title: Supramolecular structural constraints on Alzheimer's beta-amyloid fibrils from electron microscopy and solid-state nuclear magnetic resonance.
abstract: We describe electron microscopy (EM), scanning transmission electron microscopy (STEM), and solid-state nuclear magnetic resonance (NMR) measurements on amyloid fibrils formed by the 42-residue beta-amyloid peptide associated with Alzheimer's disease (Abeta(1)(-)(42)) and by residues 10-35 of the full-length peptide (Abeta(10)(-)(35)). These measurements place constraints on the supramolecular structure of the amyloid fibrils, especially the type of beta-sheets present in the characteristic amyloid cross-beta structural motif and the assembly of these beta-sheets into a fibril. EM images of negatively stained Abeta(10)(-)(35) fibrils and measurements of fibril mass per length (MPL) by STEM show a strong dependence of fibril morphology and MPL on pH. Abeta(10)(-)(35) fibrils formed at pH 3.7 are single "protofilaments" with MPL equal to twice the value expected for a single cross-beta layer. Abeta(10)(-)(35) fibrils formed at pH 7.4 are apparently pairs of protofilaments or higher order bundles. EM and STEM data for Abeta(1)(-)(42) fibrils indicate that protofilaments with MPL equal to twice the value expected for a single cross-beta layer are also formed by Abeta(1)(-)(42) and that these protofilaments exist singly and in pairs at pH 7.4. Solid-state NMR measurements of intermolecular distances in Abeta(10)(-)(35) fibrils, using multiple-quantum (13)C NMR, (13)C-(13)C dipolar recoupling, and (15)N-(13)C dipolar recoupling techniques, support the in-register parallel beta-sheet organization previously established by Lynn, Meredith, Botto, and co-workers [Benzinger et al. (1998) Proc. Natl. Acad. Sci. U.S.A. 95, 13407-13412; Benzinger et al. (2000) Biochemistry 39, 3491-3499] and show that this beta-sheet organization is present at pH 3.7 as well as pH 7.4 despite the differences in fibril morphology and MPL. Solid-state NMR measurements of intermolecular distances in Abeta(1)(-)(42) fibrils, which represent the first NMR data on Abeta(1)(-)(42) fibrils, also indicate an in-register parallel beta-sheet organization. These results, along with previously reported data on Abeta(1)(-)(40) fibrils, suggest that the supramolecular structures of Abeta(10)(-)(35), Abeta(1)(-)(40), and Abeta(1)(-)(42) fibrils are quite similar. A schematic structural model of these fibrils, consistent with known experimental EM, STEM, and solid-state NMR data, is presented.
authors.affiliation: Division of Chemistry, Luleå University of Technology, Luleå, Sweden.
authors.forename: Oleg N
authors.initials: ON
authors.lastname: Antzutkin
authors.forename: Richard D
authors.initials: RD
authors.lastname: Leapman
authors.forename: John J
authors.initials: JJ
authors.lastname: Balbach
authors.forename: Robert
authors.initials: R
authors.lastname: Tycko
mesh_terms: D000544:Alzheimer Disease / Q000378:metabolism* / Q000473:pathology; D000595:Amino Acid Sequence; D016229:Amyloid beta-Peptides / Q000737:chemistry* / Q000648:ultrastructure; D002247:Carbon Isotopes; D006801:Humans; D018625:Microscopy, Atomic Force; D008855:Microscopy, Electron, Scanning; D008969:Molecular Sequence Data; D019906:Nuclear Magnetic Resonance, Biomolecular / Q000379:methods; D010446:Peptide Fragments / Q000737:chemistry* / Q000648:ultrastructure; D017433:Protein Structure, Secondary; D011789:Quantum Theory; D013329:Structure-Activity Relationship
chemical_list: D016229:Amyloid beta-Peptides; D002247:Carbon Isotopes; D010446:Peptide Fragments; C075222:amyloid beta-protein (1-42); C407125:amyloid beta-protein (10-35)