Background: Rhoptries are specialized organelles from parasites belonging to the phylum Apicomplexa; 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.
Methods: Plasmodium falciparum RON2 amino acid sequence was used as bait for screening the codifying gene
for the homologous protein in the Plasmodium vivax genome. Gene synteny, as well as identity and similarity
values, were determined for ron2 and its flanking genes among P. falciparum, P. vivax and other malarial parasite
genomes available at PlasmoDB and Sanger Institute databases. Pvron2 gene transcription was determined by
RT-PCR of cDNA obtained from the P. vivax VCG-1 strain. Protein expression and localization were assessed by
Western blot and immunofluorescence using polyclonal anti-PvRON2 antibodies. Co-localization was confirmed
using antibodies directed towards specific microneme and rhoptry neck proteins.
Results and discussion: The first P. vivax rhoptry neck protein (named here PvRON2) has been identified in this
study. PvRON2 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 a-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. PvRON2 is expressed in late schizonts and localized in rhoptry necks similar to
what has been reported for PfRON2, which suggests its participation during target cell invasion.
Conclusions: The identification and partial characterization of the first P. vivax rhoptry neck protein are described
in the present study. This protein is homologous to PfRON2 which has previously been shown to be associated
with PfAMA-1, suggesting a similar role for PvRON2
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