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DNA converts cellular prion protein into the beta-sheet conformation and inhibits prion peptide aggregation
Y Cordeiro1, F Machado, L Juliano
1Programa de Biologia Estrutural, Departamento de Bioquimica Médica, Instituto de Ciências Biomédicas and Centro Nacional de Ressonância Magnética Nuclear de Macromoléculas, Universidade Federal do Rio de Janeiro, Rio de Janeiro RJ 21941-590, Brazil.
Abstract:
The main hypothesis for prion diseases proposes that the cellular protein (PrP(C)) can be altered into a misfolded, beta-sheet-rich isoform (PrP(Sc)), which in most cases undergoes aggregation. In an organism infected with PrP(Sc), PrP(C) is converted into the beta-sheet form, generating more PrP(Sc). We find that sequence-specific DNA binding to recombinant murine prion protein (mPrP-(23-231)) converts it from an alpha-helical conformation (cellular isoform) into a soluble, beta-sheet isoform similar to that found in the fibrillar state. The recombinant murine prion protein and prion domains bind with high affinity to DNA sequences. Several double-stranded DNA sequences in molar excess above 2:1 (pH 4.0) or 0.5:1 (pH 5.0) completely inhibit aggregation of prion peptides, as measured by light scattering, fluorescence, and circular dichroism spectroscopy. However, at a high concentration, fibers (or peptide aggregates) can rescue the peptide bound to the DNA, converting it to the aggregating form. Our results indicate that a macromolecular complex of prion-DNA may act as an intermediate for the formation of the growing fiber. We propose that host nucleic acid may modulate the delicate balance between the cellular and the misfolded conformations by reducing the protein mobility and by making the protein-protein interactions more likely. In our model, the infectious material would act as a seed to rescue the protein bound to nucleic acid. Accordingly, DNA would act on the one hand as a guardian of the Sc conformation, preventing its propagation, but on the other hand may catalyze Sc conversion and aggregation if a threshold level is exceeded.
Insights
DNA binding to prion protein converts it to a misfolded form, potentially influencing prion disease. DNA can inhibit or promote prion aggregation, acting as a key factor in disease propagation.
Area of Science:
- Biochemistry
- Molecular Biology
- Neuroscience
Background:
- Prion diseases involve the misfolding of cellular prion protein (PrP(C)) into a pathogenic isoform (PrP(Sc)).
- PrP(Sc) aggregation is a hallmark of prion diseases, leading to neurodegeneration.
Purpose of the Study:
- To investigate the role of DNA in prion protein conformation and aggregation.
- To explore the potential of DNA as a modulator of prion protein misfolding.
Main Methods:
- Utilized recombinant murine prion protein (mPrP-(23-231)) and sequence-specific DNA.
- Assessed protein conformation using spectroscopy (circular dichroism, fluorescence) and aggregation via light scattering.
- Investigated DNA-protein interactions at varying pH and molar ratios.
Main Results:
- Sequence-specific DNA binding induced a conformational change in mPrP-(23-231) from alpha-helical to beta-sheet.
- DNA inhibited prion peptide aggregation at specific concentrations and pH.
- High concentrations of aggregated prion peptides could overcome DNA's inhibitory effect, promoting aggregation.
Conclusions:
- A prion-DNA complex may serve as an intermediate in prion fiber formation.
- Host nucleic acids, like DNA, might regulate the balance between cellular and misfolded prion conformations.
- DNA can act as both an inhibitor and a catalyst for PrP(Sc) conversion and aggregation, depending on concentration and context.