1. Institute for Protein Research, Osaka University, Suita, Osaka 565-0871, Japan, Biotechnology Research Laboratories, Takara Shuzo Co., Ltd., Sunaike, Nojicho, Kusatsu, Shiga 525-0055, Japan, and School of Pharmaceutical Science, Nagasaki University, Bunkyo-machi, Nagasaki 852-8131, Japan