Enables aspartic endopeptidase activity, intramembrane cleaving and protein homodimerization activity. Involved in several processes, including T cell receptor signaling pathway; positive regulation of calcineurin-NFAT signaling cascade; and positive regulation of protein dephosphorylation. Located in Golgi-associated vesicle membrane; plasma membrane; and rough endoplasmic reticulum. Is integral component of cytoplasmic side of endoplasmic reticulum membrane and integral component of lumenal side of endoplasmic reticulum membrane. [From Alliance of Genome Resources]