1. Department of Biomolecular Medicine, Division of Surgery, Oncology, Reproductive Biology & Anaesthetics, Sir Alexander Fleming Building, Imperial College, London SW7 2AZ, U.K., Structural Bioinformatics Group, Division of Molecular Bioscience, Imperial College, London SW7 2AY, U.K., and Computational Bioinformatics Group, Department of Computing, Imperial College, London SW7 2AZ, U.K.