Visualization of lipid membrane reorganization induced by interactions with proteins and peptides

Abstract

The cell membrane is a thin lipid bilayer composed of various phospholipids and proteins, consisting of laterally segregated domains with different chemical compositions and physical properties. The dynamic organization of membranes is crucial for a variety of biological functions and is closely related to the interaction of cell membranes with various biomolecules, including proteins, peptides, and drug molecules. This thesis aims to analyze the reorganization of lipid membranes induced by proteins and peptides using freestanding planar lipid membranes. Through real-time visualization of membranes, we tried to understand how interactions with proteins or peptides can rearrange membrane lipids, and how this could be related to their biological functions. First, we studied protein condensation that occurs on the surface of lipid membranes. By enabling protein binding on both sides of the lipid membrane, we observed a new phenomenon, the transmembrane coupling of protein condensates, which is mediated by the lateral rearrangement of the lipid membrane. Second, using phase-separated membranes that mimic the lateral heterogeneity of cell membranes, we examined the dynamic reorganization of the membranes by the arginine-rich cell-penetrating peptide. Furthermore, by analyzing the membrane penetration of the peptide, we found that cell-penetrating peptides can actively facilitate their membrane translocation by fluidizing the membranes. Our findings reveal a new mechanism for how protein condensates or cell-penetrating peptides act on cell membranes, and we expect that our work will also offer valuable insights for exploring the dynamic membrane remodeling induced by membrane-biomolecule interactions, which could be responsible for a variety of biological processes.