FunctionMay 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.
Tissue specificityExpressed 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.
Sequence similaritiesBelongs to the peptidase A1 family.
Post-translational modificationsGlycosylated. 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.
Cellular localizationEndosome. The proenzyme is localized to the endoplasmic reticulum and Golgi apparatus, while the mature enzyme is localized to the endosome.