1. Department of Chemistry, Massachusetts Institute of Technology, Cambridge, Massachusetts 02139, United States
2. High-Throughput Sciences Facility, Koch Institute for Integrative Cancer Research, Massachusetts Institute of Technology, Cambridge, Massachusetts 02139, United States
3. W. M. Keck Microscopy Facility, The Whitehead Institute, Cambridge, Massachusetts 02142, United States
4. Departments of Ophthalmology and Pharmacology, University of Texas Southwestern Medical Center, Dallas, Texas 75390, United States