1. Program in Biomolecular Pharmacology, Boston University School of Medicine, Boston, Massachusetts 02118, United States
2. Department of Chemistry and Biochemistry, University of California San Diego, 9500 Gilman Drive, La Jolla, California 92093, United States
3. Department of Bacteriology, University of Wisconsin, 1550 Linden Drive, Madison, Wisconsin 53706, United States
4. Department of Chemistry, Boston University, 590 Commonwealth Avenue, Boston, Massachusetts 02215, United States