REVISITING SME16, A CALCIUM-BINDING PROTEIN FROM SCHISTOSOMA MANSONI WITH UNKOWN FUNCTIONS

Schistosoma mansoni is the causative agent of schistosomiasis, a disease that affects thousands of people worldwide. The primary drug available for treating this disease is praziquantel, which affects calcium homeostasis in adult worms. The SmE16 protein, initially discovered in the 1990s as specific to S. mansoni eggs, is the focus of our work. Our aim is to explore the function of SmE16 using biophysical and biochemical techniques. We synthesized an RNA probe from SmE16 and conducted in situ hybridization in adult worms. Additionally, the protein was cloned in pET28a+, expressed in E. coli and purified to assess its conformational change upon calcium binding. The results revealed enriched transcripts of SmE16 in the esophageal glands of adult worms, indicating its presence at the host-parasite interface. Circular Dichroism experiments in the far-UV region indicated slight alterations in the protein's secondary structure after calcium addition. However, in the near-UV region (260-320 nm), corresponding to the aromatic residues, significant changes were observed, suggesting modifications in its tertiary structure. Native gel electrophoresis in the presence of EGTA, calcium, and barium showed distinct migration patterns when SmE16 was incubated with Ca2+. Moreover, SDS-PAGE analysis of SmE16 incubated with and without calcium, upon mild trypsin digestion, produced different band patterns. Tryptophan fluorescence spectroscopy further confirmed changes in the protein's tertiary structure in the presence of Ca2+. In conclusion, our findings indicate that SmE16 is expressed at the host-parasite interface in adult worms and might be a potential target for future interventions. Additionally, the binding of calcium induces conformational changes in the protein, suggesting it might have a sensor function. Further studies on the functional role of SmE16 could contribute to the development of novel approaches to combat schistosomiasis.