1. Faculty of Life Sciences, The University of Manchester, Michael Smith Building, Manchester M13 9PT, U.K.
2. Faculty of Life Sciences, Manchester Interdisciplinary Biocentre, The University of Manchester, Manchester M1 7DN, U.K.
3. Division of Protein Chemistry, Institute for Protein Research, 3-2 Yamadaoka, Suita, Osaka 565-0879, Japan