Lipid Structure in Triolein Lipid Droplets

Abstract

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-<i>sn</i>-glycero-3-phosphocholine (POPC), 1-palmitoyl-2-oleoyl-<i>sn</i>-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