1. Biochemistry Department, University of Missouri, 117 Schweitzer Hall, Columbia, Missouri 65211, USA
2. College of Pharmacy, Dalhousie University, 5968 College Street, Halifax, Nova Scotia B3H 3J5, Canada
3. Department of Chemistry, Dalhousie University, Halifax, Nova Scotia B3H 4R2, Canada
4. Molecular Biology Consortium, Advanced Light Source, Lawrence Berkeley National Laboratory, Berkeley, California 94720, USA