Mapping abeta amyloid fibril secondary structure using scanning proline mutagenesis

Area of Science:

• Biochemistry
• Structural Biology
• Neuroscience

Background:

• Alzheimer's disease is characterized by amyloid beta (Abeta) peptide aggregation into fibrils.
• Amyloid fibrils are primarily composed of cross-beta sheet structures.
• The precise conformation and stability determinants of Abeta within fibrils are not fully understood.

Purpose of the Study:

• To investigate the structural organization and stability of Abeta(1-40) within amyloid fibrils.
• To identify regions of the Abeta peptide susceptible to structural disruption by proline substitution.
• To elucidate the forces contributing to amyloid fibril stability.

Main Methods:

• Generation of single-proline replacement mutants of Abeta(1-40).
• Determination of thermodynamic stabilities of amyloid fibrils formed from these mutants.
• Analysis of fibril structure using hydrogen-deuterium exchange and other biophysical techniques.

Main Results:

• Abeta(1-40) in fibrils adopts a conformation with three structured segments (residues 15-21, 24-28, 31-36) sensitive to proline substitution.
• Residues 1-14 and 37-40 appear unstructured, while residues 22, 23, 29, 30 form turns.
• Fibril stability is influenced by a balance of stabilizing and destabilizing forces, similar to globular proteins, not solely beta-sheet content.

Conclusions:

• Amyloid fibril stability is a complex interplay of structural elements and forces.
• A model resembling a parallel beta-helix motif is proposed for Abeta protofilament structure.
• These findings provide insights into the structural basis of amyloid formation in Alzheimer's disease.