triolein and 1-palmitoyl-2-oleoylphosphatidylethanolamine

The tear film is a thin multilayered structure covering the cornea. Its outermost layer is a lipid film underneath of which resides on an aqueous layer. This tear film lipid layer (TFLL) is itself a complex structure, formed by both polar and nonpolar lipids. It was recently suggested that due to tear film dynamics, TFLL contains inhomogeneities in the form of polar lipid aggregates. The aqueous phase of tear film contains lachrymal-origin proteins, whereby lysozyme is the most abundant. These proteins can alter TFLL properties, mainly by reducing its surface tension. However, a detailed nature of protein-lipid interactions in tear film is not known. We investigate the interactions of lysozyme with TFLL in molecular details by employing coarse-grained molecular dynamics simulations. We demonstrate that lysozyme, due to lateral restructuring of TFLL, is able to penetrate the tear lipid film embedded in inverse micellar aggregates.

Topics: Adsorption; Cholesterol Esters; Humans; Kinetics; Molecular Dynamics Simulation; Muramidase; Phosphatidylcholines; Phosphatidylethanolamines; Sphingomyelins; Sulfoglycosphingolipids; Surface Tension; Tears; Thermodynamics; Triolein; Water

Lipid droplets (LDs) are primary repositories of esterified fatty acids and sterols in animal cells. These organelles originate on the lumenal or cytoplasmic side of endoplasmic reticulum (ER) membrane and are released to the cytosol. In contrast to other intracellular organelles, LDs are composed of a mass of hydrophobic lipid esters coved by phospholipid monolayer. The small size and unique architecture of LDs makes it complicated to study LD structure by modern experimental methods. We discuss coarse-grained molecular dynamics (MD) simulations of LD formation in systems containing 1-palmitoyl-2-oleoyl-sn-glycero-3-phosphocholine (POPC), 1-palmitoyl-2-oleoyl-sn-glycero-3-phosphoethanolamine (POPE), triolein (TO), cholesterol (CHOL), and water. We find that (1) there is more cholesterol in the LD core, than at the interface. (2) No crystallization occurs inside the LD core. (3) According to coarse-grained simulations, the presence of PE lipids at the interface has a little impact on distribution of components and on the overall LD structure. (4) The thickness of the lipid monolayer at the surface of the droplet is similar to the thickness of one leaflet of a bilayer. Computer simulations are shown to be a mighty tool to provide molecular-level insights, which are not available to the experimental techniques.

Topics: Cholesterol; Dimerization; Lipid Bilayers; Lipid Droplets; Molecular Dynamics Simulation; Phosphatidylcholines; Phosphatidylethanolamines; Solvents; Triolein; Water