1. Wellcome Trust Laboratories for Molecular Parasitology, Imperial College London, London SW7 2AZ, U.K.
2. Division of Cell and Molecular Biology, Centre for Molecular Microbiology and Infection, Imperial College London, London SW7 2AZ, U.K.
3. Department of Chemistry, Imperial College London, London SW7 2AZ, U.K.
4. Division of Parasitology, MRC National Institute for Medical Research, Mill Hill, London NW7 1AA, U.K.
5. Immunology and Infection Unit, Department of Biology/Hull York Medical School, University of York, Heslington, York YO10 5YW, U.K.