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

^*Department of Chemistry and Center for Magnetic Resonance, Francis Bitter Magnet Laboratory, Massachusetts Institute of Technology, Cambridge, MA 02139; ^‡Cavendish Laboratory, University of Cambridge, Madingley Road, Cambridge CB3 0HE, United Kingdom; and ^∥Department of Chemistry, University of Cambridge, Lensfield Road, Cambridge CB2 1EW, United Kingdom

Edited by Alfred G. Redfield, Brandeis University, Waltham, MA, and approved November 19, 2003 (received for review July 31, 2003)

Abstract

Amyloid fibrils are self-assembled filamentous structures associated with protein deposition conditions including Alzheimer's disease and the transmissible spongiform encephalopathies. Despite the immense medical importance of amyloid fibrils, no atomic-resolution structures are available for these materials, because the intact fibrils are insoluble and do not form diffraction-quality 3D crystals. Here we report the high-resolution structure of a peptide fragment of the amyloidogenic protein transthyretin, TTR(105–115), in its fibrillar form, determined by magic angle spinning NMR spectroscopy. The structure resolves not only the backbone fold but also the precise conformation of the side chains. Nearly complete ¹³C and ¹⁵N resonance assignments for TTR(105–115) formed the basis for the extraction of a set of distance and dihedral angle restraints. A total of 76 self-consistent experimental measurements, including 41 restraints on 19 backbone dihedral angles and 35 ¹³C–¹⁵N distances between 3 and 6 Å were obtained from 2D and 3D NMR spectra recorded on three fibril samples uniformly ¹³C, ¹⁵N-labeled in consecutive stretches of four amino acids and used to calculate an ensemble of peptide structures. Our results indicate that TTR(105–115) adopts an extended β-strand conformation in the amyloid fibrils such that both the main- and side-chain torsion angles are close to their optimal values. Moreover, the structure of this peptide in the fibrillar form has a degree of long-range order that is generally associated only with crystalline materials. These findings provide an explanation of the unusual stability and characteristic properties of this form of polypeptide assembly.

Footnotes

↵ § To whom correspondence may be addressed. E-mail: cem48{at}cam.ac.uk or rgg{at}mit.edu.
↵ † Present address: Laboratory of Chemical Physics, National Institute of Diabetes and Digestive and Kidney Diseases, National Institutes of Health, Bethesda, MD 20892.
↵ ¶ Present address: Department of Radiology, Johns Hopkins University School of Medicine, 1721 East Madison Street, Baltimore, MD 21205.
This paper was submitted directly (Track II) to the PNAS office.
Abbreviations: MAS, magic angle spinning; rmsd, rms deviation; ZF TEDOR, z-filtered transferred-echo double-resonance; TTR, transthyretin.
Data deposition: The atomic coordinates have been deposited in the Protein Data Bank, www.rcsb.org (PDB ID code 1RVS).