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.