Functional display of HA on yeast surface. A schematic diagram of HA display on yeast surface. The Aga2-HA fusion protein binds to Aga1 through two disulfide bonds after its secretion from the yeast. Aga1 is the first subunit of the yeast a-agglutinin receptor. It is secreted from the cell and becomes covalently attached to β-glucan in the extracellular matrix of the yeast cell wall. A GS linker is inserted between Aga2 and HA to stabilize the fusion protein expression.