1. Department
of Integrative Structural and Computational Biology, Scripps Research Institute, La
Jolla, California 92037, United States
2. Molecular
Structure and Function Program, Hospital for Sick Children, Toronto, Ontario M5G 0A4, Canada
3. Department
of Biochemistry, University of Toronto, Toronto, Ontario M5S 1A8, Canada
4. Department
of Chemistry, Stanford University, Stanford, California 94305, United States