Differential effects of ionic and non-ionic surfactants on lysozyme fibrillation

Fibril formation is a common property of many proteins, though not all are associated with diseases. Protein surface charges and the added co-solvents play vital roles in determining fibrillation pathways and kinetics. In order to understand these phenomena, the effects of anionic, cationic and non-ionic surfactants on lysozyme fibrillation were studied. Lysozyme forms fibrils in 2 M and 4 M urea solutions following nucleation-dependent and nucleation-independent pathways, respectively, at neutral pH. Under these conditions, the effects of sodium dodecyl sulfate (SDS), cetyltrimethylammonium bromide (CTAB), and triton X-100 (Tx) were investigated on the lysozyme structure and fibrillation. The results indicate that there are differential effects of ionic and non-ionic surfactants on fibrillation. In the presence of SDS and CTAB, above their critical micelle concentrations (CMC), lysozyme could not form fibrils. However, non-ionic Tx does not inhibit fibril formation at all concentrations. Note that the time for complete fibril formation is increased by Tx. All of the surfactants are found to increase the initial nucleation phase; however, the extent of increase is less at near the CMC of the ionic surfactants and at above the CMC of Tx. The rates of fibril elongation show varying effects in the presence of different surfactants. The results suggest that the nucleation phase of lysozyme fibrillation is primarily controlled by charge interactions and micellation of the surfactants, but multiple factors might influence the fibril elongation. Furthermore, the surfactants do not alter the fibrillation pathway from nucleation-dependent to nucleation-independent or vice versa in the studied conditions.