Structural and immunological characterization of an epitope within the PAN motif of ectodomain I in Babesia bovis apical membrane antigen 1

Abstract

Background Bovine babesiosis caused by Babesia bovis (B. bovis) affects the cattle industry worldwide with high mobility and mortality. Live-attenuated vaccines are currently used in some of the endemic countries, but their wide use is limited due to various reasons. Although recombinant vaccines have been proposed as an alternative to the live vaccines, such vaccines are not commercially available to date. Apical membrane antigen-1 (AMA-1) is one of the leading candidates for vaccine development against diseases caused by apicomplexan parasite species. In this study, we predicted an epitope from the plasminogen, apple and nematode (PAN) motif of domain I in the B. bovis AMA-1 (BbAMA-1) using a combination of linear and conformational B-cell epitope prediction software. The selected epitope was bioinformatically analyzed, synthesized as a peptide (sBbAMA-1), and then used to immunize a rabbit. Results The anti-sBbAMA-1 serum obtained was evaluated for its growth- and invasion-inhibitory effects on B. bovis merozoites in vitro. Our results demonstrated that the predicted BbAMA-1 epitope, which is located on surface-exposed α-helix of PAN motif in domain I at the apex area, elicits antibodies capable of recognizing the native BbAMA-1 in immunoassays. Importantly, as compared to the control groups, the rabbit anti-sBbAMA-1 serum at dilution of 1:5 significantly inhibited (p < 0.05) the growth of B. bovis merozoites by approximately 50–70% on day 3 and 4 of cultivation and the invasion of merozoites by approximately 60% within 4 h of incubation. Conclusion Our results indicate the epitope predicted from the PAN motif of BbAMA-1 domain I is neutralization-sensitive and may serve as a target antigen for vaccine development against bovine babesiosis caused by B. bovis.