Protective roles of highly conserved motif 1 in tardigrade cytosolic‐abundant heat soluble protein in extreme environments

Abstract Tardigrades are remarkable microscopic animals that survive harsh conditions such as desiccation and extreme temperatures. Tardigrade‐specific intrinsically disordered proteins (TDPs) play an essential role in the survival of tardigrades in extreme environments. Cytosolic‐abundant heat soluble (CAHS) protein, a key TDP, is known to increase desiccation tolerance and to protect the activity of several enzymes under dehydrated conditions. However, the function and properties of each CAHS domain have not yet been elucidated in detail. Here, we aimed to elucidate the protective role of highly conserved motif 1 of CAHS in extreme environmental conditions. To examine CAHS domains, three protein constructs, CAHS Full (1–229), CAHS ∆Core (1–120_184–229), and CAHS Core (121–183), were engineered. The highly conserved CAHS motif 1 (124–142) in the CAHS Core formed an amphiphilic α helix, reducing the aggregate formation and protecting lactate dehydrogenase activity during dehydration–rehydration and freeze–thaw treatments, indicating that CAHS motif 1 in the CAHS Core was essential for maintaining protein solubility and stability. Aggregation assays and confocal microscopy revealed that the intrinsically disordered N‐ and C‐terminal domains were more prone to aggregation under our experimental conditions. By explicating the functions of each domain in CAHS, our study proposes the possibility of using engineered proteins or peptides derived from CAHS as a potential candidate for biological applications in extreme environmental stress responses.