Biomimetic Block Copolymer Membranes for Reconstitution of Transmembrane Proteins
Structure and function of many transmembrane proteins are affected by their surrounding environment. In this respect, reconstitution of a membrane protein into a biomimetic polymer membrane can alter its function. To overcome this problem we synthesized new poly(1,4-isoprene-block-ethylene oxide) block copolymers (PIPEO) and studied their self-assembly in aqueous media with respect to the polymer molecular weight, block ratio, polymer concentration in aqueous solution, and the added fraction of phospholipids. The results show, that the amount of isoprene blocks mainly determined the morphology of formed aggregates. Within the prepared samples, block copolymer molecular weight and concentration showed only a minor influence regarding the self-assembly. Mixtures of block copolymers and phospholipids revealed a demixing regime of the amphiphiles, depending on block copolymer molecular weight. To show feasibility of transmembrane protein reconstitution into membranes formed by PIPEO blended with 1,2-diphytanoyl-sn-glycero-3-phosphocholine we used the well characterized outer membrane protein OmpF from Escherichia coli. We demonstrate functionality of this protein in biomimetic lipopolymer membranes, independent of the molecular weight of the block copolymers. In line with these experiments, integration of OmpF was also revealed by impedance spectroscopy. Our results indicate that blending of our new synthetic polymer membranes with phospholipids allows reconstitution of transmembrane proteins under preservation of protein function, independent of the membrane thickness.