1. Department of Biochemistry and Molecular Biology, The University of Chicago, 929 East 57th Street, Chicago, Illinois 60637, Biosciences Division, Argonne National Laboratory, 9700 South Cass Avenue, Argonne, Illinois 60649, Department of Chemistry and Biochemistry, Concordia University, Montréal, Québec, H4B 1R6, Canada, and Department of Pharmaceutical Sciences, School of Pharmacy, University of Maryland, Baltimore, Maryland 21201