Copper Binding to the Neurotoxic Peptide PrP_106–126: Thermodynamic and Structural Studies

Abstract

The human prion protein fragment PrP(106-126) is a highly fibrillogenic peptide, resistant to proteinases and toxic to neurons; it derives from the normal prion protein (PrP(C)), with which it can interact, thus inhibiting its superoxide dismutase-like activity. The same properties are also shown by the abnormal isoform of the prion protein (PrP(Sc)), and this similarity makes PrP(106-126) an interesting model for the neurotoxic action of PrP(Sc). A role for copper in PrP(106-126) aggregation and toxicity has recently been evidenced, and the interaction of terminal Lys, His and Met residues with the copper ion at neutral pH has been suggested. In order to shed more light on the complex-formation equilibria of PrP(106-126) with the copper ion, a thorough investigation has been carried out by means of several experimental techniques: potentiometry, solution calorimetry, VIS spectrophotometry, circular dichroism, EPR and NMR spectroscopy. A shorter and more soluble fragment-PrP(106-113), which lacks the hydrophobic C-terminal domain of PrP(106-126) but contains all the potential donor groups-has also been considered for the sake of comparison. The involvement of terminal amino, imidazolic and amido nitrogens in complex formation has been confirmed, while no evidence was found for the interaction of side chains of Met and Lys residues with the copper ion. Solution structures for the main complexes are suggested.

Preferential Cu2+ Coordination by His96 and His111 Induces β-Sheet Formation in the Unstructured Amyloidogenic Region of the Prion Protein

“…There have also been some spectroscopic studies on Cu(II) binding to the neurotoxic fragment PrP-(106 -126) (39,68). However, the peptide fragment studied did not have its N terminus acetylated, and is therefore not a good model for this unstructured region of the full-length PrP as Cu 2ϩ will coordinate to the N-terminal amino group at position 106.…”

Environmental Effects on a Prion's Helix II Domain: Copper(II) and Membrane Interactions with PrP180–193 and Its Analogues

“…[8] Although additional binding sites have been discovered involving either the unstructured domain between the N-terminal region and the structured domain or the a-helical region, only the speciation of complexes involved in the copper binding to PrP106-126, which encompasses the unstructured domain, and the related stability constant values have been reported. [5,45] In this latter case, the use of the PrP106-126 peptide fragment with its N-terminus unblocked might not be fully representative of this part of the PrP C protein. In fact, copper(ii) binds to the N-terminal amino nitrogen at position 106, a donor atom that is not present in the protein chain.…”

Cross‐Talk Between the Octarepeat Domain and the Fifth Binding Site of Prion Protein Driven by the Interaction of Copper(II) with the N‐terminus

“…[66] For clearer understanding of the copper-related functions of PrP, much effort has been directed to characterise the coordination and affinity of Cu 2+ binding to PrP. [44,[67][68][69] There is a general consensus that PrP can bind at least six copper(II) ions: [70][71][72][73][74][75][76] four copper-binding sites are present in the octarepeat region (residues 60-91), which is composed, in the human sequence, of four identical PHGGGWGQ units, with the histidine of each repeat being the primary copper(II) anchoring site. [77][78][79][80][81][82][83][84][85][86][87] Moreover, the hPrP91-127 region, which is next to the repeat domain, provides two further copper(II) binding sites, each associated with a histidine residue, His96 and His111, respectively.…”