1H NMR analysis of fibril-forming peptide fragments of transthyretin.

Peptide fragments of the protein transthyretin, previously shown to form cross beta-sheet amyloid-like fibrils in vitro, were investigated using 1H 1D and 2D NMR techniques. TTR 10-20, TTR 105-115 as well as a substituted analogue, (TTR 105-115Met111) all formed amyloid-like fibrils readily in 20-30% acetonitrile/water at room temperature. It was found that the presence of fibrils in the peptide solutions did not affect the observable NMR spectra, which may have been due to the line-broadening that would be associated with these macromolecular species. 1H NMR spectra were thus representative of the monomeric form of the peptide in solution. Information from D2O exchange, 3JNH-alpha H coupling measurements, temperature coefficients and NOESY experiments suggested that these peptides have some propensity for turn or helix but were predominantly unstructured. There was no indication of the monomeric species existing predominantly in an extended form, suggesting that the formation of beta-sheet based fibrils does not require preformed extended structures. TTR 105-115Met111 displayed slight structural differences from TTR 105-115 which may be related to the fibril-forming propensity of the corresponding mutant TTR.