1. Contribution from the Leiden Institute of Chemistry, Gorlaeus Laboratories, P.O. Box 9502, 2300 RA Leiden, The Netherlands, Unidad de Rayos X (RIAIDT), Laboratorio Integral de Dinámica y Estructura de Biomoléculas “José R. Carracido”, Edificio CACTUS, Campus Sur, Universidad de Santiago de Compostela, 15782 Santiago de Compostela, Spain, National Institute of Public Health and the Environment, Research Laboratory for Infectious Diseases, P.O. Box 1, 3720 BA Bilthoven, The Netherlands, and TNO, Prins...