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Separation and properties of cellular and scrapie prion proteins
Abstract:
Purified preparations of scrapie prions contain a sialoglycoprotein of Mr 27,000-30,000, designated PrP 27-30, which is derived from the scrapie prion protein [Mr, 33,000-35,000 (PrP 33-35Sc)] by limited proteolysis. Under these same conditions of proteolysis, a cellular protein of the same size (PrP 33-35C) is completely degraded. Subcellular fractionation of hamster brain showed that both PrP 33-35Sc and PrP 33-35C were found only in membrane fractions. NaCl, EDTA, and osmotic shock failed to release the prion proteins from microsomal membranes. Electron microscopy of these microsomal fractions showed membrane vesicles but not prion amyloid rods. Detergent treatment of scrapie-infected membranes solubilized PrP 33-35C, while PrP 33-35Sc aggregated into amyloid rods; the concentration of PrP 33-35C was similar to that recovered from analogous fractions prepared from uninfected control brains. The apparent amphipathic character of the PrP 33-35Sc may explain the association of scrapie infectivity with both membranes and amyloid filaments.
Insights
Scrapie prions contain a specific glycoprotein (PrP 27-30) resistant to proteolysis, unlike its cellular counterpart. This protein aggregates into amyloid rods, suggesting its role in prion infectivity and membrane association.
Area of Science:
- Neuroscience
- Biochemistry
- Molecular Biology
Background:
- Scrapie is a fatal neurodegenerative disease caused by prions.
- Prions are infectious proteins associated with specific diseases.
- The scrapie prion protein (PrP) exists in different forms.
Purpose of the Study:
- To investigate the biochemical properties and cellular localization of the scrapie prion protein (PrP).
- To understand the relationship between the disease-associated PrP (PrPSc) and its normal cellular counterpart (PrPC).
- To elucidate the structural basis for prion infectivity and its association with cellular membranes.
Main Methods:
- Limited proteolysis of purified scrapie prions and hamster brain fractions.
- Subcellular fractionation to isolate membrane components.
- Electron microscopy to visualize protein structures.
- Detergent treatment to assess protein solubility and aggregation.
Main Results:
- Purified scrapie prions contain PrP 27-30, derived from PrP 33-35Sc by proteolysis.
- PrP 33-35Sc is resistant to proteolysis, while PrP 33-35C is degraded.
- Both PrP forms are localized to membrane fractions.
- PrP 33-35Sc aggregates into amyloid rods upon detergent treatment, while PrP 33-35C remains soluble.
- PrP 33-35C concentration is similar in infected and uninfected brains.
Conclusions:
- The scrapie prion protein (PrP 33-35Sc) exhibits resistance to proteolysis and aggregates into amyloid structures.
- The cellular localization and detergent-induced aggregation suggest an amphipathic nature of PrP 33-35Sc.
- These properties likely contribute to the association of scrapie infectivity with both cellular membranes and amyloid filaments.