1. State Key Laboratory of Genetic Engineering, School of Life Sciences, Zhongshan Hospital, Fudan University, Shanghai 200438, China;
2. Department of Molecular Biophysics and Biochemistry, Yale University, New Haven, Connecticut 06520, USA;
3. Department of Chemistry, Yale University, New Haven, Connecticut 06520, USA
4. Howard Hughes Medical Institute, Yale University, New Haven, Connecticut 06520, USA
5. Department of Biological Sciences, and Department of Medicinal Chemistry and Pharmacognosy, University of Illinois at Chicago, Chicago, Illinois 60607, USA;
6. Current affiliation: Department of Microbiology and Immunology, and Sealy Center for Structural Biology and Molecular Biophysics, University of Texas Medical Branch, Galveston, Texas 77555, USA;