title: Optimum amyloid fibril formation of a peptide fragment suggests the amyloidogenic preference of beta2-microglobulin under physiological conditions.
abstract: Beta(2)-microglobulin (beta(2)m) is a major component of amyloid fibrils deposited in patients with dialysis-related amyloidosis. Although full-length beta(2)m readily forms amyloid fibrils in vitro by seed-dependent extension with a maximum at pH 2.5, fibril formation under physiological conditions as detected in patients has been difficult to reproduce. A 22-residue K3 peptide of beta(2)m, Ser(20)-Lys(41), obtained by digestion with Acromobacter protease I, forms amyloid fibrils without seeding. To obtain further insight into the mechanism of fibril formation, we studied the pH dependence of fibril formation of the K3 peptide and its morphology using a ThT fluorescence assay and electron microscopy, respectively. K3 peptide formed amyloid fibrils over a wide range of pH values with an optimum around pH 7 and contrasted with the pH profile of the seed-dependent extension reaction of full-length beta(2)m. This suggests that once the rigid native-fold of beta(2)m is unfolded and additional factors triggering the nucleation process are provided, full-length beta(2)m discloses an intrinsic potential to form amyloid fibrils at neutral pH. The fibril formation was strongly promoted by dimerization of K3 through Cys(25). The morphology of the fibrils varied depending on the fibril formation conditions and the presence or absence of a disulfide bond. Various fibrils had the potential to seed fibril formation of full-length beta(2)m accompanied with a characteristic lag phase, suggesting that the internal structures are similar.
authors.affiliation: Institute for Protein Research, Osaka University, and CREST, Japan Science Corporation, Yamadaoka 3-2, Suita, Osaka 565-0871, Japan.
authors.forename: Yumiko
authors.initials: Y
authors.lastname: Ohhashi
authors.forename: Kazuhiro
authors.initials: K
authors.lastname: Hasegawa
authors.forename: Hironobu
authors.initials: H
authors.lastname: Naiki
authors.forename: Yuji
authors.initials: Y
authors.lastname: Goto
mesh_terms: D000595:Amino Acid Sequence; D016229:Amyloid beta-Peptides / Q000737:chemistry*; D002942:Circular Dichroism; D019281:Dimerization; D004220:Disulfides / Q000737:chemistry; D006801:Humans; D006863:Hydrogen-Ion Concentration; D007700:Kinetics; D008854:Microscopy, Electron; D008856:Microscopy, Fluorescence; D008969:Molecular Sequence Data; D010455:Peptides / Q000737:chemistry*; D017510:Protein Folding; D017433:Protein Structure, Secondary; D011994:Recombinant Proteins / Q000737:chemistry; D013696:Temperature; D013997:Time Factors; D001613:beta 2-Microglobulin / Q000737:chemistry*
chemical_list: D016229:Amyloid beta-Peptides; D004220:Disulfides; D010455:Peptides; D011994:Recombinant Proteins; D001613:beta 2-Microglobulin