title: gamma-Secretase: successive tripeptide and tetrapeptide release from the transmembrane domain of beta-carboxyl terminal fragment.
abstract: Amyloid beta protein (Abeta), a pathogenic molecule associated with Alzheimer's disease, is produced by gamma-secretase, which cleaves the beta-carboxyl terminal fragment (betaCTF) of beta-amyloid precursor protein in the middle of its transmembrane domain. How the cleavage proceeds within the membrane has long been enigmatic. We hypothesized previously that betaCTF is cleaved first at the membrane-cytoplasm boundary, producing two long Abetas, Abeta(48) and Abeta(49), which are processed further by releasing three residues at each step to produce Abeta(42) and Abeta(40), respectively. To test this hypothesis, we used liquid chromatography tandem mass spectrometry (LC-MS/MS) to quantify the specific tripeptides that are postulated to be released. Using CHAPSO (3-[(3-cholamidopropyl)dimethylammonio]-2-hydroxyl-1-propanesulfonate)-reconstituted gamma-secretase system, we confirmed that Abeta(49) is converted to Abeta(43/40) by successively releasing two or three tripeptides and that Abeta(48) is converted to Abeta(42/38) by successively releasing two tripeptides or these plus an additional tetrapeptide. Most unexpectedly, LC-MS/MS quantification revealed an induction period, 3-4 min, in the generation of peptides. When extrapolated, each time line for each tripeptide appears to intercept the same point on the x-axis. According to numerical simulation based on the successive reaction kinetics, the induction period exists. These results strongly suggest that Abeta is generated through the stepwise processing of betaCTF by gamma-secretase.
authors.affiliation: Department of Neuropathology, Faculty of Life and Medical Sciences, Doshisha University, Kizugawa 619-0225, Japan.
authors.forename: Mako
authors.initials: M
authors.lastname: Takami
authors.forename: Yu
authors.initials: Y
authors.lastname: Nagashima
authors.forename: Yoshihisa
authors.initials: Y
authors.lastname: Sano
authors.forename: Seiko
authors.initials: S
authors.lastname: Ishihara
authors.forename: Maho
authors.initials: M
authors.lastname: Morishima-Kawashima
authors.forename: Satoru
authors.initials: S
authors.lastname: Funamoto
authors.forename: Yasuo
authors.initials: Y
authors.lastname: Ihara
mesh_terms: D053829:Amyloid Precursor Protein Secretases / Q000502:physiology*; D016229:Amyloid beta-Peptides / Q000737:chemistry* / Q000378:metabolism*; D016564:Amyloid beta-Protein Precursor / Q000737:chemistry / Q000378:metabolism*; D000704:Analysis of Variance; D000818:Animals; D016466:CHO Cells / Q000648:ultrastructure; D002462:Cell Membrane / Q000187:drug effects / Q000378:metabolism; D002793:Cholic Acids / Q000494:pharmacology; D002853:Chromatography, Liquid / Q000379:methods; D006224:Cricetinae; D003412:Cricetulus; D003902:Detergents / Q000494:pharmacology; D047468:Immunoprecipitation / Q000379:methods; D008954:Models, Biological; D009842:Oligopeptides / Q000737:chemistry / Q000378:metabolism; D010446:Peptide Fragments / Q000032:analysis / Q000378:metabolism*; D017434:Protein Structure, Tertiary / Q000502:physiology; D013379:Substrate Specificity; D053719:Tandem Mass Spectrometry / Q000379:methods; D013997:Time Factors
chemical_list: D016229:Amyloid beta-Peptides; D016564:Amyloid beta-Protein Precursor; D002793:Cholic Acids; D003902:Detergents; D009842:Oligopeptides; D010446:Peptide Fragments; C048531:chapso; D053829:Amyloid Precursor Protein Secretases