1. Bioinformatics and Drug Design Group, Centre for Computational Science and Engineering, National University of Singapore, Blk S16, Level 8, 3 Science Drive 2, Singapore 117543, State Key Laboratory of Biotherapy, Sichuan University, Chengdu 610064, P. R. China, College of Chemistry, Sichuan University, Chengdu, 610064, P. R. China, and Department of Biological Science, National University of Singapore, Blk S2, Level 5, Science Drive 4, Singapore 117543