1. Departments of Biochemistry & Molecular Biology, Medicine, and Physiology & Pharmacology, Oregon Heath & Science University, Portland, Oregon 97239-3098, United States
2. Stanford University, SLAC/SSRL Building 137, 2575 Sand Hill Road MS69, Menlo Park, California 94025, United States
3. Department of Chemistry, Portland State University, Portland, Oregon 97207, United States