Perturbation of surfactant-induced amyloids by abolishing electrostatic interactions

Abstract

Protein amyloid fibrils are supramolecular homopolymers that play a role in numerous biological processes and illnesses. The link between type 2 diabetes and insulin-induced amyloidosis has prompted much research on the production of insulin amyloid fibrils. Many in vitro investigations have shown that insulin can turn into amyloid fibrils under certain conditions. Insulin was used as a model protein in this study to determine the role of electrostatic interactions in surfactant-induced amyloids. Our results showed that SDS-induced amyloid formation was nucleation-independent at pH 2.0, and the solubilization was also instantaneous upon electrostatic interaction disruption. Far UV circular dichroism (CD), turbidity, Rayleigh light scattering (RLS), thioflavin T (ThT), and transmission electron microscopy (TEM) imaging showed the attainment of the different structural forms of insulin due to varying degrees of electrostatic interactions between the anionic surfactant (SDS) and the cationic to the anionic state of insulin. Treatment of SDS with the cationic state of insulin strongly induces amyloid-like aggregate while anionic state insulin reverts to native-like alpha-helical structures. In all samples, SDS concentration remained unchanged. Thus, hydrophobicity remained constant; only the electrostatic interaction between anionic SDS and cationic insulin was abolished as pH increased.