Gamma secretase (γ-secretase), a member of the intramembrane cleaving protease (i-CLiP) family, is a promiscuous di-aspartyl protease that catalyzes the regulated intramembrane proteolysis (RIP), in which substrate proteins are cleaved within their membrane-spanning domain. A functional γ-secretase is a multi-protein complex consisting of the catalytic component, presenilin (PSEN), and three protein cofactors, including nicastrin (NCT), anterior-pharynx defective-1 (APH1) and PSEN enhancer-2 (PEN2). So far, 90 substrates of γ-secretase have been identified, which are type-I transmembrane proteins, except for glutamate receptor GluR3, polycystin-1 and glucosaminyltransferase (GnT-V), and appear to function as signaling proteins regulating a wide variety of cellular events, such as Notch signaling pathway.