1. Department of Chemistry, Imperial College London, South Kensington Campus, London, SW7 2AZ, U.K.
2. York Structural Biology Laboratory, Department
of Chemistry, University of York, York,
YO10 5DD, U.K.
3. Division of
Parasitology, MRC National Institute for Medical Research, The Ridgeway, Mill Hill, London, NW7 1AA, U.K.