title: AlphaB-crystallin, a small heat-shock protein, prevents the amyloid fibril growth of an amyloid beta-peptide and beta2-microglobulin.
abstract: AlphaB-crystallin, a small heat-shock protein, exhibits molecular chaperone activity. We have studied the effect of alphaB-crystallin on the fibril growth of the Abeta (amyloid beta)-peptides Abeta-(1-40) and Abeta-(1-42). alphaB-crystallin, but not BSA or hen egg-white lysozyme, prevented the fibril growth of Abeta-(1-40), as revealed by thioflavin T binding, total internal reflection fluorescence microscopy and CD spectroscopy. Comparison of the activity of some mutants and chimaeric alpha-crystallins in preventing Abeta-(1-40) fibril growth with their previously reported chaperone ability in preventing dithiothreitol-induced aggregation of insulin suggests that there might be both common and distinct sites of interaction on alpha-crystallin involved in the prevention of amorphous aggregation of insulin and fibril growth of Abeta-(1-40). alphaB-crystallin also prevents the spontaneous fibril formation (without externally added seeds) of Abeta-(1-42), as well as the fibril growth of Abeta-(1-40) when seeded with the Abeta-(1-42) fibril seed. Sedimentation velocity measurements show that alphaB-crystallin does not form a stable complex with Abeta-(1-40). The mechanism by which it prevents the fibril growth differs from the known mechanism by which it prevents the amorphous aggregation of proteins. alphaB-crystallin binds to the amyloid fibrils of Abeta-(1-40), indicating that the preferential interaction of the chaperone with the fibril nucleus, which inhibits nucleation-dependent polymerization of amyloid fibrils, is the mechanism that is predominantly involved. We found that alphaB-crystallin prevents the fibril growth of beta2-microglobulin under acidic conditions. It also retards the depolymerization of beta2-microglobulin fibrils, indicating that it can interact with the fibrils. Our study sheds light on the role of small heat-shock proteins in protein conformational diseases, particularly in Alzheimer's disease.
authors.affiliation: Centre for Cellular and Molecular Biology, Uppal Road, Hyderabad 500 007, India.
authors.forename: Bakthisaran
authors.initials: B
authors.lastname: Raman
authors.forename: Tadato
authors.initials: T
authors.lastname: Ban
authors.forename: Miyo
authors.initials: M
authors.lastname: Sakai
authors.forename: Saloni Y
authors.initials: SY
authors.lastname: Pasta
authors.forename: Tangirala
authors.initials: T
authors.lastname: Ramakrishna
authors.forename: Hironobu
authors.initials: H
authors.lastname: Naiki
authors.forename: Yuji
authors.initials: Y
authors.lastname: Goto
authors.forename: Ch Mohan
authors.initials: ChM
authors.lastname: Rao
mesh_terms: D000682:Amyloid / Q000737:chemistry* / Q000378:metabolism*; D016229:Amyloid beta-Peptides / Q000737:chemistry / Q000378:metabolism*; D006360:Heat-Shock Proteins / Q000737:chemistry / Q000378:metabolism*; D006801:Humans; D006863:Hydrogen-Ion Concentration; D009154:Mutation; D010446:Peptide Fragments / Q000737:chemistry / Q000378:metabolism*; D038202:alpha-Crystallin A Chain / Q000737:chemistry / Q000378:metabolism*; D038203:alpha-Crystallin B Chain / Q000737:chemistry / Q000378:metabolism*; D001613:beta 2-Microglobulin / Q000737:chemistry / Q000378:metabolism*
chemical_list: D000682:Amyloid; D016229:Amyloid beta-Peptides; D006360:Heat-Shock Proteins; D010446:Peptide Fragments; D038202:alpha-Crystallin A Chain; D038203:alpha-Crystallin B Chain; C078592:amyloid beta-protein (1-40); C075222:amyloid beta-protein (1-42); D001613:beta 2-Microglobulin