XK and influenza: For example, G219S and K58I combined mutations or three-amino-acid mutations (V186G/K-K193T-G228S or V186N-N224K-G228S) in H7N9 HA protein resulted in high affinity to α-2,6-linked sialic acid (SA) and increased HA stability [10, 41], and a R292K mutation in H7N9 NA protein facilitated drug resistance through decreasing the binding interaction with oseltamivir, the most commonly used anti-influenza drug [11].