1. Department of Cell Biology and Cell Pathology, Philipps University of Marburg, Robert Koch Strasse 6, 35037 Marburg, Germany, Max-Planck-Institute of Molecular Biomedicine, Röntgenstrasse 20, 48149 Münster, Germany, Max-Planck-Institute for Molecular Physiology, Otto-Hahn-Strasse 11, 44227 Dortmund, Germany, Department of Chemistry, and Centre for Cell Biology and Department of Biology, University of Aveiro, Campus Universitário de Santiago, 3810-193 Aveiro, Portugal