MEG-28 FROM SCHISTOSOMA MANSONI: BIOPHYSICAL CHARACTERIZATION AND INVOLVEMENT IN HOST CELL LYSIS

The survival of intravascular trematodes depends on their ability to resist the bloodstream environment and manipulate host components. In Schistosoma mansoni, the causative parasite of schistosomiasis, proteins encoded by microexon genes (MEGs) are highly expressed in the esophageal gland, which is involved in the processing of blood cells. Predictive analyses indicate that some MEGs contain amphipathic α-helices capable of interacting with lipid membranes, suggesting a possible role in membrane destabilization and host cell lysis. However, the function of most of these proteins, including MEG-28, remains poorly understood. In this study, a preliminary characterization of the ability of MEG-28 to interact with biomimetic membrane models, as well as its structural characteristics in different environments, was performed. Intrinsic tryptophan fluorescence and circular dichroism (CD) assays were performed using small unilamellar vesicles (SUVs) composed of POPC, POPS, and cholesterol, allowing the evaluation of changes in protein emission at different membrane concentrations. Fluorescence assays demonstrated variations in the emission intensity of MEG-28 according to membrane concentration, with a marked reduction in the presence of 50 and 100 µM SUVs, followed by an increase at 500 and 1000 µM. CD analyses revealed a greater contribution of β-sheet structures and signals associated with aggregation in MEG-28, despite the theoretical prediction of an α-helical structure. However, the addition of 2,2,2-trifluoroethanol (TFE) increased the α-helical contribution, in agreement with the theoretical structural prediction. In the presence of SUVs, changes in the MEG-28 spectrum were observed, including a slight shift toward shorter wavelengths (blue shift), accompanied by a greater contribution of signals that may be associated with aggregation. These results suggest that MEG-28 has structural characteristics compatible with α-helix formation and that its conformational behavior is influenced by the presence of model membranes. The observed changes in fluorescence and CD spectra provide preliminary evidence of its interaction with the lipid environment. To investigate its ability to promote changes in membrane permeability and lysis, fluorescent probe leakage and hemolysis assays will be performed, while differential scanning calorimetry (DSC) and dynamic light scattering (DLS) analyses will be used to further characterize the physicochemical properties of the protein–membrane interaction.