title: A presenilin-independent aspartyl protease prefers the gamma-42 site cleavage.
abstract: beta-Amyloid peptides (Abeta40 and Abeta42) are the major constituents of amyloid plaques, which are one of the hallmarks of Alzheimer's disease (AD). The Abeta is derived from sequential cleavages of amyloid precursor protein (APP) by beta- and gamma-secretases. gamma-Secretase consists of at least four proteins where presenilins (PS1 and PS2 or PS) are the catalytic subunit involved in the gamma-site cleavage of APP. Secretion of both Abeta40 and Abeta42 is significantly reduced in PS1 knock-out cells and completely abolished in cells deficient for both PS1 and PS2. Consequently, both the PS proteins play essential roles in the production of the secretory of Abeta from cells. Recent studies in primary neurons, however, suggest that PSs are not required for intracellular Abeta42 accumulation; thus the intracellular Abeta42 appears to be generated in a PS-independent manner. Here we present the first biochemical evidence indicating that Abeta, especially Abeta42, can be generated in the absence of PS based on an in vitrogamma-secretase assay employing membranes prepared from PS-deficient Blastocyst-derived (BD) cells. This PS-independent gamma-secretase (PSIG) activity is sensitive to the changes in pH and displays an optimal activity at pH 6.0. Pepstatin A is a potent inhibitor for this proteolytic activity with IC50 of 1.2 nm and 0.4 nm for Abeta40 and Abeta42 generation, respectively. These results indicate that these PS-independent gamma-site cleavages are mediated by an aspartyl protease. More importantly, the PSIG activity displays a distinct preference in mediating the 42-site cleavage over the 40-site cleavage, thereby generating Abeta42 as the predominant product.
authors.affiliation: Department of Biological Chemistry, Merck Research Laboratories, West Point, Pennsylvania, USA.
authors.forename: Ming-Tain
authors.initials: MT
authors.lastname: Lai
authors.forename: Ming-Chih
authors.initials: MC
authors.lastname: Crouthamel
authors.forename: Jillian
authors.initials: J
authors.lastname: DiMuzio
authors.forename: Beth Lynn
authors.initials: BL
authors.lastname: Pietrak
authors.forename: Dorit B
authors.initials: DB
authors.lastname: Donoviel
authors.forename: Alan
authors.initials: A
authors.lastname: Bernstein
authors.forename: Stephen J
authors.initials: SJ
authors.lastname: Gardell
authors.forename: Yue-Ming
authors.initials: YM
authors.lastname: Li
authors.forename: Daria
authors.initials: D
authors.lastname: Hazuda
mesh_terms: D053829:Amyloid Precursor Protein Secretases; D016229:Amyloid beta-Peptides / Q000378:metabolism*; D000818:Animals; D016282:Aspartic Acid Endopeptidases / Q000378:metabolism*; D001755:Blastocyst / Q000378:metabolism; D002219:Carbamates / Q000494:pharmacology; D002462:Cell Membrane / Q000378:metabolism; D002478:Cells, Cultured; D004247:DNA / Q000235:genetics; D004151:Dipeptides / Q000494:pharmacology; D010450:Endopeptidases / Q000378:metabolism; D006863:Hydrogen-Ion Concentration; D008163:Luminescent Measurements; D008565:Membrane Proteins / Q000235:genetics / Q000502:physiology; D051379:Mice; D009474:Neurons / Q000201:enzymology / Q000378:metabolism; D053764:Presenilin-1; D053766:Presenilin-2; D014162:Transfection
chemical_list: D016229:Amyloid beta-Peptides; D002219:Carbamates; D004151:Dipeptides; C410009:L 685458; D008565:Membrane Proteins; D053764:Presenilin-1; D053766:Presenilin-2; D004247:DNA; D053829:Amyloid Precursor Protein Secretases; D010450:Endopeptidases; D016282:Aspartic Acid Endopeptidases; C509282:Bace1 protein, mouse