A Disulfide-Stabilized Aβ that Forms Dimers but Does Not Form Fibrils

Area of Science:

• Biochemistry
• Neuroscience
• Molecular Biology

Background:

• Amyloid-beta (Aβ) dimers are key neurotoxic species in Alzheimer's disease (AD).
• Studying homogeneous Aβ dimers is challenging due to rapid aggregation into heterogeneous oligomers and fibrils.
• Existing Aβ preparations yield complex mixtures, hindering detailed analysis of toxic dimer species.

Purpose of the Study:

• To introduce a novel disulfide-stabilized analogue of Aβ42, termed AβC18C33.
• To create a stable, homogeneous Aβ dimer that does not form fibrils.
• To provide a reliable model for studying Aβ dimers in lipid environments relevant to AD pathogenesis.

Main Methods:

• Expression of AβC18C33 in Escherichia coli and purification via reverse-phase HPLC.
• Characterization using SDS-PAGE, mass spectrometry (MS) with dodecyl maltoside (DDM), circular dichroism (CD) spectroscopy.
• Assessment of fibril formation using Thioflavin T (ThT) fluorescence assays and transmission electron microscopy (TEM).

Main Results:

• AβC18C33 was successfully expressed and purified, yielding homogeneous dimers in SDS and DDM environments.
• CD spectroscopy confirmed a β-sheet conformation, supporting a β-hairpin dimer model induced by the disulfide bond.
• ThT assays and TEM demonstrated the absence of fibril formation, with the disulfide bond preventing aggregation.

Conclusions:

• AβC18C33 serves as a stable, homogeneous, non-fibrilizing Aβ dimer model.
• The disulfide bond effectively stabilizes dimers and prevents the formation of heterogeneous oligomers and fibrils.
• This AβC18C33 model is valuable for investigating the role of Aβ dimers in Alzheimer's disease.