Desiccation-Induced Structuralization and Glass Formation of Group 3 Late Embryogenesis Abundant Protein Model Peptides

Abstract

Anhydrobiotic (i.e., life without water) organisms are known to produce group 3 late embryogenesis abundant (G3LEA) proteins during adaptation to severely water-deficient conditions. Their primary amino acid sequences are composed largely of loosely conserved 11-mer repeat units. However, little information has been obtained for the structural and functional roles of these repeat units. In this study, we first explore the consensus sequences of the 11-mer repeat units for several native G3LEA proteins originating from anhydrobiotic organisms among insects (Polypedilum vanderplanki), nematodes, and plants. Next, we synthesize four kinds of model peptides (LEA models), each of which consists of four or two repeats of the 11-mer consensus sequences for each of the three organisms. The structural and thermodynamic properties of the LEA models were examined in solution, in dehydrated and rehydrated states, and furthermore in the presence of trehalose, since a great quantity of this sugar is known to be produced in the dried cells of most anhydrobiotic organisms. The results of Fourier transform infrared (FTIR) spectroscopic measurements indicate that all of the LEA models transform from random coils to alpha-helical coiled coils on dehydration and return to random coils again on rehydration, both with and without trehalose. In contrast, such structural changes were never observed for a control peptide with a randomized amino acid sequence. Furthermore, our differential scanning calorimetry (DSC) measurements provide the first evidence that the above 11-mer motif-containing peptides themselves vitrify with a high glass transition temperature (>100 degrees C) and a low enthalpy relaxation rate. In addition, they play a role in reinforcing the glassy matrix of the coexisting trehalose. On the basis of these results, we discuss the underlying mechanism of G3LEA proteins as desiccation stress protectants.

LEA Proteins During Water Stress: Not Just for Plants Anymore

“…%, again matching experimental results with CD and FTIR (e.g., (59,60,63,64)). In the dehydrated state the structure is primarily α-helix.…”

“…Interestingly, slow drying reversibly led to both α-helical and intermolecular extended β-sheet structures, which suggested the final protein conformation was not predetermined. Increase in secondary structure during drying also has been reported for LEA proteins from groups 1 and group 2 (dehydrins) (61,62), and for other group 3 proteins and peptides (63,64).…”

Late embryogenesis abundant proteins protect human hepatoma cells during acute desiccation

“…The most remarkable result is the striking integrity of 93.6 ± 4.6% (n = 9) measured for HepG2-AfrLEA3m cells in the absence of trehalose. Consistent with this finding, evidence indicates that model synthetic peptides composed of several tandem motifs of group 3 LEA proteins (22-to 44-aa residues) vitrify at a high T g , which suggests that dried LEA proteins themselves may vitrify and act in this way as excellent protectants against desiccation damage (45). It is appropriate to emphasize that although AfrLEA3m is indeed mitochondrialtargeted, synthesis occurs in the cytosol, and importation into mitochondria is time-dependent (26), and thus presumably some fraction of the protein is continuously present in the cytoplasm.…”

“…Thus, both cellular treatments containing LEA-sugar mixtures display ∼98% membrane integrity after severe desiccation. In vitro studies have shown that mixing LEA-like peptides into trehalose solutions stabilizes the vitrified sugar glasses on drying, as judged by upward shifts in T g (45). Growth studies conducted across ensuing days after rehydration of dried cells revealed the greatest proliferation for those cells containing AfrLEA3m plus trehalose compared with all other treatment groups (Fig.…”

The induction of anhydrobiosis in the sleeping chironomid: Current status of our knowledge

“…This is a characteristic of highly hydrophilic proteins, such as LEA proteins and this suggests that PvLEA proteins may protect other proteins from aggregation and denaturation during anhydrobiosis in P. vanderplanki. Recently, a study on group 3 LEA model peptides, obtained from P. vanderplanki and other anhydrobiotes, showed that LEA proteins participate actively in the vitrification process (49), not only by forming glass by themselves but also by stabilizing the trehalose glassy matrix (see below). This mechanism for combating dehydration stress is probably common to animals, plants, and microorganisms, because LEA proteins are widespread throughout many phyla, although limited to desiccation tolerant organisms.…”