1. Bruker Biospin Corporation, 15 Fortune Drive, Billerica, Massachusetts 01821, United States
2. Department of Chemistry and Biochemistry, University of Delaware, Newark, Delaware 19716, United States
3. Department of Structural Biology, University of Pittsburgh School of Medicine, Pittsburgh, Pennsylvania15260, United States
4. Pittsburgh Center for HIV Protein Interactions, University of Pittsburgh School of Medicine, Pittsburgh, Pennsylvania 15260, United States