1. Department of Chemistry, University of Pittsburgh, Pittsburgh, Pennsylvania 15260, USA
2. Molecular Biophysics and Structural Biology Graduate Program, University of Pittsburgh and Carnegie Mellon University, Pittsburgh, Pennsylvania 15260, USA
3. School of Computer Science and Engineering, University of Washington, Seattle, Washington 98115, USA
4. Department of Chemistry and Chemical Biology, Rutgers University, New Brunswick, New Jersey 008854, USA