BPS2026 – Vesicle budding through membrane asymmetry: Lipid phase transitions and asymmetric insertion

Lipid bilayers are inherently asymmetric. Imbalances between the inner and outer leaflets generate asymmetry stress that can drive membrane fission, fusion, and vesiculation. Here, we present two complementary strategies to induce such imbalances, respectively, asymmetry stress in large unilamellar vesicles (LUVs). Both approaches trigger curvature stress that leads to vesicle fission and the formation of smaller daughter vesicles. We resolve and quantify the resulting vesicle populations using asymmetric flow field-flow fractionation (AF4). Our results demonstrate that leaflet area imbalance alone is sufficient to induce fission, establishing asymmetry stress as a potent mechanical driver of membrane remodeling. The first strategy focuses on cyclic lipopeptides (CLiPs) such as surfactin. CLiPs are inserted into the outer leaflet of LUVs. This insertion creates a surface area excess in the outer leaflet. We have shown for the first time that CLiPs trigger vesicle budding. Second, we prepared asymmetric LUVs (aLUVs) via cyclodextrin-mediated lipid exchange. Temperature variations can induce a gel-to-fluid or fluid-to-gel transition of lipids within a single leaflet, resulting in an abrupt change in the area per lipid and consequently generating asymmetry stress. Moreover, temperature variations not only induce budding but also influences lipid coupling which we investigate with pressure perturbation calorimetry (PPC).Together, these findings provide direct evidence for the role of asymmetry stress in membrane dynamics and shed new light on how CLiPs may exploit this mechanism in their antimicrobial activity.