Mimicking the Plant Cell Interior under Water Stress by Macromolecular Crowding: Disordered Dehydrin Proteins Are Highly Resistant to Structural Collapse

Abstract

The dehydrins are a class of drought-induced proteins in plants that lack a fixed three-dimensional structure. Their specific molecular action, as well as the reason for their disordered character, is as yet poorly understood. It has been speculated, however, that the dehydrins are tuned to acquire a biologically active structure only under the conditions in which they normally function (i.e. upon dehydration). To test this hypothesis, we here investigate the effect of reduced water content and macromolecular crowding on three dehydrins from Arabidopsis (Arabidopsis thaliana). As a simplistic model for mimicking cellular dehydration, we used polyethylene glycol, glycerol, and sugars that plants naturally employ as compatible solutes (i.e. sucrose and glucose). Macromolecular crowding was induced by the large polysaccharides Ficoll and dextran. The results show that the dehydrins are remarkably stable in their disordered state and are only modestly affected by the solvent alterations. A notable exception is the dehydrin Cor47, which shows a small, intrinsic increase in helical structure at high concentrations of osmolytes. We also examined the effect of phosphorylation but found no evidence that such posttranslational modifications of the dehydrin sequences modulate their structural response to osmolytes and crowding agents. These results suggest that the dehydrins are highly specialized proteins that have evolved to maintain their disordered character under conditions in which unfolded states of several globular proteins would tend to collapse.

Tunable Membrane Binding of the Intrinsically Disordered Dehydrin Lti30, a Cold-Induced Plant Stress Protein

“…With CKII, we observe no corresponding effect, consistent with previous reports from other groups (Alsheikh et al, 2005). We previously showed that phosphorylation has no detectable effect on the structures of solubilized dehydrins (Mouillon et al, 2008), and, in line with this, CD analysis of Lti30 reveals no structural changes upon phosphorylation (see Supplemental Figure 5 online). Nevertheless, we see here that phosphorylation of Lti30 significantly affects the protein's ability to assemble vesicles in vitro (Figure 8).…”

“…Dehydrins are found to be highly resistant to unspecific chain collapse in vitro (Mouillon et al, 2008). Taken together, this suggests a functional adaptation to remain coil like in the highly crowded cytosol of desiccated plant cells, most likely to assure maximum exposure of the local, conserved segments to their biological targets (Mouillon et al, 2006(Mouillon et al, , 2008. In accordance with these sequence characteristics, an early hypothesis has been that dehydrins interact as a group with cellular membranes and modulate their properties via the characteristic K-segments (Dure, 1993;Close, 1996).…”

“…Combined with their unusually high proportion of hydrophilic and charged amino acids, this modular sequence pattern makes them unsuitable for adapting a specific hydrophobic core (Figure 1). Dehydrins are found to be highly resistant to unspecific chain collapse in vitro (Mouillon et al, 2008). Taken together, this suggests a functional adaptation to remain coil like in the highly crowded cytosol of desiccated plant cells, most likely to assure maximum exposure of the local, conserved segments to their biological targets (Mouillon et al, 2006(Mouillon et al, , 2008.…”

“…Comparison of the different phosphorylation sites among the divergent proteins in Table 1 points again at a functional division within the dehydrin family. As demonstrated earlier, the Arabidopsis dehydrins Cor47 and Lti29 (both SK n dehydrins), but not Lti30, become phosphorylated in vitro by CKII (Riera et al, 2004;Alsheikh et al, 2005;Mouillon et al, 2008). The main reason for this different kinase selectivity is the lack of conserved multi-S-segments, which constitute the prime target for CKII activity, in the K n dehydrins, such as Lti30.…”

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

“…The disorder confers structural flexibility and malleability to adapt to changes in the protein environment, including water potential, pH, ionic strength, and temperature, and to undergo structural transition when complexed with ligands such as other proteins, DNA, RNA, or membranes (Prestrelski et al, 1993;Uversky, 2002). Structural changes from disorder to ordered functional structure also can be induced by the folding of a partner protein (Wright and Dyson, 1999;Tompa, 2002;Mouillon et al, 2008).…”