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Updated: May 30, 2026
Isolation of Soluble and Insoluble PrP Oligomers in the Normal Human Brain
Published on: October 3, 2012
Identification and removal of proteins that co-purify with infectious prion protein improves the analysis of its
Roger A Moore1, Andrew G Timmes, Phillip A Wilmarth
1Rocky Mountain Laboratories/Laboratory of Persistent Viral Diseases, National Institute of Allergy and Infectious Diseases, National Institutes of Health, 903 S. 4th St., Hamilton, MT 59840, USA. rmoore@niaid.nih.gov
Abstract:
Prion diseases are neurodegenerative disorders associated with the accumulation of an abnormal isoform of the mammalian prion protein (PrP). Fourier transform infrared spectroscopy (FTIR) has previously been used to show that the conformation of aggregated, infectious PrP (PrP(Sc) ) varies between prion strains and these unique conformations may determine strain-specific disease phenotypes. However, the relative amounts of α-helix, β-sheet and other secondary structures have not always been consistent between studies, suggesting that other proteins might be confounding the analysis of PrP(Sc) secondary structure. We have used FTIR and LC-MS/MS to analyze enriched PrP(Sc) from mouse and hamster prion strains both before and after the removal of protein contaminants that commonly co-purify with PrP(Sc) . Our data show that non-PrP proteins do contribute to absorbances that have been associated with α-helical, loop, turn and β-sheet structures attributed to PrP(Sc) . The major contaminant, the α-helical protein ferritin, absorbs strongly at 1652 cm(-1) in the FTIR spectrum associated with PrP(Sc) . However, even the removal of more than 99% of the ferritin from PrP(Sc) did not completely abolish absorbance at 1652 cm(-1) . Our results show that contaminating proteins alter the FTIR spectrum attributed to PrP(Sc) and suggest that the α-helical, loop/turn and β-sheet secondary structure that remains following their removal are derived from PrP(Sc) itself.
Insights
Contaminating proteins like ferritin can alter Fourier transform infrared spectroscopy (FTIR) analysis of prion protein (PrP(Sc)) structure. Removing these contaminants reveals the true secondary structure of PrP(Sc) itself.
Area of Science:
- Neuroscience
- Biochemistry
- Spectroscopy
Background:
- Prion diseases involve abnormal prion protein (PrP(Sc)) accumulation.
- Fourier transform infrared spectroscopy (FTIR) is used to study PrP(Sc) conformation.
- Inconsistent FTIR results suggest confounding factors in PrP(Sc) analysis.
Purpose of the Study:
- To investigate the impact of protein contaminants on PrP(Sc) secondary structure analysis using FTIR.
- To determine the actual secondary structure of PrP(Sc) after removing co-purifying proteins.
Main Methods:
- Enriched PrP(Sc) from prion strains was analyzed using FTIR and liquid chromatography-tandem mass spectrometry (LC-MS/MS).
- Analysis was performed before and after the removal of protein contaminants.
- The influence of ferritin, a major contaminant, on FTIR spectra was specifically examined.
Main Results:
- Non-PrP proteins significantly contribute to FTIR absorbances previously attributed to PrP(Sc) secondary structures (α-helix, β-sheet, loop, turn).
- Ferritin strongly absorbs at 1652 cm⁻¹, a key spectral region for PrP(Sc).
- Even after >99% ferritin removal, the 1652 cm⁻¹ absorbance persisted, indicating PrP(Sc) contributes to this signal.
Conclusions:
- Contaminating proteins alter the FTIR spectra of PrP(Sc).
- The secondary structure components (α-helical, loop/turn, β-sheet) observed in PrP(Sc) after contaminant removal are intrinsic to PrP(Sc) itself.
- This study clarifies the structural basis of PrP(Sc) conformation and its relation to prion strains.
