Effect of pH and ionic strength on phospholipid nanomechanics and on deposition process onto hydrophilic surfaces measured by AFM

Garcia-Manyes, Sergi; Oncins, Gerard; Sanz, Fausto

doi:10.1016/j.electacta.2006.03.062

Cited by 80 publications

(111 citation statements)

References 43 publications

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“…The above findings are in good agreement with experimental data [6][7][8][9] and with previously reported computational results. 6,12,15 It is, however, very instructive to consider the sensitivity of the results to a force-field employed for modeling salt ions.…”

Section: Resultssupporting

confidence: 93%

Effect of NaCl and KCl on Phosphatidylcholine and Phosphatidylethanolamine Lipid Membranes: Insight from Atomic-Scale Simulations for Understanding Salt-Induced Effects in the Plasma Membrane

Gurtovenko

Vattulainen²

2008

J. Phys. Chem. B

230

253

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To gain a better understanding of how monovalent salt under physiological conditions affects plasma membranes, we have performed 200 ns atomic-scale molecular dynamics simulations of phosphatidylcholine (PC) and phosphatidylethanolamine (PE) lipid bilayers. These two systems provide representative models for the outer and inner leaflets of the plasma membrane, respectively. The implications of cation-lipid interactions in these lipid systems have been considered in two different aqueous salt solutions, namely NaCl and KCl, and the sensitivity of the results on the details of interactions used for ions is determined by repeating the simulations with two distinctly different force fields. We demonstrate that the main effect of monovalent salt on a phospholipid membrane is determined by cations binding to the carbonyl region of a membrane, while chloride anions mostly stay in the water phase. It turns out that the strength and character of the cation-lipid interactions are quite different for different types of lipids and cations. PC membranes and Na + ions demonstrate strongest interactions, leading to notable membrane compression. This finding was confirmed by both force fields (Gromacs and Charmm) employed for the ions. The binding of potassium ions to PC membranes (and the overall effect of KCl), in turn, was found to be much weaker mainly due to the larger size of a K + ion compared to Na + . Furthermore, the effect of KCl on PC membranes was found to be force-field sensitive: The binding of a potassium ion was not observed at all in simulations performed with the Gromacs forcefield, which seems to exaggerate the size of a K + ion. As far as PE lipid bilayers are concerned, they are found to be influenced by monovalent salt to a significantly lesser extent compared to PC bilayers, which is a direct consequence of the ability of PE lipids to form both intra-and intermolecular hydrogen bonds and hence to adopt a more densely packed bilayer structure. Whereas for NaCl we observed weak binding of Na + cations to the PE lipid-water interface, in the case of KCl we witnessed almost complete lack of cation binding. Overall, our findings indicate that monovalent salt ions affect lipids in the inner and outer leaflets of plasma cell membranes in substantially different ways.

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Section: Resultssupporting

confidence: 93%

Effect of NaCl and KCl on Phosphatidylcholine and Phosphatidylethanolamine Lipid Membranes: Insight from Atomic-Scale Simulations for Understanding Salt-Induced Effects in the Plasma Membrane

Gurtovenko

Vattulainen²

2008

J. Phys. Chem. B

230

253

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“…28,30 During the past decade, however, this view has been challenged. Indirect evidence from infrared spectroscopy, 32 fluorescence correlation spectroscopy, 33 atomic force microscopy, 35,36 smallangle X-ray diffraction, 41 spin-labeling electron paramagnetic resonance spectroscopy, 41 and calorimetric 33,41 studies suggest the possibility of Na + interacting with lipid carbonyl oxygens, binding lipids into complexes, and thus leading to detectable changes in area per lipid, bilayer thickness and rigidity, 41 as Hopping greatly promoted the lateral diffusion of Na + within the carbonyl region. The lateral mean squared displacement (MSD) of sodiums continuously complexed with DMPC (thick dashed red line) is considerably smaller than if lipid-free hops are allowed (thick continuous black).…”

Section: Discussionmentioning

confidence: 99%

“…Experiments have shown that anionic 4, [22][23][24][25] and cationic 26,27 membranes interact readily with their counterions (especially divalent ones), whereas the interactions of zwitterionic lipid bilayers with salt ions appear rather sensitive to the size and valency of ions. [28][29][30][31][32][33][34][35][36][37][38][39][40][41] As for molecular-level computational studies, the increase in computing power in the past few years has made it possible to extend computer simulations beyond the relatively long relaxation times of tens to hundreds of nanoseconds required for equilibration of ions in lipid/water systems. Although most computational studies by far have focused on the effects of salt ions on zwitterionic (neutral) lipid bilayers, 33,[42][43][44][45][46][47][48][49][50][51][52][53] there is also an increasing number of studies on anionic [54][55][56][57][58][59] and cationic 60,61 lipid bilayers.…”

Section: Introductionmentioning

confidence: 99%

Ion Dynamics in Cationic Lipid Bilayer Systems in Saline Solutions

et al. 2009

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Positively charged lipid bilayer systems are a promising class of nonviral vectors for safe and efficient gene and drug delivery. Detailed understanding of these systems is therefore not only of fundamental but also of practical biomedical interest. Here, we study bilayers comprising a binary mixture of cationic dimyristoyltrimethylammoniumpropane (DMTAP) and zwitterionic (neutral) dimyristoylphosphatidylcholine (DMPC) lipids. Using atomistic molecular dynamics simulations, we address the effects of bilayer composition (cationic to zwitterionic lipid fraction) and of NaCl electrolyte concentration on the dynamical properties of these cationic lipid bilayer systems. We find that, despite the fact that DMPCs form complexes via Na + ions that bind to the lipid carbonyl oxygens, NaCl concentration has a rather minute effect on lipid diffusion. We also find the dynamics of Cl -and Na + ions at the water-membrane interface to differ qualitatively. Cl -ions have well-defined characteristic residence times of nanosecond scale. In contrast, the binding of Na + ions to the carbonyl region appears to lack a characteristic time scale, as the residence time distributions displayed power-law features. As to lateral dynamics, the diffusion of Na + ions within the water-membrane interface consists of two qualitatively different modes of motion: very slow diffusion when ions are bound to DMPC, punctuated by fast rapid jumps when detached from the lipids. Overall, the prolonged dynamics of the Na + ions are concluded to be interesting for the physics of the whole membrane, especially considering its interaction dynamics with charged macromolecular surfaces.

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“…This conclusion has since been strengthened by further studies showing that bilayer properties remain unaltered upon the addition of sub-molar concentrations of monovalent salt 4,10,11 . Since 2000, however, another view has emerged, suggesting much stronger interactions between phospholipids and monovalent cations, and strong Na + binding in particular [6][7][8][9][12][13][14][15][16][17][18] .…”

Section: Introductionmentioning

confidence: 99%

“…At sub-molar NaCl concentrations, the rotational and translational dynamics of membraneembedded fluorescent probes decreased 7,9,12 , and atomic force microscopy (AFM) experiments showed changes in bilayer hard-ness [14][15][16][17][18] ; in atomistic molecular dynamics (MD) simulations, phospholipid bilayers consistently bound Na + , although the binding strength depended on the model used 12,13,[21][22][23][24][25][26] .…”

Section: Introductionmentioning

confidence: 99%

Molecular electrometer and binding of cations to phospholipid bilayers

Catte

Girych

Javanainen

et al. 2016

Phys. Chem. Chem. Phys.

256

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Despite the vast amount of experimental and theoretical studies on the binding affinity of cations -especially the biologically relevant Na + and Ca 2+ -for phospholipid bilayers, there is no consensus in the literature. Here we show that by interpreting changes in the choline headgroup order parameters according to the 'molecular electrometer' concept [Seelig et al., Biochemistry, 1987, 26, 7535], one can directly compare the ion binding affinities between simulations and experiments. Our findings strongly support the view that in contrast to Ca 2+ and other multivalent ions, Na + and other monovalent ions (except Li + ) do not specifically bind to phosphatidylcholine lipid bilayers at sub-molar concentrations. However, the Na + binding affinity was overestimated by several molecular dynamics simulation models, resulting in artificially positively charged bilayers and exaggerated structural effects in the lipid headgroups. While qualitatively correct headgroup order parameter response was observed with Ca 2+ binding in all the tested models, no model had sufficient quantitative accuracy to interpret the Ca 2+ :lipid stoichiometry or the induced atomistic resolution structural changes. All scientific contributions to this open collaboration work were made publicly, using nmrlipids.blogspot.fi as the main communication platform.

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Effect of pH and ionic strength on phospholipid nanomechanics and on deposition process onto hydrophilic surfaces measured by AFM

Cited by 80 publications

References 43 publications

Effect of NaCl and KCl on Phosphatidylcholine and Phosphatidylethanolamine Lipid Membranes: Insight from Atomic-Scale Simulations for Understanding Salt-Induced Effects in the Plasma Membrane

Effect of NaCl and KCl on Phosphatidylcholine and Phosphatidylethanolamine Lipid Membranes: Insight from Atomic-Scale Simulations for Understanding Salt-Induced Effects in the Plasma Membrane

Ion Dynamics in Cationic Lipid Bilayer Systems in Saline Solutions

Molecular electrometer and binding of cations to phospholipid bilayers

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