Meeting Abstract
Late Embryogenesis Abundant (LEA) proteins are a remarkable group of intrinsically disordered proteins (IDPs) that confer desiccation tolerance to plants and animals that can enter a cryptobiotic state during their life cycle. AfrLEA6 contains seed maturation domains (SMD) and is expressed in the anhydrobiotic cysts of the brine shrimp Artemia franciscana. in vitro analyses of AfrLEA6 reveal a series of protein phase transitions during desiccation. As ionic strength or molecular crowding with Ficoll-400 increases, AfrLEA6 undergoes a liquid-liquid phase separation (LLPS), forming protein droplets. AfrLEA6 droplets are also inducible by reducing the sample pH from 8.0 to 6.5 and cooling protein solutions from 25˚C to 4˚C. These conditions are notable in the context of the cysts of A. franciscana, which can naturally undergo a cytoplasmic pH shift from 7.9 to 6.5 in response to severe hypoxia. In the hydrated state, AfrLEA6 droplets exclude green fluorescent protein demonstrating that the protein droplet may be selective for inclusions of specific targets. SEM and AFM reveal that AfrLEA6 may also undergoes a phase shift to a hydrogel structure, as ionic strength and crowding increase, which is reversible upon rehydration. However, early during dehydration formed hydrogels dry into a reversible glassy state during complete desiccation. The LLPS of AfrLEA6 may confer desiccation tolerance by selectively incorporating sensitive protein targets and shielding them from desiccation induced denaturation during early drying. Any incorporated proteins may then be stabilized within a glassy compartment in the fully desiccated state and released upon rehydration (supported by NSF IOS-1659970).
