1. Molecular and Systems Pharmacology, Emory University, Atlanta, GA 30322, USA.
2. Department of Biology, Brookhaven National Laboratory, Upton, NY 11973, USA.
3. Department of Chemistry, Emory University, Atlanta, GA 30322, USA.
4. Laboratory of Structural Biology, National Institute of Environmental Health Sciences, Research Triangle Park, NC 27709, USA.
5. Life Sciences Division, Lawrence Berkeley National Laboratory, Berkeley, CA 94720, USA.