1. Manchester Interdisciplinary Biocentre, Faculty of Life Sciences, University of Manchester, Princess Street, Manchester M1 7DN, U.K., Michael Smith Building, Faculty of Life Sciences, University of Manchester, Oxford Road, Manchester M13 9PT, U.K., MRC Immunochemistry Unit, Department of Biochemistry, University of Oxford, South Parks Road, Oxford OX1 3QU, U.K., and Department of Pharmaceutical Chemistry, School of Pharmacy, University of Maryland, 20 Penn Street, Baltimore, Maryland 21201