A Novel Thioredoxin Homologous Protein of Babesia Microti Involved in Erythrocyte Invasion

Background: Erythrocyte invasion by merozoites is an important stage in the life cycle of Babesia microti . Several merozoite proteins have previously been demonstrated to play important roles in this process. Methods and Results: We identified a novel merozoite protein of B. microti with structural characteristics similar to those of the thioredoxin (Trx)-like domain of the Trx family and named it as Bmi Trx-like protein. Western blot assays demonstrated that this protein was continuously expressed throughout the erythrocyte phase and peaked on the 11 th day post-infection. Immunofluorescence assay showed that the protein might mainly be expressed on the membrane of B. microti merozoites. Bmi Trx-like protein had both heparin- and erythrocyte-binding properties, which are critical functions of the invasion-related proteins. Immunization with recombinant Bmi Trx-like protein imparted considerable protection against B. microti infection in mice. Conclusions: : These results suggest that the novel merozoite protein, Bmi Trx-like protein, is an important molecule in the invasion process of B. microti and may be a possible target for the design of babesiosis vaccines.