1. Duchossois Family Institute, University of Chicago, Chicago, Illinois 60637, United States
2. Department of Microbiology, University of Chicago, Chicago, Illinois 60637, United States
3. Department of Biochemistry, University of Illinois at Urbana─Champaign, Urbana, Illinois 61801, United States
4. Department of Chemistry, The Howard Hughes Medical Institute, University of Illinois at Urbana─Champaign, Urbana, Illinois 61801, United States
5. Departments of Medicine and Pathology, University of Chicago, Chicago, Illinois 60637, United States