1. Department of Biochemistry, Stanford University School of Medicine, Stanford, California 94305, United States
2. Biophysics Program, Stanford University, Stanford, California 94305, United States
3. Department of Biochemistry, Duke University School of Medicine, Durham, North Carolina 27710, United States
4. Biophysics Program, University of Michigan, Ann Arbor, Michigan 48109, United States
5. Department of Chemistry, University of Michigan, Ann Arbor, Michigan 48109, United States
6. Department of Chemistry, Duke University School of Medicine, Durham, North Carolina 27710, United States
7. Department of Physics, Stanford University, Stanford, California 94305, United States