1. Department of Chemistry, Brandeis University, Waltham, Massachusetts 02454-9110, United States
2. Department of Integrative Structural and Computational Biology and the Skaggs Institute for Chemical Biology, The Scripps Research Institute, La Jolla, California 92037, United States
3. Department of Surgery, Duke University Medical Center, Durham, North Carolina 27710, United States
4. Department of Biology, Brandeis University, Waltham, Massachusetts 02454-9110, United States