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Călinescu O, Paulino C, Kühlbrandt W, Fendler K. Keeping it simple, transport mechanism and pH regulation in Na+/H+ exchangers. J Biol Chem 2014; 289:13168-76. [PMID: 24644283 PMCID: PMC4036328 DOI: 10.1074/jbc.m113.542993] [Citation(s) in RCA: 33] [Impact Index Per Article: 3.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/23/2022] Open
Abstract
Na+/H+ exchangers are essential for regulation of intracellular proton and sodium concentrations in all living organisms. We examined and experimentally verified a kinetic model for Na+/H+ exchangers, where a single binding site is alternatively occupied by Na+ or one or two H+ ions. The proposed transport mechanism inherently down-regulates Na+/H+ exchangers at extreme pH, preventing excessive cytoplasmic acidification or alkalinization. As an experimental test system we present the first electrophysiological investigation of an electroneutral Na+/H+ exchanger, NhaP1 from Methanocaldococcus jannaschii (MjNhaP1), a close homologue of the medically important eukaryotic NHE Na+/H+ exchangers. The kinetic model describes the experimentally observed substrate dependences of MjNhaP1, and the transport mechanism explains alkaline down-regulation of MjNhaP1. Because this model also accounts for acidic down-regulation of the electrogenic NhaA Na+/H+ exchanger from Escherichia coli (EcNhaA, shown in a previous publication) we conclude that it applies generally to all Na+/H+ exchangers, electrogenic as well as electroneutral, and elegantly explains their pH regulation. Furthermore, the electrophysiological analysis allows insight into the electrostatic structure of the translocation complex in electroneutral and electrogenic Na+/H+ exchangers.
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52
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Vošahlíková M, Jurkiewicz P, Roubalová L, Hof M, Svoboda P. High- and low-affinity sites for sodium in δ-OR-Gi1α (Cys (351)-Ile (351)) fusion protein stably expressed in HEK293 cells; functional significance and correlation with biophysical state of plasma membrane. Naunyn Schmiedebergs Arch Pharmacol 2014; 387:487-502. [PMID: 24577425 DOI: 10.1007/s00210-014-0962-8] [Citation(s) in RCA: 11] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/15/2013] [Accepted: 02/10/2014] [Indexed: 12/31/2022]
Abstract
The effect of sodium, potassium, and lithium on δ-opioid receptor ligand binding parameters and coupling with the cognate G proteins was compared in model HEK293 cell line stably expressing PTX-insensitive δ-OR-Gi1α (Cys(351)-Ile(351)) fusion protein. Agonist [(3)H]DADLE binding was decreased in the order Na(+) ≫ Li(+) > K(+) > (+)NMDG. When plotted as a function of increasing NaCl concentrations, the binding was best-fitted with a two-phase exponential decay considering two Na(+)-responsive sites (r (2) = 0.99). High-affinity Na(+)-sites were characterized by Kd = 7.9 mM and represented 25 % of the basal level determined in the absence of ions. The remaining 75 % represented the low-affinity sites (Kd = 463 mM). Inhibition of [(3)H]DADLE binding by lithium, potassium, and (+)-NMDG proceeded in low-affinity manner only. Surprisingly, the affinity/potency of DADLE-stimulated [(35)S]GTPγS binding was increased in a reverse order: Na(+) < K(+) < Li(+). This result was demonstrated in PTX-treated as well as PTX-untreated cells. Therefore, it is not restricted to Gi1α(Cys(351)-Ile(351)) within the δ-OR-Gi1α fusion protein, but is also valid for stimulation of endogenous G proteins of Gi/Go family in HEK293 cells. Biophysical studies of interaction of ions with polar head-group region of lipids using Laurdan generalized polarization indicated the low-affinity type of interaction only proceeding in the order: Cs(+) < K(+) < Na(+) < Li(+). The results are discussed in terms of interaction of Na(+), K(+) and Li(+) with the high- and low-affinity sites located in water-accessible part of δ-OR binding pocket. We also consider the role of negatively charged Cl(-), Br(-), and I(-) counter anions in inhibition of both [(3)H]DADLE and [(35)S]GTPγS binding.
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Affiliation(s)
- Miroslava Vošahlíková
- Institute of Physiology, Academy of Sciences of the Czech Republic v.v.i., Vídeňská 1083, 14220, Prague 4, Czech Republic
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53
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Raudino A, Marrink SJ, Pannuzzo M. Anomalous viscosity effect in the early stages of the ion-assisted adhesion/fusion event between lipid bilayers: a theoretical and computational study. J Chem Phys 2014; 138:234901. [PMID: 23802979 DOI: 10.1063/1.4809993] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/14/2022] Open
Abstract
The effect of viscosity on the encounter rate of two interacting membranes was investigated by combining a non-equilibrium Fokker-Planck model together with extensive Molecular Dynamics (MD) calculations. The encounter probability and stabilization of transient contact points represent the preliminary steps toward short-range adhesion and fusion of lipid leaflets. To strengthen our analytical model, we used a Coarse Grained MD method to follow the behavior of two charged palmitoyl oleoyl phosphatidylglycerol membranes embedded in a electrolyte-containing box at different viscosity regimes. Solvent friction was modulated by varying the concentration of a neutral, water-soluble polymer, polyethylene glycol, while contact points were stabilized by divalent ions that form bridges among juxtaposed membranes. While a naïve picture foresees a monotonous decrease of the membranes encounter rate with solvent viscosity, both the analytical model and MD simulations show a complex behavior. Under particular conditions, the encounter rate could exhibit a maximum at a critical viscosity value or for a critical concentration of bridging ions. These results seem to be confirmed by experimental observations taken from the literature.
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Affiliation(s)
- Antonio Raudino
- Dipartimento di Scienze Chimiche, Università di Catania, Viale A. Doria 6, 95125 Catania, Italy.
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54
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Redondo-Morata L, Giannotti MI, Sanz F. Structural impact of cations on lipid bilayer models: Nanomechanical properties by AFM-force spectroscopy. Mol Membr Biol 2013; 31:17-28. [DOI: 10.3109/09687688.2013.868940] [Citation(s) in RCA: 39] [Impact Index Per Article: 3.5] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/07/2023]
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55
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Sacconi A, Moncelli MR, Margheri G, Tadini-Buoninsegni F. Enhanced adsorption of Ca-ATPase containing vesicles on a negatively charged solid-supported-membrane for the investigation of membrane transporters. LANGMUIR : THE ACS JOURNAL OF SURFACES AND COLLOIDS 2013; 29:13883-13889. [PMID: 24131452 DOI: 10.1021/la4034386] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/02/2023]
Abstract
A convenient model system for a biological membrane is a solid-supported membrane (SSM), which consists of a gold-supported alkanethiol|phospholipid bilayer. In combination with a concentration jump method, SSMs have been used for the investigation of several membrane transporters. Vesicles incorporating sarcoplasmic reticulum Ca-ATPase (SERCA) were adsorbed on a negatively charged SSM (octadecanethiol|phosphatidylserine bilayer). The current signal generated by the adsorbed vesicles following an ATP concentration jump was compared to that produced by SERCA-containing vesicles adsorbed on a conventional SSM (octadecanethiol|phosphatidylcholine bilayer). A significantly higher current amplitude was recorded on the serine-based SSM. The adsorption of SERCA-incorporating vesicles on the SSM was then characterized by surface plasmon resonance (SPR). The SPR measurements clearly indicate that in the presence of Ca(2+) and Mg(2+), the amount of adsorbed vesicles on the serine-based SSM is about twice that obtained using the conventional SSM, thereby demonstrating that the higher current amplitude recorded on the negatively charged SSM is correlated with a greater quantity of adsorbed vesicles. The enhanced adsorption of membrane vesicles on the PS-based SSM may be useful to study membrane preparations with a low concentration of transport protein generating small current signals, as in the case of various recombinantly expressed proteins.
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Affiliation(s)
- Alessio Sacconi
- Department of Chemistry "Ugo Schiff", University of Florence , via della Lastruccia 3, 50019 Sesto Fiorentino, Italy
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56
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Harb FF, Tinland B. Effect of ionic strength on dynamics of supported phosphatidylcholine lipid bilayer revealed by FRAPP and Langmuir-Blodgett transfer ratios. LANGMUIR : THE ACS JOURNAL OF SURFACES AND COLLOIDS 2013; 29:5540-5546. [PMID: 23581462 DOI: 10.1021/la304962n] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/02/2023]
Abstract
To determine how lipid bilayer/support interactions are affected by ionic strength, we carried out lipid diffusion coefficient measurements by fluorescence recovery after patterned photobleaching (FRAPP) and transfer ratio measurements using a Langmuir balance on supported bilayers of phosphatidylcholine lipids. The main effect of increasing ionic strength is shown to be enhanced diffusion of the lipids due to a decrease in the electrostatic interaction between the bilayer and the support. We experimentally confirm that the two main parameters governing bilayer behavior are electrostatic interaction and bilayer/support distance. Both these parameters can therefore be used to vary the potential that acts on the bilayer. Additionally, our findings show that FRAPP is an extremely sensitive tool to study interaction effects: here, variations in diffusion coefficient as well as the presence or absence of leaflet decoupling.
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57
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Haverkort F, Stradomska A, de Vries AH, Knoester J. Investigating the Structure of Aggregates of an Amphiphilic Cyanine Dye with Molecular Dynamics Simulations. J Phys Chem B 2013; 117:5857-67. [DOI: 10.1021/jp4005696] [Citation(s) in RCA: 18] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/30/2022]
Affiliation(s)
- Frank Haverkort
- Zernike Institute for Advanced
Materials, University of Groningen, Nijenborgh
4, 9747 AG Groningen, The Netherlands
| | - Anna Stradomska
- Zernike Institute for Advanced
Materials, University of Groningen, Nijenborgh
4, 9747 AG Groningen, The Netherlands
| | - Alex H. de Vries
- Zernike Institute for Advanced
Materials, University of Groningen, Nijenborgh
4, 9747 AG Groningen, The Netherlands
- Groningen Biomolecular Sciences
and Biotechnology Institute, University of Groningen, Nijenborgh 7, 9747 AG Groningen, The Netherlands
| | - Jasper Knoester
- Zernike Institute for Advanced
Materials, University of Groningen, Nijenborgh
4, 9747 AG Groningen, The Netherlands
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58
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Schwierz N, Horinek D, Netz RR. Anionic and cationic Hofmeister effects on hydrophobic and hydrophilic surfaces. LANGMUIR : THE ACS JOURNAL OF SURFACES AND COLLOIDS 2013; 29:2602-14. [PMID: 23339330 DOI: 10.1021/la303924e] [Citation(s) in RCA: 170] [Impact Index Per Article: 15.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/20/2023]
Abstract
Using a two-step modeling approach, we address the full spectrum of direct, reversed, and altered ionic sequences as the charge of the ion, the charge of the surface, and the surface polarity are varied. From solvent-explicit molecular dynamics simulations, we extract single-ion surface interaction potentials for halide and alkali ions at hydrophilic and hydrophobic surfaces. These are used within Poisson-Boltzmann theory to calculate ion density and electrostatic potential distributions at mixed polar/unpolar surfaces for varying surface charge. The resulting interfacial tension increments agree quantitatively with experimental data and capture the Hofmeister series, especially the anomaly of lithium, which is difficult to obtain using continuum theory. Phase diagrams that feature different Hofmeister series as a function of surface charge, salt concentration, and surface polarity are constructed from the long-range force between two surfaces interacting across electrolyte solutions. Large anions such as iodide have a high hydrophobic surface affinity and increase the effective charge magnitude on negatively charged unpolar surfaces. Large cations such as cesium also have a large hydrophobic surface affinity and thereby compensate an external negative charge surface charge most efficiently, which explains the well-known asymmetry between cations and anions. On the hydrophilic surface, the size-dependence of the ion surface affinity is reversed, explaining the Hofmeister series reversal when comparing hydrophobic with hydrophilic surfaces.
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Affiliation(s)
- Nadine Schwierz
- Fachbereich für Physik, Freie Universität Berlin, 141954 Berlin, Germany
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59
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Pokorna S, Jurkiewicz P, Cwiklik L, Vazdar M, Hof M. Interactions of monovalent salts with cationic lipid bilayers. Faraday Discuss 2013; 160:341-58; discussion 389-403. [DOI: 10.1039/c2fd20098h] [Citation(s) in RCA: 14] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022]
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60
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Rycovska A, Hatahet L, Fendler K, Michel H. The nitrite transport protein NirC from Salmonella typhimurium is a nitrite/proton antiporter. BIOCHIMICA ET BIOPHYSICA ACTA-BIOMEMBRANES 2012; 1818:1342-50. [DOI: 10.1016/j.bbamem.2012.02.004] [Citation(s) in RCA: 20] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Track Full Text] [Subscribe] [Scholar Register] [Received: 08/12/2011] [Revised: 02/01/2012] [Accepted: 02/06/2012] [Indexed: 12/31/2022]
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61
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Specific thermoresponsiveness of PMMA-block-PDMAEMA to selected ions and other factors in aqueous solution. Colloid Polym Sci 2012. [DOI: 10.1007/s00396-012-2651-9] [Citation(s) in RCA: 23] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/25/2022]
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62
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Structure, dynamics, and hydration of POPC/POPS bilayers suspended in NaCl, KCl, and CsCl solutions. BIOCHIMICA ET BIOPHYSICA ACTA-BIOMEMBRANES 2012; 1818:609-16. [DOI: 10.1016/j.bbamem.2011.11.033] [Citation(s) in RCA: 90] [Impact Index Per Article: 7.5] [Reference Citation Analysis] [Track Full Text] [Subscribe] [Scholar Register] [Received: 08/30/2011] [Revised: 11/09/2011] [Accepted: 11/28/2011] [Indexed: 11/24/2022]
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63
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Zimmermann R, Küttner D, Renner L, Kaufmann M, Werner C. Fluidity modulation of phospholipid bilayers by electrolyte ions: insights from fluorescence microscopy and microslit electrokinetic experiments. J Phys Chem A 2012; 116:6519-25. [PMID: 22304400 DOI: 10.1021/jp212364q] [Citation(s) in RCA: 20] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
Abstract
Fluidity and charging of supported bilayer lipid membranes (sBLMs) prepared from 1,2-dioleoyl-sn-glycero-3-phosphatidylcholine (DOPC) were studied by fluorescence recovery after photobleaching (FRAP) and microslit electrokinetic measurements at varying pH and ionic composition of the electrolyte. Measurements in neutral electrolytes (KCl, NaCl) revealed a strong correlation between the membrane fluidity and the membrane charging due to unsymmetrical water ion adsorption (OH(-) ≫ H(3)O(+)). The membrane fluidity significantly decreased below the isoelectric point of 3.9, suggesting a phase transition in the bilayer. The interactions of both chaotropic anions and strongly kosmotropic cations with the zwitterionic lipids were found to be related with nearly unhindered lipid mobility in the acidic pH range. While for the chaotropic anions the observed effect correlates with the increased negative net charge at low pH, no correlation was found between the changes in the membrane fluidity and charge in the presence of kosmotropic cations. We discuss the observed phenomena with respect to the interaction of the electrolyte ions with the lipid headgroup and the influence of this process on the headgroup orientation and hydration as well as on the lipid packaging.
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Affiliation(s)
- Ralf Zimmermann
- Leibniz Institute of Polymer Research Dresden, Max Bergmann Center of Biomaterials Dresden, Hohe Strasse 6, 01069 Dresden, Germany.
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64
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Redondo-Morata L, Oncins G, Sanz F. Force spectroscopy reveals the effect of different ions in the nanomechanical behavior of phospholipid model membranes: the case of potassium cation. Biophys J 2012; 102:66-74. [PMID: 22225799 DOI: 10.1016/j.bpj.2011.10.051] [Citation(s) in RCA: 37] [Impact Index Per Article: 3.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/28/2011] [Revised: 10/06/2011] [Accepted: 10/24/2011] [Indexed: 10/14/2022] Open
Abstract
How do metal cations affect the stability and structure of phospholipid bilayers? What role does ion binding play in the insertion of proteins and the overall mechanical stability of biological membranes? Investigators have used different theoretical and microscopic approaches to study the mechanical properties of lipid bilayers. Although they are crucial for such studies, molecular-dynamics simulations cannot yet span the complexity of biological membranes. In addition, there are still some experimental difficulties when it comes to testing the ion binding to lipid bilayers in an accurate way. Hence, there is a need to establish a new approach from the perspective of the nanometric scale, where most of the specific molecular phenomena take place. Atomic force microscopy has become an essential tool for examining the structure and behavior of lipid bilayers. In this work, we used force spectroscopy to quantitatively characterize nanomechanical resistance as a function of the electrolyte composition by means of a reliable molecular fingerprint that reveals itself as a repetitive jump in the approaching force curve. By systematically probing a set of bilayers of different composition immersed in electrolytes composed of a variety of monovalent and divalent metal cations, we were able to obtain a wealth of information showing that each ion makes an independent and important contribution to the gross mechanical resistance and its plastic properties. This work addresses the need to assess the effects of different ions on the structure of phospholipid membranes, and opens new avenues for characterizing the (nano)mechanical stability of membranes.
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Affiliation(s)
- Lorena Redondo-Morata
- Institute for Bioengineering of Catalonia, University of Barcelona, Barcelona, Spain
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65
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Hadorn M, Boenzli E, Hotz PE. A quantitative analytical method to test for salt effects on giant unilamellar vesicles. Sci Rep 2011; 1:168. [PMID: 22355683 PMCID: PMC3240971 DOI: 10.1038/srep00168] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/29/2011] [Accepted: 10/21/2011] [Indexed: 11/24/2022] Open
Abstract
Today, free-standing membranes, i.e. liposomes and vesicles, are used in a multitude of
applications, e.g. as drug delivery devices and artificial cell models. Because current
laboratory techniques do not allow handling of large sample sizes, systematic and
quantitative studies on the impact of different effectors, e.g. electrolytes, are limited.
In this work, we evaluated the Hofmeister effects of ten alkali metal halides on giant
unilamellar vesicles made of palmitoyloleoylphosphatidylcholine for a large sample size by
combining the highly parallel water-in-oil emulsion transfer vesicle preparation method with
automatic haemocytometry. We found that this new quantitative screening method is highly
reliable and consistent with previously reported results. Thus, this method may provide a
significant methodological advance in analysis of effects on free-standing model
membranes.
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Affiliation(s)
- Maik Hadorn
- Center for Fundamental Living Technology (FLinT), Department of Physics, Chemistry and Pharmacy, University of Southern Denmark, Odense, Denmark.
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66
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Klasczyk B, Knecht V. Validating affinities for ion-lipid association from simulation against experiment. J Phys Chem A 2011; 115:10587-95. [PMID: 21859136 DOI: 10.1021/jp202928u] [Citation(s) in RCA: 18] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
Abstract
Understanding biological membranes at physiological conditions requires comprehension of the interaction of lipid bilayers with sodium and potassium ions. These cations are adsorbed at palmitoyl-oleoyl-phosphatidylcholine (POPC) bilayers as indicated from previous studies. Here we compare the affinity of Na(+) and K(+) for POPC in molecular dynamics (MD) simulations with recent data from electrophoresis experiments and isothermal calorimetry (ITC) at neutral pH. NaCl and KCl were described using GROMOS or parameters matching solution activities on the basis of Kirkwood-Buff theory (KBFF), and K(+) was also described using parameters by Dang et al., all in conjunction with the Berger parameters for the lipids and the SPC water model. Apparent binding constants of GROMOS-Na(+) and KBFF-K(+) are the same within error and in good agreement with values from ITC. Although these force fields yield the same number of bound ions per number of lipids for Na(+) and K(+), they give a larger number of Na(+) ions per surface area compared to K(+), in agreement with the electrophoresis experiments, because Na(+) causes a stronger reduction in the area per lipid than K(+). The intrinsic binding constants, on the other hand, are reproduced by Dang-K(+) but overestimated by GROMOS-Na(+) and KBFF-K(+). That no ion force field reproduces the intrinsic and the apparent binding constant simultaneously arises from the fact that in MD simulations, implicitly meant to mimic neutral pH, pure PC is usually modeled with zero surface charge. In contrast, POPC at neutral conditions in experiment carries a low but significant negative surface charge and is uncharged only at acidic pH as indicated from electrophoretic mobilities. Implications for future simulation and experimental studies are discussed.
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Affiliation(s)
- Benjamin Klasczyk
- Max Planck Institute of Colloids and Interfaces, Science Park Golm, 14424 Potsdam, Germany
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67
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Wilson MA, Wei C, Bjelkmar P, Wallace BA, Pohorille A. Molecular dynamics simulation of the antiamoebin ion channel: linking structure and conductance. Biophys J 2011; 100:2394-402. [PMID: 21575573 DOI: 10.1016/j.bpj.2011.03.054] [Citation(s) in RCA: 30] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/19/2010] [Revised: 03/21/2011] [Accepted: 03/24/2011] [Indexed: 11/19/2022] Open
Abstract
Molecular-dynamics simulations were carried out to ascertain which of the potential multimeric forms of the transmembrane peptaibol channel, antiamoebin, is consistent with its measured conductance. Estimates of the conductance obtained through counting ions that cross the channel and by solving the Nernst-Planck equation yield consistent results, indicating that the motion of ions inside the channel can be satisfactorily described as diffusive. The calculated conductance of octameric channels is markedly higher than the conductance measured in single channel recordings, whereas the tetramer appears to be nonconducting. The conductance of the hexamer was estimated to be 115 ± 34 pS and 74 ± 20 pS, at 150 mV and 75 mV, respectively, in satisfactory agreement with the value of 90 pS measured at 75 mV. On this basis, we propose that the antiamoebin channel consists of six monomers. Its pore is large enough to accommodate K⁺ and Cl⁻ with their first solvation shells intact. The free energy barrier encountered by K⁺ is only 2.2 kcal/mol whereas Cl⁻ encounters a substantially higher barrier of nearly 5 kcal/mol. This difference makes the channel selective for cations. Ion crossing events are shown to be uncorrelated and follow Poisson statistics.
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Affiliation(s)
- Michael A Wilson
- Department of Pharmaceutical Chemistry, University of California, San Francisco, California, USA
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68
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Wang C, Ge Y, Mortensen J, Westh P. Interaction Free Energies of Eight Sodium Salts and a Phosphatidylcholine Membrane. J Phys Chem B 2011; 115:9955-61. [DOI: 10.1021/jp112203p] [Citation(s) in RCA: 12] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Affiliation(s)
- Chunhua Wang
- Research Unit for Functional Biomaterials, Roskilde University NSM, 1 Universitetsvej DK-4000 Roskilde, Denmark
- MEMPHYS — Center for Biomembrane Physics, Department of Physics and Chemistry, University of Southern Denmark, Campusvej 55, DK-5230 Odense M, Denmark
| | - Ying Ge
- Research Unit for Functional Biomaterials, Roskilde University NSM, 1 Universitetsvej DK-4000 Roskilde, Denmark
| | - John Mortensen
- Research Unit for Functional Biomaterials, Roskilde University NSM, 1 Universitetsvej DK-4000 Roskilde, Denmark
| | - Peter Westh
- Research Unit for Functional Biomaterials, Roskilde University NSM, 1 Universitetsvej DK-4000 Roskilde, Denmark
- MEMPHYS — Center for Biomembrane Physics, Department of Physics and Chemistry, University of Southern Denmark, Campusvej 55, DK-5230 Odense M, Denmark
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69
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Mager T, Rimon A, Padan E, Fendler K. Transport mechanism and pH regulation of the Na+/H+ antiporter NhaA from Escherichia coli: an electrophysiological study. J Biol Chem 2011; 286:23570-81. [PMID: 21566125 PMCID: PMC3123120 DOI: 10.1074/jbc.m111.230235] [Citation(s) in RCA: 78] [Impact Index Per Article: 6.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
Using an electrophysiological assay the activity of NhaA was tested in a wide pH range from pH 5.0 to 9.5. Forward and reverse transport directions were investigated at zero membrane potential using preparations with inside-out and right side-out-oriented transporters with Na(+) or H(+) gradients as the driving force. Under symmetrical pH conditions with a Na(+) gradient for activation, both the wt and the pH-shifted G338S variant exhibit highly symmetrical transport activity with bell-shaped pH dependences, but the optimal pH was shifted 1.8 pH units to the acidic range in the variant. In both strains the pH dependence was associated with a systematic increase of the K(m) for Na(+) at acidic pH. Under symmetrical Na(+) concentration with a pH gradient for NhaA activation, an unexpected novel characteristic of the antiporter was revealed; rather than being down-regulated, it remained active even at pH as low as 5. These data allowed a transport mechanism to advance based on competing Na(+) and H(+) binding to a common transport site and a kinetic model to develop quantitatively explaining the experimental results. In support of these results, both alkaline pH and Na(+) induced the conformational change of NhaA associated with NhaA cation translocation as demonstrated here by trypsin digestion. Furthermore, Na(+) translocation was found to be associated with the displacement of a negative charge. In conclusion, the electrophysiological assay allows the revelation of the mechanism of NhaA antiport and sheds new light on the concept of NhaA pH regulation.
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Affiliation(s)
- Thomas Mager
- Max-Planck-Institut für Biophysik, 60438 Frankfurt/Main, Germany
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70
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Petrov M, Cwiklik L, Jungwirth P. Interactions of molecular ions with model phospholipid membranes. ACTA ACUST UNITED AC 2011. [DOI: 10.1135/cccc2011026] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/05/2022]
Abstract
The affinities of a series of biologically relevant ions for a hydrated phospholipid membrane were investigated using molecular dynamics simulation. Interactions of molecular ions, such as guanidinium, tetramethylammonium, and thiocyanate with the bilayer were computationally characterized for the first time. Simulations reveal strong ion specificity. On one hand, ions like guanidinium and thiocyanate adsorb relatively strongly to the headgroup region of the membrane. On the other hand, potassium or chloride interact very weakly with the phospholipids and merely act as neutralizing counterions. Calculations also show that these ions affect differently biophysical properties of the membrane, such as lipid diffusion, headgroup hydration and tilt angle.
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71
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Confining the sodium pump in a phosphoenzyme form: the effect of lead(II) ions. Biophys J 2011; 99:2087-96. [PMID: 20923642 DOI: 10.1016/j.bpj.2010.07.050] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/27/2010] [Revised: 07/22/2010] [Accepted: 07/23/2010] [Indexed: 11/21/2022] Open
Abstract
The effect of Pb(2+) ions on the Na(+),K(+)-ATPase was investigated in detail by means of steady-state fluorescence spectroscopy. Experiments were performed by using the electrochromic styryl dye RH421. It is shown that Pb(2+) ions can bind reversibly to the protein and do not affect the Na(+) and K(+) binding affinities in the E(1) and P-E(2) conformations of the enzyme. The pH titrations indicate that lead(II) favors binding of one H(+) to the P-E(2) conformation in the absence of K(+). A model scheme is proposed that accounts for the experimental results obtained for backdoor phosphorylation of the enzyme in the presence of Pb(2+) ions. Taken together, our results clearly indicate that Pb(2+) bound to the enzyme stabilizes an E(2)-type conformation. In particular, under conditions that promote enzyme phosphorylation, Pb(2+) ions are able to confine the Na(+),K(+)-ATPase into a phosphorylated E(2) state.
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Ferber UM, Kaggwa G, Jarvis SP. Direct imaging of salt effects on lipid bilayer ordering at sub-molecular resolution. EUROPEAN BIOPHYSICS JOURNAL: EBJ 2010; 40:329-38. [PMID: 21153636 DOI: 10.1007/s00249-010-0650-7] [Citation(s) in RCA: 27] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 06/30/2010] [Revised: 10/21/2010] [Accepted: 11/23/2010] [Indexed: 11/29/2022]
Abstract
The interactions of salts with lipid bilayers are known to alter the properties of membranes and therefore influence their structure and dynamics. Sodium and calcium cations penetrate deeply into the headgroup region and bind to the lipids, whereas potassium ions only loosely associate with lipid molecules and mostly remain outside of the headgroup region. We investigated a dipalmitoylphosphatidylcholine (DPPC) bilayer in the gel phase in the presence of all three cations with a concentration of Ca²+ ions an order of magnitude smaller than the Na+ and K+ ions. Our findings indicate that the area per unit cell does not significantly change in these three salt solutions. However the lipid molecules do re-order non-isotropically under the influence of the three different cations. We attribute this reordering to a change in the highly directional intermolecular interactions caused by a variation in the dipole-dipole bonding arising from a tilt of the headgroup out of the membrane plane. Measurements in different NaCl concentrations also show a non-isotropic re-ordering of the lipid molecules.
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Affiliation(s)
- Urs M Ferber
- Conway Institute of Biomolecular and Biomedical Research, University College Dublin, Belfield, Dublin 4, Ireland
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73
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Schulz P, Werner J, Stauber T, Henriksen K, Fendler K. The G215R mutation in the Cl-/H+-antiporter ClC-7 found in ADO II osteopetrosis does not abolish function but causes a severe trafficking defect. PLoS One 2010; 5:e12585. [PMID: 20830208 PMCID: PMC2935355 DOI: 10.1371/journal.pone.0012585] [Citation(s) in RCA: 37] [Impact Index Per Article: 2.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/14/2010] [Accepted: 08/15/2010] [Indexed: 12/25/2022] Open
Abstract
BACKGROUND ClC-7 is a ubiquitous transporter which is broadly expressed in mammalian tissues. It is implied in the pathogenesis of lysosomal storage disease and osteopetrosis. Because of its endosomal/lysosomal localization it is still poorly characterized. METHODOLOGY/PRINCIPAL FINDINGS An electrophysiological characterization of rat ClC-7 using solid-supported membrane-based electrophysiology is presented. The measured currents show the characteristics of ClC-7 and confirm its function as a Cl(-)/H(+)-antiporter. We have used rat ClC-7 in CHO cells as a model system to investigate the functionality and cellular localization of the wt transporter and its variant G213R ClC-7 which is the analogue of human G215R ClC-7 responsible for autosomal dominant osteopetrosis type II. Our study shows that rat G213R ClC-7 is functional but has a localization defect in CHO cells which prevents it from being correctly targeted to the lysosomal membrane. The electrophysiological assay is tested as a tool for drug discovery. The assay is validated with a number of drug candidates. It is shown that ClC-7 is inhibited by DIDS, NPPB and NS5818 at micromolar concentrations. CONCLUSIONS/SIGNIFICANCE It is suggested that the scenario found in the CHO model system also applies to the human transporter and that mislocalization rather than impaired functionality of G215R ClC-7 is the primary cause of the related autosomal dominant osteopetrosis type II. Furthermore, the robust solid-supported membrane-based electrophysiological assay is proposed for rapid screening for potential ClC-7 inhibitors which are discussed for treatment of osteoporosis.
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Affiliation(s)
- Patrick Schulz
- Department of Biophysical Chemistry, Max Planck Institute of Biophysics, Frankfurt, Germany
| | - Johannes Werner
- Department of Biophysical Chemistry, Max Planck Institute of Biophysics, Frankfurt, Germany
| | - Tobias Stauber
- Leibniz-Institut für Molekulare Pharmakologie (FMP) and Max-Delbrück-Centrum für Molekulare Medizin (MDC), Berlin, Germany
| | | | - Klaus Fendler
- Department of Biophysical Chemistry, Max Planck Institute of Biophysics, Frankfurt, Germany
- * E-mail:
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74
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Vácha R, Jurkiewicz P, Petrov M, Berkowitz ML, Böckmann RA, Barucha-Kraszewska J, Hof M, Jungwirth P. Mechanism of Interaction of Monovalent Ions with Phosphatidylcholine Lipid Membranes. J Phys Chem B 2010; 114:9504-9. [DOI: 10.1021/jp102389k] [Citation(s) in RCA: 82] [Impact Index Per Article: 5.9] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/24/2022]
Affiliation(s)
- Robert Vácha
- Institute of Organic Chemistry and Biochemistry, Academy of Sciences of the Czech Republic and Center for Biomolecules and Complex Molecular Systems, Flemingovo nám. 2, 16610 Prague 6, Czech Republic; Department of Chemistry, University of Cambridge, Lensfield Road, Cambridge, CB21EW, United Kingdom; J. Heyrovský Institute of Physical Chemistry, Academy of Sciences of the Czech Republic, v. v. i., Dolejškova 3, 18223 Prague 8, Czech Republic; Department of Chemistry, University of North Carolina, Chapel
| | - Piotr Jurkiewicz
- Institute of Organic Chemistry and Biochemistry, Academy of Sciences of the Czech Republic and Center for Biomolecules and Complex Molecular Systems, Flemingovo nám. 2, 16610 Prague 6, Czech Republic; Department of Chemistry, University of Cambridge, Lensfield Road, Cambridge, CB21EW, United Kingdom; J. Heyrovský Institute of Physical Chemistry, Academy of Sciences of the Czech Republic, v. v. i., Dolejškova 3, 18223 Prague 8, Czech Republic; Department of Chemistry, University of North Carolina, Chapel
| | - Michal Petrov
- Institute of Organic Chemistry and Biochemistry, Academy of Sciences of the Czech Republic and Center for Biomolecules and Complex Molecular Systems, Flemingovo nám. 2, 16610 Prague 6, Czech Republic; Department of Chemistry, University of Cambridge, Lensfield Road, Cambridge, CB21EW, United Kingdom; J. Heyrovský Institute of Physical Chemistry, Academy of Sciences of the Czech Republic, v. v. i., Dolejškova 3, 18223 Prague 8, Czech Republic; Department of Chemistry, University of North Carolina, Chapel
| | - Max L. Berkowitz
- Institute of Organic Chemistry and Biochemistry, Academy of Sciences of the Czech Republic and Center for Biomolecules and Complex Molecular Systems, Flemingovo nám. 2, 16610 Prague 6, Czech Republic; Department of Chemistry, University of Cambridge, Lensfield Road, Cambridge, CB21EW, United Kingdom; J. Heyrovský Institute of Physical Chemistry, Academy of Sciences of the Czech Republic, v. v. i., Dolejškova 3, 18223 Prague 8, Czech Republic; Department of Chemistry, University of North Carolina, Chapel
| | - Rainer A. Böckmann
- Institute of Organic Chemistry and Biochemistry, Academy of Sciences of the Czech Republic and Center for Biomolecules and Complex Molecular Systems, Flemingovo nám. 2, 16610 Prague 6, Czech Republic; Department of Chemistry, University of Cambridge, Lensfield Road, Cambridge, CB21EW, United Kingdom; J. Heyrovský Institute of Physical Chemistry, Academy of Sciences of the Czech Republic, v. v. i., Dolejškova 3, 18223 Prague 8, Czech Republic; Department of Chemistry, University of North Carolina, Chapel
| | - Justyna Barucha-Kraszewska
- Institute of Organic Chemistry and Biochemistry, Academy of Sciences of the Czech Republic and Center for Biomolecules and Complex Molecular Systems, Flemingovo nám. 2, 16610 Prague 6, Czech Republic; Department of Chemistry, University of Cambridge, Lensfield Road, Cambridge, CB21EW, United Kingdom; J. Heyrovský Institute of Physical Chemistry, Academy of Sciences of the Czech Republic, v. v. i., Dolejškova 3, 18223 Prague 8, Czech Republic; Department of Chemistry, University of North Carolina, Chapel
| | - Martin Hof
- Institute of Organic Chemistry and Biochemistry, Academy of Sciences of the Czech Republic and Center for Biomolecules and Complex Molecular Systems, Flemingovo nám. 2, 16610 Prague 6, Czech Republic; Department of Chemistry, University of Cambridge, Lensfield Road, Cambridge, CB21EW, United Kingdom; J. Heyrovský Institute of Physical Chemistry, Academy of Sciences of the Czech Republic, v. v. i., Dolejškova 3, 18223 Prague 8, Czech Republic; Department of Chemistry, University of North Carolina, Chapel
| | - Pavel Jungwirth
- Institute of Organic Chemistry and Biochemistry, Academy of Sciences of the Czech Republic and Center for Biomolecules and Complex Molecular Systems, Flemingovo nám. 2, 16610 Prague 6, Czech Republic; Department of Chemistry, University of Cambridge, Lensfield Road, Cambridge, CB21EW, United Kingdom; J. Heyrovský Institute of Physical Chemistry, Academy of Sciences of the Czech Republic, v. v. i., Dolejškova 3, 18223 Prague 8, Czech Republic; Department of Chemistry, University of North Carolina, Chapel
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75
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Schwierz N, Horinek D, Netz RR. Reversed anionic Hofmeister series: the interplay of surface charge and surface polarity. LANGMUIR : THE ACS JOURNAL OF SURFACES AND COLLOIDS 2010; 26:7370-7379. [PMID: 20361734 DOI: 10.1021/la904397v] [Citation(s) in RCA: 206] [Impact Index Per Article: 14.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/26/2023]
Abstract
We describe a two-scale modeling approach toward anion specificity at surfaces of varying charge and polarity. Explicit-solvent atomistic molecular dynamics simulations at neutral hydrophobic (i.e., nonpolar) and neutral hydrophilic (i.e., polar) self-assembled monolayers furnish potentials of mean force for Na(+) and the halide anions F(-), Cl(-), and I(-) which are then used within Poisson-Boltzmann theory to calculate ionic distributions at surfaces of arbitrary charge for finite ion concentration. On the basis of calculated long-ranged electrostatic forces and coagulation properties, we obtain the direct anionic Hofmeister series at negatively charged hydrophobic surfaces. Reversal takes place when going to negative polar or to positive nonpolar surfaces, leading to the indirect series, while for positive polar surfaces the direct series is again obtained. This is in full accordance with a recent experimental classification of colloidal coagulation kinetics and also reflects the trends of the ion specific solubility properties of proteins. A schematic Hofmeister phase diagram is proposed. Partial series reversal is understood as a transient phenomenon for surfaces of intermediate polarity or charge.
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Affiliation(s)
- Nadine Schwierz
- Physik Department, Technische Universität München, 85748 Garching, Germany.
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76
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77
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Raudino A, Pannuzzo M. Nucleation theory with delayed interactions: An application to the early stages of the receptor-mediated adhesion/fusion kinetics of lipid vesicles. J Chem Phys 2010; 132:045103. [DOI: 10.1063/1.3290823] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/31/2022] Open
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78
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Kalcher I, Horinek D, Netz RR, Dzubiella J. Ion specific correlations in bulk and at biointerfaces. JOURNAL OF PHYSICS. CONDENSED MATTER : AN INSTITUTE OF PHYSICS JOURNAL 2009; 21:424108. [PMID: 21715843 DOI: 10.1088/0953-8984/21/42/424108] [Citation(s) in RCA: 18] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/31/2023]
Abstract
Ion specific effects are ubiquitous in any complex colloidal or biological fluid in bulk or at interfaces. The molecular origins of these 'Hofmeister effects' are not well understood and their theoretical description poses a formidable challenge to the modeling and simulation community. On the basis of the combination of atomistically resolved molecular dynamics (MD) computer simulations and statistical mechanics approaches, we present a few selected examples of specific electrolyte effects in bulk, at simple neutral and charged interfaces, and on a short α-helical peptide. The structural complexity in these strongly Coulomb-correlated systems is highlighted and analyzed in the light of available experimental data. While in general the comparison of MD simulations to experiments often lacks quantitative agreement, mostly because molecular force fields and coarse-graining procedures remain to be optimized, the consensus as regards trends provides important insights into microscopic hydration and binding mechanisms.
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Affiliation(s)
- I Kalcher
- Physics Department T37, Technical University Munich, 85748 Garching, Germany
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79
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Schulz P, Dueck B, Mourot A, Hatahet L, Fendler K. Measuring ion channels on solid supported membranes. Biophys J 2009; 97:388-96. [PMID: 19580777 DOI: 10.1016/j.bpj.2009.04.022] [Citation(s) in RCA: 11] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/12/2009] [Revised: 04/06/2009] [Accepted: 04/13/2009] [Indexed: 10/20/2022] Open
Abstract
Application of solid supported membranes (SSMs) for the functional investigation of ion channels is presented. SSM-based electrophysiology, which has been introduced previously for the investigation of active transport systems, is expanded for the analysis of ion channels. Membranes or liposomes containing ion channels are adsorbed to an SSM and a concentration gradient of a permeant ion is applied. Transient currents representing ion channel transport activity are recorded via capacitive coupling. We demonstrate the application of the technique to liposomes reconstituted with the peptide cation channel gramicidin, vesicles from native tissue containing the nicotinic acetylcholine receptor, and membranes from a recombinant cell line expressing the ionotropic P2X2 receptor. It is shown that stable ion gradients, both inside as well as outside directed, can be applied and currents are recorded with an excellent signal/noise ratio. For the nicotinic acetylcholine receptor and the P2X2 receptor excellent assay quality factors of Z' = 0.55 and Z' = 0.67, respectively, are obtained. This technique opens up new possibilities in cases where conventional electrophysiology fails like the functional characterization of ion channels from intracellular compartments. It also allows for robust fully automatic assays for drug screening.
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Affiliation(s)
- Patrick Schulz
- Max Planck Institut für Biophysik, D-60438 Frankfurt/Main, Germany
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80
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Vácha R, Berkowitz ML, Jungwirth P. Molecular model of a cell plasma membrane with an asymmetric multicomponent composition: water permeation and ion effects. Biophys J 2009; 96:4493-501. [PMID: 19486672 PMCID: PMC2711485 DOI: 10.1016/j.bpj.2009.03.010] [Citation(s) in RCA: 57] [Impact Index Per Article: 3.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/05/2008] [Revised: 03/10/2009] [Accepted: 03/11/2009] [Indexed: 10/20/2022] Open
Abstract
We present molecular dynamics simulations of a multicomponent, asymmetric bilayer in mixed aqueous solutions of sodium and potassium chloride. Because of the geometry of the system, there are two aqueous solution regions in our simulations: one mimics the intracellular region, and one mimics the extracellular region. Ion-specific effects are evident at the membrane/aqueous solution interface. Namely, at equal concentrations of sodium and potassium, sodium ions are more strongly adsorbed to carbonyl groups of the lipid headgroups. A significant concentration excess of potassium is needed for this ion to overwhelm the sodium abundance at the membrane. Ion-membrane interactions also lead to concentration-dependent and cation-specific behavior of the electrostatic potential in the intracellular region because of the negative charge on the inner leaflet. In addition, water permeation across the membrane was observed on a timescale of approximately 100 ns. This study represents a step toward the modeling of realistic biological membranes at physiological conditions in intracellular and extracellular environments.
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Affiliation(s)
- Robert Vácha
- Institute of Organic Chemistry and Biochemistry, Academy of Sciences of Czech Republic, and Center for Biomolecules and Complex Molecular Systems, 16610 Prague 6, Czech Republic.
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81
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Vácha R, Siu SWI, Petrov M, Böckmann RA, Barucha-Kraszewska J, Jurkiewicz P, Hof M, Berkowitz ML, Jungwirth P. Effects of Alkali Cations and Halide Anions on the DOPC Lipid Membrane. J Phys Chem A 2009; 113:7235-43. [DOI: 10.1021/jp809974e] [Citation(s) in RCA: 134] [Impact Index Per Article: 8.9] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/30/2022]
Affiliation(s)
- Robert Vácha
- Institute of Organic Chemistry and Biochemistry, Academy of Sciences of the Czech Republic and Center for Biomolecules and Complex Molecular Systems, Flemingovo nám. 2, 16610 Prague 6, Czech Republic, Theoretical & Computational Membrane Biology, Center for Bioinformatics, Saarland University, P.O. Box 15 11 50, 66041 Saarbrücken, Germany, J. Heyrovsky Institute of Physical Chemistry, Academy of Sciences of the Czech Republic, v. v. i., Dolejskova 3, 18223 Prague 8, Czech Republic, and Department of
| | - Shirley W. I. Siu
- Institute of Organic Chemistry and Biochemistry, Academy of Sciences of the Czech Republic and Center for Biomolecules and Complex Molecular Systems, Flemingovo nám. 2, 16610 Prague 6, Czech Republic, Theoretical & Computational Membrane Biology, Center for Bioinformatics, Saarland University, P.O. Box 15 11 50, 66041 Saarbrücken, Germany, J. Heyrovsky Institute of Physical Chemistry, Academy of Sciences of the Czech Republic, v. v. i., Dolejskova 3, 18223 Prague 8, Czech Republic, and Department of
| | - Michal Petrov
- Institute of Organic Chemistry and Biochemistry, Academy of Sciences of the Czech Republic and Center for Biomolecules and Complex Molecular Systems, Flemingovo nám. 2, 16610 Prague 6, Czech Republic, Theoretical & Computational Membrane Biology, Center for Bioinformatics, Saarland University, P.O. Box 15 11 50, 66041 Saarbrücken, Germany, J. Heyrovsky Institute of Physical Chemistry, Academy of Sciences of the Czech Republic, v. v. i., Dolejskova 3, 18223 Prague 8, Czech Republic, and Department of
| | - Rainer A. Böckmann
- Institute of Organic Chemistry and Biochemistry, Academy of Sciences of the Czech Republic and Center for Biomolecules and Complex Molecular Systems, Flemingovo nám. 2, 16610 Prague 6, Czech Republic, Theoretical & Computational Membrane Biology, Center for Bioinformatics, Saarland University, P.O. Box 15 11 50, 66041 Saarbrücken, Germany, J. Heyrovsky Institute of Physical Chemistry, Academy of Sciences of the Czech Republic, v. v. i., Dolejskova 3, 18223 Prague 8, Czech Republic, and Department of
| | - Justyna Barucha-Kraszewska
- Institute of Organic Chemistry and Biochemistry, Academy of Sciences of the Czech Republic and Center for Biomolecules and Complex Molecular Systems, Flemingovo nám. 2, 16610 Prague 6, Czech Republic, Theoretical & Computational Membrane Biology, Center for Bioinformatics, Saarland University, P.O. Box 15 11 50, 66041 Saarbrücken, Germany, J. Heyrovsky Institute of Physical Chemistry, Academy of Sciences of the Czech Republic, v. v. i., Dolejskova 3, 18223 Prague 8, Czech Republic, and Department of
| | - Piotr Jurkiewicz
- Institute of Organic Chemistry and Biochemistry, Academy of Sciences of the Czech Republic and Center for Biomolecules and Complex Molecular Systems, Flemingovo nám. 2, 16610 Prague 6, Czech Republic, Theoretical & Computational Membrane Biology, Center for Bioinformatics, Saarland University, P.O. Box 15 11 50, 66041 Saarbrücken, Germany, J. Heyrovsky Institute of Physical Chemistry, Academy of Sciences of the Czech Republic, v. v. i., Dolejskova 3, 18223 Prague 8, Czech Republic, and Department of
| | - Martin Hof
- Institute of Organic Chemistry and Biochemistry, Academy of Sciences of the Czech Republic and Center for Biomolecules and Complex Molecular Systems, Flemingovo nám. 2, 16610 Prague 6, Czech Republic, Theoretical & Computational Membrane Biology, Center for Bioinformatics, Saarland University, P.O. Box 15 11 50, 66041 Saarbrücken, Germany, J. Heyrovsky Institute of Physical Chemistry, Academy of Sciences of the Czech Republic, v. v. i., Dolejskova 3, 18223 Prague 8, Czech Republic, and Department of
| | - Max L. Berkowitz
- Institute of Organic Chemistry and Biochemistry, Academy of Sciences of the Czech Republic and Center for Biomolecules and Complex Molecular Systems, Flemingovo nám. 2, 16610 Prague 6, Czech Republic, Theoretical & Computational Membrane Biology, Center for Bioinformatics, Saarland University, P.O. Box 15 11 50, 66041 Saarbrücken, Germany, J. Heyrovsky Institute of Physical Chemistry, Academy of Sciences of the Czech Republic, v. v. i., Dolejskova 3, 18223 Prague 8, Czech Republic, and Department of
| | - Pavel Jungwirth
- Institute of Organic Chemistry and Biochemistry, Academy of Sciences of the Czech Republic and Center for Biomolecules and Complex Molecular Systems, Flemingovo nám. 2, 16610 Prague 6, Czech Republic, Theoretical & Computational Membrane Biology, Center for Bioinformatics, Saarland University, P.O. Box 15 11 50, 66041 Saarbrücken, Germany, J. Heyrovsky Institute of Physical Chemistry, Academy of Sciences of the Czech Republic, v. v. i., Dolejskova 3, 18223 Prague 8, Czech Republic, and Department of
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82
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Vlachy N, Jagoda-Cwiklik B, Vácha R, Touraud D, Jungwirth P, Kunz W. Hofmeister series and specific interactions of charged headgroups with aqueous ions. Adv Colloid Interface Sci 2009; 146:42-7. [PMID: 18973869 DOI: 10.1016/j.cis.2008.09.010] [Citation(s) in RCA: 321] [Impact Index Per Article: 21.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/16/2008] [Accepted: 09/22/2008] [Indexed: 11/28/2022]
Abstract
In this paper, we propose a Hofmeister-like ordering of charged headgroups. To this purpose we review various literature data and complete them with some new experimental and computational results on interactions of ions with alkyl sulfates and carboxylates. We further combine the proposed headgroup ordering with the law of matching water affinities in order to obtain a general description and predictions of ion-headgroup interactions. Examples from colloidal chemistry and from biological systems are provided to illustrate the power of this approach.
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Affiliation(s)
- Nina Vlachy
- Institute of Physical and Theoretical Chemistry, University of Regensburg, D-93040 Regensburg, Germany
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83
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Leontidis E, Aroti A, Belloni L. Liquid Expanded Monolayers of Lipids As Model Systems to Understand the Anionic Hofmeister Series: 1. A Tale of Models. J Phys Chem B 2009; 113:1447-59. [DOI: 10.1021/jp809443d] [Citation(s) in RCA: 54] [Impact Index Per Article: 3.6] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/17/2022]
Affiliation(s)
- E. Leontidis
- Department of Chemistry, University of Cyprus, Nicosia 1678, Cyprus
| | - A. Aroti
- Department of Chemistry, University of Cyprus, Nicosia 1678, Cyprus
| | - L. Belloni
- CEA/SACLAY, LIONS at Service de Chimie Moléculaire, 91191-Gif-sur-Yvette Cedex, France
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84
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Kotyńska J, Dobrzyńska I, Figaszewski ZA. Effect of monovalent ion adsorption on the electric charge of phosphatidylcholine - decylamine liposomal membranes. J Bioenerg Biomembr 2009; 40:637-41. [PMID: 19139977 DOI: 10.1007/s10863-008-9194-2] [Citation(s) in RCA: 9] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/25/2008] [Accepted: 12/17/2008] [Indexed: 12/01/2022]
Abstract
We examined the effect of adsorbed monovalent ions on the surface charge of phosphatidylcholine (PC) - decylamine (DA) liposomal membranes. Surface charge density values were determined from electrophoretic mobility measurements of lipid vesicles performed at various pH levels. The interaction between solution ions and the PC-DA liposomal surface was described by a six component equilibrium model. The previously determined association constants of the -PO((-)) and -N((+))(CH(3))(3) groups of PC with H(+), OH(-), Na(+) and Cl(-) ions (K (A1H), K (B1OH), K (A1Na), K (B1C1)) were used to calculate K (B2OH), and K (B2C1), the association constants of the -N((+))H(3) group of DA with OH(-) and Cl(-) ions, providing an experimental verification for the proposed model.
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Affiliation(s)
- Joanna Kotyńska
- Institute of Chemistry, University of Bialystok, Al. Pilsudskiego 11/4, 15-443, Bialystok, Poland
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85
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Krause R, Watzke N, Kelety B, Dörner W, Fendler K. An automatic electrophysiological assay for the neuronal glutamate transporter mEAAC1. J Neurosci Methods 2008; 177:131-41. [PMID: 18996149 DOI: 10.1016/j.jneumeth.2008.10.005] [Citation(s) in RCA: 15] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/04/2008] [Revised: 09/30/2008] [Accepted: 10/02/2008] [Indexed: 11/26/2022]
Abstract
A rapid and robust electrophysiological assay based on solid supported membranes (SSM) for the murine neuronal glutamate transporter mEAAC1 is presented. Measurements at different concentrations revealed the EAAC1 specific affinities for l-glutamate (K(m)=24microM), l-aspartate (K(m)=5microM) and Na(+) (K(m)=33mM) and an inhibition constant K(i) for dl-threo-beta-benzyloxyaspartic acid (TBOA) of 1microM. Inhibition by 3-hydroxy-4,5,6,6a-tetrahydro-3aH-pyrrolo[3,4-d]isoxazole-6-carboxylic acid (HIP-B) was not purely competitive with an IC(50) of 13microM. Experiments using SCN(-) concentration jumps yielded large transient currents in the presence of l-glutamate showing the characteristics of the glutamate-gated anion conductance of EAAC1. Thus, SSM-based electrophysiology allows the analysis of all relevant transport modes of the glutamate transporter on the same sample. K(+) and Na(+) gradients could be applied to the transporter. Experiments in the presence and absence of Na(+) and K(+) gradients demonstrated that the protein is still able to produce a charge translocation when no internal K(+) is present. In this case, the signal amplitude is smaller and a lower apparent affinity for l-glutamate of 144microM is found. Finally the assay was adapted to a commercial fully automatic system for SSM-based electrophysiology and was validated by determining the substrate affinities and inhibition constants as for the laboratory setup. The combination of automatic function and its ability to monitor all transport modes of EAAC1 make this system an universal tool for industrial drug discovery.
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Affiliation(s)
- Robin Krause
- Max-Planck-Institute für Biophysik, Max-von-Laue Str. 3, D-60438 Frankfurt am Main, Germany
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86
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Garcia-Celma JJ, Dueck B, Stein M, Schlueter M, Meyer-Lipp K, Leblanc G, Fendler K. Rapid activation of the melibiose permease MelB immobilized on a solid-supported membrane. LANGMUIR : THE ACS JOURNAL OF SURFACES AND COLLOIDS 2008; 24:8119-8126. [PMID: 18572928 DOI: 10.1021/la800428h] [Citation(s) in RCA: 28] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/26/2023]
Abstract
Rapid solution exchange on a solid-supported membrane (SSM) is investigated using fluidic structures and a solid-supported membrane of 1 mm diameter in wall jet geometry. The flow is analyzed with a new technique based on specific ion interactions with the surface combined with an electrical measurement. The critical parameters affecting the time course of the solution exchange and the transfer function describing the time resolution of the SSM system are determined. The experimental data indicate that solution transport represents an intermediate situation between the plug flow and the Hagen-Poiseuille laminar flow regime. However, to a good approximation the rise of the surface concentration can be described by Hagen-Poiseuille flow with ideal mixing at the surface of the SSM. Using an improved cuvette design, solution exchange as fast as 2 ms was achieved at the surface of a solid-supported membrane. As an application of the technique, the rate constant of a fast electrogenic reaction in the melibiose permease MelB, a bacterial ( Escherichia coli) sugar transporter, is determined. For comparison, the kinetics of a conformational transition of the same transporter was measured using stopped-flow tryptophan fluorescence spectroscopy. The relaxation time constant obtained for the charge displacement agrees with that determined in the stopped-flow experiments. This demonstrates that upon sugar binding MelB undergoes an electrogenic conformational transition with a rate constant of k approximately 250 s (-1).
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Affiliation(s)
- Juan J Garcia-Celma
- Department of Biophysical Chemistry, Max Planck Institute of Biophysics, D-60438 Frankfurt, Germany
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87
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Schulz P, Garcia-Celma JJ, Fendler K. SSM-based electrophysiology. Methods 2008; 46:97-103. [PMID: 18675360 DOI: 10.1016/j.ymeth.2008.07.002] [Citation(s) in RCA: 73] [Impact Index Per Article: 4.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/20/2008] [Revised: 06/12/2008] [Accepted: 07/02/2008] [Indexed: 10/21/2022] Open
Abstract
An assay technique for the electrical characterization of electrogenic transport proteins on solid supported membranes is presented. Membrane vesicles, proteoliposomes or membrane fragments containing the transporter are adsorbed to the solid supported membrane and are activated by providing a substrate or a ligand via a rapid solution exchange. This technique opens up new possibilities where conventional electrophysiology fails like transporters or ion channels from bacteria and from intracellular compartments. Its rugged design and potential for automation make it suitable for drug screening.
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Affiliation(s)
- Patrick Schulz
- Department of Biophysical Chemistry, Max Planck Institute of Biophysics, Max von Laue Str. 3, D-60438 Frankfurt/Main, Germany
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