1. Departments of Molecular and Cell Biology and Chemistry, University of California at Berkeley, Berkeley, CA 94720, USA.
2. Department of Physiology and Biophysics, Weill Cornell Medical College of Cornell University, New York, NY 10065, USA.
3. Weill Cornell/Rockefeller University/Sloan-Kettering Tri-Institutional MD-PhD Program, New York, NY 10065, USA.
4. Department of Biochemistry, Duke University Medical Center, Durham, NC 27710, USA.
5. Physical Biosciences Division, Lawrence Berkeley National Laboratory, Berkeley, CA 94720, USA.