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Molecular characterizations of three distinct Babesia gibsoni rhoptry-associated protein-1s (RAP-1s)

  • M. A. TERKAWI (a1), A. AMORNTHEP (a2), H. OOKA (a1), G. ABOGE (a1), H. JIA (a1), Y.-K. GOO (a1), B. NELSON (a1), J. YAMAGISHI (a1), Y. NISHIKAWA (a1), I. IGARASHI (a1), S.-I. KAWAZU (a1), K. FUJISAKI (a3) and X. XUAN (a1)...


Three cDNAs encoding rhoptry-associated protein 1 (RAP-1) homologues were found in the Babesia gibsoni EST database. Based on similarities to BgRAP-1a, which was identified previously by serological screening of a cDNA merozoite library, the two new genes were designated BgRAP-1b (33·7%) and BgRAP-1c (57%). Mice antiserum raised against each recombinant protein reacted specifically with B. gibsoni parasites 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 of B. gibsoni.


Corresponding author

*Corresponding author: National Research Center for Protozoan Diseases, Obihiro University of Agriculture and Veterinary Medicine, Inada-cho, Obihiro, Hokkaido 080-8555, Japan. Tel: +81 155 49 5648. Fax: +81 155 49 5643. E-mail:


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