title: Nearly reversible conformational change of amyloid fibrils as revealed by pH-jump experiments.
abstract: pH-jump induced conformational transitions between substates of preformed amyloid fibrils made by a fragmented peptide of helix 2 (H2 peptide) of MoPrP were detected, and their kinetics were analyzed using a novel pH-jump apparatus specially designed for observing amyloids. Previously, we reported that H2 peptide formed ordered fibrils with a minimum at 207 nm on CD spectra at pH 2.9 (named pH 2.9 fibrils), but formed aggregate-like fibrils with a minimum at 220 nm at pH 7.5 (named pH 7.5 fibrils). When pH-jump from 2.9 to 7.5 was performed, the CD spectrum changed instantly, but the finally observed ellipticities were clearly distinct from those of pH 7.5 fibrils. Thus, the finally observed state is termed 'pH 7.5-like fibrils'. However, pH 7.5-like fibrils reverted to the conformation very similar to that of the pH 2.9 fibrils when the pH of the solution was restored to 2.9. Then, we examined the kinetics of the nearly reversible conformational changes between pH 2.9 fibrils and pH 7.5-like fibrils using ANS fluorescence stopped-flow, and we observed relatively fast phases (0.7-18 s(-1)). In contrast, the conversion between pH 7.5-like fibrils and pH 7.5 fibrils never occurred (<0.2 day(-1)). Thus, H2 fibrils can be switched readily between distinct conformations separated by a low energy barrier, while a large energy barrier clearly separated the different conformations. These conformational varieties of amyloid fibrils may explain the physical basis of the diversity in prion.
authors.affiliation: United Graduate School of Drug Discovery and Medical Information Sciences, ‡Center for Emerging Infectious Diseases, §Life Science Research Center, and ¶Supporting and Development Center for Technology Education, Faculty of Engineering, Gifu University , Yanagido 1-1, Gifu 501-1193, Japan.
authors.forename: Kei-ichi
authors.initials: K
authors.lastname: Yamaguchi
authors.forename: Yuji O
authors.initials: YO
authors.lastname: Kamatari
authors.forename: Mayuko
authors.initials: M
authors.lastname: Fukuoka
authors.forename: Reiji
authors.initials: R
authors.lastname: Miyaji
authors.forename: Kazuo
authors.initials: K
authors.lastname: Kuwata
mesh_terms: D000682:Amyloid / Q000737:chemistry*; D000818:Animals; D006863:Hydrogen-Ion Concentration; D007700:Kinetics; D051379:Mice; D010316:Particle Size; D010446:Peptide Fragments / Q000138:chemical synthesis / Q000737:chemistry; D000072002:Prion Proteins; D011328:Prions / Q000737:chemistry*; D011487:Protein Conformation; D013499:Surface Properties
chemical_list: D000682:Amyloid; D010446:Peptide Fragments; D000072002:Prion Proteins; D011328:Prions; C512657:Prnp protein, mouse