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Updated: Aug 29, 2026
Assessing Transmissible Spongiform Encephalopathy Species Barriers with an In Vitro Prion Protein Conversion Assay
Published on: March 10, 2015
Autocatalytic conversion of recombinant prion proteins displays a species barrier
1Medical Biotechnology Center, University of Maryland Biotechnology Institute, Baltimore, Maryland 21201, USA. Baskakov@umbi.umd.edu
Abstract:
The most unorthodox feature of the prion disease is the existence of an abnormal infectious isoform of the prion protein, PrP(Sc). According to the "protein-only" hypothesis, PrP(Sc) propagates its abnormal conformation in an autocatalytic manner using the normal isoform, PrP(C), as a substrate. Because autocatalytic conversion is considered a key element of prion replication, in this study I tested whether in vitro conversion of recombinant PrP into abnormal isoform displays specific features of an autocatalytic process. I found that recombinant human PrP formed two distinct beta-sheet rich isoforms, the beta-oligomer and the amyloid fibrils. The kinetics of the fibrils formation measured at different pH values were consistent with a model in which the beta-oligomer was not on the kinetic pathway to the fibrillar form. As judged by electron microscopy, an acidic pH favored to the long fibrils, whereas short fibrils morphologically similar to "prion rods" were formed at neutral pH. At neutral pH the conversion to the fibrils can be seeded with small aliquots of preformed fibrils. As small as 0.001% aliquot displayed seeding activity. The conversion of human PrP was seeded with high efficacy only with the preformed fibrils of human but not mouse PrP and vice versa. These studies illustrate that in vitro conversion of recombinant PrP displays specific features of an autocatalytic process and mimics the transmission barrier of prion propagation observed in vivo. I speculate that this model can be used as a rapid assay for assessing the intrinsic propensities of prion transmission between different species.
Insights
This study demonstrates that in vitro conversion of recombinant prion protein (PrP) exhibits autocatalytic properties, mimicking prion replication and transmission barriers. This finding offers a new model for studying prion diseases.
Area of Science:
- Neuroscience
- Biochemistry
- Molecular Biology
Background:
- Prion diseases are characterized by an abnormal infectious prion protein isoform (PrPSc).
- The "protein-only" hypothesis posits that PrPSc propagates by converting the normal prion protein isoform (PrPC) in an autocatalytic manner.
- Autocatalytic conversion is crucial for prion replication.
Purpose of the Study:
- To investigate whether in vitro conversion of recombinant PrP into an abnormal isoform displays autocatalytic features.
- To explore the kinetics and structural characteristics of recombinant PrP conversion.
- To assess the potential of this in vitro system as an assay for prion transmission.
Main Methods:
- Recombinant human PrP was converted into beta-sheet rich isoforms in vitro.
- Fibril formation kinetics were analyzed at various pH values.
- Electron microscopy was used to characterize the formed isoforms.
- Seeding experiments were conducted using preformed fibrils.
Main Results:
- Recombinant human PrP formed two distinct beta-sheet rich isoforms: beta-oligomers and amyloid fibrils.
- Fibril formation kinetics indicated beta-oligomers were not on the pathway to fibril formation.
- Acidic pH favored long fibrils, while neutral pH produced short fibrils resembling "prion rods".
- Conversion was efficiently seeded by preformed fibrils, demonstrating autocatalysis and species-specific seeding.
- A transmission barrier was observed, with human PrP fibrils seeding human PrP but not mouse PrP, and vice versa.
Conclusions:
- In vitro conversion of recombinant PrP exhibits autocatalytic features, mirroring prion replication.
- The study successfully mimics the prion transmission barrier in vitro.
- This model system can potentially serve as a rapid assay for assessing prion transmission propensities between species.
