title: Bovine insulin filaments induced by reducing disulfide bonds show a different morphology, secondary structure, and cell toxicity from intact insulin amyloid fibrils.
abstract: Amyloid fibrils are associated with more than 20 diseases, including Alzheimer's disease and type II diabetes. Insulin is a 51-residue polypeptide hormone, with its two polypeptide chains linked by one intrachain and two interchain disulfide bonds, and has long been known to self-assemble in vitro into amyloid fibrils. We demonstrate here that bovine insulin forms flexible filaments in the presence of a reducing agent, Tris (2-carboxyethyl) phosphine. The insulin filaments, possibly formed due to partial reduction of S-S bonds in insulin molecules, differ from intact insulin fibrils in terms of their secondary structure. The insulin filaments were determined to have an antiparallel beta-sheet structure, whereas the insulin fibrils have a parallel beta-sheet structure. Of importance, the cell toxicity of the insulin filaments was remarkably lower than that of the insulin fibrils. This finding supports the idea that cell toxicity of amyloids correlates with their morphology. The remarkably low toxicity of the filamentous structure should shed new light on possible pharmacological approaches to the various diseases caused by amyloid fibrils.
authors.affiliation: Bioengineering Laboratory, RIKEN Institute, Saitama, Japan.
authors.forename: Tamotsu
authors.initials: T
authors.lastname: Zako
authors.forename: Masafumi
authors.initials: M
authors.lastname: Sakono
authors.forename: Naomi
authors.initials: N
authors.lastname: Hashimoto
authors.forename: Masaki
authors.initials: M
authors.lastname: Ihara
authors.forename: Mizuo
authors.initials: M
authors.lastname: Maeda
mesh_terms: D000682:Amyloid / Q000737:chemistry* / Q000378:metabolism / Q000633:toxicity; D000818:Animals; D052160:Benzothiazoles; D002417:Cattle; D016923:Cell Death; D002942:Circular Dichroism; D003224:Congo Red; D007328:Insulin / Q000737:chemistry* / Q000378:metabolism / Q000633:toxicity*; D046529:Microscopy, Electron, Transmission; D010720:Phosphines; D017433:Protein Structure, Secondary; D013050:Spectrometry, Fluorescence; D017550:Spectroscopy, Fourier Transform Infrared; D013059:Spectrum Analysis, Raman; D013844:Thiazoles / Q000378:metabolism; D014466:Ultraviolet Rays
chemical_list: D000682:Amyloid; D052160:Benzothiazoles; D003224:Congo Red; D007328:Insulin; D010720:Phosphines; D013844:Thiazoles; C080938:tris(2-carboxyethyl)phosphine; C009462:thioflavin T