Phase separation and domain registry in giant multilamellar vesicles prepared with biologically-relevant lipid compositions.*

Lipids are amphiphiles that commonly form bilayer sheets in the form of vesicles when exposed to excess water. Most commonly lipids have been studied in the context of the plasma membrane and other unilamellar vesicles containing a single bilayer. However, several key biological systems such as the myelin sheath, tubular myelin, or pulmonary lipid-based membranes are known to rely on correlated stacks of lipid bilayers into onion-like multi-lamellar vesicles. Lateral ordering of lipids is well-understood mostly in single-bilayer systems. Most often, the macroscopic distribution of phases is only well-characterized for giant unilamellar vesicles. Here we report on the macroscopic arrangement of phase-separated domains in multilamellar forms with biologically-relevant compositions. We will show how the registration of individual domains results in large changes in macroscopic vesicle structure and properties. Confocal fluorescence microscopy allows direct visualization of phase separation, supported by SAXS and spectrometry studies of lipid ordering.