Receptor-binding specificity of yeast surface-displayed HA. Yeast surface-displayed HA binds to (a) α2,3-linked sialylglycan receptor (SAα2,3) and (b) α2,6-linked sialylglycan receptor (SAα2,6). EBY100/pYD1 served as a negative control, and an inactivated H5N1 vaccine as a positive control. Error bars represent standard deviations of the mean, which is calculated with three independent repeats. (c) Results of hemagglutination assay. Inactivated H5N1 vaccine served as a positive control, and PBS and EBY100/pYD1 as two negative controls.