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16 pages, 1139 KiB

Open AccessArticle

Lipid Membrane State Change by Catalytic Protonation and the Implications for Synaptic Transmission

by Christian Fillafer, Yana S. Koll and Matthias F. Schneider

Membranes 2022, 12(1), 5; https://doi.org/10.3390/membranes12010005 - 21 Dec 2021

Viewed by 2061

In cholinergic synapses, the neurotransmitter acetylcholine (ACh) is rapidly hydrolyzed by esterases to choline and acetic acid (AH). It is believed that this reaction serves the purpose of deactivating ACh once it has exerted its effect on a receptor protein (AChR). The protons [...] Read more.

In cholinergic synapses, the neurotransmitter acetylcholine (ACh) is rapidly hydrolyzed by esterases to choline and acetic acid (AH). It is believed that this reaction serves the purpose of deactivating ACh once it has exerted its effect on a receptor protein (AChR). The protons liberated in this reaction, however, may by themselves excite the postsynaptic membrane. Herein, we investigated the response of cell membrane models made from phosphatidylcholine (PC), phosphatidylserine (PS) and phosphatidic acid (PA) to ACh in the presence and absence of acetylcholinesterase (AChE). Without a catalyst, there were no significant effects of ACh on the membrane state (lateral pressure change

\leq 0.5

mN/m). In contrast, strong responses were observed in membranes made from PS and PA when ACh was applied in presence of AChE (>5 mN/m). Control experiments demonstrated that this effect was due to the protonation of lipid headgroups, which is maximal at the pK (for PS:

{pK}_{COOH} \approx 5.0

; for PA:

{pK}_{{HPO}_{4}^{-}} \approx 8.5

). These findings are physiologically relevant, because both of these lipids are present in postsynaptic membranes. Furthermore, we discussed evidence which suggests that AChR assembles a lipid-protein interface that is proton-sensitive in the vicinity of pH

7.5

. Such a membrane could be excited by hydrolysis of micromolar amounts of ACh. Based on these results, we proposed that cholinergic transmission is due to postsynaptic membrane protonation. Our model will be falsified if cholinergic membranes do not respond to acidification. Full article

(This article belongs to the Special Issue Electrostatics in Cell Membranes and in Artificial Membrane Models)

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11 pages, 1986 KiB

Open AccessArticle

Free Energy Analyses of Cell-Penetrating Peptides Using the Weighted Ensemble Method

by Seungho Choe

Membranes 2021, 11(12), 974; https://doi.org/10.3390/membranes11120974 - 09 Dec 2021

Cited by 2 | Viewed by 2240

Abstract

Cell-penetrating peptides (CPPs) have been widely used for drug-delivery agents; however, it has not been fully understood how they translocate across cell membranes. The Weighted Ensemble (WE) method, one of the most powerful and flexible path sampling techniques, can be helpful to reveal [...] Read more.

Cell-penetrating peptides (CPPs) have been widely used for drug-delivery agents; however, it has not been fully understood how they translocate across cell membranes. The Weighted Ensemble (WE) method, one of the most powerful and flexible path sampling techniques, can be helpful to reveal translocation paths and free energy barriers along those paths. Within the WE approach we show how Arg

_{9}

(nona-arginine) and Tat interact with a DOPC/DOPG(4:1) model membrane, and we present free energy (or potential mean of forces, PMFs) profiles of penetration, although a translocation across the membrane has not been observed in the current simulations. Two different compositions of lipid molecules were also tried and compared. Our approach can be applied to any CPPs interacting with various model membranes, and it will provide useful information regarding the transport mechanisms of CPPs. Full article

(This article belongs to the Special Issue Electrostatics in Cell Membranes and in Artificial Membrane Models)

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12 pages, 25188 KiB

Open AccessArticle

Phosphodiesterase Type 5 Inhibitors Greatly Affect Physicochemical Properties of Model Lipid Membranes

by Anastasiia A. Zakharova, Svetlana S. Efimova and Olga S. Ostroumova

Membranes 2021, 11(11), 893; https://doi.org/10.3390/membranes11110893 - 19 Nov 2021

Cited by 2 | Viewed by 1570

Abstract

Although phosphodiesterase type 5 inhibitors are widely used and well-studied drugs, the potential benefits of their application in the treatment of various diseases and new drug delivery systems, including liposome forms, are still being discussed. In this regard, the role of the lipid [...] Read more.

Although phosphodiesterase type 5 inhibitors are widely used and well-studied drugs, the potential benefits of their application in the treatment of various diseases and new drug delivery systems, including liposome forms, are still being discussed. In this regard, the role of the lipid matrix of cell membranes in the pharmacological action of the inhibitors is of special interest. It was shown that sildenafil, vardenafil, and tadalafil caused a significant decrease in the boundary potential of model membranes composed of palmitoyloleoylphosphatidylcholine or its mixture with cholesterol, by 70–80 mV. The reduction in the membrane dipole potential induced by inhibitors led to a 20–25% increase in the conductance of cation-selective pores formed by the antimicrobial peptide gramicidin A. The addition of sildenafil or vardenafil also led to a significant decrease in the temperature of the main phase transition of dipalmytoylphosphatidylcholine, by about 1.5 °C, while tadalafil did not change the melting temperature. Sildenafil, vardenafil, and tadalafil enhanced the pore-forming activity of the antifungal polyene antibiotic nystatin by 11, 13, and 2 times, respectively. This fact might indicate the induction of membrane curvature stress by the inhibitors. The data obtained might be of special interest for the development of lipid-mediated forms of drugs. Full article

(This article belongs to the Special Issue Electrostatics in Cell Membranes and in Artificial Membrane Models)

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21 pages, 21394 KiB

Open AccessArticle

Exploring the Conformational Changes Induced by Nanosecond Pulsed Electric Fields on the Voltage Sensing Domain of a Ca²⁺ Channel

by Alvaro R. Ruiz-Fernández, Leonardo Campos, Felipe Villanelo, Sebastian E. Gutiérrez-Maldonado and Tomas Perez-Acle

Membranes 2021, 11(7), 473; https://doi.org/10.3390/membranes11070473 - 26 Jun 2021

Cited by 12 | Viewed by 2518

Abstract

Nanosecond Pulsed Electric Field (nsPEF or Nano Pulsed Stimulation, NPS) is a technology that delivers a series of pulses of high-voltage electric fields during a short period of time, in the order of nanoseconds. The main consequence of nsPEF upon cells is the [...] Read more.

Nanosecond Pulsed Electric Field (nsPEF or Nano Pulsed Stimulation, NPS) is a technology that delivers a series of pulses of high-voltage electric fields during a short period of time, in the order of nanoseconds. The main consequence of nsPEF upon cells is the formation of nanopores, which is followed by the gating of ionic channels. Literature is conclusive in that the physiological mechanisms governing ion channel gating occur in the order of milliseconds. Hence, understanding how these channels can be activated by a nsPEF would be an important step in order to conciliate fundamental biophysical knowledge with improved nsPEF applications. To get insights on both the kinetics and thermodynamics of ion channel gating induced by nsPEF, in this work, we simulated the Voltage Sensing Domain (VSD) of a voltage-gated Ca

^{2 +}

channel, inserted in phospholipidic membranes with different concentrations of cholesterol. We studied the conformational changes of the VSD under a nsPEF mimicked by the application of a continuous electric field lasting 50 ns with different intensities as an approach to reveal novel mechanisms leading to ion channel gating in such short timescales. Our results show that using a membrane with high cholesterol content, under an nsPEF of 50 ns and

\vec{E}

= 0.2 V/nm, the VSD undergoes major conformational changes. As a whole, our work supports the notion that membrane composition may act as an allosteric regulator, specifically cholesterol content, which is fundamental for the response of the VSD to an external electric field. Moreover, changes on the VSD structure suggest that the gating of voltage-gated Ca

^{2 +}

channels by a nsPEF may be due to major conformational changes elicited in response to the external electric field. Finally, the VSD/cholesterol-bilayer under an nsPEF of 50 ns and

\vec{E}

= 0.2 V/nm elicits a pore formation across the VSD suggesting a new non-reported effect of nsPEF into cells, which can be called a “protein mediated electroporation”. Full article

(This article belongs to the Special Issue Electrostatics in Cell Membranes and in Artificial Membrane Models)

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13 pages, 2082 KiB

Open AccessArticle

Simulations on Simple Models of Connexin Hemichannels Indicate That Ca²⁺ Blocking Is Not a Pure Electrostatic Effect

by Felipe Villanelo, Jorge Carrasco, Joaquin Jensen-Flores, Jose Antonio Garate and Tomas Perez-Acle

Membranes 2021, 11(5), 372; https://doi.org/10.3390/membranes11050372 - 20 May 2021

Viewed by 2083

Abstract

Connexin hemichannels allow the unspecific but regulated interchange of molecules from ions to second messenger and ATP, between the eukariotic cell and its extracellular space. The transport of ions and water through hemichannels is important for physiological functions and also in the progression [...] Read more.

Connexin hemichannels allow the unspecific but regulated interchange of molecules from ions to second messenger and ATP, between the eukariotic cell and its extracellular space. The transport of ions and water through hemichannels is important for physiological functions and also in the progression of several pathological conditions. Extracellular Ca²⁺ concentration is one of the regulators that drives the channel to a closed state. However the relation between their functional and structural states is far for being totally understood. In this work, we modelled connexin hemichannels using simple systems based on a fixed array of carbon atoms and assess the Ca²⁺ regulation using molecular dynamics simulations. The two proposed mechanism described so far for calcium action were studied combined, e.g., an electrostatic effect and a pore stretching. Our results show that the addition of positive charge density inside the channel cannot stop the flow of potassium, chloride nor water. Only a pore stretching at the center of the pore can explain the channel blocking. Full article

(This article belongs to the Special Issue Electrostatics in Cell Membranes and in Artificial Membrane Models)

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16 pages, 1698 KiB

Open AccessArticle

Modulatory Effects of Acidic pH and Membrane Potential on the Adsorption of pH-Sensitive Peptides to Anionic Lipid Membrane

by Dayane dos Santos Alvares, Ingrid Bernardes Santana Martins, Taisa Giordano Viegas, Mario Sergio Palma, Alexandre Suman de Araujo, Sidney Jurado de Carvalho and João Ruggiero Neto

Membranes 2021, 11(5), 307; https://doi.org/10.3390/membranes11050307 - 22 Apr 2021

Cited by 6 | Viewed by 2499

Abstract

Anionic lipid membrane electrostatic potential and solution pH can influence cationic peptide adsorption to these bilayers, especially those containing simultaneously acid and basic residues. Here, we investigate the effects of the pH solution on MP1 (IDWKKLLDAAKQIL-NH2) adsorption to anionic (7POPC:3POPG) lipid vesicles in [...] Read more.

Anionic lipid membrane electrostatic potential and solution pH can influence cationic peptide adsorption to these bilayers, especially those containing simultaneously acid and basic residues. Here, we investigate the effects of the pH solution on MP1 (IDWKKLLDAAKQIL-NH2) adsorption to anionic (7POPC:3POPG) lipid vesicles in comparison to its analog H-MP1, with histidines substituting lysines. We used the association of adsorption isotherms and constant pH molecular dynamic simulations (CpHMD) to explore the effects of membrane potential and pH on peptides’ adsorption on this lipid membrane. We analyzed the fluorescence and zeta potential adsorption isotherms using the Gouy–Chapman theory. In CpHMD simulations for the peptides in solution and adsorbed on the lipid bilayer, we used the conformations obtained by conventional MD simulations at a μs timescale. Non-equilibrium Monte Carlo simulations provided the protonation states of acidic and basic residues. CpHMD showed average pKa shifts of two to three units, resulting in a higher net charge for the analog than for MP1, strongly modulating the peptide adsorption. The fractions of the protonation of acidic and basic residues and the peptides’ net charges obtained from the analysis of the adsorption isotherms were in reasonable agreement with those from CpHMD. MP1 adsorption was almost insensitive to solution pH. H-MP1 was much more sensitive to partitioning, at acidic pH, with an affinity ten times higher than in neutral ones. Full article

(This article belongs to the Special Issue Electrostatics in Cell Membranes and in Artificial Membrane Models)

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33 pages, 617 KiB

Open AccessArticle

Competition between Cations via Classical Poisson–Nernst–Planck Models with Nonzero but Small Permanent Charges

by Mingji Zhang

Membranes 2021, 11(4), 236; https://doi.org/10.3390/membranes11040236 - 26 Mar 2021

Cited by 11 | Viewed by 1583

Abstract

We study a one-dimensional Poisson–Nernst–Planck system for ionic flow through a membrane channel. Nonzero but small permanent charge, the major structural quantity of an ion channel, is included in the model. Two cations with the same valences and one anion are included in [...] Read more.

We study a one-dimensional Poisson–Nernst–Planck system for ionic flow through a membrane channel. Nonzero but small permanent charge, the major structural quantity of an ion channel, is included in the model. Two cations with the same valences and one anion are included in the model, which provides more rich and complicated correlations/interactions between ions. The cross-section area of the channel is included in the system, and it provides certain information of the geometry of the three-dimensional channel, which is critical for our analysis. Geometric singular perturbation analysis is employed to establish the existence and local uniqueness of solutions to the system for small permanent charges. Treating the permanent charge as a small parameter, through regular perturbation analysis, we are able to derive approximations of the individual fluxes explicitly, and this allows us to study the competition between two cations, which is related to the selectivity phenomena of ion channels. Numerical simulations are performed to provide a more intuitive illustration of our analytical results, and they are consistent. Full article

(This article belongs to the Special Issue Electrostatics in Cell Membranes and in Artificial Membrane Models)

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13 pages, 433 KiB

Open AccessArticle

Debye-Hückel Free Energy of an Electric Double Layer with Discrete Charges Located at a Dielectric Interface

by Guilherme Volpe Bossa and Sylvio May

Membranes 2021, 11(2), 129; https://doi.org/10.3390/membranes11020129 - 14 Feb 2021

Cited by 6 | Viewed by 2083

Abstract

Poisson–Boltzmann theory provides an established framework to calculate properties and free energies of an electric double layer, especially for simple geometries and interfaces that carry continuous charge densities. At sufficiently small length scales, however, the discreteness of the surface charges cannot be neglected. [...] Read more.

Poisson–Boltzmann theory provides an established framework to calculate properties and free energies of an electric double layer, especially for simple geometries and interfaces that carry continuous charge densities. At sufficiently small length scales, however, the discreteness of the surface charges cannot be neglected. We consider a planar dielectric interface that separates a salt-containing aqueous phase from a medium of low dielectric constant and carries discrete surface charges of fixed density. Within the linear Debye-Hückel limit of Poisson–Boltzmann theory, we calculate the surface potential inside a Wigner–Seitz cell that is produced by all surface charges outside the cell using a Fourier-Bessel series and a Hankel transformation. From the surface potential, we obtain the Debye-Hückel free energy of the electric double layer, which we compare with the corresponding expression in the continuum limit. Differences arise for sufficiently small charge densities, where we show that the dominating interaction is dipolar, arising from the dipoles formed by the surface charges and associated counterions. This interaction propagates through the medium of a low dielectric constant and alters the continuum power of two dependence of the free energy on the surface charge density to a power of 2.5 law. Full article

(This article belongs to the Special Issue Electrostatics in Cell Membranes and in Artificial Membrane Models)

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24 pages, 954 KiB

Open AccessReview

On the Coupling between Mechanical Properties and Electrostatics in Biological Membranes

by Vanesa Viviana Galassi and Natalia Wilke

Membranes 2021, 11(7), 478; https://doi.org/10.3390/membranes11070478 - 28 Jun 2021

Cited by 28 | Viewed by 4369

Abstract

Cell membrane structure is proposed as a lipid matrix with embedded proteins, and thus, their emerging mechanical and electrostatic properties are commanded by lipid behavior and their interconnection with the included and absorbed proteins, cytoskeleton, extracellular matrix and ionic media. Structures formed by [...] Read more.

Cell membrane structure is proposed as a lipid matrix with embedded proteins, and thus, their emerging mechanical and electrostatic properties are commanded by lipid behavior and their interconnection with the included and absorbed proteins, cytoskeleton, extracellular matrix and ionic media. Structures formed by lipids are soft, dynamic and viscoelastic, and their properties depend on the lipid composition and on the general conditions, such as temperature, pH, ionic strength and electrostatic potentials. The dielectric constant of the apolar region of the lipid bilayer contrasts with that of the polar region, which also differs from the aqueous milieu, and these changes happen in the nanometer scale. Besides, an important percentage of the lipids are anionic, and the rest are dipoles or higher multipoles, and the polar regions are highly hydrated, with these water molecules forming an active part of the membrane. Therefore, electric fields (both, internal and external) affects membrane thickness, density, tension and curvature, and conversely, mechanical deformations modify membrane electrostatics. As a consequence, interfacial electrostatics appears as a highly important parameter, affecting the membrane properties in general and mechanical features in particular. In this review we focus on the electromechanical behavior of lipid and cell membranes, the physicochemical origin and the biological implications, with emphasis in signal propagation in nerve cells. Full article

(This article belongs to the Special Issue Electrostatics in Cell Membranes and in Artificial Membrane Models)

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27 pages, 14581 KiB

Open AccessFeature PaperReview

Mitochondrial Cristae Architecture and Functions: Lessons from Minimal Model Systems

by Frédéric Joubert and Nicolas Puff

Membranes 2021, 11(7), 465; https://doi.org/10.3390/membranes11070465 - 23 Jun 2021

Cited by 31 | Viewed by 9934

Abstract

Mitochondria are known as the powerhouse of eukaryotic cells. Energy production occurs in specific dynamic membrane invaginations in the inner mitochondrial membrane called cristae. Although the integrity of these structures is recognized as a key point for proper mitochondrial function, less is known [...] Read more.

Mitochondria are known as the powerhouse of eukaryotic cells. Energy production occurs in specific dynamic membrane invaginations in the inner mitochondrial membrane called cristae. Although the integrity of these structures is recognized as a key point for proper mitochondrial function, less is known about the mechanisms at the origin of their plasticity and organization, and how they can influence mitochondria function. Here, we review the studies which question the role of lipid membrane composition based mainly on minimal model systems. Full article

(This article belongs to the Special Issue Electrostatics in Cell Membranes and in Artificial Membrane Models)

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