1. Department of Chemistry, Sogang University, 35 Baekbeomro Mapogu, Seoul 121-742, Republic of Korea
2. Graduate School of Medical Science & Engineering, Korea Advanced Institute of Science and Technology (KAIST), Daejeon 34141, Republic of Korea
3. Center for Biomolecular & Cellular Structure, Institution for Basic Science (IBS), Daejeon 34126, Republic of Korea