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Published on: February 5, 2021
W8, a new Sup35 prion strain, transmits distinctive information with a conserved assembly scheme
Yu-Wen Huang1, Yuan-Chih Chang, Ruben Diaz-Avalos
1a Molecular and Cell Biology; Taiwan International Graduate Program; Academia Sinica and National Defense Medical Center ; Taipei , Taiwan.
Abstract:
Prion strains are different self-propagating conformers of the same infectious protein. Three strains of the [PSI] prion, infectious forms of the yeast Sup35 protein, have been previously characterized in our laboratory. Here we report the discovery of a new [PSI] strain, named W8. We demonstrate its robust cellular propagation as well as the protein-only transmission. To reveal strain-specific sequence requirement, mutations that interfered with the propagation of W8 were identified by consecutive substitution of residues 5-55 of Sup35 by proline and insertion of glycine at alternate sites in this segment. Interestingly, propagating W8 with single mutations at residues 5-7 and around residue 43 caused the strain to transmute. In contrast to the assertion that [PSI] existed as a dynamic cloud of sub-structures, no random drift in transmission characteristics was detected in mitotically propagated W8 populations. Electron diffraction and mass-per-length measurements indicate that, similar to the 3 previously characterized strains, W8 fibers are composed of about 1 prion molecule per 4.7-Å cross-β repeat period. Thus differently folded single Sup35 molecules, not dimeric and trimeric assemblies, form the basic repeating units to build the 4 [PSI] strains.
Insights
Researchers discovered a new yeast prion strain, W8, which propagates reliably and transmutes with specific mutations. This finding challenges the idea of dynamic prion structures, suggesting single protein molecules form the basic units of prion strains.
Area of Science:
- Biochemistry
- Molecular Biology
- Prion Biology
Background:
- Prion strains are distinct self-propagating protein conformers.
- The yeast [PSI] prion, an infectious form of Sup35 protein, has three previously characterized strains.
Purpose of the Study:
- To report the discovery and characterization of a new yeast [PSI] prion strain, designated W8.
- To investigate strain-specific sequence requirements for prion propagation and stability.
Main Methods:
- Introducing specific mutations (proline substitutions, glycine insertions) in Sup35 residues 5-55.
- Assessing cellular propagation and protein-only transmission of the W8 strain.
- Utilizing electron diffraction and mass-per-length measurements for fiber analysis.
Main Results:
- A novel [PSI] prion strain, W8, was identified with robust cellular propagation and protein-only transmission.
- Specific mutations at residues 5-7 and around residue 43 induced W8 strain transmutation.
- Mitotic propagation of W8 showed no random drift, contradicting the dynamic cloud hypothesis.
- W8 fibers, like other strains, are composed of single Sup35 molecules per cross-β repeat unit.
Conclusions:
- The discovery of W8 expands the known diversity of yeast prion strains.
- Strain-specific sequence requirements influence prion stability and can induce transmutation.
- Yeast prion strains are built from differently folded single Sup35 molecules, not larger assemblies.
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