Aqueous Phase Separation in Giant Vesicles

Abstract

We report the synthesis and initial characterization of approximately 10 mum diameter lipid vesicles that contain two distinct aqueous phases. The aqueous two-phase system is a dextran/poly(ethylene glycol) solution that exhibits temperature-dependent phase behavior. Vesicles were prepared above the phase transition temperature of the polymer solution. Upon cooling to room temperature, the polymer solution phase separated both within the vesicles and in the bulk solution. The location of poly(ethylene glycol)-rich and dextran-rich phases was determined by fluorescence microscopy. These structures are exciting in that they enable for the first time the interior volume of liposomes to be structured.

RETRACTED: Probing osmolyte participation in the unfolding transition state of a protein

“…Furthermore, regulation of cellular solvent composition, by membrane channel proteins such as GlpF, may be an important mechanism under conditions of mechanical stress where sustained mechanical forces applied to tissues may trigger widespread protein unfolding (44,45). Phase separation and active selection of specific osmolytes may allow the control of protein dynamics through modulation of the unfolding transition state (46).…”

Rapid RNA Exchange in Aqueous Two-Phase System and Coacervate Droplets

“…Their ability to concentrate primitive reactants and catalysts, such as ribozymes, could increase reaction rates without requiring a lipid-based boundary (Strulson et al 2012). Both ATPSs and coacervates also function as compartments in vitro (Williams et al 2012; Strulson et al 2012) and in the case of a dextran/PEG ATPS, within a phospholipid vesicle (Helfrich et al 2002; Long et al 2005). Coacervate droplets are particularly attractive due to the simplicity of their components, e.g.…”

Microfluidic Formation of Monodisperse Coacervate Organelles in Liposomes

“…These internal organelle‐like compartments allow for a high level of control over the spatial organization of biochemical processes. Similar liposomes containing a synthetic polymer‐based aqueous two phase system (ATPS), that is, polyethylene glycol and dextran (PEG‐DEX),12 have already been reported through a bulk hydration of dried lipid membranes and shown diverse cell‐like properties, such as microcompartmentalization,12a,12b protein relocalization in response to stimuli,12c and asymmetric vesicle division 12d. However, more bio‐relevant coacervate systems have not been achieved in phospholipid vesicles until now, probably because complex coacervates are highly charged, which interferes with conventional liposome preparation methods 13.…”

“…Additionally, typical liposome formation methods lead to polydisperse structures, give low yields, and show inefficient encapsulation. Furthermore, ATPS phase transitions often require undesired heating and cooling steps (the temperature applied is as high as 50 °C)12a or osmotic shocks,14 which are incompatible with biological processes and cause instability of liposomes.…”