Abstract
Fluorinated alcohols such as hexafluoroisopropanol (HFIP) and trifluoroethanol (TFE) have the ability to promote α-helix and β-hairpin structure in proteins and peptides. HFIP has been used extensively to dissolve various amyloidogenic proteins and peptides including Aβ, in order to ensure their monomeric status. In this paper, we have investigated the self-assembly of Aβ40, Aβ42, and Aβ43 in aqueous mixtures of fluorinated alcohols from freshly dissolved stock solutions in HFIP. We have observed that formation of fibrillar and non-fibrillar structures are dependent on the solvent composition. Peptides form fibrils with ease when reconstituted in deionized water from freshly dissolved HFIP stocks. In aqueous mixtures of fluorinated alcohols, either predominant fibrillar structures or clustered aggregates were observed. Aqueous mixtures of 20% HFIP are more favourable for Aβ fibril formation as compared to 20% TFE. When Aβ40, Aβ42, and Aβ43 stocks in HFIP are diluted in 50% aqueous mixtures in phosphate buffer or deionized water followed by slow evaporation of HFIP, Aβ peptides form fibrils in phosphate buffer and deionized water. The clustered structures could be off-pathway aggregates. Aβ40, Aβ42, and Aβ43 showed significant α-helical content in freshly dissolved HFIP stocks. The α-helical conformational intermediate in Aβ40, Aβ42, and Aβ43 could favour the formation of both fibrillar and non-fibrillar aggregates depending on solvent conditions and rate of α-helical to β-sheet transition.
Highlights
The aggregation behaviour of Aβ peptides has attracted considerable attention since its characterization in pathological conditions of Alzheimer’s disease [1,2,3,4]
We have examined the self-assembly of Aβ40, Aβ42, and Aβ43 from fresh HFIP stocks reconstituted under aqueous condition and aqueous mixtures of fluorinated alcohols (HFIP and TFE)
Dried films of Aβ40, Aβ42 and Aβ43 from freshly dissolved HFIP stocks were dissolved in deioinized water at peptide concentrations of 100 μM and incubated at 37°C in order to confirm that the peptides form amyloid fibrils as reported
Summary
The aggregation behaviour of Aβ peptides has attracted considerable attention since its characterization in pathological conditions of Alzheimer’s disease [1,2,3,4]. Non-fibrillar morphology of Aβ40 and Aβ42 have been observed during in vitro aggregation experiments which could be either off-pathway or onpathway aggregates [12,13,14]. The structural changes in proteins and peptides such as α-synuclein, Aβ40, Aβ42, vitronectin and K3 peptide from β2-microglobulin in aqueous mixtures of fluorinated alcohols have been shown to induce amyloid fibril formation [25,26,27,28,29]. Mixtures of fluorinated alcohols and water can give useful insights in understanding aggregation pathways and intermediate structures of amyloid assembly in amyloidogenic proteins and peptides. We have observed the formation of fibrils and non-fibrillar aggregates in aqueous mixtures of fluorinated alcohols
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