title: Cellular localization of Babesia bovis merozoite rhoptry-associated protein 1 and its erythrocyte-binding activity.
abstract: The cellular localization of Babesia bovis rhoptry-associated protein 1 (RAP-1) and its erythrocyte-binding affinity were examined with anti-RAP-1 antibodies. In an indirect immunofluorescent antibody test, RAP-1 was detectable in all developmental stages of merozoites and in extracellular merozoites. In the early stage of merozoite development, RAP-1 appears as a dense accumulation, which later thins out and blankets the host cell cytoplasm, but retains a denser mass around newly formed parasite nuclei. The preferential accumulations of RAP-1 on the inner surface of a host cell membrane and bordering the parasite's outer surface were demonstrable by immunoelectron microscopy. An erythrocyte-binding assay with the lysate of merozoites demonstrated RAP-1 binding to both bovine and equine erythrocytes. Anti-RAP-1 monoclonal antibody 1C1 prevented the interaction of RAP-1 with bovine erythrocytes and significantly inhibited parasite proliferation in vitro. With the recombinant RAP-1, the addition of increasing concentrations of Ca(2+) accentuated its binding affinity with bovine erythrocytes. The present findings lend support to an earlier proposition of an erythrocytic binding role for RAP-1 expressed in B. bovis merozoites and, possibly, its involvement in the escape of newly formed merozoites from host cells.
authors.affiliation: National Research Center for Protozoan Diseases, Obihiro University of Agriculture and Veterinary Medicine, Obihiro, Hokkaido 080-8555, Japan.
authors.forename: Naoaki
authors.initials: N
authors.lastname: Yokoyama
authors.forename: Boonchit
authors.initials: B
authors.lastname: Suthisak
authors.forename: Haruyuki
authors.initials: H
authors.lastname: Hirata
authors.forename: Tomohide
authors.initials: T
authors.lastname: Matsuo
authors.forename: Noboru
authors.initials: N
authors.lastname: Inoue
authors.forename: Chihiro
authors.initials: C
authors.lastname: Sugimoto
authors.forename: Ikuo
authors.initials: I
authors.lastname: Igarashi
mesh_terms: D000818:Animals; D000911:Antibodies, Monoclonal / Q000494:pharmacology; D000913:Antibodies, Protozoan / Q000494:pharmacology; D016793:Babesia bovis / Q000235:genetics / Q000254:growth & development / Q000276:immunology / Q000378:metabolism*; D001404:Babesiosis / Q000469:parasitology / Q000662:veterinary; D001483:Base Sequence; D002417:Cattle; D002418:Cattle Diseases / Q000469:parasitology; D016054:DNA, Protozoan / Q000235:genetics; D004912:Erythrocytes / Q000469:parasitology*; D017125:Genes, Protozoan; D006736:Horses; D066298:In Vitro Techniques; D011485:Protein Binding; D015800:Protozoan Proteins / Q000235:genetics / Q000276:immunology / Q000378:metabolism*
chemical_list: D000911:Antibodies, Monoclonal; D000913:Antibodies, Protozoan; D016054:DNA, Protozoan; D015800:Protozoan Proteins; C097551:rhoptry-associated protein-1, Babesia