Molecular conformation of a peptide fragment of transthyretin in an amyloid fibril

Abstract

The molecular conformation of peptide fragment 105–115 of transthyretin, TTR(105–115), previously shown to form amyloid fibrils in vitro , has been determined by magic-angle spinning solid-state NMR spectroscopy. 13 C and 15 N linewidth measurements indicate that TTR(105–115) forms a highly ordered structure with each amino acid in a unique environment. 2D 13 C- 13 C and 15 N- 13 C- 13 C chemical shift correlation experiments, performed on three fibril samples uniformly 13 C, 15 N-labeled in consecutive stretches of 4 aa, allowed the complete sequence-specific backbone and side-chain 13 C and 15 N resonance assignments to be obtained for residues 105–114. Analysis of the 15 N, 13 CO, 13 C α , and 13 C β chemical shifts allowed quantitative predictions to be made for the backbone torsion angles φ and ψ. Furthermore, four backbone 13 C– 15 N distances were determined in two selectively 13 C, 15 N-labeled fibril samples by using rotational-echo double-resonance NMR. The results show that TTR(105–115) adopts an extended β-strand conformation that is similar to that found in the native protein except for substantial differences in the vicinity of the proline residue.