1. Bredesen Center, University of Tennessee, Knoxville, TN 37996, USA.
2. Neutron Scattering Division, Oak Ridge National Laboratory, Oak Ridge, TN 37831, USA.
3. Large Scale Structures Group, Institut Laue-Langevin, Grenoble Cedex 9, 38042, France.
4. Department of Chemistry, University of Minnesota, Minneapolis, MN 55455, USA.
5. Department of Biochemistry, Molecular Biology, and Biophysics, University of Minnesota, Minneapolis, MN 55455, USA.
6. Department of Pharmacology, University of California at San Diego, La Jolla, CA 92093, USA.
7. Department of Chemistry and Biochemistry, University of California at San Diego, La Jolla, CA 92093, USA.