1. Department of Biochemistry and Biophysics, Stockholm University, SE 106 91 Stockholm, Sweden
2. Center of Structural and Cell Biology in Medicine, Institute of Biochemistry, University of Lübeck, D-23538, Lübeck, Germany
3. Structural Biology Research Center, Institute of Materials Structure Science, High Energy Accelerator Research Organization (KEK), Oho 1-1, Tsukuba, Ibaraki 305-0801, Japan