1. Department of Chemistry, School of Science, The University of Tokyo, Hongo, Bunkyo-ku, Tokyo 113-0033, Japan, Protein Research Group, RIKEN Genomic Sciences Center, Suehiro-cho, Tsurumi-ku, Yokohama 230-0045, Japan, and Division of Supramolecular Biology, Yokohama City University, Suehiro-cho, Tsurumi-ku, Yokohama 230-0045, Japan