1. Department of Chemistry and Biochemistry, Baylor University, Waco, TX 76798, USA
2. Department of Biology, New York University, New York, NY 10003, USA
3. Department of Chemistry, The University of Chicago, Chicago, IL 60637, USA
4. Department of Chemistry, University of Illinois at Chicago, Chicago, IL 60607, USA
5. Department of Physics, University of Illinois at Chicago, Chicago, IL 60607, USA
6. Department of Biochemistry and Molecular Biology, Howard Hughes Medical Institute, The University of Chicago, Chicago, IL 60637, USA