1. Department of Molecular and Structural Biochemistry, North Carolina State University, Raleigh, North Carolina 27695, United States
2. Department of Biochemistry, Duke University, Durham, North Carolina 27710, United States
3. Department of Radiology, Duke University, Durham, North Carolina 27710, United States
4. Duke University NMR Center, Duke University Medical Center, Durham, North Carolina 27710, United States