1. Department of Chemistry, Umeå University, SE90187 Umeå, Sweden
2. Interfaculty Institute of Biochemistry, University of Tübingen, 72076 Tübingen, Germany
3. Department of Clinical Microbiology, Umeå University, SE90185 Umeå, Sweden
4. Vanderbilt University School of Medicine, Nashville, Tennessee 37232, USA