Protein Binding to Artificial Lipid Droplets Demonstrates the Importance of Phospholipid Composition

Abstract

All cells and tissues store excess lipid in intracellular structures known as lipid droplets. Each lipid droplet consists of a neutral lipid core (primarily made of triacylglyceride and cholesteryl ester) surrounded by a phospholipid monolayer. Several proteins interact specifically with the surface of the lipid droplet and control their growth and degradation. Here, we share the development of an in vitro binding assay, that utilizes synthetic lipid droplets and partially purified lipid droplet proteins, to study protein binding to lipid droplets. We separate bound from unbound proteins with sucrose gradient ultracentrifugation and detect lipid droplet proteins following SDS‐PAGE and western blotting. We have used this assay to show that changing the phospholipid composition of the lipid droplet surface alters interactions with perilipin 2, a ubiquitously expressed lipid droplet protein that is predicted to interact with lipid droplets through an amphipathic alpha helix. Specifically, perilipin 2 association with synthetic lipid droplets was increased when the amount of phosphatidylethanolamine relative to phosphatidylcholine was increased. We hypothesize that the smaller headgroups of phosphatidylethanolamine allows additional interaction with the underlying neutral lipid. These results may be relevant to the formation of lipid droplets in alcoholic fatty liver disease, where lipid droplets form with altered levels of phosphatidylethanolamine and phosphatidylcholine.Support or Funding InformationFunding for this research was provided by an ASBMB Undergraduate Research Award and the Lowell and Doris Kispert Endowment at St. Olaf College.