1. Max F. Perutz Laboratories, University Departments at the Vienna Biocenter, Department of Medical Biochemistry, Medical University of Vienna, 1030 Vienna, Austria
2. Gene Expression and Cell Biology/Biophysics Programmes, European Molecular Biology Laboratory, 69117 Heidelberg, Germany
3. CREST of JST Kansai Advanced Research Center, Kobe 651-2492, Japan
4. Department of Chemistry, Faculty of Sciences, Niigata University, Niigata 950-2181, Japan