1. Institute of Structural and Molecular Biology, University College London, Gower Street, London WC1E 6BT, U.K.
2. Department of Biological and Environmental Sciences and Technologies, DISTEBA, University of Salento, Via per Arnesano, I-73100 Lecce, Italy
3. Department of Frontier Materials, Nagoya Institute of Technology, Gokiso Nagoya 466-8555, Japan