Sometimes there is an art to doing biology, especially when it comes to overcoming technical limitations to your research. Cellular biologists, for example, have to trade off between the frustrating challenge of growing cells for experimental use and the considerable “lifelessness” of synthetic cell models. Back in August of 2019, a team of researchers at Penn State published a paper in Nano Letters describing how they successfully created a synthetic cell which mimics the movement of living cells, without all the extra baggage that living cells bring with them.
The team's protocell doesn't do anything else that normal cells do. It doesn't reproduce or mutate, for example, because it doesn't have any DNA to do so. They made what's called a liposome – just an empty cell membrane – but the twist is that they embedded into the membrane an enzyme called ATPase. They did this because the whole purpose of their study was to study how cells move (which involves ATPase), and by building a fake cell that had only the one feature they were interested in, they could isolate that variable from all the other nonsense living cells do that they weren't interested in.
How cells move is actually poorly understood, so starting from scratch like this allows the scientists to deconstruct and understand the mechanics of their movement one enzyme at a time.
In the research team’s experiments, the protocells have artificial membranes composed of a naturally occurring lipid called phosphatidylcholine. The ATPase enzymes were incorporated directly into the membrane. ATPase works by breaking down ATP into ADP. This chemical reaction in central to how cells store and use energy. In the membrane, this reaction is able to fuel motion and propel the cell.
The scientists in this case used a liposome structure to create their synthetic cells. Cell membranes are built from the same mechanics here, in which the heads of the phospholipids are hyprophillic and their tails are hydrophobic.
Explaining the significance of this study to the Penn State News, lead author Subhadip Ghosh said, “Our results basically give other researchers the first steps toward making artificial cells with enzymatic activity.” You can read the paper in it's entirety here – it's called “Motility of Enzyme-Powered Vesicles.
Fabricating enzymatically active protocells opens new opportunities. Armed with these mimics of motile living cells, the researchers aim to reveal the fundamental mechanisms governing active membrane dynamics and cellular movement. Given the current limited understanding of how cells move, including how enzyme action plays into cell movement, the research team members believe their work can have significant implications for future medical research.