Complex N-linked glycosylated nicastrin associates with active γ-secretase and undergoes tight cellular regulation

Abstract

The intramembranous proteolysis of Notch and the amyloid precursor protein by γ-secretase exemplifies an unusual and newly recognized mechanism of signal transduction in multicellular organisms. Here, we show that only a form of nicastrin (NCT) containing N-linked complex oligosaccharides is present in active γ-secretase complexes. Overexpression of NCT does not generate more of this mature protein, a phenomenon analogous to the strictly regulated formation of mature presenilin heterodimers from immature holoprotein. The absence of presenilin severely limits the maturation of NCT, yet combined overexpression of both proteins does not increase respective mature types. Taken together, our findings describe unusual regulatory features of this key signaling protease: the association of NCT with γ-secretase is tightly regulated via glycosylation; at least one other cofactor exists; the least abundant member of the complex becomes limiting; and the cofactor that serves this role may vary by cell type.