A Disulfide-Linked Amyloid-β Peptide Dimer Forms a Protofibril-like Oligomer through a Distinct Pathway from Amyloid Fibril Formation

Abstract

The conversion of the soluble, nontoxic amyloid-beta (Abeta) peptide into an aggregated, toxic form rich in beta-sheets is considered a key step in the development of Alzheimer's disease. Whereas growing evidence indicates that the Abeta amyloid fibrils consist of in-register parallel beta-sheets, little is known about the structure of soluble oligomeric intermediates because of their transient nature. To understand the mechanism by which amyloid fibrils form, especially the initial development of the "nucleus" oligomeric intermediates, we prepared covalently linked dimeric Abeta peptides and analyzed the kinetics of the fibril-forming process. A covalent bond introduced between two Abeta molecules dramatically facilitated the spontaneous formation of aggregates with a beta-sheet structure and affinity for thioflavin T. Transmission electron microscopy revealed, however, that these aggregates differed in morphology from amyloid fibrils, more closely resembling protofibrils. The protofibril-like aggregates were not the most thermodynamically stable state but were a kinetically trapped state. The results emphasize the importance of the conformational flexibility of the Abeta molecule and a balance in the association and dissociation rate for the formation of rigid amyloid fibrils.

Transient formation of intermediate conformational states of amyloid-β peptide revealed by heteronuclear magnetic resonance spectroscopy

“…According to these observations, we found recently that disulfide-linked dimeric Ab peptides aggregated very rapidly to form kinetically trapped protofibril-like oligomers [14]. The results indicated the importance of the conformational flexibility of the Ab molecule and a balance in the association and dissociation rate for the formation of rigid amyloid fibrils.…”

“…Expression and purification of the Ab-(1-40) peptide were performed as described previously [14]. For the preparation of uniformly 15 N-, or 13 …”

Unfolding and aggregation of lysozyme: A thermodynamic and kinetic study by FTIR spectroscopy

“…The study of aggregation phenomena is of great importance, owing to their well recognized implication into a number of systemic and neurodegenerative diseases [4,5]; it offers the possibility of identifying pathways able to reduce the risk of a pathological event. Also, the shell-life of foods and drugs can be sensitively extended if one of the dominant degradation routes, i.e.…”

Synthesis of chemically-tethered amyloid-β segment trimer possessing amyloidogenic properties

“…Therefore, in principle, using the chemically-tethering method, we can isolate defined and unique Ab oligomers in an assembly state-pure form using affordable analytical instruments. There are several previous reports of chemically-tethered Ab oligomers, but they are limited to dimers [7][8][9][10][11] and there has been no report on the synthesis of oligomers larger than dimers, as the synthesis of trimers is considered more difficult than that of dimers. Some reports, however, advocate an important role for Ab trimers in Ab pathogenicity.…”