1. Department of Chemistry and Biochemistry, University of Arizona, Tucson, Arizona 85721, United States
2. New York Consortium on Membrane Protein Structure, New York Structural Biology Center, New York, New York 10027, United States
3. Department of Chemistry and Biochemistry, University of California, San Diego, La Jolla, California 92093, United States
4. Bio5 Institute, The University of Arizona, Tucson, Arizona 85721, United States