A screening method comprising the following steps: (1) specifying a receptor-binding site by transferring a mutation； and (2) specifying a binding site-specific peptide motif based on an amino acid selection ration by comparing apeptide motif binding to a wild type subunit with a peptide motif binding to amutant functionally lacking the above-described binding site by the peptidelibrary method. Thus, a peptide inhibiting a toxin having a subunit structurein the receptor-binding part is screened. Accordingly, it is possible toprovide an STX2 inhibitor which has an STX2 inhibitory peptide integrated intoa molecular nucleus structure having three lysine (Lys) molecules bondedtogether via peptide bonds, can be easily synthesized and can inhibit Verotoxin.
