1
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Alvero-Gonzalez LM, Aurora Perini D, Queralt-Martín M, Perálvarez-Marín A, Viñas C, Alcaraz A. Probing electrophysiological activity of amphiphilic Dynorphin A in planar neutral membranes reveals both ion channel-like activity and neuropeptide translocation. Bioelectrochemistry 2023; 154:108527. [PMID: 37531663 DOI: 10.1016/j.bioelechem.2023.108527] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/26/2023] [Revised: 07/10/2023] [Accepted: 07/26/2023] [Indexed: 08/04/2023]
Abstract
Dynorphin A (DynA) is an endogenous neuropeptide that besides acting as a ligand of the κ-opioid receptor, presents some non-opioid pathophysiological properties associated to its ability to induce cell permeability similarly to cell-penetrating peptides (CPPs). Here, we use electrophysiology experiments to show that amphiphilic DynA generates aqueous pores in neutral membranes similar to those reported previously in charged membranes, but we also find other events thermodynamically incompatible with voltage-driven ion channel activity (i.e. non-zero currents with no applied voltage in symmetric salt conditions, reversal potentials that exceed the theoretical limit for a given salt concentration gradient). By comparison with current traces generated by other amphiphilic molecule known to spontaneously cross membranes, we hypothesize that DynA could directly translocate across neutral bilayers, a feature never observed in charged membranes following the same electrophysiological protocol. Our findings suggest that DynA interaction with the cellular membrane is modulated by the lipid charge distribution, enabling either passive ionic transport via membrane remodeling and pore formation or by peptide direct internalization independent of cellular transduction pathways.
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Affiliation(s)
- Laidy M Alvero-Gonzalez
- Laboratory of Molecular Biophysics, Department of Physics, University Jaume I, 12071 Castellón, Spain
| | - D Aurora Perini
- Laboratory of Molecular Biophysics, Department of Physics, University Jaume I, 12071 Castellón, Spain
| | - María Queralt-Martín
- Laboratory of Molecular Biophysics, Department of Physics, University Jaume I, 12071 Castellón, Spain
| | - Alex Perálvarez-Marín
- Biophysics Unit, Department of Biochemistry and Molecular Biology, School of Medicine, Universitat Autònoma de Barcelona, 08193 Cerdanyola del Vallès, Spain; Institute of Neuroscience, Universitat Autònoma de Barcelona, 08193 Cerdanyola del Vallès, Spain.
| | - Clara Viñas
- Institut de Ciència de Materials de Barcelona, ICMAB-CSIC, Campus Universitat Autònoma de Barcelona, 08193 Bellaterra, Spain
| | - Antonio Alcaraz
- Laboratory of Molecular Biophysics, Department of Physics, University Jaume I, 12071 Castellón, Spain.
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2
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Queralt-Martín M, Pérez-Grau JJ, Alvero González LM, Perini DA, Cervera J, Aguilella VM, Alcaraz A. Biphasic concentration patterns in ionic transport under nanoconfinement revealed in steady-state and time-dependent properties. J Chem Phys 2023; 158:064701. [PMID: 36792514 DOI: 10.1063/5.0136668] [Citation(s) in RCA: 1] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/19/2023] Open
Abstract
Ion permeation across nanoscopic structures differs considerably from microfluidics because of strong steric constraints, transformed solvent properties, and charge-regulation effects revealed mostly in diluted solutions. However, little is known about nanofluidics in moderately concentrated solutions, which are critically important for industrial applications and living systems. Here, we show that nanoconfinement triggers general biphasic concentration patterns in a myriad of ion transport properties by using two contrasting systems: a biological ion channel and a much larger synthetic nanopore. Our findings show a low-concentration regime ruled by classical Debye screening and another one where ion-ion correlations and enhanced ion-surface interactions contribute differently to each electrophysiological property. Thus, different quantities (e.g., conductance vs noise) measured under the same conditions may appear contradictory because they belong to different concentration regimes. In addition, non-linear effects that are barely visible in bulk conductivity only in extremely concentrated solutions become apparent in nanochannels around physiological conditions.
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Affiliation(s)
- María Queralt-Martín
- Department of Physics, Laboratory of Molecular Biophysics, Universitat Jaume I, E-12071 Castellón, Spain
| | - José J Pérez-Grau
- Department of Physics, Laboratory of Molecular Biophysics, Universitat Jaume I, E-12071 Castellón, Spain
| | - Laidy M Alvero González
- Department of Physics, Laboratory of Molecular Biophysics, Universitat Jaume I, E-12071 Castellón, Spain
| | - D Aurora Perini
- Department of Physics, Laboratory of Molecular Biophysics, Universitat Jaume I, E-12071 Castellón, Spain
| | - Javier Cervera
- Departament de Física de la Terra i Termodinàmica, Universitat de València, E-46100 Burjassot, Spain
| | - Vicente M Aguilella
- Department of Physics, Laboratory of Molecular Biophysics, Universitat Jaume I, E-12071 Castellón, Spain
| | - Antonio Alcaraz
- Department of Physics, Laboratory of Molecular Biophysics, Universitat Jaume I, E-12071 Castellón, Spain
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3
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Queralt-Martín M, Perini DA, Alcaraz A. Specific adsorption of trivalent cations in biological nanopores determines conductance dynamics and reverses ionic selectivity. Phys Chem Chem Phys 2021; 23:1352-1362. [PMID: 33367433 DOI: 10.1039/d0cp04486e] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/25/2022]
Abstract
Adsorption processes are central to ionic transport in industrial and biological membrane systems. Multivalent cations modulate the conductive properties of nanofluidic devices through interactions with charged surfaces that depend principally on the ion charge number. Considering that ion channels are specialized valves that demand a sharp specificity in ion discrimination, we investigate the adsorption dynamics of trace amounts of different salts of trivalent cations in biological nanopores. We consider here OmpF from Escherichia coli, an archetypical protein nanopore, to probe the specificity of biological nanopores to multivalent cations. We systematically compare the effect of three trivalent electrolytes on OmpF current-voltage relationships and characterize the degree of rectification induced by each ion. We also analyze the open channel current noise to determine the existence of equilibrium/non-equilibrium mechanisms of ion adsorption and evaluate the extent of charge inversion through selectivity measurements. We show that the interaction of trivalent electrolytes with biological nanopores occurs via ion-specific adsorption yielding differential modulation of ion conduction and selectivity inversion. We also demonstrate the existence of non-equilibrium fluctuations likely related to ion-dependent trapping-detrapping processes. Our study provides fundamental information relevant to different biological and electrochemical systems where transport phenomena involve ion adsorption in charged surfaces under nanoscale confinement.
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Affiliation(s)
- María Queralt-Martín
- Laboratory of Molecular Biophysics, Department of Physics, Universitat Jaume I, 12071 Castellón, Spain.
| | - D Aurora Perini
- Laboratory of Molecular Biophysics, Department of Physics, Universitat Jaume I, 12071 Castellón, Spain.
| | - Antonio Alcaraz
- Laboratory of Molecular Biophysics, Department of Physics, Universitat Jaume I, 12071 Castellón, Spain.
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4
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Prajapati JD, Mele C, Aksoyoglu MA, Winterhalter M, Kleinekathöfer U. Computational Modeling of Ion Transport in Bulk and through a Nanopore Using the Drude Polarizable Force Field. J Chem Inf Model 2020; 60:3188-3203. [DOI: 10.1021/acs.jcim.0c00389] [Citation(s) in RCA: 10] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/05/2023]
Affiliation(s)
| | - Crystal Mele
- Department of Physics and Earth Sciences, Jacobs University Bremen, 28759 Bremen, Germany
| | | | - Mathias Winterhalter
- Department of Life Sciences and Chemistry, Jacobs University Bremen, 28759 Bremen, Germany
| | - Ulrich Kleinekathöfer
- Department of Physics and Earth Sciences, Jacobs University Bremen, 28759 Bremen, Germany
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5
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Puiggalí-Jou A, Pérez-Madrigal MM, Del Valle LJ, Armelin E, Casas MT, Michaux C, Perpète EA, Estrany F, Alemán C. Confinement of a β-barrel protein in nanoperforated free-standing nanomembranes for ion transport. NANOSCALE 2016; 8:16922-16935. [PMID: 27714137 DOI: 10.1039/c6nr04948f] [Citation(s) in RCA: 10] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/07/2023]
Abstract
Bioinspired free-standing nanomembranes (FSNMs) for selective ion transport have been tailored by immobilizing the Omp2a β-barrel membrane protein inside nanoperforations created in flexible poly(lactic acid) (PLA) nanomembranes. Perforated PLA FSNMs have been prepared by spin-coating a 99 : 1 PLA : poly(vinyl alcohol) mixture, and through a phase segregation process nanofeatures with dimensions similar to the entire nanomembrane thickness (∼110 nm) were induced. These nanofeatures have subsequently been transformed into nanoperforations (diameter: ∼51 nm) by selective solvent etching. The protein confined inside the nanopores of PLA FSNMs preserves the β-barrel structure and organizes in ovoid aggregates. The transport properties of Na+, K+, and Ca2+ across non-perforated PLA, nanoperforated PLA, and Omp2a-filled nanoperforated PLA have been monitored by measuring the nanomembrane resistance with electrochemical impedance spectroscopy (EIS). The incorporation of nanoperforations enhances the transport of ions across PLA nanomembranes, whereas the functionality of immobilized Omp2a is essential to exhibit effects similar to those observed in biological nanomembranes. Indeed, Omp2a-filled nanoperforated PLA nanomembranes exhibit stronger affinity towards Na+ and Ca2+ ions than towards K+. In summary, this work provides a novel bioinspired strategy to develop mechanically stable and flexible FSNMs with channels for ion transport, which are precisely located inside artificial nanoperforations, thus holding great potential for applications in biofiltration and biosensing.
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Affiliation(s)
- Anna Puiggalí-Jou
- Departament d'Enginyeria Química, ETSEIB, Universitat Politècnica de Catalunya, Avda. Diagonal 647, Barcelona E-08028, Spain. and Center for Research in Nano-Engineering, Universitat Politècnica de Catalunya, Campus Sud, Edifici C', C/Pasqual i Vila s/n, Barcelona E-08028, Spain
| | - Maria M Pérez-Madrigal
- Departament d'Enginyeria Química, ETSEIB, Universitat Politècnica de Catalunya, Avda. Diagonal 647, Barcelona E-08028, Spain. and Center for Research in Nano-Engineering, Universitat Politècnica de Catalunya, Campus Sud, Edifici C', C/Pasqual i Vila s/n, Barcelona E-08028, Spain
| | - Luis J Del Valle
- Departament d'Enginyeria Química, ETSEIB, Universitat Politècnica de Catalunya, Avda. Diagonal 647, Barcelona E-08028, Spain. and Center for Research in Nano-Engineering, Universitat Politècnica de Catalunya, Campus Sud, Edifici C', C/Pasqual i Vila s/n, Barcelona E-08028, Spain
| | - Elaine Armelin
- Departament d'Enginyeria Química, ETSEIB, Universitat Politècnica de Catalunya, Avda. Diagonal 647, Barcelona E-08028, Spain. and Center for Research in Nano-Engineering, Universitat Politècnica de Catalunya, Campus Sud, Edifici C', C/Pasqual i Vila s/n, Barcelona E-08028, Spain
| | - María T Casas
- Departament d'Enginyeria Química, ETSEIB, Universitat Politècnica de Catalunya, Avda. Diagonal 647, Barcelona E-08028, Spain.
| | - Catherine Michaux
- Laboratoire de Chimie Physique des Biomolécules, Unité de Chimie Physique Théorique et Structurale (UCPTS), University of Namur, Rue de Bruxelles, 61, 5000 Namur, Belgium
| | - Eric A Perpète
- Laboratoire de Chimie Physique des Biomolécules, Unité de Chimie Physique Théorique et Structurale (UCPTS), University of Namur, Rue de Bruxelles, 61, 5000 Namur, Belgium
| | - Francesc Estrany
- Center for Research in Nano-Engineering, Universitat Politècnica de Catalunya, Campus Sud, Edifici C', C/Pasqual i Vila s/n, Barcelona E-08028, Spain and Departament d'Enginyeria Química, Escola Universitària d'Enginyeria Tècnica Industrial de Barcelona, Universitat Politècnica de Catalunya, Comte d'Urgell 187, 08036 Barcelona, Spain
| | - Carlos Alemán
- Departament d'Enginyeria Química, ETSEIB, Universitat Politècnica de Catalunya, Avda. Diagonal 647, Barcelona E-08028, Spain. and Center for Research in Nano-Engineering, Universitat Politècnica de Catalunya, Campus Sud, Edifici C', C/Pasqual i Vila s/n, Barcelona E-08028, Spain
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6
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Hoque MN, Das G. Implications of hydrogen/halogen-bond in the stabilization of confined water and anion-water clusters by a cationic receptor. J Mol Struct 2016. [DOI: 10.1016/j.molstruc.2015.12.035] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/30/2022]
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7
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Goulart CL, Bisch PM, von Krüger WMA, Homblé F. VCA1008: An Anion-Selective Porin of Vibrio Cholerae. BIOCHIMICA ET BIOPHYSICA ACTA-BIOMEMBRANES 2014; 1848:680-7. [PMID: 25462170 DOI: 10.1016/j.bbamem.2014.11.009] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Received: 08/15/2014] [Revised: 11/05/2014] [Accepted: 11/10/2014] [Indexed: 01/14/2023]
Abstract
A putative porin function has been assigned to VCA1008 of Vibrio cholerae. Its coding gene, vca1008, is expressed upon colonization of the small intestine in infant mice and human volunteers, and is essential for infection. In vitro, vca1008 is expressed under inorganic phosphate limitation and, in this condition, VCA1008 is the major outer membrane protein of the bacterium. Here, we provide the first functional characterization of VCA1008 reconstituted into planar lipid bilayers. Our main findings were: 1) VCA1008 forms an ion channel that, at high voltage (~±100 mV), presents a voltage-dependent activity and displays closures typical of trimeric porins, with a conductance of 4.28±0.04 nS (n=164) in 1M KCl; 2) It has a preferred selectivity for anions over cations; 3) Its conductance saturates with increasing inorganic phosphate concentration, suggesting VCA1008 contains binding site(s) for this anion; 4) Its ion selectivity is controlled by both fixed charged residues within the channel and diffusion along the pore; 5) Partitioning of poly (ethylene glycol)s (PEGs) of different molecular mass suggests that VCA1008 channel has a pore exclusion limit of 0.9 nm.
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Affiliation(s)
- Carolina L Goulart
- Structure et Fonction des Membranes Biologiques, Centre de Biologie Structurale et de Bioinformatique, Faculté des Sciences, Université Libre de Bruxelles, Campus Plaine (CP 206/2), B - 1050 Brussels, Belgium
| | - Paulo M Bisch
- Laboratório de Física Biológica, Instituto de Biofísica Carlos Chagas Filho, Universidade Federal do Rio de Janeiro, Rio de Janeiro, Brazil
| | - Wanda M A von Krüger
- Laboratório de Física Biológica, Instituto de Biofísica Carlos Chagas Filho, Universidade Federal do Rio de Janeiro, Rio de Janeiro, Brazil
| | - Fabrice Homblé
- Structure et Fonction des Membranes Biologiques, Centre de Biologie Structurale et de Bioinformatique, Faculté des Sciences, Université Libre de Bruxelles, Campus Plaine (CP 206/2), B - 1050 Brussels, Belgium.
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8
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Dhakshnamoorthy B, Ziervogel BK, Blachowicz L, Roux B. A structural study of ion permeation in OmpF porin from anomalous X-ray diffraction and molecular dynamics simulations. J Am Chem Soc 2014; 135:16561-8. [PMID: 24106986 DOI: 10.1021/ja407783a] [Citation(s) in RCA: 18] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
Abstract
OmpF, a multiionic porin from Escherichia coli, is a useful protypical model system for addressing general questions about electrostatic interactions in the confinement of an aqueous molecular pore. Here, favorable anion locations in the OmpF pore were mapped by anomalous X-ray scattering of Br(–) ions from four different crystal structures and compared with Mg(2+) sites and Rb(+) sites from a previous anomalous diffraction study to provide a complete picture of cation and anion transfer paths along the OmpF channel. By comparing structures with various crystallization conditions, we find that anions bind in discrete clusters along the entire length of the OmpF pore, whereas cations find conserved binding sites with the extracellular, surface-exposed loops. Results from molecular dynamics simulations are consistent with the experimental data and help highlight the critical residues that preferentially contact either cations or anions during permeation. Analysis of these results provides new insights into the molecular mechanisms that determine ion selectivity in OmpF porin.
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Affiliation(s)
- Balasundaresan Dhakshnamoorthy
- Department of Biochemistry and Molecular Biology, Gordon Center for Integrative Science, University of Chicago Chicago, IL 60637, USA
| | - Brigitte K Ziervogel
- Department of Biochemistry and Molecular Biology, Gordon Center for Integrative Science, University of Chicago Chicago, IL 60637, USA
| | - Lydia Blachowicz
- Department of Biochemistry and Molecular Biology, Gordon Center for Integrative Science, University of Chicago Chicago, IL 60637, USA
| | - Benoît Roux
- Department of Biochemistry and Molecular Biology, Gordon Center for Integrative Science, University of Chicago Chicago, IL 60637, USA
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9
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Anil Kumar AV. Anomalous dynamics of binary colloidal mixtures over a potential barrier: Effect of depletion interaction. J Chem Phys 2014; 141:034904. [DOI: 10.1063/1.4890282] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/14/2022] Open
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10
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MATSUURA Y, YAMATO I, ANDO T, SUENAGA A. Ion Selectivity Mechanism of Escherichia Coli OmpF Porin: a Molecular Dynamics Simulation/ free Energy Calculation Study. JOURNAL OF COMPUTER CHEMISTRY-JAPAN 2014. [DOI: 10.2477/jccj.2014-0040] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/05/2022]
Affiliation(s)
- Yasuhiro MATSUURA
- Department of Biological Science and Technology, Tokyo University of Science, 6-3-1 Niijuku, Katsushika-ku, Tokyo 125-8585, Japan
| | - Ichiro YAMATO
- Department of Biological Science and Technology, Tokyo University of Science, 6-3-1 Niijuku, Katsushika-ku, Tokyo 125-8585, Japan
| | - Tadashi ANDO
- RIKEN, Laboratory for Biomolecular Function Simulation, International Medical Device Alliance (IMDA) 6F, 1-6-5 Minatojima-minamimachi, Chuo-ku, Kobe, Hyogo 650-0047, Japan
| | - Atsushi SUENAGA
- Computational Biology Research Center, National Institute of Advanced Industrial Science and Technology, 2-4-7 Aomi, Koto-ku, Tokyo 135-0064, Japan
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11
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Queralt-Martín M, Verdiá-Báguena C, Aguilella VM, Alcaraz A. Electrostatic interactions drive the nonsteric directional block of OmpF channel by La3+. LANGMUIR : THE ACS JOURNAL OF SURFACES AND COLLOIDS 2013; 29:15320-15327. [PMID: 24256306 DOI: 10.1021/la402700m] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/02/2023]
Abstract
Ion channels regulate the transport of molecules and the electric signal transduction in living cells by means of complex and even highly sophisticated mechanisms. We focus here on the crucial role that polyvalent ions, well-known modulators of many biological nanosystems, play in ion channel function. In particular, we show that trace amounts of lanthanum are able to block the bacterial porin OmpF, a large biological pore of Escherichia coli wide enough to exchange antibiotics and other larger molecules. The underlying mechanism has a strong directional character: it is sensitive to the sign of the applied voltage and to the side of the blocker addition. We explore these channel features by combining planar lipid bilayer electrophysiology at the single channel level, site-directed mutagenesis, and inductively coupled plasma mass spectrometry (ICP-MS). In contrast to other well-described channel blockers, which seem to occlude the narrower part of the pore, we envisage a nonsteric mechanism based on electrostatic interactions.
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Affiliation(s)
- María Queralt-Martín
- Laboratory of Molecular Biophysics, Department of Physics, Universitat Jaume I , 12071 Castellón, Spain
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12
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Zhao S, Zheng YB, Cai SL, Weng YH, Cao SH, Yang JL, Li YQ. Sugar-stimulated robust nanodevice: 4-Carboxyphenylboronic acid modified single glass conical nanopores. Electrochem commun 2013. [DOI: 10.1016/j.elecom.2013.09.009] [Citation(s) in RCA: 22] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022] Open
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13
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Kumar AVA. Binary colloidal mixtures in a potential barrier: Demixing due to depletion. J Chem Phys 2013; 138:154903. [DOI: 10.1063/1.4801333] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/15/2022] Open
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14
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Alcaraz A, Queralt-Martín M, García-Giménez E, Aguilella VM. Increased salt concentration promotes competitive block of OmpF channel by protons. BIOCHIMICA ET BIOPHYSICA ACTA-BIOMEMBRANES 2012; 1818:2777-82. [DOI: 10.1016/j.bbamem.2012.07.001] [Citation(s) in RCA: 12] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Track Full Text] [Subscribe] [Scholar Register] [Received: 05/03/2012] [Revised: 07/02/2012] [Accepted: 07/03/2012] [Indexed: 10/28/2022]
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15
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Divalent Metal Ion Transport across Large Biological Ion Channels and Their Effect on Conductance and Selectivity. Biochem Res Int 2012; 2012:245786. [PMID: 23008773 PMCID: PMC3449104 DOI: 10.1155/2012/245786] [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: 06/04/2012] [Revised: 07/27/2012] [Accepted: 07/30/2012] [Indexed: 11/17/2022] Open
Abstract
Electrophysiological characterization of large protein channels, usually displaying multi-ionic transport and weak ion selectivity, is commonly performed at physiological conditions (moderate gradients of KCl solutions at decimolar concentrations buffered at neutral pH). We extend here the characterization of the OmpF porin, a wide channel of the outer membrane of E. coli, by studying the effect of salts of divalent cations on the transport properties of the channel. The regulation of divalent cations concentration is essential in cell metabolism and understanding their effects is of key importance, not only in the channels specifically designed to control their passage but also in other multiionic channels. In particular, in porin channels like OmpF, divalent cations modulate the efficiency of molecules having antimicrobial activity. Taking advantage of the fact that the OmpF channel atomic structure has been resolved both in water and in MgCl2 aqueous solutions, we analyze the single channel conductance and the channel selectivity inversion aiming to separate the role of the electrolyte itself, and the counterion accumulation induced by the protein channel charges and other factors (binding, steric effects, etc.) that being of minor importance in salts of monovalent cations become crucial in the case of divalent cations.
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16
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Krammer EM, Homblé F, Prévost M. Concentration dependent ion selectivity in VDAC: a molecular dynamics simulation study. PLoS One 2011; 6:e27994. [PMID: 22164223 PMCID: PMC3229507 DOI: 10.1371/journal.pone.0027994] [Citation(s) in RCA: 28] [Impact Index Per Article: 2.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/18/2011] [Accepted: 10/29/2011] [Indexed: 11/19/2022] Open
Abstract
The voltage-dependent anion channel (VDAC) forms the major pore in the outer mitochondrial membrane. Its high conducting open state features a moderate anion selectivity. There is some evidence indicating that the electrophysiological properties of VDAC vary with the salt concentration. Using a theoretical approach the molecular basis for this concentration dependence was investigated. Molecular dynamics simulations and continuum electrostatic calculations performed on the mouse VDAC1 isoform clearly demonstrate that the distribution of fixed charges in the channel creates an electric field, which determines the anion preference of VDAC at low salt concentration. Increasing the salt concentration in the bulk results in a higher concentration of ions in the VDAC wide pore. This event induces a large electrostatic screening of the charged residues promoting a less anion selective channel. Residues that are responsible for the electrostatic pattern of the channel were identified using the molecular dynamics trajectories. Some of these residues are found to be conserved suggesting that ion permeation between different VDAC species occurs through a common mechanism. This inference is buttressed by electrophysiological experiments performed on bean VDAC32 protein akin to mouse VDAC.
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Affiliation(s)
- Eva-Maria Krammer
- Structure et Fonction des Membranes Biologiques, Université Libre de Bruxelles, Brussels, Belgium
| | - Fabrice Homblé
- Structure et Fonction des Membranes Biologiques, Université Libre de Bruxelles, Brussels, Belgium
| | - Martine Prévost
- Structure et Fonction des Membranes Biologiques, Université Libre de Bruxelles, Brussels, Belgium
- * E-mail:
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17
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Calero C, Faraudo J, Aguilella-Arzo M. First-passage-time analysis of atomic-resolution simulations of the ionic transport in a bacterial porin. PHYSICAL REVIEW. E, STATISTICAL, NONLINEAR, AND SOFT MATTER PHYSICS 2011; 83:021908. [PMID: 21405864 DOI: 10.1103/physreve.83.021908] [Citation(s) in RCA: 12] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 11/15/2010] [Indexed: 05/30/2023]
Abstract
We have studied the dynamics of chloride and potassium ions in the interior of the Outer membrane porin F (OmpF) under the influence of an external electric field. From the results of extensive all-atom molecular dynamics (MD) simulations of the system, we computed several first-passage-time (FPT) quantities to characterize the dynamics of the ions in the interior of the channel. Such FPT quantities obtained from MD simulations demonstrate that it is not possible to describe the dynamics of chloride and potassium ions inside the whole channel with a single constant diffusion coefficient. However, we showed that a valid, statistically rigorous description in terms of a constant diffusion coefficient D and an effective deterministic force F(eff) can be obtained after appropriate subdivision of the channel in different regions suggested by the x-ray structure. These results have important implications for popular simplified descriptions of channels based on the one-dimensional Poisson-Nernst-Planck equations. Also, the effect of entropic barriers on the diffusion of the ions is identified and briefly discussed.
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Affiliation(s)
- Carles Calero
- Institut de Ciència dels Materials de Barcelona (ICMAB-CSIC), Campus de la UAB, E-08193 Bellaterra, Spain.
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18
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Queralt-Martín M, García-Giménez E, Mafé S, Alcaraz A. Divalent cations reduce the pH sensitivity of OmpF channel inducing the pKashift of key acidic residues. Phys Chem Chem Phys 2011; 13:563-9. [DOI: 10.1039/c0cp01325k] [Citation(s) in RCA: 15] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022]
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19
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Aguilella VM, Queralt-Martín M, Aguilella-Arzo M, Alcaraz A. Insights on the permeability of wide protein channels: measurement and interpretation of ion selectivity. Integr Biol (Camb) 2010; 3:159-72. [PMID: 21132209 DOI: 10.1039/c0ib00048e] [Citation(s) in RCA: 46] [Impact Index Per Article: 3.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022]
Abstract
Ion channels are hollow proteins that have evolved to exhibit discrimination between charged solutes. This property, known as ion selectivity is critical for several biological functions. By using the bacterial porin OmpF as a model system of wide protein channels, we demonstrate that significant insights can be gained when selectivity measurements are combined with electrodiffusion continuum models and simulations based on the atomic structure. A correct interpretation of the mechanisms ruling the many sources of channel discrimination is a first, indispensable step for the understanding of the controlled movement of ions into or out of cells characteristic of many physiological processes. We conclude that the scattered information gathered from several independent approaches should be appropriately merged to provide a unified and coherent picture of the channel selectivity.
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Affiliation(s)
- Vicente M Aguilella
- Dept. Physics, Lab. Molecular Biophysics, Universitat Jaume I, 12080 Castellón, Spain.
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García-Giménez E, López ML, Aguilella VM, Alcaraz A. Linearity, saturation and blocking in a large multiionic channel: divalent cation modulation of the OmpF porin conductance. Biochem Biophys Res Commun 2010; 404:330-4. [PMID: 21134352 DOI: 10.1016/j.bbrc.2010.11.118] [Citation(s) in RCA: 13] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/10/2010] [Accepted: 11/27/2010] [Indexed: 11/16/2022]
Abstract
Measurement of unitary conductance is a fundamental step in the characterization of a protein ion channel permeabilizing a membrane. We study here the effect of salts of divalent cations on the OmpF channel conductance with a particular emphasis in dissecting the role of the electrolyte itself, the role of the counterion accumulation induced by the protein channel charges and other effects not found in salts of monovalent cations. We show that current saturation and blocking are not exclusive properties of narrow (single-file) ion channels but may be observed in large, multiionic channels like bacterial porins. Single-channel conductance measurements performed over a wide range of salt concentrations (up to 3 M) combined with continuum electrodiffusion calculations demonstrate that current saturation cannot be simply ascribed to ion interaction with protein channel residues.
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Affiliation(s)
- Elena García-Giménez
- Laboratory of Molecular Biophysics, Department of Physics, Universitat Jaume I, Av. Sos Baynat s/n, 12080 Castellón, Spain
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López ML, García-Giménez E, Aguilella VM, Alcaraz A. Critical assessment of OmpF channel selectivity: merging information from different experimental protocols. JOURNAL OF PHYSICS. CONDENSED MATTER : AN INSTITUTE OF PHYSICS JOURNAL 2010; 22:454106. [PMID: 21339594 DOI: 10.1088/0953-8984/22/45/454106] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/30/2023]
Abstract
The ion selectivity of a channel can be quantified in several ways by using different experimental protocols. A wide, mesoscopic channel, the OmpF porin of the outer membrane of E. coli, serves as a case study for comparing and analysing several measures of the channel cation-anion permeability in chlorides of alkali metals (LiCl, NaCl, KCl, CsCl). We show how different insights can be gained and integrated to rationalize the global image of channel selectivity. To this end, reversal potential, channel conductance and bi-ionic potential (two different salts with a common anion on each side of the channel but with the same concentration) experiments are discussed in light of an electrodiffusion model based on the Poisson-Nernst-Planck formalism. Measurements and calculations based on the atomic crystal structure of the channel show that each protocol displays a particular balance between the different sources of selectivity.
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Affiliation(s)
- M L López
- Department of Physics, Laboratory of Molecular Biophysics, Universitat Jaume I, Avenida Sos Baynat s/n, 12080 Castellón, Spain
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García-Giménez E, Alcaraz A, Aguilella VM. Overcharging below the nanoscale: multivalent cations reverse the ion selectivity of a biological channel. PHYSICAL REVIEW. E, STATISTICAL, NONLINEAR, AND SOFT MATTER PHYSICS 2010; 81:021912. [PMID: 20365600 DOI: 10.1103/physreve.81.021912] [Citation(s) in RCA: 25] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 09/01/2009] [Revised: 12/14/2009] [Indexed: 05/29/2023]
Abstract
We report charge inversion within a nanoscopic biological protein ion channel in salts of multivalent ions. The presence of positive divalent and trivalent counterions reverses the cationic selectivity of the OmpF channel, a general diffusion porin located in the outer membrane of E. coli. We discuss the conditions under which charge inversion can be inferred from the change in sign of the measured quantity, the channel zero current potential. By comparing experimental results in protein channels whose charge has been modified after site-directed mutagenesis, the predictions of current theories of charge inversion are critically examined. It is emphasized that charge inversion does not necessarily increase with the bare surface charge density of the interface and that even this concept of surface charge density may become meaningless in some biological ion channels. Thus, any theory based on electrostatic correlations or chemical binding should explicitly take into account the particular structure of the charged interface.
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Affiliation(s)
- Elena García-Giménez
- Department of Physics, Laboratory of Molecular Biophysics, University Jaume I, Avenida Sos Baynat, s/n 12080 Castellón, Spain
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