Is aggregation of beta-amyloid peptides a mis-functioning of a current interaction process?

Area of Science:

• Biochemistry
• Molecular Biology
• Neuroscience

Background:

• Previous studies demonstrated amyloid beta (Abeta) peptide self-interaction using a two-hybrid system.
• The amyloid peptide sequence can be divided into hydrophilic and hydrophobic clusters.
• Understanding Abeta self-interaction is key to defining sequences involved in nucleation-dependent aggregation.

Purpose of the Study:

• To investigate the role of specific Abeta peptide regions and hydrophobicity distribution in Abeta-Abeta interaction.
• To identify critical domains within the Abeta sequence essential for self-interaction.
• To elucidate the structural basis of Abeta self-interaction and its implications for aggregation.

Main Methods:

• Molecular modeling was employed to design Abeta peptide mutations.
• A two-hybrid assay system was used to test the interaction of native and mutated Abeta peptides.
• Mutations targeted changes in hydrophobicity distribution and spatial hindrance across the Abeta sequence.

Main Results:

• The two-hybrid assay successfully reproduced the interaction of native Abeta.
• Mutational screening identified the C-domain (residues 29-40(42)), median domain (residues 17-22), and N-domain (1-16) as crucial for Abeta interaction.
• Almost all Abeta peptide fragments, excluding a loop (residues 23-28) and the C-terminal amino acid, are important for native interaction.

Conclusions:

• The interacting species of Abeta is a folded three-dimensional (3D) structure.
• The entire Abeta sequence contributes to this 3D fold, which exhibits low secondary structure propensity and high susceptibility to mutations, suggesting low stability.
• Stabilization of the native Abeta fold within Abeta-Abeta complexes may facilitate the nucleation event leading to senile plaque formation.