1. Department of Biochemistry and Molecular Biology, Sealy Center for Structural Biology and Molecular Biophysics, University of Texas Medical Branch , Galveston , TX 77555 , USA
2. Department of Medicine, The University of North Carolina at Chapel Hill, Chapel Hill, NC 27517 , USA
3. Lineberger Comprehensive Cancer Center, The University of North Carolina at Chapel Hill , Chapel Hill , NC 27517 , USA
4. Department of Microbiology and Immunology, The University of North Carolina at Chapel Hill , Chapel Hill, NC 27517, USA
5. Department of Molecular and Cellular Biochemistry, Indiana University , Bloomington , IN 47405 , USA