Cu and Zn Interactions with Peptides Revealed by High-Resolution Mass Spectrometry

Alzheimer's disease (AD) is a progressive neurodegenerative disease characterized by abnormal extracellular amyloid-beta (A beta) peptide depositions in the brain. Among amorphous aggregates, altered metal homeostasis is considered a common risk factor for neurodegeneration known to accelerate plaque formation. Recently, peptide-based drugs capable of inhibiting amyloid aggregation have achieved unprecedented scientific and pharmaceutical interest. In response to metal ions binding to A beta peptide, metal chelation was also proposed as a therapy in AD. The present study analyzes the interactions formed between NAP octapeptide, derived from activity-dependent neuroprotective protein (ADNP), amyloid A beta(9-16) fragment and divalent metal ions such as Cu and Zn. The binding affinity studies for Cu and Zn ions of synthetic NAP peptide and A beta(9-16) fragment were investigated by matrix-assisted laser desorption/ionization mass spectrometry (MALDI-MS), electrospray ion trap mass spectrometry (ESI-MS) and atomic force microscopy (AFM). Both mass spectrometric methods confirmed the formation of metal-peptide complexes while the AFM technique provided morphological and topographic information regarding the influence of metal ions upon peptide crystallization. Our findings showed that due to a rich histidine center, the A beta(9-16) fragment is capable of binding metal ions, thus becoming stiff and promoting aggregation of the entire amyloid peptide. Apart from this, the protective effect of the NAP peptide was found to rely on the ability of this octapeptide to generate both chelating properties with metals and interactions with A beta peptide, thus stopping its folding process.

Automated summary

Alzheimer's disease is a progressive neurodegenerative disease characterized by abnormal amyloid depositions in the brain. This study investigated the binding affinity between NAP peptide, Aβ(9-16) fragment, and Cu, Zn ions. The results showed that the Aβ(9-16) fragment can bind metal ions and promote peptide aggregation, while the NAP peptide can inhibit the folding process by chelating metals and interacting with Aβ peptide.