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A neuropathological hallmark of Alzheimer disease (AD) is a widespread amyloid deposition. We analyzed the entire amino acid sequences in an amyloid preparation and found, in addition to the major I3/A4-protein (AP) fragment, two unknown peptides. We raised antibodies against synthetic peptides using subsequences ofthese peptides. These antibodies immunostained amyloid in neuritic and diffuse plaques as well as vascular amyloid. Electron microscopic analysis demonstrated that the immunostaining was localized on amyloid fibrils. We have isolated an apparently full-length cDNA encoding a 140-amino-acid protein within which two previously unreported amyloid sequences are encoded in tandem in the most hydrophobic domain. We tentatively named this 35-amino acid peptide NAC (non-A(8 component of AD amyloid) and its precursor NACP. NAC is the second component, after A.8, identified chemically in the purified AD amyloid preparation. Secondary structure predictions indicate that the NAC peptide sequence has a strong tendency to form (structures consistent with its association with amyloid. NACP is detected as a M, 19,000 protein in the cytosolic fraction of brain homogenates and comigrates on immunoblots with NACP synthesized in Escherichia coli from NACP cDNA. NACP mRNA is expressed principally in brain but is also expressed in low concentrations in all tissues examined except in liver, suggesting its ubiquitous and brain-specific functions. The availability of the cDNA encoding full-length NACP should help to elucidate the mechanisms of amyloidosis in AD.Amyloid deposition in the neuritic plaque and blood vessels is the most consistent neuropathology in Alzheimer disease (AD) (1, 2). The major constituent of amyloid has been found to be a 39-to 43-amino acid amyloid 13/A4-protein (AP3) (3,4) derived from its precursor, APP (5-8). The isolation of APP cDNA prompted a burst-of research in AD, culminating in the identification of APP mutations in several familial types of AD (9-12). Thus, APP and AP have been proposed to play a key role in the pathogenesis of this disease (13, 14). Additionally, heparan sulfate proteoglycan, ferritin, immunoglobulins, and many acute-phase proteins, such as a1-antichymotrypsin (ACT), apolipoprotein E, complements, serum amyloid P, and trace peptides were also reported to be associated with plaque core amyloid (15-29), although supportive biochemical data demonstrating their presence in amyloid preparations are not yet available, raising the possibility that those might not be the intrinsic components of amyloid. We have further pursued the biochemical examination of the intrinsic constituents of AD amyloid by purification in SDS and sequencing, and we detected a previouslyThe publication costs of this article were defrayed in part by page charge payment. This article must therefore be hereby marked "advertisement" in accordance with 18 U.S.C. §1734 solely to indicate this fact.unrecognized component that we tentatively call NAC (non-AP component of AD amyloid) in this communication...

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Amyloid ␤ protein (A␤), a pathogenic molecule associated with Alzheimer's disease, is produced by ␥-secretase, which cleaves the ␤-carboxyl terminal fragment (␤CTF) of ␤-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 ␤CTF is cleaved first at the membranecytoplasm boundary, producing two long A␤s, A␤ 48 and A␤ 49 , which are processed further by releasing three residues at each step to produce A␤ 42 and A␤ 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 ␥-secretase system, we confirmed that A␤ 49 is converted to A␤ 43/40 by successively releasing two or three tripeptides and that A␤ 48 is converted to A␤ 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 A␤ is generated through the stepwise processing of ␤CTF by ␥-secretase.

We analyzed an amino-terminal modification of beta-amyloid (A beta) peptide in brain, using anti-A beta antibodies that distinguish distinct molecular species. Examination of cortical sections from 28 aged individuals with a wide range in senile plaque density revealed that a molecular species distinct from the standard A beta is deposited in the brain in a dominant and differential manner. This modified A beta peptide (A beta N3(pE)) starts at the 3rd aminoterminal residue of the standard A beta, glutamate, converted to pyroglutamate through intramolecular dehydration. Because plaques composed of A beta N3(pE) are present in equivalent or greater densities than those composed of standard A beta bearing the first amino-terminal residue (A beta N1) and because deposition of the former species appears to precede deposition of the latter, as confirmed with specimens from Down's syndrome patients, the processes involved in A beta N3(pE) production and retention may play an early and critical role in senile plaque formation.

The earliest event so far known that occurs in the brain affected with Alzheimer's disease (AD) is the deposition and fibril formation of amyloid beta-protein (A beta). A beta is cleaved from a glycosylated membrane protein, called beta-amyloid protein precursor, and normally secreted into the extracellular space. Here we report on the presence of membrane-bound A beta that tightly binds GM1 ganglioside. This suggests that this novel A beta species, rather than secreted A beta, may act as a 'seed' for amyloid and further that intracellular abnormalities in the membrane recycling already exist at the stage of amyloidogenesis.

To gain insight into the abnormal phosphorylation of PHF-tau, we have determined the phosphorylation sites by identifying phosphopeptides by means of ion spray mass spectrometry followed by sequencing of ethane-thiol-modified peptides. Nineteen sites have been identified; all but Ser-262 are localized to the amino- and carboxyl-terminal flanking regions of the microtubule-binding domain. Eleven sites correspond to fetal type sites. Unexpectedly, 10 are non-proline-directed, whereas the others are proline-directed. Thus, the abnormal phosphorylation of PHF-tau can be considered to consist of fetal type phosphorylation and additional proline-directed and non-proline-directed phosphorylation. This non-fetal type phosphorylation may provide PHF-tau with the unusual characteristics.

is presenilin dependent and is suppressed by {1S-benzyl-4R-[1S-carbamoyl-2-phenylethylcarbamoyl-1S-3-methylbutylcarbamoyl]-2R-hydroxy-5-phenylpentyl}carbamic acid tert-butyl ester, a transition state analog inhibitor for aspartyl protease. In contrast, N-[N-(3,5-difluorophenacetyl)-L-alanyl]-S-phenylglycinet-butyl ester, a potent dipeptide ␥-secretase inhibitor, builds up A␤1-43 and A␤1-46 intracellularly, which was also confirmed by mass spectrometry. Notably, suppression of A␤40 appeared to lead to an increase in A␤43, which in turn brings an increase in A␤46, in a dose-dependent manner. We therefore propose an ␣-helical model in which longer A␤ species generated by ⑀-cleavage is cleaved at every three residues in its carboxyl portion.