1. Department of Molecular Cell Biology Center for Medical Biotechnology University of Duisburg-Essen 45141 Essen Germany
2. Department of Chemistry and Chemical Biology and Department of Systemic Cell Biology TU Dortmund University and Max-Planck-Institute of Molecular Physiology 44227 Dortmund Germany
3. Department of Chemistry Umeå Centre for Microbial Research Umeå University 901 87 Umeå Sweden