1. Department of Molecular Biophysics and Biochemistry, Yale University, New Haven, Connecticut 06520-8114, United States
2. Department of Chemistry, Yale University, New Haven, Connecticut 06511-8499, United States
3. Department of Pharmacology, Yale University, New Haven, Connecticut 06520-8066, United States
4. Department of Molecular and Cell Biology and Biochemistry, Brown University, Providence, Rhode Island 02912, United States