Domain formation in cholesterol–phospholipid membranes exposed to adhesive surfaces or environments

Abstract

Domain formation in binary mixtures of cholesterol and a single phospholipid has been studied for a long time but the nature of these domains is still a matter of some debate. One interpretation of these domains is that they arise from the coexistence of liquid-ordered and liquid-disordered phases within the membranes. Here, we study the effect of adhesive surfaces and environments on the proposed phase behavior theoretically. The adhesion or partial support of the membranes leads to two or several membrane segments that exhibit different molecular interactions with their environments and, thus, have different molecular affinities to these environments. We show that the affinity contrasts between different environments strongly affect the phase behavior of the membranes. First, the affinity contrasts confine the domain formation spatially to single membrane segments. Second, these contrasts lead to a partitioning of the coexistence region in the composition-temperature plane into distinct coexistence regions for the different membrane segments. Third, the range of membrane compositions, for which one can observe domain formation in one of the membrane segments, is always reduced compared to the composition range of the free membrane. Furthermore, small affinity contrasts represent singular perturbations in the sense that the phase diagrams change in a discontinuous manner as one varies the affinity contrast from small positive to small negative values. All of these results are quite general because they follow from thermodynamic stability alone and apply to any two-component membrane with fluid-fluid coexistence. In addition to these generic features, we also provide a computational scheme, by which one can explicitly calculate the partitioning of the coexistence regions for a specific binary mixture, and illustrate this scheme for binary cholesterol-DPPC membranes. Both the generic and the specific features of domain formation as predicted by our theory are accessible to experimental studies.

Modulating Vesicle Adhesion by Electric Fields

“…Combined with lateral control over the distribution in the membrane and tethered vesicles (see, e.g., Yoshina-Ishii and Boxer ( 47 )), our approach offers possibilities for a variety of membrane manipulation approaches based on the use of electric fields. Future experiments on GUVs composed of ternary lipid mixtures will provide insight into possible adhesion-induced domain formation as predicted by recent theoretical work ( 48 ).…”

Phase separation in pore-spanning membranes induced by differences in surface adhesion

“…Such reorganisation and preferential localization of certain lipid phases as a function of a difference in surface adhesion has been described previously by Sarmento et al 72 using surface adhered GUVs. Lipowsky et al 73,74 treated this phenomenon theoretically relating the phase diagram of a binary DPPC/Chol mixture to the surface adhesion energies (affinity contrast). Our observation clearly demonstrates that the interaction of the l d -phase lipids with the support is stronger than that of the l o -phase lipids and leads to lipid sorting as a function of a partial interaction with the support.…”

Effect of tetracaine on DMPC and DMPC+cholesterol biomembrane models: Liposomes and monolayers

“…CHOL is the main sterol component in the biological membranes, being its content rather high (30 -50 mol %). CHOL molecules are known to distribute in the regions with saturated hydrocarbon chains, forming separate liquid ordered phases which coexist with liquid-disordered phases [15], and cause a reduction in the average cross-sectional area of phosphatidylcholines in the liquid crystalline membranes (known as condensing effect) [16].…”