Fig. 1. Production and validation of functional H7 HA1 protein.

a–d The H7 HA1 proteins in forms of GST-HA1 fusion proteins (a, b) and S₆₀-HA1 particles (c, d) were produced in E. coli. Their expression constructs are schematically illustrated in a (GST-fusion protein) and c (norovirus S domain fusion protein), while the expressed and purified proteins were analyzed by SDS-PAGE, respectively (b, d). Lane M is the prestained protein markers with indicated sizes. The remaining three lanes are three purified protein fractions that eluted from the affinity column. e Both GST-HA1 (upper panel, black) and S₆₀-HA1 (lower panel, black) proteins reacted with H7-specific antibody, while the GST and S₆₀ particles (negative controls, green) did not. After heat-inactivation both HA1 proteins reduced the reactivity to the H7 antibody. f Both S₆₀-HA1 and GST-HA1 proteins agglutinated chicken (upper panel) and human (lower panel) red blood cells (RBCs). S₆₀ particle and GST without HA1 were used as negative controls that did not agglutinate RBCs. The serially diluted protein concentrations are indicated. g, h Both GST-HA1 (g) and S₆₀-HA1 (h) proteins bound certain sialyl glycans. X-axis, various sialyl glycans in the indicated names. Y-axis, binding signal intensity of the H7 HA1 proteins to various sialyl glycans. Error bars are standard deviations that are calculated by the software GraphPad Prism 6