1. Department of Molecular Biology, University of California, San Diego, La Jolla, California 92093, United States
2. Department of Chemistry and Biochemistry, The Ohio State University, Columbus, Ohio 43210, United States
3. Environmental Molecular Sciences Laboratory, Pacific Northwest National Laboratory, Richland, Washington 99354, United States
4. Department of Chemistry and Biochemistry, University of California, San Diego, La Jolla, California 92093, United States