Yeast Sup35 Prion Structure: Two Types, Four Parts, Many Variants

Area of Science:

• Yeast prion biology
• Protein misfolding and aggregation
• Molecular genetics

Background:

• The yeast [PSI+] prion, a self-templating aggregate of the Sup35 protein (also known as eRF3), exists in multiple variants.
• These variants differ in their structural properties and the strength of the nonsense suppression phenotype they confer.
• The precise structural basis for [PSI+] variation remains poorly understood.

Purpose of the Study:

• To map the amyloid cores of diverse ex vivo [PSI+] prion variants.
• To investigate the relationship between Sup35 prion core structure and phenotypic characteristics.
• To identify structural determinants that distinguish different [PSI+] variants.

Main Methods:

• Proteinase K digestion of 26 different [PSI+] ex vivo prion isolates.
• Mass spectrometry for identification of proteinase K-resistant Sup35 peptides.
• Correlation of digestion patterns with nonsense suppressor phenotype strength and genetic assays (HSP104, SUP35 copy number).

Main Results:

• The N-terminal residues 2-32 of Sup35 formed a stable amyloid core in all [PSI+] variants.
• Distinct proteinase K digestion patterns of the Sup35 N-terminal region (residues 2-72) correlated with 'strong' and 'weak' [PSI+] phenotypes.
• Specific structural elements within Sup35 (residues 2-32, 73-124, 125-153, 154-221) contribute to prion core composition, with variable presence across isolates.

Conclusions:

• Yeast [PSI+] prion variants can be reliably classified into two main groups based on the structure of their Sup35 prion core, particularly the N-terminal region.
• These structural classes exhibit distinct phenotypic properties, including responses to changes in HSP104 and SUP35 gene dosage.
• The findings provide a structural basis for understanding [PSI+] prion diversity and its functional consequences.