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Bioinorganic Chemistry and Applications
Volume 2007, Article ID 54232, 9 pages
Research Article

Folding and Unfolding in the Blue Copper Protein Rusticyanin: Role of the Oxidation State

1Instituto de Biología Molecular y Celular, Universidad Miguel Hernández de Elche, Edificio Torregaitán, Avda. de la Universidad s/n, Elche, Alicante 03202, Spain
2Departamento de Química Física, Universidad de Sevilla, C/Professor García González s/n, Sevilla 41012, Spain
3Departamento de Química Inorgánica, Facultad de Química, Universidad de Murcia, Campus Universitario, Apdo. 4021, Murcia 30071, Spain

Received 1 March 2007; Revised 2 May 2007; Accepted 27 June 2007

Academic Editor: Luigi Casella

Copyright © 2007 Luis A. Alcaraz et al. This is an open access article distributed under the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.


The unfolding process of the blue copper protein rusticyanin has been studied from the structural and the thermodynamic points of view at two pH values (pH 2.5 and 7.0). When Rc unfolds, copper ion remains bound to the polypeptide chain. Nuclear magnetic resonance data suggest that three of the copper ligands in the folded state are bound to the metal ion in the unfolded form, while the other native ligand is detached. These structural changes are reflected in the redox potentials of the protein in both folded and unfolded forms. The affinities of the copper ion in both redox states have been also determined at the two specified pH values. The results indicate that the presence of two histidine ligands in the folded protein can compensate the change in the net charge that the copper ion receives from their ligands, while, in the unfolded protein, charges of aminoacids are completely transferred to the copper ion, altering decisively the relative stability of its two-redox states.