1. Laboratory of Crystallography, University of Geneva, 24 quai E. Ansermet, CH-1211 Geneva 4, Switzerland
2. Department of Chemistry, University of Pittsburgh, 219 Parkman Avenue, Pittsburgh, Pennsylvania 15260, United States
3. Centre de Biophysique Moléculaire, CNRS UPR 4301, Rue Charles-Sadron, 45071 Orléans Cedex 2, France