3.4 The amino acid at position 158 alters virus reactivity with antibodies due to steric effect.
To investigate how the HA gene affects the antigenic differences between GX/18 and GD/104 viruses, we compared the 3D structure of GX/18-HA-158G and GX/18-HA-158E proteins. As shown in Figure 4, the amino acid mutation from G to E caused the R group changing from -H to -(CH2)2-COOH, and the consequent steric effect directly hindered the recognition of antibody to HA protein. Additionally, the polarity of -H was almost negligible compared to that of -(CH2)2-COOH, so E was comparatively more hydrophilic than G. Since the hydrophobic interaction is the principle driving force for protein folding(Zhu et al., 2016a), the G158E mutation might also affect the local folding of HA protein through altering the degrees of hydrophobicity and further impact the binding affinity with antibody, resulting in antigenic drift ultimately.