Abstract
An unidentified environmental reservoir of infectivity contributes to the natural transmission of prion diseases (transmissible spongiform encephalopathies [TSEs]) in sheep, deer, and elk. Prion infectivity may enter soil environments via shedding from diseased animals and decomposition of infected carcasses. Burial of TSE-infected cattle, sheep, and deer as a means of disposal has resulted in unintentional introduction of prions into subsurface environments. We examined the potential for soil to serve as a TSE reservoir by studying the interaction of the disease-associated prion protein (PrPSc) with common soil minerals. In this study, we demonstrated substantial PrPSc adsorption to two clay minerals, quartz, and four whole soil samples. We quantified the PrPSc-binding capacities of each mineral. Furthermore, we observed that PrPSc desorbed from montmorillonite clay was cleaved at an N-terminal site and the interaction between PrPSc and Mte was strong, making desorption of the protein difficult. Despite cleavage and avid binding, PrPSc bound to Mte remained infectious. Results from our study suggest that PrPSc released into soil environments may be preserved in a bioavailable form, perpetuating prion disease epizootics and exposing other species to the infectious agent.
Highlights
Transmissible spongiform encephalopathies (TSEs, prion diseases) are a group of fatal neurodegenerative diseases that affect a variety of mammalian species and include bovine spongiform encephalopathy (BSE, ‘‘mad cow’’ disease), chronic wasting disease (CWD) of deer and elk, sheep scrapie, and Creutzfeldt-Jakob disease in humans [1]
Binding of disease-associated prion protein (PrPSc) to Soil Minerals We examined the sorption of purified PrPSc to three common soil minerals (Table S1): quartz, montmorillonite (Mte, an expandable layered silicate clay mineral), and kaolinite (Kte, a nonexpandable phyllosilicate mineral)
We provide evidence indicating that soil and soil minerals serve as a reservoir of TSE infectivity
Summary
Transmissible spongiform encephalopathies (TSEs, prion diseases) are a group of fatal neurodegenerative diseases that affect a variety of mammalian species and include bovine spongiform encephalopathy (BSE, ‘‘mad cow’’ disease), chronic wasting disease (CWD) of deer and elk, sheep scrapie, and Creutzfeldt-Jakob disease in humans [1]. The agricultural, economic, and social impacts of prion diseases have been intensified by evidence suggesting transmissibility of BSE to humans [2]. The putative infectious agent in these diseases, designated PrPSc, is a misfolded isoform of the normal cellular prion protein (PrPC). The amino acid sequences of PrPSc and PrPC are identical [3]; normal and abnormal forms of the protein differ only in conformation. The normal isoform is soluble and primarily monomeric in solution, whereas PrPSc forms insoluble aggregates
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