An avian-origin human-infecting influenza (H7N9) virus was recently identified in China. We have evaluated the viral hemagglutinin (HA) receptor-binding properties of two human H7N9 isolates, A/Shanghai/1/2013 (SH-H7N9) (containing the avian-signature residue Gln226) and A/Anhui/1/2013 (AH-H7N9) (containing the mammalian-signature residue Leu 226). We found that SH-H7N9 HA preferentially binds the avian receptor analog, whereas AH-H7N9 HA binds both avian and human receptor analogs. Furthermore, an AH-H7N9 mutant HA (Leu226 ? Gln) was found to exhibit dual receptor-binding property, indicating that other amino acid substitutions contribute to the receptor-binding switch. The structures of SH-H7N9 HA, AH-H7N9 HA, and its mutant in complex with either avian or human receptor analogs show how AH-H7N9 can bind human receptors while still retaining the avian receptor-binding property.
Shi, Y., Zhang, W., Wang, F., Qi, J., Wu, Y., Song, H., Gao, F., Bi, Y., Zhang, Y., Fan, Z., Qin, C., Sun, H., Liu, J., Haywood, J., Liu, W., Gong, W., Wang, D., Shu, Y., Wang, Y., ... Gao, G. F. (2013). Structures and receptor binding of hemagglutinins from human-infecting h7n9 influenza viruses. Science, 342(6155), 243-247. https://doi.org/10.1126/science.1242917