Structural properties of Aβ protofibrils stabilized by a small molecule

Authors:
Publisher website
Google Scholar
Abstract
Metastable oligomeric and protofibrillar forms of amyloidogenic proteins have been implicated as on-pathway assembly intermediates in amyloid formation and as the major toxic species in a number of amyloid diseases including Alzheimer's disease. We describe here a chemical biology approach to structural analysis of Aβ protofibrils. Library screening yielded several molecules that stimulate Aβ aggregation. One of these compounds, calmidazolium chloride (CLC), rapidly and efficiently converts Aβ(1-40) monomers into clusters of protofibrils. As monitored by electron microscopy, these protofibrils persist for days when incubated in PBS at 37°C, with a slow transition to fibrillar structures apparent only after several weeks. Like normal protofibrils, the CLC-Aβ aggregates exhibit a low thioflavin T response. Like Aβ fibrils, the clustered protofibrils bind the anti-amyloid Ab WO1. The CLC-Aβ aggregates exhibit the same protection from hydrogen-deuterium exchange as do protofibrils isolated from a spontaneous Aβ fibril formation reaction: ≈12 of the 39 Aβ(1-40) backbone amide protons are protected from exchange in the protofibril, compared with approximately twice that number in amyloid fibrils. Scanning proline mutagenesis analysis shows that the Aβ molecule in these protofibrillar assemblies exhibits the same flexible N and C termini as do mature amyloid fibrils. The major difference in Aβ conformation between fibrils and protofibrils is added structural definition in the 22-29 segment in the fibril. Besides aiding structural analysis, compounds capable of facilitating oligomer and protofibril formation might have therapeutic potential, if they act to sequester Aβ in a form and/or location that cannot engage the toxic pathway.

This publication has 31 references indexed in Scilit: