1. Center for Integrated Molecular Systems, Division of Molecular and Life Sciences, Pohang University of Science and Technology, San 31 Hyoja-dong, Namku, Pohang 790-784 Korea, and Center for Cellular Switch Protein Structure, Korea Research Institute of Bioscience and Biotechnology, 52 Euh-eun-dong, Yusong-gu, Deajeon 305-806 Korea