Probable catalytic subunit of the gamma-secretase complex, an endoprotease complex that catalyzes the intramembrane cleavage of integral membrane proteins such as Notch receptor. Required for S3 cleavage of Notch, which releases activated Notch protein from the cell membrane. Involved in the patterning of the optic lobes. Homodimer (By similarity). Component of the gamma-secretase complex, a complex composed of a presenilin (Psn) homodimer, nicastrin (Nct), Aph-1 and Pen-2. Interacts with Metl. Isoform 2 shows a better interaction with Metl than isoform 1. Maternally expressed in nurse and follicle cells. In early embryos, expressed in all or most cells and later increases in CNS and epidermal tissues. In larvae, expression is seen in all imaginal disks, brain and optic lobes. In pupae, expression is seen in eye disk and brain. Expressed both maternally and zygotically throughout development. The PAL motif is required for normal active site conformation. Cleaved. The cleavage, which probably takes place between the 6th and the 7th transmembrane regions, may be required for activation of the gamma-secretase activity. Belongs to the peptidase A22A family.