May have a role in immune function. Probably involved in the processing of antigenic peptides during MHC class II-mediated antigen presentation. May play a role in activation-induced lymphocyte depletion in the thymus, and in neuronal degeneration and glial cell activation in the brain.
Expressed abundantly in the stomach, the Clara cells of the lung and activated B-lymphocytes, and at lower levels in lymph nodes, skin and spleen. Not expressed in resting B-lymphocytes.
Belongs to the peptidase A1 family.
Glycosylated. The nature of the carbohydrate chain varies between cell types. In fibroblasts, the proenzyme contains a high mannose-type oligosaccharide, while the mature enzyme contains a complex-type oligosaccharide. In erythrocyte membranes, both the proenzyme and mature enzyme contain a complex-type oligosaccharide. Two forms are produced by autocatalytic cleavage, form I begins at Ile-54, form II begins at Thr-57.
Endosome. The proenzyme is localized to the endoplasmic reticulum and Golgi apparatus, while the mature enzyme is localized to the endosome.