Abstract
Mammalian prion strains are believed to arise from the propagation of distinct conformations of the misfolded prion protein PrP(Sc). One key operational parameter used to define differences between strains has been conformational stability of PrP(Sc) as defined by resistance to thermal and/or chemical denaturation. However, the structural basis of these stability differences is unknown. To bridge this gap, we have generated two strains of recombinant human prion protein amyloid fibrils that show dramatic differences in conformational stability and have characterized them by a number of biophysical methods. Backbone amide hydrogen/deuterium exchange experiments revealed that, in sharp contrast to previously studied strains of infectious amyloid formed from the yeast prion protein Sup35, differences in β-sheet core size do not underlie differences in conformational stability between strains of mammalian prion protein amyloid. Instead, these stability differences appear to be dictated by distinct packing arrangements (i.e. steric zipper interfaces) within the amyloid core, as indicated by distinct x-ray fiber diffraction patterns and large strain-dependent differences in hydrogen/deuterium exchange kinetics for histidine side chains within the core region. Although this study was limited to synthetic prion protein amyloid fibrils, a similar structural basis for strain-dependent conformational stability may apply to brain-derived PrP(Sc), especially because large strain-specific differences in PrP(Sc) stability are often observed despite a similar size of the PrP(Sc) core region.
Highlights
Prion strains are believed to be enciphered by distinct conformations of misfolded prion protein (PrP)
This study was limited to synthetic prion protein amyloid fibrils, a similar structural basis for strain-dependent conformational stability may apply to brain-derived PrPSc, especially because large strain-specific differences in PrPSc stability are often observed despite a similar size of the PrPSc core region
In sharp contrast to previously studied Sup35 amyloid strains, we found that differences in rPrP amyloid conformational stability do not correspond to -sheet core size but are dictated by differences in the assembly of the steric zipper interfaces within the core region
Summary
Prion strains are believed to be enciphered by distinct conformations of misfolded prion protein (PrP). It is generally believed that PrPSc itself represents the infectious prion agent, which self-propagates by first binding to PrPC and inducing conformational conversion of the protein into the PrPSc state This “protein-only” model is supported by wealth of experimental data [1,2,3,4,5,6], including the recent success in generating infectious prions in vitro from bacterially expressed recombinant PrP [7,8,9,10,11]. Progress in a detailed understanding of the molecular basis of mammalian prion strains has been slow (largely due to technical difficulties associated with structural studies using brain-derived PrPSc), some light has been shed on this phenomenon by recent studies using distinct strains of amyloid fibrils formed from the recombinant mouse PrP that induce prion diseases in transgenic mice overexpressing PrPC [21, 22]
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