1. Architecture et Fonction des Macromolecules Biologiques–AFMB-UMR 6098, CNRS and Universités d'Aix-Marseille I et II, 31 Chemin Joseph Aiguier, F13402 Marseille Cedex 20, France
2. Department of Biology, Virginia Polytechnic Institute & State University, Blacksburg, VA 24061, U.S.A.
3. European Synchrotron Radiation Facility, BP 220, F-38043 Grenoble Cedex, France
4. Department of Biochemistry, Virginia Polytechnic Institute & State University, Blacksburg, VA 24061, U.S.A.