SDS induces cross beta-sheet amyloid as well as alpha-helical structure in conconavalin A

Abstract

Surfactants stimulate amyloid fibril formation, but the mechanism of action is still not very clear. In the present study, we examined the effects of negatively charged surfactants, i.e., sodium dodecyl sulfate (SDS) on the concanavalin A (ConA) lectin fibrillation process, at pH 3.5. To determine the effect of SDS treatment on amyloid fibrillation of ConA protein in vitro, we used a variety of techniques for example turbidity, intrinsic fluorescence, ThT fluorescence, far-UV CD and transmission electron microscope (TEM) to assess the amyloid fibrillation process of ConA. Assessing turbidity, it was found that ConA aggregation was dependent on the concentration of SDS. ConA aggregated with incubation with 0.1 to 2.5 mM SDS concentration i.e., (SDS/ConA molar ratio in between 13.3 and 333). However, ConA aggregation was not detected below 0.1 and above 2.5 mM SDS. Thioflavin-T (ThT) strongly binds with aggregated ConA and led to increased fluorescence intensity. The secondary structure of ConA changed from β-sheeted into a cross-β sheet structure with ConA aggregation. Upon interaction with a concentration of SDS higher than 2.5 mM at the same pH, the ConA becomes a total α-helical structure. TEM suggests that in the presence of SDS, the aggregate form of ConA develops into a curly-shaped amyloid structure. This study provides insight into the molecular mechanisms of ConA amyloid fibrillation, which is essential for understanding and preventing surfactant or lipid-induced fibrillation for therapeutic purposes.