Energy Barrier of a Monolayer Stalk Formation during Lipid Droplet Fusion

Lipid droplets are organelles responsible for the accumulation and breakdown of neutral fats in the human body. Lipid droplets have a monolayer shell of phospholipids, which prevents their spontaneous fusion. The fusion of lipid droplets is carried out by specialized fusion proteins and is regulated by the lipid composition of the monolayer membrane. The efficiency of fusion is determined by the energy needed for the local approach of lipid droplets and the topological rearrangement of their monolayers. In this work, the fusion of monolayers is modeled within the framework of the theory of membrane elasticity. The energy barrier for fusion is calculated under various conditions simulating possible compositions of monolayers, as well as the possible effects of proteins. The calculation results show that the height of the barrier is most dependent on the distance between lipid droplets, which is determined by the fusion proteins. Lipid composition also affects the fusion efficiency and can change it several tens of times, which is consistent with previously obtained data on bilayer fusion.