1. Department of Biochemistry, The Protein Engineering Network of Centers of Excellence, CIHR Group in Protein Structure and Function, and National High Field Nuclear Magnetic Resonance Center, University of Alberta, Edmonton, Alberta, T6G 2H7 Canada, Université de Sherbrooke, Sherbrooke, Québec, J1K 2R1 Canada, University of Southampton, Highfield, Southhampton, SO17 1BJ U.K., and Université Laval, Québec, G1K 7P4 Canada