A novel substrate for analyzing Alzheimer's disease γ‐secretase

Abstract
Proteolytic processing of Alzheimer's disease amyloid precursor protein (APP) by β‐secretase leads to A4CT (C99), which is further cleaved by the as yet unknown protease called γ‐secretase. To study the enzymatic properties of γ‐secretase independently of β‐secretase, A4CT together with an N‐terminal signal peptide (SPA4CT) may be expressed in eukaryotic cells. However, in all existing SPA4CT proteins the signal peptide is not correctly cleaved upon membrane insertion. Here, we report the generation of a mutated SPA4CT protein that is correctly cleaved by signal peptidase and, thus, identical to the APP‐derived A4CT. This novel SPA4CT protein is processed by γ‐secretase in the same manner as APP‐derived A4CT and might be valuable for the generation of transgenic animals showing amyloid pathology.