1. Department of Biochemistry, Yong Loo Lin School of Medicine, National University of Singapore, 8 Medical Drive, Singapore 117597, Singapore
2. Department of Chemistry, University of Wisconsin—Madison, 1101 University Ave., Madison, Wisconsin 53706-1322
3. Chemical Biology and Biotechnology Lab, Research Center for Advanced Science and Technology (RCAST), The University of Tokyo, 4-6-1 Komaba, Meguro-ku, Tokyo 153-8904, Japan