Atomistic Model for Nearly Quantitative Simulations of Langmuir Monolayers.

Lung surfactant and a tear film lipid layer are examples of biologically relevant macromolecular structures found at the air-water interface. Because of their complexity, they are often studied in terms of simplified lipid layers, the simplest example being a Langmuir monolayer. Given the profound biological significance of these lipid assemblies, there is a need to understand their structure and dynamics on the nanoscale, yet there are not many techniques able to provide this information.

Toward Atomistic Resolution Structure of Phosphatidylcholine Headgroup and Glycerol Backbone at Different Ambient Conditions.

Phospholipids are essential building blocks of biological membranes. Despite a vast amount of very accurate experimental data, the atomistic resolution structures sampled by the glycerol backbone and choline headgroup in phoshatidylcholine bilayers are not known. Atomistic resolution molecular dynamics simulations have the potential to resolve the structures, and to give an arrestingly intuitive interpretation of the experimental data, but only if the simulations reproduce the data within experimental accuracy.

Coarse-grained computational studies of supported bilayers: current problems and their root causes.

The supported bilayer is an important experimental method for probing the features of lipid bilayers, yet relatively few computational studies have taken up its modeling. Using coarse-grained molecular dynamics simulations based on the MARTINI force field, we show that some of the few previous attempts employing similar methodologies are problematic, and have indeed led to erroneous conclusions. We further build a theoretical framework to see where exactly the failures of parametrization lie and suggest how these earlier results should be interpreted.

Freezing of stressed bilayers and vesicles.

We show using a minimalistic theoretical framework that phase transition decoupling in lipid bilayers is caused by a nonuniform stress profile due to an asymmetric distribution of lipids between the two leaflets. Applying this framework to vesicles, we demonstrate that their anomalous freezing is also caused by a stress asymmetry, but that this is due to lipid tail extension on freezing. Finally, we predict a previously unknown dependence of surface tension on temperature, find the phenomenon also in coarse grained molecular dynamics simulations, and suggest that it might have relevance in thermosensitive protein gating.

Interfacial tension and surface pressure of high density lipoprotein, low density lipoprotein, and related lipid droplets.

Lipid droplets play a central role in energy storage and metabolism on a cellular scale. Their core is comprised of hydrophobic lipids covered by a surface region consisting of amphiphilic lipids and proteins. For example, high and low density lipoproteins (HDL and LDL, respectively) are essentially lipid droplets surrounded by specific proteins, their main function being to transport cholesterol.