1. School of Life Sciences, Tsinghua University, Beijing 100084, P.R. China.
2. McGovern Institute of Brain Research, Beijing 100084, P.R. China.
3. Department of Computer Science, Brandeis University, Waltham, MA 02453, USA.
4. School of Medicine, Tsinghua University, Beijing 100084, P.R. China.
5. Tsinghua-Peking Center for Life Sciences, Tsinghua University, Beijing 100084, P.R. China.
6. MOE Key Laboratory of Protein Sciences, Tsinghua University, Beijing 100084, P.R. China.