SDS‐induced amyloid fibrillation of acidic fibroblast growth factor

Abstract

Fibroblast growth factors and their receptors regulate a broad range of biological functions from developmental processes during embryogenesis to various physiological roles in the adult state, including regulation of angiogenesis, wound healing, and metabolism. hFGF‐1 also plays a key role in neuroprotection against neurotoxicity in Alzheimer’s disease (AD). The anionic surfactant sodium dodecyl sulfate (SDS) is widely used as a model for induction of amyloid‐like fibrils. In this context, we examined the effects of SDS on FGF1 using a variety of biophysical techniques including, Transmission Electron Microscopy (TEM). The secondary structure of hFGF1 was monitored by incubating hFGF1 with different concentrations of SDS utilizing the far‐UV CD (190‐250 nm) spectroscopy. We found that from 0.08‐0.15mM concentration of SDS, the negative peak at ~206 shifted gradually towards ~212nm while at 0.2mM concentration, far‐UV CD spectra of hFGF‐1 exhibit significant changes with striking shifting of negative peak ~212 nm to ~218 nm and disappearance of positive band at ~228nm which signifies substantial loss of native β‐barrel structure. The aggregation of hFGF‐1 is detected systematically by observing the absorbance at 350nm. The results indicate that at 0.2mM SDS, hFGF1 highly aggregates. In addition to far‐UV CD spectra and turbidity measurement, the influence of SDS on the tertiary structural changes of hFGF1 was studied by mentoring the intrinsic fluorescence of hFGF1 incubated with various concentrations of SDS. The study reveals that 0.2mM SDS is the concentration that affect mostly on the tertiary structure of hFGF1 because of the highest ratio of 305 to 350 at this concentration. Thioflavin‐T (ThT) assay for quantification of Amyloid‐like fibril formation was used to investigate the concentration of SDS that induce maximum hfGF1 fibrils. This study showed that 0.2mM SDS is the concentration that induced the optimum formation of fibrils hFGF1. Based on the results of these experiments, we wanted to do more investigation to achieve more evidence about the effect of SDS on the fibrils hFGF1. Therefore, morphological study by TEM was employed to examine the effect of 0.2mM SDS and 0.6mM SDS on the formation of fibrils hFGF1. At incubation for 1‐hour fibrillar aggregates of hFGF‐1 with average diameter at about 20‐25nm is observed in presence of 0.2mM SDS. All the previous results using biophysical techniques indicate that SDS induces formation of fibrils hFGF1 concentration which assist to better understanding about the causative of the fibrils hFGF1 which lead to find a remedy for the disease related with it.