1. Bredesen Center, University of Tennessee, Knoxville, Tennessee 37996, United States
2. Department of Pharmacology and Chemical Biology, Baylor College of Medicine, Houston, Texas 77030, United States
3. Large-Scale Structures Group, Institut Laue Langevin, 38042 Grenoble Cedex 9, France
4. Verna and Marrs McLean Department of Biochemistry and Molecular Biology, Baylor College of Medicine, Houston, Texas 77030, United States
5. Neutron Scattering Division, Neutron Sciences Directorate, Oak Ridge National Laboratory, Oak Ridge, Tennessee 37831, United States