Prion protein helix1 promotes aggregation but is not converted into beta-sheet.
Prion diseases are caused by the aggregation of the native alpha-helical prion protein PrP(C) into its pathological beta-sheet-rich isoform PrP(Sc). In current models of PrP(Sc), helix1 is assumed to be preferentially converted into beta-sheet during aggregation of PrP(C). This was supported by the NMR structure of PrP(C) since, in contrast to the isolated helix1, helix2 and helix3 are connected by a small loop and are additionally stabilized by an interhelical disulfide bond. However, helix1 is extremely hydrophilic and has a high helix propensity. This prompted us to investigate the role of helix1 in prion aggregation using humPrP(23-159) including helix1 (144-156) compared with the C-terminal-truncated isoform humPrP(23-144) corresponding to the pathological human stop mutations Q160Stop and Y145Stop, respectively. Most unexpectedly, humPrP(23-159) aggregated significantly faster compared with the truncated fragment humPrP(23-144), clearly demonstrating that helix1 is involved in the aggregation process. However, helix1 is not resistant to digestion with proteinase K in fibrillar humPrP(23-159), suggesting that helix1 is not converted to beta-sheet. This is confirmed by Fourier transformation infrared spectroscopy since there is almost no difference in beta-sheet content of humPrP(23-159) fibrils compared with humPrP(23-144). In conclusion, we provide strong direct evidence that in contrast to earlier assumptions helix1 is not converted into beta-sheet during aggregation of PrP(C) to PrP(Sc).
Watzlawik
Jens
J
Prion and Dementia Research Unit, Institute of Neuropathology, University of Goettingen, 37075 Goettingen, Germany.
Skora
Lukasz
L
Frense
Dieter
D
Griesinger
Christian
C
Zweckstetter
Markus
M
Schulz-Schaeffer
Walter J
WJ
Kramer
Michael L
ML
D002942:Circular Dichroism; D004351:Drug Resistance / Q000502:physiology; D019286:Endopeptidase K / Q000502:physiology; D006801:Humans; D009682:Magnetic Resonance Spectroscopy; D010446:Peptide Fragments; D011328:Prions / Q000737:chemistry* / Q000502:physiology* / Q000648:ultrastructure; D017433:Protein Structure, Secondary; D017550:Spectroscopy, Fourier Transform Infrared; D055672:Static Electricity
D010446:Peptide Fragments; D011328:Prions; D019286:Endopeptidase K