Structural defects in amyloid-β fibrils drive secondary nucleation

Area of Science:

• Biochemistry
• Neuroscience
• Structural Biology

Background:

• Amyloid fibril formation drives neurodegenerative diseases, including Alzheimer's and Parkinson's.
• Secondary nucleation on existing fibrils is a critical but poorly understood process.
• The structural basis for secondary nucleation, particularly the role of growth defects, remains unclear.

Purpose of the Study:

• To investigate whether secondary nucleation sites are predominantly located at rare fibril growth defects.
• To characterize the role of growth defects in amyloid secondary nucleation using Alzheimer's disease-associated peptides.
• To explore the potential for targeting these defects in drug design.

Main Methods:

• Utilized the secondary nucleation inhibitor Brichos to assess the prevalence of nucleation sites on Aβ40 and Aβ42 fibrils.
• Grew and annealed Aβ40 fibrils under controlled conditions to minimize growth defects, confirmed by cryo-electron microscopy.
• Quantified the secondary nucleation activity and site stoichiometry of annealed fibrils.

Main Results:

• Secondary nucleation sites on Alzheimer's disease-associated fibrils are rare relative to the total number of protein molecules.
• Annealed fibrils, with significantly reduced growth defects, exhibited greatly diminished secondary nucleation activity and site stoichiometry.
• Analysis suggests fibril growth defects generally drive secondary nucleation across various amyloid proteins.

Conclusions:

• Secondary nucleation predominantly occurs at rare structural defects within amyloid fibrils.
• Eliminating these growth defects substantially reduces amyloid propagation.
• Findings support targeting fibril growth defects for structure-based drug design against amyloid disorders.