1. Life Sciences Institute, Departments of Medicinal Chemistry, Chemistry, and Microbiology and Immunology, University of Michigan, Ann Arbor, MI 48109 (USA)
2. Department of Genetics, Harvard Medical School, Boston, MA 02115 (USA)
3. Life Sciences Institute and Department of Biological Chemistry, University of Michigan, Ann Arbor, MI 48109 (USA)
4. Department of Biological Chemistry, University of Michigan, Ann Arbor, MI 48109 (USA)
5. Scripps Institution of Oceanography and Skaggs School of Pharmacy and Pharmaceutical Sciences, University of California at San Diego, La Jolla, CA 92093 (USA)