The Molecular Mechanism of Monolayer-Bilayer Transformations of Lung Surfactant from Molecular Dynamics Simulations

Baoukina, Svetlana; Monticelli, Luca; Amrein, Matthias; Tieleman, D. Peter

doi:10.1529/biophysj.107.113399

Cited by 93 publications

(96 citation statements)

References 36 publications

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“…The subphase for folding is determined by the balance of surface energies, which depend on the surfactant constituting the monolayer and on the polar-apolar interface. For lipid monolayers at the air-water interface, the folding proceeds into the water subphase, reducing the surface energy of the hydrocarbon chains exposed to air (44). Immediately after collapse, the bilayer folds are connected to the monolayer and have a semielliptical shape.…”

Section: Discussionmentioning

confidence: 99%

The molecular mechanism of lipid monolayer collapse

Baoukina

Monticelli

Risselada

et al. 2008

Proc. Natl. Acad. Sci. U.S.A.

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249

253

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Lipid monolayers at an air-water interface can be compressed laterally and reach high surface density. Beyond a certain threshold, they become unstable and collapse. Lipid monolayer collapse plays an important role in the regulation of surface tension at the air-liquid interface in the lungs. Although the structures of lipid aggregates formed upon collapse can be characterized experimentally, the mechanism leading to these structures is not fully understood. We investigate the molecular mechanism of monolayer collapse using molecular dynamics simulations. Upon lateral compression, the collapse begins with buckling of the monolayer, followed by folding of the buckle into a bilayer in the water phase. Folding leads to an increase in the monolayer surface tension, which reaches the equilibrium spreading value. Immediately after their formation, the bilayer folds have a flat semielliptical shape, in agreement with theoretical predictions. The folds undergo further transformation and form either flat circular bilayers or vesicles. The transformation pathway depends on macroscopic parameters of the system: the bending modulus, the line tension at the monolayer-bilayer connection, and the line tension at the bilayer perimeter. These parameters are determined by the system composition and temperature. Coexistence of the monolayer with lipid aggregates is favorable at lower tensions of the monolayerbilayer connection. Transformation into a vesicle reduces the energy of the fold perimeter and is facilitated for softer bilayers, e.g., those with a higher content of unsaturated lipids, or at higher temperatures.lung surfactant ͉ bilayer reservoir ͉ course grain ͉ vesicle budding ͉ molecular dynamics L ipid molecules are insoluble in both polar and apolar media because of their amphipathic nature. At polar-apolar interfaces, they form monomolecular films that reduce the surface tension. Lipid monolayers form the main structural component (Ϸ97% by weight) of lung surfactant at the gas-exchange interface in the lung alveoli (1) and constitute the outer layer of tear film in the eyes (2). The properties of lipid monolayers vary with their surface density (3). For example, the higher the density, the lower is the resulting surface tension at the interface. At a certain very high surface density, however, a further reduction of the surface tension is not possible: the monolayers become unstable at the interface and collapse (4) (see scheme in Fig. 1). Besides being of fundamental interest for surface science, lipid monolayer collapse is crucial for maintaining low surface tension at the gas-exchange interface in the lungs during breathing (5).Collapse is characterized by loss of material from the interface and can proceed through different pathways. The modes of collapse and the surface tension at which collapse occurs depend on the molecular composition of the monolayer and on temperature (6-13), which determine the morphology and material properties of the monolayer. Although lipid monolayers in the liquid state do not usually ...

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Section: Discussionmentioning

confidence: 99%

The molecular mechanism of lipid monolayer collapse

Baoukina

Monticelli

Risselada

et al. 2008

Proc. Natl. Acad. Sci. U.S.A.

Self Cite

249

253

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“…99,100 It has also been successfully applied to studies of monolayers as a function surface tension. 101 III. Coarse graining of molecular structures with self-organizing maps A Introduction to SOMs and clustering in coarse graining…”

Section: This Journal Is C the Owner Societies 2009mentioning

confidence: 99%

Multiscale modeling of emergent materials: biological and soft matter

Murtola

Bunker

Vattulainen

et al. 2009

Phys. Chem. Chem. Phys.

255

234

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On using a too large integration time step in molecular dynamics simulations of coarse-grained molecular models Moritz Winger, Daniel Trzesniak, Riccardo Baron and Wilfred F. In this review, we focus on four current related issues in multiscale modeling of soft and biological matter. First, we discuss how to use structural information from detailed models (or experiments) to construct coarse-grained ones in a hierarchical and systematic way. This is discussed in the context of the so-called Henderson theorem and the inverse Monte Carlo method of Lyubartsev and Laaksonen. In the second part, we take a different look at coarse graining by analyzing conformations of molecules. This is done by the application of self-organizing maps, i.e., a neural network type approach. Such an approach can be used to guide the selection of the relevant degrees of freedom. Then, we discuss technical issues related to the popular dissipative particle dynamics (DPD) method. Importantly, the potentials derived using the inverse Monte Carlo method can be used together with the DPD thermostat. In the final part we focus on solvent-free modeling which offers a different route to coarse graining by integrating out the degrees of freedom associated with solvent.

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“…Simulations were performed by version 4.5.4 of the GRO-MACS simulation package 43 and the MARTINI force field was used for DPPC lipids, 44 POPG lipids, 45 and PEG. 46 The Berendsen weak coupling temperature and pressure coupling algorithms 47 were utilized with coupling constants of 0.3 ps and 3.0 ps, respectively.…”

Section: A Coarse Grained Setupmentioning

confidence: 99%

Anomalous viscosity effect in the early stages of the ion-assisted adhesion/fusion event between lipid bilayers: A theoretical and computational study

Raudino

Marrink

Pannuzzo

2013

The Journal of Chemical Physics

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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, watersoluble 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. © 2013 AIP Publishing LLC.

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The Molecular Mechanism of Monolayer-Bilayer Transformations of Lung Surfactant from Molecular Dynamics Simulations

Cited by 93 publications

References 36 publications

The molecular mechanism of lipid monolayer collapse

The molecular mechanism of lipid monolayer collapse

Multiscale modeling of emergent materials: biological and soft matter

Anomalous viscosity effect in the early stages of the ion-assisted adhesion/fusion event between lipid bilayers: A theoretical and computational study

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