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The incredible resistance of tardigrades to different environmental stresses, explained by a gel

​Researchers at the CEA-Irig have partly lifted the veil on the extraordinary resistance of a small animal, the tardigrade. At play is a disordered protein capable of transforming itself into a protective gel for other biomolecules during drought or extreme cold.

Published on 20 December 2021

With a life expectancy of only one to three years, tardigrades are the only known animals able to survive in the vacuum of space without assistance. Their remarkable ability to resist extreme stress (desiccation, cold, radiation, etc.) makes them an interesting model to study.

According to recent studies, these animals possess intrinsically disordered proteins – meaning that they lack a persistent three-dimensional structure and remain functional in a disordered state – that play a key role in anhydrobiosis, a physiological state allowing them to survive dormant for decades under extreme drought conditions. How do these proteins contribute to the exceptional resistance of tardigrades?

To find out, Irig researchers studied one of these proteins from Hypsibius exemplaris, CAHS-8 (Cytosolic Abundant Heat-Soluble protein), using nuclear magnetic resonance (NMR) and atomic force microscopy (AFM) combined with other biophysical techniques.

They discovered that this protein has disordered and highly flexible arms surrounding a long central helical domain, whose behavior is highly temperature dependent.

Next, they hypothesized that an environmental disturbance (low temperature, high concentration) could lead these proteins to associate, through a portion of this helical domain. And indeed, they observed this (reversible) association in the form of oligomers and then fibrils, and finally a gel displaying regularly sized pores.

They then trapped other proteins in this gel in order to study them. Their structure was not altered inside this matrix, although their movements were significantly slower.

The formation of such an intracellular matrix could be used to maintain biomolecules in their functional state by reducing, for example, the volume of water they require. It could also prevent the formation of ice crystals and ensure their "cryoprotection".

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