Deciphering the role of premicellar and micellar concentrations of sodium dodecyl benzenesulfonate surfactant in insulin fibrillation at pH 2.0.

Amyloid fibril formation by proteins and their deposition in cells and tissues are associated with several amyloid-based disorders. Understanding the mechanism of amyloid fibril formation is thus of the utmost importance for the designing ligands that could prevent or inhibit the fibrillation process and help to treat of such disorders. We describe the stimulatory effect of sodium dodecyl benzenesulfonate (SDBS) on insulin amyloid fibrillation at pH 2.0 and the characterization of SDBS-induced insulin aggregation using spectroscopy and microscopy. We found that SDBS induced amyloid-like aggregates of insulin at sub-micellar (0.1-1.2 mM), but not post-micellar (≥2.0 mM) concentrations. The amyloid fibrillation of insulin induced by SDBS was kinetically rapid and escaped the lag phase. Far-UV CD findings suggested that the α-helical content of insulin transformed into cross-β structure and mixed α and β structures when incubated with sub-micellar and post-micellar SDBS concentrations, respectively. The overall results indicated that low, but not high SDBS concentrations induce amyloid-like insulin aggregates and fibrils.