1. Department of Chemistry, Tufts University, Medford, Massachusetts 02155, United States
2. Institute of Biological Information Processing, Structural Biochemistry (IBI-7), Forschungszentrum Jülich, 52425 Jülich, Germany
3. Institut für Physikalische Biologie, Heinrich-Heine-Universität Düsseldorf, 40225 Düsseldorf, Germany
4. Department of Experimental Therapeutics, The University of Texas MD Anderson Cancer Center, Houston, Texas 77030, United States