title: γ-Secretase associated with lipid rafts: multiple interactive pathways in the stepwise processing of β-carboxyl-terminal fragment.
abstract: γ-Secretase generates amyloid β-protein (Aβ), a pathogenic molecule in Alzheimer disease, through the intramembrane cleavage of the β-carboxyl-terminal fragment (βCTF) of β-amyloid precursor protein. We previously showed the framework of the γ-secretase cleavage, i.e. the stepwise successive processing of βCTF at every three (or four) amino acids. However, the membrane integrity of γ-secretase was not taken into consideration because of the use of the 3-[(3-cholamidopropyl)dimethylammonio]-2-hydroxy-1-propanesulfonic acid-solubilized reconstituted γ-secretase system. Here, we sought to address how the membrane-integrated γ-secretase cleaves βCTF by using γ-secretase associated with lipid rafts. Quantitative analyses using liquid chromatography-tandem mass spectrometry of the βCTF transmembrane domain-derived peptides released along with Aβ generation revealed that the raft-associated γ-secretase cleaves βCTF in a stepwise sequential manner, but novel penta- and hexapeptides as well as tri- and tetrapeptides are released. The cropping of these peptides links the two major tripeptide-cleaving pathways generating Aβ40 and Aβ42 at several points, implying that there are multiple interactive pathways for the stepwise cleavages of βCTF. It should be noted that Aβ38 and Aβ43 are generated through three routes, and γ-secretase modulator 1 enhances all the three routes generating Aβ38, which results in decreases in Aβ42 and Aβ43 and an increase in Aβ38. These observations indicate that multiple interactive pathways for stepwise successive processing by γ-secretase define the species and quantity of Aβ produced.
authors.affiliation: From the Department of Molecular Neuropathology, Graduate School of Pharmaceutical Sciences, Hokkaido University, Sapporo 060-0812.
authors.forename: Nobutaka
authors.initials: N
authors.lastname: Matsumura
authors.forename: Mako
authors.initials: M
authors.lastname: Takami
authors.forename: Masayasu
authors.initials: M
authors.lastname: Okochi
authors.forename: Satoko
authors.initials: S
authors.lastname: Wada-Kakuda
authors.forename: Hitomi
authors.initials: H
authors.lastname: Fujiwara
authors.forename: Shinji
authors.initials: S
authors.lastname: Tagami
authors.forename: Satoru
authors.initials: S
authors.lastname: Funamoto
authors.forename: Yasuo
authors.initials: Y
authors.lastname: Ihara
authors.forename: Maho
authors.initials: M
authors.lastname: Morishima-Kawashima
mesh_terms: D053829:Amyloid Precursor Protein Secretases / Q000737:chemistry / Q000378:metabolism*; D016229:Amyloid beta-Peptides / Q000378:metabolism*; D000818:Animals; D001921:Brain / Q000378:metabolism; D016466:CHO Cells; D006224:Cricetinae; D003412:Cricetulus; D021962:Membrane Microdomains / Q000378:metabolism*; D008954:Models, Biological; D009842:Oligopeptides / Q000378:metabolism; D011499:Protein Processing, Post-Translational; D051381:Rats; D017208:Rats, Wistar; D015398:Signal Transduction; D013997:Time Factors
chemical_list: D016229:Amyloid beta-Peptides; D009842:Oligopeptides; D053829:Amyloid Precursor Protein Secretases
keywords: Alzheimer Disease; Amyloid Precursor Protein; Amyloid β-Protein; Lipid Raft; Membrane; Secretases; γ-Secretase