Transition from Natively Unfolded to Folded State Induced by Desiccation in an Anhydrobiotic Nematode Protein

Abstract

Late embryogenesis abundant (LEA) proteins are associated with desiccation tolerance in resurrection plants and in plant seeds, and the recent discovery of a dehydration-induced Group 3 LEA-like gene in the nematode Aphelenchus avenae suggests a similar association in anhydrobiotic animals. Despite their importance, little is known about the structure of Group 3 LEA proteins, although computer modeling and secondary structure algorithms predict a largely ␣-helical monomer that forms coiled coil oligomers. We have therefore investigated the structure of the nematode protein, Aav-LEA1, in the first such analysis of a well characterized Group 3 LEA-like protein. Immunoblotting and subunit cross-linking experiments demonstrate limited oligomerization of AavLEA1, but analytical ultracentrifugation and gel filtration show that the vast majority of the protein is monomeric. Moreover, CD, fluorescence emission, and Fourier transform-infrared spectroscopy indicate an unstructured conformation for the nematode protein. Therefore, in solution, no evidence was found to support structure predictions; instead, Aav-LEA1 seems to be natively unfolded with a high degree of hydration and low compactness. Such proteins can, however, be induced to fold into more rigid structures by partner molecules or by altered physiological conditions. Because AavLEA1 is associated with desiccation stress, its Fourier transform-infrared spectrum in the dehydrated state was examined. A dramatic but reversible increase in ␣-helix and, possibly, coiled coil formation was observed on drying, indicating that computer predictions of secondary structure may be correct for the solid state. This unusual finding offers the possibility that structural shifts in Group 3 LEA proteins occur on dehydration, perhaps consistent with their role in anhydrobiosis.

The K-Segment of Maize DHN1 Mediates Binding to Anionic Phospholipid Vesicles and Concomitant Structural Changes

“…While some LEA proteins (generally groups 3 and 4) adopt predominantly a-helical structure upon drying or addition of SDS or trifluoroethanol (Goyal et al, 2003;Shih et al, 2004;Tolleter et al, 2007), others (generally groups 1 and 2) assume only partial (about 10%) a-helical structure upon addition of trifluoroethanol, SDS, liposomes, and other helical inducers (Koag et al, 2003;Soulages et al, 2003;Shih et al, 2004;Mouillon et al, 2006Mouillon et al, , 2008. In accordance with those previous results, CD spectra of full-length DHN1 displayed low overall percentages of a-helical structure with SDS and liposomes, while a more prominent percentage of a-helical transition was observed with the K-segment alone.…”

Genetic approaches towards overcoming water deficit in plants - special emphasis on LEAs

“…The LEA proteins confer increased resistance to osmotic or freeze stress when introduced into yeast and also improved water deficit tolerance in the transformants (Wang et al, 2003, also see Table 1). Structural information in both hydrated and dry states is known in a group 3 LEA-like protein (AavLEA1) from Aphelenchus avenae provides new insights in to the molecular mechanism especially under stress conditions (Goyal et al, 2003).…”

Chaperone Activity of ERD10 and ERD14, Two Disordered Stress-Related Plant Proteins

“…Their amino acid compositions provide an overall hydrophilic character, which potentially confers a high potential hydration capacity (McCubbin et al, 1985;Goyal et al, 2003), also demonstrated recently experimentally (Bokor et al, 2005). It was also reported that both ERD10 and ERD14 can be phosphorylated at various sites, which promotes the binding of bivalent metal ions, and this might be related to their ionsequestering activity (Rorat, 2006;Tunnacliffe and Wise, 2007).…”