Conformational variations in an infectious protein determine prion strain differences

Area of Science:

• Biochemistry
• Molecular Biology
• Yeast Genetics

Background:

• Prion biology exhibits strain diversity, where identical proteins form distinct transmissible states.
• The 'protein-only' hypothesis suggests these strains arise from different protein misfolding conformations.
• Distinguishing cause from effect in prion strain conformation has been challenging due to difficulties in generating pure infectious material.

Purpose of the Study:

• To investigate if distinct prion protein conformations directly cause prion strain variation.
• To develop a method for generating infectious prion material from purified protein.
• To test the 'protein-only' hypothesis by linking specific protein conformations to distinct prion strains.

Main Methods:

• Developed a high-efficiency yeast infection protocol using recombinant Sup35 fragment (Sup-NM) amyloids.
• Utilized thermal stability and electron paramagnetic resonance (EPR) spectroscopy to characterize amyloid conformations.
• Inoculated yeast with distinct Sup-NM amyloid conformations to observe resulting prion phenotypes.

Main Results:

• Sup-NM amyloids formed at different temperatures exhibited distinct and stable conformations.
• Infection of yeast with these conformationally different amyloids resulted in the emergence of different [PSI+] prion strains.
• Demonstrated that Sup-NM adopts an infectious conformation prior to cellular entry.

Conclusions:

• Prion strain variation is directly determined by the specific conformation of the infectious prion protein.
• This study provides direct evidence that protein conformation dictates prion strain diversity, supporting the 'protein-only' hypothesis.
• The findings establish a direct link between the structural state of the prion protein and its resulting biological strain.