1. Institute of Complex Systems, Structural Biochemistry, Forschungszentrum Jülich; Jülich, 52425 Germany
2. Department of Cell and Molecular Biology; Uppsala University, BMC Box 596; Uppsala, 751 24 Sweden
3. Institute of Theoretical and Computational Chemistry; Heinrich Heine University Düsseldorf, Universitätsstraße 1; Düsseldorf, 40225 Germany