Blocking the cleavage at midportion between γ- and ε-sites remarkably suppresses the generation of amyloid β-protein

To examine how γ- and ε-cleavages of β-amyloid precursor protein (APP) are related, each cleavage site was replaced with a stretch of Trp that cannot be cleaved by γ-secretase. Replacement of the γ- or ε-site significantly suppressed secretion of amyloid β-protein (Aβ), and produced longer Aβ or longer APP intracellular domain, respectively. This cleavage at the midportion between γ- and ε-sites was also γ-secretase-dependent. Blocking this cleavage with a Trp stretch remarkably suppressed Aβ generation, indicating that the midportion cleavage is required for the generation of Aβ.