Fungal prion HET-s as a model for structural complexity and self-propagation in prions

Area of Science:

• Structural Biology
• Biophysics
• Prion Biology

Background:

• Prions are self-propagating proteins implicated in fatal diseases.
• The fungal prion HET-s exhibits a highly ordered, reproducible structure, making it an ideal model system.
• The HET-s prion-forming domain folds into a complex two-rung β-solenoid amyloid structure.

Purpose of the Study:

• To investigate the structural features essential for HET-s prion formation and self-propagation.
• To determine the biophysical effects of mutations on the assembly and stability of the prion-forming domain.
• To understand the role of specific interactions, such as buried polar residues and asparagine ladders, in prion structure.

Main Methods:

• Site-directed mutagenesis to alter specific structural features.
• X-ray fiber diffraction to analyze the β-solenoid structure.
• Fibrillization kinetics and chemical stability assays to assess biophysical effects.

Main Results:

• A diversity of structural features confers redundancy, enabling robust folding and stability.
• Mutations and suboptimal conditions did not prevent stable prion formation due to this redundancy.
• Specific features like flexible loops, buried polar residues, salt bridges, and asparagine ladders are crucial for β-solenoid formation.

Conclusions:

• Prion propagation requires a complex, multi-feature structure for robustness and stability.
• Redundancy in structural elements allows for adaptation to sequence alterations and environmental stress.
• Short peptide models may not fully replicate the complexity necessary for prion self-propagation.