Nanoscale Phase Separation in DSPC–Cholesterol Systems

Abstract

The lipid arrangement of eukaryotic cell membranes has been shown to be heterogeneous, with domains enriched in cholesterol and saturated phospholipids, coexisting with a continuous phase that is enriched in unsaturated phospholipids. While the existence of these domains is well-established, there is still a lack of consensus regarding domain size and the factors influencing it. In this work, we investigate model membranes consisting of 1,2-dioleoyl-sn-glycero-3-phosphocholine (DOPC)-1,2-distearoyl-sn-glycero-3-phosphocholine (DSPC)-cholesterol (Chol) and 1-palmitoyl-2-oleoyl-sn-glycero-3-phosphocholine (POPC, 18:1-16:0)-DSPC-Chol with a steady-state fluorescence assay and report the influence of phospholipid chain saturation and chain length on domain size. The spectral shifts of 1-myristoyl-2-[12-[(5-dimethylamino-1-naphthalenesulfonyl)amino]dodecanoyl]-sn-glycero-3-phosphocholine (DAN-PC) and a Förster resonance energy transfer (FRET) assay were used, along with an analytical model, to estimate domain sizes. A region of nanoscale domain existence was observed in both ternary systems; however, the domains formed in the system containing the asymmetric lipid (POPC, 18:1-16:0) were larger than those formed in the diunsaturated lipid (DOPC, 18:1-18:1). This is a new finding, as domains were not previously known to exist in similar POPC-based systems.