Serine peptidase whose precise substrate specificity remains unclear (PubMed:21692504). Does not cleave peptides after a arginine or lysine residue (By similarity). Regulates trans-Golgi network morphology and sorting by regulating the membrane binding of the AP-1 complex (PubMed:23321636). May play a role in the regulation of synaptic vesicle exocytosis (By similarity). Inhibited by 1-isobutyl-3-oxo-3,5,6,7-tetrahydro-2H-cyclopenta[c]pyridine-4-carbonitrile. Homodimer (By similarity). Interacts with the AP-1 complex (By similarity). Co-localizes with AP-1 in the trans-Golgi network (PubMed:23321636). Co-localizes with MAP2 and ACTB on the cytoskeleton (PubMed:23485813). Co-localizes with STX6 and GOSR2 at the Golgi apparatus (PubMed:23485813). Highly expressed in the brain, specifically in neurons of the neocortex, substantia nigra, locus coeruleus, and cerebellum, and a slightly lesser extent in neurons in the hypothalamus and hippocampus (at protein level) (PubMed:23321636, PubMed:23485813). Also expressed in interneurons in the stratum lacunosum moleculare and stratum radiatum (PubMed:23485813). PREPL-null mice are significantly shorter and lighter than their wild-type littermates and suffer from neonatal hypotonia. Belongs to the peptidase S9A family.