1. Division of Biology and Biological Engineering, California Institute of Technology , Pasadena, CA 91125, United States
2. California Institute of Technology , Pasadena, CA 91125, United States
3. Structural and Computational Biology Unit, European Molecular Biology Laboratory (EMBL) , 69117 Heidelberg, Germany
4. Department of Computing and Mathematical Sciences, California Institute of Technology , Pasadena, CA 91125, United States