How Do the Properties of Amphiphilic Polymer Membranes Influence the Functional Insertion of Peptide Pores?

Pore-forming peptides are of high biological relevance particularly as cytotoxic agents, but their properties are also applicable for the permeabilization of lipid membranes for biotechnological applications, which can then be translated to the more stable and versatile polymeric membranes. However, their interactions with synthetic membranes leading to pore formation are still poorly understood, hampering the development of peptide-based nano technological applications, such as biosensors or catalytic compartments. To elucidate these interactions, we chose the model peptide melittin, the main component of bee venom. Here, we present our systematic investigation on how melittin interacts with and inserts into synthetic membranes, based on amphiphilic block copolymers, to induce pore formation in three different setups (planar membranes and micrometric and nanometric vesicles). By varying selected molecular properties of block copolymers and resulting membranes (e.g., hydrophilic to hydrophobic block ratio, membrane thickness, surface roughness, and membrane curvature) and the stage of melittin addition to the synthetic membranes, we gained a deeper understanding of melittin insertion requirements. In the case of solid-supported planar membranes, melittin interaction was favored by membrane roughness and thickness, but its insertion and pore formation were hindered when the membrane was excessively thick. The additional property provided by micrometric vesicles, curvature, increased the functional insertion of melittin, which was evidenced by the even more curved nanometric vesicles. Using nanometric vesicles allowed us to estimate the pore size and density, and by changing the stage of melittin addition, we overcame the limitations of peptide-polymer membrane interaction. Mirroring the functionality assay of planar membranes, we produced glucose-sensing vesicles. The design of synthetic membranes permeabilized with melittin opens a new path toward the development of biosensors and catalytic compartments based on pore-forming peptides functionally inserted in synthetic planar or three-dimensional membranes.