Synthetic peptide homologous to beta protein from Alzheimer disease forms amyloid-like fibrils in vitro.

Abstract

Progressive amyloid deposition in senile plaques and cortical blood vessels may play a central role in the pathogenesis of Alzheimer disease. We have used x-ray diffraction and electron microscopy to study the molecular organization and morphology of macromolecular assemblies formed by three synthetic peptides homologous to fi protein of brain amyloid: fl-(1-28), residues 1-28 of the fi protein;[Ala"Jfl-(1-28), P-(1-28) with alanine substituted for lysine at position 16; and fl-(18-28), residues 18-28 of the fi protein.fl-(1-28) readily formed fibrils in vitro that were similar in ultrastructure to the in vivo amyloid and aggregated into large bundles resembling those ofsenile plaque cores. X-ray patterns from partially dried, oriented pellets showed a cross-fl-conformation. A series of small-angle, equatorial maxima were consistent with a tubular fibril having a mean diameter of 86 A and a wall composed of pairs of cross-fl-pleated sheets. The data may also be consistent with pairs ofcross-13-sheets that are centered 71-apart. [Ala]fl-(1-28) formed pleated sheet assemblies that were dissimilar to in vivo fibrils. The width of the to-A spacing indicated stacks of about six sheets. Thus, substitution of the uncharged alanine for the positively charged lysine in the fl-strand region enhances the packing of the sheets and dramatically alters the type of macromolecular aggregate formed. f8-(18-28) formed assemblies that had even a greater number of stacked sheets, w24 per diffracting domain as indicated by the sharp intersheet reflection. Our findings on these homologous synthetic assemblies help to define the specific sequence that is required to form Alzheimer-type amyloid fibrils, thus providing an in vitro model of age-related cerebral amyloidogenesis.The major histopathological features ofAlzheimer disease (AD) are neurofibrillary tangles, neuritic or senile plaques, and amyloid angiopathy (1). The plaques contain cores of extracellular proteinaceous filaments that have been identified as amyloid, based on their green birefringence after staining with Congo red and their 40-to 90-A diameter (2, 3). Structurally similar amyloid filaments also occur in the walls of some capillaries, arterioles, and small arteries in the cerebral cortex and in some meningeal arteries in patients with AD (4-10). These amyloid deposits are also found in the brains of Down syndrome patients over 30 years of age (11), as well as in the brains of aged normal humans (12) and lower mammals (13).The major proteinaceous component of amyloid both from the cerebral blood vessel walls and the plaque cores is an --4-kDa protein (8, 9, 14-17) designated the 3 protein (15) or A4 (8). The first 28 amino acids of this protein have been sequenced (7). A gene coding for the f3-amyloid protein has been mapped to chromosome 21 of the human genome (18)(19)(20), and the complete sequence of the putative precursor protein has been determined (21).The current study was carried out to investigate the amyloidogenic properties of peptides sharing se...

Thioflavine T interaction with synthetic Alzheimer's disease β‐amyloid peptides: Detection of amyloid aggregation in solution

“…These octamers add relatively slowly to protofilament ends yielding long thin 5-nm filaments, which can associate laterally to form ribbons. All of these structures are observed in electron micrographs of naturally occurring amyloid fibrils and are similar or slightly smaller than synthetic amyloid fibrils (Kirschner et al, 1987;Fraser et al, 1991;Hilbich et al, 1991). The kinetics of the peptide aggregation process monitored by the light scattering technique suggest that in such a reaction scheme ThT would probably bind to an oligomeric form such as the octamer since the fluorescence enhancement is observed within seconds after aggregation is initiated, and it is not observed to be effected by the subsequent slower addition of octamers at filament ends.…”

Application and use of differential scanning calorimetry in studies of thermal fluctuation associated with amyloid fibril formation

“…In vitro experiments have provided evidence supporting the capability of a large variety of proteins and peptides, including those unrelated to any disease, to self-assemble into amyloid fibrils or amyloid-like structures when incubated under appropriate solution conditions. This has led to the suggestion that the ability to form amyloid fibrils is a fundamental property of polypeptide chains (Glenner et al 1974;Kirschner et al 1987;Maggio and Mantyh 1996;Fändrich and Dobson 2002;Makin and Serpell 2005;Chiti and Dobson 2006;Goldschmidt et al 2010).…”

Nicotine Inhibits Amyloid Formation by the β-Peptide

“…The -(1-42) peptide adopts 100% oligomeric -sheet structure in solution before it precipitates as an amyloidlike, oligomeric -pleated sheet structure (Kirschner et al, 1987;Barrow et al, 1992). Once the precipitation starts, the solution conformation will remain 100% -sheet and the ellipticities will decrease in amplitude since the peptide concentration in solution decreases.…”

“…The -(1-28) peptide is an appropriate structural model for the complete -(1-42) peptide, since it produces soluble monomeric R-helical structures (Barrow & Zagorski, 1991;Otvos et al, 1993), as well as plaque-like oligomeric -sheet structures, similar to those found in natural amyloid plaques (Gorévic et al, 1987;Kirschner et al, 1987). The hydrophobic 29-42 region increases the rate of aggregation and -sheet production (Hilbich et al, 1991;Barrow et al, 1992;Burdick et al, 1992; but should not affect the ability of nicotine to bind to the -peptide.…”

“…The -peptide is a normal, soluble physiological component (Gravina et al, 1995). However, under certain environmental conditions, the -peptide can produce oligomeric -sheet structures that eventually precipitate as amyloid plaques (Kirschner et al, 1987;Gorévic et al, 1987;Hilbich et al, 1991;Barrow & Zagorski, 1991;Burdick et al, 1992;Terzi et al, 1994). The soluble -sheet structure has the following properties that are relevant to amyloidosis in AD: (1) it is a precursor to the insoluble -pleated sheet structure in amyloid plaque, (2) it can act as a seed that nucleates amyloid formation Snyder et al, 1994), and (3) it is neurotoxic to hippocampal neuronal cultures (Simmons et al, 1994;Harrigan et al, 1995;Pike et al, 1995).…”