Aß(25-35) and its C-and/or N-blocked derivatives: copper driven structural features and neurotoxicity.

The toxic properties of b-amyloid protein, Ab(1-42), the major component of senile plaques in Alzheimer's disease, depend on nucleation-dependent oligomerization and aggregation. In addition, Ab(1-42) toxicity is favored by the presence of trace metals, which affect the secondary structure of the peptide. A peptide comprising 11 residues within Ab(1-42) [Ab(25-35)] aggregates and retains the neurotoxic activity of Ab(1-42). We have used both Ab(25-35) and its C-amidated or N-acetylated/C-amidated derivatives to investigate the role of copper(II) in modulating the conformation and aggregation state as well as the neurotoxic properties of amyloid peptides. Electrospray ionization mass spectrometry (ESI-MS) and electron paramagnetic resonance (EPR) measurements were performed to verify the formation of copper(II)/Ab(25-35) complexes and to determine the coordination mode, respectively. Ab(25- 35) and its derivatives were analyzed by circular dichroism spectroscopy to assess their secondary structure, subjected to thioflavine-T (Th-T) binding assay to reveal b-sheet structured aggregates formation, and imaged by scanning force microscopy. Toxicity was assessed on mature cultures of rat cortical neurons. We found that b-sheet-structured species of Ab(25-35) were neurotoxic, whereas the random-coil-structured derivatives were devoid of effect. Interestingly, copper promoted the random-coil/b-sheet transition of Ab(25-35), with ensuing peptide toxicity, but it induced the toxicity of the N-acetylated/C-amidated derivative without affecting peptide folding. Moreover, copper did not influence either the folding or the activity of the C-amidated Ab(25-35), suggesting that blockade of the C-terminus of Ab peptides might be sufficient to prevent Ab toxicit