SOLID-STATE NMR-STUDIES OF THE PRION PROTEIN H1 FRAGMENT

Conformational changes in the prion protein (PrP) seem to be responsib le for prion diseases. We have used conformation-dependent chemical-sh ift measurements and rotational-resonance distance measurements to ana lyze the conformation of solid-state peptides lacking long-range order , corresponding to a region of PrP designated H1. This region is predi cted to undergo a transformation of secondary structure in generating the infectious form of the protein. Solid-state NMR spectra of specifi cally C-13-enrrched samples of H1, residues 109-122 (MKHMAGAAAAGAVV) o f Syrian hamster PrP, have been acquired under cross-polarization and magic-angle spinning conditions. Samples lyophilized from 50% acetonit rile/50% water show chemical shifts characteristic of a beta-sheet con formation in the region corresponding to residues 112-121, whereas sam ples lyophilized from hexafluoroisopropanol display shifts indicative of alpha-helical secondary structure in the region corresponding to re sidues 113-117. Complete conversion to the helical conformation was no t observed and conversion from alpha-helix back to beta-sheet, as infe rred from the solid-state NMR spectra, occurred when samples were expo sed to water. Rotational-resonance experiments were performed on seven doubly C-13-labeled H1 samples dried from water. Measured distances s uggest that the peptide is in an extended, possibly beta-strand, confo rmation. These results are consistent with the experimental observatio n that PrP can exist in different conformational states and with struc tural predictions based on biological data and theoretical modeling th at suggest that H1 may play a key role in the conformational transitio n involved in the development of prion diseases.