Linking structural changes with desiccation protection of intrinsically disordered proteins

All life depends on water, yet numerous organisms ranging from bacteria to plants must contend with extreme dehydration in order to survive. Remarkably, many of these organisms independently evolved intrinsically disordered proteins (IDPs) that help them survive in a dry state. The molecular mechanism by which these protective disordered proteins work remains unknown. It has been hypothesized that the protective effect of such IDPs stems from a structural change that occurs as their surroundings dehydrate. To test this hypothesis we use circular dichroism (CD) spectroscopy to observe the helicity of protective IDPs from four different organisms before, during, and after desiccation, and in the presence and absence of cosolutes such as trehalose and sucrose that are abundant in these desiccated organisms. We then compare our structural data with enzymatic assays that gauge the ability of the same IDPs to protect proteins from desiccation in the same conditions. Our results link structural changes with the protective ability of IDPs. They also highlight the importance of the full-length sequence in ensuring reversible structural changes and increased protective ability of this important class of disordered proteins.