1. Department of Biology, Graduate School of Science, Osaka University, 1-1 Machikaneyama, Toyonaka, Osaka 560-0043, Japan, Institute for Protein Research, Osaka University, 2-2 Yamadaoka, Suita, Osaka 565-0871, Japan, and Department of Chemistry, Juntendo University, Inba, Chiba 270-1695, Japan