1. Department of Chemistry and Biochemistry, Center for Biomolecular Structure and Organization, University of Maryland, College Park, Maryland 20742, United States
2. Departments of Molecular Genetics, Biochemistry and Chemistry, University of Toronto, Toronto, Ontario, Canada M5S 1A8
3. Hospital for the Sick Children, Program in Molecular Structure and Function, 555 University Avenue, Toronto, Ontario, Canada M5G 1X8