Self-Assembly of Aβ_1-42into Globular Neurotoxins

Abstract

Amyloid beta 1-42 (Abeta(1-42)) is a self-associating peptide that becomes neurotoxic upon aggregation. Toxicity originally was attributed to the presence of large, readily formed Abeta fibrils, but a variety of other toxic species are now known. The current study shows that Abeta(1-42) can self-assemble into small, stable globular assemblies free of fibrils and protofibrils. Absence of large molecules was verified by atomic force microscopy (AFM) and nondenaturing gel electrophoresis. Denaturing electrophoresis revealed that the globular assemblies comprised oligomers ranging from trimers to 24mers. Oligomers prepared at 4 degrees C stayed fibril-free for days and remained so when shifted to 37 degrees C, although the spectrum of sizes shifted toward larger oligomers at the higher temperature. The soluble, globular Abeta(1-42) oligomers were toxic to PC12 cells, impairing reduction of MTT and interfering with ERK and Rac signal transduction. Occasionally, oligomers were neither toxic nor recognized by toxicity-neutralizing antibodies, suggesting that oligomers could assume alternative conformations. Tests for oligomerization-blocking activity were carried out by dot-blot immunoassays and showed that neuroprotective extracts of Ginkgo biloba could inhibit oligomer formation at very low doses. The observed neurotoxicity, structure, and stability of synthetic Abeta(1-42) globular assemblies support the hypothesis that Abeta(1-42) oligomers play a role in triggering nerve cell dysfunction and death in Alzheimer's disease.

Are amyloid diseases caused by protein aggregates that mimic bacterial pore-forming toxins?

“…2a) and during the reconstitution of Ab in lipid bilayers (Fig. 3a) (Hafner et al 2001 ;Lin et al 2001 ;Chromy et al 2003 ;Klug et al 2003;Lashuel et al 2003 ;. The similar heights of the spheres, chain-like and annular protofibrils suggests that the spheres are the precursors of the others .…”

“…Any model for pathogenesis must explain these cases. It is important to emphasize that the wild-type proteins will also form amyloid pores in vitro, albeit more reluctantly than the disease-associated mutants (Hafner et al 2001;Ding et al 2002 ;Lashuel et al 2002aLashuel et al , b, 2003Shtilerman et al 2002 ;Chromy et al 2003 ;Chung, 2003 ;Klug et al 2003 ;. Factors other than mutations could trigger pore formation pathogenesis in sporadic disease (Fig.…”

Preparation and characterization of toxic Aβ aggregates for structural and functional studies in Alzheimer's disease research

“…Results showed that void volume ( > 70 kDa) fractions selectively bound to the cell surface and processes of neurons. No such binding was reported for fractions containing monomers to tetramers, suggesting that advanced oligomer states, protofibrils, are more likely to be the culprit toxic species in ADDL preparation 67 . Subsequent solution-state characterization of ADDL preparations revealed that they consist of a heterogeneous population of Aβ species encompassing molecular sizes ranging from monomers to aggregates larger than 1 mDa, resembling the distribution observed for protofibrils.…”

“…ADDLs are soluble Aβ aggregates that, by atomic force microscopy, appear as spherical structures of 3-5 nm in diameter 15 . SEC was used to fractionate ADDLs and different fractions were compared for binding to the neuronal surface 67 . Results showed that void volume ( > 70 kDa) fractions selectively bound to the cell surface and processes of neurons.…”

Effects of Peptides Derived from Terminal Modifications of the Aβ Central Hydrophobic Core on Aβ Fibrillization

“…Recently, extensive investigation of the aggregation pathway reveals that oligomeric assemblies and not mature fibrils are responsible for Aβ neurotoxicity (4)(5)(6)(7)(8)(9). Several approaches have been designed to target the Aβ assembly process in an effort to reduce toxic species in the brain.…”