Computer Model Exposes Tardigrade Superpower

By Gunnar De Winter

Gunnar De Winter
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I am water bear, hear me roar (Wikimedia commons, Goldstein lab)

Tardigrades, aka water bears or moss piglets, are a group of microscopic animals (about 0.5mm long as adults). The roughly 1,300 known species can be found anywhere, from the freezing cold of the Antarctic to the humid heat of the tropical rainforest.

Their wide-ranging distribution is not their main claim to fame, though. The resilience that enables this distribution is. Tardigrades are among the hardiest animals we know.

They’ve been recovered alive from inside layers of ice as well as the inside of hot springs. They laugh at radiation doses that are several thousand times the lethal dose for us feeble humans. They float happily in a vacuum (up to ten days in outer space), but some species are equally comfortable under a pressure several times higher than that measured at the bottom of the Mariana trench.

They may be small, but they’re superheroes nonetheless. In fact, it’s been proposed that in the event of a (limited) astrophysical apocalypse, earth might not be entirely sterile. There will probably be some tardigrades sticking around…

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Structural model of Dsup, quickly assembled on UniProt (colors are electrical charges, becomes important later on).

The reason for their resilience is that they can enter a state known as cryptobiosis. Think supercharged hibernation. In this state, metabolism drops to practically zero and, in tardigrades, the water content in the body’s tissues falls to roughly 1%. In this state, they don’t need food or water. And they can stay that way for many (dozens of) years, while still being able to come out of it and go about their perambulating way.

Another interesting superpower they have, and one which is unique to tardigrades, is the protein Dsup. If I tell you this stands for ‘damage suppressor’, you know it’s something cool. Dsup is a DNA protector protein. Radiation that would shred every picogram of DNA in any other animals? A little dsup and the tardigrades will be alright.

The power of disorder

How Dsup exercises its DNA-protecting superpower, however, was a mystery. Now, a new study gives us a little peek behind the curtain of Dsup’s capabilities.

Investigations into Dsup so far have suggested that the protein might physically protect DNA by literally hugging it and acting as shield. The authors of this new study, though, took a different approach. They employed the power of a supercomputer to model Dsup’s structure and its interaction with DNA.

Modelling all 750,000 atoms of the Dsup-DNA system strained even the supercomputer’s resources.

But eventually, results trickled out.

The model suggests that Dsup is an intrinsically disordered protein, aka a protein that doesn’t have a fixed 3D structure. This means that Dsup is able to flexibly alter its shape to match that of the DNA it can shield. The researchers also found that Dsup and DNA were electrostatically complementary, which is a fancy way to say that the electric fields of the molecules (Dsup and DNA) do not repulse each other — however small these fields might be, they do play an important role in the world of molecules and their interactions.

As the authors put it:

The picture that emerges from our results is that the intrinsic disorder of Dsup and the strong electrostatic attractions between the protein and DNA drive the formation of flexible aggregates with Dsup and DNA closely associated.

It is tempting to speculate about tailoring a human version of Dsup. When we’re considering ways to ‘enhance’ astronauts for travels in space (including with CRISPR), Dsup (or at least a future version tested and approved for use in humans) can be useful. But there might be applications closer to home. Right now, radiation therapy is often used in the fight against cancer, but it’s indiscriminate in the damage it inflicts. What if a targeted delivery of human-grade Dsup could protect the healthy cells?

Dsup powers, activate.