Abstract
Group 1 (Dur-19, PF00477, LEA_5) Late Embryogenesis Abundant (LEA) proteins are present in organisms from all three domains of life, Archaea, Bacteria, and Eukarya. Surprisingly, Artemia is the only genus known to include animals that express group 1 LEA proteins in their desiccation-tolerant life-history stages. Bioinformatics analysis of circular dichroism data indicates that the group 1 LEA protein AfLEA1 is surprisingly ordered in the hydrated state and undergoes during desiccation one of the most pronounced disorder-to-order transitions described for LEA proteins from A. franciscana. The secondary structure in the hydrated state is dominated by random coils (42%) and β-sheets (35%) but converts to predominately α-helices (85%) when desiccated. Interestingly, AfLEA1 interacts with other proteins and nucleic acids, and RNA promotes liquid–liquid phase separation (LLPS) of the protein from the solvent during dehydration in vitro. Furthermore, AfLEA1 protects the enzyme lactate dehydrogenase (LDH) during desiccation but does not aid in restoring LDH activity after desiccation-induced inactivation. Ectopically expressed in D. melanogaster Kc167 cells, AfLEA1 localizes predominantly to the cytosol and increases the cytosolic viscosity during desiccation compared to untransfected control cells. Furthermore, the protein formed small biomolecular condensates in the cytoplasm of about 38% of Kc167 cells. These findings provide additional evidence for the hypothesis that the formation of biomolecular condensates to promote water stress tolerance during anhydrobiosis may be a shared feature across several groups of LEA proteins that display LLPS behaviors.
Highlights
Since their discovery in cotton seeds by Dure et al [1], the importance of late embryogenesis abundant (LEA) proteins in the abiotic stress tolerance of plants has been firmly established
Utilizing similar techniques and guided by computation tools, we performed a comprehensive analysis of the behavior of Af LEA1 during desiccation, and our findings provide new insights into two specific hypotheses regarding LEA protein functions: molecular shielding [22] and hydration buffering [23]
The protein Af LEA1 was readily expressed in E. coli, and an approximately 90%
Summary
Since their discovery in cotton seeds by Dure et al [1], the importance of late embryogenesis abundant (LEA) proteins in the abiotic stress tolerance of plants has been firmly established. Their actual function(s) are still largely unresolved [2–4]. Using the classification proposed by Tunnacliffe and Wise, most investigated anhydrobiotic animals express LEA proteins from Group 3 (PF02987) [3]. The only exception is the brine shrimp, Artemia franciscana, which expresses LEA proteins from two additional families. These LEA proteins are from Group 1 (PF00477) and Group
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