Bio-hybrid polymer membranes as tools for mimicking cell compartments

Abstract

In cells, membrane proteins naturally insert in lipid bilayers. The thickness of a lipid bilayer cell membrane is around 5 nm, with little variation in the hydrophobic mismatch (difference between the hydrophobic region of the membrane protein and the hydrophobic region of the spanned membrane) allowing them to function properly. In this work, the challenge was to identify the proper conditions in which selected ion channels (gramicidin), ion carriers (ionomycin), and other biopores (engineered α-hemolysins and glycerol facilitator) maintain their function in synthetic membranes of polymersomes with thicknesses up to 16 nm. This raised a set of questions. Gramicidin has a length of 2.5 nm, therefore: is it possible to insert and function in membranes up to 6 times thicker than the ion-channel’s size? Is there a limit of membrane thickness at which the inserted membrane protein does not function anymore? Does a biopore preserve its full known function in thicker membranes? How does an ionophore of 1.5 nm in diameter, such as ionomycin, move through a thick hydropobic layer of a polymerosme membrane? Is it possible to explain the mechanism of permeabilization in thick polymer membranes? Moreover, these biopores require solubilization in organic solvents or detergents which might also impact the permeabilization of the synthetic membranes. Is there a way of avoiding detergent/organic solvent induced permeabilization and thus preservation of the architecture of the vesicles? Is the permeability induced only by the successful insertion of biopores? The insertion of membrane proteins is just a part of the challenge, as the final 3D architecture of polymersomes might also be affected in presence of additional biomolecules. The system becomes even more complex once enzymes are involved, or the designed vesicular systems are attached on solid supports. Therefore, the list of questions can be extended. As a result, this thesis aims to answer many of the above listed questions. The proposed solutions, described in this body of work, represent the foundation for the development of nano-scaled biosensors, nanoreactors and active surfaces.