1. Department of Biology, Hong Kong University of Science and Technology, Clear Water Bay, Kowloon, Hong Kong, People's Republic of China
2. Key Laboratory of Ministry of Education for Cell Biology and Tumor Cell Engineering, School of Life Sciences, Xiamen University, Fujian 361005, People's Republic of China
3. Protein Science Laboratory of Ministry of Education, Department of Biological Sciences and Biotechnology, Tsinghua University, Beijing, People's Republic of China