Influence of oligomeric and fibrillar lysozyme on physical properties of model membranes

Abstract

A pathological hallmark of more than 20 human diseases including Alzheimer’s disease, Parkinson’s disease, type II diabetes is the deposition in organs and tissues of insoluble highly ordered protein aggregates, called amyloid fibrils. It is becoming widely recognized that toxicity of amyloid species is related to their interactions with cell membranes. In the present study we focused our efforts on the examination of the influence of amyloid fibrils and their precursors (oligomeric aggregates) of lysozyme on the structural and physical properties of the model membranes composed of phosphatidylcholine and its mixture with cholesterol. For evaluating the extent of lipid bilayer modifications, we used fluorescence spectroscopy technique. The results of pyrene excimerization measurements showed that amyloid protein reduces membrane fluidity. Analysis of Laurdan emission spectra revealed the ability of lysozyme aggregates to produce bilayer dehydration. The most pronounced membrane-modifying effects were observed in the case of oligomeric lysozyme. Significantly less influence of pathogenic protein aggregates on the physical properties of cholesterol-containing vesicles confirmed the hypothesis on the preventive role of cholesterol in amyloid-related diseases.