Hao Wu1,2, Eddy Arnold3. 1. Department of Biological Chemistry and Molecular Pharmacology, Harvard Medical School, Boston, MA, USA. wu@crystal.harvard.edu. 2. Program in Cellular and Molecular Medicine, Boston Children's Hospital, Boston, MA, USA. wu@crystal.harvard.edu. 3. Center for Advanced Biotechnology and Medicine, and Department of Chemistry and Chemical Biology, Rutgers University, Piscataway, NJ, USA.