Formation of Thermally Stable Vesicles from a Cyclic Tetraether Archaeal Lipid

The formation of thermostable vesicles by the archaeal lipid β-l-gulopyranosyl-caldarchaetidyl-glycerol (CaldA) is investigated. This caldarchaeol-based lipid comprises the main polar lipid of the archaeon Thermoplasma acidophilum. Vesicle formation is shown and quantitatively analyzed through a combination of laser scanning confocal microscopy, cryogenic-transmission electron microscopy (cryo-TEM), dynamic light scattering (DLS), and small-angle X-ray scattering (SAXS). The thermal stability of the CaldA vesicles is then studied after autoclaving. The vesicles are found to be intact after this treatment via cryo-TEM and DLS and fluorescent dye release studies. The limited fluorescence release for CaldA is contrasted with results for the conventional lipid DPPC [1,2-dipalmitoyl-sn-glycero-3-phosphocholine], for which significant release of encapsulated calcein is observed on heating. The vesicles are also stable against detergent lysis. Laurdan fluorescence polarization measurements show that the lipid membrane remains in a fluid state across a broad temperature range. The experiments were complemented by atomistic molecular dynamics (MD) simulations which confirm a stable single layer arrangement of the lipids, and also a molecular packing-dependent curvature tendency. The thermostable vesicles of CaldA may be useful for encapsulation applications.