An Investigation of the Underlying Mechanism in Insulin Aggregation and Fibrillogenesis with Chelators

Abstract

Amyloid is a proteastasis condition implicated in more than 50 different diseases. At the core of it is the protein structural modifications that leads to assembly of protein molecules into a unique cross-ß structure. Since the disease is prevalent in the west, lifestyle, genetics and environmental factors are supposed to aggravate the condition. Metals are one such environmental factor the exposure to which has been proved to de deleterious for these diseases. Metal chelators on the other hand have thus found a utility as therapeutic agents in many clinical trials. Here we explore the effect of chelators EDTA or EGTA on the fibrillation propensity of insulin. Using Thioflavin T (ThT) we first found that both these chelators are able to influence the fibrillation propensity of insulin. Since the changes were not monotonous and did not follow a set pattern, we felt compelled to explore it further. We used divalent metal ions, Ca2+ and Mg2+, to alter the effect of chelators and monovalent metal ions, Na+ and K+ as controls. We observed that when EDTA was engaged with metals its effect on insulin aggregation altered at least at lower concentrations of the chelator. We then explored if the cause of this effect was binding or interaction of EDTA or EGTA to insulin molecule. Employing the biophysical techniques like ANS, tryptophan fluorescence quenching and FTIR we were able to identify that EDTA or EGTA both cause structural modifications in insulin. We concluded therefore, that chelators EDTA or EGTA can interact with the protein itself and can induce fibrillation of the protein especially at higher concentrations. This conclusion was further proved by studying the fibrillation in the presence of EGTA or EGTA at different pHs in light of the fact that chelator binding is pH sensitive.