Membrane functionalization of polymersomes: alleviating mass transport limitations by integrating multiple selective membrane transporters for the diffusion of chemically diverse molecules

Abstract

Recently, the interest in polymersomes as nanoreactors for synthetic applications has increased due to interesting proof-of-concept studies, indicating a versatile use of polymeric vesicles to compartmentalize complex reaction cascades. However, the low permeability of polymeric membranes and the requirement for a controlled mass transport across the compartment boundaries have posed a major limitation to the broad applicability of polymersomes for synthetic reactions. Current advances in the functional integration of membrane proteins (MPs) into poly(2-dimethylsiloxane)-based membranes have allowed the selective increase of the permeability for a controlled mass transport of the desired compounds across the membrane. Herein we demonstrate that polymer membranes are capable of harboring different MPs to alleviate the mass transport limitations of chemically diverse molecules, thereby enabling complex cascade reactions to be performed within the nanoreactors. The ability to functionalize the polymer membrane with multiple, highly selective MPs allows a reduction in mass transport limitations without abandoning compartmentalization of the reaction space on a low molecular mass level. As the model reaction, a two enzyme system consisting of a ketoreductase (KR) and a formate dehydrogenase was studied. For the transport of the hydrophobic substrate and product of the KR, the MPs AlkL, OmpW, OprG and TodX were investigated. For the transport of formate, OmpF, PhoE and FocA were used. AlkL showed the highest integration efficiency (39%) and a maximum of 120 AlkL molecules were successfully inserted into each polymersome. The highest channel-specific effects on the mass transfer were achieved using TodX and PhoE, respectively. The combination of both proteins led to an improvement of the space-time yield of the product (S)-pentafluorophenyl ethanol by 2.32-fold compared to nanoreactors without MPs.