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

Abstract

An abnormal interaction between copper and the prion protein is believed to play a pivotal role in the pathogenesis of prion diseases. Copper binding has been mainly attributed to the N-terminal domain of the prion protein, but this hypothesis has recently been challenged in some papers which suggest that the C-terminal domain might also compete for metal anchoring. In particular, the segment corresponding to the helix II region of the prion protein, namely PrP180-193, has been shown both to bind copper and to exhibit a copper-enhanced cytotoxicity, as well as to interact with artificial membranes. The present work is aimed at extending these results by choosing the most representative model of this domain and by determining its copper affinity. With this aim, the different role played by the electrostatic properties of the C- and N-termini of PrP180-193 (VNITIKQHTVTTTT) in determining its conformational behaviour, copper coordination and ability to perturb model membranes was investigated. Owing to the low solubility of PrP180-193, its copper affinity was evaluated by using the shorter PrPAc184-188NH2 (IKQHT) analogue as a model. ESI-MS, ESR, UV/Vis, and CD measurements were carried out on the copper(II)/PrPAc184-188NH2 and copper(II)/PrP180-193NH2 systems, and showed that PrPAc184-188NH2 is a reliable model for the metal interaction with the helix II domain. The affinity of copper(II) for the helix II fragment is higher than that for the octarepeat and PrP106-126 peptides. Finally, the different ability of PrP180-193 analogues to perturb the DPPC model membrane was assessed by DSC measurements. The possible biological consequences of these findings are also discussed briefly.

Nickel(II) complexes of the multihistidine peptide fragments of human prion protein

“…Our previous studies led to the same conclusions and the high copper(II) binding ability of His96, His111 and even His187 residues was unambiguously demonstrated in the small fragments of the protein [22][23][24]. The results obtained for the 31-and 39-mer peptide fragments, namely HuPrP(84-114) and HuPrP(76-114), made it possible to compare the metal binding affinities of histidyl residues inside and outside the octarepeat domain.…”

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

“…[67,70,72,73,75,76,[88][89][90][91][92][93][94][95][96] Although there is no general consensus, most of the results obtained so far indicate His111 as the preferential, if not exclusive, copper(II) binding site. [67,72,73,75,76,90,91,95,96] Our systematic studies carried out on small peptide fragments of PrP led to the same conclusions, and the high copper(II) binding affinities of the His96, [97] His111, [98] and even His187 [99] residues have unambiguously been demonstrated. A comparison of the thermodynamic stabilities of the histidinecontaining fragments revealed that the peptides that encompass the amino acid sequences outside the octarepeat domain are even more efficient chelators of copper(II) than the single octarepeat fragments.…”

A Doppel α‐Helix Peptide Fragment Mimics the Copper(II) Interactions with the Whole Protein

“…Figure 11 shows the distribution diagram obtained for copper(II) complexes with Dpl-A C H T U N G T R E N N U N G (122-139) and the peptide fragment PrP C A C H T U N G T R E N N U N G (184-188) blocked at the C and N terminus, which has been shown to be a reliable model for the interaction between metals and the helix II domain of prion. [38] The diagram shows that at acidic pH …”