Experimental studies on the spontaneous entrapment of macromolecules inside liposomes: synthetic models of minimal cells

One of the most ambitious goals of synthetic biology is to construct cell-like systems of minimal complexity for understanding fundamental aspects of biology – as the origin of life problem, for example –. In our research group, we focus on understanding how primitive cells originated from non-living components by combining liposome technology and biomolecular systems. In this project, we have investigated the origin of primitive metabolism-supporting cells via the construction of experimental models. By a careful study of lipid vesicle populations, prepared in the presence of several types of solutes, we have reported the coexistence of empty and super-filled lipid vesicles. The large number of experiments and the many different tested conditions strongly suggest that our observations are general and correspond to a spontaneous pathway for concentrating solute molecules inside (a small number of) vesicles. The lipid shell plays an active role recruiting molecules in the vesicle lumen, so that critical concentration thresholds to trigger biochemical reactions in a microenvironment are easily reached. A simple enzymatic reaction is facilitated inside a liposome water pool as opposed to bulk or other vesicles. We have also conducted experiments by forming liposomes in a diluted solution of a protein synthesis minimal kit observing that the reaction did not work efficiently in bulk due to the macromolecules’ dilution; however, a certain number of liposomes could efficiently entrap all 80 macromolecules needed for the desired reaction in a sufficient number of copies. Our results indicate that unsolved problems in origin of life scenarios, like the issue of low solute concentration and the low membrane permeability, could have been solved by the reported spontaneous entrapment and self-concentration of molecules in cell-like particles