The world knows no toughness like that of the water bear, which looks like a cannon wearing a pair of wrinkled khakis. This microscopic critter can survive boiling water (and alcohol too, just to be safe), some of the lowest temperatures in the universe, and blasts of radiation that would kill a human. In the slightly edited but still immortal words of Austin Powers: “Why won’t the water bear die?”
The question has for decades baffled scientists, who suspected the water bear---also known as a tardigrade---mobilizes a sugar called trehalose to reinforce its body and keep its cells from swift destruction. But no longer. In a paper out today in Molecular Cell, researchers claim they’ve found an exclusively tardigradean protein that the creature produces, forming it into a glass bead. It’s in this state that the water bear can pull off such extreme feats of survival---which might be very convenient for human medicine one day.
The problem with the trehalose theory, as it turned out, was that while many other organisms like nematode worms and brine shrimp use it to survive desiccation, not all water bear species produce the sugar under stress. Some of those other organisms produce enough trehalose to make up 20 percent of their body weight. The water bear? Only about 2 percent. Pitiful, really.
That didn’t jibe with the water bear’s uncanny toughness. So researchers looked closely at the genes that turned on as water bears dried out. At the top of the list of the switched-on genes: those that encode what are known as intrinsically disordered proteins. Those amino acid chains don’t have a neat 3-D structure like most proteins, so they act very loosey-goosey and strange. “One of the things we're really interested in is figuring out how exactly these tardigrade intrinsically disordered proteins are working,” says biologist and study co-author Thomas C. Boothby of University of North Carolina at Chapel Hill. “It's a really interesting question about how a protein without a defined three-dimensional structure can actually carry out its function in a cell.”
Regardless, Boothby and his colleagues seem to have pinpointed the genes that make the water bear’s life-saving proteins. “We went on to show that if you reduce expression of these genes in tardigrades, they can no longer survive desiccation very well,” Boothby says. “If you take those genes and put them into organisms like bacteria and yeast, which normally do not have these proteins, they actually become much more desiccation-tolerant.” The water bear's secret ingredient can make other organisms up to 100 times hardier.
The mechanism of these intrinsically disordered proteins looks a lot like how the trehalose sugar protects animals like nematode worms from dessication. Like something out of a fairy tale or the very least an ‘80s movie, the protein turns the water bear into a frozen glass figurine, a process known as vitrification. Normally, dessication crystallizes living cells, shredding up proteins and DNA in the process. But with the gentler, smoother process of vitrification, the water bear can ride out the desiccation, only to reanimate once it hits water perhaps 30 years later.
Great news for the hardy little water bear, and potentially even better news for humanity. Vaccines, for instance, are extremely fragile, requiring refrigeration as doctors ship them around the world. That costs a whole lot of money and means the vaccines are easily destroyed. “One potential application would be to use these tardigrade proteins to stabilize vaccines or pharmaceuticals in a dry state that you can keep at room temperature and not have to worry about refrigeration during transportation and storage,” says Boothby.
Not bad, little water bear. Consider me sorry for the cannon-wearing-khakis thing.
