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First published online March 24, 2006; 10.1104/pp.106.079848 Plant Physiology 141:638-650 (2006) © 2006 American Society of Plant Biologists Structural Investigation of Disordered Stress Proteins. Comparison of Full-Length Dehydrins with Isolated Peptides of Their Conserved Segments1Department of Chemistry and Biomedical Sciences, Kalmar University, S–391 82 Kalmar, Sweden (J.-M.M.); Umeå Plant Science Centre, Department of Plant Physiology, Umeå University, SE–901 87 Umea, Sweden (P.G.); and Department of Biochemistry and Biophysics, Arrhenius Laboratories for Natural Sciences, Stockholm University, 106 91 Stockholm, Sweden (P.H.)
Dehydrins constitute a class of intrinsically disordered proteins that are expressed under conditions of water-related stress. Characteristic of the dehydrins are some highly conserved stretches of seven to 17 residues that are repetitively scattered in their sequences, the K-, S-, Y-, and Lys-rich segments. In this study, we investigate the putative role of these segments in promoting structure. The analysis is based on comparative analysis of four full-length dehydrins from Arabidopsis (Arabidopsis thaliana; Cor47, Lti29, Lti30, and Rab18) and isolated peptide mimics of the K-, Y-, and Lys-rich segments. In physiological buffer, the circular dichroism spectra of the full-length dehydrins reveal overall disordered structures with a variable content of poly-Pro helices, a type of elongated secondary structure relying on bridging water molecules. Similar disordered structures are observed for the isolated peptides of the conserved segments. Interestingly, neither the full-length dehydrins nor their conserved segments are able to adopt specific structure in response to altered temperature, one of the factors that regulate their expression in vivo. There is also no structural response to the addition of metal ions, increased protein concentration, or the protein-stabilizing salt Na2SO4. Taken together, these observations indicate that the dehydrins are not in equilibrium with high-energy folded structures. The result suggests that the dehydrins are highly evolved proteins, selected to maintain high configurational flexibility and to resist unspecific collapse and aggregation. The role of the conserved segments is thus not to promote tertiary structure, but to exert their biological function more locally upon interaction with specific biological targets, for example, by acting as beads on a string for specific recognition, interaction with membranes, or intermolecular scaffolding. In this perspective, it is notable that the Lys-rich segment in Cor47 and Lti29 shows sequence similarity with the animal chaperone HSP90.
1 This work was supported by the Swedish Research Council for Environment, Agricultural Sciences, and Spatial Planning (P.H.) and Carl Tryggers Stiftelse (P.H.). 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). Article, publication date, and citation information can be found at www.plantphysiol.org/cgi/doi/10.1104/pp.106.079848. * Corresponding author; e-mail pia.harryson{at}dbb.su.se; fax 46–8–153679. Received March 6, 2006; returned for revision March 6, 2006; accepted March 10, 2006. This article has been cited by other articles:
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