Self-assembly of biological membranes into 200-400 nm aqueous compartments.

Membrane formation by amphipathic mixtures in aqueous environments is central to eukaryotic biology. Formation of aqueous compartments enclosed by membranes is of immense importance in designing liposomal systems for pharmaceutical applications. It is also continuously controlled within the dynamic environment of a living cell and, during cell division. In spite of over four decades of research on protein-free lipid bilayers, membrane compartment formation is still an art rather than science. This is because the experimental efforts to date have been aimed at making aqueous compartments from different lipid mixtures in different buffers and solutions of different ionic strengths. Thus, even similar methodologies produce varying results in different laboratories. In this work, we provide for the first time, experimental parameters of minimum hydration volume and maximum possible volumes for aqueous entrapments formed by DOPE:DOPC:Chol stoichiometries similar to intracellular environments and those used in pharmaceutical research for liposomal systems. We define a new experimental parameter of "Critical Compartmentalization Concentration" for formation of membrane-bound 200-400 nm aqueous compartments by these amphipathic mixtures in the simplest possible controlled environment of pure water. We report the first experimental insights into "equations" governing self-assembly leading to formation of membrane compartments encapsulating aqueous volumes. Our work opens a completely new avenue for engineering of aqueous compartment and liposomal preparations using known biological lipids in different aqueous environments.