1. Department of Biochemistry, University of Toronto, Toronto M5S 1A8, Canada
2. Department of Molecular Genetics, University of Toronto, Toronto M5S 1A8, Canada
3. Department of Chemistry, University of Toronto, Toronto M5S 3H6, Canada
4. Program in Molecular Medicine, The Hospital for Sick Children Research Institute, Toronto M5G 0A4, Canada
5. Laboratory of Dynamics of Macromolecular Assembly, National Institute of Biomedical Imaging and Bioengineering, National Institutes of Health, Bethesda, Maryland 20892, United States