1. Department of Applied Chemistry and Microbiology, University of Helsinki, 00014 Helsinki, Finland
2. Department of Biology, Copenhagen Biocenter, University of Copenhagen, 2200 Copenhagen, Denmark
3. Protein Chemistry Research Group and Core Facility, Institute of Biotechnology, University of Helsinki, 00014 Helsinki, Finland
4. Lehrstuhl für Biochemie, Friedrich-Alexander-Universität Erlangen-Nürnberg, 91058 Erlangen, Germany