Molecular Mechanism of Insulin Fibrillation in the Presence of a Cationic Gemini Surfactant: Spectroscopic and Conductometric Studies

Amyloid fibrils are a kind of protein aggregations that cause different degenerative humandiseases, including Huntingtons’ disease, Alzheimers’ disease, etc. [1]. Recently, great effortshave been focused on elucidating the molecular mechanism of amyloid formation and screeningof effective inhibitors to interrupt amyloid structures. In this project, the amyloid formation ofinsulin under conditions stimulating fibrillation was studied. Moreover, the effect of a cationicgemini surfactant having 4 methylene units as a spacer (C4), on the amyloid formation of theprotein was investigated. Geminis are dimeric surfactants formed by two polar head groups andtwo hydrophobic chains per molecule linked by a spacer [2]. Studies performed via ThT emissionmeasurements, show that the C4-surfactants have an inhibitory effect on insulin fibrillation.Furthermore, electrical conductivity measurements of surfactant dispersions havingvarious concentrations in the presence of insulin was used to determine the onset of proteinsurfactantinteraction (cac), as well as the onset of micellization (protein saturation point: psp). Inaddition, circular dichroism spectroscopy in the far-UV region (Far-UV CD) were conducted todetermine the secondary structure of fibrils. Results show that in the presence of surfactant, thesecondary structure of protein is very similar to that of the control. Based on these results andthose of conductivity measurements the inhibitory effect of the surfactant on amyloid fibrilformation is attributed to the entrapment of insulin monomers within the C4-micelles. Hence, thehydrophobic interactions between insulin monomers, stimulating the fibrillation, does not occur.

Keywords:

Fibrillation , Gemini Surfactant , Conductivity Measurements , Circular Dichroism Spectroscopy