Plant Physiology Preview
Published on March 24, 2006; 10.1104/pp.106.079848
Received March 6, 2006
Returned for revision March 10, 2006
Accepted March 10, 2006
Structural investigation of disordered stress proteins: comparison of full-length Dehydrins with isolated peptides of their conserved segments
Jean-Marie Mouillon , Petter Gustafsson , and Pia Harryson *
Department of Chemistry and Biomedical Sciences, Kalmar University, S-391 82 KALMAR, SWEDEN, Phone: +46(0)480-446267
UMPC, Department of Plant Physiology, Umeå University, SE-901 87 UMEÅ, SWEDEN, Phone: +46 (0)90 786 50 00 Fax: +46 (0)90 786 66 76
Department of Biochemistry and Biophysics, Arrhenius Laboratories for Natural Sciences, Stockholm University, 106 91 Stockholm, Sweden, Tel: + 46 8 164238 Fax: + 46 8 153679
* Corresponding author; email: pia.harryson{at}dbb.se.su.
Dehydrins constitute a class of intrinsically disordered proteins that are expressed under conditions of water-related stress. Characteristic to the dehydrins are some highly conserved stretches of 7-17 residues that are repetitively scattered in their sequences, the K-, S-, Y- and lysine 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 thaliana (Cor47, Lti29, Lti30 and Rab18) and isolated peptide mimics of the K-, Y- and lysine rich segments. In physiological buffer, the CD spectra of the full-length dehydrins reveal overall disordered structures with a variable content of poly-proline helices (PII), 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-stabilising 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 for maintaining 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 inter-molecular scaffolding. In this perspective, it is notable that the lysine rich segment in Cor47 and Lti29 show sequence similarities with the animal chaperone HSP90.
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