1. California Institute for Quantitative Biosciences, University of California—Berkeley, Berkeley, California 94720, United States
2. Department of Chemistry, Boston University, Boston, Massachusetts 02215, United States
3. Department of Chemistry, University of California—Davis, Davis, California 95616, United States
4. Department of Molecular and Cell Biology, University of California—Berkeley, Berkeley, California 94720, United States
5. Department of Chemistry, University of California—Berkeley, Berkeley, California 94720, United States