Kosmotropic anions promote conversion of recombinant prion protein into a PrPSc-like misfolded form

Prions are self-propagating proteins involved in transmissible spongiform encephalopaties in mammals. An aberrant conformation with amyloid-like features of a cell surface protein, termed prion protein (PrP), is thought to be the essential component of the infectious particle, though accessory co-factor molecules such as lipids and nucleotides may be involved. The cellular co-factors and environmental conditions implicated in PrP misfolding are not completely understood. To address this issue, several studies have been done inducing misfolding of recombinant PrP (recPrP) into classical amyloid structures using partially denaturing conditions. In this work, we report that misfolding of recPrP into PrP(Sc)-like aggregates can be induced by simply incubating the protein in the presence of kosmotropic salts at concentrations that are known to retain or increase the stability of the protein. We used a simple experimental reaction (protein, buffer and salts) submitted to agitation/incubation cycles at physiological temperature and pH. The formation of protease resistant-recPrP was time and salt-concentration dependent and required the presence of kosmotropic anions such as F(-) or SO(4)(-2). The molecular weights of the protease resistant recPrP fragments are reminiscent of those found in degradation assays of bona fide PrP(Sc). The aggregates also exhibited PrP(Sc)-like ultrastructural features including rod-shape morphology under electron microscope, high beta-sheet content and thioflavin-T positive signal. The formation of recPrP aggregates with PrP(Sc) biochemical features under conditions closer to physiological in the absence of organic co-factor molecules provides a simple setup that may prove helpful to understand the molecular mechanism of PrP misfolding.