1. Chinese Academy of Sciences Key Laboratory of Pathogenic Microbiology and Immunology, Institute of Microbiology, Chinese Academy of Sciences, Beijing 100190, China, School of Life Sciences, University of Science and Technology of China, Hefei 230026, China, Graduate University of Chinese Academy of Sciences, Beijing 100049, China, and Division of Chemistry and Structural Biology, Institute for Molecular Bioscience, The University of Queensland, St. Lucia, Queensland 4072, Australia