In fact, the mechanical properties of polymersomes vary greatly 23, whereby the expanded design freedom and tunability are the particular assets of synthetic intervention. This said, polymer membranes are not by default less permeable than natural ones 21 and light-driven proton pumps have also been reconstituted in “frozen” amphiphiles based on polystyrene 22. Thereby, membrane fluidity, which was found to scale with the length of the hydrophobic block 19, and the hydrophobic mismatch between the bilayer and the MP 20, i.e., the membrane thickness, were found to be crucial parameters for unrestricted enzyme activity. More fluid hydrophobic blocks like poly(dimethylsiloxane) (PDMS) combined with other hydrophilic chains such as poly(2-methyloxazoline) (PMOXA) and poly(2-ethyloxazoline) (PEtOz) have alone facilitated the reconstitution of complex bioenergetic proteins, e.g., ATP synthase 8 or complex I 17, next to plentiful channels like aquaporin 18. The latter strategy of membrane “hybridization” has been proposed to alleviate the drawbacks of natural and synthetic building blocks 15 and such mixed membranes have been investigated in detail, e.g., with respect to phase separation 16. For instance, the rigidity of the historical polymer poly(butadiene)-poly(ethylene oxide) (PBd-PEO) 14 arrested the oxygen reduction by a proton pumping terminal oxidase in a purely polymeric environment, though blending with phospholipids resulted in prolonged activity 10. Altogether, the biocompatibility of the amphiphile to the MP is still explored on a case-to-case basis but a general roadmap is beginning to crystalize. This substitution led to extended functional lifetimes 9, 10, by counteracting enzyme delipidation for instance 11, while providing enhanced chemical resistance and lower permeability 11, 12, 13. In recent years, lipid membranes were successfully replaced with synthetic polymers, which even enabled successful insertion of ATP-synthesizing apparatus and retention of MP activity 7, 8. On the other hand, significant progress can be achieved by augmenting the common delimiter and an essential component of artificial cells and organelles. Hereby, protein optimization via extremophilic sources and mutations is ultimately constrained by the intrinsic fragility of biomolecules, while chemical mimicking of complex MPs such as the rotary engine ATP synthase, nearly perfected through millions of years of evolution, is currently beyond our reach. Unsurprisingly, a good amount of effort is invested in increasing their stability and performance by replacing natural parts with man-made ones. Even though these mimics rapidly develop complexity and elegance, they remain short-lived without the natural mechanisms for repair and replacement. In analogy to natural cells, the current synthetic constructs (synthetic cells and organelles 1, 2, 3, 4, 5, 6) that are being assembled from molecular building blocks in a bottom-up fashion, are predominantly envisioned as enclosed structures made of phospholipids, while cytosolic and membrane proteins (MPs) endow a plethora of natural functionalities to the otherwise passive containers. Nature Communications volume 12, Article number: 4972 ( 2021)Īt the dawn of a new genesis, as envisioned and facilitated by humankind, artificial life in its current iterations appears to be vividly reminiscent of the zygotic stage of multicellular life-full of potential and of ever-increasing complexity. En route to dynamic life processes by SNARE-mediated fusion of polymer and hybrid membranes
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