1. Laboratoire International Associé Centre National de la Recherche Scientifique et University of Illinois at Urbana-Champaign, Unité Mixte de Recherche No 7019, Université de Lorraine, B.P. 70239, Vandœuvre-lès-Nancy Cedex 54506, France
2. School of Physics, Georgia Institute of Technology, Atlanta, Georgia 30332, United States
3. Theoretical and Computational Biophysics Group, Beckman Institute, and Department of Physics, University of Illinois at Urbana-Champaign, Urbana Illinois 61802, United States
4. Department of Biochemistry and Molecular Biology, The University of Chicago, 929 E. 57th Street W225, Chicago, Illinois 60637, United States