1. Protein Design Laboratory, Yokohama City University, Suehiro 1-7-29, Kanagawa 230-0045, Japan, Protonic NanoMachine Project, ERATO, JST, 3-4 Hikaridai, Seika, Kyoto 619-0237, Japan, Advanced Technology Research Laboratories, Matsushita Electric Industrial Co., Ltd., 3-4 Hikaridai, Seika, Kyoto 619-0237, Japan, York Structural Biology Laboratory, Department of Chemistry, University of York, York YO10 5DD, England, and Department of Biological Sciences, University of Warwick, Coventry CV4 7AL, England