1. National Laboratory of Biomacromolecules, CAS Center for Excellence in BiomacromoleculesInstitute of Biophysics, Chinese Academy of Sciences Beijing 100101 People's Republic of China
2. College of Life SciencesUniversity of Chinese Academy of Sciences Beijing 100049 People's Republic of China
3. Department of Biological StructureUniversity of Washington School of Medicine Seattle, Washington, DC 98195