1. Department of Biomolecular Engineering, Tokyo Institute of Technology, Nagatsuta 4259, Midori-ku, Yokohama 226-8501, Japan, Polymer Chemistry Laboratory, RIKEN Institute, 2-1 Hirosawa, Wako-shi, Saitama 351-0198, Japan, Takasago Research Laboratories, Kaneka Corporation, Takasago, Hyogo 678-8688 Japan, and Department of Biological Science & Biotechnology, Tsinghua University, Beijing 100084, China