1. Department of Biochemistry, University of Utah School of Medicine, 15 North Medical Drive East, Room 4100, Salt Lake City, Utah 84112-5650, United States
2. Department of Chemistry & Biochemistry, 8051 Regents Drive, University of Maryland, College Park, Maryland 20742-4454, United States
3. Centre de Biophysique Moléculaire, CNRS UPR4301, Rue Charles Sadron, Orléans CEDEX 2 45071, France