Differential lipid interaction of the C-terminus and full length perilipin 3.

Abstract

Lipid Droplets (LDs) are highly complex, dynamic organelles critical for cellular energy regulation. They are found in almost all cell types. The structure of LDs consists of a neutral lipid core surrounded by a phospholipid-protein monolayer instead of a lipid-protein bilayer. This sets them apart from all other intracellular organelles. It is well known that the LD monolayer contains predominantly phosphatidylcholine (PC), significant amounts of phosphatidylethanolamine (PE), and other lipid species in smaller amounts. Because of LD structural complexity and heterogeneity within a cell, it is critical to inquire how each lipid component affects LD function and its ability to recruit binding proteins. Cytosolic LD binding proteins contain complex physical structures such as amphipathic α-helices some of which can form helix bundles. Perilipins are the most abundant LD-associated protein family expressed in humans. An amphipathic α-helix bundle is found at the C-terminus of perilipins 2, 3, and 5. This α-helix is similar to the well-known lipid-binding domains of the apolipoproteins apoE and apoLp-III. In this study, we show that the C-terminus of perilipin 3 may help the protein to bind to the LDs after the initial localization from the N-terminal 11-mer repeat region. We use pendant drop tensiometry to get a measure of the recruitment and insertion of perilipin 3 to model LD lipid monolayers at aqueous-phospholipid-oil interfaces. We identified a higher insertion of an unsaturated PC monolayer for both the full length and the C-terminus of perilipin 3 in this interface. By adding PE to the monolayer, we identify an increase in the insertion of the C-terminus but not for the full-length protein.