1. Department of Biochemistry and Montreal Joint Centre for Structural Biology, Department of Pharmacology and Therapeutics, and Department of Oncology, McGill University, 3655 Promenade Sir William Osler, Montréal, Québec H3G 1Y6, Canada, and Biomolecular NMR Group, Pharmaceutical Biotechnology Sector and Montreal Joint Centre for Structural Biology, Biotechnology Research Institute, National Research Council of Canada, 6100 Royalmount Avenue, Montréal, Québec H4P 2R2, Canada