The HA or NA subtypes exhibited low similarities of amino acid sequences in all subtypes while maintaining identical structures, which revealed that the functions of various HA or NA subtypes remain conserved. Notably, some of the glycosites near the cysteines were found to also be conserved. The cysteines take the main role in stabilizing the tertiary structure; the conservation verifies that cysteines and N-glycans played an important role in the protein folding and quality control.