γ-Secretase-dependent proteolysis of transmembrane domain of amyloid precursor protein: Successive tri-and tetrapeptide release in amyloid β-protein production

Abstract

γ-Secretase cleaves the carboxyl-terminal fragment (βCTF) of APP not only in the middle of the transmembrane domain (γ-cleavage), but also at sites close to the membrane/cytoplasm boundary (ε-cleavage), to produce the amyloid β protein (Aβ) and the APP intracellular domain (AICD), respectively. The AICD49-99 and AICD50-99 species were identified as counterparts of the long Aβ species Aβ48 and Aβ49, respectively. We found that Aβ40 and AICD50-99 were the predominant species in cells expressing wild-type APP and presenilin, whereas the production of Aβ42 and AICD49-99 was enhanced in cells expressing familial Alzheimer's disease mutants of APP and presenilin. These long Aβ species were identified in cell lysates and mouse brain extracts, which suggests that ε-cleavage is the first cleavage of βCTF to produce Aβ by γ-secretase. Here, we review the progress of research on the mechanism underlying the proteolysis of the APP transmembrane domain based on tri- and tetrapeptide release. © 2012 Mako Takami and Satoru Funamoto.