1. Department of Molecular and Cellular Physiology, Stanford University School of Medicine, Stanford, CA 94305, USA.
2. Howard Hughes Medical Institute, Stanford University School of Medicine, Stanford, CA 94305, USA.
3. Toyota Technological Institute at Chicago, Chicago, IL 60637, USA.
4. Department of Biosystems Science and Engineering, ETH Zurich, Basel, Switzerland.
5. Departments of Pathology and Family Medicine, University of Chicago, Chicago, IL 60637, USA.
6. Department of Structural Biology, Stanford University School of Medicine, Stanford, CA 94305, USA.