Study: Tardigrades’ Unique Protein Forms Protective Cloud against Extreme Survival Threats

Tardigrades, also known as water bears and moss piglets, are small invertebrate animals that are found in marine, freshwater, and terrestrial habitats throughout the Earth. These tiny creatures have the remarkable ability to survive extremes including very low temperatures, high levels of radiation and exposure to chemicals that are harmful to other forms of life. According to new research from the University of California, San Diego, tardigrades are able to withstand extreme conditions because of a unique nuclear protein termed Dsup (Damage suppression protein) that binds and forms a protective cloud.

This scanning electron microscope image shows a tardigrade. Image credit: Diane Nelson, National Park Service, U.S. Department of the Interior.

Tardigrades are typically about 0.1 to 1 mm in length, and comprise a head segment in addition to four body segments that each contains two legs with claws.

Terrestrial tardigrades require a thin film of water to remain active. In the absence of water, they undergo ‘anhydrobiosis’ into a dormant dehydrated state from which they can be rehydrated to an active form.

In the anhydrobiotic state, tardigrades are resistant to extreme conditions of heat, cold, vacuum, pressure, radiation, and chemical treatments. Remarkably, they have been found to survive exposure to the vacuum and radiation of outer space.

Previous studies identified Dsup in a tardigrade called Ramazzottius varieornatus that can protect human cells from damage by X-rays.

However, it was not known whether Dsup binds directly to chromatin or plays a more indirect role in protecting DNA.

Professor James Kadonaga and colleagues used biochemical approaches to study Dsup.

Their experiments revealed that Dsup from Ramazzottius varieornatus binds to chromatin to protect the DNA from damage by hydroxyl radicals, and that the Dsup protein in another tardigrade species, Hypsibius exemplaris, also works in a similar way.

Further analysis showed that a region of Dsup that is needed to bind to chromatin is very similar to a region that had been previously found only in chromatin-binding proteins from humans and other vertebrates.

Chavez et al discover that the tardigrade protein Dsup binds and forms a protective cloud against extreme survival threats such as radiation damage. Image credit: James Kadonaga, University of California, San Diego.

“We now have a molecular explanation for how Dsup protects cells from X-ray irradiation,” Professor Kadonaga said.

“We see that it has two parts, one piece that binds to chromatin and the rest of it forming a kind of cloud that protects the DNA from hydroxyl radicals.”

“However, we don’t think this protection was meant specifically to shield against radiation.”

“Instead, it’s probably a survival mechanism against hydroxyl radicals in the mossy environments that many terrestrial tardigrades inhabit.”

“When the moss dries up, tardigrades enter anhydrobiosis during which Dsup protection should help them survive.”

The findings eventually could help researchers develop animal cells that can live longer under extreme environmental conditions.

In biotechnology, this knowledge could be used to increase the durability and longevity of cells, such as for the production of some pharmaceuticals in cultured cells.

“In theory, it seems possible that optimized versions of Dsup could be designed for the protection of DNA in many different types of cells,” Professor Kadonaga said.

“Dsup might thus be used in a range of applications, such as cell-based therapies and diagnostic kits in which increased cell survival is beneficial.”

The study is published in the journal eLife.

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Carolina Chavez et al. 2019. The tardigrade damage suppressor protein binds to nucleosomes and protects DNA from hydroxyl radicals. eLife 8: e47682; doi: 10.7554/eLife.47682