Abstract
A gene encoding a Babesia bovis protein that shares significant degree of similarity to other apicomplexan thrombospondin-related anonymous proteins (TRAPs) was found in the genomic database and designated as BbTRAP2. Recombinant protein containing a conserved region of BbTRAP2 was produced in E. coli. A high antigenicity of recombinant BbTRAP2 (rBbTRAP2) was observed with field B. bovis-infected bovine sera collected from geographically different regions of the world. Moreover, antiserum against rBbTRAP2 specifically reacted with the authentic protein by Western blot analysis and an indirect fluorescent antibody test. Three bands corresponding to 104-, 76-, and 44-kDa proteins were identified in the parasite lysates and two bands of 76- and 44-kDa proteins were detected in the supernatant of cultivated parasites, indicating that BbTRAP2 was proteolytically processed and shed into the culture. Apical and surface localizations of BbTRAP2 were observed in the intracellular and extracellular parasites, respectively, by confocal laser microscopic examination. Moreover, native BbTRAP2 was precipitated by bovine erythrocytes, suggesting its role in the attachment to erythrocytes. Furthermore, the specific antibody to rBbTRAP2 inhibited the growth of B. bovis in a concentration-dependent manner. Consistently, pre-incubation of the free merozoites with the antibody to rBbTRAP2 resulted in an inhibition of the parasite invasion into host erythrocytes. Interestingly, the antibody to rBbTRAP2 was the most inhibitive for the parasite’s growth as compared to those of a set of antisera produced against different recombinant proteins, including merozoite surface antigen 2c (BbMSA-2c), rhoptry-associated protein 1 C-terminal (BbRAP-1CT), and spherical body protein 1 (BbSBP-1). These results suggest that BbTRAP2 might be a potential candidate for development of a subunit vaccine against B. bovis infection.
Highlights
Babesia bovis is tick-borne haemoprotozoan parasite of cattle that causes significant economic losses in dairy and beef industries
Analyses of the B. bovis genomic database (T2Bo strain) revealed the presence of four genes encoding BbTRAPs that were designated as BbTRAP1–4 (GenBank accession numbers XM_001609738, XM_001609762, XM_001609736, and XM_001609760, respectively) based on the identities to a previously reported BbTRAP of Israel strain [18]
Bioinformatics analyses demonstrated that BbTRAPs had typical structures of thrombospondin-related anonymous proteins (TRAPs) from other apicomplexan parasites, as determined by the presence of von Willebrand factor A (vWFA), TSP1 domains, and a transmembrane domain followed by a cytoplasmic C-terminal tail containing a conserved tryptophan residue (Figure S1)
Summary
Babesia bovis is tick-borne haemoprotozoan parasite of cattle that causes significant economic losses in dairy and beef industries. Despite the fact that chemotherapy is still the mainstay for treatment and control, the high prevalence of infection worldwide and the emergence of drug resistance [3] have spurred an interest in developing more effective measures that can counter the spread of infection and reduce its significant impact of the infection on livestock industry. Vaccines based on killed parasites and soluble parasite antigens derived from different Babesia species have shown partial protection characterized by reduction of the manifestations of clinical disease in animals [6,7]. The efforts of vaccine development have shifted toward the use of antigenically defined immunogens, the molecules interacting or disrupting the process of parasite invasion into host RBCs [8]
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