Blocking the cleavage at midportion between gamma- and epsilon-sites remarkably suppresses the generation of amyloid beta-protein

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