Intrinsically Disordered Tardigrade Proteins Self-Assemble into Fibrous Gels in Response to Environmental Stress

Tardigrades are remarkable for their ability to survive drastic stress conditions as diverse as extreme temperature and desiccation. The molecular mechanisms that confer this unusual resistance to physical stress remain unknown. Recently, tardigrade-unique intrinsically disordered proteins have been shown to play an essential role in tardigrade anhydrobiosis. Here, we characterize the conformational and physical behaviour of CAHS-8 from Hypsibius exemplaris. NMR spectroscopy reveals that the protein comprises an extended central helical domain, flanked by disordered termini. Upon concentration, the protein is shown to successively form oligomers, long fibres and finally gels constituted of fibres, in a strongly temperature-dependent manner. The helical domain forms the core of the fibrillar structure, with the disordered termini remaining highly dynamic within the gel. Soluble proteins can be encapsulated within cavities in the gel, maintaining their functional form. The ability to reversibly form fibrous gels may be associated with the enhanced protective properties of these proteins.