1. College of Chemistry and Molecular Engineering; Peking University; Beijing 100871 China
2. Beijing National Laboratory for Molecular Sciences (BNLMS); Peking University; Beijing 100871 China
3. State Key Laboratory for Structural Chemistry of Unstable and Stable Species; Peking University; Beijing 100871 China
4. Center for Quantitative Biology, Peking University; Beijing 100871 China
5. Department of Structural Biology; St. Jude Children's Research Hospital; Memphis Tennessee 38105