1. Protein Design Laboratory, Graduate School of Integrated Science, Yokohama City University, 1-7-29 Suehiro, Tsurumi, Yokohama 230-0045, Japan, and Department of Physiology, Division of Biophysics, Jichi Medical School, 3311-1 Yakushiji, Minamikawachi, Kawachi, Tochigi 329-0498, Japan