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.

Evaluation of protease resistance and toxicity of amyloid-like food fibrils from whey, soy, kidney bean, and egg white

“…conformation or non-toxic filaments with anti-parallel b-sheet character under reducing conditions (Zako, Sakono, Hashimoto, Ihara, & Maeda, 2009).…”

Insulin aggregation tracked by its intrinsic TRES

“…Several techniques have been employed to study fibril formation including circular dichroism (CD), 14,15 transmission electron microscopy (TEM), 16 atomic force microscopy (AFM), 17 X-ray diffraction 18 and others. [19][20][21] CD spectroscopy studies showed that insulin adopts -helical conformations that can convert to appreciably -pleated structures as a function of time.…”

Oligomerization of neutral peptides derived from the JC virus agnoprotein through a cysteine residue

“…Conversion from a helical structure to a β-sheet structure has been reported for the pathogenic prion protein (Prusiner 1998) and amyloid beta peptide (Rauk 2008). Similar change in CD spectra is reported for fibril forming peptides such as insulin (Zako et al 2009) and Aβ peptide (Tomaselli et al 2006). Recently, Agno was reported to exist outside of the infected cell (Otlu et al 2014).…”