γ‐Secretase complexes containing N‐ and C‐terminal fragments of different presenilin origin retain normal γ‐secretase activity

The γ‐secretase complex processes substrate proteins within membranes and consists of four proteins: presenilin (PS), nicastrin, Aph‐1 and Pen‐2. PS harbours the enzymatic activity of the complex, and there are two mammalian PS homologues: PS1 and PS2. PS undergoes endoproteolysis, generating the N‐ and C‐terminal fragments, NTF and CTF, which represent the active species of PS. To characterize the functional similarity between complexes of various PS composition, we analysed PS1, PS2, and chimeric PS composed of the NTF from PS1 and CTF from PS2, or vice versa, in assembly and function of the γ‐secretase complex. Chimeric PSs, like PS1 and PS2, undergo normal endoproteolysis when introduced into cells devoid of endogenous PS. Furthermore, PS2 CTF can, at least partially, restore processing in a truncated PS1, which cannot undergo endoproteolysis. All PS forms enable maturation of nicastrin and cleave full length Notch receptors, indicating that both PS1 and PS2 are present at the cell surface. Finally, when co‐introduced as separate molecules, NTF and CTF of different PS origin reconstitute γ‐secretase activity. In conclusion, these data show that endoproteolysis, NTF–CTF interactions, and the assembly and activity of γ‐secretase complexes are very conserved between PS1 and PS2.