High CJD infectivity remains after prion protein is destroyed

Area of Science:

• Neuroscience
• Biochemistry
• Infectious Diseases

Background:

• The traditional hypothesis posits that host prion protein (PrP) misfolds into an infectious form (PrP-res) responsible for transmissible spongiform encephalopathies (TSEs).
• This hypothesis is based on the observed correlation between PrP reduction by proteinase K (PK) and decreased infectivity.
• Recent proposals suggest a PK-sensitive PrP form might be the infectious agent.

Purpose of the Study:

• To re-evaluate the role of total prion protein (PrP), including both sensitive and resistant forms, in TSE infectivity.
• To compare the efficacy of proteinase K (PK) and keratinase (NAP) in degrading PrP and reducing infectivity.
• To investigate the potential role of non-PrP proteins in protecting infectious agents.

Main Methods:

• Utilized a cell-based assay for titrating infectious particles in FU-CJD infected brain and cell cultures.
• Compared the effects of limited proteinase K (PK) digestion versus keratinase (NAP) digestion on PrP levels and infectivity.
• Analyzed residual proteins using colloidal gold visualization after enzymatic digestion.

Main Results:

• Extensive PK digestion (≤0.3% residual PrP) of infected brain homogenate did not reduce infectivity titer, with non-PrP proteins remaining.
• Keratinase (NAP) digestion, leaving 0.8% residual PrP, significantly reduced infectivity (>2.5 log) and removed most other proteins.
• Infected cells showed substantial infectivity (>3.5 log reduction with NAP) even after extreme PK treatment (<0.2% residual PrP).

Conclusions:

• The findings challenge the central role of PrP as the sole infectious agent in TSEs, as infectivity persists despite significant PrP degradation.
• Residual non-PrP proteins may play a protective role for agent nucleic acids within infectious particles.
• Further research is needed to identify the specific non-PrP components responsible for maintaining infectivity.