1. Center for Genomic and Computational Biology, Duke University School of Medicine, Durham, North Carolina 27710, United States
2. Department of Biochemistry, Duke University School of Medicine, Durham, North Carolina 27710, United States
3. Department of Chemistry, Duke University, Durham, North Carolina 27708, United States
4. Department of Chemistry and Biophysics, University of Michigan, Ann Arbor, Michigan 48109, United States
5. Department of Biochemistry and Molecular Biophysics, Columbia University, New York, New York 10032, United States