Figure 2 Antigenic sites on the surface of the HA protein of H9N2 AIV. The HA amino acid sequence of CQY-2014 isolate and mutations were uploaded to the SWISS-MODEL website for model prediction, and the predicted trimeric proteins were annotated using the ChimeraX 1.3 software. A: Forty-six antigenic sites were labeled gray in the α-subunits, and the six preselected high-frequency mutation sites were labeled yellow in the β-subunits.B: When asparagine was substituted with glycine at site 201 (D201G), the α helix structure remained unchanged, but the surface structure changed significantly (red boxes).