title: Bovipain-2, the falcipain-2 ortholog, is expressed in intraerythrocytic stages of the tick-transmitted hemoparasite Babesia bovis.
abstract: BACKGROUND
  Cysteine proteases have been shown to be highly relevant for Apicomplexan parasites. In the case of Babesia bovis, a tick-transmitted hemoparasite of cattle, inhibitors of these enzymes were shown to hamper intraerythrocytic replication of the parasite, underscoring their importance for survival.
  
  
  RESULTS
  Four papain-like cysteine proteases were found to be encoded by the B. bovis genome using the MEROPS database. One of them, the ortholog of Plasmodium falciparum falcipain-2, here named bovipain-2, was further characterized. Bovipain-2 is encoded in B. bovis chromosome 4 by an ORF of 1.3 kb, has a predicted molecular weight of 42 kDa, and is hydrophilic with the exception of a transmembrane region. It has orthologs in several other apicomplexans, and its predicted amino acid sequence shows a high degree of conservation among several B. bovis isolates from North and South America. Synteny studies demonstrated that the bovipain-2 gene has expanded in the genomes of two related piroplasmids, Theileria parva and T. annulata, into families of 6 and 7 clustered genes respectively. The bovipain-2 gene is transcribed in in vitro cultured intra-erythrocyte forms of a virulent and an attenuated B. bovis strain from Argentina, and has no introns, as shown by RT-PCR followed by sequencing. Antibodies against a recombinant form of bovipain-2 recognized two parasite protein bands of 34 and 26 kDa, which coincide with the predicted sizes of the pro-peptidase and mature peptidase, respectively. Immunofluorescence studies showed an intracellular localization of bovipain-2 in the middle-rear region of in vitro cultured merozoites, as well as diffused in the cytoplasm of infected erythrocytes. Anti-bovipain-2 antibodies also reacted with B. bigemina-infected erythrocytes giving a similar pattern, which suggests cross-reactivity among these species. Antibodies in sera of two out of six B. bovis-experimentally infected bovines tested, reacted specifically with recombinant bovipain-2 in immunoblots, thus demonstrating expression and immunogenicity during bovine-infecting stages.
  
  
  CONCLUSIONS
  Overall, we present the characterization of bovipain-2 and demonstrate its in vitro and in vivo expression in virulent and attenuated strains. Given the involvement of apicomplexan cysteine proteases in essential parasite functions, bovipain-2 constitutes a new vaccine candidate and potential drug target for bovine babesiosis.
authors.affiliation: Instituto de Patobiología, Centro de Investigaciones en Ciencias Veterinarias y Agronómicas, Instituto Nacional de Tecnología Agropecuaria, INTA-Castelar, Argentina. mflorin@cnia.inta.gov.ar.
authors.forename: María
authors.initials: M
authors.lastname: Mesplet
authors.forename: Ignacio
authors.initials: I
authors.lastname: Echaide
authors.forename: Mariana
authors.initials: M
authors.lastname: Dominguez
authors.forename: Juan J
authors.initials: JJ
authors.lastname: Mosqueda
authors.forename: Carlos E
authors.initials: CE
authors.lastname: Suarez
authors.forename: Leonhard
authors.initials: L
authors.lastname: Schnittger
authors.forename: Monica
authors.initials: M
authors.lastname: Florin-Christensen