1. Laboratory of Structural and Mechanistic Enzymology, School of Biological and Chemical Sciences, Fogg Building, Queen Mary, University of London, Mile End Road, London E1 4NS, U.K., School of Biological and Chemical Sciences, Walter Bessant Building, Queen Mary, University of London, Mile End Road, London E1 4NS, U.K., Bioinformatics Institute, 30, Biopolis Way, #07-01 Matrix, Singapore 138671, and Department of Biological Sciences, University of Salford, The Crescent, Salford M5 4JW, U.K.