A Study of Lipid Interactions for the exchangeable PAT protein, Perilipin 3

Abstract

Perilipin 3 (TIP 47) is a ubiquitously expressed PAT family protein carrying a C-terminal amphipathic α-helix bundle. In this work we focus on the mechanism of lipid binding by perilipin 3. Perilipin 3 associates with growing lipid droplets (LDs) and not with cellular membranes in vivo but the mechanism behind this specificity is not clear. We used several N-terminal truncation mutants as well as the full length perilipin 3 protein to investigate its lipid binding properties. Lipid monolayers at the air – buffer interface were used to study the lipid binding properties of all these constructs. Since monolayers are incredibly sensitive to surface active contaminants we had to purify large quantities of recombinant protein in order to carry out this work. The insertion of perilipin 3 into lipid monolayers was monitored by the increase in surface pressure of the lipid monolayer after injecting the proteins beneath a (phospho-)lipid monolayer. By systematically varying the lipid composition of the lipid monolayer we address the type of interactions responsible for perilipin 3 – LD interaction. This work addresses the types of interactions responsible for perilipin 3 – lipid insertion and also of the role of amphipathic α-helix bundles in lipid binding. We provide a model that describes the interactions responsible for perilipin 3 – LD interaction that help explain what sets this protein apart from other phospholipid membrane binding proteins.