1. Department of Microbiology, University of Texas (UT) Southwestern Medical Center, Dallas, TX 75390, USA.
2. Department of Biochemistry, University of Texas (UT) Southwestern Medical Center, Dallas, TX 75390, USA.
3. Channing Laboratory, Brigham and Women's Hospital, Harvard Medical School, Boston, MA 02115, USA.
4. Department of Pharmacology, University of Texas (UT) Southwestern Medical Center, Dallas, TX 75390, USA.