Artificial Organelles for Energy Regeneration

Abstract

cell's total energy budget. [2] The universal energy currency that is used for these purposes and can be found in all forms of life is adenosine triphosphate (ATP). A vast majority of the cellular energy demand is covered by either converting a large variety of energy-rich substrates into ATP in a process called oxidative phosphorylation, or by converting light (electromagnetic) energy into ATP in a process called photophosphorylation (or photosynthesis).These naturally existing energy conversions are valid in in the context of bottomup synthetic biology as well. In the latter, an artificial cell is envisioned as a compendium of functional modules, each hand-tailored to partially or entirely mimic one of the essential life processes, such as reproduction, growth, motility, etc. [3] Like their natural counterparts, all these reenvisioned synthetic processes are energy demanding, therefore, the deliberate design of synthetic cells should involve suitable energy management strategy, by, for example, continuous regeneration of ATP. Apart from the importance in the context of artificial cells, new energy conversion strategies can be considered as a standalone feature for enzymatic and cell-free biotechnology, wherein bottom-up synthetic biology might also deliver new and sustainable solutions.The notion of synthetic in terms of engineered and/or non-natural can be even expanded to other forms of energy (like electrical energy) and non-natural building blocks. The chemically driven ATP synthesis, as in oxidative phosphorylation, represents a spontaneous process, in which the electrons of a fuel (glucose, NADH) are transferred to an electron acceptor such as oxygen with the concomitant generation of proton gradient, which is afterwards stored again as chemical energy in ATP. In the realm of synthetic biology, other options might also be feasible, for example: can we use electrical energy and directly plug it in to drive biological processes [4,5] or make use of natural electron transfer mechanisms to produce electricity? [6] The Electron Transport Chain-a Natural Toolbox of Functional Parts for the Construction of Artificial OrganellesDuring the process of oxidative phosphorylation, electrons are passed from an electron donor ("fuel") with a more negative One of the critical steps in sustaining life-mimicking processes in synthetic cells is energy, i.e., adenosine triphosphate (ATP) regeneration. Previous studies have shown that the simple addition of ATP or ATP regeneration systems, which do not regenerate ATP directly from ADP and P i , have no or only limited success due to accumulation of ATP hydrolysis products. In general, ATP regeneration can be achieved by converting light or chemical energy into ATP, which may also involve redox transformations of cofactors. The present contribution provides an overview of the existing ATP regeneration strategies and the related nicotinamide adenine dinucleotide (NAD + ) redox cycling, with a focus on compartmentalized systems. Special attention is being paid to those approach...

Toward Artificial Cells: Novel Advances in Energy Conversion and Cellular Motility

“…The lipid compositions used to form vesicles also vary remarkably among research teams. The most common natural lipid source is soybean lipid extract due to its convenience, availability, and low cost . Bacterial lipid extract can also be used, but its use is not popular .…”

“…In 1977, Sone et al reconstituted ATP synthase from a thermophilic bacterium PS3 into vesicles containing bacteriorhodopsin. Other bacterial ATP synthases were successfully co‐reconstituted with bacteriorhodopsin into liposomes, including those from Rhodospirillum rubrum ,123c Synechococcus sp.,124a Bacillus PS3, and especially E. coli 116,120,124b,125. Spinach chloroplast ATP synthase has also been extensively used to develop ATP synthesis systems (see Table ).…”

“…The most common natural lipid source is soybean lipid extract due to its convenience, availability, and low cost. [120,123] Bacterial lipid extract can also be used, but its use is not popular. [124] In many other studies, synthetic lipid compositions in various ratios have been empirically combined, and success has been achieved using different combinations of ATP synthase and proton pumps.…”

Microfluidic Handling and Analysis of Giant Vesicles for Use as Artificial Cells: A Review

“…These include energy conversion, [100] metabolism, [101] polarisation, [19] growth, [14,16,102] division, [103] signaling/communication, [97,104] and motility. In the context of using the bottom-up approach for the construction artificial cells, there are a number of functionalities currently being explored.…”

“…In the context of using the bottom-up approach for the construction artificial cells, there are a number of functionalities currently being explored. These include energy conversion, [100] metabolism, [101] polarisation, [19] growth, [14,16,102] division, [103] signaling/communication, [97,104] and motility. [105,106] Giant vesicles, and in particular GUVs, are excellent compartments systems well suited for the reconstitution of the necessary machinery to achieve these goals and microfluidic technologies for handling them will play a major role.…”