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

ABSTRACT

Misfolding of the normally folded prion protein of mammals (PrP^C) into infectious fibrils causes a variety of diseases, from scrapie in sheep to chronic wasting disease (CWD) in cervids. The misfolded form of PrP^C, termed PrP^Sc, or in this case PrP^CWD, interacts with PrP^C to create more PrP^CWD. This process is not clearly defined but is affected by the presence and interactions of biotic and abiotic cofactors. These include nucleic acids, lipids, glycosylation, pH, and ionic character. PrP^C 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 action has not been conclusively elucidated. Previous reports have shown that metal binding sites occur throughout the N-terminal region of PrP^C. Other cations like manganese have also been shown to affect PrP^C abundance in a transcript-independent fashion. Here, we examined the ability of different divalent cations to influence the stability and in vitro conversion of two variants of PrP from elk (L/M132, 26–234). We find that copper and zinc de-stabilize PrP. We also find that PrP M132 exhibits a greater degree of divalent cation induced destabilization than L132. This supports findings that leucine at position 132 confers resistance to CWD, while M132 is susceptible. However, in vitro conversion of PrP is equally suppressed by either copper or zinc, in both L132 and M132 backgrounds. This report demonstrates the complex importance of ionic character on the PrP^C folding pathway selection on the route to PrP^Sc formation.

KEYWORDS:

• Prion
• chronic wasting disease
• PrP
• transmissible spongiform encephalopathies
• cervid
• CWD
• amyloid
• misfolding

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Disclosure of potential conflicts of interest

No potential conflicts of interest were disclosed.

Acknowledgments

We would like to thank Trudy Tatum and Semakaleng Lebepe-Mazur for excellent technical support.

Additional information

Funding

U.S. Department of Agriculture (USDA) DOE | Oak Ridge Institute for Science and Education (ORISE) This study was funded by the USDA-ARS, DS was supported in part by an appointment to the ARS-USDA Research Participation Program administered by the Oak Ridge Institute for Science and Education (ORISE) through an interagency agreement between the U.S. Department of Energy (DOE) and USDA. ORISE is managed by ORAU under DOE contract number DE-AC05-006OR23100.