The interplay between a GC-rich oligonucleotide and copper ions on prion protein conformational and phase transitions.

The prion protein (PrP) misfolding to its infectious form is critical to the development of prion diseases, whereby various ligands are suggested to participate, such as copper and nucleic acids (NA). The PrP globular domain was shown to undergo NA-driven liquid-liquid phase separation (LLPS); this latter may precede pathological aggregation. Since Cu(II) is a physiological ligand of PrP, we argue whether it modulates phase separation altogether with nucleic acids. Using recombinant PrP, we investigate the effects of Cu(II) (at 6 M equivalents) and a previously described PrP-binding GC-rich DNA (equimolarly to protein) on PrP conformation, oligomerization, and phase transitions using a range of biophysical techniques. Raman spectroscopy data reveals the formation of the ternary complex. Microscopy suggests that phase separation is mainly driven by DNA, whereas Cu(II) has no influence. Our results show that DNA can be an adjuvant, leading to the structural conversion of PrP, even in the presence of an endogenous ligand, copper. These results provide new insights into the role of Cu(II) and NA on the phase separation, structural conversion, and aggregation of PrP, which are critical events leading to neurodegeneration.

Biophysical and morphological studies on the dual interaction of non-octarepeat prion protein peptides with copper and nucleic acids.

Conversion of prion protein (PrP) to an altered conformer, the scrapie PrP (PrP(Sc)), is a critical step in the development of transmissible spongiform encephalopathies. Both Cu(II) and nucleic acid molecules have been implicated in this conversion. Full-length PrP can bind up to six copper ions; four Cu(II) binding sites are located in the octarepeat domain (residues 60-91), and His-96 and His-111 coordinate two additional copper ions. Experimental evidence shows that PrP binds different molecules, resulting in diverse cellular signaling events. However, there is little information about the interaction of macromolecular ligands with Cu(II)-bound PrP. Both RNA and DNA sequences can bind PrP, and this interaction results in reciprocal conformational changes. Here, we investigated the interaction of Cu(II) and nucleic acids with amyloidogenic non-octarepeat PrP peptide models (comprising human PrP residues 106-126 and hamster PrP residues 109-149) that retain His-111 as the copper-anchoring residue. The effect of Cu(II) and DNA or RNA sequences in the aggregation, conformation, and toxicity of PrP domains was investigated at low and neutral pH. Circular dichroism and EPR spectroscopy data indicate that interaction of the PrP peptides with Cu(II) and DNA occurs at pH 7. This dual interaction induces conformational changes in the peptides, modulating their aggregation, and affecting the morphology of the aggregated species, resulting in different cytotoxic effects. These results provide new insights into the role of Cu(II) and nucleic acid sequences in the structural conversion and aggregation of PrP, which are both critical events related to prion pathogenesis.

Synthesis and anti-prion activity evaluation of aminoquinoline analogues.

Transmissible spongiform encephalopathies form a group of neurodegenerative diseases that affect humans and other mammals. They occur when the native prion protein is converted into an infectious isoform, the scrapie PrP, which aggregates, leading to neurodegeneration. Although several compounds were evaluated for their ability to inhibit this conversion, there is no effective therapy for such diseases. Previous studies have shown that antimalarial compounds, such as quinolines, possess anti-scrapie activity. Here, we report the synthesis and evaluate the effect of aminoquinoline derivatives on the aggregation of a prion peptide. Our results show that 4-amino-7-chloroquinoline and N-(7-chloro-4-quinolinyl)-1,2-ethanediamine inhibit the aggregation significantly. Therefore, such aminoquinolines might be considered as candidates for the further development of therapeutics to prevent the development of prion diseases.