PvRON2, a new Plasmodium vivax rhoptry neck antigen

Abstract

<p>Abstract</p> <p>Background</p> <p>Rhoptries are specialized organelles from parasites belonging to the phylum <it>Apicomplexa</it>; they secrete their protein content during invasion of host target cells and are sorted into discrete subcompartments within rhoptry neck or bulb. This distribution is associated with these proteins' role in tight junction (TJ) and parasitophorous vacuole (PV) formation, respectively.</p> <p>Methods</p> <p><it>Plasmodium falciparum </it>RON2 amino acid sequence was used as bait for screening the codifying gene for the homologous protein in the <it>Plasmodium vivax </it>genome. Gene synteny, as well as identity and similarity values, were determined for <it>ron2 </it>and its flanking genes among <it>P. falciparum</it>, <it>P. vivax </it>and other malarial parasite genomes available at PlasmoDB and Sanger Institute databases. <it>Pvron2 </it>gene transcription was determined by RT-PCR of cDNA obtained from the <it>P. vivax </it>VCG-1 strain. Protein expression and localization were assessed by Western blot and immunofluorescence using polyclonal anti-<it>Pv</it>RON2 antibodies. Co-localization was confirmed using antibodies directed towards specific microneme and rhoptry neck proteins.</p> <p>Results and discussion</p> <p>The first <it>P. vivax </it>rhoptry neck protein (named here <it>Pv</it>RON2) has been identified in this study. <it>Pv</it>RON2 is a 2,204 residue-long protein encoded by a single 6,615 bp exon containing a hydrophobic signal sequence towards the amino-terminus, a transmembrane domain towards the carboxy-terminus and two coiled coil α-helical motifs; these are characteristic features of several previously described vaccine candidates against malaria. This protein also contains two tandem repeats within the interspecies variable sequence possibly involved in evading a host's immune system. <it>Pv</it>RON2 is expressed in late schizonts and localized in rhoptry necks similar to what has been reported for <it>Pf</it>RON2, which suggests its participation during target cell invasion.</p> <p>Conclusions</p> <p>The identification and partial characterization of the first <it>P. vivax </it>rhoptry neck protein are described in the present study. This protein is homologous to <it>Pf</it>RON2 which has previously been shown to be associated with <it>Pf</it>AMA-1, suggesting a similar role for <it>Pv</it>RON2.</p