Tardigrade Secretory-Abundant Heat-Soluble Protein Has A Flexible Beta-Barrel Structure In Solution And Keeps This Structure In Dehydration

Secretory-abundant heat-soluble (SAHS) proteins are unique heat-soluble proteins of Tardigrada and are believed to play an essential role in anhydrobiosis, a latent state of life induced by desiccation. To investigate the dynamic properties, molecular dynamics (MD) simulations of a SAHS protein, RvSAHS1, were performed in solution and under dehydrating conditions. For comparison purposes, MD simulations of a human liver-type fattyacid binding protein (LFABP) were performed in solution. Furthermore, high-speed atomic force microscopy observations were conducted to ascertain the results of the MD simulations. Three properties of RvSAHS1 were found as follows. (1) The entrance region of RvSAHS1 is more flexible and can be more extensive in solutions compared with that of a human LFABP because there is no salt bridge between the beta D and beta E strands. (2) The intrinsically disordered domain in the N-terminal region significantly fluctuates and can form an amphiphilic alpha-helix. (3) The size of the entrance region gets smaller along with dehydration, keeping the beta-barrel structure. Overall, the obtained results provide atomic-level dynamics of SAHS proteins.