1 State Key Laboratory of Protein and Plant Gene Research, Peking-Tsinghua Joint Center for Life Sciences, School of Life Sciences, Peking University, Beijing 100871, China. Electronic address: guo.qiang@pku.edu.cn.
2 Department of Molecular Structural Biology, Max Planck Institute of Biochemistry, Martinsried 82152, Germany.
3 State Key Laboratory of Membrane Biology, Peking-Tsinghua Joint Center for Life Sciences, School of Life Sciences, Peking University, Beijing 100871, China. Electronic address: gaon@pku.edu.cn.