2.F.7.  The Artificial Respiratory Chain in Polymer Compartments (ARC-PC) Family

Cytochrome bo₃ ubiquinol oxidase is a  4 subunit transmembrane protein, which oxidizes ubiquinone and reduces oxygen, while pumping protons (see TC# 3.D.4.5.1). Apart from its combination with F₁F_o-ATPase to assemble a minimal ATP regeneration module, the utility of the proton pump can be extended to other applications in the context of synthetic cells such as transport, signaling, and control of enzymatic reactions. In parallel, polymers have been speculated to be phospholipid mimics with respect to their ability to self-assemble in compartments with increased stability. Marušič et al. 2020 optimized a fusion/electroformation approach to reconstitute bo₃ oxidase in giant unilamellar vesicles made of PDMS-g-PEO and/or phosphatidylcholine (PC). This enabled optical access, while microfluidic trapping allowed for online analysis of individual vesicles. The tight polymer membranes and the inward oriented enzyme caused 1 pH unit difference in 30 min, with an initial rate of 0.35 pH·min^-1 To understand the interplay in these composite systems, Marušič et al. 2020 studied the relevant mechanical and rheological membrane properties. The proton permeability of polymer/lipid hybrids decreased after protein insertion, while the latter also led to a 20% increase of the polymer diffusion coefficient in polymersomes. PDMS-g-PEO increased the activity lifetime and the resistance to free radicals. These advantageous properties may open diverse applications, ranging from cell-free biotechnology to biomedicine. The presented study serves as a comprehensive road map for studying the interactions between membrane proteins and synthetic membranes, which will be fundamental for the successful engineering of such hybrid systems.

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