Pyroglutamate-Modified Amyloid-β(3-42) Shows α-Helical Intermediates before Amyloid Formation

Area of Science:

• Neuroscience
• Biochemistry
• Structural Biology

Background:

• Pyroglutamate-modified amyloid-beta (pEAβ), particularly the pEAβ (3-42) isoform, is prevalent in Alzheimer's disease brains.
• Amyloid-beta (Aβ) (1-40) and Aβ (1-42) are well-studied, but the structural basis for pEAβ's increased aggregation is unclear.

Purpose of the Study:

• To investigate the structural properties of pEAβ (3-42) that contribute to its heightened aggregation propensity compared to Aβ (1-42).
• To characterize the conformational changes induced by the N-terminal modification in pEAβ (3-42).

Main Methods:

• Circular dichroism (CD) spectroscopy to assess secondary structure.
• Thioflavin-T (ThT) kinetic assays to monitor aggregation rates.
• Electron microscopy (EM) to visualize fibril formation.
• Nuclear Magnetic Resonance (NMR) spectroscopy for detailed structural assignments.

Main Results:

• Soluble pEAβ (3-42) exhibits a greater propensity for β-sheet structures than Aβ (1-42).
• pEAβ (3-42) undergoes drastically accelerated aggregation into large fibrils compared to Aβ (1-42).
• NMR analysis revealed significant chemical shift differences in over 20% of residues due to the N-terminal modification, indicating altered chemical environments.
• Monomeric pEAβ (3-42) possesses two α-helical regions and an unstructured N-terminus, with helices acting as intermediates in β-sheet and fibril formation.

Conclusions:

• The N-terminal pyroglutamate modification in pEAβ (3-42) significantly impacts its structure and dramatically enhances its aggregation into amyloid fibrils.
• These findings provide structural insights into the accelerated fibrillogenesis of pEAβ (3-42), a key species in Alzheimer's disease pathogenesis.