The biology of tardigrade disordered proteins in extreme stress tolerance

Abstract

Disordered proteins have long been known to help mediate tolerance to different abiotic stresses including freezing, osmotic stress, high temperatures, and desiccation in a diverse set of organisms. Recently, three novel families of intrinsically disordered proteins were identified in tardigrades, microscopic animals capable of surviving a battery of environmental extremes. These three families include the Cytoplasmic-, Secreted-, and Mitochondrial- Abundant Heat Soluble (CAHS, SAHS, and MAHS) proteins, which are collectively termed Tardigrade Disordered Proteins (TDPs). At the level of sequence conservation TDPs are unique to tardigrades, and beyond their high degree of disorder the CAHS, SAHS, and MAHS families do not resemble one another. All three families are either highly expressed constitutively, or significantly enriched in response to desiccation. In vivo, ex vivo, and in vitro experiments indicate functional roles for members of each TDP family in mitigating cellular perturbations induced by various abiotic stresses. What is currently lacking is a comprehensive and holistic understanding of the fundamental mechanisms by which TDPs function, and the properties of TDPs that allow them to function via those mechanisms. A quantitative and systematic approach is needed to identify precisely what cellular damage TDPs work to prevent, what sequence features are important for these functions, and how those sequence features contribute to the underlying mechanisms of protection. Such an approach will inform us not only about these fascinating proteins, but will also provide insights into how the sequence of a disordered protein can dictate its functional, structural, and dynamic properties. Graphical abstract

Room-temperature Storage of Lyophilized Engineered Bacteria using Tardigrade Intrinsically Disordered Proteins

“…Result 1: TDPs can protect recombinant strains based on E. coli BL21 under conditions of lyophilization, allowing them to be preserved at room temperature [23] . CAHS 106094 expression in BL21 resulted in the highest survival rate at room temperature after lyophilization.…”

Mitochondrial alternative oxidase contributes to successful tardigrade anhydrobiosis

“…These proteins are highly expressed constitutively or significantly enriched in response to desiccation (e.g. [ 18 , 19 ],) but seem to be missing in some tardigrades, suggesting that anhydrobiosis in tardigrades cannot be attributed solely to TDPs [ 20 , 21 ]. However, available data appear to support a common and important role of proper mitochondria function in anhydrobiosis.…”

Desiccation-induced fibrous condensation of CAHS protein from an anhydrobiotic tardigrade

“…It is The copyright holder for this preprint this version posted June 22, 2021. ; https://doi.org/10.1101/2021.06. 22.449423 doi: bioRxiv preprint 3 their biological components or cell membrane without water. Early studies on desiccation tolerance identified the disaccharide trehalose and the late embryogenesis abundant (LEA) proteins as the functional mediators of anhydrobiosis (9).…”

“…In extremotolerant tardigrades, through heat-soluble proteomics in a search for LEA and LEAlike proteins, highly hydrophilic and heat-soluble protein families have been identified as cytosolic abundant heat-soluble (CAHS) proteins (19)(20)(21)(22). Although these proteins are distinct from LEA proteins based on their conserved sequences, they share some similarities with LEA proteins in terms of the bioinformatic prediction of high propensity for α-helix formation (19,20).…”