Degrades proteins damaged by L-isoaspartyl residue formation (also known as beta-Asp residues). Probably performs the final step in the degradation of the reserve polymer cyanophycin (depolymerizes the building block L-beta-Asp-Arg). Also has L-asparaginase activity. Cleavage of a beta-linked Asp residue from the N-terminus of a polypeptide. Enzyme is inactive on alpha-aspartyl dipeptides. Heterotetramer of two alpha and two beta chains arranged as a dimer of alpha/beta heterodimers. Cleaved into an alpha and beta chain by autocatalysis; this activates the enzyme. The N-terminal residue of the beta subunit is responsible for the nucleophile hydrolase activity. Belongs to the Ntn-hydrolase family.