Abstract
Previous studies on the phase behaviour of multicomponent lipid bilayers found an intricate interplay between membrane geometry and its composition, but a fundamental understanding of curvature-induced effects remains elusive. Thanks to a combination of experiments on lipid vesicles supported by colloidal scaffolds and theoretical work, we demonstrate that the local geometry and global chemical composition of the bilayer determine both the spatial arrangement and the amount of mixing of the lipids. In the mixed phase, a strong geometrical anisotropy can give rise to an antimixed state, where the lipids are mixed, but their relative concentration varies across the membrane. After phase separation, the bilayer organizes in multiple lipid domains, whose location is pinned in specific regions, depending on the substrate curvature and the bending rigidity of the lipid domains. Our results provide critical insights into the phase separation of cellular membranes and, more generally, two-dimensional fluids on curved substrates.
Highlights
Previous studies on the phase behaviour of multicomponent lipid bilayers found an intricate interplay between membrane geometry and its composition, but a fundamental understanding of curvature-induced effects remains elusive
small unilamellar vesicles (SUVs) are prepared from a ternary mixture of porcine brain sphingomyelin (BSM), 1-palmitoyl-2-oleoyl-sn-glycero-3-phosphocholine (POPC), and cholesterol (Chol) in a 2:1:1 mole ratio[22] by extrusion
While the global mole ratio of the three lipids of the SUVs is fixed at 2:1:1 of BSM:POPC:Chol, our setup leads to the deposition of a random amount of lipids of each kind on any given scaffolded lipid vesicles (SLVs)
Summary
Previous studies on the phase behaviour of multicomponent lipid bilayers found an intricate interplay between membrane geometry and its composition, but a fundamental understanding of curvature-induced effects remains elusive. Recent experiments on cells subject to controlled deformation, have confirmed the primary role of spatial curvature for inducing actin polymerization and recruiting curvature sensitive proteins[6,7] Inspired by these observations, the correlation between membrane geometry and chemical composition has been extensively studied in model lipid membranes consisting of ternary mixtures of phospholipids and cholesterol. Experiments on giant unilamellar vesicles (GUVs)[9,11,12,13,14,15,16,17,18] reported a twofold correlation between these lipid domains and membrane geometry: while local membrane curvature can favour lipid segregation and domain nucleation and localization, the presence of lipid domains can drive the formation of curved regions, including buds, necks, and protrusions To solve this causality dilemma, several experimental setups have been proposed to control membrane shape and investigate its effect on phase separation patterns. The LO (LD) domains were found to occupy regions of low (high) curvature
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