Probable subunit of the gamma-secretase complex, an endoprotease complex that catalyzes the intramembrane cleavage of integral membrane proteins such as Notch receptors. Homodimer. Probable component of the gamma-secretase complex, a complex composed of a presenilin homodimer, nicastrin, APH1 and PEN2 (By similarity). The PAL motif is required for normal active site conformation. Belongs to the peptidase A22A family.