Dynamic, artificial cells and vesicles

Scott Long et al. have constructed synthetic cells comprised of lipid bilayer membranes surrounding a two-phase, aqueous polymer solution that can be reversibly converted to a single phase. An understanding of compartmentalization in cell function has been hampered by the lack of an experimental model system. Using a previously developed method, the authors constructed artificial cells by encapsulating a poly(ethylene glycol) (PEG)/ dextran aqueous two-phase system (ATPS) within a giant lipid vesicle. The researchers tagged each macromolecule, PEG, dextran, and lipid, with an individual f luorescent marker to monitor transitions by confocal microscopy. The two encapsulated phases were found to contain different polymer concentrations, and the authors were able to create microcompartments within the synthetic cells by introducing molecules with varying affinities for PEG or dextran. Fluorescently tagged streptavidin accumulated preferentially in the PEG-rich phase of a vesicle containing biotinylated PEG, whereas SBA, a carbohydrate-binding lectin, partitioned into the dextran-rich phase of the vesicles. Through osmotically driven dehydration, Long et al. were able to partition single-stranded DNA oligonucleotides into the dextran-rich phase of an ATPS-containing vesicle.