Structure and textures of fibrous crystals of the Abeta (11-25) peptide fragment from Alzheimer's Abeta Amyloid protein.

Amyloid fibril deposition is central to the pathology of Alzheimer's disease. X-ray diffraction from amyloid fibrils formed from full-length Aß(1¿40) and from a shorter fragment, Aß(11¿25), have revealed cross-ß diffraction fingerprints. Magnetic alignment of Aß(11¿25) amyloid fibrils gave a distinctive X-ray diffraction texture, allowing interpretation of the diffraction data and a model of the arrangement of the peptides within the amyloid fiber specimen to be constructed. An intriguing feature of the structure of fibrillar Aß(11¿25) is that the ß sheets, of width 5.2 nm, stack by slipping relative to each other by the length of two amino acid units (0.70 nm) to form ß ribbons 4.42 nm in thickness. Aß(1¿40) amyloid fibrils likely consist of once-folded hairpins, consistent with the size of the fibers obtained using electron microscopy and X-ray diffraction.