1. John Sealy School of Medicine, The University of Texas Medical Branch , Galveston, TX 77550, USA
2. Department of Biochemistry and Molecular Biology, The University of Texas Medical Branch , Galveston, TX 77550, USA
3. Sealy Center for Structural Biology and Molecular Biophysics, The University of Texas Medical Branch , Galveston, TX 77550, USA
4. Institute for Human Infections and Immunity, University of Texas Medical Branch , Galveston, TX, USA