title: Full-length and truncated Alzheimer amyloid precursors in chromaffin granules: solubilization of membrane amyloid precursor is mediated by an enzymatic mechanism.
abstract: The amyloid beta peptide (A beta) of Alzheimer disease is derived from the proteolytic processing of the amyloid precursor proteins (APPs), which are considered type I transmembrane proteins. Here we report that the soluble fraction of isolated adrenal medullary chromaffin granules (CG), a model neuronal secretory vesicle system, contains an antigen that immunochemically and on sodium dodecyl sulfate-polyacrylamide gel electrophoresis was indistinguishable from full-length APP. A truncated APP fragment with intact A beta sequence was also detected in the soluble fraction of CG. In vitro experiments showed that full-length APP was solubilized from CG membranes at 37 degrees C as a function of pH, with a peak of activity between pH 8.5 and pH 9.0. Solubilization of full-length APP was inhibited by several protease inhibitors, including aprotinin, cystatin, and iodoacetamide, by the divalent cations Ca2+ and Zn2+, and by preheating of the membranes. These results are consistent with and suggest the involvement of an enzymatic mechanism in the solubilization of potentially amyloidogenic full-length APP. Production of A beta from a transmembrane APP predicts a proteolytic cleavage within the lipid bilayer, a site relatively inaccessible to proteases. Thus, the detected soluble, potentially amyloidogenic, full-length APP may be a substrate for the proteases producing A beta. The detection of soluble APP with intact A beta sequence in secretory vesicles is consistent with the extracellular topology of amyloid depositions.
authors.affiliation: Mount Sinai School of Medicine, Department of Psychiatry and Neurobiology, New York, NY 10029, USA.
authors.forename: D
authors.initials: D
authors.lastname: Vassilacopoulou
authors.forename: J A
authors.initials: JA
authors.lastname: Ripellino
authors.forename: N
authors.initials: N
authors.lastname: Tezapsidis
authors.forename: V Y
authors.initials: VY
authors.lastname: Hook
authors.forename: N K
authors.initials: NK
authors.lastname: Robakis
mesh_terms: D000313:Adrenal Medulla / Q000648:ultrastructure*; D016564:Amyloid beta-Protein Precursor / Q000032:analysis* / Q000302:isolation & purification / Q000378:metabolism; D000818:Animals; D002118:Calcium / Q000494:pharmacology; D002413:Cations, Divalent; D002417:Cattle; D002837:Chromaffin Granules / Q000737:chemistry*; D003546:Cysteine Endopeptidases / Q000378:metabolism; D004591:Electrophoresis, Polyacrylamide Gel; D010450:Endopeptidases / Q000378:metabolism; D006358:Hot Temperature; D006863:Hydrogen-Ion Concentration; D007425:Intracellular Membranes / Q000737:chemistry / Q000201:enzymology*; D011480:Protease Inhibitors / Q000494:pharmacology; D012697:Serine Endopeptidases / Q000378:metabolism; D012995:Solubility; D015032:Zinc / Q000494:pharmacology
chemical_list: D016564:Amyloid beta-Protein Precursor; D002413:Cations, Divalent; D011480:Protease Inhibitors; D010450:Endopeptidases; D012697:Serine Endopeptidases; D003546:Cysteine Endopeptidases; D015032:Zinc; D002118:Calcium