1. Department of Chemistry New York University New York NY 10003 USA
2. Present Address: Department of Organic Synthesis and Process Chemistry CSIR-Indian Institute of Chemical Technology (CSIR-IICT) Hyderabad 500007 India
3. Biology Program New York University Abu Dhabi P.O. Box 129188, Saadiyat Island Campus Abu Dhabi United Arab Emirates
4. Institut für Physikalische Biologie Heinrich-Heine-Universität Düsseldorf 40225 Düsseldorf Germany
5. Institute of Biological Information Processing (IBI-7: Structural Biochemistry) and JuStruct: Jülich Center for Structural Biology Forschungszentrum Jülich 52425 Jülich Germany