Role of Intrinsic Disorder in Animal Desiccation Tolerance

This review compares the molecular strategies employed by anhydrobiotic invertebrates to survive extreme water stress. Intrinsically disordered proteins (IDPs) play a central role in desiccation tolerance in all species investigated. Various hypotheses about the functions of anhydrobiosis-related intrinsically disordered (ARID) proteins, including late embryogenesis abundant (LEA) and tardigrade-specific intrinsically disordered proteins, are evaluated by broad sequence characterization. A surprisingly wide range in sequence characteristics, including hydropathy and the frequency and distribution of charges, is discovered. Interestingly, two clusters of similar proteins are found that potentially correlate with distinct functions. This may indicate two broad groups of ARID proteins, composed of one group that folds into functional conformations during desiccation and a second group that potentially displays functions in the hydrated state. A broad range of physiochemical properties suggest that folding may be induced by factors such as hydration level, molecular crowding, and interactions with binding partners. This plasticity may be required to fine-tune the ARID-proteome response at different hydration levels during desiccation. Furthermore, the sequence properties of some LEA proteins share qualities with IDPs known to undergo liquid-liquid phase separations during environmental challenges.