The Structural Architecture of an Infectious Mammalian Prion Using Electron Cryomicroscopy

Area of Science:

• Structural biology
• Neuroscience
• Biochemistry

Background:

• The infectious prion protein (PrPSc) structure is crucial for understanding prion diseases like Creutzfeldt-Jakob disease and bovine spongiform encephalopathy.
• PrPSc's insolubility and aggregation hinder structural determination, impeding knowledge of its replication mechanism.
• PrPSc converts cellular PrPC into infectious conformers via an unknown process, forming aggregates, crystals, and fibrils.

Purpose of the Study:

• To determine the high-resolution structure of infectious prion protein aggregates.
• To elucidate the molecular architecture of mammalian prions.
• To provide a structural basis for understanding prion replication and developing therapeutics.

Main Methods:

• Electron cryomicroscopy was employed to analyze the structure of GPI-anchorless PrP 27-30 amyloid fibrils.
• Fourier-transform analyses were performed on averaged fibril segments to identify repeating units.
• 3D reconstructions were generated to visualize the protofilament arrangement and molecular volume.

Main Results:

• A repeating unit of 19.1 Å was identified within the prion fibrils.
• 3D reconstructions revealed two distinct protofilaments, with each PrP 27-30 molecule measuring approximately 17.7 Å in height.
• The data indicate a four-rung β-solenoid structure as a fundamental feature of infectious mammalian prions.

Conclusions:

• The determined four-rung β-solenoid structure is a key feature of infectious mammalian prions.
• This structural knowledge allows for the formulation of a molecular mechanism for prion replication.
• Understanding prion structure provides critical insights into protein misfolding self-propagation mechanisms.