The pathognomonic plaques of Alzheimer's disease are composed primarily of the 39-to 43-aa ␤-amyloid (A␤) peptide. Crosslinking of A␤ peptides by tissue transglutaminase (tTg) indicates that Gln 15 of one peptide is proximate to Lys 16 of another in aggregated A␤. Here we report how the fibril structure is resolved by mapping interstrand distances in this core region of the A␤ peptide chain with solid-state NMR. Isotopic substitution provides the source points for measuring distances in aggregated A␤. Peptides containing a single carbonyl 13 C label at Gln 15 , Lys 16 , Leu 17 , or Val 18 were synthesized and evaluated by NMR dipolar recoupling methods for the measurement of interpeptide distances to a resolution of 0.2 Å. Analysis of these data establish that this central core of A␤ consists of a parallel ␤-sheet structure in which identical residues on adjacent chains are aligned directly, i.e., in register. Our data, in conjunction with existing structural data, establish that the A␤ fibril is a hydrogen-bonded, parallel ␤-sheet defining the long axis of the A␤ fibril propagation.

The primary component of the amyloid plaques in Alzheimer's disease (AD) is a highly ordered fibril composed of the 39−43 amino acid peptide, β-amyloid (Aβ). The presence of this fibril has been correlated with both the onset and severity of the disease. Using a combination of synthetic model peptides, solid-state NMR, electron microscopy, and small angle neutron scattering (SANS), methods that allowed fibrils to be studied directly both in solution and in the solid state, the three-dimensional structure of fibrils formed from Aβ(10 - 35) is assigned. The structure consists of six laminated β-sheets propagating and twisting along the fibril axis. Each peptide strand is oriented perpendicular to the helical axis in a parallel β-sheet, with each like amino acid residue in register along the sheet. The six sheets are laminated, probably also in parallel arrays, to give a fibril with dimensions of about 60 × 80 Å. Both the methodology developed and the structural insight gained here lay the foundation for strategies to characterize and design materials capable of amyloid-like self-assembly.

Beta-amyloid (Abeta) peptides are the main protein component of the pathognomonic plaques found in the brains of patients with Alzheimer's disease. These heterogeneous peptides adopt a highly organized fibril structure both in vivo and in vitro. Here we use solid-state NMR on stable, homogeneous fibrils of Abeta(10-35). Specific interpeptide distance constraints are determined with dipolar recoupling NMR on fibrils prepared from a series of singly labeled peptides containing (13)C-carbonyl-enriched amino acids, and skipping no more that three residues in the sequence. From these studies, we demonstrate that the peptide adopts the structure of an extended parallel beta-sheet in-register at pH 7.4. Analysis of DRAWS data indicates interstrand distances of 5.3 +/- 0.3 A (mean +/- standard deviation) throughout the entire length of the peptide, which is compatible only with a parallel beta-strand in-register. Intrastrand NMR constraints, obtained from peptides containing labels at two adjacent amino acids, confirm the secondary structural findings obtained using DRAWS. Using peptides with (13)C incorporated at the carbonyl position of adjacent amino acids, structural transitions from alpha-helix to beta-sheet were observed at residues 19 and 20, but using similar techniques, no evidence for a turn could be found in the putative turn region comprising residues 25-29. Implications of this extended parallel organization for Abeta(10-35) for overall fibril formation, stability, and morphology based upon specific amino acid contacts are discussed.