Synthetic ATP Production for a Synthetic Cell

Scientists at the University of Groningen have constructed synthetic vesicles in which ATP is produced. The vesicles use the ATP to maintain their volume and their ionic strength homeostasis. This metabolic network will eventually be used in the creation of synthetic cells, but it can already be used to study ATP-dependent processes. The researchers describe the synthetic system in an article that was published today in Nature Communications.

“Our aim is the bottom-up construction of a synthetic cell that can sustain itself and that can grow and divide,” says senior author Bert Poolman. Different groups of scientists are producing different modules for the cell, and Poolman’s group was tasked with energy production.

All living cells produce ATP as an energy carrier, but achieving sustainable production of ATP in a test tube is not a small task. “In known synthetic systems, all components for the reaction were included inside a vesicle. However, after about half an hour, the reaction reached equilibrium and ATP production declined,” Poolman explains. “We wanted our system to stay away from equilibrium, just like in living systems.”

The team fitted a lipid vesicle with a transport protein that could import the substrate arginine and export the product ornithine. Inside the vesicle, enzymes were present that could break down the arginine into ornithine. The free energy that this reaction provided was used to link phosphate to ADP, forming ATP. Ammonium and carbon dioxide were produced as waste products that diffused through the membrane.

“The export of ornithine produced inside the vesicle drives the import of arginine, which keeps the system running for as long as the vesicles are provided with arginine,” explains Poolman. The system was left to run for 16 hours in the longest experiment that the scientists have performed.

The current system is based on biochemical components. However, Poolman’s colleagues are busy collecting the genes needed for the production of enzymes used by the system and incorporating them into an artificial chromosome. Others are working on lipid and protein synthesis, for example, or cell division. The final synthetic cell should contain DNA for all these modules and operate them autonomously like a living cell, but in this case, engineered from the bottom-up and including new properties.

“In the meantime, we are already using our ATP-producing system to study ATP-dependent processes and advance the field of membrane transport,” says Poolman.

Image: This is an artist's impression of a synthetic cell, with the ATP production system in green. Image courtesy of Bert Poolman / BaSyC consortium.