Activation and intrinsic γ-secretase activity of presenilin 1

A complex composed of presenilin (PS), nicastrin, PEN-2, and APH-1 is absolutely required for gamma-secretase activity in vivo. Evidence has emerged to suggest a role for PS as the catalytic subunit of gamma-secretase, but it has not been established that PS is catalytically active in the absence of associated subunits. We now report that bacterially synthesized, recombinant PS (rPS) reconstituted into liposomes exhibits gamma-secretase activity. Moreover, an rPS mutant that lacks a catalytic aspartate residue neither exhibits reconstituted gamma-secretase activity nor interacts with a transition-state gamma-secretase inhibitor. Importantly, we demonstrate that rPS harboring mutations that cause early onset familial Alzheimer's disease (FAD) lead to elevations in the ratio of A beta 42 to A beta 40 peptides produced from a wild-type APP substrate and that rPS enhances the A beta 42/A beta 40 peptide ratio from FAD-linked mutant APP substrates, findings that are entirely consistent with the results obtained in in vivo settings. Thus, gamma-secretase cleavage specificity is an inherent property of the polypeptide. Finally, we demonstrate that PEN2 is sufficient to promote the endoproteolysis of PS1 to generate the active form of gamma-secretase. Thus, we conclusively establish that activated PS is catalytically competent and the bimolecular interaction of PS1 and PEN2 can convert the PS1 zymogen to an active protease.