Metal Loading Capacity of Aβ N-Terminus: a Combined Potentiometric and Spectroscopic Study of Zinc(II) Complexes with Aβ(1-16), Its Short or Mutated Peptide Fragments and Its Polyethylene Glycol-ylated Analogue

Aggregation of the amyloidp-peptide (A beta) into insoluble fibirils is a key pathological event in Alzheimer's Disease (AD). There is now compelling evidence that metal binding to A beta is involved in AD pathogenesis. The amino acid region 1-16 is widely considered as the metal binding domain of A beta. In this work, we used a combined potentiometric, NMR, and electrospray ionization mass spectrometry (ESI-MS),approach to study the zinc(II) binding to a new polyethylene glycol (PEG)-conjugated peptide fragment encompassing the 1-16 amino acid sequence of A beta (A beta(1-16)PEG). Our results demonstrate for the first time that the A beta(1-16) is able to coordinate up to three zinc ions, all the histidyl residues acting as independent anchor sites. The study was complemented by systematically investigating the zinc(II) complexes of a series of shorter peptide fragments related to the A beta(1-16) sequence, namely, A beta(1-4), A beta(1-6), AcA beta(1-6), AcA beta(8-16)Y10A. The comparison of the whole results allowed the identification of the zinc(II) preferred binding sites within the longer M(1-16) amino acid sequence. Unlike copper(II) that prefers the N-terminal amino group as the main binding site, the zinc(II) is preferentially placed in the 8-16 amino acidic region of A beta(1-16).