1. Center for Molecular Neurobiology Hamburg , , Falkenried 94, D-20251 Hamburg , Germany
2. University Medical Center Hamburg-Eppendorf , , Falkenried 94, D-20251 Hamburg , Germany
3. Institute for Chemistry and Biochemistry , Feie Universität Berlin, Berlin , Germany
4. Institute of Biology, Humboldt-Universität zu Berlin , Berlin , Germany