1. Department
of Molecular Biology and Biochemistry, University of California, Irvine, California 92697-3900, United States
2. Department
of Chemistry, University of California, Irvine, California 92697-2025, United States
3. Department
of Chemistry, Stanford University, Stanford, California 94305, United States
4. Stanford
Synchrotron Radiation Lightsource, SLAC, Stanford University, Menlo Park, California 94025, United States