Phospholipid membrane formation templated by coacervatedroplets

We report formation of coacervate-supported phospholipid membranes by hydrating a dried lipid film in the presence of coacervate droplets. In contrast to traditional giant lipid vesicles formed by gentle hydration in the absence of coacervates, the coacervate-templated membrane vesicles are more uniform in size, shape, and apparent lamellarity. Due to their fully-coacervate model cytoplasm, these simple artificial cells are macromolecularly crowded and can be easily pre-loaded with high concentrations of proteins or nucleic acids. Coacervate-supported membranes were characterized by fluorescence imaging, polarization, fluorescence recovery after photobleaching of labeled lipids, lipid quenching experiments, and solute uptake experiments. Our findings are consistent with the presence of lipid membranes around the coacervates, with many droplets fully coated with what appear to be continuous lipid bilayers. Within the same population, other coacervate droplets are coated with membranes having defects or pores that permit solute entry, and still others are coated with multilayered membranes. These membranes surrounding protein-based coacervate droplets provided protection from a protease added to the external solution. The simplicity of producing artificial cells having a coacervate model cytoplasm surrounded by a model membrane is at the same time interesting as a potential mechanism for prebiotic protocell formation and appealing for biotechnology. We anticipate that such structures could serve as a new type of model system for understanding interactions between intracellular phases and cell- or organelle membranes, which are implicated in a growing number of processes ranging from neurotransmission to signaling.