depends on the composition of the monolayer and the chemical nature of the ion.
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Affiliation(s)
- Hélder A Santos
- Department of Chemical Technology, Laboratory of Physical Chemistry and Electrochemistry, Helsinki University of Technology, P.O. Box 6100, Kemistintie 1, 02015 TKK Espoo, Finland.
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Neville F, Gidalevitz D, Kale G, Nelson A. Electrochemical screening of anti-microbial peptide LL-37 interaction with phospholipids. Bioelectrochemistry 2006; 70:205-13. [PMID: 16949887 DOI: 10.1016/j.bioelechem.2006.07.006] [Citation(s) in RCA: 18] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/10/2006] [Revised: 05/18/2006] [Accepted: 07/07/2006] [Indexed: 11/25/2022]
Abstract
LL-37 is an alpha-helical antimicrobial peptide of human origin. It is a 37 residue cathelicidin peptide. This paper explores the use of electrochemical methods to investigate the interaction of LL-37 with phospholipid and lipid A monolayers on a mercury drop electrode. Experiments were carried out in Dulbecco's phosphate buffered saline at pH approximately 7.6. The capacity-potential curves of the coated electrode in the presence and absence of LL-37 were measured using out-of-phase ac voltammetry. The frequency dependence of the complex impedance of the coated electrode in the presence and absence of LL-37 was estimated at -0.4 V versus Ag/AgCl 3.5 mol dm(-3) KCl. The monolayer permeability to ions was studied by following the reduction of Tl(I) to Tl(Hg) at the coated electrode. LL-37 shows no significant interaction with DOPC. However, LL-37 shows a small interaction with DOPG and lipid A within a DOPC monolayer where the monolayer permeability is marginally increased and the zero frequency capacitance (ZFC) is marginally decreased in both cases. LL-37 shows a significant interaction with a lipid A monolayer thereby decreasing the ZFC by 30%. The results concur with the known membrane active properties of LL-37 and establish this electrochemical approach as a key technique for screening peptides.
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Affiliation(s)
- Frances Neville
- Institute for Materials Research, School of Process, Environmental and Materials Engineering, University of Leeds, LS2 9JT, UK
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Bizzotto D, Yang Y, Shepherd JL, Stoodley R, Agak J, Stauffer V, Lathuillière M, Akhtar AS, Chung E. Electrochemical and spectroelectrochemical characterization of lipid organization in an electric field. J Electroanal Chem (Lausanne) 2004. [DOI: 10.1016/j.jelechem.2003.11.002] [Citation(s) in RCA: 35] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/26/2022]
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Whitehouse C, Gidalevitz D, Cahuzac M, Koeppe Ii RE, Nelson A. Interaction of gramicidin derivatives with phospholipid monolayers. LANGMUIR : THE ACS JOURNAL OF SURFACES AND COLLOIDS 2004; 20:9291-9298. [PMID: 15461520 DOI: 10.1021/la048797l] [Citation(s) in RCA: 24] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/24/2023]
Abstract
A study of the interaction of gramicidin A (gA), tert-butyloxycarbonyl-gramicidin (g-BOC), and desformyl gramicidin (g-des) with dioleoyl phosphatidylcholine (DOPC) and DOPC/phosphatidylserine (PS) mixed monolayers on a mercury electrode is reported in this paper. Experiments were carried out in electrolytes KCl (0.1 mol dm(-3)) and Mg(NO3)2 (0.05 mol dm(-3)). The channel-forming properties of the gramicidins were studied by following the reduction of Tl(I) to Tl(Hg). The frequency dependence of the complex impedance of coated electrode surfaces in the presence and absence of the gramicidins was estimated between 65,000 and 0.1 Hz at potentials of -0.4 V versus Ag/AgCl with 3.5 mol dm(-3) KCl. Epifluorescence microscopy was used to qualitatively correlate the interaction of the gramicidin peptides with dipalmitoyl phosphatidylcholine (DPPC) and dipalmitoyl phosphatidylglycerol (DPPG) at the air-water interface. gA was shown to form Tl+ conducting channels in a DOPC monolayer, while g-BOC and g-des did not. In DOPC-30% PS (DOPC-0.3PS) layers, there is a marked increase in channel activity of all three gramicidin derivatives. None of the peptides facilitate the permeability of the DOPC-0.3PS layer to Cd2+. All three peptides interact with the layer as shown by capacitance-potential curves and impedance spectroscopy indicated by penetration of the peptide into the dielectric, an increase in surface "roughness", and an increased significance of low-frequency relaxations. The order of interaction is gA > g-des > g-BOC. The epifluorescence study of DPPC and DPPG layers at the air-water interface shows a selective action of the different gramicidins.
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Affiliation(s)
- C Whitehouse
- Center for Self-Organising Molecular Systems, School of Chemistry, University of Leeds, LS2 9JT, United Kingdom
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Prieto F, Navarro I, Rueda M. Impedance study of thallous ion movement through gramicidin–dioleoylphosphatidylcholine self-assembled monolayers supported on mercury electrodes: the C–(C)–CE mechanism. J Electroanal Chem (Lausanne) 2003. [DOI: 10.1016/s0022-0728(03)00262-6] [Citation(s) in RCA: 13] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
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20
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Becucci L, Moncelli MR, Guidelli R. Thallous ion movements through gramicidin channels incorporated in lipid monolayers supported by mercury. Biophys J 2002; 82:852-64. [PMID: 11806927 PMCID: PMC1301894 DOI: 10.1016/s0006-3495(02)75447-7] [Citation(s) in RCA: 31] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/18/2022] Open
Abstract
The potential independent limiting flux of hydrated Tl(+) ions through gramicidin (GR) channels incorporated in phospholipid monolayers self assembled on a hanging mercury-drop electrode is shown to be controlled both by diffusion and by a dehydration step. Conversely, the potential independent limiting flux of dehydrated Tl(+) ions stemming from Tl amalgam electro-oxidation is exclusively controlled by diffusion of thallium atoms within the amalgam. Modulating the charge on the polar heads of dioleoylphosphatidylserine (DOPS) by changing pH affects the limiting flux of hydrated Tl(+) ions to a notable extent, primarily by electrostatic interactions. The dipole potential of DOPS and dioleoylphosphatidylcholine (DOPC), positive toward the hydrocarbon tails, does not hinder the translocation step of Tl(+) ions to such an extent as to make it rate limiting. Consequently, incorporation in the lipid monolayer of phloretin, which decreases such a positive dipole potential, does not affect the kinetics of Tl(+) flux through GR channels. In contrast, the increase in the positive dipole potential produced by the incorporation of ketocholestanol causes the translocation step to contribute to the rate of the overall process. A model providing a quantitative interpretation of the kinetics of diffusion, dehydration-hydration, translocation, and charge transfer of the Tl(+)/Tl(0)(Hg) couple through GC channels incorporated in mercury-supported phospholipid monolayers is provided. A cut-off disk model yielding the profile of the local electrostatic potential created by an array of oriented dipoles located in the lipid monolayer along the axis of a cylindrical ion channel is developed.
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Affiliation(s)
- Lucia Becucci
- Department of Chemistry, Florence University, 50121 Florence, Italy
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Adsorption of DOPC onto Hg from the G∣S interface and from a liposomal suspension. J Electroanal Chem (Lausanne) 2001. [DOI: 10.1016/s0022-0728(01)00655-6] [Citation(s) in RCA: 31] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/23/2022]
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Abstract
Potential step amperometry (chronoamperometry) of the Tl(I)/Tl(Hg) electrochemical reduction process has been used to investigate the underlying mechanisms of gramicidin activity in phospholipid monolayers. The experiments were carried out at gramicidin-modified dioleoyl phosphatidylcholine (DOPC)-coated electrodes. Application of a potential step to the coated electrode system results in a current transient that can be divided into two regions. An initial exponential decay of current corresponds to the inactivation of monomer channel conductance and a longer time scale quasi-steady-state represents the diffusion of ions to a bimolecular surface reaction. Concentrations of monomer conducting channels are relatively low, and the results indicate that two or more forms of gramicidin are in equilibrium with each other in the layer. Aromatic/conjugated compounds incorporated into the monolayer increase the reduction current by decreasing the rate of channel inactivation and increasing the stability of the conducting channel. This effect is positively correlated with the degree of the compound's aromaticity. The anomalous influence of alkali metal ions on the reduction current is consistent with the model of gramicidin being speciated in the monolayer in more than one form. The results have implications on the lability of the peptide conformation in biological membranes and its dependence on lipid environment, solution composition, and applied potential.
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Affiliation(s)
- A Nelson
- Marine Biological Association of the United Kingdom, The Laboratory, Plymouth PL1 2PB, United Kingdom.
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