1. Department of Biological Chemistry University of California Los Angeles 615 Charles E. Young Drive South Los Angeles CA 90095 USA
2. Howard Hughes Medical Institute University of California Los Angeles Los Angeles CA 90095 USA
3. Department of Chemistry–BMC Uppsala University Husargatan 3 Uppsala 75237 Sweden
4. Department of Physiology University of California Los Angeles 615 Charles E. Young Drive South Los Angeles CA 90095 USA