1. School of Physical Science and Technology; ShanghaiTech University; 393 Middle Huaxia Road Shanghai 201210 China
2. National Facility for Protein Science Shanghai; Shanghai Advanced Research Institute (Zhangjiang Lab); Chinese Academy of Sciences; Shanghai 201210 China
3. National Synchrotron Radiation Laboratory; University of Science and Technology of China; Hefei 230029 China
4. Department of Biomedical Engineering; Tufts University; Medford MA 02155 USA