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ENVIRONMENTAL STRESS AND ADAPTATION TO STRESS

Mimicking the Plant Cell Interior under Water Stress by Macromolecular Crowding: Disordered Dehydrin Proteins Are Highly Resistant to Structural Collapse^1,[W]

Umeå Plant Science Center, Department of Plant Physiology, Umeå University, S–901 87 Umeå, Sweden (J.-M.M.); and Department of Biochemistry and Biophysics, Arrhenius Laboratories for Natural Sciences, Stockholm University, S–106 91 Stockholm, Sweden (S.K.E., P.H.)

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.

² Present address: Fluxome Sciences A/S, Diplomvej 378, DK–2800 Lyngby, Denmark.

The author responsible for distribution of materials integral to the findings presented in this article in accordance with the policy described in the Instructions for Authors (www.plantphysiol.org) is: Pia Harryson (pia.harryson{at}dbb.su.se).

^[W] The online version of this article contains Web-only data.

www.plantphysiol.org/cgi/doi/10.1104/pp.108.124099

^* Corresponding author; e-mail pia.harryson{at}dbb.su.se.

Received July 18, 2008; accepted October 1, 2008; published October 10, 2008.

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