One of the great mysteries of the microscopic animals known as tardigrades is their uncanny ability survive almost anything: extreme heat, extreme cold, desiccation or drying out, and even the vacuum of space. Now, we are a little closer to understanding how they do it. The key, at least for surviving desiccation, is a special protein that tardigrades use to replace the water in their bodies with a form of glass.

Tardigrades are also known as water bears, and they normally live in moist, mossy environments. But when those environments dry up, tardigrades go into a state known as "tun"—it's a kind of suspended animation, which the animals can remain in for up to 10 years. When water begins to flow again, water bears absorb it and return to life.

Tardigrades aren't the only creatures who do this. Brine shrimp and certain kinds of worms can also dry up and come to life again. But what makes tardigrades different is that they use a special kind of disordered protein, unique to these animals, to literally suspend their cells in a glasslike matrix that prevents damage.

In a recent paper for Molecular Cell, a group of researchers analyzed the genomes of tardigrades to see which genes were active during the desiccation process. That's when the researchers discovered genes manufacturing the previously unknown protein, which they dubbed "tardigrade-specific intrinsically disordered protein" (TDP). The more TDP genes a tardigrade species has, the more quickly and efficiently it goes into the tun state. Splicing the TDP genes into yeast and other microorganisms led to a similar process of vitrification, or conversion into a glass-like state. At that point, the scientists knew they had identified a cluster of genes responsible for the tardigrades' survival in dry weather. University of North Carolina, Chapel Hill, biology researcher Thomas Boothby worked on the paper and told Ars via e-mail how the protein works:

What we think is happening is basically that, as the tardigrades are drying out, they are making a lot of these disordered proteins. These proteins essentially fill the cytoplasm of the tardigrade cells and, as they dry, form a glassy matrix within the cell. All the desiccation-sensitive stuff (proteins, nucleic acids, membranes) in the tardigrade cells get trapped in the pores of this matrix, essentially encapsulated in a protective glass-like coating. This encapsulation prevents the unfolding, rupture, breakage, and/or aggregation of desiccation-sensitive biological material. Once water is added back to the system, the disordered proteins that make up this glassy matrix melt back into solution, leaving behind all the protected parts of the cell.

In other words, the animal can replace all the water in its body with glass. This is just one of many survival mechanisms in the tardigrade's arsenal. Boothby and his colleagues tested to see whether the TDP genes were active when tardigrades respond to extreme temperatures, and they were not. That means water bears use another set of genes and chemical defenses, as yet undiscovered, to endure other deadly scenarios.

Boothby and his colleagues believe that the tardigrades' unique genetic defense against desiccation has widespread implications. For one thing, it might prevent drought from killing plants. Boothby told Ars that he and his team want to splice TDP genes into plants. "It would be awesome, and obviously a huge economic boon, if we could generate crops that could undergo drought, but instead of dying would just go into dry state of suspended animation, and then spring back to life once the drought is over," he said. Even more exciting is the possibility of using TDP to prevent protein-based medicines like vaccines from going bad:

Typically, if you dry out an enzyme and rehydrate it, the desiccation cycle destroys the enzyme's ability to function properly. In our study we showed that, if we mix an enzyme, lactate dehydrogenase, with tardigrade disordered proteins before it is desiccated, we can protect and recover up to 100% [of] the activity of the enzyme after desiccation and rehydration. We envision doing the same with protein-based pharmaceuticals (e.g. vaccines). This would allow us to store pharmaceuticals in a dry state without the need for refrigeration. Right now, most protein-based pharmaceuticals have to be stored and transported under constant refrigeration. This is a huge economic and logistical hurdle, especially in remote or developing parts of the world. [Eliminating] the need to refrigerate these pharmaceuticals would help ensure people everywhere have better and more reliable access to life-saving medicine.

Tardigrades are the ultimate survivors—and one day, they may help humanity survive, too.

Molecular Cell, 2017. DOI: 10.1016/j.molcel.2017.02.018 (About DOIs).