The available structures of HA and NA would help us to explore the distinctive function of various glycosites. Therefore, we collected the structures of various HA or NA subtypes from the PDB (Protein Data Bank, http://www.rcsb.org/pdb/home/ home.do). To obtain the whole multimer, these monomer structures were processed with a VMD 1.9 transformation matrix using a Tcl script [45] . The code for each representative structure of the various subtypes of HA and NA and the corresponding source of IVs are shown in Table S2 .