Region II of Duffy binding protein (PvDBP-II) is one of the most promising blood-stage vaccine candidate antigens against Plasmodium vivax and having knowledge of the nature and genetic polymorphism of PvDBP-II among global P. vivax isolates is important for developing a DBP-based vaccine. By using PCR and sequencing, the present molecular population genetic approach was carried out to investigate sequence diversity and natural selection of dbp-II gene in 63 P. vivax isolates collected from unstable and low transmission malaria-endemic areas of Iran during 2008-2012. Also, phylogenetic analysis, the diversifying natural selection, and recombination across the pvdbp-II gene, including regions containing B-cell epitopes were analyzed using the DnaSP and MEGA4 programs. Twenty two single nucleotide polymorphisms (SNPs, including 20 non-synonymous and 2 synonymous) were identified in PvDBP-II, resulting in 16 different PvDBP-II haplotypes among the Iranian P. vivax isolates. High binding inhibitory B-cell epitope (H3) overlapping with intrinsically unstructured/disordered region (aa: 384-392) appeared to be highly polymorphic (D384G/E385K/ K386N/Q/R390H), and positive selective pressure acted on this region. Most of the polymorphic amino acids, which are located on the surface of the protein, are under selective pressure that implies increased recombination events and exposure to the human immune system. In summary, PvDBP-II gene displays genetic polymorphism among Iranian P. vivax isolates and it is under selective pressure. Mutations, recombination, and positive selection seem to play a role in the resulting genetic diversity, and phylogenetic analysis of DNA sequences demonstrates that Iranian isolates represent a sample of the global population. These results are useful for understanding the nature of the P. vivax population in Iran and also for development of PvDBP-II-based malaria vaccine.
Keywords: Duffy binding protein; Iran; Natural selection; Plasmodium vivax; Population genetics.
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