An Unexpected Driving Force for Lipid Order Appears in Asymmetric Lipid Bilayers.

An ordered phase in one leaflet of an asymmetric bilayer can induce a precisely superimposed in the apposed leaflet. Order is induced in such simple lipid compositions as dioleoylphosphatidylcholine/cholesterol (DOPC)/chol) which is expected to be a uniform and disordered lipid mixture. Dye partitioning can be used to label and identify coexisting liquid-disordered (Ld), liquid-ordered (Lo), or gel-ordered (Lβ) molecules in a phase-separated leaflet.

Nano-scale domains in the plasma membrane are like macroscopic domains in asymmetric bilayers.

Unfavorable lipid-lipid pairwise interactions between HiTm and LowTm lipids drive liquid-disordered (Ld) + liquid-ordered (Lo) phase separation. Large size of phase domains is opposed by lipid dipole repulsions, which are more significant compared with the pairwise interactions for naturally abundant LowTm lipids such as palmitoyl oleoyl phosphatidylcholine. During the nano-to-macro domain size transition, no lipid phase transition occurs, and measured properties of Ld + Lo nanodomains are found to be essentially the same as those of macrodomains.

Improving our picture of the plasma membrane: Rafts induce ordered domains in a simplified model cytoplasmic leaflet.

By study of asymmetric membranes, models of the cell plasma membrane (PM) have improved, with more realistic properties of the asymmetric lipid composition of the membrane being explored. We used hemifusion of symmetric giant unilamellar vesicles (GUVs) with a supported lipid bilayer (SLB) to engineer bilayer leaflets of different composition. During hemifusion, only the outer leaflets of GUV and SLB are connected, exchanging lipids by simple diffusion.

On the small size of liquid-disordered + liquid-ordered nanodomains.

Four-component phase diagrams reveal that Liquid-disordered + liquid-ordered (Ld + Lo) nanodomains are exclusively found adjacent to a three-phase region, and so cannot be a one-phase microemulsion. Of importance for understanding biological membranes, a small change in lipid bilayer composition can change the size of these coexisting phase domains hundreds of fold, between tens of nanometers and microns. Nanodomain diameter, measured from small angle neutron scattering, is in the range 15-35 nm, consistent with stabilization by repulsive dipole fields.

Dataset of asymmetric giant unilamellar vesicles prepared via hemifusion: Observation of anti-alignment of domains and modulated phases in asymmetric bilayers.

The data provided with this paper are confocal fluorescence images of symmetric giant unilamellar vesicles (GUVs) and asymmetric giant unilamellar vesicles (aGUVs). In this work, aGUVs were prepared using the hemifusion method and are labelled with two different fluorescent dyes, named TFPC and DiD. Both dyes show strong preference for the liquid-disordered (Ld) phase instead of the liquid-ordered (Lo) phase.