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-lactalbumin refolding by metal ions
1 Laboratoire de Biophysique Moléculaire et Cellulaire, Unité Mixte de Recherche 5090, Département Réponse et Dynamique Cellulaires, CEA-Grenoble, 38054 Grenoble cedex 9, France
2 Institute of Cytology, Russian Academy of Sciences, St. Petersburg 194064, Russia
(RECEIVED October 11, 2005; FINAL REVISION December 21, 2005; ACCEPTED January 5, 2006)
About 30% of proteins require cofactors for their proper folding. The effects of cofactors on the folding reaction have been investigated with
-lactalbumin as a model protein and metal ions as cofactors. Metal ions accelerate the refolding of
-lactalbumin by lessening the energy barrier between the molten globule state and the transition state, mainly by decreasing the difference of entropy between the two states. These effects are linked to metal ion binding to the protein in the native state. Hence, relationships between the metal affinities for the intermediate states and those for the native state are observed. Some residual specificity for the calcium ion is still observed in the molten globule state, this specificity getting closer in the transition state to that of the native state. The comparison between kinetic and steady-state data in association with the
value method indicates the binding of the metal ions on the unfolded state of
-lactalbumin. Altogether, these results provide insight into cofactor effects on protein folding. They also suggest new possibilities to investigate the presence of residual native structures in the unfolded state of protein and the effects of such structures on the protein folding reaction and on protein stability.
Keywords: protein folding; cofactors;
-lactalbumin;
value
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