N-Terminal deletions modify the Cu2+ binding site in amyloid-beta

Area of Science:

• Neuroscience
• Biochemistry
• Biophysics

Background:

• Copper ions are implicated in Alzheimer's disease (AD) amyloid plaque formation and toxicity.
• The beta-amyloid (Abeta) peptide is a key component of these plaques.
• Understanding copper-Abeta interactions is crucial for AD pathogenesis research.

Purpose of the Study:

• To investigate the role of the N-terminus in the copper (Cu2+) binding site of Abeta.
• To determine the specific ligands involved in copper coordination within Abeta peptides and fibrils.
• To characterize the dynamics of copper binding to pre-formed Abeta fibrils.

Main Methods:

• Low-temperature electron paramagnetic resonance (EPR) spectroscopy was used to study copper binding.
• Mutant Abeta peptides, including a Y10F variant, were synthesized and analyzed.
• Isotopic labeling experiments were performed to identify oxygen donors.
• Copper binding to pre-assembled Abeta fibrils was assessed.

Main Results:

• Abeta peptides lacking N-terminal amino acids showed altered Cu2+ coordination compared to native Abeta.
• The Cu2+ coordination environment in Abeta peptides and fibrils was consistently 3N1O (three nitrogen, one oxygen donors).
• Mutation of tyrosine at position 10 (Y10F) did not alter the Cu2+ coordination environment.
• Water was not identified as the oxygen donor in fibrils or the Y10F mutant.
• Cu2+ bound irreversibly to existing fibrils and could exchange into and out of fibril structures.

Conclusions:

• The N-terminus of Abeta significantly influences the Cu2+ binding site's coordination environment.
• Tyrosine is not the primary oxygen donor ligand for Cu2+ in Abeta.
• Copper ions can readily exchange into and out of Abeta fibrils, suggesting a dynamic role in plaque formation.