CREATING ASYMMETRIC BILAYERS TO STUDY THE PLASMA MEMBRANE

Cell membranes consist of lipids, proteins, and glycoproteins. Although their primary role is to separate the intracellular and extracellular environments, their function is diversified. The intricate mechanisms of the cell membrane enable it to regulate the passage of ions and nutrients, maintain cell shape, and facilitate intercellular communication. As such, understanding the structure and function of the cell membrane is critical to comprehend cellular physiology and pathology. The lipid matrix of these membranes is diverse, containing lipids with distinct chemical structures and physicochemical properties. In particular, the plasma membrane (PM) in eukaryotic cells has an asymmetric bilayer formed by an inner (cytoplasmic) leaflet enriched in phosphatidylethanolamine (PE), phosphatidylserine (PS) and cholesterol (chol), while the outer (exoplasmic) is consisting of sphingomyelin (SM), phosphatidylcholine (PC) and cholesterol. The proper organization of the lipid bilayer is crucial to maintain the normal activities of cells. Any disruption in the plasma membrane's structure, such as the loss of the bilayer asymmetry, might be related to diseases and the process of apoptosis. Intriguingly, leaflets with different lipid compositions, phase behaviors, and order parameters can reciprocally influence the packing and order of lipids. For example, a leaflet with Ld+Lo domains can induce an ordered domain in contrast to the genuine Lo phase. Previous results suggest that these induced ordered domains are enriched in cholesterol. Here, we show preliminary results of constructing asymmetric lipid bilayers in vitro. We plan to use the hemifusion method to prepare asymmetric giant unilamellar vesicles (aGUVs). We induce the hemifusion of GUVs and a supported lipid bilayer (SLB). Then, their connected outer leaflet can exchange lipids, forming aGUVs. The present study focuses on learning this new and innovative approach.

This work was supported by Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP #2024/02663-1) and by the Instituto de Física of the University of São Paulo.