To define the epitope precisely, four mutants with deletions at C-and N-termini of the motif SVQYHPL (Table 1) were constructed to express the GST fusions GST-H7DS, GST-H7DL, GST-H7DSV, and GST-H7DPL representing -VQYHPL, SVQYHP-, -QYHPL and SVQYH-(deletions were shown as dashes) in E. coli, respectively. We found that only the full-length SVQYHPL polypeptide (GST-H7wt) was recognized by the mAb A9E8 ( Figure 3A ). Removal of one or more amino acids at either the amino or carboxyl terminus of the peptide abolished antibody binding, indicating that the peptide SVQYHPL represented the minimal requirement for the reactivity of the epitope with A9E8. Minimal Unit of the Epitope with the Maximal Binding Activity to mAb A9E8