Differential effects of divalent cations on elk prion protein fibril formation and stability

Authors: SAMORODNITSKY, DANIEL - Orise Fellow; Nicholson, Eric

Submitted to: Prion
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 12/25/2017
Publication Date: 1/2/2018
Citation: Samorodnitsky, D., Nicholson, E.M. 2018. Differential effects of divalent cations on elk prion protein fibril formation and stability. Prion. 12(1):63-71. https://doi.org/10.1080/19336896.2017.1423187.
DOI: https://doi.org/10.1080/19336896.2017.1423187

Interpretive Summary: Misfolding of the normally folded prion protein in mammals results in chronic wasting disease in deer and elk. The binding of divalent metal ions is known to influence some aspects of prion folding but has not been well characterized for the elk prion protein. In this manuscript we address the binding of a several divalent metal ions to elk prion protein and evaluate changes in the folding, stability, and misfolding of the protein. We find that 2 metal ions (copper and manganese) destabilize the prion protein and that these same metal ios decrease the tendency for the protein to misfold. This report demonstrates the complex importance of metal ions on the folding, stability, and misfolding of the prion protein with the potential to impact disease.

Technical Abstract: Misfolding of the normally folded prion protein of mammals (PrPC) into infectious fibrils causes a variety of different diseases, from scrapie in sheep to bovine spongiform encephalopathy in cattle to chronic wasting disease (CWD) in deer and elk. The misfolded form of PrPC, termed PrPSc, or in this case PrPCWD, interacts with PrPC to create more PrPCWD. This process is not clearly defined but is evidently affected by the presence and interactions of numerous cofactors, both biotic and abiotic. This includes the presence of nucleic acids, lipids, glycosylation patterns, pH, and the presence of ions. PrPC has been shown to act as a copper-binding protein in vivo, though it also binds to other divalents as well. The significance of this binding action has not been conclusively elucidated. Previous reports have shown that metal binding sites occur throughout the N-terminal region of PrPC. Other cations like manganese have also been shown to affect PrPC abundance in a transcript-independent fashion. In this study, we examined the ability of a variety of divalent cations to influence the stability and in vitro conversion of two variants of PrP from an elk background (L/M132, 26-234, equivalent to human 23-231). We find that both copper and manganese de-stabilize PrP. However, we also find that PrP L132 exhibits a greater degree of divalent cation induced destabilization than M132. This stands in contrast to the finding that the occurrence of leucine at position 132 confers resistance to CWD, while M132 is susceptible. However, in vitro conversion of PrP is suppressed by the presence of either copper or manganese, in both L132 and M132 backgrounds. This report demonstrates the complex importance of ionic character on the PrPC folding pathway selection on the route to PrPSc formation.