Unstructured Proteins Help Tardigrades Survive Desiccation

Proteins with unstable 3-D structures help the microscopic animals withstand drying.

By | March 16, 2017

Scanning electron micrograph of six tardigradesTHOMAS BOOTHBYHardy, microscopic animals called tardigrades, also known as water bears, can survive desiccation. Until now, it wasn’t clear exactly how. The results of a study published in Molecular Cell today (March 16) suggest that proteins lacking stable 3-D structures, called tardigrade-specific intrinsically disordered proteins (TDPs), form glass-like solids that protect the animals during drying.

Other organisms achieve desiccation tolerance with a sugar called trehalose, which forms glass-like solids upon drying. For years, researchers assumed that tardigrades used trehalose, too, but many species of water bears only express small amounts of the sugar—likely not enough to confer the substance’s preservative capabilities.

TDPs “seem to work by a mechanism which is similar to this sugar, trehalose,” said coauthor Thomas Boothby, a postdoc at the University of North Carolina, Chapel Hill. “It seems like evolution has basically come up with two different ways to do the same trick.”

Boothby and colleagues identified a group of TDPs during a screen for tardigrade genes upregulated during desiccation. They confirmed that many of the genes’ protein products were disordered, and that these genes were expressed in three different tardigrade species, either constitutively or during drying. When the team used RNA interference (RNAi) to knock down TDP genes, the tardigrades were less able to survive desiccation.

Next, the researchers introduced TDP genes into yeast and bacteria, finding that the proteins increased desiccation tolerance in both organisms. TDPs also preserved the activity of an enzyme, lactate dehydrogenase, during drying in vitro. The authors showed that, upon desiccation, isolated TDPs transform into a glass-like substance, which also is present in—and increases survival of—both yeast that express TDPs and tardigrades during drying.

The study is “very solidly done,” biologist John Crowe of the University of California, Davis, who did not participate in the work, told The Scientist. He added that one direction for future research would be to examine the effects of TDPs on cell membranes.

“It’s been well known for some time that polymers like this can prevent fusion between membranes during drying, but they don’t preserve them completely,” Crowe said. “Small molecules like trehalose or glucose, or some other small sugar, are required in addition. It may well be that the small amount of trehalose that’s found in tardigrades in conjunction with those proteins may do the job. You might need both.”

According to Boothby, another open question is whether tardigrade species other than the three examined in this study use a similar mechanism to protect against desiccation. There are more than 1,200 tardigrade species, divided into two classes.

“It’s going to be really instructive if and when we can start looking at differences between those classes,” said Carl Johansson, an instructor at Fresno City College in California who was not involved in the work.

Probing how TDPs function at a molecular level to protect the animals from desiccation could have applications beyond water bears. “This represents the first step that could be used to improve the capability of other organisms to desiccate in the future,” said coauthor Lorena Rebecchi of the University of Modena and Reggio Emilia in Italy. Rebecchi explained that learning more about tardigrade proteins could eventually enable researchers to safely desiccate plants and other animals.

“People don’t know about tardigrades, but they are very important,” she said. “They have a lot of biological secrets that could be used to improve the quality of human life.”

T.C. Boothby et al., “Tardigrades use intrinsically disordered proteins to survive desiccation,” Molecular Cell, doi:10.1016/j.molcel.2017.02.018, 2017.

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Avatar of: James V. Kohl

James V. Kohl

Posts: 453

March 20, 2017

There is no such thing as an unstructured protein. All protein folding chemistry must link chirality to autophagy and the physiology of reproduction via endogenous RNA interference and amino acid substitutions. If that was not a fact, the nutrient energy-dependent stability of supercoiled DNA would fail to prevent:

1) virus-driven energy therft and

2) the degradation of messenger RNA, which leads to

3) genomic entropy.

Example: Bacteria become archaea and L-forms in the context of the viral hecatomb.

Example: The transgenerational epigenetic inheritance of Zika virus-damaged DNA is linked to craniofacial morphology and brain development that is more characteristic of non-human primates that failed to ecologically adapt..

See also: DNA 'ingesting': A tenth of quirky creature's active genes are foreign

What tardigrades eat is the key to their RNA-mediated protein structure and function via the physiology of their pheromone-controlled reproduction, which links ecological variation to ecological adaptation via the molecular mechanisms common to all species that must eat to survive. The diversity of the diet is linked to the survival of all species via amino acid substitutions in structured proteins.

Avatar of: Azur

Azur

Posts: 2

March 21, 2017

It always annoys me a bit when tardigrades are described as extremely hardy: they are not. It is ONLY in the desiccated, cryptobiotic, form they are resistant to adverse conditions. In their active, feeding, stage they are sensitivie to and quickly die from e.g low oxygen levels, temperatures below freezing or above 40 celsius, radiation, starvation, or rapid desiccation.

Even in desicated form they are no more resistant to adverse conditions than other organisms which can form desiccated cryptobiotic spores, like for instance many rotifers and ciliates. Or even the macroscopic crustacean _Artemia_ ("sea monkeys").

If you want the actually toughest animals on the planet, the most extreme survivors _also when moving around and feeding_, then look at nematodes. They're not as cute as tardigrades, but far more hardy.

Or why not loriciferans or gnathostomulids, which are the only animals which can live indefinitely and even reproduce without oxygen.

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