1. Laboratoire International Associé Centre National de la Recherche Scientifique et University of Illinois at Urbana−Champaign, Unité Mixte de Recherche n◦7019, Université de Lorraine, 54500 Vandœuvre-lès-Nancy cedex, France
2. Beckman Institute for Advanced Science and Technology, and Department of Physics, University of Illinois at Urbana−Champaign, Urbana, Illinois 61820, United States
3. Department of Biochemistry and Molecular Biology, University of Chicago, Chicago, Illinois 60637, United States