Degrades proteins damaged by L-isoaspartyl residue formation (also known as beta-Asp residues). Degrades L-isoaspartyl-containing di- and tripeptides. Acts best on iso-Asp-Leu, followed by iso-Asp-Ala, -His and to a lesser extent iso-Asp-Lys, -Phe and iso-Asp-Leu-Ala. Does not act on internal iso-Asp bonds (Als-iso-Asp-Leu-Ala). Does not act on alpha-Asp bonds. Has poor L-asparaginase activity. Cleavage of a beta-linked Asp residue from the N-terminus of a polypeptide. Heterotetramer of two alpha and two beta chains arranged as a dimer of alpha/beta heterodimers. Autocleaved. Generates the alpha and beta subunits. The beta subunit is thought to be responsible for the nucleophile hydrolase activity. Subunit alpha. Subunit beta. Belongs to the Ntn-hydrolase family.