title: Pressure-dissociable reversible assembly of intrinsically denatured lysozyme is a precursor for amyloid fibrils.
abstract: Although a diversity of proteins is known to form amyloid fibers, their common mechanisms are not clear. Here, we show that an intrinsically unfolded protein (U), represented by a disulfide-deficient variant of hen lysozyme with no tertiary structure, forms an amyloid-like fibril after prolonged incubation. Using variable pressure NMR along with sedimentation velocity, circular dichroism, and fluorescence measurements, we show that, before the fibril formation, the protein forms a pressure-dissociable, soluble assemblage (U'(n)) with a sedimentation coefficient of 17 S and a rich intermolecular beta-sheet structure. The reversible assemblage is characterized with a Gibbs energy for association of -23.3 +/- 0.8 kJ.mol(-1) and a volume increase of 52.7 +/- 11.3 ml.mol(-1) per monomer unit, and involves preferential interaction of hydrophobic residues in the initial association step. These results indicate that amyloid fibril formation can proceed from an intrinsically denatured protein and suggest a scheme N <==>U <==>U'(n)-->fibril as a common mechanism of fibril formation in amyloidogenic proteins, where two-way arrows represent reversible processes, one-way arrow represents an irreversible process, and N, U, and U'(n)represent, respectively, the native conformer, the unfolded monomeric conformer, and the soluble assemblage of unfolded conformers.
authors.affiliation: Department of Molecular Science, Graduate School of Science and Technology, Kobe University, 1-1 Rokkodai-cho, Nada-ku, Kobe 657-8501, Japan.
authors.forename: Tara N
authors.initials: TN
authors.lastname: Niraula
authors.forename: Takashi
authors.initials: T
authors.lastname: Konno
authors.forename: Hua
authors.initials: H
authors.lastname: Li
authors.forename: Hiroaki
authors.initials: H
authors.lastname: Yamada
authors.forename: Kazuyuki
authors.initials: K
authors.lastname: Akasaka
authors.forename: Hideki
authors.initials: H
authors.lastname: Tachibana
mesh_terms: D000682:Amyloid / Q000096:biosynthesis*; D000818:Animals; D002645:Chickens / Q000502:physiology; D002942:Circular Dichroism; D057927:Hydrophobic and Hydrophilic Interactions; D009113:Muramidase / Q000096:biosynthesis*; D011312:Pressure; D011489:Protein Denaturation / Q000502:physiology; D013816:Thermodynamics
chemical_list: D000682:Amyloid; D009113:Muramidase