Isolation and Identification of an Actin Gene From Babesia gibsoni

Evaluation of recombinant BgSA3 protein based indirect-ELISA for sero-diagnosis and sero-surveillance of Babesia gibsoni in dogs

Canine babesiosis, a tick-borne haemoprotozoan disease of dogs, is of significance globally due to its rapid spread. A precise confirmatory diagnosis is required to curtail the rapid spread of infection. Our study described the evaluation of recombinant BgSA3 protein based indirect ELISA for sero-diagnosis and sero-surveillance of Babesia gibsoni infection in dogs. A partial BgSA3 gene segment (1921 bp) of B. gibsoni, encoding for recombinant truncated BgSA3 (75 kDa) protein devoid of predicted signal peptide (23 aa) at N-terminus and transmembrane region (20 aa) at C-terminus, was expressed in E. coli using a pET28a(+) vector. The rBgSA3 protein purified under native conditions using Ni-NTA superflow cartridge was confirmed by SDS-PAGE and Western blotting using sera from dogs infected/uninfected with B. gibsoni, and erythrocyte lysate/ plasma from infected/uninfected dogs. The rBgSA3 protein was specific only to B. gibsoni antibodies but did not react with uninfected sera. Further, rBgSA3 protein was evaluated for sero-diagnosis/sero-surveillance using Indirect-ELISA format. There was no cross reactivity to B. vogeli, E. canis, H. canis and D. repens infected dogs serum samples. The diagnostic sensitivity and specificity of rBgSA3 based I-ELISA was found to be 86.4 and 93.1 % respectively, in comparison with cytb based PCR assay. Additionally, rBgSA3-ELISA evaluated using survey serum samples (n = 287), detected 11.85 % samples as positive. In conclusion, B. gibsoni infection, an emerging disease is prevalent in the present study area and the standardized rBgSA3 protein based indirect-ELISA was found to be a specific and sensitive test for large scale sero-diagnosis and sero-surveillance of B. gibsoni infection in dogs.

Actin polymerization mediated by Babesia gibsoni aldolase is required for parasite invasion

Host cell invasion by apicomplexan parasites driven by gliding motility and empowered by actin-based movement is essential for parasite survival and pathogenicity. The parasites share a conserved invasion process: actin-based motility led by the coordination of adhesin-cytoskeleton via aldolase. A number of studies of host cell invasion in the Plasmodium species and Toxoplasma gondii have been performed. However, the mechanisms of host cell invasion by Babesia species have not yet been studied. Here, we show that Babesia gibsoni aldolase (BgALD) forms a complex with B. gibsoni thrombospondin-related anonymous protein (BgTRAP) and B. gibsoni actin (BgACT), depending on tryptophan-734 (W-734) in BgTRAP. In addition, actin polymerization is mediated by BgALD. Moreover, cytochalasin D, which disrupts actin polymerization, suppressed B. gibsoni parasite growth and inhibited the host cell invasion by parasites, indicating that actin dynamics are essential for erythrocyte invasion by B. gibsoni. This study is the first molecular approach to determine the invasion mechanisms of Babesia species.

Molecular characterizations of three distinctBabesia gibsonirhoptry-associated protein-1s (RAP-1s)

Three cDNAs encoding rhoptry-associated protein 1 (RAP-1) homologues were found in theBabesia gibsoniEST database. Based on similarities to BgRAP-1a, which was identified previously by serological screening of a cDNA merozoite library, the two new genes were designatedBgRAP-1b(33·7%) andBgRAP-1c(57%). Mice antiserum raised against each recombinant protein reacted specifically withB. gibsoniparasites as determined by Western blotting, which showed native molecular sizes of the BgRAP-1a (51 kDa), BgRAP-1b (53 kDa) and BgRAP-1c (47 kDa) consistent with predictable molecular weights. Immunofluoresence using these antibodies revealed localization of all BgRAP-1s within the matrix of merozoites; however, BgRAP-1a appeared to diverge from the other two when it was found secreted into the cytoplasm of infected erythrocytes. Apical localization of all 3 BgRAP-1s during the extracellular stage of the parasite combined with their ability to bind a canine erythrocyte membrane fraction was suggestive of a role for these proteins in erythrocyte attachment. Lastly, the ability of these recombinant proteins to be used as diagnostic reagents was tested by ELISA and the sensitivities of BgRAP-1a and BgRAP-1c were found increased through N-terminal truncation. Taken together, our data suggest divergent roles for the 3 BgRAP-1s in the merozoite stage ofB. gibsoni.

Characterization of actin genes inBonamia ostreaeand their application to phylogeny of the Haplosporidia

Bonamia ostreaeis a protozoan parasite that infects the European flat oysterOstrea edulis, causing systemic infections and resulting in massive mortalities in populations of this valuable bivalve species. In this work, we have characterizedB. ostreaeactin genes and used their sequences for a phylogenetic analysis. Design of different primer sets was necessary to amplify the central coding region of actin genes ofB. ostreae. Characterization of the sequences and their amplification in different samples demonstrated the presence of 2 intragenomic actin genes inB. ostreae, without any intron. The phylogenetic analysis placedB. ostreaein a clade withMinchinia tapetis,Minchinia teredinisandHaplosporidium costaleas its closest relatives, and demonstrated that the paralogous actin genes found inBonamiaresulted from a duplication of the original actin gene after theBonamiaorigin.

Babesia gibsoni rhoptry-associated protein 1 and its potential use as a diagnostic antigen

A cDNA encoding the rhoptry-associated protein 1 (RAP-1) homologue was obtained by immunoscreening an expression library prepared from Babesia gibsoni merozoite mRNA. The complete nucleotide sequence of the gene was 1740bp. Computer analysis suggested that the sequence contains an open reading frame of 1425bp encoding an expected protein with a molecular weight of 52kDa. Based on the sequence similarity, this putative protein was designated as the B. gibsoni RAP-1 (BgRAP-1). The BgRAP-1 gene was expressed in the Escherichia coli BL21 strain, and the recombinant BgRAP-1 was used as the antigen in the enzyme-linked immunosorbent assay (ELISA). The results can differentiate between the B. gibsoni-infected dog sera and the Babesia canis infected dog sera or the normal dog sera. Furthermore, the antibody response against the recombinant protein was maintained during the chronic stage of infection, indicating that the recombinant BgRAP-1 protein might be a useful diagnostic antigen for the detection of antibodies to B. gibsoni infection in dogs.

A 38-kDa protein from Babesia gibsoni and its antibody response in an experimentally infected dog

A cDNA encoding the Babesia bovis 12D3 antigen homologue was obtained by immunoscreening the expression library prepared from Babesia gibsoni merozoite mRNA. The complete nucleotide sequence of the gene was 1406 bp. Computer analysis suggested that the sequence contains an open reading frame of 1052 bp encoding an expected protein with a molecular weight of 36kDa. Based on homology analysis, this putative protein was designated as the B. gibsoni 12D3 antigen (Bg12D3). The Bg12D3 gene was expressed in the Escherichia coli BL21 strain, and the chronically infected dog serum reacted with the recombinant protein. The antiserum against the recombinant Bg12D3 protein can recognize a 38-kDa native protein, which is consistent with its expected size. Moreover, the purified recombinant proteins were used as the antigen to detect the antibody response in an experimentally infected dog by the enzyme-linked immunosorbent assay (ELISA). Our results indicated that the Bg12D3 protein was recognized by the host immune system and that it induced an antibody response in chronic B. gibsoni infection. These results allowed us to identify a new member of the 12D3 antigens and its characteristic immune response in canine B. gibsoni infection.