An example AEP: Human legumain with catalytic triad in red, bound to product in black.

[4] It can be detected in spleen, liver, brain, testis tissue and heart[5] and the protein is mostly localised to lysosomes and endosomes.

[8][9] This enzyme catalyses the following chemical reaction: Both plant and animal legumains are most active in acidic environments.

[10] Once in the acidic environment of the vacuole or lysosome, the prodomain is cleaved off to reveal the active enzyme.

[11] It uses a catalytic triad of Cysteine-Histidine-Asparagine in its active site to perform covalent proteolysis of its substrate.

The chemical structure at this point shows that breaks which occurs at pH 4.5 can be healed under the basic crystallization conditions.

and AEP can initiate removal of invariant chain in MHC-II complex, which can critically influence peptide generation and activity of MHCII.

In patients with PD, alpha synuclein is cut by AEP into toxic chunks.,[4][21] which are hypothesized to possibly play a role in the initiation or pathogenesis of PD [22] Active AEP was found at increased levels and translocated to the cytoplasm of neuronal cells of AD patients.

[23] In AD the plaques are composed of amyloid beta, intracellular neurofibrillary tangles and tau protein.

The dysfunction of APP proteolysis and the abnormal phosphorylation of tau lead to the formation of neuritic plaques and neurofibrillary tangles (NFTs), respectively, causing neuronal degeneration and dementia[24] It also play a crucial role in behavior disorders connected with AD such as anxiety and depression.

Since stroke elicits acidity in the brain AEP become active due to low pH level.