A New Mechanism for Domain Size Selection in Curved Lipid Membranes

Lipid membranes, composed of saturated lipids, unsaturated phospholipids and cholesterols, play important roles in maintaining cellular activities. It is now well established that lipid membranes under proper conditions separate into saturated-lipid-enriched liquid-ordered (L$_{o})$ phase regions and unsaturated-lipid-enriched liquid-disordered (L$_{d})$ phase regions, with the L$_{o}$ phase having a larger bending modulus than the L$_{d}$ phase. In this project, we study how the bending modulus difference between L$_{o}$ and L$_{d}$ phases may affect the phase separation behavior of uniformly curved lipid membranes. We predict that, for membranes of a spherical lipid vesicle, when the line tension between the L$_{o}$ phase and L$_{d}$ phase is small the phase separation process is truncated and the underlying curvature leads to formation of stable L$_{o}$-phase domains of finite size. We also compare these predictions with experiments on lipid rafts.