Hexafluoroisopropanol Induces Amyloid Fibrils of Islet Amyloid Polypeptide by Enhancing Both Hydrophobic and Electrostatic Interactions

Abstract

Although amyloid fibrils deposit with various proteins, the comprehensive mechanism by which they form remains unclear. We studied the formation of fibrils of human islet amyloid polypeptide associated with type II diabetes in the presence of various concentrations of 1,1,1,3,3,3-hexafluoroisopropanol (HFIP) under acidic and neutral pH conditions using CD, amyloid-specific thioflavin T fluorescence, fluorescence imaging with thioflavin T, and atomic force microscopy. At low pH, the formation of fibrils was promoted by HFIP with an optimum at 5% (v/v). At neutral pH in the absence of HFIP, significant amounts of amorphous aggregates formed in addition to the fibrils. The addition of HFIP suppressed the formation of amorphous aggregates, leading to a predominance of fibrils with an optimum effect at 25% (v/v). Under both conditions, higher concentrations of HFIP dissolved the fibrils and stabilized the ␣-helical structure. The results indicate that fibrils and amorphous aggregates are different types of precipitates formed by exclusion from water-HFIP mixtures. The exclusion occurs through the combined effects of hydrophobic interactions and electrostatic interactions, both of which are strengthened by low concentrations of HFIP, and a subtle balance between the two types of interactions determines whether the fibrils or amorphous aggregates dominate. We suggest a general view of how the structure of precipitates varies dramatically from single crystals to amyloid fibrils and amorphous aggregates.

Dual Role of an N-terminal Amyloidogenic Mutation in Apolipoprotein A-I

“…AFM images of the 1-83, 1-83/G26R, and 1-83/G26K variants incubated for 5 days at 37°C demonstrated the formation of long and straight fibrils with heights of ranging from 5 to 10 nm. The coexistence of large aggregates is likely to be due to the strong hydrophobic interactions resulting in the formation of amorphous aggre- gates as well as amyloid fibrils (37). AFM image of 1-83/G26E reveals that there is no fibril formation with this variant.…”

Polymorphism of β2-Microglobulin Amyloid Fibrils Manifested by Ultrasonication-enhanced Fibril Formation in Trifluoroethanol

“…The slightly different characteristics of f10%, i.e. a remarkably twisted morphology and the burial of tryptophan residues that are uncoupled with a linear decrease in hydrophobic interactions predicted with an increase in the concentration of TFE would be caused by the complicated mechanism of TFE action, forming dynamic clusters that directly binds protein molecules observed specifically below the alcohol clustering concentration (23,24,45).…”

“…␤2-m, a light chain of the type I major histocompatibility antigen (MHC-1) with 99 amino acid residues, is the main component of the amyloid fibrils deposited in patients with dialysis-related amyloidosis (21,22). We have previously clarified that alcohols, in particular TFE and hexafluoroisopropanol, markedly accelerated the formation of fibrils by a 22-residue fragment of ␤2-m (K3 peptide) and human islet amyloid polypeptide (23,24). This acceleration was eminent, especially at concentrations slightly below the alcohol clustering concentration, exhibiting a bell-shaped dependence on the concentration of alcohol as a result of a balancing of hydrophobic and electrostatic interactions.…”

Amyloidogenic Mutation Promotes Fibril Formation of the N-terminal Apolipoprotein A-I on Lipid Membranes

“…These results indicate that the G26R mutation impairs ␣-helical formation of 8 -33 residues, perhaps resulting in the different helical conformation of the N-terminal region of apoA-I on the membrane surface. Such a different helical conformation is expected to modify fibril formation for amyloidogenic proteins (30,31,50).…”