1. Department of Chemistry, University College London, 20 Gordon Street, London WC1H 0AJ, U.K., Department of Biochemical Engineering, University College London, Torrington Place, London WC1E 7JE, U.K., Institute of Structural and Molecular Biology, University College London, Gower Street, London WC1E 6BT, U.K., and Department of Chemical and Biochemical Engineering, Technical University of Denmark, 2800 Lyngby, Denmark