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J. Biol. Chem., Vol. 283, Issue 45, 31142-31152, November 7, 2008

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An Unusual Intrinsically Disordered Protein from the Model Legume Lotus japonicus Stabilizes Proteins in Vitro^*

Svend Haaning¹, Simona Radutoiu², Søren V. Hoffmann, Jens Dittmer^¶, Lise Giehm^||, Daniel E. Otzen^||3, and Jens Stougaard⁴

From the Centre for Carbohydrate Recognition and Signalling, Department of Molecular Biology, Institute for Storage Ring Facilities, ^¶Department of Chemistry, and ^||Interdisciplinary Nanoscience-Centre, University of Aarhus, 8000 Aarhus, Denmark

Intrinsic structural disorder is a prevalent feature of proteins with chaperone activity. Using a complementary set of techniques, we have structurally characterized LjIDP1 (intrinsically disordered protein 1) from the model legume Lotus japonicus, and our results provide the first structural characterization of a member of the Lea5 protein family (PF03242). Contrary to in silico predictions, we show that LjIDP1 is intrinsically disordered and probably exists as an ensemble of conformations with limited residual β-sheet, turn/loop, and polyproline II secondary structure. Furthermore, we show that LjIDP1 has an inherent propensity to undergo a large conformational shift, adopting a largely -helical structure when it is dehydrated and in the presence of different detergents and alcohols. This is consistent with an overrepresentation of order-promoting residues in LjIDP1 compared with the average of intrinsically disordered proteins. In line with functioning as a chaperone, we show that LjIDP1 effectively prevents inactivation of two model enzymes under conditions that promote protein misfolding and aggregation. The LjIdp1 gene is expressed in all L. japonicus tissues tested. A higher expression level was found in the root tip proximal zone, in roots inoculated with compatible endosymbiotic M. loti, and in functional nitrogen-fixing root nodules. We suggest that the ability of LjIDP1 to prevent protein misfolding and aggregation may play a significant role in tissues, such as symbiotic root nodules, which are characterized by high metabolic activity.

Received for publication, July 2, 2008 , and in revised form, September 5, 2008.

^* The costs of publication of this article were defrayed in part by the payment of page charges. This article must therefore be hereby marked "advertisement" in accordance with 18 U.S.C. Section 1734 solely to indicate this fact.

¹ Supported by the Danish Biotech Research Academy (DBRA) and the Danish National Research Foundation (Research Centre CARB).

² Supported by the Danish National Research Foundation (Research Centre CARB).

³ Supported by the Danish Research Science Foundation (Research Centre inSPIN) and the Villum Kann Rasmussen Foundation (Research Centre BioNET).

⁴ Supported by the Danish National Research Foundation (Research Centre CARB). To whom correspondence should be addressed: Gustav Wieds Vej 10, Aarhus 8000, Denmark. Fax: 45-86123178; E-mail: stougaard{at}mb.au.dk.

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