1. Departments of Chemistry and of Biochemistry, Molecular Biology, and Cell Biology, Center for Molecular Innovation and Drug Discovery, and Chemistry of Life Processes Institute, Northwestern University, Evanston, Illinois 60208-3113, Departments of Molecular Biology and Biochemistry, of Pharmaceutical Chemistry, and of Chemistry, University of California, Irvine, California 92697-3900, Macromolecular Crystallographic Group, Stanford Synchrotron Radiation Lightsource, SLAC, Stanford University, Stanford,...