Revisiting SmE16, a calcium-binding protein from Schistosoma mansoni with unknown functions.

Schistosoma mansoni is the causative agent of schistosomiasis, a disease that affects millions of people worldwide. Calcium signaling, essential for various parasite processes, emerges as a potential target. In this study, we focused on the calcium binding protein SmE16, initially identified as an egg-specific antigen from S. mansoni. However, our results indicate that SmE16 is a widely expressed protein, present across all developmental stages and tissues, with high expression in the adult worm's esophagus, evidenced by our in situ hybridization experiments. The recombinant protein was expressed in Escherichia coli and purified to assess its conformational change upon calcium binding. Biophysical analyses demonstrated that SmE16 undergoes significant structural alterations in the presence of calcium ions. Furthermore, calcium binding promotes partial oligomerization and significantly enhances the thermal stability of the protein. These structural changes are often associated with proteins recognized as calcium sensors, suggesting that SmE16 might play an active role in calcium-mediated signaling pathways. These findings highlight the importance of SmE16 in potential cellular signaling, paving the way for further research into its biological functions.