1. Department of Bionano Engineering, Hanyang University, Ansan 155-88, South Korea
2. Tsinghua-Peking Center for Life Sciences, Beijing Frontier Research Center for Biological Structure, Beijing Advanced Innovation Center for Structural Biology, School of Medicine, School of Pharmaceutical Sciences, Tsinghua University, Beijing 100084, China
3. Department of Neuroscience, University of Copenhagen, Copenhagen DK-2200, Denmark
4. Department of Cell Physiology and Molecular Biophysics, Center for Membrane Protein Research, School of Medicine, Texas Tech University Health Sciences Center, Lubbock, Texas 79430, United States
5. Department of Life Sciences, Imperial College London, London SW7 2AZ, U.K.