1. Department of Chemistry and Pharmacy, Friedrich-Alexander Universität Erlangen-Nürnberg, Nikolaus-Fiebiger-Str. 10, 91058 Erlangen, Germany
2. Department of Chemistry and Center for Integrated Protein Science (CIPSM), Ludwig-Maximilians Universität München, Butenandtstr. 5-13, 81377 Munich, Germany