A protein found only in microscopic tardigrades, one that allows them to survive extreme conditions like dehydration, can convey similar durability in synthetic cells, according to new research from the University of Chicago Pritzker School of Molecular Engineering (UChicago PME) and University of Michigan Engineering.
The findings, published last week in Nature Communications, could reveal a new way to store and transport synthetic cellular factories for producing medicines and other biological products in desiccated form and subsequent rehydration at the point of use.
"A major bottleneck in modern biotech is that many valuable biological products, things like vaccines, enzymes, cell-free reagents or biosensors, are fragile and require refrigeration or freezing during transport from factory to end-user," said Yongkang Xi, a U-M research fellow in mechanical engineering and co-first author on the study. "This work shows a plausible way to change that."
The study, exploring how synthetic cells could come back from dehydration, was funded by the U.S. Army Research Office and the National Science Foundation.
Tardigrades, or "water bears" as they're often called, are microscopic animals that are among the most resilient creatures on Earth. When they become dehydrated, protective structures form within cells to protect them from collapsing. This allows the cells to work again once they are rehydrated. In normal animal cells, where this protein is not present, dehydration kills.
One such protein is called cytoplasmic abundant heat-soluble protein (CAHS12). Until now, researchers knew that it was important in preserving tardigrade cells under duress, but they didn't know whether it could preserve biochemical functionality within cells for long periods of time and do so within synthetic cells.
"What we found is that there are particular parts of the proteins that are really important for binding to the cell membrane and other parts that are involved in building the fibrous support system," said UChicago PME Prof. Andrew Ferguson, co-corresponding author of the study. "We used molecular modeling to show why CAHS12 causes this protective behavior within synthetic cells and understand which parts of the protein lead to these properties."
The molecular simulations showed that each CAHS12 protein has parts that are attracted to the watery cell interior and the fat molecules of the cell membrane. In a hydrated cell, they float free, but as the cell dries out, the attraction to the membrane begins to dominate. The proteins, gathering and aligning near the membrane, trigger a chain reaction in which they link together, forming a 3D gel network that fills the cell. This stabilizes both the cell's surface and its delicate insides.
To see whether other cells could take advantage of the same proteins, U-M researchers created synthetic cells containing CAHS12 and subjected them to a dehydration-rehydration process. Constructed from biological materials such as lipids, proteins, and nucleic acids, synthetic cells are engineered to perform specific tasks.
In this demonstration, the cells contained DNA that encoded a green fluorescent protein and the parts needed to turn those instructions into a neon glow. However, researchers are excited about the potential for synthetic cells to produce medicines in less expensive facilities and detect or consume pollutants in the environment, among other biotechnology possibilities.
After dehydrating and rehydrating the synthetic cells, the team then tested whether the internal machinery of the cell had survived—namely, whether it retained the ability to read DNA and produce proteins. When the synthetic cells glowed red under the microscope, the team knew the process worked.
"What we see is that CAHS12 not only protects the membrane, but it also preserves the internal content, maintaining the biological activity," said Allen Liu, a U-M professor of both mechanical and biomedical engineering and co-corresponding author of the study.