1. Institute for Organic Chemistry and Chemical Biology Center for Biomolecular Magnetic Resonance (BMRZ) Johann Wolfgang Goethe-University Max-von-Laue-Str. 7+9 60438 Frankfurt/M. Germany
2. Saverna Therapeutics Pumpmattenweg 3 4105 Biel-Benken Switzerland
3. Department of Biology Technical University of Darmstadt Schnittspahnstr. 10 64287 Darmstadt Germany
4. Present address: EMBL Heidelberg Meyerhofstr. 1 69117 Heidelberg Germany
5. Institute for Molecular Biosciences Center for Biomolecular Magnetic Resonance (BMRZ) Johann Wolfgang Goethe-University Max-von-Laue-Str. 7+9 60438 Frankfurt/M. Germany