Pathogenic prion protein is degraded by a manganese oxide mineral found in soils

Abstract

Prions, the aetiological agents of transmissible spongiform encephalopathies, exhibit extreme resistance to degradation. Soil can retain prion infectivity in the environment for years. Reactive soil components may, however, contribute to the inactivation of prions in soil. Members of the birnessite family of manganese oxides (MnO₂) rank among the strongest natural oxidants in soils. Here, we report the abiotic degradation of pathogenic prion protein (PrP^TSE) by a synthetic analogue of naturally occurring birnessite minerals. Aqueous MnO₂ suspensions degraded the PrP^TSE as evidenced by decreased immunoreactivity and diminished ability to seed protein misfolding cyclic amplification reactions. Birnessite-mediated PrP^TSE degradation increased as a solution's pH decreased, consistent with the pH-dependence of the redox potential of MnO₂. Exposure to 5.6 mg MnO₂ ml⁻¹ (PrP^TSE : MnO₂=1 : 110) decreased PrP^TSE levels by ≥4 orders of magnitude. Manganese oxides may contribute to prion degradation in soil environments rich in these minerals.