Fluorescence Study of the Membrane Effects of Aggregated Lysozyme

The last decade has seen unprecedented upsurge of interest in the structural and toxic properties of particular type of protein aggregates, amyloid fibrils, associated with a number of pathological states. In the present study fluorescence spectroscopy technique has been employed to gain further insight into the membrane-related mechanisms of amyloid toxicity. To this end, erythrocyte model system composed of liposomes and hemoglobin was subjected to the action of oligomeric and fibrillar lysozyme. Acrylamide quenching of lysozyme fluorescence showed that solvent accessibility of Trp 62 and Trp 108 increases upon the protein fibrillization. Resonance energy transfer measurements suggested the possibility of direct complexation between hemoglobin and aggregated lysozyme. Using the novel squaraine dye SQ-1 it was demonstrated that aggregated lysozyme is capable of inhibiting lipid peroxidation processes. Fluorescent probes pyrene, Prodan and diphenylhexatriene were employed to characterize the membrane-modifying properties of hemoglobin and lysozyme. Both oligomeric and fibrillar forms of lysozyme were found to exert condensing influence on lipid bilayer structure, with the membrane effects of fibrils being less amenable to modulation by hemoglobin.