1. Department of Molecular Biology and Biochemistry, Simon Fraser University, Burnaby, British Columbia V5A 1S6, Canada
2. Department of Chemistry, Simon Fraser University, Burnaby, British Columbia V5A 1S6, Canada
3. Department of Chemistry, Massachusetts Institute of Technology, Cambridge, Massachusetts 02139, United States
4. Michael Smith Laboratories, University of British Columbia, Vancouver, British Columbia V6T 1Z4, Canada
5. Department of Biochemistry and Molecular Biology, University of British Columbia, Vancouver, British Columbia V6T 1Z4, Canada