title: Association of thin filaments into thick filaments revealing the structural hierarchy of amyloid fibrils.
abstract: Beta2-Microglobulin (beta2-m) is a major structural component of dialysis-related amyloid fibrils. Kozhukh et al. [J. Biol. Chem. 277 (2002) 1310] prepared a series of peptide fragments of beta2-m by the protease digestion and examined their ability to form amyloid fibrils in citrate buffer at pH 2.5. Among various peptides, a 22-residue K3 peptide corresponding to Ser20-Lys41 spontaneously formed amyloid fibrils in aqueous solution. This peptide also formed amyloid protofibrils in 20% (v/v) 2,2,2-trifluoroethanol (TFE). To investigate the influence of solvent conditions on fibril formation, we studied their structures by atomic force microscopy. In aqueous solution, fibrils had a diameter of 4 or 8 nm and tended to cluster each other. On the other hand, protofibrils in 20% (v/v) TFE had a diameter of 2 nm with no tendency of clustering. Intriguingly, when the K3 protofibrils were transferred from 20% (v/v) TFE to aqueous solution, some of them associated to form thicker fibrils with a diameter of 4-15 nm and a left-handed helical twist. TFE is a hydrophobic solvent, so that hydrophobic interactions between molecules may be weakened. The results suggest that the fibrils in aqueous conditions are formed by the cooperative association of protofibrils at the growing ends of the fibrils, in which hydrophobic interactions play a major role.
authors.affiliation: Institute of Scientific and Industrial Research, Osaka University, Ibaraki, Osaka 567-0047, Japan.
authors.forename: Takashi
authors.initials: T
authors.lastname: Kanno
authors.forename: Keiichi
authors.initials: K
authors.lastname: Yamaguchi
authors.forename: Hironobu
authors.initials: H
authors.lastname: Naiki
authors.forename: Yuji
authors.initials: Y
authors.lastname: Goto
authors.forename: Tomoji
authors.initials: T
authors.lastname: Kawai
mesh_terms: D000682:Amyloid / Q000378:metabolism* / Q000648:ultrastructure; D002021:Buffers; D006863:Hydrogen-Ion Concentration; D006868:Hydrolysis; D018625:Microscopy, Atomic Force; D010446:Peptide Fragments / Q000187:drug effects / Q000378:metabolism; D012996:Solutions; D014270:Trifluoroethanol / Q000494:pharmacology; D014867:Water / Q000737:chemistry; D001613:beta 2-Microglobulin / Q000737:chemistry / Q000378:metabolism* / Q000648:ultrastructure
chemical_list: D000682:Amyloid; D002021:Buffers; D010446:Peptide Fragments; D012996:Solutions; D001613:beta 2-Microglobulin; D014867:Water; D014270:Trifluoroethanol