Conformational change, aggregation and fibril formation induced by detergent treatments of cellular prion protein

Authors


Address correspondence and reprint requests to Dr Byron Caughey, Laboratory of Persistent Viral Diseases, Rocky Mountain Laboratories, NIAID, NIH, 903 S 4th St., Hamilton, MT 59840, USA.E-mail: bcaughey@nih.gov

Abstract

The conversion of protease-sensitive prion protein (PrP-sen) to a high β-sheet, protease-resistant and often fibrillar form (PrP-res) is a central event in transmissible spongiform encephalopathies (TSE) or prion diseases. This conversion can be induced by PrP-res itself in cell-free conversion reactions. The detergent sodium N-lauroyl sarkosinate (sarkosyl) is a detergent that is widely used in PrP-res purifications and is known to stimulate the PrP-res-induced conversion reaction. Here we report effects of sarkosyl and other detergents on recombinant hamster PrP-sen purified from mammalian cells under oxidizing conditions that maintain the single native disulfide bond. Low concentrations of sarkosyl (0.001–0.1%) induced aggregation of PrP-sen molecules, increased light scattering, altered fluorescence excitation and emission spectra, and enhanced the proportion of β-sheet secondary structure according to circular dichroism and infrared spectroscopies. An enhancement of β-sheet content was also seen with 0.001% sodium dodecyl sulfate (SDS) but not several other types of detergents. Electron microscopy revealed that sarkosyl induced the formation of both amorphous and fibrillar aggregates. The fibrils appeared to be constructed from spherical bead-like protofibrils. Neither TSE infectivity nor the characteristic partial proteinase K resistance of PrP-res was detected in the sarkosyl-induced PrP aggregates. We conclude that certain anionic detergents can disrupt the conformation of PrP-sen and induce high β-sheet aggregates that are distinct from scrapie-associated PrP-res in terms of protease-resistance, infrared spectrum and infectivity. These results reinforce the idea that not all high-β aggregates of PrP are equivalent to the pathologic form, PrP-res.

Ancillary