title: Structural properties of Abeta protofibrils stabilized by a small molecule.
abstract: Metastable oligomeric and protofibrillar forms of amyloidogenic proteins have been implicated as on-pathway assembly intermediates in amyloid formation and as the major toxic species in a number of amyloid diseases including Alzheimer's disease. We describe here a chemical biology approach to structural analysis of Abeta protofibrils. Library screening yielded several molecules that stimulate Abeta aggregation. One of these compounds, calmidazolium chloride (CLC), rapidly and efficiently converts Abeta(1-40) monomers into clusters of protofibrils. As monitored by electron microscopy, these protofibrils persist for days when incubated in PBS at 37 degrees C, with a slow transition to fibrillar structures apparent only after several weeks. Like normal protofibrils, the CLC-Abeta aggregates exhibit a low thioflavin T response. Like Abeta fibrils, the clustered protofibrils bind the anti-amyloid Ab WO1. The CLC-Abeta aggregates exhibit the same protection from hydrogen-deuterium exchange as do protofibrils isolated from a spontaneous Abeta fibril formation reaction: approximately 12 of the 39 Abeta(1-40) backbone amide protons are protected from exchange in the protofibril, compared with approximately twice that number in amyloid fibrils. Scanning proline mutagenesis analysis shows that the Abeta molecule in these protofibrillar assemblies exhibits the same flexible N and C termini as do mature amyloid fibrils. The major difference in Abeta conformation between fibrils and protofibrils is added structural definition in the 22-29 segment in the fibril. Besides aiding structural analysis, compounds capable of facilitating oligomer and protofibril formation might have therapeutic potential, if they act to sequester Abeta in a form and/or location that cannot engage the toxic pathway.
authors.affiliation: Graduate School of Medicine, University of Tennessee, 1924 Alcoa Highway, Knoxville, TN 37920, USA.
authors.forename: Angela D
authors.initials: AD
authors.lastname: Williams
authors.forename: Matt
authors.initials: M
authors.lastname: Sega
authors.forename: Maolian
authors.initials: M
authors.lastname: Chen
authors.forename: Indu
authors.initials: I
authors.lastname: Kheterpal
authors.forename: Merav
authors.initials: M
authors.lastname: Geva
authors.forename: Valerie
authors.initials: V
authors.lastname: Berthelier
authors.forename: David T
authors.initials: DT
authors.lastname: Kaleta
authors.forename: Kelsey D
authors.initials: KD
authors.lastname: Cook
authors.forename: Ronald
authors.initials: R
authors.lastname: Wetzel
mesh_terms: D000595:Amino Acid Sequence; D016229:Amyloid beta-Peptides / Q000737:chemistry* / Q000378:metabolism* / Q000648:ultrastructure; D000906:Antibodies / Q000378:metabolism; D007093:Imidazoles / Q000378:metabolism*; D013058:Mass Spectrometry; D008854:Microscopy, Electron; D008969:Molecular Sequence Data; D016296:Mutagenesis; D010446:Peptide Fragments / Q000737:chemistry* / Q000378:metabolism* / Q000648:ultrastructure; D011392:Proline / Q000235:genetics; D011487:Protein Conformation
chemical_list: D016229:Amyloid beta-Peptides; D000906:Antibodies; D007093:Imidazoles; D010446:Peptide Fragments; C098994:amyloid beta-protein (1-43); C031938:calmidazolium; D011392:Proline