1. Department of Chemistry, University of Massachusetts, Amherst, Massachusetts 01003, United States
2. Department of Cell Biology, University of Alberta, Edmonton, AB T6G 2H7, Canada
3. Department of Pharmaceutical Chemistry and Department of Cellular and Molecular Pharmacology, University of California, San Francisco, California 94158, United States
4. Department of Biochemistry, University of Alberta, Edmonton, AB T6G 2H7, Canada