1. Department of Molecular Structure and Function, Research Institute, Hospital for Sick Children, Toronto, Ontario, Canada M5G 1X8, Department of Laboratory Medicine and Pathobiology, University of Toronto, Toronto, Ontario, Canada M5G 1L5, Dipartimento di Fisica and CNISM, Universitá di Parma, V. le Usberti, 7/A, 43100 Parma, Italy, and Department of Molecular and Cellular Biology and Biophysics Interdepartmental Group, University of Guelph, Guelph, Ontario, Canada N1G 2W1