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

• Published in: Chemistry : a European journal 2015-03, Vol.21 (10), p.4071-4084
• Main Authors: Di Natale, Giuseppe, Turi, Ildikó, Pappalardo, Giuseppe, Sóvágó, Imre, Rizzarelli, Enrico
• Format: Article
• Language: English
• Subjects: Binding sites; Canonical forms; Chemistry; Circular Dichroism; Conversion; Coordination; Copper; Copper - chemistry; Copper converters; Dichroism; Fragmentation; Histamine - chemistry; human prion protein; Mass Spectrometry; Mass spectroscopy; Neurodegenerative diseases; Peptides; Peptides - chemistry; pH effects; Physiology; Prion protein; Prions; Prions - chemistry; Protein Binding; Proteins; Scrapie; Ultraviolet Rays
• ISSN: 0947-6539; 1521-3765
• DOI: 10.1002/chem.201405502

Prion diseases are a group of neurodegenerative diseases based on the conformational conversion of the normal form of the prion protein (PrPC) to the disease‐related scrapie isoform (PrPSc). Copper(II) coordination to PrPC has attracted considerable interest for almost 20 years, mainly due to the possibility that such an interaction would be an important event for the physiological function of PrPC. In this work, we report the copper(II) coordination features of the peptide fragment Ac(PEG11)3PrP(60‐114) [Ac=acetyl] as a model for the whole N‐terminus of the PrPC metal‐binding domain. We studied the complexation properties of the peptide by means of potentiometric, UV/Vis, circular dichroism and electrospray ionisation mass spectrometry techniques. The results revealed that the preferred histidyl binding sites largely depend on the pH and copper(II)/peptide ratio. Formation of macrochelate species occurs up to a 2:1 metal/peptide ratio in the physiological pH range and simultaneously involves the histidyl residues present both inside and outside the octarepeat domain. However, at increased copper(II)/peptide ratios amide‐bound species form, especially within the octarepeat domain. On the contrary, at basic pH the amide‐bound species predominate at any copper/peptide ratio and are formed preferably with the binding sites of His96 and His111, which is similar to the metal‐binding‐affinity order observed in our previous studies. Coordination features of the peptide fragment Ac(PEG11)3PrP(60–114) were used as a model for the whole N‐terminal prion protein metal‐binding domain. A macrochelate species forms in the physiological pH range at low copper occupancy. At increased copper(II)/peptide ratios amide‐bound species form, especially within the octarepeat domain.