1 Biomedical Research Foundation, Academy of Athens, 11527 Athens, Greece.
2 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, B.P. 70239, 54506 Vandœuvre-lès-Nancy Cedex, France.
3 Department of Biochemistry and Molecular Biology, The University of Chicago, 929 East 57th Street W225, Chicago, Illinois 60637, United States.
4 Theoretical and Computational Biophysics Group, Beckman Institute, and Department of Physics, University of Illinois at Urbana-Champaign, Urbana, Illinois 61801, United States.