The Importance of Planarity for Lipid Bilayers as Biomembranes

Abstract

Abstract Questions like “What is the cell or vesicle size that frees lipid molecules in bilayers from membrane curvature strains?” and “Why is the size of self-reproducible eukaryotic cell over 10 μm?” are topics regarding membrane shape deformation caused by cationic peptide interacted with anionic head group of membrane lipids. The mechanism of direct translocation (cytolysis) of cell-penetrating peptides (CPPs) and antimicrobial peptides (AMPs) through biomembranes is discussed in relation to membrane curvature and lipid mobility. It is confirmed that cytolysis happens when cationic CPP or AMP molecules interact with anionic lipid head groups to generate local and transient catenoid pores with negative Gaussian curvature. The translocation of CPP and AMP, or more generally, the vesicle shape change caused by physical or chemical modifiers is possible only under the condition that the lipid is under a lamellar liquid crystal ( L d ) phase to be mobile. This condition could be given primarily for the planar membrane with negligible curvature strain to make local or even whole topological modification. There must be a threshold level in the vesicle size that forces lipids to become immobile to maintain vesicle structures, which exceeds the bending energy provided by CPP or AMP to release curvature strain. As such, planarity is important for biomembranes to be flexible enough to accommodate necessary local topology changes, which is the key of controlling the stimuli responsive barrier function of cell membrane.