PDZ1 Domain inhibitor peptide, a cyclic peptide, incorporates a β-Ala lactam side chain linker and targets the PDZ1 domains of the postsynaptic density protein 95 (PSD-95). PDZ1 Domain inhibitor peptide disrupts the GluR6/PSD-95 interaction and is very efficient in competing against the C terminus of GluR6 for the PDZ1 domain.