1. Department of Molecular and Experimental Medicine, The Scripps Research Institute, 10550 N. Torrey Pines, La Jolla, CA 92037, U.S.A.
2. Department of Immunology and Microbial Science, The Scripps Research Institute, 10550 N. Torrey Pines, La Jolla, CA 92037, U.S.A.
3. Department of Chemistry, The Scripps Research Institute, 10550 N. Torrey Pines, La Jolla, CA 92037, U.S.A.