Solid‐state NMR studies of the prion protein H1 fragment

Abstract

Conformational changes in the prion protein (PrP) seem to be responsible for prion diseases. We have used conformation-dependent chemical-shift measurements and rotational-resonance distance measurements to analyze the conformation of solid-state peptides lacking long-range order, corresponding to a region of PrP designated H I . This region is predicted to undergo a transformation of secondary structure in generating the infectious form of the protein. Solid-state NMR spectra of specifically '3C-enriched samples of HI, residues 109-122 (MKHMAGAAAAGAVV) of Syrian hamster PrP, have been acquired under cross-polarization and magic-angle spinning conditions. Samples lyophilized from 50% acetonitrile/50% water show chemical shifts characteristic of a 0-sheet conformation in the region corresponding to residues 112-121, whereas samples lyophilized from hexafluoroisopropanol display shifts indicative of a-helical secondary structure in the region corresponding to residues 113-1 17. Complete conversion to the helical conformation was not observed and conversion from a-helix back to 0-sheet, as inferred from the solid-state NMR spectra, occurred when samples were exposed to water. Rotational-resonance experiments were performed on seven doubly I3C-labeled H1 samples dried from water. Measured distances suggest that the peptide is in an extended, possibly &strand, conformation. These results are consistent with the experimental observation that P r P can exist in different conformational states and with structural predictions based on biological data and theoretical modeling that suggest that HI may play a key role in the conformational transition involved in the development of prion diseases.

Hydrophobic interactions in the formation of secondary structures in small peptides

“…Taken together, our results underscore the importance of desolvation effects in the relative favorability of α versus β conformations in polypeptides, and serve to emphasize that these effects should be taken into account in modeling [41,43] and in interpreting experimental data on conformational dependence of water-peptide interactions [61]. For example, as mentioned above, some amyloid peptides form β or coil conformations in water but they adopt α-helical conformations in membrane mimicking environments [24]. In light of our model results, a possible scenario is that the desolvation effects are not conducive to helix formation when these peptides are in an aqueous environment.…”

“…[59,60] implicated in Parkinson's disease. Explicit solvent simulations and experiments have shown that these sequences assume a large amount of β and coiled conformations in aqueous environments whereas the α helix is their dominant conformational pattern in solvents that mimic the interior of membranes (e.g., hexafluoroisopropanol-water mixture) [23,24,56]. Figure 10 shows how R cutoff affects secondary structure content.…”

“…For example, fragments of * diasc@biosimulations.org † mkarttu@uwo.ca ‡ chan@arrhenius.med.toronto.edu amyloid peptides with many hydrophobic residues form preferentially β or coil conformations in aqueous environments; but they form α-helical structures in membrane-mimicking environments [23,24]. This indicates that, aside from protein core packing, hydrophobicity plays an important role in the conformation of small peptides.…”

From conversion to aggregation: Protofibril formation of the prion protein

“…By using a structure from this ensemble, we modeled a prion aggregate that agrees with electron microscopy (EM) data from in vitro infectious Syrian hamster and mouse PrP two-dimensional protofibril crystals (24). Other experimental results such as changes in PrP C antibody binding sites (25,26), PrP Sc selective epitopes (27), differential proteinase K digestion (13,28), fiber diffraction (29), solid-state NMR (30)(31)(32), and peptide binding studies of PrP Sc (33)(34)(35) are consistent with our model.…”

High-resolution molecular structure of a peptide in an amyloid fibril determined by magic angle spinning NMR spectroscopy

“…Such techniques can also be applied to the structural characterization of amyloid fibrils and other incompletely ordered biological systems. Indeed, site-specific structural measurements have been performed for various amyloidogenic peptides (17)(18)(19)(20)(21)(22)(23)(24)(25)(26), and a structural model for fibrils formed by the full length Alzheimer's ␤-amyloid peptide has recently been proposed (24). In this article we report the success of these techniques in permitting the determination of the high-resolution structure of a peptide in an amyloid fibril, elucidating not only the backbone fold but also the precise conformation of the side chains.…”