Thiocyanate and hydroxyl ions inactivate the scrapie agent

Area of Science:

• Neuroscience
• Biochemistry
• Molecular Biology

Background:

• The scrapie agent's macromolecular structure remains incompletely understood.
• Investigating the scrapie agent's stability under various conditions is crucial for understanding its composition.

Purpose of the Study:

• To determine the stability of the scrapie agent in low concentrations of inorganic ions.
• To explore conditions that may lead to the monomerization of the scrapie agent.

Main Methods:

• Exposure of the scrapie agent to inorganic ions, including potassium thiocyanate (KSCN) and sodium hydroxide (NaOH).
• Assessment of scrapie agent titer reduction after ion exposure.
• Removal of ions via dialysis or chromatography to assess infectivity recovery.
• Addition of non-chaotropic salts to counteract inactivation.
• Acidification of partially purified fractions.

Main Results:

• A significant reduction (10^5-fold) in scrapie titer was observed upon exposure to 1 M KSCN or 0.3 M NaOH.
• Other chaotropic ions like guanidinium and trichloroacetate also inactivated the scrapie agent.
• Removal of thiocyanate ions by dialysis or chromatography prevented infectivity loss.
• Addition of ammonium sulfate, a non-chaotropic salt, protected against KSCN-induced inactivation.
• Neutralization of alkali-treated fractions with HCl did not restore infectivity.
• Acidification led to precipitation of the infectious agent without causing inactivation.

Conclusions:

• Inactivation by chaotropic ions suggests a protein component essential for scrapie agent infectivity.
• The findings argue against the scrapie agent being composed solely of a 'naked' nucleic acid.
• The agent's lability in alkali makes a single-stranded DNA composition highly unlikely.