Collapse of a Monolayer by Three Mechanisms

Ybert, Christophe; Lu, Weixing; Möller, G.; Knobler, Charles M.

doi:10.1021/jp013173z

Cited by 143 publications

(189 citation statements)

References 17 publications

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“…A direct relation exists between the surface tension of a leaflet and the area per head group of its constituent lipids, which is typically expressed by surface pressure͞area per lipid isotherms (21). We use 2D tessellations with Voronoi polyhedra (22) to study local instantaneous changes in the area per head group of the lipids in the vicinity of the NT* tube.…”

Section: Resultsmentioning

confidence: 99%

Understanding nature's design for a nanosyringe

López

Nielsen

Moore

et al. 2004

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

277

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Synthetic and natural peptide assemblies can possess transport or conductance activity across biomembranes through the formation of nanopores. The fundamental mechanisms of membrane insertion necessary for antimicrobial or synthetic pore formation are poorly understood. We observe a lipid-assisted mechanism for passive insertion into a model membrane from molecular dynamics simulations. The assembly used in the study, a generic nanotube functionalized with hydrophilic termini, is assisted in crossing the membrane core by transleaflet lipid flips. Lipid tails occlude a purely hydrophobic nanotube. The observed insertion mechanism requirements for hydrophobic-hydrophilic matching have implications for the design of synthetic channels and antibiotics.T he interaction between biological membranes and synthetic or natural macromolecules that have activity through the formation of transmembrane nanopores is intrinsic to the functioning of ion channels (1-8) and antimicrobial peptides (6, 9). It is surprising, therefore, that the insertion mechanism of amphiphilic molecules into (and even across) biomembranes is poorly understood (10-13). The use of fully atomistic computer simulations to probe the interactions of membrane proteins with lipid bilayers is of considerable current interest (8). However, despite many recent successes, such simulations are hampered by the accessible system size and timescale. To glean some insight into possible mechanisms associated with the membrane insertion process we have used molecular dynamics (MD) calculations to study the interaction of tubular macromolecules with a fully hydrated dimyristoylphosphatidylcholine (DMPC) lipid bilayer in its physiologically relevant liquid-crystalline phase. The calculations we report have been carried out by using a coarse-grain (CG) model, inspired by the model successfully used to study self-organizing surfactant systems (14). The tubular nanostructures we study are generic models for preassembled bundles of membrane-spanning proteins (3, 11), antimicrobial peptides (4), and cyclic peptides (1) and for a synthetic nanosyringe based on functionalizing a carbon nanotube (2, 15). Although many naturally existing ion channels and antimicrobial peptides form pores with a hydrophilic lumen, many systems exist, including viral ion channels, synthetic peptides, and nanodevices, for which the present model should be an adequate description.The present simulations involve molecular systems that represent Ϸ70,000 atoms altogether. Simulations with larger systems have been reported (8,16). The present CG approach, however, allows us to routinely calculate dynamics in the hundreds or thousands of nanoseconds and therefore allows us to study events that take place at longer scales than those currently accessible by all-atom calculations. Methods CG Model. In the CG model (17, 18), each DMPC lipid molecule consists of 13 interaction sites, eight of which are hydrophobic (four for each alkanoyl tail) and five of which are hydrophilic, three for the glycerol moiety ...

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Section: Resultsmentioning

confidence: 99%

Understanding nature's design for a nanosyringe

López

Nielsen

Moore

et al. 2004

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

277

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“…by mechanism 10,15 , e.g., fracture and solubilization; and by topography 16 18 , e.g., multilayer 19,20 , fold, micro-and nano-disk, etc. A variety of techniques have been also developed to fabricate, characterize, and visualize the morphology of the collapsed structures of monolayers, e.g., laser light scattering 15 , X-ray diffraction and reflectivity 21 , fluorescence 10 , and Brewster angle microscopy 22 .…”

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confidence: 99%

“…A variety of techniques have been also developed to fabricate, characterize, and visualize the morphology of the collapsed structures of monolayers, e.g., laser light scattering 15 , X-ray diffraction and reflectivity 21 , fluorescence 10 , and Brewster angle microscopy 22 . In the following sections, the topography of collapsed states, in association with the molecular structures and mechanical properties of monolayer-constituent molecules will be discussed.…”

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confidence: 99%

Collapsed States of Langmuir Monolayers

2016

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“…The modes of collapse and the surface tension at which collapse occurs depend on the molecular composition of the monolayer and on temperature (6)(7)(8)(9)(10)(11)(12)(13), which determine the morphology and material properties of the monolayer. Although lipid monolayers in the liquid state do not usually sustain low surface tensions, the monolayers in a condensed state [e.g., pure dipalmitoylphosphatidylcholine (DPPC) below its main-phase transition temperature, 314K] can achieve high surface densities and low surface tensions (9,14) (near-zero values).…”

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confidence: 99%

The molecular mechanism of lipid monolayer collapse

Baoukina

Monticelli

Risselada

et al. 2008

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

255

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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Collapse of a Monolayer by Three Mechanisms

Cited by 143 publications

References 17 publications

Understanding nature's design for a nanosyringe

Understanding nature's design for a nanosyringe

Collapsed States of Langmuir Monolayers

The molecular mechanism of lipid monolayer collapse

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