[4][5] Prolyl endopeptidase is a large cytosolic enzyme that belongs to a distinct class of serine peptidases.

Its activity is confined to action on oligopeptides of less than 10 kD and it has an absolute requirement for the trans-configuration of the peptide bond preceding proline.

Only short protein residues are able to enter the active site of prolyl endopeptidase due to the distinct beta-propeller region that acts as a gating filter mechanism.

[9] Altered PREP activity may be associated with autism spectrum disorders and various psychological diseases such as schizophrenia, mania and clinical depression.

[11][12] Some types of prolyl endopeptidase have been used in studies to decrease the propensity of gluten-containing wheat products to aggravate coeliac disease.