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Volume 18, Issue 2, Pages 301-309

Molecular events involved in the activation of calpain from human erythrocytes

Enrico Dainese,1,4 Annalaura Sabatucci,1 Roberto Minafra,2 Patrice Vachette,3 Edon Melloni,2 and Ivo Cozzani1

1Department of Biomedical Sciences, University of Teramo, Piazza A. Moro 45, 64100 Teramo, Italy
2Department of Experimental Medicine and Centre of Excellence for Biomedical Research, University of Genoa, Viale Benedetto XV 1, 16032 Genoa, Italy
3LURE, Bât. 209d, University of Paris-Sud, B.P. 34, F91898 Orsay Cedex, France
4Department of Biomedical Sciences, University of Teramo, Piazza A. Moro 45, 64100 Teramo, Italy

Copyright © 2004 Hindawi Publishing Corporation. 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.


Calpains are intracellular cysteine endopeptidases that combine protease activity with a dependence on Ca2+ binding. Here we describe the conformational changes leading to the calpain activation, occurring in the enzyme purified from human erythrocytes, studied in solution using small angle X-ray scattering (SAXS). Addition of Ca2+ determines the formation of large soluble aggregates that can be dissociated either chelating these ions or adding cahotropic salts in solution. On the other side, our SAXS studies revealed that the addition of Ca2+ in the presence of inhibitors as E64 or leupeptin triggers a reversible conformational transition leading to a proper assembly of the active site without any aggregation or dissociation process. It is suggested that the observed conformational changes can be considered as the early step in the sequence of molecular events leading to calpain activation.